A method and apparatus for achieving optical microscopic images and monitoring metabolic processes of living biological specimens such as cells at a resolution superior to the diffraction limit is disclosed. A primary difficulty in performing near-field scanning optical microscopy of living cells, e.g., determining the separation between the cell surface and the illuminating probe tip, is overcome by using a photon-density feedback method in which a fluorescent dye signal strength is monitored in the cell as the tip is brought to the cell surface, and registering a maximum value, at which point the tip begins to dimple the cell surface and can get no closer to the dye. Thereafter the tip is either maintained in contact with the membrane for point measurements of metabolic processes or is withdrawn a selected distance from the surface as measured against a corresponding decrease in the fluorescent dye signal strength The signal strength serves as a photon-density feedback for maintaining the probe tip at a constant elevation above the cell surface as scanning is performed or time-series measurements of metabolism are recorded. Advantageously, the apparatus also combines confocal means in the form of a pin-hole or the like for high-fidelity light detection in three dimensions from the cell surface in the near-field of the probe tip.

One long-standing limitation on the resolution achievable in optical-regime microscopy has been the diffraction limit of the illuminating light. Details having size equal to or less than half the wavelength of the illuminating light are beneath the resolving powers of traditional optical microscopes. Thus, details in the range of 250 nanometers or smaller cannot be resolved using conventional focal optical microscopy.
In recent years, a solution has been provided to this problem by near-field scanning optical microscopy (NSOM). This technology permits optical resolution below the normal diffraction limit by using a fiber optic light guide to direct illuminating light from an aperture with dimensions of less than half the wavelength of the light (typically about 20-100 nanometers) at the light guide tip onto an equally small area of the specimen. The tip is located very close to the specimen, so that the specimen lies in the near-field region of the light emanating from the tip, and diffraction limitations play no role. The near field is generally the area within less than a wavelength or so of the aperture from which the illuminating light emanates.
The illumination is measured by collecting either reflected, transmitted or fluorescent light, and that measurement yields a single pixel of the microscopic image. The sample is typically scanned in a raster pattern across the surface of the specimen to yield an image having a pixel resolution on the order of the tip dimensions, namely about 20-50 nanometers, which lies below the normal diffraction barrier. Some examples of an NSOM are disclosed in U.S. Pat. No. 4,917,462 to Lewis et al., and in U.S. Pat. Nos. 5,272,330 and 5,286,970 to Betzig, et al.
U.S. Pat. No. 4,917,462 to Lewis et al. discloses an NSOM apparatus involving a metal-coated glass pipette having a thin tip. Lewis teaches the application of an electrical potential between the pipette and the stage, resulting in a measurable current to provide a feedback signal used to determine the distance between aperture and object, see col. 11, 1. 27-52, although he also mentions the possibility of using light for feedback, col. 11, line 53 et seq. Lewis teaches general epi-fluorescence illumination of the specimen, although he also mentions the possibility of providing light through the pipette to the specimen.
In NSOM, it may be preferable to use a fiber optic light guide with a fine tip in order to provide more light directly to the specimen than could be provided through a pipette. See U.S. Pat. Nos. 5,272,330 and 5,286,970 to Betzig, et al. Desirably, illuminating light will be directed from a very small aperture at the light guide tip onto a very small area of a nearby specimen.
A significant difficulty in NSOM has been determining when the fiber optic light guide tip has reached a location close enough to the specimen that the specimen surface lies within the near-field of the illuminating light. Furthermore, the tip must be maintained at a constant elevation above the surface being scanned. Various feedback techniques have been developed in the field to maintain this tip-sample registration. Generally, the light guide tip is moved toward the specimen until the tip is in the immediate vicinity of the specimen. Then, using a "shear-force" feedback method, the tip is held within 5-20 nanometers of the sample. The scanning is then performed by mechanically moving the sample under the tip and registering light reflectance on transmission values.
These techniques generally work well for relatively dry, hard and flat samples, but do not work well with biological specimens, which are soft, have greater topological variation, and do not advantageously yield mechanical and electrical signals which can be measured to determine the proximity of the tip to the specimen surface. Furthermore, these techniques tend to have a destructive effect on the biological material.
For example, using "shear force" feedback, the tip is vibrated side-to-side at its resonant frequency as it is brought down toward the surface of the specimen. A phase shift or damping of the vibration caused by forces of interaction between the tip and the sample is used as a measure of separation to hold the tip at a constant distance from the sample. This technique works well for dry, relatively flat surfaces. Unfortunately, such a technique, if used on living cells in solution, can result in damage to biological cell membranes from the side-to-side vibration. In U.S. Pat. No. 5,354,985 to Quate, a cantilever light guide is disclosed which determines proximity to the specimen surface by measuring changes in the resonant vibration frequency of the cantilever. As the cantilever aperture tip approaches the surface of the specimen, Van der Waals forces influence the resonant frequency. In an alternative embodiment disclosed in Quate, the cantilever is brought into contact with the surface by measuring deflection of the cantilever from a rest position by the force of the surface. The cantilever is then dragged over the surface while maintaining a constant force on it.
The microscope of Quate works well with well-defined, crystalline surfaces of relatively homogenous composition. However, biological specimens such as cells have surfaces littered with structures which often extend relatively far from the cell membrane. The apparatus of Quate is not well-adapted to measure proximity to the cell membrane because these structures also impart Van der Waals forces affecting the resonant frequency of the cantilever. Furthermore, the surface of the cell is composed of a wide variety of molecules with varying Van der Waal attraction forces. No consistent or useful scanning of a living biological specimen can be carried out using the apparatus of Quate.
U.S. Pat. No. 5,340,981 to De Fornel et al. discloses a means of bringing a NSOM within the near-field of a specimen using the electromagnetic coupling between the incident illumination radiation and the reflected radiation. The invention is best suited for coupling the modes of the reflected light with the illumination light when the surface being scanned is well-defined and preferably near-crystalline Biological cells with their highly heterogeneous surface structures do not present the kind of surfaces from which the reflective modes used in De Fornel can be advantageously obtained. Furthermore, the form of microscopy described by DeFornell specifically relates to reflection and not fluorescence microscopy.
Another genre of microscopes related to NSOMs is scanning tunneling microscopes. Again, the technique used in the scanning tunneling microscope is suited for flat, dry specimens, but not for living biological cells. Scanning tunneling microscopy utilizes tunneling electrons as a signal source to indicate distance between the probe tip and the specimen. As the tip approaches the specimen, the tunneling phenomenon of electrons becomes measurable and increases with increasing proximity. However, an electrically conductive specimen is required for this kind of microscopy.
In the field of biological microscopy, it is desirable to achieve nanometer-scale optical resolution in order to study cellular metabolism, and in particular cell membrane metabolism. Metabolism is studied both in terms of the spatial distribution of molecular structures and also in terms of the time-variation of molecular concentrations. An example of the need for such optical resolution is the study of ion channels in the cell membrane. Such membrane structures have dimensions on the order of 1-30 nanometers. The flow of ions across the membrane into the cell is desirably monitored by measuring the fluorescence of an indicator activated in the presence of the ions. Traditional microscopy produces a volume-averaged measurement, since the contribution to fluorescence by indicators just below the cell membrane is swamped by the dye throughout the cell. If it were possible to map fluorescence locally at tens-of-nanometers resolution, the volume-averaged effect would be avoided, and it would be possible to map the distribution of functional ion channels and potentially individual molecules over the cell membrane.
In view of the above prior techniques, it is apparent there are obstacles to sub-diffraction limit microscopic resolution in imaging living biological cells. The techniques described above generally require the specimen to be flat, dry, well-defined at the surface, hard or crystalline. When practiced on living biological cells, the techniques either yield inaccurate results or may damage a living biological cell.
A further problem in optical microscopy of biological specimens has been that virtually all of the above-described techniques are designed to measure only the surface topology of a specimen, usually for fractures or inconsistencies in crystalline structure. None of the above techniques is suitable for monitoring metabolic activity through time, for monitoring cortical concentrations of fluorescent-tagged molecules at the cell membrane, or for detecting fluorescence-labelled molecules associated with the cell membrane.
What is needed is a means for generating accurate microscopic images of living biological structures below the 250 nanometer resolution limitation of conventional optical microscopy, and preferably in the range of tens of nanometers More importantly, such a needed microscopic apparatus must not damage the biological structures, and must be able to provide an accurate image of metabolic activity without interfering with such activity.

Probe-type near-field confocal having feedback for adjusting probe distance

Iowa State University Research Foundation


A power supply control IC is mounted on a surface of a multilayer body that defines a power supply control circuit module. A first inner-layer electrode connecting an inductor element and a switching regulator element for the power supply control IC, another first inner-layer electrode connecting the inductor element and a capacitor element, and still another first inner-layer electrode connecting the switching regulator element and the capacitor element are located on upper layer regions of the multilayer body and are routed in between a mounting area of the power supply control IC and a peripheral wall of the multilayer body. The first inner-layer electrodes have widths that are wider than those of second inner-layer electrodes which are located near a center region of the multilayer body and transmit control signals.

1. Field of the Invention
The present invention relates to power supply control circuit modules including a plurality of switching regulators.
2. Description of the Related Art
At present, higher packing densities of circuit elements are required for circuit modules for use in communication devices. Thus, such a circuit module is generally made from a multilayer body, which is formed by stacking a plurality of dielectric layers that include electrode patterns, and surface-mount type electronic components which are to be mounted on the multilayer body.
In such a circuit module for use in a communication device, a communication control circuit and a power supply control circuit are formed in the multilayer body, as illustrated in Japanese Unexamined Patent Application Publication No. 2009-231606. The communication control circuit includes a communication control IC element mounted on a surface of the multilayer body. The power supply control circuit includes a DC-DC converter switching IC element mounted on the surface of the multilayer body.
In this conventional circuit module, heat dissipation efficiency of the DC-DC converter switching IC element is being increased by mounting the DC-DC converter switching IC element on the surface of the multilayer body, namely the surface on a side opposite to a side facing a mother board when the multilayer body is mounted thereon.
In the foregoing conventional circuit module, however, electrode patterns for connecting the DC-DC converter switching IC element to other circuit elements are determined based on positional relationships between the DC-DC converter switching IC element and the other circuit elements. Thus, depending on the positional relationship, there may be a case where the heat dissipation of the whole DC-DC converter circuit is not adequate, not only in the DC-DC converter switching IC element but also in the electrode patterns, etc, which is positioned on a output side of the DC-DC converter switching IC element and through which large currents flow.


Superalloy component castings, such as turbine blades and vanes, are fabricated or repaired by an electroslag or electrogas welding process that at least partially replicates the crystal structure of the original cast substrate in a cast-in-place substrate extension. The process re-melts the base substrate surface and grows it with new molten filler material. As the base substrate and the filler material solidify, the newly formed “re-cast” component has a directionally solidified uniaxial substrate extension portion that at least in part replicates the crystalline structure of the base substrate. The “re-cast” component can be fabricated with a unified single crystal structure, including the extension portion. In other applications, a substrate extension can replicate a directionally solidified uniaxial crystal structure of an original base substrate casting. Polycrystalline substrate base structures can be re-cast with a substrate extension that replicates base substrate crystals that are most parallel to the uniaxial casting direction.

1. Field of the Invention
The invention relates to repair of service-degraded superalloy component castings, such as turbine blades and vanes. More particularly the invention relates to repair or new fabrication of superalloy component castings by an electroslag welding process that re-melts a base substrate casting surface and grows it within a pool of molten filler material. As the combined melted material solidifies it forms a cast-in-place substrate extension that at least partially replicates the original substrate casting's crystal structure.
2. Description of the Prior Art
"Structural" repair of service-degraded gas turbine or other superalloy component castings is commonly recognized as replacing damaged material with matching alloy material and achieving properties, such as strength, that are close to the original manufacture component specifications (e.g., at least seventy percent ultimate tensile strength of the original specification). For example, it is preferable to perform structural repairs on turbine blades that have experienced surface cracks or blade tip erosion, so that risk of further cracking is reduced, and the blades are restored to original material structural and dimensional specifications.
Structural repair or new fabrication of nickel and cobalt based superalloy material that is used to manufacture turbine components, such as cast turbine blades, is challenging, due to the metallurgic properties of the finished blade material. For example, a superalloy having more than 6% aggregate aluminum or titanium content, such as CM247 alloy, is more susceptible to strain age cracking when subjected to high temperature welding than a lower aluminum-titanium content X-750 superalloy. The finished turbine blade alloys are typically strengthened during post casting heat treatments which render them difficult to perform subsequent structural welding. Currently used welding processes for superalloy structural fabrication or repair generally involve substantial melting of the substrate adjoining the weld preparation, and complete melting of the welding rod or other filler material added, in order to repair cracks or build up eroded surfaces. When a blade constructed of such a material is welded with filler metal of the same or similar alloy, the blade is susceptible to solidification (aka liquation) cracking within and proximate to the weld, and/or strain age (aka reheat) cracking during subsequent heat treatment processes intended to restore the superalloy original strength and other material properties comparable to a new component.
Alternative superalloy welding processes, including laser microcladding with chill fixtures, welding in so called "hot" boxes at elevated temperatures, and inertia friction welding may still lead to post weld heat treatment strain age cracking. Other friction welding processes, such as friction stir welding, can reduce superalloy cracking propensity, but the employed welding apparatus has relatively limited tool life. The alternative superalloy welding processes are not well-suited for rebuilding large gross volume of eroded component substrate material, such as for example rebuilding of an eroded turbine blade tip or vane.
In comparison to structural repair or fabrication, "cosmetic" repair or fabrication of superalloys is recognized as replacing damaged material (or joining two components of newly fabricated material) with unmatching alloy material of lesser structural property specifications, where the localized original structural performance is not needed. For example, cosmetic repair may be used in order to restore the repaired component's original profile geometry, including relatively mild turbine blade tip or vane erosion. As noted above, it is desirable to perform structural repairs on surface cracks in order to reduce their likelihood of subsequent spreading when the component is returned to service. Conversely, an example of cosmetic repair is for filling surface pits (as opposed to structural cracks) on a turbine blade airfoil in order to restore its original aerodynamic profile, where the blade's localized exterior surface is not critical for structural integrity of the entire blade. Cosmetic repair or fabrication is often achieved by using oxidation resistant weld or braze alloys of lower strength than the blade body superalloy substrate, but having higher ductility and lower application temperature that does not negatively impact the superalloy substrate's material properties.
Given the shortcomings of superalloy structural repair welding, often the only commercially acceptable solution is to scrap damaged turbine blades that require structural repair, because past experience has shown limited success of such structural repairs. Thus repairs have been limited to those that have in the past been proven to be performed successfully by alternative superalloy welding processes described above, or by cosmetic welding, employing more ductile welding rod filler materials with reduced structural strength.
Thus, a need exists in the art for a method for performing structural fabrication of superalloy component castings, or a method for performing structural repairs on surfaces of service-degraded superalloy component castings, such as turbine vanes and blades, so that structural cracks, eroded surfaces and other surface defects can be repaired.
Another need exists in the art to increase successful rates of structural repairs of service-degraded superalloy component castings, such as turbine vanes and blades, so that damaged component scrap rates can be reduced.
Yet another need exists in the art for a method for performing structural fabrication of superalloy component castings, or repairs on surfaces of service-degraded superalloy component castings, such as turbine vanes and blades, that do not require complex welding or post-repair heat treatment procedures.

Electroslag and electrogas repair of superalloy components


In an optical coupled isolation circuit, a PWM encoder encodes a one-bit binary data signal supplied from a sigma-delta analog-digital converter in synchronization with a clock signal of a cycle T to produce a pulse width modulation signal. The pulse width modulation signal includes a narrower pulse having a width of 1/T and a wider pulse having a width of 3/T according to binary codes “0” and “1”. The pulse width modulation signal is transmitted to a decoder as a recovered pulse width modulation signal through a light emitting device, a light detector and an optical recovery circuit. A decoder decodes the recovered pulse width modulation signal at timing of a half of the clock cycle from each rising edge of the recovered pulse width modulation signal. The rising edge is synchronized with the clock signal. Thus, the clock signal and the data signal can be transmitted in one channel.

This invention relates to an optical coupled type isolation circuit which is used to transmit an analog signal with high accuracy from an input part to an output part in a state that the input part and the output part are electrically isolated from each other. In particular, this invention relates to an optical coupled type isolation circuit capable of reliable transmission of a one-bit data signal together with a clock signal easily.
An existing isolation circuit, e.g. an isolation amplifier, is used in various places, such as a factory, a plant, a hospital providing medical instruments, or the like to remove large common mode noises and/or to secure safety. The large common node noises are frequently caused at a place, e.g. the factory or the plant, where high power apparatuses and high sensitive electronic devices, which have different source voltages of over 1000 volts, are arranged close to one another.
A type of the isolation amplifier using a photo coupler transmits a signal in a form of light and thereby obtains electrical isolation between input and output parts thereof. Accordingly, the type of the isolation amplifier using the photo coupler is superior to a type of the isolation amplifier using an electromagnetic coupling in resistance to noises.
The isolation amplifier using the photo coupler, for example, is provided between a motor (or an AC servo, or an inverter for the motor) and a precision instrument, such as a microcomputer as a controller for the motor, in the factory or the plant to control the motor with high accuracy.
To improve accuracy and to reduce a cost of the isolation amplifier, a sigma-delta modulation is employed in an optical isolation amplifier. However, the optical isolation amplifier can not transmit a clock signal from an input part to an output part thereof, even if the clock signal is necessary in the output part.
Such an optical isolation amplifier is disclosed in U.S. Pat. No. 5,287,107 or Japanese Patent Publication No. 3174200.
As another exiting isolation circuit, there is a digital-analog (D/A) converter which adopts a pulse width modulation method.
The D/A converter converts input digital data into a pulse width modulation signal. The pulse width modulation signal is transmitted from an input part to an output part through a photo coupler. In the output part, the pulse width modulation signal is converted into an analog signal.
However, the D/A converter has a problem that jitters are caused to rising edges and falling edges of a light signal in the photo coupler and superimposed on the analog signal.
Such a D/A converter disclosed in Unexamined Japanese Patent Publication No. 6-209261.


A method of manufacturing a collimator assembly is provided. The method includes placing a first core element within a first center collimator path of a first collimator tube to create a first base-tube couple. A couple cross-section of the first base-tube couple is reduced such that the first base-tube couple becomes a first single-fiber fiber. The first single-fiber fiber is assembled into a collimator group. The first core element is dissolved such that a first hollow fiber is generated.

The present invention relates generally to a collimator assembly, and, more particularly to a collimator assembly and method of manufacture.
Computed tomography has been utilized for a wide variety of imaging applications. One such category of applications is comprised of medical imaging. Although it is known that computed tomography may take on a wide variety of configurations within the medical industry, it commonly is based on the transmission of low energy rays through a body structure. These low energy rays are subsequently received and processed to formulate an image, often three-dimensional, of the body structure that can by analyzed by clinicians as a diagnostic aid.
The reception of the low energy rays, such as gamma-rays or x-rays, is often accomplished through the use of a device referred to as a scintillator detector. The scintillator detector is typically comprised of a plurality of structures working in concert to receive and process the incoming energy rays after they have passed through the body structure. A collimator is an element often found in a scintillator detector that is used to limit the direction of photons as they approach the scintillator element. The collimator is commonly used to increase the magnification of a viewed object or control resolution or field of view. Their primary purpose, in a scintillator detector, however, is to control the photons impinging on the scintillator element.
The scintillator element, in turn, is commonly a material with the ability to absorb the photons and convert their energy into visible light. This allows the low energy rays received by the scintillator detector to be converted into useful information. Scintillator elements may come in a wide variety of forms and may be adapted to receive a wide variety of incoming rays. The light produced by the scintillator element is commonly processed by way of a device such as a light sensitive photodiode which converts the light from the scintillator element into an amplified electronic signal. In this fashion, the information from the scintillator detector can be easily transferred, converted, and processed by electronic modules to facilitate viewing and manipulation by clinicians.
Current post-patient collimator assemblies provide crucial functioning for image quality by reducing the scattering of transmitted x-ray photons. Scattered photons can cause noise and reduce resolution causing image artifacts. As imaging applications require increased z-coverage, manufacturing of suitable collimator assemblies becomes more challenging. Traditional methodologies can decrease reliability and cost of manufacture as the burden on collimator performance increases. The additional press for increased resolution requirements further burdens collimator design.
It would, however, be highly desirable to have a method of producing a collimator assembly with improved manufacturing characteristics. Similarly, it would be highly desirable to have a collimator assembly and method of manufacturing that was compatible with the increasing resolution requirements of imaging systems.

Method of making a post-patent collimator assembly


A semiconductor processing method of forming a contact pedestal includes, a) providing a node location to which electrical connection is to be made; b) providing insulating dielectric material over the node location; c) etching a contact opening into the insulating dielectric material over the node location to a degree insufficient to outwardly expose the node location, the contact opening having a base; d) providing a spacer layer over the insulating dielectric material to within the contact opening to a thickness which less than completely fills the contact opening; e) anisotropically etching the spacer layer to form a sidewall spacer within the contact opening; f) after forming the sidewall spacer, etching through the contact opening base to outwardly expose the node location; g) filling the contact opening to the node location with electrically conductive material; h) rendering the sidewall spacer electrically conductive; and i) etching the electrically conductive material to form an electrically conductive contact pedestal comprising the sidewall spacer, the pedestal having an outer surface which is substantially coplanar with opposing laterally adjacent electrically insulative surfaces. Also disclosed is integrated circuitry including contact pedestals. Also disclosed are methods of forming storage nodes of capacitors.

This invention relates to semiconductor processing methods of forming contact pedestals and to integrated circuitry employing contact pedestals. The invention also relates to methods of forming a storage node of a capacitor.
As DRAMs increase in memory cell density, there is a continuing challenge to maintain sufficiently high storage capacitance despite decreasing cell area. Additionally, there is a continuing goal to further decrease cell area. The principal way of increasing cell capacitance is through cell structure techniques. Such techniques include three-dimensional cell capacitors, such as trenched or stacked capacitors.
Conventional stacked capacitor DRAM arrays utilize either a buried bit line or a non-buried bit line construction. With buried bit line constructions, bit lines are provided in close vertical proximity to the bit line contacts of the memory cell field effect transistors (FETs), with the cell capacitors being formed horizontally over the top of the wordlines and bit lines. With non-buried bit line constructions, deep vertical contacts are made through a thick insulating layer to the cell FETs, with the capacitor constructions being provided over the word lines and beneath the bit lines. Such non-buried bit line constructions are also referred to as xe2x80x9ccapacitor-under-bit linexe2x80x9d or xe2x80x9cbit line-over-capacitorxe2x80x9d constructions.
In DRAM and other integrated circuitry, ohmic electrical contact is typically made relative to an electrically conductive diffusion region in a semiconductor substrate between a pair of conductive lines provided over the substrate. In some instances, contact plugs or pedestals are utilized to facilitate making electrical connection to the substrate, and contend with adverse vertical topography. Such can provide the advantage of producing a larger targeting area for a subsequent conductive line contact to the diffusion region through the pedestal. My earlier U.S. Pat. Nos. 5,338,700; 5,340,763; 5,362,666; and 5,401,681 are hereby incorporated by reference into this disclosure.


A time-of-flight mass spectrometer which has an iron source, an evacuated tube proximate the ion source and adapted to receive ions from the ion source, and a detector disposed at an end of the evacuated tube opposite an end proximate the ion source. The ion source is constructed to generate an electric field that changes non-linearly as a function of position along a path from the ion source to the detector. The ion source is constructed to generate an electric field that changes as a function of time, the electric field being provided to accelerate ions from the ion source to the detector.

1. Field of Invention
The present invention relates to a mass spectrometer in general and in particular to a mass spectrometer that employs ion focusing fields which are non-linear in both space and time to improve mass resolution.
2. Description of Related Art
Mass spectrometers are instruments that are used to determine the chemical composition of substances and the structures of molecules. In general they consist of an ion source where neutral molecules are ionized, a mass analyzer where ions are separated according to their mass/charge ratio, and a detector. Mass analyzers come in a variety of types, including magnetic field (B) instruments, combined electric and magnetic field or double-focusing instruments (EB or BE), quadrupole electric field (Q) instruments, and time-of-flight (TOF) instruments. In addition, two or more analyzers may be combined in a single instrument to produce tandem (MS/MS) mass spectrometers. These include triple analyzers (EBE), four sector mass spectrometers (EBEB or BEEB), triple quadrupoles (QqQ) and hybrids (such as the EBqQ).
In tandem mass spectrometers, the first mass analyzer is generally used to select a precursor ion from among the ions normally observed in a mass spectrum. Fragmentation is then induced in a region located between the mass analyzers, and the second mass analyzer is used to provide a mass spectrum of the product ions. Tandem mass spectrometers may be utilized for ion structure studies by establishing the relationship between a series of molecular and fragment precursor ions and their products.
Alternatively, they are now commonly used to determine the structures of biological molecules in complex mixtures that are not completely fractionated by chromatographic methods. These may include mixtures of (for example) peptides, glycopeptides or glycolipids. In the case of peptides, fragmentation produces information on the amino acid sequence.
One type of mass spectrometer is time-of-flight (TOF) mass spectrometers. The simplest version of a time-of-flight mass spectrometer, illustrated in FIG. 1A (Cotter, Robert J., Time-of-Flight Mass Spectrometry: Instrumentation and Applications in Biological Research, American Chemical Society, Washington, D.C., 1997), the entire contents of which is hereby incorporated by reference, consists of a short source region 10, a longer field-free drift region 12 and a detector 14. Ions are formed and accelerated to their final kinetic energies in the short source region 10 by an electric field defined by voltages on a backing plate 16 and drawout grid 18. The longer field-free drift region 12 is bounded by drawout grid 18 and an exit grid 20.
In the most common configuration, the drawout grid 18 and exit grid 20 (and therefore the entire drift length) are at ground potential, the voltage on the backing plate 16 is V, and the ions are accelerated in the source region to an energy: mv2/2=z eV, where m is the mass of the ion, v is its velocity, z the number of charges, and e is the charge on an electron. The ions then pass through the drift region 12 and their (approximate) flight time(s) is given by the formula:t=[(m/z)/2 eV]1/2D  (I)which shows a square root dependence upon mass. Typically, the length s of source region 10 is of the order of 0.5 cm, while drift lengths (D) ranges from 15 cm to 8 meters. Accelerating voltages (V) can range from a few hundred volts to 30 kV, and flight time are of the order of 5 to 100 microseconds. Generally, the accelerating voltage is selected to be relatively high in order to minimize the effects on mass resolution arising from initial kinetic energies and to enable the detection of large ions. For example, the accelerating voltage of 20 KV (as illustrated, for example, in FIG. 1A) has been found to be sufficient for detection of masses in excess of 300 kDaltons.
A profile of the acceleration potential in the source region 10 (shown in FIG. 1A) is shown in FIG. 1B. The potential in this embodiment decreases linearly from a maximum value at the backing plate 16 (shown in FIG. 1A) to zero at the drawout grid 18 (Shown in FIG. 1A).
In recent years, the development of an ionization technique for mass spectrometers known as matrix-assisted laser desorption ionization (MALDI) has generated considerable interest in the use of time-of-flight mass spectrometers and in improvement of their performance. MALDI is particularly effective in ionizing large molecules (e.g. peptides and proteins, carbohydrates, glycolipids, glycoproteins, and oligonucleotides(DNA)) as well as other polymers. The TOF mass spectrometer provides an advantage for MALDI analysis by simultaneously recording ions over a broad mass range, which is the so called multichannel advantage. In the MALDI method of ionization, biomolecules to be analyzed are recrystallized in a solid matrix (e.g., sinnipinic acid, 3-hydroxy picolinic acid, etc.) of a low mass chromophore that is strongly absorbing in the wavelength region of the pulsed laser used to initiate ionization. Following absorption of the laser radiation by the matrix, ionization of the analyte molecules occurs as a result of desorption and subsequent charge exchange processes. In TOF instruments, all ion optical elements and the detector are enclosed within a vacuum chamber to ensure that ions, once formed, reach the detector without collisions with the background gas.
One performance criterion for all TOF mass spectrometers is the resolving power, which represents the extent to which ions of different m/z can be distinguished from each other. Ideally, nearly infinite resolving power could be attained if all ions having the same m/z would arrive at the detector simultaneously. This ideal circumstance could be achieved if 1) all the ions possessed identical (or no) initial energy or motion, 2) all started from the same point, and 3) all were accelerated to identical kinetic energy. However, any one of these conditions is rarely achieved and the resolving power is consequently diminished. Therefore, some mechanism or combination thereof must be used to compensate for these variations in ion starting conditions in order to attain sufficient resolving power.
For a gaseous sample, there is both a distribution of initial ion starting positions and a thermal Maxwell-Boltzman distribution of ion energies (˜0.1 eV) that is subsequently manifested as a distribution of ion detection times within each iso-mass group. These temporal variations are often referred to as the space and energy effects. The energy effect also creates a distinct detrimental effect known as the turn-around time, whereby those ions having a thermal energy vector directed against the accelerating field travel away from the ion source exit before being turned around.
This results in ions of the same m/z, same initial position, and same magnitude of thermal energy, exiting the ion source at different times and consequently results in a difference in arrival-times at the detector.
The three ions' starting parameters are modeled, for the single, linear field case and shown in FIG. 2. The effect of each case can be compared with the reference ion of the same mass located at the initial position s0, with no internal energy. The energy, Us0, applied to the reference ion isUs0=s0E  (II)
which represents the total kinetic energy of the reference ion. It is assumed that ions originating from the same plane, orthogonal to the flight axis, receive equal kinetic energy when the accelerating field is applied.
In the first case S, an ion initially located at a position s0+δs, receives a total energy directly proportional to its initial position when the accelerating electric field is applied. The energy applied to this ion will differ from Us0 by the relationship
                              U          s                =                                                            s                0                            +                              δ                                                                                s                                                    s              0                                                      U                          s              0                                                          (        III        )
Ions located farther from the exit of the ion source receive greater energy than those ions closer to the exit and overtake the less energetic ions at a distance 2s0 from the ion source exit; a phenomenon known as space focusing. The location along the flight axis where this occurs, in this case 2s0, is traditionally known as the space focus plane and represents the position along the flight path where Rs, that portion of the resolving power attributable to space focusing, is the highest.
In the case of U+, an ion having some initial energy δU and an initial velocity directed toward the detector is compared to the reference ion located in the same plane. While both ions receive a total energy of Us as a consequence of their location within the source, the ion having the initial thermal motion leaves the source with a final energy of Us+δU, achieves a greater velocity and arrives at the detector before the reference ion. Methods correcting for this variance are known as energy focusing methods, discussed below.
In the special case of U−, the initial energy δU is the same, but the initial velocity is directed away from the detector, and the ion initially travels against the electric field before being turned around and accelerated out of the source. For two ions of the cases U+ and U− where both ions have the same magnitude of initial energy but velocities in opposite directions, each ion will leave the source with identical energy. However, the U− ion will arrive at the detector later due to the turn-around time in the ion source.
The resolving power is independently degraded by each of the starting parameters, with the overall resolving power representing the combined effect of the space and energy resolutions. The total resolving power, R, is defined as
                              1          R                =                              1                          R              S                                +                      1                          R                              U                +                                              +                      1                          R                              U                -                                              +                      1                          R              t                                +                      1                          R              electronics                                                          (        IV        )
While not a fundamental parameter of ion motion, the term Rt is included for those cases where ions may be formed during the finite time of ion extraction from the source. The term Relectronics is also included here to acknowledge that in practice, if all ion space and energy effects can be corrected or eliminated, the ultimate limitation to R is that imposed by the speed and precision of the detector and electronics circuitry.
Improvements to Resolving Power
The first major improvement to resolving power incorporated two design features that improved both mass resolving power and overall mass range. The first of these was the development of the two-field ion source (Wiley, W. C., McLaren, I. H. Rev. Sci. Instrumen. 1955, 26, 1150-1157; Wiley, W. C. Science, 1956, 124, 817-820; Wiley, W. C. U.S. Pat. No. 2,685,035).
Earlier ion sources used a single electric field for ion extraction that imposed a tradeoff between energy and space focusing. FIG. 3A shows a graph of the voltage potential versus the length s0 between the ion source (backing-plate) and the drawout grid or exit grid. The voltage potential decreases linearly to reach zero volt at the exit grid, illustrated in FIG. 3A by a dotted vertical line. The focus position lies at a distance of 2s0 from the exit grid. The focus position is indicated on FIG. 3A by a vertical line.
In order to maximize energy resolution, it was desirable to use a high electric field strength and accelerate the ions to their final velocity quickly. However, this required an axially short ion source geometry and, as the detector must consequently be placed only a short distance (2s0) from the ion source in order to achieve a space focus condition, little time was available for mass separation. The total flight time could only be increased by either lowering the electric field strength (and consequently the energy resolution), or lengthening the flight path by moving the detector well beyond where the space focus region would be found using a single field source.
Since the dominant parameter limiting resolving power was the initial energy spread, the latter option was required. Using the two-field ion source, as shown in FIG. 3B, the space focus region could be located farther than 2s0 from the ion source at a distance which is a function of the two accelerating electric field strengths. Thus, while the low amplitude first accelerating field slightly reduced the energy resolution, the ability to achieve both space focusing and an increase in the total flight time for all ions yielded an overall increase in resolving power.
The second early design provided additional focusing by introducing an adjustable time delay between ion formation and application of the accelerating field (Wiley, W. C., McLaren, I. H. Rev. Sci. Instrumen. 1955, 26, 1150-1157; Wiley, W. C. Science, 1956, 124, 817-820; Wiley, W. C. U.S. Pat. No. 2,685,035). During this time, ions move to new locations in the ion source due to their thermal energies and, upon extraction, acquire total kinetic energies dependent on these new locations. This energy focusing method, known then as time-lag focusing and now as pulsed or delayed extraction, essentially attempts to transform the energy distribution of the initial ion population into a spatial distribution, thus reducing the temporal effect of the energy distribution at the space focus position. The combined use of time-lag and space focusing yields a significant increase in resolving power. However, the optimal time lag is mass dependent, limiting the m/z range that could be simultaneously measured.
Another way to improve the resolving power is with the use of a reflectron or ion mirror, which provides mass-independent ion focusing (Karataev, V. I., Mamyrin, B. A., Shmikk, D. V. Sov. Phys. Tech. Phys. 1972, 16, 1177; Mamyrin, B. A., Karataev, V. I., Shmikk, D. V., Zagulin, V. A. Sov. Phys. JETP 1973, 37, 45; Mamyrin, B. A., Shmikk, D. V. Sov. Phys. JETP 1979, 49, 762; Mamyrin, B. A., Karataev, V. I., Shrmikk, D. V. U.S. Pat. No. 4,072,862).
In its most basic form, as shown in FIG. 4A, this device is simply a series of electrostatic diaphragms that provide a retarding electric field, as shown in FIG. 4B, with enough potential to reflect ions. Ions with different kinetic energies penetrate the mirror to different depths before being turned around and repelled from the mirror. While all ions leave the mirror having exactly the same magnitude of energy with which they entered, those ions possessing the greater energy travel farther into the mirror before being repelled and thus experience a time delay that compensates for their higher velocity in the field-free region. The ions are then focused at a second space-focus position SFP2 where they achieve a higher resolving power than the first space-focus position SFP1 due to the additional energy focusing. The original ion mirror design generates a single, linear electric field behind a field isolating mesh and is capable of first-order focusing. A subsequent design incorporates two fields and is capable of first or second-order focusing.
Non-Linear Fields
Mass spectrometers using linear-field or combinations of linear-field focusing devices such as the two-field ion source and the two-field ion mirror generate adequate resolving power for applications having a relatively small initial ion energy distribution. However, for applications having a relatively large initial ion energy distribution, the achievable resolving power is diminished. This is expected since the relationship between energy, velocity and time is fundamentally non-linear, and linear-field devices provide only an approximation of complete temporal focusing. One approach to compensate for this overcomes the energy focusing limitation by delivering externally-generated ions to the TOF mass analyzer in a direction orthogonal to the analysis axis [11,12]. Thus, while the overall magnitude of initial ion energy may be relatively large, the magnitude along the analysis axis is minimal. However, this still does not overcome the spatial problem, and for some methods where the ionization process occurs within the source, a large initial ion energy distribution may inherent to the analysis.
The fundamentally non-linear relationship between time and energy in ion motion indicates that the ultimate attainable resolving power can only be achieved using non-linear fields. Devices that generate non-linear fields can be classified as static, where the non-homogeneous field is established in space using a particular electrode design, and dynamic, where the magnitude of the electric field is altered over time.
Static Field Devices
To date, the majority of development in non-linear-field generating devices has been with static devices. Several ion mirror designs using a non-linear field have been developed (Glashchenko, V. P., Semkin, N. D., Sysoev, A. A., Oleinikov, V. A., Tatur, V. Yu. Sov. Phys. Tech. Phys. 1985, 30, 540-541; Mamyrin, B. A. Int J. Mass Spectrom. Ion Processes, 1994, 131, 1-19; Rockwood, A. L. Proc. 34th ASMS Conf. on Mass Spectrom & Allied Topics, 1986, Cincinnati, Ohio, 173), while other designs have been proposed and/or patented (Yoshida, Y. U.S. Pat. No. 4,625,112; Frey, R., Schlag, E. W. U.S. Pat. No. 4,731,532; Kutscher, R., Grix, R., Li, G.; Wollnik, H. U.S. Pat. No. 5,017,780; Managadze, G. G., Shutyaev, I. Yu. In Laser Ionization Mass Spectrometry; Vertes, A., Gijbels, R., Adams, F., Eds., John Wiley & Sons: New York, 1993, 505-549; Flory, C. A., Taber, R. C., Yefchak, G. E. Int. J. Mass Spectrom. Ion Proc. 1996, 152, 177-184; Doroshenko, V. M., Cotter, R. J. J. Am. Soc. Mass Spectrom., 1999, 10, 992-999; Cotter, R. J., Doroshenko, V. M. U.S. Pat. No. 6,365,892). Each of these designs provides only minor improvement to the resolving power achieved using linear-field ion mirrors, and each is suitable to only a relatively narrow initial range of ion energies.
Non-linear-field mirrors that focus a broad range of initial ion energies have also been developed using either an entirely gridless design to achieve a single non-linear field (Cornish, T. J., Cotter, R. J. Rapid Comm. Mass Spectrom., 1993, 7, 1037-1040), or a gridded design generating a combination of linear and non-linear fields (Beussman, Douglas J., Vlasak, Paul R., McLane, Richard D.; Seeterlin, Mary A.; Enke, Christie G. Anal. Chem. 1995, 67(21), 3952-3957). While non-linear fields are theoretically preferable to linear fields, one of the practical drawbacks to generating such fields in ion mirrors is the result of their inherent radial field-inhomogeneity. Linear fields generate an electric potential that is constant in all directions orthogonal to the electric field. Thus, an ion beam entering a linear-field ion mirror at a fixed point and angle will experience the same force regardless of the entry point. In contrast, an ion beam entering a non-linear field will experience a force that depends on the exact point of entry. An ion beam of finite diameter will thus experience a range of non-linear fields, which reduces the resultant resolving power and radially disperses the ion beam, diminishing the ion transmission. A non-linear design has been developed that exploits the radial dispersion using a single-electrode can-shaped "endcap" ion mirror (Cornish, T. J., Cotter, R. J. Anal. Chem. 1997, 69(22), 4615-4618; Cornish, T. J.; Cotter, R. J. U.S. Pat. No. 5,814,813). A more recent and somewhat more complicated design also uses a minimum number (2 to 3) of electrodes to achieve the desired non-linear field (Zhang, J., Enke, C. G. J. Am. Soc. Mass Spectrom., 2000, 11(9), 759-764; Zhang, J., Gardner, B. D., Enke, C. G. J. Am. Soc. Mass Spectrom., 2000, 11(9), 765-769; Zhang, J., Gardner, B. D., Enke, C. G. patent pending).
In contrast to the developments in non-linear ion mirror design, the use of non-linear fields in ion source design is less prevalent. Several designs have been developed, for the analysis of gas-phase ions, where a "quadratic" non-linear ion-accelerating field is generated (Crane, W. S., Mills, A. P. Rev. Sci. Instrum. 1985, 56, 1723; Hulett, L. D., Donohue, D. L., Lewis, T. A. Rev. Sci. Instrum. 1991, 62, 2131-2137; Rockwood, A. L., Udseth, H. R., Gao, Q., Smith, R. D. Proc. 42nd ASMS Conf. on Mass Spectrom. & Allied Topics, 1994, Chicago, Ill., 1038). A mass spectrometer based on one of these designs, for the analysis of orthogonally-injected gas-phase ions, is commercially available (LECO Corp. product literature on the Jaguar LC-TOF mass spectrometer). A separate design incorporating both linear and non-linear fields has been reported (Gardner, B. D., Holland, J. F. J. Am. Soc. Mass Spectrom., 1999, 10(11), 1067-1073; Gardner, B. D. Doctoral Dissertation, Michigan State University, 1997), also for the analysis of gas-phase ions. A gridless ion source, which consequently generates a non-linear field by default, is also commercially available on a MALDI-TOF instrument, although the design has not been described (Kratos Analytical Instruments AXIMA).
Dynamic Field Devices
Several dynamic-field ion optical devices have been developed. The technique of post source pulse focusing is a simple variation of time-lag focusing where a voltage pulse can be applied to a short field-free region located after the ionization and acceleration regions (Kinsel, G. R.; Johnston, M. V. Int. J. Mass Spectrom. Ion Phys. 1989, 91, 157). Properly timed, the pulse could be applied once the ions of interest have entered the region and thus provide discrete focusing. A velocity compaction technique was proposed (Muga, M. L. Anal. Instrum. 1987, 16, 31), in which a synchronized, continuously increasing potential is applied to the drift region subsequent to ion extraction. This increases the velocity of all ions as they travel toward the detector. However, those ions farthest from the detector in a given isomass packet experience a greater increase in energy, allowing them to catch up to those ions closer to the detector, and thus decrease the temporal distribution of the ion packet. A similar technique called dynamic field focusing (DFF) (Yefchak, G. E., Enke, C. G., Holland, J. F. Int. J. Mass Spectrom. Ion Phys. 1989, 87, 313) was modeled, where the synchronized potential was increased only on the latter portion of an initial drift region. More recently, mass-correlated acceleration has been developed, where a synchronized dynamic field is located directly at the ion source exit (Kovtoun, S. V. Rapid Commun. Mass Spectrom. 1997, 11, 433-436; Kovtoun, S. V. Rapid Commun. Mass Spectrom. 1997, 11, 810-815; Kovtoun, S. V.; Cotter, R. J. J. Am. Soc. Mass Spectrom. 2000, 11, 841-853).
For the analysis of a 3-dimensional ion population having a random vector distribution of thermal energies, the effect of static and dynamic non-linear fields can be qualitatively described using FIGS. 5A-5D. FIGS. 5A and 5B show the graphs of the potential applied function of the distance S0. As shown in FIG. 5A′, the time required to exit a single-field ion source is plotted as a function of total energy for three series of ions having the same m/z and beginning from various starting positions centered about a grand average, S0 (as shown in FIG. 5A). Measuring the time of flight required to reach the ion source exit reveals that the initial spatial distribution is the primary factor contributing to the temporal distribution. At a distance of 2S0 beyond the ion source exit (FIG. 5B), space focusing is achieved and the ion population achieves a reduction in the temporal distribution (FIG. 5B′). However, even under optimum conditions, using linear fields in either a single-stage or dual-stage ion source configuration with first or second-order focusing, the temporal distribution resulting from the initial spatial distribution can be minimized but not eliminated.
As shown in FIG. 5C, the use of a non-linear-field ion source (Kovtoun, S. V., Cotter, R. J. U.S. Patent Pending, WO 0076638) has been demonstrated to achieve a complete space focus, further reducing the overall temporal distribution (FIG. 5C′) with the primary remaining temporal distribution being a function of the initial energy distribution.
A fundamental property of this non-linear theory predicts that the inclusion of a subsequent temporally static energy-correcting device such as an ion mirror should reduce the temporal distribution due to the initial energy spread. However, such devices cannot completely eliminate the distribution due to the fact that some ions in the initial ion population have positive initial energy vectors while others have negative initial energy vectors (i.e. the turn-around effect). One method for overcoming this phenomenon incorporates a short-duration, high amplitude voltage pulse to the back plate of the ion source prior to ion ejection in order to bias the initial energy distribution of the entire ion population to positive vectors (Sanzone, G. Rev. Sci. Instrum. 1970, 41, 741; Marable, N. L., Sanzone, G. Int. J. Mass Spectrom. Ion Phys. 1974, 13, 185). However, for ion populations possessing both positive and negative vectors, complete energy focusing is not possible.
The remaining problem of reducing the temporal distribution due to the initial energy spread can only be solved using a dynamic field, as shown in FIG. 5D and FIG. 5D′. Here, a combination of static and dynamic non-linear fields is required to achieve the maximum resolving power possible. One presentation suggesting the combined use of dynamic mass correlated acceleration and a static non-linear ion mirror has recently been proposed (Bowdler, A. R., Cotter, R. J.; Kovtoun, S. V. Proc. of the 49th ASMS Conf. on Mass Spectrom. And Allied Topics; Chicago, Ill., May, 2001). However, this was proposed for the limited analysis of MALDI-generated ions and has not been thoroughly developed. It also does not account for a static non-linear-field ion source.

Time-of-flight mass spectrometer combining fields non-linear in time and space


A recessed-gate thin-film transistor (RG-TFT) with a self-aligned lightly doped drain (LDD) is provided, along with a corresponding fabrication method. The method deposits an insulator overlying a substrate and etches a trench in the insulator. The trench has a bottom and sidewalls. An active silicon (Si) layer is formed overlying the insulator and trench, with a gate oxide layer over the active Si layer. A recessed gate electrode is then formed in the trench. The TFT is doped and LDD regions are formed in the active Si layer overlying the trench sidewalls. The LDD regions have a length that extends from a top of the trench sidewall, to the trench bottom, with a doping density that decreases in response to the LDD length. Alternately stated, the LDD length is directly related to the depth of the trench.

1. Field of the Invention
This invention generally relates to integrated circuit (IC) fabrication and, more particularly, to a recessed-gate thin-film transistor (RG-TFT) having a self-aligned lightly doped drain (LDD).
2. Description of the Related Art
The integration of complex circuit functions such as drivers, serial-parallel converters, video decoders, and the like on the glass panels used for LCD displays requires very high performance TFT transistors. These TFTs must operate at supply voltages of 5 V and below, to increase operating speed and decrease power consumption. MOSFET transistor performance is expressed in terms of switching speed or gate delay, and performance can be increased by decreasing operating voltage, gate oxide thickness, or channel length (Leff), increasing transistor drive current while decreasing the parasitic capacitances associated with the transistor structure. Devices with performance sufficient to meet the needs of advanced circuits operating at 5 V typically have gate lengths less than 1 micrometer (um) and gate oxide thickness below 15 nanometers (nm). An important side effect of decreasing transistor gate length and gate oxide thickness is the increase in field strength that occurs at the edge of the gate electrode adjacent to the drain. This increased field leads to several undesirable effects such as Vt roll-off, hot carrier injection, and drain induced barrier lowering (DIBL), which are generally referred to as short channel effects or SCE. An additional unfavorable effect that is applicable to fully depleted SOI and thin film transistors is the kink effect which causes high current instability for NMOS transistors.
FIG. 1 is a cross-sectional view of a TFT and a graph of current v. voltage (I-V) illustrating the kink effect at a high drain voltage (prior art). The kink effect is caused by the following chain of events. A high field is generated at the gate—drain edge, due to the applied voltages Vd and Vg, causing hot carrier injection, which in turn, generates electron-hole pairs. The field between source and drain moves holes to the source junction where they are trapped between the source junction and the substrate. The pile up of holes leads to a decrease in potential at the source edge of the gate, which has the effect of decreasing the channel length and increasing current. If the effect is severe, this current increase can lead to thermal cascade, melting, and failure of the device.
FIG. 2 is a partial cross-section of a TFT device and a simulation of the magnitude of the electric field under the gate for different device architectures (prior art). One widely-used strategy for improving short channel effects is to use lower doping at the edge of the MOSFET gate, as compared to the source/drain doping, in order to decrease the magnitude of the maximum field. Simulations of three approaches (Double Diffused Drain, Lightly Doped Drain, and gate overlapping Drain) are shown (from R. Izawa et al., "Impact of the Gate-Drain Overlapped Devices (GOLD) for Deep Submicrometer VLSI", IEEE Trans. Electron Devices 35, 2088 1988). The Double Diffused Drain architecture is not appropriate for liquid crystal display (LCD) fabrication because the process flow requires a very high temperature anneal to diffuse arsenic and phosphorus dopants at different rates. Both the LDD and GOLD architectures have been used for fabrication of TFT devices on glass substrates, and they are described briefly below.
FIG. 3 shows partial cross-sectional views of a transistor, depicting steps in the fabrication of an LDD structure formed with spacers (prior art). The use of a Lightly Doped Drain (LDD) structure to decrease the field intensity at the edge of the gate and improve short channel effects is well known in conventional CMOS processing. A schematic summary of the process of forming a device with an LDD structure is shown. Briefly, the process flow is as follows. After patterning the gate electrode, a low dose N or P type implant forms the LDD region. The implant density is typically about 1 to 3e13 cm−2, and the dopant is self-aligned with the gate electrode. A dielectric such as SiO2 or a composite layer of SiO2 and Si3N4 is deposited as a conformal layer over the gate and etched anisotropically to form spacers. The source and drain regions are doped with a high dose N or P type implant (typically implant density is about 1 to 7e15 cm−2), and the spacers protect the LDD region from the source/drain implant. In this case, the width of the LDD region is determined by the spacer width.
Thus, the LDD region has a higher resistance than the source/drain regions, and the voltage drop between drain and gate is spread over a larger distance than it would be if the junction between drain and channel regions were abrupt. In this way, the maximum field is decreased and short channel effects are decreased. Other methods are also known for forming lateral offsets between LDD and S/D implant.
FIG. 4 shows partial cross-sectional views of a transistor, depicting steps in the fabrication of a TFT using a GOLD process (prior art). A technique similar to the LDD approach, which has been used on TFT devices with long channels, is the Gate-Overlapping-Drain or GOLD process, which uses a medium dose implant prior to gate deposition to form a lightly doped drain region under the gate edge. Briefly, the process flow is as follows. Photoresist is patterned to protect the active silicon layer where the transistor channel is to be formed. An ion implant with a low dose of N (for NMOS transistor) or P (for PMOS transistor) type dopant forms the GOLD region. The implant density is typically about 1 to 9e13 cm−2. The position of the photoresist pattern with respect to the gate electrode determines the GOLD region width, so the GOLD process is not self-aligned. The gate dielectric (typically CVD SiO2) is deposited followed by the gate electrode, which may be doped polysilicon or a metal such as WTa, and the gate is patterned. The source and drain regions are doped with a high dose N or P type implant (typically implant density is about 1 to 7e15 cm−2). The gate electrode protects the GOLD region from the source/drain implant, so the width of the GOLD region is determined by the overlap between the gate edge and the GOLD implant edge.
All of the LDD formation techniques based on the use of a spacer suffer from variations in dopant due to the changes in thickness and step coverage of the spacer layer, and especially in the amount of over etch and the degree of isotropic etching in the spacer etch. In addition, the width of the spacer is limited to being less than the height of the gate stack used to form the edge of the spacer. If a wider spacer is required for high voltage devices, it is not practical to increase the gate electrode thickness.
The GOLD technique is limited by the resolution of lithography used for LCD panel fabrication and by the amount of overlay matching between the GOLD photo pattern and the gate patterning. For current fabrication methods the resolution limits for a step is about 1 um. Overlay matching, particularly across the very large glass substrates used for LCD panel fabrication, is very difficult and the variation in GOLD width due to differences in placement between the gate and GOLD layers may be as much as 1 um. As a consequence, the GOLD technique can only be used for long channel devices with gate lengths of about 4 um. The GOLD technique is not suitable for controlling SCE in high performance devices with sub-micron gate lengths.
It would be advantageous if a device structure and corresponding process existed for producing an LDD region with a well controlled LDD width in a single ion doping step, self-aligned to the gate, and suitable for sub-micron gate lengths.

Recessed-gate thin-film transistor with self-aligned lightly doped drain


The apparatus for coating a photosensitive material (M) with a processing liquid comprises an activator coating mechanism (43) for metering a constant amount of activator to apply the metered activator to the photosensitive surface of the photosensitive material fed by the pair of introduction rollers. The activator is supplied form a plurality of discharge holes (121) bored in a pipe (122) and is once received by a receiving portion (124). The activator is diffused horizontally and flows downwardly through a plurality of openings (123) bored at the bottom of the receiving portion onto a coating roller (125). The activator is diffused again at the contact between the coating roller and a diffusion film (126) and is coated to the photosensitive material by the coating roller.

1. Field of the Invention
The present invention relates to an apparatus for processing a photosensitive material with a processing liquid.
2. Description of the Background Art
Photosensitive materials, such as photosensitive films, photographic paper, printing plates and the like, on which images have been recorded are processed with a processing liquid such as activator, fixing solution, stabilizer, and rinsing water. Apparatuses for performing such processes upon photosensitive materials include a known dip-type processing apparatus wherein the photosensitive materials are fed into a processing tank storing a processing liquid by feeding means comprising pairs of feed rollers and the like and then dipped in the processing liquid, thereby subjected to processing.
Such an dip-type processing apparatus requires a great amount of processing liquid to dip the photosensitive materials therein. In the dip-type processing apparatus, the processing liquid is deactivated due to repeated processings for many photosensitive materials or developing degradation with time resulting from carbon dioxide and oxygen in the atmosphere. The processing liquid is recovered from the deactivation by adding a replenisher fluid to the processing liquid. This causes a difference between the ingredients of the processing liquid when the process starts and the ingredients of the processing liquid after a certain amount of process continues, failing to achieve exactly uniform processing.
To solve the problem, a coat-type photosensitive material processing apparatus has been used for coating a photosensitive surface of the photosensitive material with the processing liquid in amounts required to process the photosensitive material to perform processing in place of dipping the photosensitive material in the processing liquid. An example of the coat-type processing apparatus known in the art is such that the processing liquid is discharged from a processing liquid supply nozzle having a plurality of processing liquid discharge holes onto a roller (referred to hereinafter as a "roughened roller") having a surface roughened by forming grooves therein, and the roughened roller is rotated in contact with the photosensitive material, whereby the processing liquid is applied to the photosensitive material through the roughened roller.
In the background art processing apparatus, a pump for supplying the processing liquid by the application of pressure is used to force the processing liquid from a processing liquid tank storing the processing liquid into a processing liquid supply pipe having a plurality of processing liquid discharge holes. Since the pump is required to correctly supply a small constant amount of processing liquid per unit time, a pump for generating pulsation (referred to hereinafter as a "pulsation pump" in the present application) such as a peristaltic pump, an oscillating pump, and a bellows pump is used.
The background art apparatus has drawbacks to be described below.
1) For example, in the process step of coating a stabilizer to stabilize a lithographic printing plate employing a silver complex salt diffusion transfer reverse method (DTR method) after the development of the lithographic printing plat, the photosensitive layer of the photosensitive material has been swelled by the activator in the development step. When the swelled photosensitive material contacts the roughened roller of the background art apparatus, the photosensitive surface of the photosensitive material is damaged. PA1 2) The coat-type processing apparatus preferably uses a minimum amount of processing liquid in terms of running costs required for processing and environmental issues. However, supply of a small amount of processing liquid to the processing liquid supply nozzle makes it difficult for the background art apparatus to provide a uniform amount of processing liquid discharged from the processing liquid discharge holes to the roughened roller, accordingly resulting in a non-uniform amount of processing liquid applied to the photosensitive material. This phenomenon is liable to occur particularly in the leading edge portion of the photosensitive material. PA1 3) A processing liquid supply apparatus employing the pulsation pump repeats a discharging state wherein the processing liquid is discharged from the processing liquid discharge holes and a non-discharging state wherein the processing liquid is not discharged as the processing liquid delivered from the pulsation pump produces a pulsating flow. In the non-discharging state of the processing liquid, air is sometimes drawn into the processing liquid supply pipe through such a processing liquid discharge hole in the reverse direction to form an air bubble in the processing liquid supply pipe. If such a bubble in the processing liquid supply pipe is greater in size than the processing liquid discharge hole, the surface tension of the processing liquid defining the bubble causes the bubble to block the processing liquid discharge hole to preclude the processing liquid to pass through the discharge hole. This results in a non-uniform amount of processing liquid discharged from the plurality of processing liquid discharge holes of the processing liquid supply pipe. PA1 4) In the coat-type photosensitive material processing apparatus, when a puddle of processing liquid having a sufficient volume is not formed between the roughened roller and a support roller prior to the application of the processing liquid to the photosensitive material, processing unevenness resulting from the shortage of the processing liquid occurs particularly in a leading edge portion of the photosensitive material. PA1 5) The coat-type photosensitive material processing apparatus is intended to promote processing by supplying the processing liquid from a processing liquid tank for storing the processing liquid heated to a predetermined temperature to a processing liquid coating portion for coating the photosensitive material with the processing liquid to apply the heated processing liquid to the photosensitive material. At the start of coating of the photosensitive material, the temperatures of a feed passage of the processing liquid from the processing liquid tank to the processing liquid coating portion and the temperatures of the above described roughened roller and support roller have been decreased to room temperature. This decreases the temperature of the processing liquid to be applied to the photosensitive material through the processing liquid feed passage, resulting in processing unevenness. PA1 6) In the coat-type processing apparatus employing the roughened roller, contaminants such as silver sludge (referred to hereinafter as "silver sludge and the like") are produced from the processing liquid when the processing liquid is continuously applied to the photosensitive material. The silver sludge and the like is deposited in recesses, such as grooves, of the roughened roller.
Additionally, the use of the lithographic printing plate employing the silver complex salt diffusion transfer reverse method (DTR method) wherein development proceeds rapidly as the photosensitive material not only makes the above described drawback pronounced but also decreases printing performance, particularly the plate life, which is a problem inherent in the lithographic printing plate.
The non-uniform amount of processing liquid coating the photosensitive material creates processing unevenness of the developed photosensitive material. The occurrence of the processing unevenness is particularly pronounced in the lithographic printing plates utilizing the silver complex salt diffusion transfer reverse method (DTR method) in which development proceeds rapidly.
To solve this problem, there has been proposed a photosensitive material processing apparatus wherein the processing liquid is supplied from a slit opening formed between a pair of sheets to a processing liquid coating portion comprising a pair of non-rotatable rod-shaped members and the photosensitive material is passed through a puddle of processing liquid stored between the pair of rod-shaped members whereby the processing liquid is applied to the photosensitive material.
This photosensitive material processing apparatus is capable of relatively uniformly supplying a small amount of processing liquid. In this case, however, the amount of processing liquid coating the photosensitive material depends on the amount of processing liquid supplied to between the pair of rod-shaped members. Thus, the attempt to coat the entire photosensitive material with an exactly uniform amount of processing liquid has an inevitable limitation.
In the presence of the silver sludge and the like covering the recesses, such as grooves, of the roughened roller, the decrease in the amount of processing liquid to be applied to the photosensitive material causes the shortage or non-uniformity of the amount of processing liquid to be applied to the photosensitive material. The shortage or non-uniformity of the processing liquid to be applied to the photosensitive material results in the processing unevenness of the developed photosensitive material and the reduction in plate life in printing using the photosensitive material. Such phenomena are particularly pronounced when the lithographic printing plate employing the silver complex salt diffusion transfer reverse method (DTR method) wherein development proceeds rapidly is used as the photosensitive material.
Thus, an operator must repeatedly clean the roughened roller to remove the silver sludge and the like deposited on the roughened roller.

Apparatus for processing photosensitive material


A multimedia optical disc including data area and index area is provided. The data area includes objects each of which includes video data. The index area includes sub-areas. Each sub-area includes addresses of objects selected from the objects in the data area, a flag indicating a random reproduction of the objects selected, and a number of repeats of the random reproduction.

(1) Field of the Invention
The present invention relates to an optical disc which stores information signals recorded and to a reproduction apparatus for reproducing such optical discs, more specifically to an optical disc which stores multimedia data including digital moving picture data, audio data, and sub-picture data and to an optical disc reproduction apparatus for reproducing such optical discs.
(2) Description of the Prior Art
Interactive software titles of various genres, such as aerobics, education and cooking, have been becoming increasingly noticeable of late in the market of music and movie software titles. Such interactive software titles include a plurality of branches during the reproduction of an optical disc, with the user being able to select the branch-to addresses. Interactive software titles with simple mechanisms have already been achieved for conventional video CD applications.
The first basic technique for the achievement of interactive software is distributed recording. This refers, for example, to the division of a one-hour-long movie into, say, one-minute-long or five-minute-long sections which are recorded in separate areas on a spiral track, but not in a sequential order. The second basic technique is random accessing in which pieces of image information stored in separate areas are read in an arbitrary order using a plurality of sets of control information. Such sets of control information for random accessing each include a reading order of the pieces of image information and address information specifying areas on the spiral track in which the pieces of image information are recorded. Here, there can be as many sets of control information as there are reading orders, with the user being able to select a reading order from a menu displayed on the screen.
In this way, interactive software can provide several courses that can be selected by the user using menus.
The following is a description of an interactive aerobics software title. This aerobics interactive software title has a plurality of shots of an instructor doing different exercises, with several reproduction routes being recorded in the title. These reproduction routes correspond to courses such as xe2x80x9cmake your waist slim,xe2x80x9d xe2x80x9cmake your legs slim,xe2x80x9d and xe2x80x9cLose five kilosxe2x80x9d which can be selected by the user according to his/her purpose. As one example, if the user selects the xe2x80x9cmake your legs slimxe2x80x9d course, a series of shots including leg exercises, such as moving around with rhythmical steps, jumping, raising right leg high, and raising left leg high, are reproduced in succession.
If the user selects the xe2x80x9cmake your waist slimxe2x80x9d course, a series of shots concerning waist exercises, such as twisting the waist to the right and left or bending over, are reproduced in succession.
A menu which is displayed using image data and which includes these course titles is displayed on the screen when the user loads the optical disc into the disc reproduction apparatus. Then, after the user has selected a desired course from the menu in accordance with his/her purpose, physical condition and quickness, the disc reproduction apparatus sequentially reads a plurality of shots in a reproduction route which corresponds to the selected course. The read shots are converted into image signals to be displayed on the screen. Here, by following the instructor""s movements which are displayed on the screen, the user can enjoy a desired exercise program in the comfort of their own home. Should the user get bored with the selected program or wish to try something new, he/she can select another course and adjust its level to suit him/her.
This kind of interactive software title recorded on an optical disc is ideal for a housewife who is on a diet since she can select an exercise program according to her physical condition and purpose and can exercise in between her chores. Such interactive software titles are also beneficial for company employees since they can complete a short exercise program, such as before going to work, in order to compensate for their lack of exercise.
Here, although conventional interactive software titles include a plurality of courses, these courses use a same reproduction order every time. For this reason, users tend to get bored with the exercise programs provided by such titles. For the example of an aerobics software title, the user can soon master the movements repeated in the lesson, so that such software titles quickly become routine to users. Here, there have been suggestions to provide a random reproduction function to the disc reproduction apparatus so as to avoid this tendency for the reproduced content to become routine. Such a random reproduction function, which is a function for reproducing pieces of data recorded on a storage medium in a random order, is widely used in the reproduction of music software. However, it is not desirable to use this function for interactive software titles since the function regards every piece of data recorded on the optical disc as a potential reproduction object. This is to say, for the example of an interactive aerobics title, conventional random reproduction could have a menu, a shot of the instructor raising his/her leg, and a shot of the instructor shaking his/her arms displayed in that order, which would clearly make no sense to the user and would be of little value as exercise.
As can be clearly seen from the above example, for certain kinds of interactive title, the reproduction of pieces of data recorded on the optical disc at complete random destroys the logical structure of reproduction routes for each course. To avoid such disordered reproduction, a user programming function may be used. Here, a user programming function is a function which invites the user to set the reproduction order of the course by himself/herself. Here, the manual or jacket of the software title can assist the user in setting such a reproduction order, with most modern disc reproduction apparatuses being equipped with this function. However, the setting of such functions tend to be rather complicated, so that users, such as housewives or office workers, may not have enough time for setting reproduction orders by themselves. Such time-consuming procedures may end up only discouraging users from using such aerobics software titles.
It is therefore the first object of the present invention to provide a multimedia optical disc and a reproduction apparatus which achieve an interactive software title in which a plurality of pieces"" of moving picture data in a course selected by the user can be reproduced in a random order without making the user feel confused.
It is the second object of the present invention to provide a multimedia optical disc and a reproduction apparatus which achieve an interactive software title in which a plurality pieces of moving picture data in a course selected by the user can be reproduced in a random order without requiring prior programming by the user.
The above objects are achieved by a multimedia optical disc comprising a data area and an index area, the data area comprising a plurality of objects each of which includes video data, and the index area comprising a plurality of sub-areas each of which includes addresses of objects selected from the plurality of objects stored in the data area, a flag indicating a random reproduction of the objects selected, and a number of repeats of the random reproduction.
With such a construction, the disc reproduction apparatus generates random numbers and selects the addresses in the same sub-area at random after reading data recorded as above. As understood from the above description, since each of the sub-areas includes a random reproduction instruction and selected addresses, the objects to be selected at random are limited to the addresses in each of the sub-areas. Here, if each course such as xe2x80x9cmake your legs slimxe2x80x9d and xe2x80x9cmake your waist slimxe2x80x9d corresponds to a sub-area, the objects in each course are read and reproduced at random. As a result, the objects of each course are reproduced in arbitrary order, with the regularity of the course, which is constructed under the logical structure of the interactive software title, being maintained. Accordingly, the reproduction of the optical disc does not make the user feel confused and provides the user freshness for a long time by reproducing objects in a course in a random order, without requiring prior programming by the user.

Optical disc for coordinating a variable reproduction of video images


Selective erase method for a flash memory device including a group of memory cells arranged in rows and columns include performing an erase operation on the group of memory cells and verifying the erase operation on the group of memory cells to determine threshold voltages of the memory cells. At least one row of memory cells including memory cells having a threshold voltage lower than a desired erase threshold voltage is identified. A further erase operation is performed on the group of memory cells excluding memory cells of the at least one row of memory cells including memory cells having a threshold voltage lower than a desired erase threshold voltage.

The present invention relates to integrated circuit devices and, more particularly, to flash memory devices and programming methods thereof.
Non-volatile memory devices are generally capable of storing data even when no power is supplied. One type of non-volatile memory device is a flash memory. Flash memories typically operate by electrically erasing data in a plurality of cells at the same time. Flash memories have been widely used in the field of computers and memory cards in recent years.
FIG. 1 is a cross-sectional view illustrating a conventional NOR-type flash memory cell 10. As shown in FIG. 1, an electrically programmable and erasable NOR-type flash memory cell 10 includes N-type source and drain regions 13 and 14, insulating layers 15 and 17, a floating gate 16, a control gate 18 and a P-type semiconductor substrate (bulk) 19. The source and drain regions 13 and 14 are shown formed on the semiconductor substrate 19. The floating gate 16 is shown formed adjacent a channel region of the source and drain regions 13 and 14 on a thin insulating layer 15 having approximately 100 Angrstrom (Å) thickness. The control gate 18 is formed on an upper portion of the floating gate 16 with the insulating layer 17 therebetween. The control gate 18 is connected to a word line of a NOR-type flash memory device including the cell 10.
While only a single cell is illustrated in FIG. 1, it will be understood that a cell array of the NOR-type flash memory devices is generally arranged in rows (selectable by word lines) and columns (selectable by bit lines) and may include a plurality of banks, each having a row and column arrangement of cells. Each of the banks may include a plurality of sectors and each sector may include a plurality of memory cells. Typically, an erase operation of the NOR-type flash memory is performed a sector at a time. The sector may include 1024 word lines. A program operation is typically performed a word line at a time (or by byte unit).
Flash memory cells within a sector are generally erased concurrently by F-N tunneling (Fowler-Nordheim tunneling). In F-N tunneling, a negative high voltage, for example, about −10 volts (V), is typically applied to the control gate 18, and a positive voltage of, for example, 5 to 10V, suitable to generate the F-N tunneling, is applied to the semiconductor substrate 19. At this time, the source and drain regions 13 and 14 are maintained in a floating state. An erase operation under this bias condition may be referred to as a Negative Gate and Bulk Erase (NGBE). Under this bias condition, an electric field of about 6 to 7 millivolts/centimer (MV/cm) is typically formed between the control gate 18 and the semiconductor substrate 19 to generate F-N tunneling. As a result, negative charges that accumulate on the floating gate 16 are discharged to the source region 13 through the insulating layer 15, and the threshold voltage of the flash memory cell 10 becomes low.
FIG. 2 is a flowchart showing a conventional erase operation of a NOR-type flash memory. As shown in FIG. 2, the erase operation of the NOR-type flash memory includes: performing a pre-program and verification (block 110); performing a main erase by sector unit and verification of the same (block 120); and, performing a post-program operation with verification (block 160).
At block 110, in order to prevent or limit a memory cell from being over-erased during the main erase operation, the pre-program may be performed by applying the same bias as a normal program operation to the memory cell. After performing the pre-program, the verification of the pre-program may be performed. If the state of a selected memory cell is not a program state, a program operation may be repeatedly performed until the selected memory cell reaches the program state.
At block 120, a main erase operation may be continuously performed to set all the memory cells within a sector unit to the same erase state, such as an "on" state. After performing the erasing operation, the verification operation to verify that all cells have been erased is typically performed. If the state of a selected one of the memory cells is determined not to be in the erase state during verification, an erase operation is typically performed again until the selected memory cell is set to the erase state.
As a result of the repeated erase operations due to individual memory cells not being initially set to the erase state while other cells have already reached the erase state, previously erased memory cells may be over-erased. The pre-program operation is typically performed as indicated at block 110. However, the post-program operation is performed at block 160 after the main erase is completed (i.e., all the cells in the sector unit verify as having been erased). This post program operation is generally performed after the main erase is completed as there may be over-erased memory cells (memory cells having a threshold voltage of a lower level than a target erase threshold voltage) after the main erase operation due to an erase speed difference of the respective memory cell.
To perform the post-program, a source and substrate of the over-erased memory cell are generally grounded. In addition, a voltage (e.g., 3V) lower than a program voltage (e.g., 10V) is typically applied to a control gate, and a voltage of about 5 to 6V is typically applied to a drain region. By applying this voltage bias condition, a small amount of negative charge, in comparison with the pre-program operation, is generally accumulated on the floating gate during the post-program operation. After performing the post-program operation, a verification of the post-program is generally performed as indicated at block 160. The verification process for the post-program operation may be performed in substantially the same manner as described with reference to the verification for the pre-program operation at block 110.
Using the erase method described with reference to FIG. 2, over-erased memory cells may generally be cured. However, it is, as a practical matter, essentially impossible to fundamentally prevent memory cells from being over-erased. This limitation generally arises because the erase and verify operations at block 120 are typically performed based on characteristics of a memory cell having the highest threshold voltage. In other words, according to a conventional erase method, an erase operation is typically performed repeatedly so that the threshold voltages of all memory cells drops to the maximum value of a distribution of threshold voltages for an erase state of a memory cell. During the repeated erase operations, a memory cell having fast erase speed (high coupling ratio (R)) is typically erased relatively faster than a memory cell having slow erase speed. A threshold voltage difference between a cell with a fast erase speed and a cell with the slowest erase speed is generally referred to as a distribution of erase threshold voltages within a sector unit. The distribution of erase threshold voltages generally increases in proportion to a difference of the erase speeds. If the distribution of erase threshold voltages is great, the erase threshold voltages of several cells may drop to less than 0V before the slowest cell is erased. Such cells are generally referred to called as over-erased cells. A cell having a threshold voltage of less than 0V should have its threshold voltage raised to more than 0V again by the post-program operation. However, with an increase in over-erased cells, excessive current may flow.
In addition, on occasion, attempts to raise a threshold voltage to more than 0V may fail. This phenomenon may be referred to as an over-erase problem. Accordingly, it may be beneficial to decrease the distribution of threshold voltages in an erase state in designing high-integration NOR-type flash memory devices.


Tracking of measured depth with intervening depositing of one or more layers provides a way of improving the accuracy of surface reconstruction. For example, knowledge of the desired or expected thickness of each layer, in combination with the scan data is combined to yield higher accuracy than is available from scan data of a single scan alone. One application of such an accurate surface reconstruction is in a feedback arrangement in which the desired thickness of one or more subsequent layers to be deposited after scanning is determined from the estimate of the surface depth and a model of the object that is being fabricated, and by increasing accuracy of the surface depth estimate, the precision of the fabrication of the object may be increased.

This invention relates to reconstruction of surfaces during additive manufacturing.
Additive manufacturing is a set of methods that allows objects to be fabricated via selective addition of material. A typical additive manufacturing process works by slicing a digital model (for example, represented using an STL file) into a series of layers. Then the layers are sent to a fabrication apparatus that deposits the layers one by one from the bottom to the top. Additive manufacturing is rapidly gaining popularity in a variety of markets including automotive, aerospace, medical devices, pharmaceuticals, and industrial tooling.
Inkjet 3D printing is a method of additive manufacturing where printheads deposit droplets of printable material, also called ink. Printheads are typically mounted on a gantry system to allow deposition of printable liquid matrix material in different locations of the build volume. A build platform may also move with respect to the printheads, which may be stationary. The printable liquid matrix material is solidified using UV or visible-light radiation.
Multiple printheads may be used in one system in order to build objects with multiple base materials. For example, materials that have different optical, mechanical, thermal, electromagnetic properties can be used. These materials can be combined to achieve composite materials with a wide range of material properties.
Surface reconstruction is important for various machine vision applications. In some examples, to reconstruct a surface, a sensor system is used to measure the depth of the surface (e.g., the distance between a sensor over the object and the surface of the object). Given a known distance from the platform on which the object is being fabricated, a thickness of the object can be determined based on the depth of the surface. However, surface reconstruction based on depth measurements is potentially unreliable. For example, the sensor may receive data that is ambiguous or has high measurement error (e.g., there might be two or more possible values for the depth that are consistent with a measurement or the signal at the correct depth value might be weak resulting in the high measurement error).

Reconstruction of surfaces for additive manufacturing