Method and system for detecting endpoint for a plasma etch process are provided. In accordance with one embodiment, the method provides a semiconductor substrate having a film to be processed thereon. The film is processed in a plasma environment during a time period to provide for device structures. Information associated with the plasma process is collected. The information is characterized by a first signal intensity. Information on a change in the first signal intensity is extracted. The change in the first signal intensity has a second signal intensity. The change in signal intensity at the second signal intensity is associated to an endpoint of processing the film in the plasma environment. The second signal intensity may be about 0.25% and less of the first signal intensity.

Embodiments in accordance with the present invention are directed to integrated circuits and their processing for the manufacture of semiconductor devices. More particularly, embodiments in accordance with the present invention provide a method and a system for endpoint detection in an etch process. But it would be recognized that embodiments in accordance with the present invention have a much broader range of applicability.
Integrated circuits or "ICs" have evolved from a handful of interconnected devices fabricated on a single chip of silicon to millions of devices. Current ICs provide performance and complexity far beyond what was originally imagined. In order to achieve improvements in complexity and circuit density (i.e., the number of devices capable of being packed onto a given chip area), the size of the smallest device feature, also known as the device "geometry", has become smaller with each generation of ICs. Semiconductor devices are now being fabricated with features less than a quarter of a micron across.
As merely an example, etching processes are often used to remove or partially remove a layer to form structures there from. Etching is often performed by an etching tool, such as a dry etcher or wet etcher. The wet etcher often includes a vessel that has an etchant chemical to selectively remove one material from another material. The dry etcher often includes a plasma source and treatment chamber. The dry etcher often uses gases such as fluorine bearing species and chlorine bearing species to remove semiconductor materials such as silicon, or metal such as aluminum, or dielectric material such as silicon oxide. Much work has been done to use real-time metrology to characterize semiconductor manufacturing processes and the effect of these processes on the wafers being processed. One of the big difficulties is that in contrast to ex situ metrology, which allows detailed scrutiny of the wafer surface, real-time metrology requires in situ measurement, which rarely allows such a close investigation of the wafer. Consequently, one needs to measure parameters such as the power being delivered into a process chamber, or the effluent emanating from a process chamber in order to make inferences about the state of the wafer.
Typical objectives of real-time metrology for semiconductor processes include identification of a particular wafer state, such as that point at which a particular thin film is fully etched in a plasma etch process (the end point0; or characterization of key process parameters, such as the rate at which a thin film is being deposited or etched.
One of the primary difficulties in such metrology is the correlation between the measurement and the desired objective. Changes in the measured parameter, such as effluent composition, or the voltage associated with the power being delivered into the process chamber, depend on a myriad different process, chamber, and/or wafer parameters. For example, the amount of effluent being measured depends on whether or not one has completely etched though a particular film, but it will also depend on the temperature of the wafer, the rate at which gases are flowing into the chamber, the power being delivered, and many other parameters.
Currently, this problem is being addressed by running the process under different conditions, either with a design of experiments or with the natural variations that occur in a manufacturing environment, and using techniques such as neural network analysis to find those correlations between the measured parameters and the desired objective such that one can depend on the correlation across a variety of process conditions. Unfortunately, such an approach is not highly robust.
Other conventional techniques such as optical emission spectroscopy (OES) or radio frequency (RF) measurement are also used to determine when a target layer is completely removed or endpoint of the etch process. However as device shrinks, the area of the material removed is a very small fraction of the overall area. In a typical via etch, for example, the area of dielectric layer to be removed is only about 1% or less of the total area. Since OES or RF measurements measure an overall plasma state, the effect from other interferences often overwhelms the signal of the measurement. In addition, conventional endpoint detection relies on mathematic techniques such as multivariate analysis or neural networks to identify the endpoint signal. In absence of physical understanding of factors affecting the signal of measurement, the problem of looking at a wrong signal is further exacerbated. This leads to an over etch or an under etch of the material and impact device performance.
From the above, it is seen that an improved technique for processing semiconductor devices is desired

Use of modeled parameters for real-time semiconductor process metrology applied to semiconductor processes


Toner particulates include a release agent which comprises a functionalized enhancing agent and a wax. The toner particulates may be used to improve dry fuser release and to improve color clarity in overhead transparencies.

This invention relates to release agents, toner particulates and toner compositions. This invention also relates to methods of improving dry fuser release for the prevention of fuser jamming and fuser wrapping, and of methods of improving overhead projection transparencies.
Numerous methods and apparatuses for electrophotography, electrostatic recording and electrostatic printing are known in the art. Typically, a charged photosensitive surface, for example a charged photosensitive drum, is irradiated with an optical image and an electrostatic latent image is formed on the photosensitive surface. In the development process, a developing agent, i.e., toner, is adhered to the electrostatic latent image.
Typically, toner is fed to a developer roller by a metering blade positioned against the surface of the developing roller. The developer roller, with the toner on its surface, is typically rotated in a direction opposite to that of the photosensitive drum (or in the same direction at a different speed), and toner adheres to the electrostatic latent image to develop the image. Various toner compositions have been developed in order to provide improved copying, recording and/or printing with such apparatus.
One method of fusing a toner image to a substrate is to bring the toner in contact with a hot surface such as a heated roller. However, there is a tendency for a fuser to collect small amounts of toner which in turn causes toner offset to build up on the fuser surface. This toner may be then transferred to a subsequent substrate, thereby causing a poor image.
The fuser roll surface may be wetted with a release agent such as a silicone oil in order to decrease the problem of toner offset. Unfortunately, the silicone oil release agent may leave oil residues on the paper, thereby interfering with the image quality. Additionally, the release agent material tends to migrate to other surfaces within the printer where it interferes with proper development of the latent image to diminish print quality, especially in the case of duplex printing. Therefore, a dry fuser, that is a fuser without any oil on its surface, is often desirable.
In order to solve the problem of toner offset with dry fusers, lubricants or waxes are often added to the toner. Unfortunately, at high concentrations effective for the purpose of dry fuser release many conventional lubricants tend to separate from the toner during the process of development, and stick to the doctor blade causing a filming problem which adversely affects print quality.
Toner release from dry fusers has been enhanced by modification of toner resin rheology. High molecular weight resins or resins having crosslinks may exhibit improved release. Unfortunately, use of such high molecular weight or crosslinked resins generally results in poor clarity of overhead projection transparencies or in inadequate fuse grade at higher speeds. Generally, high transparency or excellent high speed fuse grade requires lower melt temperature resins or higher fusing temperatures, but such resins or temperatures cause toners to adhere easily to dry fuser rollers. Thus, it is difficult to develop toners for transparencies or lower temperature fusing applications which exhibit good release, good fuse grade and the good transparency needed for reproduction of a large color gamut and for clarity. Generally, in order to maintain good clarity and high speed fuse grade, the lower melt temperature resins used in toners require that a separate release agent be used.
Tomita et al., U.S. Pat. No. 5,225,303, disclose a toner comprising binder resin, coloring agent, and a release agent, which contains as the main components a carnauba wax substantially free of aliphatic acids and/or a montan ester wax, and an oxidized rice wax with an acid value of 10 to 30. Tomita et al. teach that the acid value of the montan ester wax is preferably in the range of from 5 to 14, and that the carnauba wax preferably comprises 5 weight percent or less free aliphatic acids.
Inoue et al., U.S. Pat. No. 5,643,705, disclose a toner comprising a toner particulate containing a polyolefin wax and a modified polyolefin wax. Inoue et al. disclose the polyolefin wax is a low number-average molecular weight polyethylene or low number-average molecular weight polypropylene having a softening point of from 80xc2x0 C. to 160xc2x0 C., and that the modified polyolefin wax is mainly composed of low number-average molecular weight polyethylene, wherein the modifying component used to modify the polyolefin wax is an aromatic vinyl monomer, an acrylate monomer, an unsaturated dicarboxylic acid ester or a mixture thereof.
Taguchi et al., U.S. Pat. No. 5,466,555, disclose a releasing composition comprising 60 to 99.5% by weight of a low molecular weight polypropylene having a melt viscosity of 15 to 2,000 cps at 160xc2x0 C., and 0.5 to 40% by weight of at least one modified polyolefin selected from the group consisting of low molecular weight polypropylene having a melt viscosity at 160xc2x0 C. higher than that of the first polypropylene, modified with an ethylenically unsaturated carboxylic acid or an anhydride thereof, and a modified polyethylene comprising a low molecular weight polypropylene having a melt viscosity of 10 to about 8,000 cps at 1 40xc2x0 C., modified with an ethylenically unsaturated carboxylic acid or an anhydride thereof.
Katada et al., U.S. Pat. No. 5,972,553, disclose a toner comprising polymer components, a colorant, a charge control agent, and a wax terminally modified with at least one of maleic acid, maleic acid half ester, or maleic anhydride. Katada et al. teach that the polymer components include a low molecular weight polymer component having an acid value Avl and a high molecular weight polymer component having an acid value Avh such that Avl is greater than Avh. Katada et al. further teach that the wax has an acid value Avwax satisfying Avl greater than Avwax, and Avwax greater than 0 mg KOH/g, and that the wax may have an acid value of 1 to 15.
Unfortunately, many prior art toner compositions comprise large amounts of release agents such as waxes, and such large amounts tend to interfere with print quality. Other prior art toners comprising waxes have a poor fuse grade, that is, the print is not resistant to abrasion and may be abraded or scraped off. Some waxes, such as polyolefin waxes, tend to migrate to the photoreceptor causing poor print quality, or causing staining of the photoreceptors. Further, many color toners which contain release agents fail to exhibit both good release and the good transparency needed for reproduction of a large color gamut and for clarity.
In the pursuit of high quality, vibrantly colored overhead transparencies, it has been discovered that the achievement of this goal through electrophotography is dependent not only upon the inherent transparency of the binder resin, but upon the release/transparency (r/t) window of said binder resin. The r/t window of a toner is defined as that range of temperatures in which a toner is sufficiently fused to produce a bright, colorful image when projected and where it releases cleanly from the fuser hot roll. This window is the cross section of the independent release and transparency windows. Each resin system has its own characteristic cross section. xe2x80x9cReleasexe2x80x9d refers to the tendency of a developed image to wrap the fuser roll upon nip exit at a given temperature. The release window is a range of temperatures bounded at the low end by cold offset and at the high end by fuser adhesion or hot offset. xe2x80x9cTransparencyxe2x80x9d refers to the ability of a toner to transmit light without scatter. The transparency window can be measured by evaluating the percentage transmitted light through a sample that has been fused at a given temperature. It is a range of temperatures bounded by low fuse grade, characterized by muddy projected color, and hot offset, where the rough toner surface begins to scatter light. The overlap of the release range and the transparency range of a given toner at a specific mass per unit area is the release/transparency window for that toner.
It is desirable that the r/t window be wide and achievable at temperatures sustainable for the lifetime of a fuser assembly. Typically the range of temperatures where a binder resin achieves transparency corresponds to the onset of fuser wrapping. The properties that lead to excellent transparency, low molecular weight, low melt temperatures, low viscosity, and low gel content, also generally yield poor wrapping, filming, and hot offset performance.
These principles of release may also be applied to black toners. The market trend is not merely to color toner but also toward higher speed printing. Though obviously lacking any requirement for the achievement of transparency, like requirements for the projection of color, high speed fusing requires toners with rapid melting characteristics. Black toners must achieve adequate fuse grade, sufficient melting of the toner powder to cause tenacious adhesion of the toner image to the substrate. Black toners may be said to have a release/fuse grade window analogous to the release/transparency window defined above for color toners. Like with the color example, the properties that support rapid fusing, low molecular weight, low melt temperatures, low viscosity, and low gel content, generally yield poor wrapping, filming, and hot offset performance.
High molecular weight resins may release effectively but cannot achieve a satisfactory transparency or fuse grade at temperatures that can be maintained without damage to the fuser assembly. Crosslinked resins may contain sufficient elasticity to release at a wide range of temperatures, but are likely to be characterized by low fuse grade. The balance of release and transparency/fuse grade is difficult to achieve with resin chemistry alone. Conventional solutions to this challenge include the incorporation of release agents, such as polypropylene waxes, into the toner formula, or the application of low melt release agents, such as silicone oil, to the surface of the hot roll. Chemically polymerized toners using high levels of encapsulated wax have also appeared. Though these methods are each utilized in the industry each has its own disadvantages.
The level of internal release agent required for adequate release in low melt systems is generally high, forming large domains of incompatible material, and therefore usually accompanied by a strong tendency to film the electrophotographic (EP) components. This filming leads to the destruction of image quality. Higher levels of internal wax in conventional toner can be achieved through the use of compatibilizing agents, but these agents tend to decrease the effectiveness of the wax and also have a negative effect on transparency. Chemically prepared toners (CPTs) with high levels of encapsulated wax suffer from haze. Though use of an oiled hot roll avoids the occurrence of filming and the appearance of haze, the oil has a tendency to migrate. This migration of oil results in the disruption of the duplexing capability of the machine. Metering mechanisms have been designed to limit the amount of oil flowing through the system at any given time. These metering devices, however, are expensive and dramatically increase the price of a printer.
Thus, there is a need for methods of improving toner release which produce high image quality overhead transparencies with vibrant projected color. Particularly, there is a need for methods of improving or enhancing toner release which avoids the need for expensive metering mechanisms. Further, there is a need for release agents which may be incorporated into toner particles thereby providing toner compositions with adequate fuse grade and good dry fuser roller release, and which provide good print quality and acceptable clarity for overhead projection transparencies. The release agent should not promote smearing or blocking of toner, or filming on the doctoring blade, developer roller or the photoconductor drum.
Accordingly, an object of this invention is to provide improved release agents, toner particulates and toner compositions.
It is another object of this invention to provide methods for improving dry fuser roller release.
It is a further object of this invention to provide methods of improving color clarity in overhead projection transparencies.
It is yet another object of this invention to provide toner compositions having adequate fuse grade.
It is yet another object of this invention to avoid component contamination by residual oil by using an oil-free dry fuser roller and toners which release from the dry fuser roller without filming.
It is yet another object of the invention to provide toner compositions exhibiting good dry fuser roller release.
In accordance with one aspect of the invention there are provided release agents comprising, by weight, no more than about 50% wax and at least about 50% functionalized enhancing agent, while in accordance with another aspect of the invention there are provided release agents comprising from about 15% to about 75%, by weight, wax and from about 25% to about 85%, by weight, functionalized enhancing agent. The wax has a number-average molecular weight of no greater than about 10,000.
In accordance with one aspect of the invention there are provided toner particulate comprising a release agent comprising wax and functionalized enhancing agent; wherein the release agent comprises, by weight of total release component, no more than about 50% wax and at least about 50% functionalized enhancing agent, while in accordance with another aspect of the invention there are provided toner particulates comprising a toner binder resin, a colorant, a charge controlling additive and a release agent, wherein the release agent comprises from about 15% to about 75%, by weight, wax and from about 25% to 85%, by weight, functionalized enhancing agent. The wax has a number-average molecular weight of at no greater than about 10,000.
In accordance with one aspect of the invention there are provided methods of improving the release/transparency window of an overhead projection substrate of a color toner image using a low oil or oil-less fuser roll comprising the step of printing the overhead projection substrate with a composition comprising toner particulates, wherein the toner particulates comprise a colorant, resin and a release agent comprising, by weight of total release agent, no more than about 50% of a wax having an acid value of no more than about 10 and a number-average molecular weight of at no greater than about 10,000, and at least about 50% of a functionalized enhancing agent having an acid value of from about 10 to about 100.
In accordance with yet another aspect of the invention there are provided methods of improving dry fuser release of a toner composition, comprising the step of providing the toner composition with a release agent, wherein the release agent comprises, by weight, no more than about 45% wax and at least about 55% functionalized enhancing agent.
In accordance with yet another aspect of the invention there are provided toner compositions comprising a wax, and a functionalized enhancing agent comprising a polyalkylene having at least one maleic half ester moiety grafted onto the polyalkylene.
Additional embodiments and advantages of the toner compositions, toner particulates, release agents and methods herein will be apparent from the following description.

Toner comprising wax and functionalized enhancing agent


A flat-panel, quantum-limited x-ray imager for fluoroscopy is configured for converting very low levels of x-rays into electrical signals suitable for standard processing by a computer into real-time images, and comprises a screen for converting x-rays into visible light, a very fast demagnification lens system/array positioned behind the screen and configured to provide quantum-limited performance, and an array of CCD image sensors optically coupled, via the lens system, to the screen. The CCD sensors have a high signal-to-noise ratio and an onboard CCD amplification mechanism in the form of an extended section of “gain” register between the normal serial register and the final detection node or output amplifier. The sensors' sequential, internal electrodes are controlled by way of a clocking scheme that produces a slight and well-controlled avalanche multiplication (a slight gain) at each stage in the gain register.

Fluoroscopy is a process for obtaining continuous, real-time images of an interior area of a patient via the application and detection of penetrating x-rays. Put simply, x-rays are transmitted through the patient and converted into visible spectrum light by some sort of conversion mechanism (e.g., x-ray-to-light conversion screen and/or x-ray image intensifier). Subsequently, the visible light is captured by a video camera system (or similar device) and displayed on a monitor for use by a medical professional. Typically, this is done to examine some sort of ongoing biological process in the human body, e.g., the functioning of the lower digestive tract.
Currently, most fluoroscopy is done using x-ray image intensifiers. These are large, vacuum tube devices (i.e., akin to a CRT or conventional television) that typically receive the x-rays in an input end, convert the x-rays to light and then electron beams, guide, accelerate, and amplify the electron beams via internal electrodes, and convert the electron beams to a minified visible image at the device's output end. An example of an x-ray image intensifier is shown in U.S. Pat. No. 5,773,923 to Tamagawa (see FIGS. 1 and 2 and accompanying description).
Typically, directly viewing the output end of an x-ray image intensifier is difficult and/or undesirable. For example, x-ray image intensifiers usually have to be positioned where direct viewing of the intensifier output is physically difficult (e.g., on a positioning gantry above a patient). Furthermore, tube outputs are often times not optimized for direct viewing, and it may be necessary to record or process the image for enhanced viewing, archival purposes, or for image analysis. Accordingly, image intensifiers are oftentimes used in conjunction with television cameras with computer imaging systems that transfer the tube image to a television or computer monitor. An example of such a system is shown in U.S. Pat. No. 4,503,460 to Sklebitz.
While x-ray image intensifiers (alone or as part of a larger system) are well established and have proven very useful over the years, they have certain drawbacks. One of these is that the image intensifier tubes are necessarily quite bulky and heavy, e.g., like a television CRT. Accordingly, they are ill suited for applications where space and/or weight are an issue. Additionally, x-ray image intensifiers suffer from inherent temporal and spatial instability, poor contrast ratios, and pincushion distortions.
Numerous recent attempts have been made to replace vacuum tube image intensifiers with solid-state, "flat panel" x-ray detectors for "directly" converting x-rays into electronic signals suitable for computer processing and display. Such detectors usually comprise some sort of large-area, composite, semiconductor-based panel configured to detect x-rays that hit the panel. For example, a typical flat panel detector might include a layer of photoconductor for converting incident x-rays into electrical charge, and a very large area integrated circuit, itself comprising an array of field effect transistors interconnected with thin film transistor switches, for readout of the charge. Systems based on optical photodiodes in an array in contact with a scintillator are also known.
While such detectors are thin and easy to hold and position, they are not well suited for fluoroscopy. This is because they have an almost irresolvable noise problem at the very low x-ray dose rates required for fluoroscopy. More specifically, because fluoroscopy involves examining an ongoing biological process (as opposed to taking an x-ray "snapshot"), patients are subjected to an ongoing dosage which must be minimized. As such, only a small amount of x-rays can be applied, or patients would quickly be injured. This is a problem for existing flat panel detectors, because the millions of signal lines used to read the x-ray induced charge (i.e., to scan the pixels) are as long as the panel itself, which is typically 25–50 cm (10–20 in) long to provide a large enough viewing area (i.e., the panel has to have a large enough area to facilitate viewing of the area(s) of interest—typically, the same or similar size as conventional x-ray film). As such, these long lines have significant electrical capacity (on the order of picofarads) to other lines and to ground. This limits the detectable signal, as electrons forming the signal current will have to charge and discharge this parasitic capacitance. When the signal is only a few hundred electrons (as may be the case with low levels of x-rays), the voltage changes in the signal lines may only be in the order of microvolts, which are too low to be seen above the inherent input device thermal noise exhibited by all amplifiers. This inherent electrical noise gets worse with high speed readout (higher bandwidth), which is required for 30 frames-per-second ("fps") fluoroscopy. For example, for low numbers of x-ray photons (e.g., 10) per detector pixel, as needed for fluoroscopy, each x-ray photon results in a signal per pixel (as finally read out in a flat panel device) of around 600 electrons, meaning that image data is lost in the typically high noise levels of 2000–8000 electrons of the readout line amplifiers. Furthermore, because the manufacturing yields of such large-area (e.g., 900 cm2) transistor arrays are typically quite small, existing flat panel detectors can be very expensive. Subdividing the panel readout may help, but that quadruples the already large number (1000's) of output amplifiers, since one is associated with each readout line.
Other x-ray detectors utilize optical systems and associated components as an alternative to oversized semiconductor panels. For example, in U.S. Pat. No. 5,723,865 to Trissel et al. ("Trissel"), a CCD camera (CCD sensor coupled to a lens system) is focused on the output surface of a special, composite x-ray conversion or scintillation screen, at the heart of which is a flat, single crystal of cesium iodide (CsI). In use, x-rays fall on the scintillation screen, and are converted into visible light, which is then picked up by the camera. However, because a single-crystal CsI screen and single CCD camera are used, the system in Trissel is only suitable for viewing small areas, e.g., as in a mammogram, its intended purpose.
U.S. Pat. No. 5,412,705 to Snoeren et al. ("Snoeren") shows another x-ray imaging device. Here, x-rays are applied to an object under examination, and are then converted into visible light by way of a special screen. The light from the screen is then focused by a lens system/array, the output of which is directed to an array of CCD (charge-coupled device) image sensors, which is operably connected to a computer or other electronic processing equipment for image reconstruction and/or display. This provides a wide viewing area without a large-area semiconductor panel. However, the CCD sensors in Snoeren utilize weak-avalanche photodiodes for detecting incident light. These provide signal gain at each pixel, but also have disadvantageously-increased noise levels because of random fluctuations in the avalanche process, meaning that the detector is not well suited for very low levels of x-rays. Additionally, the lens system in Snoeren is not claimed as optimized for use with the low light levels associated with x-ray quantum limited imaging. Rather, Snoeren tries to improve the situation by causing more of the emitted light to be aimed toward the CCD array by a complex fluorescent screen fabrication using special optical techniques.
Accordingly, a primary object of the present invention is to provide a flat-panel x-ray detector or imager, suitable for use in fluoroscopy and other very low x-ray dosage applications, and that does not require the use of large-area semiconductor or integrated circuit arrays and associated long signal lines.
Another object of the present invention is to provide a system where every single, individual x-ray photon that interacts in the input screen produces an unambiguous signal in the output voltage. This is called "quantum limited" imaging, where x-ray statistics alone determine the noise level in the final image.

Low noise x-ray detector for fluoroscopy


In a transmission device having a first transmission path which is provided on a first printed circuit board and is connected to a connector, and over which a signal which does not vary with time is transmitted, and a second transmission path which is provided on a second printed circuit board and is connected to a second connector, and over which the above-mentioned signal is transmitted, a first resistor is connected to couple the second transmission path with a power supply of the second printed circuit board, and a first capacitor connected to couple the second transmission path with the ground. The first transmission path may also be grounded via a capacitor. The capacitive coupling to the ground will effectively ground the transmission path, and the crosstalk from another transmission path over which a signal which varies with time is transmitted is reduced.

The present invention relates to a transmission device including circuit components formed on a printed circuit board provided with a connector and with an arrangement for reducing crosstalk in the connector.
Electrical connection between printed circuit boards is often achieved by means of connectors which are fixed to the respective printed circuit boards, and are engaged and electrically connected with each other. Such connectors may be formed of a block of an insulating material and pins extending parallel with each other and from one side to the opposite side of the block. One of the connectors which are engaged with each other has male-type pins, while the other connector has female-type pins which mate with the male-type pins.
A problem associated with such type of connectors is crosstalk between pins. This crosstalk is increased as the distance between the pins is shorter, and as the signal transmitted through the pins has higher frequency components. To reduce the crosstalk, some of the pins in the connectors may be grounded, but this means that the number of pins available for transmitting signals is decreased.


In a liquid crystal display device which uses an electric field whereby a sufficient reset effect or sufficient overdrive effect is obtained at a lower-limit temperature at which the device is used, but which does not produce bounce at normal temperatures, the electric field applied has an intensity greater than that of an electric field at which a 99% response is obtained, and less than that of an electric field at which a 99.9% response is obtained, between a white image and a black image at the lower-limit temperature at which the device is used. Alternatively, the electric field applied has an intensity greater than that of an electric field at which average tilt angle of the liquid crystal exceeds 81 degrees, and at which average tilt angle does not exceed 85 degrees.

With the progression of the multimedia era, various types of liquid crystal display devices, from a small one used in a projector device, a cellular phone, a viewfinder, and the like to a large one used in a notebook PC, a monitor, a television, and the like, have rapidly become widespread. A medium-sized liquid crystal display device has become essential in electronic equipment such as a viewer and a PDAs (Personal Digital Assistants) and in amusement devices such as portable game machines and pachinko (Japanese pinball game) machines. These liquid crystal display devices find use in a variety of locations even in such appliances as refrigerators and microwave ovens.
At present, almost all liquid crystal display elements are of the twisted nematic (referred to as "TN" below) display type. A liquid crystal display element of the TN display type utilizes a nematic liquid crystal substance. If a conventional TN cell is subjected to direct matrix drive, display quality is not very high and the number of scan lines is limited. Accordingly, if direct matrix drive is adopted, use is made mainly of liquid crystal of the STN (Super Twisted Nematic) type, rather than of the TN type. Liquid crystal of this type exhibits improved contrast and viewing angle dependence in comparison with early direct matrix drive employing TN-type liquid crystal. Since the speed of response is low, however, this approach is not suited to display of moving pictures.
In order to improve upon the display performance afforded by direct matrix drive, an active matrix scheme in which each pixel is provided with a switching element has been developed and is now in wide use. By way of example, TN-TFT-type liquid crystal generally is used. Such a liquid crystal cell employs a thin-film transistor (TFT) in a TN-type display scheme. Since an active matrix scheme using a TFT provides a display quality higher than that obtained with direct matrix drive, TN-TFT liquid crystal presently dominates the market.
Owing to demand for ever-higher image quality, methods that provide an improved viewing angle have undergone research and development and some of these methods are in practical use. As a result, high-performance liquid crystal displays that are primarily in use at the present time are TFT-type active matrix liquid crystal displays of the following three types:                displays that employ a compensating film in a TN-type cell;        in-plane-switching (IPS) mode displays; and        multidomain vertically aligned (MVA) mode displays.
In order to perform positive and negative write using a 30-Hz image signal in these active matrix liquid crystal display devices, rewriting is carried out every 60 Hz and the duration of one field is about 16.7 ms (the total time of both positive and negative fields is referred to as one frame and is about 33.3 ms).
By contrast, the response speed of liquid crystal at the present time is on the order of this frame period even in a fastest condition when one considers the response during display of halftones. This means that a response speed faster than the present frame period is necessary when an image signal comprising a moving picture is to be displayed, when high-speed computerized images (computer graphics) are displayed, and when a high-speed game image is displayed.
On the other hand, mainstream pixel size at present is on the order of 100 ppi (pixels per inch), and higher definition is contemplated using the following two methods:
The first method is to raise machining precision to reduce pixel size.
The second method is to employ a field-sequential (time-division) color liquid crystal display device in which backlighting for illuminating the liquid crystal display is changed over to red, green and blue in time-wise fashion and red, green and blue images are displayed in sync with this changeover. This approach makes possible a three-fold increase in definition over the prior art since it is unnecessary to spatially dispose color filters.
With a field-sequential liquid crystal display device, it is necessary to display single color for one-third time of the single field, and therefore the time available for display is about 5 ms. Accordingly, it is required that the liquid crystal itself have a response faster than 5 ms.
Owing to the necessity for such high-speed liquid crystal, a various technologies have been studied and several high-speed display mode technologies have been developed. These high-speed liquid crystal technologies can be classified generally into two major trends.
The first consists of technologies for raising the speed of the above-mentioned nematic liquid crystal most widely in use.
The second consists of technologies using spontaneous-polarization smectic liquid crystal that exhibits spontaneous polarization and can respond at high speed.
The speedup of nematic liquid crystal, which is that in widest use, is mainly carried out by the following means:
(A) reducing the cell gap and increasing electric field intensity at the same voltage;
(B) applying a high voltage to raise field intensity and facilitating a change in state (this is an overdrive method);
(C) lowering viscosity; and
(D) using a mode considered to be a high-speed mode in principle.
The following problems arise even with such nematic liquid crystal of elevated speed:
Since response of liquid crystal ends substantially in one frame in the case of a high-speed nematic liquid crystal, there is very large change in the capacitance of the liquid crystal layer ascribable to anisotropy of the dielectric constant. Owing to the change in capacitance, a change occurs in holding voltage to be written to and retained in the liquid crystal layer. This change in holding voltage, i.e., a change in the effective applied voltage, results in insufficient writing and therefore lowers contrast.
Further, if the same signal continues to be written, luminance continues changing until the holding voltage no longer changes and several frames become necessary in order to obtain stable luminance.
In order to prevent such a response that necessitates several frames, it is necessary that one-to-one correspondence be established between the applied signal voltage and the transmittance obtained.
With active matrix drive, transmittance after the liquid crystal responds is decided not by the applied signal voltage but by the amount of electric charge that has accumulated in the liquid crystal capacitor after the liquid crystal responds. The reason for this is that active matrix drive is constant-charge drive that causes the liquid crystal to respond by the electric charge held.
If minute leakage and the like are ignored, the amount of electric charge supplied from an active element is decided by accumulated charge that prevailed prior to predetermined signal write, and newly written charge.
Further, accumulated charge after the liquid crystal has responded varies depending upon the physical constants of the liquid crystal, the electrical parameters thereof and pixel design values such as accumulation capacity. In order to establish one-to-one correspondence between applied signal voltage and transmittance, therefore, the following are required:
(A) correspondence between signal voltage and write charge;
(B) accumulated charge prior to write; and
(C) information for performing calculation of accumulated charge after response, as well as the actual calculation.
The above necessitates a frame memory for storing (B) over the entire screen and a calculation unit for (A) or (C).
A reset pulse method of applying a reset voltage to bring liquid crystal to a predetermined liquid crystal state is one method of establishing one-to-one correspondence between applied signal voltage and obtained transmittance without using the above-mentioned frame memory and calculation unit, and this method is often employed. An example of this method is described in the prior art set forth in H. Nakamura, K. Miwa and K. Sueoka, "Modified drive method for OCB LCD", 1997 IDRC (International Display Research Conference), SID L-66-L-69 (Non-Patent Document 1). According to this reference, use is made of an OCB (Optical Compensated Birefringence) mode in which orientation of nematic liquid crystal is made a pi-shaped orientation and a compensating film is applied.
Response speed of this liquid crystal mode is approximately 2 to 5 ms, which is much faster than the conventional TN mode. As a result, response should end in one frame. As mentioned above, however a large-scale decline in holding voltage occurs owing to a change in dielectric constant ascribable to the response of the liquid crystal, and several frames are needed to obtain stable transmittance.
A method of writing a black image without fail following the writing of a white image in one frame is indicated in FIG. 5 of Non-Patent Document 1. The diagram of FIG. 5 of this reference is cited as FIG. 13 in the drawings accompanying this application. In FIG. 13, time is plotted along the horizontal axis and luminance along the vertical axis. The dashed line in FIG. 13 indicates a change in luminance in the case of ordinary drive. A stable luminance is reached is the third frame.
In accordance with the reset pulse method, a predetermined state is always obtained when new data is written and therefore one-to-one correspondence between a written constant signal voltage and constant transmittance. Owing to this one-to-one correspondence, the generation of a driving signal becomes very simple and means such as a frame memory for storing the previously written information becomes unnecessary.
The structure of a pixel in a liquid crystal display device of active matrix type will now be described.
FIG. 10 illustrates an example of a pixel circuit for one pixel in a conventional liquid crystal display device of active matrix type. As shown in FIG. 10, the pixel of the liquid crystal display device comprises a MOS transistor Qn (referred to simply as "transistor Qn" below) having its gate electrode connected to a scan line (or scanning signal electrode) 901, either its source electrode or drain electrode connected to a signal line (or image signal electrode) 902, and the other of these source and drain electrodes connected to a pixel electrode 903; a storage capacitor 906 formed between the pixel electrode 903 and a storage capacitor electrode 905; and liquid crystal 908 sandwiched between the pixel electrode 903 and an opposing electrode (or common electrode) Vcom 907.
In notebook personal computers that constitute a large part of the market for liquid crystal displays, an amorphous silicon thin-film transistor (referred to as an "a-Si TFT below) or polycrystalline silicon thin-film transistor (referred to as a "p-Si TFT") usually is used as the transistor (Qn) 904, and NT liquid crystal is employed as the liquid crystal material.
FIG. 11 illustrates an equivalent circuit of a TN liquid crystal cell. As shown in FIG. 11, the equivalent circuit of a TN liquid crystal cell is expressed by a circuit in which a capacitor component C3 (electrostatic capacitance Cpix thereof) of the liquid crystal is connected in parallel with a resistance value Rr of a resistor R1 and a capacitor C1 (electrostatic capacitance Cr thereof). In this equivalent circuit, the resistance value Rr and electrostatic capacitance Cr are components that decide the response time constant of the liquid crystal.
FIG. 12 illustrates a timing chart of scan line voltage Vg, signal line voltage (or image signal voltage) Vd and voltage Vpix of the pixel electrode 903 (referred to as "pixel voltage" below) in a case where the above-mentioned TN liquid crystal is driven by the pixel circuit shown in FIG. 10.
As shown in FIG. 12, the scan line voltage Vg attains a high level VgH during the horizontal scanning period. As a result, the transistor (Qn) 904 is in the ON state during this period and the signal line voltage Vd being input to signal line 902 is transferred to the pixel electrode 903 through the transistor (Qn) 904. The TN liquid crystal normally operates in a mode in which light passes through when no voltage is applied. This is a so-called "normally white mode".
In the example shown in FIG. 12, the voltage for increasing optical transmittance through the TN liquid crystal is applied across several fields as the signal line voltage Vd. When the horizontal scanning period ends and the scan line voltage Vg reverts to the low level, the transistor (Qn) 904 reverts to the OFF state and the signal line voltage that has been transferred to the pixel electrode 903 is held by the storage capacitor 906 and capacitance Cpix of the liquid crystal. The pixel voltage Vpix at this time gives rise to a voltage shift, which is referred to as a "field-through voltage", via the gate-source capacitance of the transistor (Qn) 904 at the moment the transistor (Qn) 904 attains the OFF state.
This voltage shift is indicated at Vf1, Vf2 and Vf3 in FIG. 12. The amount of the voltage shifts Vf1 to Vf3 can be reduced by designing the storage capacitor 906 to have a large value.
In the next field period, the pixel voltage Vpix is held until the scan line voltage Vg attains the high level again and the transistor (Qn) 904 is selected. The TN liquid crystal is switched in accordance with the held pixel voltage Vpix, and the light transmitted through the liquid crystal shifts from the dark state to the bright state as indicated by optical transmittance T1 in FIG. 12.
In the holding period at this time, the pixel voltage Vpix fluctuates by ΔV1, ΔV2, ΔV3 in each field, as illustrated in FIG. 12. This is caused by the fact that the capacitance of the liquid crystal varies in accordance with the response of the liquid crystal. The storage capacitor 906 usually is designed to have a large value that is two, three or more times greater than the pixel capacitance Cpix so as to make this fluctuation as small as possible. The TN liquid crystal can be driven by the pixel circuit shown in FIG. 10 by adopting the arrangement described above.
A technique for modulating the common voltage [common electrode voltage (or opposing electrode voltage)], which is illustrated in Japanese Patent Kohyo Publication No. JP-P2001-506376A (Patent Document 1), is an example of a technique having an effect that is the result of mixing the overdrive method and reset method. FIG. 2C of this reference is cited as FIG. 14 in the drawings accompanying this application.
According to the technique of Patent Document 1, ordinarily a common voltage, which is the voltage of a common electrode placed opposite a pixel electrode, is modulated. In FIG. 14, VCG indicates a temporal change in the common voltage (VCG), and an underlying waveform I indicates a temporal change in optical transmittance ascribable to response of the liquid crystal. That is, a voltage waveform 151 is a voltage waveform that is applied to the common electrode, and a light-intensity waveform 152 is a light-intensity waveform corresponding to time and conforming to the waveform 151. Reference numerals 153 to 156 denote curves of pixel light intensity.
With the prior art that preceded Patent Document 1 cited above, drive was performed with the common voltage held at a constant value [where t0 to t2 (and t2 to t4) in FIG. 14 serves as the period of one frame], or common inversion drive, in which the voltage value is varied between two voltage values at a fixed interval.
According to Patent Document 1, one frame period is divided into two parts and voltage having an amplitude substantially the same as that of conventional common inversion drive is applied in the interval from t1 to t2 (and from t3 to t4).
In the interval from t0 to t1 (and from t2 to t3) in one frame period, on the other hand, a voltage higher than the amplitude of common inversion (e.g., a voltage that is higher than the amplitude of common inversion by an amount equivalent to the voltage at the time of the black image) is applied. According to this technique, the entire display area can be changed to the black image rapidly owing to the effect of an enlarged voltage difference between the pixel electrode and common electrode in the interval from t0 to t1 over which the high voltage is applied to the common electrode. In other words, drive equivalent to reset drive is carried out.
Furthermore, even if image data is written into the pixel electrode during the interval from t0 to t1, the potential difference between the pixel electrode and common electrode is sufficiently large (e.g., greater than the black image voltage) and therefore nothing is observed on the display.
After the writing of image data to the entire display area ends, the voltage of the common electrode is returned to the amplitude of common inversion. As a result, the liquid crystal layer starts responding to change the transmittance, which conforms to each gray level, in accordance with the voltage memorized by the pixel electrode. That is, when response starts, there is a change from the state of high voltage difference to a voltage difference that conforms to each gray-le v el voltage value. In this sense a kind of overdrive is performed in the interval from t0 to t1.
Note that the response time of liquid crystal is given by the following two equations (1) and (2) (see "Liquid Crystal Dictionary", Japan Society for the Promotion of Science, Organic Materials for Information Science, 142nd Committee, Sectional Meeting on Liquid Crystal, Baifu K. K., p. 24) (Non-Patent Document 2). Specifically, rise response (ON-time response) τrise at which a voltage higher than a threshold-value voltage is applied and the ON state attained is given by Equation (1) below.
                              τ          rise                =                                            d              2                        ·                          η              ~                                            Δɛ            ·                          (                                                V                  2                                -                                  V                  c                  2                                            )                                                          (        1        )
On the other hand, decay response (OFF-time response) τdecay at which the applied voltage greater than the threshold value returns rapidly to zero is given by Equation (2) below.
                              τ          decay                =                                            d              2                        ·                          η              ~                                                          π              2                        ·                          K              ~                                                          (        2        )
In Equations (1) and (2) above, d represents the thickness of the liquid crystal layer, η the rotational viscosity, Δε the dielectric anisotropy, V the applied voltage conforming to each gray level, Vc the threshold voltage, and K({tilde over ( )}) a constant based upon a Frank elastic constant. In the TN mode, the constant K is given by Equation (3) below.
                              K          ~                =                              K            11                    +                                    1              4                                                  (                                                K                  33                                -                                  2                  ·                                      K                    22                                                              )                                                          (        3        )
In Equation (3) above, K11, K22 and K33 represent elastic constants of splay, twist and bend, respectively.
With the rise response (ON-time response), the response time of the liquid crystal depends upon the reciprocal of the square of the value of the voltage applied, as will be understood from Equation (1). In other words, the response time of the liquid crystal depends upon the reciprocal of the square in accordance with a voltage value that differs for every gray level. Depending upon the gray level, therefore, response time differs widely, and if there is a voltage difference that is ten times larger, then the difference in response time will be 100 times larger.
On the other hand, in accordance with Equation (2), a disparity in response time ascribable to the gray level exists even with the decay response (OFF-time response) but the disparity falls within the range of a two-fold increase.
Turning to Non-Patent Document 2, a higher speed is achieved owing to the overdrive effect of applying a very high voltage at the time of the rise response (ON-time response).
Further, since the response used in actual image display becomes the entire decay response (OFF-time response), dependence upon the gray level is very small. As a result, a substantially equal response time is obtained over all gray levels.
[Patent Document 1]
JP Patent Kohyo Publication No. JP-P2001-506376A
[Patent Document 2]
JP Patent No. 3039506
[Non-Patent Document 1]
H. Nakamura, K. Miwa and K. Sueoka, "Modified drive method for OCB LCD", 1997 IDRC (International Display Research Conference), SID L-66-L-69
[Non-Patent Document 2]
"Liquid Crystal Dictionary", Japan Society for the Promotion of Science, Organic Materials for Information Science, 142nd Committee, Sectional Meeting on Liquid Crystal, Baifukan Co., LTD, p. 24
[Non-Patent Document 3]
Tarumi et al., "Molecular Crystals and Liquid Crystals", vol. 263, pp. 459 to 467 (Mol. Cryst. Liq. Cryst. 1995, Vol. 263, pp. 459-467

Liquid crystal display device and method of driving same


A mobile communication device is provided for wirelessly transferring information to and from a base unit. The device comprises an RFID module to receive a wake-up communication from the base unit and to send connection parameters back to the base unit. A wireless communication module is included that is responsive to the connection parameters received from the base unit. A microcontroller is coupled between the RFID module and the wireless communication module to wake-up the wireless communication module when the RFID module receives the wake-up communication from the base unit.

The transfer of information between electronic devices is now an important activity in everyday life. Often electronic information transfers occur via wired communication links involving networks that require substantial set-up and/or installation costs. Problems occur when information needs to be transferred between mobile devices because wired connections are cumbersome and tend to negate the usefulness and mobility of the devices.
There are methods and devices that facilitate wireless information transfer, but most conventional wireless networks do little more than replace wire lines with wireless communication links. A significant amount of infrastructure and user involvement in setup procedures is still common.
Certain mobile communication devices reduce the infrastructure problem by facilitating information transfer with widely accepted protocols and avoiding the need for wired networks. These devices, such as PDAs, digital cameras, cell phones, and other mobile devices, are effective in situations where information needs to be transferred between mobile devices not normally connected to networks. However, one problem with these larger devices is that they are generally too large to be carried around by a person and stored compactly in a wallet, slipped into a small purse, tucked in a pocket, or carried in some other manner on a person. This is due in part to the relatively large batteries that are needed to power cell phones, PDAs, and similar mobile devices.
As society becomes more information dependent, individuals carry an increasing amount of information on their person. In the past, the information has been encoded onto physical devices or cards that are then tucked inside a wallet or a purse or simply carried in a pocket. A multitude of cards or devices are inconvenient because in order for the information encoded devices and cards to be useful, the individual must physically carry them around anticipating their use. Eventually, the wallet, pocket, or purse gets bulky when carrying everything one might anticipate using. When the cards and devices are used they must be physically removed, as from the wallet, and then returned upon completion of the transaction.
By digitizing the information contained on the encoded devices and selectively transferring the information over a wireless link via a PDA-sized mobile communication device, these problems are partially solved. But a new problem is created because the information is merely transferred from the bulky devices or cards to a bulky PDA-sized device that facilitates the information transfer. PDAs and similar devices are sometimes too big to be conveniently carried, imposing an additional burden on the individual.
Smart card technology accommodates the size restrictions of storing information on a device which is easily carried. A smart card is generally a credit-card sized device with an embedded computer chip. The chip can either be a microprocessor with internal memory or a memory chip with non-programmable logic. A smart card generally has no user interface and the card is generally powered from an external source. Typically, a smart card is inserted into another device that allows a user to enter and retrieve information from the card. Thus, a smart card is usually physically docked with another read/write device to transfer information. Some smart cards can facilitate information transfer without direct physical contact with another device. These cards rely on a contactless electromagnetic interface to transfer information. The disadvantage of this system is limited range—usually 25 centimeters or less. Often it is not feasible or convenient to transfer information from a device within a range of just a few centimeters, especially if the device is located within a wallet or a purse.
Certain mobile communication devices assist in transferring information from smart cards at distances greater than a few centimeters. These devices allow the information on the card to be securely transferred in environments with a large number of communication devices. For example, information can be wirelessly transferred in a Point-of-Sale transaction, or other similar transactions where the information is personal and/or restricted in some way. The devices may include the smart card interface, a keypad, a display, a radio, an antenna, and a battery. A smart card is connected to these communication devices (e.g., a PDA), which facilitate the transfer of the information contained on the card. However, these devices are also bulky and do not fit inside a wallet. Like the devices above, these devices are also cumbersome and difficult to carry.
Some mobile devices make use of an embedded Bluetooth radio to facilitate the transfer of information. Bluetooth is a technology based on a short-range radio link that facilitates protected, ad-hoc connections for stationary and mobile communication units in Wireless Personal Area Network (WPAN) environments. Bluetooth technology allows for communication links connecting mobile communication devices over a range of 10 centimeters to 100 meters. Further, Bluetooth technology is designed to operate in a noisy radio frequency environment, and uses a frequency-hopping scheme to make the communication link robust.
One disadvantage of certain wireless communication technologies (such as Bluetooth) is the amount of time required to discover and fully connect with other mobile communication devices. Setting up a connection using Bluetooth takes ten seconds or even longer when the ideal conditions are not present. Long connect times (e.g., ten seconds) may be unacceptable in emergency communication situations, with multiple device interactions, or in circumstances in which two mobile devices may quickly pass out of range. Suppose communication is intended between two mobile devices approaching one another from opposite directions. Although communication may be intended, the devices may cross paths and be out of range before the device discovery process is complete.
Another significant problem with mobile wireless communication devices is power consumption. Mobility in portable devices is directly linked to the life of the battery power supply. Because of size and weight restrictions associated with mobile devices, limiting power consumption is a high priority. Reducing power consumption is important in devices that utilize wireless communication technologies, such as Bluetooth. As an example, in Bluetooth active mode, data transmission consumes a large amount of power. Even in idle or standby mode, Bluetooth modules and comparable modules consume power responding to discovery inquiries from other wireless devices that enter the WPAN space.

System and method for wireless data transfer for a mobile unit