The invention provides economically effective methods for hydraulic fracturing a subterranean formation that ensure improvement of the hydraulic fracturcconductivity because of forming strong proppant clusters uniformly placed in the fracture throughout its length. One of these methods comprises: a first stage that involves injection into a borehole of fracturing fluid containing thickeners to create a fracture in the formation; and a second stage that involves periodic introduction of proppant into the injected fracturing fluid to supply the proppant into a created fracture, to form proppant clusters within the fracture to prevent fracture closure and channels for flowing formation fluids between the clusters, wherein the second stage or its sub-stages involve additional introduction of either a reinforcing or consolidation material or both, thus increasing the strength of the proppant clusters formed into the fracture fluid.

Hydrocarbons (oil, natural gas, etc.) are obtained from a subterranean geological formation by drilling a well that penetrates the hydrocarbon-bearing formation. This provides a partial flowpath for the hydrocarbon to reach the surface. In order for the hydrocarbon to be "produced," that is, travel from the formation to the wellbore and ultimately to the surface, there must be a sufficiently unimpeded flow path.
Hydraulic fracturing is a primary tool for improving well productivity by placing or extending highly conductive fractures from the wellbore into the reservoir. During the first stage, hydraulic fracturing fluid is injected through wellbore into a subterranean formation at high rates and pressures. The fracturing fluid injection rate exceeds the filtration rate into the formation producing increasing hydraulic pressure at the formation face. When the pressure exceeds a critical value, the formation strata or rock cracks and fractures. The formation fracture is more permeable than the formation porosity.
During the next stage, proppant is deposited in the fracture to prevent it from closing after injection stops. The resulting propped fracture enables improved flow of the recoverable fluid, i.e., oil, gas or water. Sand, gravel, glass beads, walnut shells, ceramic particles, sintered bauxites and other materials may be used as a proppant.
Hydraulic fracturing fluids are aqueous solutions containing a thickener, such as a solvatable polysaccharide, to provide sufficient viscosity to transport the proppant. Typical thickeners are polymers, such as guar (phytogeneous polysaccharide), and guar derivatives (hydroxypropyl guar, carboxymethylhydroxypropyl guar). Other polymers can be used also as thickeners. Water with guar represents a linear gel with a viscosity proportional to the polymer concentration. Cross-linking agents are used which provide engagement between polymer chains to form sufficiently strong couplings that increase the gel viscosity and create visco-elasticity. Common crosslinking agents for guar include boron, titanium, zirconium, and aluminum.
Proppant-retention agents are commonly used during the latter stages of the hydraulic fracturing treatment to limit the flowback of proppant placed into the formation. For instance, the proppant may be coated with a curable resin activated under downhole conditions. Different materials, such as bundles of fibers, or fibrous or deformable materials, also have been used to retain proppants in the fracture. Presumably, fibers form a three-dimensional network in the proppant, reinforcing it and limiting its flowback.
The success of a hydraulic fracturing treatment depends upon hydraulic fracture conductivity and fracture length. Fracture conductivity is the product of proppant permeability and fracture width; units are typically expressed as millidarcy-feet. Fracture conductivity is affected by a number of known parameters. Proppant particle size distribution is one key parameter that influences fracture permeability. The concentration of proppant between the fracture faces is another (expressed in pounds of proppant per square foot of fracture surface) and influences the fracture width. One may consider high-strength proppants, fluids with excellent proppant transport characteristics (ability to minimize gravity-driven settling within the fracture itself), high-proppant concentrations, or big proppants as means to improve fracture conductivity. Weak materials, poor proppant transport, and narrow fractures all lead to poor well productivity. Relatively inexpensive materials of little strength, such as sand, are used for hydraulic fracturing of formations with small internal stresses. Materials of greater cost, such as ceramics, bauxites and others, are used in formations with higher internal stresses. Chemical interaction between produced fluids and proppants may change significantly the proppant's characteristics. One should also consider the proppant's long-term ability to resist crushing.
The proppant pack must create a layer having a higher hydraulic conductivity than the surrounding formation rock. The proppant pack within the fracture can be modeled as a permeable porous structure, and the flow of formation fluids through this layer is generally described using the well-known Darcy's law (1) or Forscheimer's equation (2):∂P/∂x=−(μu/k);  1∂P∂x=−[(μu/k)+βρu2],  2
where P is a fluid pressure in the fracture;                x is a distance along the fracture from the wellbore;        μ is a viscosity of the formation fluid;        u is a flow (filtration) speed of the formation fluid;        k is a permeability of the proppant pack;        β is a coefficient referred to as beta-factor that describes non-linear corrections to the Darcy's filtration law;        ρ is a density of the formation fluid.
The result of multiplying fracture permeability by fracture width is referred to as hydraulic conductivity. An important aspect of fracture design is optimization of the hydraulic conductivity for a particular formation's conditions. Fracture design theory and methodology are sufficiently well described in several scientific articles and monographs. Reservoir Stimulation, 3rd ed. Economides, Michael J. and Nolte, Kenneth G., John Wiley and Sons (1999) is a good example of a reference that provides good fracture design methodology.
A fracture optimization process will strike a balance among the proppant strength, hydraulic fracture conductivity, proppant distribution, cost of materials, and the cost of executing a hydraulic fracturing treatment in a specific reservoir. The case of big proppants illustrates compromises made during an optimization process. A significant hydraulic fracture conductivity increase is possible using large diameter proppants. However, large diameter proppants at a given internal formation stress crush to a greater extent when subjected to high fracture closure stresses, leading to a decrease in the effective hydraulic conductivity of the proppant pack. Further, the larger the proppant particles, the more they are subjected to bridging and trapping in the fracture near the injection point.
A particular proppant is selected based on its ability to resist crushing and provide sufficient fracture conductivity upon being subjected to the fracture closure stress; and its ability to flow deeply into the hydraulic fracture—cost effectively. Proppants are second after water according to volume and mass used during the hydraulic fracturing process. Ceramic proppant has superior beta-factors and more strength compared to sand. However, the cost of ceramic proppants is many fold higher than the cost of sand. Therefore, fracture conductivity improvement requires significant costs for hydraulic fracturing with proppant typically representing 20 to 60 percent of the total for a conventional hydraulic fracturing process.
Apart from the above considerations, there are other proppant characteristics that complicate the production of hydrocarbons. First, formation fluids often bypass a large fraction of the fluid used in the treatment. (The fluid remaining in the proppant pack damages the conductivity of the fracture.) Field studies have shown that the recovery of hydraulic fracturing fluid from fractures in natural gas wells averages only 20 to 50 percent of that injected during the treatments and can be much less. Probably formation fluids flow only along several channels in the form of "fingers" within the proppant pack, or only through that part of the proppant pack near the wellbore during the fracture clean-up process. The fracture portion containing residual viscous gel hinders fluid flow, thereby reducing effective hydraulic fracture conductivity. Lowering the fracturing fluid viscosity after the treatment is an effective way to increase the fracturing fluid recovery from the proppant pack porosity. The addition of substances called "breakers" promotes gel viscosity reduction. Breakers act by several mechanisms, but most commonly they function by cleaving polymer chains to decrease their length and, thereby, to reduce the polymer solution viscosity. Different breakers are characterized by such parameters as the rate of reaction between the breaker and the polymer, and the activation or deactivation temperatures of the specific breaker in question. Better fracture cleanup can be achieved using high breaker concentrations, but too high a breaker concentration can result in a premature gel viscosity reduction, which may compromise the treatment design and cause premature treatment completion—a screen out. Delayed action breakers, such as encapsulated, were developed to solve this problem. Encapsulated breakers are active breaker chemicals, such as oxidizer granules, coated by protective shells, which isolate the oxidizer from the polymer and delay their reaction. Shell destruction and breaker release take place through various mechanisms, including the action of mechanical stresses occurring at fracture closure. Encapsulated breakers enable higher breaker concentrations to be used in the hydraulic fracturing fluid and, therefore, increase the extent of fracture cleaning.
Another factor reducing fracture conductivity is pore clogging in the proppant pack by formation particles formed during the fracturing process, by proppant particles formed by proppant crushing; and by immiscible fluids (The Impact of Non-Darcy Flow on Production from Hydraulically Fractured Gas Wells, SPE Production and Operations Symposium, 24-27 March, Oklahoma City, Okla., 2001; A Study of Two-Phase, Non-Darcy Gas Flow Through Proppant Packs, SPE Production & Facilities, Volume 15, Number 4, November, 2000). So, evidently, a fracture in which formation fluids flow through a created channel network instead of through small pores in the proppant pack could improve the fracture's hydraulic conductivity by several mechanisms: reduced inertial losses, improved fracturing fluid clean up, reduction of capillary forces that impose significant two-phase flow pressure losses, and elimination of pore throat plugging by the capture of formation fines and crushed proppant fragments.
In recent years, fracturing treatments in many low permeability formations in North America were pumped using low viscosity hydraulic fracture fluids that were proppant-free or with only a small amount of proppant. This method has several names, the most common of which is referred to as a waterfrac. Fractures created by the waterfrac process are practically proppant-free. It is anticipated that the created fracture surfaces shift relative to each other during fracture creation and propagation. The resulting misalignment of irregular surface features (asperities) prevents the two fracture faces from forming a tight seal upon closure. Adding a small amount of proppant reportedly intensifies the effect of irregular and misaligned crack surfaces. However, due to poor transport, the proppant tends to accumulate below the casing perforations, most likely along the base of the created hydraulic fracture. This accumulation occurs due to a high rate of proppant settling in the fracturing fluid along a narrow hydraulic fracture, and insufficient proppant transport ability, (both because of low fracturing fluid viscosity). When fracturing fluid injection stops at the end of a waterfrac, the fracture immediately shortens in length and height. This slightly compacts the proppant, which remains as a "dune" at the fracture base near the wellbore. Because of the dune's limited length, width and, typically, strength (often low-strength sand is used), waterfracs are usually characterized by short, low-conductivity fractures (Experimental Study of Hydraulic Fracture Conductivity Demonstrates the Benefits of Using Proppants, SPE Rocky Mountain Regional/Low-Permeability Reservoirs Symposium and Exhibition, 12-15 March, Denver, Colo., 2000).
The previous discussion illustrates that waterfracs result from the passage of formation fluid flowing through the network of narrow channels created inside of the fracture due to incomplete closure caused by surface rock imperfections, i.e. the waterfrac process results in low conductivity fractures. One method of improving hydraulic fracture conductivity is to construct proppant clusters in the fracture, as opposed constructing a continuous proppant pack. U.S. Pat. No. 6,776,235 discloses a method for hydraulically fracturing a subterranean formation involving an initial stage of injecting hydraulic fracturing fluid into a borehole, the fluid containing thickeners to create a fracture in the formation; and alternating stages of periodically introducing into the borehole proppant-containing hydraulic fracturing fluids contrasting in their abilities to transport propping agents and, therefore, contrasting in proppant-settling rates to form proppant clusters as posts that prevent fracture closing. This method alternates the stages of proppant-laden and proppant-free fracturing fluids. The amount of proppant deposited in the fracture during each stage is modulated by varying the fluid transport characteristics (such as viscosity and elasticity), the proppant densities, diameters, and concentrations and the fracturing fluid injection rate.
Periodic injection of the proppant used in the present method involves transportation of each portion of proppant, first, down through the well; then, through perforations of the casing string into a fracture; and, further, through the fracture along its length. Since proppant-containing and proppant-free fracturing fluids have different specific gravities, the proppant-containing fluid can settle, or underride, the proppant-free fluid. Such settling results in non-uniform distribution of proppant clusters in the fracture.

Method for hydraulic fracturing of subterranean formation


A laser diode that has a pluality of semiconductor epitaxial layers grown on a substrate. The diode includes a light generating layer located between two layers of n-type material. A thin layer of p-type material is interposed between the active layer and an n-type layer. The diode includes a layer of n-doped material located adjacent to a substrate. The laser diode further includes an active layer located between the n-doped layer and a layer of p-doped material. An additional layer of n-doped material is located between the p-doped material and a contact. The contact is biased so as to induce a recombination of holes and electrons in the active region and generate light. The light travels along the active layer, p-doped layer and in both n-doped layers. Having an n-doped layer between the contact and p-doped layer reduces the amount of photon absorption within the laser diode.

1. Field of the Invention
The subject matter disclosed generally relates to the field of laser diodes.
2. Background Information
Laser diodes are used in a variety of system applications. For example, laser diodes are used as a light source in fiber optic communication systems. It is generally desirable to increase the output power and energy efficiency of a laser diode.
FIG. 1 shows an exemplary construction of a laser diode 1. The laser diode 1 includes a layer of n-doped material 2 and a layer of p-doped material 3 that are separated by an active layer 4. The n-doped and p-doped layers create a diode junction. A current is injected into the laser diode 1 through a contact 5. The current induces a migration of electrons and holes from the n-doped 2 and p-doped 3 layers into the active layer 4. The holes and electrons recombine to create a stimulated emission of photons. The laser diode 1 may also have upper 6 and lower 7 cladding layers that create a waveguide for the light generated in the active layer 4.
Unfortunately, the p-doped layers of most laser diodes have a high optical absorption coefficient. The high absorption rate of light in the p-doped layers reduces the energy efficiency of the laser diode. The lower efficiency increases the current requirements. Higher current increases the heat generated within the laser diode and reduces the life of the device. P-doped layers also have higher electrical resistivity than n-doped layers, which further reduces the electrical-to-optical conversion efficiency.

Laser diode with a low absorption diode junction


A fishhook is described which disintegrates upon standing for prolonged periods of time in an aqueous environment such as within biological tissue. In one embodiment, the fishhook comprises a biodegradable polymeric hook-shaped structure with at least one metal tip affixed thereto providing a sharp piercing element. Upon exposure to the chemical environment of the fish's tissue the polymer biodegrades. In another embodiment, a substantially insoluble or non-biodegradable body portion of the hook has a separable point and barb portion affixed to the insoluble portion by means of a biodegradable adhesive. When the fishhook penetrates the fish's tissue, the solvents and/or enzymes present in the tissue environment causes the adhesive to release the barb and/or the point of the fishhook and the fish may shed the disintegrated fragments. In yet another embodiment, the entire fishhook is fabricated from a biodegradable polymer such as polylactide or polyglycolide or a copolymer thereof.

1. Field of the Invention
This invention relates to a biodegradable fishhook and more particularly to a fishhook that disintegrates upon prolonged exposure to biological tissue and/or an aqueous environment.
2. Prior Art
It is well understood that in certain fishing areas referred to as "catch and release" areas or "quality" fishing areas, it is unlawful to harm or take a fish. To accommodate such rules, barbless hooks are usually employed to facilitate removal of the hook from the fish's mouth in the event such is required. This removal usually ii employs taking the fish out of the water, grasping it, removing the hook and releasing the fish. The act of taking the fish out of the water or even just handling the fish can do irreparable damage and seriously injure the fish. In summary, the prior art does not provide a fishhook which does not endanger the life of the animal in the event the fishhook cannot be removed such as occurs, for example, when a fish breaks the leader and escapes. For this reason, it is desirable to have a fishhook which, upon penetrating the flesh of a fish, may be cut loose from the fishing line by means of a cutting tool is leaving the hook safely embedded in the fish's tissue. Upon prolonged exposure to the aqueous/biological environment, the fishhook will disintegrate or self-release from its impaling relationship with the fish.


A light-emitting device comprising a substrate, a light-emitting stack, and a transparent adhesive layer having wavelength-converting materials embedded therein formed within the light-emitting device is provided.

1. Technical Field
The present invention relates to a light-emitting device and in particularly to a light-emitting device having a transparent adhesive layer embedded with wavelength-converting materials.
2. Description of the Related Art
Light-emitting devices have been employed in a wide variety of applications, including optical displays, traffic lights, data storage apparatus, communication devices, illumination apparatus, and medical treatment equipment. How to improve the light-emitting efficiency of light-emitting devices is an important issue in this art.
Referring to FIG. 1, according to Snell's law, when a light is directed from one material with an refractive index n1 towards another material with an refractive index n2, the light will be refracted if its incident angle is smaller than a critical angle θc. Otherwise, the light will be totally reflected from the interface between the two materials. In other words, when a light beam generated from a light-emitting diode (LED) travels across an interface from a material of a higher refractive index to a material of a lower refractive index, the angle between the incident light beam and the reflected light beam must be equal or less than 2θc for the light to be emitted out. It means that when the light generated from the LED travels from an epitaxial layer having a higher refractive index to a medium having a lower refractive index, such as a substrate, air and so on, a portion of the light will be refracted into the medium, and another portion of the light with an incident angle larger than the critical angle will be reflected back to the epitaxial layer of the LED. Owing to the environment surrounding the epitaxial layer of the LED having a lower refractive index, the reflected light is reflected back and forth for several times inside the LED and finally a certain portion of said reflected light is absorbed.
In U.S. Patent Publication No. 2002/0017652 entitled "Semiconductor Chip for Optoelectronics", an epitaxial layer of a light-emitting device forming on a non-transparent substrate is etched to form a micro-reflective structure having a multiplicity of semi-spheres, pyramids, or cones, then a metal reflective layer is deposited on the epitaxial layer. The top of the micro-reflective structure is bonded to a conductive carrier (silicon wafer), and then the non-transparent substrate of the epitaxial layer is removed. All the light generated from the light-emitting layer and incident to the micro-reflective structure will be reflected back to the epitaxial layer and emitted out of the LED with a direction perpendicular to a light-emitting surface. Therefore, the light will not be restricted by the critical angle any more.

Light-emitting device having wavelength-converting materials therewithin


Apparatus and methods for retiming an STS-3 type signal are provided. The SPE of an incoming STS-3 type signal is demultiplexed into three STS-1 payloads and fed to three FIFOs, and a byte which is synchronous with the TOH is tracked through the three FIFOs to provide an indication of the FIFO depth. A frame count is also kept to track the number of frames since a last pointer movement. Stuffs or destuffs are generated based on the FIFO depth as well as based on the frame count, with a stuff or destuff generated as quickly as four frames from a previous pointer movement if the FIFO is close to full or close to empty, and less quickly (e.g., at thirty-two frames from a previous pointer movement) if the FIFO is only starting to empty or to fill. Where the STS-3 type signal is a STS-3C signal, the decision on whether to stuff or destuff is made with reference to all three depth measurement circuits as all the STS-1 payloads must be stuffed or destuffed together. Also, to realign the STS-1 components of the STS-3C signal, the J1 bytes of the signal are tracked through the FIFOs, and a logic circuit is provided having phase 3 of the outgoing STS-3 clock, and the three J1 byte control signals as inputs. The logic circuit inhibits a read of a J1 byte from any particular FIFO unless all FIFO's have a high J1 signal at phase 3 of the clock.

This invention generally relates to the optical telecommunications network. More particularly, this invention relates to the retiming and realignment of higher speed SONET signals upon the recombination of the higher speed SONET signals after they have been broken down into lower speed components and then either cross-connected and/or sent through via different paths through a switched network.
The telecommunications network servicing the Unites States and the rest of the world is presently evolving from analog transmission to digital transmission with ever-increasing bandwidth requirements. Fiber optic cable has proved to be a valuable tool of such evolution, replacing copper cable in .nearly every application from large trunks to subscriber distribution plants. Fiber optic cable is capable of carrying much more information than copper cable and with lower attenuation.
While fiber optic cable represents the future in telecommunications, presently there remains an entire telecommunications network comprised of various cable types, served by equipment of different vintages, and run according to various coexisting transmission standards. While older standards, cables, and equipment will be eventually phased out, for the time being it is necessary that all the old and new standards, equipment and transmission lines be as compatible as possible. In fact, even where relatively new optical network equipment is in 4 place, such as cross-connection (switch) equipment capable of handling SONET signals such as STS-1 signals, even higher level signals (such as STS-3 and STS-3C, details of which are seen in prior art FIGS. 6a-6d) are being generated. Typically, cross-connection equipment for such high level signals is unavailable or not commonly in place. Thus, in order for higher level signals to be utilized, mechanisms for accommodating the higher level signals to the lower level equipment are necessary; i.e., backwards compatability is required.

Methods and apparatus for retiming and realignment of STS-1 signals into STS-3 type signal


Devices, systems, and methods are provided for automated personalized Zasshi. The system may generate a computer-executable file including first content associated with a first book, and second content associated with a second book, the first content including first image data and first text data, and the second content including second image data and second text data. The system may determine a selectable action associated with the first content or the second content, and may determine metadata associated with the first content, the second content, and the selectable action. The system may transmit the computer-executable file and may receive selection data associated with the selectable action. The system may determine, based on the metadata, that the selectable action is associated with the first content. The system may determine, based on the selectable action, third content.

Comic books and graphic novels have become increasingly popular. For example, Manga comic books and graphic novels may include panels with illustrations and text which represent a story that progresses as a reader views the panels sequentially. However, the price of Manga may be prohibitive to some readers, particularly when readers prefer to read different stories from multiple content publishers. While Manga Zasshi provides multiple Manga stories in an issue, readers may prefer to read only one comic or graphic novel series in a Manga Zasshi, and when reader purchases a Manga Zasshi, the reader may not be able to determine which stories are included, and content publishers may not be able to determine which stories the reader actually read.
Certain implementations will now be described more fully below with reference to the accompanying drawings, in which various implementations and/or aspects are shown. However, various aspects may be implemented in many different forms and should not be construed as limited to the implementations set forth herein; rather, these implementations are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Like numbers in the figures refer to like elements throughout. Hence, if a feature is used across several drawings, the number used to identify the feature in the drawing where the feature first appeared will be used in later drawings.


The present invention provides a technology capable of measuring three-dimensional shapes by applying a stereo method even in the case that an object has a specular surface. A shape measuring apparatus 1 is equipped with a pattern position specification section 20 (before-movement pattern position specification section, after-movement pattern position specification section), an image capturing position calculation section 30 (before-movement image capturing position calculation section, after-movement image capturing calculation section), a pixel area specification section 40 (second pixel area specification section), an inclination angle calculation section 50 (before-movement inclination angle calculation section, after-movement inclination angle calculation section), a height-direction coordinate determination section 60, and an output section 80.

Conventionally, as a technology for measuring the three-dimensional shape of an object, a technology (stereo method) in which the image of an object is captured in two directions and the spatial coordinates of a given point on the object are recognized has been used as disclosed in JP-A-2009-181492, for example.

Shape measuring device, shape measuring method, and method for manufacturing glass plate


An oxidizer that is usable with a fuel cell includes a catalyst, an inlet to communicate an oxidant flow, an injection tube to communicate an anode exhaust flow, a mixing tube and a divergent nozzle. The injection tube communicates the anode exhaust flow from the fuel cell into the oxidizer to produce a combined flow in which the anode exhaust flow is oriented in substantially the same direction as the oxidant flow and surrounded by the oxidant flow. The mixing tube is connected to the inlet to receive the combined flow and mix the oxidant flow and the anode exhaust flow mix together to produce a mixed flow. A cross-sectional flow area of the mixing tube is sized to prevent flashback. The divergent nozzle communicates the mixed flow to the catalyst.

The invention generally relates to an oxidizer for a fuel cell system.
A fuel cell is an electrochemical device that converts chemical energy produced by a reaction directly into electrical energy. For example, one type of fuel cell includes a polymer electrolyte membrane (PEM), often called a proton exchange membrane, that permits only protons to pass between an anode and a cathode of the fuel cell. At the anode, diatomic hydrogen (a fuel) is reacted to produce hydrogen protons that pass through the PEM. The electrons produced by this reaction travel through circuitry that is external to the fuel cell to form an electrical current. At the cathode, oxygen is reduced and reacts with the hydrogen protons to form water. The anodic and cathodic reactions are described by the following equations:H2→2H++2e− at the anode of the cell, and  Equation 1O2+4H++4e−→2H2O at the cathode of the cell  Equation 2
The anode and cathode of a typical PEM fuel cell are formed by locating a catalyst in close physical contact with each side of the PEM. An electrically conductive gas diffusion layer (GDL) is often situated on top of each anode and cathode to improve gas distribution and contact with the anode and cathode catalysts. This combined package of PEM, anode catalyst, cathode catalyst, and GDL is often referred to as a membrane electrode assembly (MEA).
A typical fuel cell has a terminal voltage near one volt DC. For purposes of producing much larger voltages, several fuel cells may be assembled together to form an arrangement called a fuel cell stack, an arrangement in which the fuel cells are electrically coupled together in series to form a larger DC voltage (a voltage near 100 volts DC, for example) and to provide more power.
The fuel cell stack may include flow plates (graphite composite or metal plates, as examples) that are stacked one on top of the other, and each plate may be associated with more than one fuel cell of the stack. The plates may include various surface flow channels and orifices to, as examples, route the reactants and products through the fuel cell stack. Several MEAs (each one being associated with a particular fuel cell) may be dispersed throughout the stack of flow plates which form the fuel cell stack. Reactant gases from each side of the MEA may leave the flow channels and diffuse through the GDLs to reach the PEM.
The fuel cell stack is one out of many components of a typical fuel cell system, as the fuel cell system includes various other components and subsystems, such as a cooling subsystem, a cell voltage monitoring subsystem, a control subsystem, a power conditioning subsystem, etc. The particular design of each of these subsystems is a function of the application that the fuel cell system serves. Many fuel cell systems include a reformer which reacts hydrocarbon fuel, steam, and often air to form a hydrogen rich gas stream, called reformate, which is the fuel used by the fuel cell stack. Reformate often contains small concentrations of hydrocarbons that passed through the reformer without reacting.
The fuel cell stack produces anode exhaust gas (or "anode tail gas"), a gas that may contain hydrogen that was not consumed in the electrochemical reactions inside the fuel cell stack. The anode exhaust may also contain unreacted hydrocarbons from the reformer. Anode tail gas may be routed to a device, such as an oxidizer, that removes the hydrogen and other hydrocarbons from the flow before venting this flow to the atmosphere. More specifically, the oxidizer reacts any residual hydrogen and/or hydrocarbon fuel that is present in the anode exhaust gas with an oxidant for purposes of removing the hydrogen and/or hydrocarbon fuel and for purposes of recovering thermal energy. Recovering all the thermal energy and minimizing the release of harmful compounds into the atmosphere requires complete, or nearly complete, oxidation of the hydrogen and any hydrocarbons present in the anode tail gas. The reactions between the hydrogen and the oxidant and the hydrocarbon fuel and the oxidant may require a relatively high temperature (a temperature above 600° C., for example).
The anode tail gas produced by some fuel cell systems has a heating value which is too low to support a conventional flame. For this reason, some fuel cell systems use a catalytic anode tail gas oxidizer to promote the oxidation of hydrogen and hydrocarbon fuel at lower temperatures than found in a flame. Catalytic tail gas oxidation typically requires premixing of the anode tail gas and the oxidant to achieve complete oxidation of the hydrogen and the hydrocarbon fuel. Some fuel cell systems also produce anode tail gas with a time-varying composition, due to changes in operating conditions and electrical load on the fuel cell system. Variations in the anode tail gas composition can result in the premixed anode tail gas and oxidant mixture sometimes falling within the flammable regime.
Hydrogen has a relatively high flame speed, which means that when the hydrogen is reacted with an oxidant, and the mixture falls within the flammable regime, the reaction front may easily travel upstream to produce flashback. A device called a flame arrestor may be used with an oxidizer in an attempt to prevent the flashback. However, the use of the flame arrestor typically increases the cost, pressure drop, and complexity of the fuel cell system. In addition, flame arrestors cannot prevent autoignition of a flammable, premixed fuel and oxidant mixture.
Thus, there is a continuing need for a premixed, catalytic oxidizer that achieves complete combustion of the fuel and prevents flashback.


In a cordless key telephone system for covering multiple service areas, access units are divided into groups corresponding respectively to the service areas, the access units of each group being located in the corresponding service area for broadcasting a recurrent sequence of address signals on a two-way radio control channel and carrying speech signals on an assigned two-way telephone channel. The access units of each group has a uniquely assigned control channel different in frequency from the control channel of the other group. Cordless stations are switchable to the control channel of a first group of the access units for detecting an address signal and subsequently switchable to the control channel of the access units of a second group if the address signal is not detected in a first sequence for detecting the addressed signal in a second sequence. A main controller is coupled to a switched telephone network for causing the access units to broadcast the address signals in response to an incoming call from the network and for establishing a connection between the network and one of the cordless stations.

The present invention relates to a cordless key telephone system.
Cordless key telephone systems have been in use today replacing wired key telephone systems as they considerably reduce the amount of cables and wires laid on office floors the arrangement of which must be altered to meet current needs of working environment. The system includes a main controller which is coupled to the public or private switched telephone network via subscriber loops to receive incoming calls and originate outgoing calls. The floor space which the system covers is divided into several service areas. One or more access units are located in each service area and coupled to the main controller to exchange control signals with it. The system has only one control channel for exchanging control signals between the access units and cordless stations and several speech channels for transmitting ringing signals and speech signals. In response to an incoming call, the main controller selects one access unit for each service area and sends an alert signal to it over the control channel. Each selected access unit then broadcasts a recurrent sequence of alert signals respectively containing the identifiers of all standby cordless stations to elicit a response therefrom. Each standby cordless station responds to the alert signal addressed to it by returning an acknowledgment signal containing it in the own station identifier as well as the system identifier.
However, since the boundaries between adjacent service areas are not sharply defined, the adjacent areas tend to partially overlap with each other, creating an area in which collision is likely to occur between control signals transmitted from the access units of the adjacent area when an incoming call is received.
Interference between control channel and speech channels is another problem. If the control channel is severely affected by noise from adjacent channels due to intermodulation distortion, an undesirable situation can occur.

Cordless key telephone system for covering multiple service areas having exclusively assigned control channels


Computer program products, methods, systems, apparatus, and computing entities are provided for an augmented reality display using an actual image of the item. Additionally, the present disclosure provides for a proportionally dimensioned representation of the item in the augmented reality display. In some aspects, a beacon/tag/sensor-based approach may be used. In some aspects, a marker-based approach may be used.

In attempting to identify particular items, a technical problem exists with prior systems providing an augmented/mixed reality environment that fails to display actual images of items, and also fails to display proportionally dimensioned representations of items to a user. To that end, a need exists for providing an augmented/mixed reality environment that displays an actual image of an item or a proportionally dimensioned representation of the item.

This patent is subject to a terminal disclaimer.

Displaying items of interest in an augmented reality environment


The present disclosure discloses an imaging lens assembly which includes, sequentially from an object side to an image side along an optical axis, a first lens to a fifth lens. The first lens has a positive refractive power and a convex object-side surface. The second lens has a negative refractive power, a concave object-side surface and a concave image-side surface. The third lens has a negative refractive power. The fourth lens has a positive or a negative refractive power. The fifth lens has a positive or a negative refractive power, a concave object-side surface, and an image-side surface of the fifth lens is a convex surface or a plane. An air spacing T23 between the second lens and the third lens on the optical axis and an air spacing T34 between the third lens and the fourth lens on the optical axis satisfy: 1.0≤T23/T34<2.0.

As the science and technology develop, portable electronic products are gradually rising, and portable electronic products having camera functions are increasingly favored by people. For imaging lens assemblies in the portable electronic products, higher requirements on the image quality of the lens assemblies are brought forward on the basis of satisfying miniaturization.
The newly proposed dual camera concept may combine wide-angle and telephoto to achieve the purpose of zooming under the premise of ensuring lightness and thinness of the electronic products, so that the lens assembly may obtain a clearer image at a short distance or at a long distance, which makes a user obtain a different visual effect and a better user experience.


Solid oxide stacks used as fuel cells generate electricity from hydrogen or other sources. By an electrolysis process such standard fuel cells can be operated in order to create hydrogen or other electro chemical by-products. Unfortunately stacks generally operate at relatively high temperatures which will be difficult to sustain purely on economic grounds. In such circumstances less efficient operation can be achieved at lower temperatures where the air-specific resistance is higher by balancing with the electrical power input in order to cause the disassociation required. In such circumstances by provision of an incident heat source, whether that be through a heat exchanger heating the compressed air flow, or recycling of a proportion of exhaust from the stack, or combustion of a product from stack disassociation the result will be a sustaining electrolysis operation reducing the amount of expensive electrical supply required to achieve dissociation.

The present invention relates to electrolysis and for example utilisation of fuel cell technologies in order to generate hydrogen as a fuel for other uses.
Electrolysis apparatus is known for a number of applications and it is proposed to use water electrolysis as a simple and clean technology for hydrogen production. Electrolysis is the reverse process to fuel oxidation in fuel cells. A schematic of the process is illustrated in FIG. 1. In an electrolysis process steam is dis-associated on a cathode with formation of hydrogen molecules. In solid oxide cells the cathode reaction is as follows:H2O+2e−=H2+O2−
Oxygen ions migrate through the electrolyte forming oxygen molecules on the anode surface with the release of electrons.O2−=½O2+2e−
The overall steam electrolysis reaction is then as follows:H2O+H2+½O2
In the above circumstances it will be understood that an electrical power source is required to draw electrons from the anode to the cathode overcoming the electrochemical reaction potential.
Although commercial water electrolysis is available at low temperatures through use of known technology the efficiency of operation for these electrolysers is relatively low. Use of high temperature fuel cell technology is inhibited by the necessity for such high temperature fuel cells to operate at temperatures in excess of 800° C. and typically in a range 800° C.-1000° C. In such circumstances it is necessary to use specific heaters which diminish effectiveness and practicability of such approaches.
Currently the most developed technology with regard to hydrogen production is related to steam re-forming. In this process a fossil fuel source is utilised and this contributes significantly to CO2 emissions. Water electrolysis is proposed as a "green house gas free" hydrogen production technology allowing utilisation of non fossil fuel electricity sources such as nuclear or renewable electrical power sources. Unfortunately there is a significant disadvantage with current hydrogen production via water electrolysis in that, as indicated above, there is a relatively low efficiency. Such low efficiency necessitates the use of a relatively high electricity consumption rate rendering the costs of the hydrogen produced by water electrolysis as too expensive for commercial viability relative to that currently produced through steam re-forming. It will also be understood that the equipment cost for current water electrolysers is high again significantly contributing to making water electrolysis the more expensive option for hydrogen production when compared to steam re-forming of natural gas or other hydro carbons.


A transurethral needle ablation device for use by a human hand to treat the prostate of a human male. The device includes a cartridge assembly having an elongate probe member and a stylet. The elongate probe member has proximal and distal extremities and is provided with a passageway extending from the proximal extremity to the distal extremity. The stylet is slidably mounted in the passageway of the elongate probe member. A housing is included in the device. The cartridge assembly is removably mountable on the housing. An assembly adapted for actuation by the human hand is carried by the housing and coupled to the proximal extremity of the stylet for causing the distal extremity of the stylet to extend into the tissue of the prostate.

Medical devices have been provided for treating benign prostatic hyperplasia by use of radio frequency energy. See, for example, U.S. Pat. Nos. 5,370,675 and 5,549,644. Some of such devices include components which are disposable so as to reduce the cost of the procedure. In this regard, see International Publication No. WO/00049 having an International Publication Date of Jan. 3, 1997. There remains, however, a need for a new and improved transurethral needle ablation device which is relatively simple in construction, easy to use and inexpensive.

Transurethral needle ablation device with replaceable stylet cartridge


One embodiment of the invention includes a product comprising: a solid polyelectrolyte membrane having a first face and an opposite second face; a first catalyst layer overlying the first face of the membrane; a first microporous layer overlying the first catalyst layer, and wherein the first microporous layer includes a plurality of microchannels formed therein open toward the first catalyst layer; and wherein each of the microchannels of the first microporous layer are defined by a surface that is free of cracks.

Liquid water is created inside a fuel cell for at least two fundamental reasons: (1) the creation of water during the electrochemical reaction, and (2) the condensation of incoming water vapor entering with humidified reaction gases. The amount of water created during the electrochemical reaction depends directly on the current density. The amount of incoming water vapor that condenses inside the gas flow channels of the collector plates depends on the operating conditions such as stoichiometry and the relative humidity of the incoming gas streams. Excess liquid water in the cell can partially block the gas flow fields creating what is known as "flooding."
Referring now to FIG. 1, many prior art fuel cells have been constructed using a solid polyelectrolyte membrane 12 having a cathode face 14 and an opposite anode face 16. A cathode electrode 18 including a catalyst supported on carbon particles, and an ionomer is formed on the cathode face 14 of the membrane 12. Similarly, an anode electrode 20 including a catalyst supported on carbon particles, and an ionomer is formed on the anode face 16 of the membrane 12. A microporous layer 22 may be provided over the cathode electrode 18. A gas diffusion media 24 may be provided over the microporous layer 22. A collector plate 26 is provided over the gas diffusion media 24, and wherein the collector plate 26 includes a plurality of lands 28 and channels 30 defining a reactant gas flow field. In this case, a reactant gas such as oxygen or air is provided through the channels 30 and diffuses through the gas diffusion media 24 and microporous layer 22 so that the cathode electrode 18 catalyzes the reaction of oxygen molecules with hydrogen protons to produce water. Such prior art fuel cell products are typically constructed to allow for the reaction produced water to diffuse through the microporous layer 22 and gas diffusion media 24. However, the water can begin to accumulate underneath the lands 28 of the bipolar plate 26 and result in a liquid layer 34 forming in the channel 30, which is known as "flooding." The flooding prevents the reactant gases from flowing towards the membrane 12 and thus adversely impacts fuel cell performance.

Fuel cell microporous layer with microchannels


There is provided a variable flow turbocharger comprising a turbine chamber (22) within which a turbine (14) is mounted for rotation, an inlet passageway (20) arranged around the turbine chamber (22) for introducing exhaust gas into the turbine chamber (22), and an outlet passageway (24) extending from the turbine chamber (22) for discharging the exhaust gas. There is provided a movable wall member (16a) whose position relative to the turbine (14) is adjustable to vary the geometry of the turbine chamber (22) at an outlet side of the turbine (14) close to the outlet passageway (24).

This invention relates to a variable flow turbocharger, and in particular the turbine stage of a turbocharger for an internal combustion engine.
Many internal combustion engines are equipped with turbochargers to improve engine efficiency. A turbocharger comprises a turbine and a compressor. In operation, the turbine captures high-temperature exhaust gas coming from the engine exhaust manifold. This exhaust gas then is used to drive the compressor which, in turn, pumps high pressure air into the engine inlet and combustion chambers. The effect of this process in an internal combustion engine is to increase the volume of air available for combustion. Because more air is available, a correspondingly greater amount of fuel can be consumed, or burnt, per cycle. In theory, the greater the fuel burnt, the greater the horsepower.
Typically, the turbine stage of a turbocharger comprises a turbine chamber within which the turbine is mounted, an inlet passageway arranged around the turbine chamber for introducing exhaust gas into the turbine chamber, and an outlet passageway extending from the turbine chamber for discharging the exhaust gas. The turbine chamber and the inlet and outlet passageways communicate such that incoming exhaust gas flows through the inlet passageway to the outlet passageway via the turbine chamber and rotates the turbine.
Under the current state of the art, it is known to vary the flow of exhaust gas in the turbine stage so that the power output of the turbine can be adjusted to suit varying engine demands. One common type of variable flow turbocharger is a wastegated (turbine bypass) turbocharger. Such turbochargers have a wastegate for bypassing exhaust gas around the turbine using a valve in the inlet passageway controlled by actuator means. Wastegated turbochargers are usually matched to give good performance at low engine speed with the valve closed. This improves transient response and reduces exhaust temperatures and emissions. As engine speed increases, the wastegate valve begins to open. This has the effect of increasing the flow capacity of the turbine stage and avoiding excess air delivery and turbine overspeed (see U.S. Pat. No. 4,643,640 for the basic concept of wastegated turbochargers).
In another type of variable flow turbocharger, a more complex method of turbocharging uses a turbine stage where the flow capacity of the turbine stage is adjusted by varying the geometry of a nozzle, the part of the inlet passageway which surrounds the turbine and directs the exhaust gas at the turbine. One common type of variable nozzle turbocharger has a set of swing or slide vanes which extend into the nozzle and which can be caused to vary in orientation so as to increase or decrease the effective cross-sectional area between the vanes. Decreasing the effective cross-sectional area between the vanes permits turbine speed to be increased by increasing the pressure differential across the turbine (see U.S. Pat. Nos. 4,643,640, 4,654,941 and 4,659,295 for the basic concept of swing vanes). In another type of variable nozzle turbocharger, one wall of the nozzle is defined by a moveable wall member, generally referred to as a nozzle ring. The position of the ring relative to a facing wall of the nozzle is adjustable to control the width of the nozzle. For instance, as gas flowing through the turbine decreases, the nozzle width may also be decreased to maintain gas velocity and optimize turbine output (see EP 1 226 580 A2 for the basic concept of a nozzle ring).


An apparatus, system, and method are provided for facilitating management of logical nodes through a single management module. The present invention includes a communication module that selectively communicates a management command from a single management module to one or more logical nodes. A translation module translates the management command into one or more functionally equivalent software-layer commands recognized by one of the software layers of the one or more logical nodes. The software-layer commands are compatible with each logical node. A direction module directs the one or more software-layer commands to an appropriate one of the software layers according to a management command scope. The present invention can address management commands to a plurality of logical nodes having disparate operating systems and executing applications.

1. Field of the Invention
The invention relates to data storage computer systems. Specifically, the invention relates to apparatus, systems, and methods for facilitating management of logical nodes through a single management module.
2. Description of the Related Art
Computer and information technology continues to progress and grow in its capabilities and complexity. In particular, data storage systems continue to evolve to meet the increasing demands for reliability, availability, and serviceability of the physical data storage system and its hardware, software, and various other components. Data storage systems often handle mission critical data. Consequently, data storage systems are expected to remain on-line and available according to a 24/7 schedule. Furthermore, data storage systems are expected to handle power and service outages, hardware and software failures, and even routine system maintenance without significantly compromising the reliability and availability to handle data Input/Output (I/O) from hosts.
FIG. 1 illustrates a conventional data storage system 100. The system 100 includes one or more hosts 102 connected to a storage subsystem 104 by a network 106 such as a Storage Area Network (SAN) 106. The host 102 communicates data I/O to the storage subsystem 104. Hosts 102 are well known in the art and comprise any computer system configured to communicate data I/O to the storage subsystem 104.
One example of a storage subsystem 104 suitable for use with the present invention is an IBM Enterprise Storage Servers® available from International Business Machines Corporation (IBM) of Armonk, N.Y. To provide reliability, availability, and redundancy, the storage subsystem 104 includes a plurality of host adapters (not shown) that connect to the SAN 106 over separate channels. The host adapters 108 may support high speed communication protocols such as Fibre Channel. Of course, various other host adapters 108 may be used to support other protocols including, but not limited to, Internet Small Computer Interface (iSCSI), Fibre Channel over IP (FCIP), Enterprise Systems Connection (ESCON), InfiniBand, and Ethernet. The storage subsystem 104 stores and retrieves data using one or more mass storage devices 108 such as, but not limited to Direct Access Storage Devices, tape storage devices, and the like.
As hardware costs have gone down, data storage systems 100 have become more complex due to inclusion of redundant hardware and hardware subsystems. Often, the hardware components are highly susceptible to failure. Consequently, the storage subsystem 104 may include one or more processors, electronic memory devices, host adapters, and the like.
Typically, to make most productive use of the redundant hardware, the hardware is specifically allocated or shared between a plurality of logical nodes 110. A logical node 110 represents an allocation of the computing hardware resources of the storage subsystem 104 such that each logical node 110 is capable of executing an Operating System (OS) 112 independent of another logical node 110. In addition, each logical node 110 operates an independent set of applications 114. The logical nodes 110 appear as separate physical computing systems to the host 102.
A coordination module 116, also known as a Hypervisor (PHYP) 116, coordinates use of dedicated and shared hardware resources between two or more defined logical nodes 110. The PHYP 116 may be implemented in firmware on a dedicated processor. Typically, the logical nodes 110 share memory. The PHYP 116 may ensure that logical nodes 110 do not access inappropriate sections of memory.
Separating the storage subsystem 104 into a plurality of logical nodes 110 allows for higher reliability. If one logical node 110 crashes/fails due to a software or hardware problem, one or more other logical nodes 110 may be used to continue or restart the tasks that were being performed by the crashed logical node 110.
Management and control of the plurality of logical nodes 110 is a challenge. Any management, control, maintenance, monitoring, troubleshooting or service operation should be coordinated with the constant I/O processing so that the 24/7 availability of the storage subsystem 104 is not compromised. Typically, a management console 118 manages the storage subsystem 104 via control communications (referred to herein as "out-of-band communication") separate from the I/O channels.
The storage subsystem 104 may include a network adapter, such as an Ethernet card, for out-of-band communications. The management console 118 may comprise a separate computer system such as a workstation executing a separate OS and set of management applications. The management console 118 allows an administrator to interface with the PHYP 116 to start (create), stop, and configure logical nodes 110.
Unfortunately, the management capabilities of the management console 118 are severely limited. In particular, the logical nodes 110 are completely independent and unrelated. Consequently, to manage a plurality of logical nodes 110 for example, to set a storage space quota, an administrator must login to each node 110 separately, make the change, and then log out. This process is very tedious and can lead to errors as the number of logical nodes 110 involved in the operation increases. Such management tasks are complicated by the fact that different OSes 112 and/or storage applications 114 may reside on each node 110. Consequently, administrators may have to use different command sets and different parameters for each node 110.
The repetitive nature of such a change is exacerbated in a storage subsystem 104 where nodes 110 may be highly uniform and may differ in configuration by something as minor as a name. Managing the nodes 110 separately may require significant time and expense. In addition, an administrator may be the only one who knows that two similar nodes 110 are to be similarly configured because there is no internal relationship between the nodes 110.
Furthermore, the management console 118 provides very few management commands. Typically, the management console 118 is limited to commands that start (create), stop, and configure logical nodes 110 themselves. The management console 118 fails to allow an administrator to send management commands to the OS 112 or applications 114 of one or more logical nodes 110. Instead, the administrator must login to each node, manually shutdown and applications 114 and then the OS 112. Then, the administrator can stop the node 110 in order to perform some maintenance operation. The management console 118 also fails to send management commands to more than one node 110 at a time regardless of whether two or more nodes 110 share a relationship.
The management console 118 conventionally only controls nodes of a single storage subsystem 104. To control multiple storage subsystems 104, which is common in modern enterprise systems, the administrator must login to each node 110 separately and may have to physically move to a different management console 118 machine to complete the management operations. The high number of nodes 110 that must each be individually managed limits the administrator's effectiveness. In addition, the independent nodes 110 make automated tools for management more difficult to implement and configure.
From the foregoing discussion, it should be apparent that a need exists for an apparatus, system, and method for facilitating management of logical nodes through a single management module. Beneficially, such an apparatus, system, and method would provide a common command set for management and control of disparate nodes 110 as well as the OSes 112 and applications 114 of the nodes 110. In addition, the apparatus, system, and method would support relationships between nodes 110 such that management commands sent to one node 110 are automatically implemented on all nodes sharing that relationship. Furthermore, the apparatus, system, and method would support management of a plurality of hardware platforms, such as for example storage subsystems 104, from a single management module. Each platform may include one or more logical nodes 110.

Apparatus, system, and method for facilitating management of logical nodes through a single management module


A quartz substrate includes a first light transmitting portion and a second light transmitting portion which transmit exposure light. The first and second light transmitting portions are formed such that exposure light transmitted through respective light transmitting portions are 180.degree. out of phase with each other. A semi-light shielding film is located between first and second light transmitting portion and formed in a part of first and second light transmitting portions. Also, semi-light shielding film has transmittance of at least 3% and not more than 30%.

1. Field of the Invention
The present invention relates to a phase shifting mask and a manufacturing method thereof as well as an exposure method using such a phase shifting mask.
2. Description of the Background Art
In semiconductor integrated circuitry, so many developments have been made for high integration and miniaturization. Accordingly, the rapid development has been made for miniaturization of a circuit pattern which is formed on a semiconductor substrate (hereinafter referred merely to as a wafer).
Among other things, photolithography has been recognized widely as the basic technology for pattern formation, in which various developments and improvements have already been made. However, as miniaturization of patterns proceeds, an improvement of resolution of the pattern is strongly required.
Photography is a technology for transferring a mask (original) pattern on a photoresist applied on a wafer and patterning an underlying film to be etched. When transferring the photoresist, the photoresist is developed. During development, the photoresist of the type in which a portion exposed to light is removed is called a positive type photoresist, while the type in which a portion not exposed to light is removed is called a negative type. Now, a conventional exposure method utilizing the photolithography technology will be described.
FIG. 45 is a schematic diagram of an optical system for illustrating a conventional exposure method. In this optical system, referring to FIG. 45, a pattern on a mask is reduced and projected onto a photoresist placed on the wafer. The optical system includes an illumination optical system covering from a light source to a photomask pattern, and a projection optical system covering from the photomask pattern to the wafer.
The illumination optical system includes a mercury lamp 111 serving as a light source, a reflection mirror 112, a light collecting lens 118, a fly eye lenses 113, a diaphragm 114b, light collecting lenses 116a-116c, a blind diaphragm 115, and a reflection mirror 117. The projection optical system includes telephoto lenses 119a-119b and a diaphragm 125.
In exposure operation, a beam of light 111a emitted from mercury lamp 111 is reflected from reflection mirror 112, so that only a g-line (wavelength:436 nm), for example, is reflected to become a beam of light having a single wavelength. Beam of light 111a then enters each lens 113a constituting fly eye lens 113, and after that, passes through diaphragm 114b.
Light passes through a light path 111b produced by one lens 113a constituting the fly eye lens, and light passes through a light path 111c produced by fly eye lens 113.
Beam of light 111a transmitted through diaphragm 114b then passes through light collecting lens 116a, blind diaphragm 115 and light collecting lens 116b, and is reflected from reflection mirror 117 at a predetermined angle.
Reflected from reflection mirror 117, beam of light 111a transmits through light collecting lens 116c and irradiates uniformly the entire surface of a photomask 720 in which a predetermined pattern is formed. Then, beam of light 111a is reduced by projection lenses 119a, 119b by a predetermined times for exposing a photoresist 121a placed on a semiconductor wafer 121.
Generally, a resolution limit R (nm) in photolithography using the demagnification exposure method is represented as EQU R=k.sub.1 .multidot..lambda./(NA)
where .lambda. is a wavelength (nm) of the light used, NA is a numerical aperture of a lens, and k.sub.1 is a constant depending on a resist process.
As can be seen from the above expression, a method conceivable to improve resolution limit R, i.e., to obtain a fine pattern, is to reduce k.sub.1 and .lambda. values and increase an NA value. In other words, it is sufficient to reduce the constant depending on the resist process while shortening the wavelength and increasing NA.
However, improvement of light source or the lens is technically difficult, and a depth of focus .delta. of the lens (.delta.=k.sub.2 .multidot..lambda./(NA).sup.2) might be shallower by proceeding shortening of the wavelength and increasing of NA, thus causing deterioration of the resolution.
With this in view, studies for attempting miniaturization of patterns by improving the photomask are under way. Lately, a phase shifting mask has been focused as a photomask capable of improving a resolution of the pattern. Now, a structure and the principle of such a phase shifting mask will be described in comparison with an ordinary photomask. The below description will be directed to a phase shifting mask of a Levenson system and a halftone system.
FIGS. 46A-46C represent, respectively, a cross section of a mask when a conventional photomask is used, an electric field on the mask, and a graph showing the light intensity on a wafer. Referring to FIG. 46A, a metal mask pattern 503 is formed on a glass substrate 501 in the conventional photomask. The electric field on such a conventional photomask is pulse-modulated spatially by metal mask pattern 503 as shown in FIG. 46B.
However, as can be seen from FIG. 46C, as the pattern is miniaturized, exposure light transmitted through the photomask also enters an unexposed region (a region where the exposure light is intercepted by metal mask pattern 503) due to diffraction of light. Therefore, light is directed also to the unexposed region on the wafer, thus decreasing contrast of light (a difference in light intensity between the exposed region and the unexposed region on the wafer). Consequently, the resolution is decreased, making transfer of fine patterns difficult.
FIGS. 47A-47C represent, respectively, a cross section of a mask when a phase shifting mask of the Levenson system is used, an electric field on the mask, and a graph showing light intensity on a wafer. Referring to FIG. 47A, the phase shifting mask includes an optical member called a phase shifter 505 provided on the conventional photomask.
More particularly, a chromium mask pattern 503 is formed on glass substrate 501 so that exposure regions and shaded regions are provided, and phase shifters 505 are provided every other exposure region. Phase shifter 505 serves to convert a phase of the transmitted light by 180.degree..
Referring to FIG. 47B, since phase shifters 505 are provided every other exposure region as described above, the electric field on the mask is structured such that phases of the light transmitted through the phase shifting mask are inverted alternately by 180.degree.. Phases of light are thus reversed in adjacent exposure regions, so that beams of light are canceled with each other due to interference of light in a portion where reverse-phased beams of light are overlapped.
As a result, as shown in FIG. 47C, the light intensity is reduced at a boundary of adjacent exposure regions, so that a sufficient difference in light intensity between exposure regions and unexposure regions on the wafer can be secured. This allows improvement of the resolution for transferring fine patterns.
FIGS. 48A-48C represent, respectively, a cross section of a mask when a phase shifting mask of the halftone system is used, the electric field on the mask, and a graph showing light intensity on the wafer. Referring to FIG. 48A, an optical member called a phase shifter 506 is also provided in the phase shifting mask of the halftone system as in the above-described Levenson system.
Only difference is that optical member 506 is formed only on an opaque film 503 on glass substrate 501, so that a two-layered structure of phase shifter 506 and opaque film 503 is provided. Phase shifter 506 serves to convert the phase of the transmitted light by 180.degree. as described above, and opaque film 503 serves to decay the intensity of the exposure light without completely intercepting the exposure light.
Referring to FIG. 48B, since the two-layered structure of phase shifter 506 and opaque film 503 is provided as described above, phases of light are converted by 180.degree. alternately in the electric field on the mask, while at the same time the intensity of one phase becomes smaller than the other. More particularly, phases of light are converted by 180.degree. due to transmission through phase shifter 506, and the intensity of light is decayed due to transmission through opaque film 503 such that a predetermined thickness of the photoresist can remain after development. The phases of the light are reversed in adjacent exposure regions so that beams of light are canceled with each other in the region where reverse-phased beams of light are overlapped.
As can be seen from FIG. 48C, the intensity of light can be reduced at an edge of the exposure pattern because the phase is reversed at the edge. Consequently, the difference in the light intensity between the region where the exposure light is transmitted through opaque film 503 and the region the light is not transmitted through the film becomes greater, whereby the resolution of the pattern image can be improved.
As described above, there are many types of phase shifting masks including the Levenson system, the halftone system and the like. Among others, a good resolution can be obtained according to the principles of a so-called phase shifting mask of the Levenson system which had been invented by Marc Levenson, and that system is considered as the most favorable system from the standpoint of resolution.
Various techniques have been invented and proposed for manufacturing such a phase shifting mask, however, none has been used in practice. Among these proposals, one prior art technique which is considered superior is a manufacturing technique by Marc Levenson which is described in Marc D. Levenson et al., "Phase-Shifting Mask Strategies: Isolated Dark Lines" MICROLITHOGRAPHY WORLD, pp.6-12, March/April 1192.
Therefore, a structure and a manufacturing method of a phase shifting mask of the Levenson system according to the above technique will be described below as a conventional first phase shifting mask.
FIG. 49 is a cross sectional view schematically showing a structure of a conventional first phase shifting mask. Referring to FIG. 49, a conventional first phase shifting mask 720 includes a quartz substrate 701 and a light shielding film 703.
Trenches are formed with a predetermined depth on a main surface of quartz substrate 701. A region where the trench is not formed serves as a first light transmitting portion 701a, while a region where the trench is formed serves as a second light transmitting portion 701b. Light shielding film 703 is formed on quartz substrate 701 so as to cover a sidewall portion of the trench and to expose predetermined regions of first and second light transmitting portions 701a and 701b. Light shielding film 703 has transmittance of not more than 1%, and a thickness of about 1000 .ANG. when chromium (Cr) is used as a material.
First and second light transmitting portions 701a and 701b are structured such that phases of the exposure light transmitted through respective portions are converted by 180.degree.. Since the phases of exposure light transmitted through adjacent light transmitting portions are thus converted by 180.degree., the resolution can be improved, as described above.
A bottom wall of the trench is substantially perpendicular to a sidewall thereof.
Now, a manufacturing method of the first phase shifting mask will be described below.
FIGS. 50-57 are schematic cross sectional views showing in this order a manufacturing method of the conventional first phase shifting mask. First, referring to FIG. 50, a chromium film 705a is formed on a surface 701a of quartz substrate 701. A resist film 707a is applied on chromium film 705a. Resist 707a is then exposed with light and developed.
Referring to FIG. 51, a resist pattern 707 having a desired shape is formed through the above exposure and development. Using resist pattern 707 as a mask, anisotropic etching is carried out. Resist pattern 707 is then removed.
Referring to FIG. 52, a chromium film pattern 705 is thus formed wherein a shifter pattern is transferred.
Referring to FIG. 53, using chromium film pattern 705 as a mask, anisotropic etching is carried out on quartz substrate 701, whereby a trench is formed on a surface 701a of quartz substrate 701 for transferring the shifter pattern. Chromium film pattern 705 is then removed.
Referring to FIG. 54, first and second light transmitting portions 701a and 701b are thus formed in quartz substrate 701.
Referring to FIG. 55, a chromium film 703a is formed on the entire surface wherein first and second light transmitting portions 701a and 701b are formed. A resist film 709a is applied on chromium film 703a. Resist film 709a is then exposed with light and developed.
Referring to FIG. 56, a resist pattern 709 having a desired shape is formed through the above exposure and development. Using resist pattern 709 as a mask, anisotropic etching is conducted to form a light shielding film 703 which exposes desired regions of first and second light transmitting portions 701a and 701b. After that, resist pattern 709 is removed, thereby completing the conventional phase shifting mask 720 shown in FIG. 57.
In the above-described manufacturing method of the conventional phase shifting mask, resist films 707a and 709a are not applied directly on quartz substrate 701. Accordingly, compare to a manufacturing method of the phase shifting mask in which the resist film is directly applied on the substrate (Japanese Patent Laying-Open Nos. 4-355758 and 2-211450), this phase shifting mask includes an advantage that a defect such as is described below will easily be repaired.
As one example of the method in which the resist film is directly applied on the substrate, a manufacturing method of the phase shifting mask described in Japanese Patent Laying-Open No. 4-355758 will be described.
FIGS. 58-61 are schematic cross sectional views showing in this order the manufacturing method of the phase shifting mask described in the above document. First, referring to FIG. 58, after a phase shifting film 803 is formed on the surface of a quartz layer 801, a light shielding film 805 is formed on the surface of the film 803.
Referring to FIG. 59, after a resist pattern 807 is formed on light shielding film 805, light shielding film 805 is patterned by etching with using resist pattern 807 as a mask. Resist pattern 807 is then removed.
Referring to FIG. 60, a photoresist 809 is directly applied on the surface of the patterned light shielding film 805 and phase shifting film 803. After patterning photoresist 809 into a desired shape, phase shifting film 803 is etched with using resist pattern 809 as a mask.
Referring to FIG. 61, a trench 811 is formed in phase shifting film 803. After that, resist pattern 809 is removed, thereby completing the phase shifting mask.
In the manufacturing method of the phase shifting mask disclosed in the above document, a shifter pattern is formed in phase shifting film 803 after light shielding film 805 is patterned, whereby resist film 809 is directly applied on the surface of phase shifting film (substrate) 803 in the step shown in FIG. 60.
In a typical method for applying the resist film, a pinhole 809a which penetrates through resist film 809 is generated as shown in FIG. 62. If etching is carried out by using resist pattern 809 as a mask with such pinhole 809a generated, a configuration shown in FIG. 63 will be obtained.
Referring to FIG. 63, an etchant enters pinhole 809a, so that phase shifting film 803 located at the bottom of pinhole 809a is also removed by etching, thus generating a defect. If the phase shifting mask including such a defect is used for exposure of a wafer, the phase of exposure light is converted in the defect portion in addition to desired regions. Therefore, the resist film applied on the wafer cannot be exposed into a desired shape.
Therefore, when the resist film is applied directly on the substrate, the defect of the shifter is introduced directly into the substrate upon carrying out etching or the like with using the resist pattern as a mask.
On the contrary, in the manufacturing method proposed by Marc Levenson, as described above, the resist film is not formed directly on the quartz substrate. Thus, even if etching is carried out to the underlying layer by using the resist film wherein pinholes are generated as a mask, direct formation of the defect of the shifter in the substrate can be prevented.
More specifically, referring to FIG. 64, even if a pinhole 707a is generated in a resist pattern 707, since a chromium film 705 is lying under resist pattern 707, only chromium film 705 at the bottom of pinhole 707a is removed by etching after etching is carried out to the underlying layer by using resist pattern 707 as a mask.
As can be seen in the figure, a pinhole defect (clear defect) 705a generated at the bottom of pinhole 707a is not in quartz substrate 701 but in chromium film 705 lying thereon. Thus, pinhole defect 705a can be easily repaired by filling up by deposition of a carbon-based film 705c in accordance with an FIB (Focussed Ion Beam) method, as shown in FIG. 65.
In some cases, as can be seen from FIG. 64, a remaining defect (opaque defect) 705b is generated at a portion where the chromium film should have been removed by etching. However, since such remaining defect 705b is not the type of defect which is formed directly in quartz substrate 701, the defect can be repaired easily by removing by blow (melt) of irradiation of laser using a YAG laser, as shown in FIG. 65.
Thus, the conventional manufacturing method proposed by Marc Levenson has the advantage that defects can easily be repaired because the defect of the shifter is not formed directly in the substrate.
Now, a structure of a phase shifting mask of the halftone system will be described below as a conventional second phase shifting mask.
FIG. 66 is a cross sectional view schematically showing a structure of a conventional second phase shifting mask. As can be seen from FIG. 66, a conventional second phase shifting mask 920 includes a quartz substrate 901 and a semi-light shielding film 903. A trench is formed with a predetermined depth in a main surface of quartz substrate 901.
A region where the trench is formed serves as a first light transmitting portion 901a, while a region where the trench is not formed serves as a second light transmitting portion 901b. Semi-light shielding film 903 is formed on quartz substrate 901 so as to cover a sidewall portion of the trench and to expose a predetermined region of first light transmitting portion 901a. Semi-light shielding film 903 serves to reduce the intensity of exposure light transmitting through semi-light shielding film 903 to such an extent that a photoresist on the wafer is not photosensitized by the exposure light or a predetermined thickness of the photoresist is left after development.
First and second light transmitting portions 901a and 901b are structured such that phases of the exposure light transmitted through respective portions are out of phase by 180.degree.. As the phases of the exposure light transmitted through adjacent light transmitting portions are thus converted by 180.degree., the resolution can be improved as described above.
In the meantime, a bottom wall of the trench is substantially perpendicular to a sidewall thereof.
With using conventional first and second phase shifting masks, as described above, a higher resolution can be obtained compared to an ordinary photomask. However, there are some problems in the conventional first and second phase shifting masks such as difficulty in obtaining a desired pattern shape because of I! increase in complexity of a circuit pattern and II! generation of a defect during formation of a shift mask. We will discuss these problems more in detail in the following.
I! Increase in Complexity of the Circuit Pattern
The recent circuit patterns of semiconductor integrated circuits have been made smaller and become complex in order to obtain the semiconductor integrated circuits which has a large capacity and multiple functions. For instance, in a DRAM (Dynamic Random Access Memory), periodic patterns are provided densely (hereinafter referred merely to as a dense pattern) in each memory cell region, while circuit patterns having individual functions are isolated from each other (hereinafter referred merely to as an isolated pattern) in its peripheral circuit region.
If a circuit pattern in which a dense pattern and an isolated pattern are mingled is to be formed by the phase shifting mask of the Levenson system, a good resolution can be obtained in the dense pattern, while at the same time, the resolution is not so good in the isolated pattern. In the meantime, if the phase shifting mask of the halftone system is used, then the resolution is better in the isolated pattern than in the dense pattern.
FIGS. 67A and 67B illustrate the reason why the phase shifting mask of the Levenson system cannot be used to obtain the isolated pattern at a good resolution, wherein FIG. 67A shows a cross sectional view of the phase shifting mask of the Levenson system, and FIG. 67B shows the light intensity on the wafer when exposure is conducted by using the phase shifting mask shown in FIG. 67A.
Referring to FIGS. 67A and 67B, the isolated pattern exists away from the other circuit pattern. Thus, an exposure region 701b (hereinafter referred to as an isolated exposure region) constituting the isolated pattern is spaced apart by a considerable amount from an exposure region constituting the other circuit pattern. Accordingly, the exposure light directed onto the wafer after being transmitted through isolated exposure region 701b will not overlap the exposure light having a reverse phase which is transmitted through the other exposure region. This prevents the phase shifting mask effect of obtaining a good resolution by canceling reverse-phased beams of light with each other due to diffraction of light.
On the contrary, in the dense pattern, reverse-phased beams of light are overlapped in adjacent exposure regions, as shown in FIG. 47. This contributes to improvement of the resolution due to canceling of beams of light in the region where beams of light are overlapped.
Next, FIGS. 68A and 68B illustrate the reason why the phase shifting mask of the halftone system cannot be used to achieve a good resolution in the dense pattern, wherein FIG. 68A shows a cross sectional view of the phase shifting mask of the halftone system, and FIG. 68B shows the light intensity on the wafer when exposure is conducted by using the phase shifting mask shown in FIG. 68A.
Referring to FIGS. 68A and 68B, since circuit patterns are dense in the dense pattern, a plurality of exposure regions 901a, 901a are disposed in proximity to each other. A portion P.sub.3 is thus generated wherein beams of light of the same phase are overlapped with each other in adjacent exposure regions 901a. When the beams of light of the same phase are overlapped, the light intensity cannot be diminished at the edge (P.sub.3 portion) of the exposure pattern because of a small intensity of the reverse-phased light transmitted through exposure region 901b. In this case, the resolution cannot be improved due to an insufficient difference of light intensity between the exposure region and the unexposure region.
On the contrary, in the isolated pattern, a portion where beams of light of the same phase are overlapped is not generated, as shown in FIG. 48. This contributes to an improvement of resolution because a sufficient difference in light intensity can be obtained at the edge of the exposure pattern due to overlap of the reverse-phased beams of light.
Therefore, in the pattern wherein the dense pattern and the isolated pattern are mingled, either one pattern cannot be formed with a good resolution even though the conventional first or second phase shifting mask is used. This prevents formation of a desired pattern in such a complex circuit pattern as having the dense pattern and the isolated pattern.
II! Generation of a Defect During Formation of a Shifting Mask
In the conventional manufacturing method proposed by Marc Levenson in which a shifter pattern is formed in quartz substrate 701, anisotropic etching is carried out to quartz substrate 701. In this respect, there is a problem of difficulty in obtaining a predetermined shape pattern in this manufacturing method because of the reasons such as (1) adherence of the light shielding film to the quartz substrate is degraded, (2) foreign objects are likely to remain on the quartz substrate, and (3) disadvantage due to remaining defects are easily generated.
(1) Adherence of the Light Shielding Film to Quartz Substrate
In the conventional manufacturing method of the phase shifting mask, anisotropic etching is conducted to quartz substrate 701 in the steps shown in FIGS. 52 and 53. The sidewall of the trench which is formed by the etching is thus substantially perpendicular to the bottom wall of the trench. In the step shown in FIG. 55, chromium film 703a is formed also to cover the trench. However, it is difficult to form the film appropriately on the sidewall portion of the trench having the above-described structure. Specially, if chromium 703a is formed by a method having a poor step coverage such as sputtering, the appropriate formation of the film becomes more difficult.
This leads to deterioration of adherence of chromium film 703a against quartz substrate 701 on the sidewall portion of the trench (a region indicated by D.sub.3 in the figure). When the adherence of chromium film 703a is not favorable, chromium film 703a will be peeled off easily during the cleaning step of the manufacturing process of the phase shifting mask. Also, light shielding film 703 will be peeled off easily during cleaning after completion of the phase shifting mask.
A portion where light shielding film 703 is thus peeled off becomes a so-called clear defect. When exposure is carried out onto the wafer by using the phase shifting mask having the clear defect, a region which should not be exposed will be exposed with light on the wafer, thus preventing formation of a pattern having a desired shape.
(2) Remaining of Foreign Objects on the Quartz Substrate
As described above, according to the manufacturing method of the conventional phase shifting mask, quartz substrate 701 is subjected to anisotropic etching in the step shown in FIGS. 52 and 53, so that the bottom wall of the trench formed during the etching is substantially perpendicular to the sidewall of the trench, as shown in FIG. 70. Since an edge of the stepped portion (a region indicated by D.sub.4 in the figure) is substantially 90.degree., a foreign object 750a is easily be trapped at the edge.
More specifically, after formation of the trench on the surface of quartz substrate 701 in the steps shown in FIGS. 53 and 54, a chromium film pattern 705 is removed. During this removal, a foreign object is trapped at the edge of the stepped portion. Also, foreign objects such as being generated internally from the etching apparatus or included in an etching solution can be trapped.
If a light shielding film is formed with foreign objects being trapped, an etchant spreads under a resist 709 through foreign object (or after melting the foreign object at a high speed) during patterning of light shielding film 703, as shown in FIGS. 71 and 72. Thus, light shielding film 703 is removed excessively by etching as shown in FIG. 73. This excessively-removed portion by etching becomes a so-called clear defect. A region which should not be exposed will be exposed with light on the wafer due to the clear defect, thus preventing formation of a pattern having a desired shape.
As can be seen from FIG. 73, a portion of light shielding film 703 indicated by an arrow K is not in contact with the sidewall of the stepped portion but is protruding into the space. This portion K of light shielding film 703 is easily be peeled off by cleaning after removal of the resist or by cleaning after repairing of the defect of light shielding film 703, thus generating the clear defect as in the above.
In the meantime, as shown in FIG. 74, the surface of light shielding film 703 which is formed on the edge of the stepped portion reflects the stepped shape of the underlying layer. Thus, a foreign object 750b will easily be trapped at a portion along the edge of the stepped portion of light shielding film 703 (a region indicated by D.sub.5 in the figure), as in the above.
If the trapped foreign object 750b is large, foreign object 750b will remain penetrating onto the light shielding portion in some cases. If foreign object 750b is made of a material through which the exposure light cannot be transmitted, the foreign object will necessarily be a so-called opaque defect. Even if the exposure light can transmits through foreign object 750b, a proper function of light shielding mask 703 as a phase shifting mask will be prevented when a phase of the transmitted light is shifted by a considerable amount (usually 10.degree.-20.degree.) or more by the material. Thus, the shape to be transferred onto the resist on the wafer is deformed, thus generating a defect.
Thus, when the foreign object is trapped in the stepped portion or the like in quartz substrate 701 during processing of the phase shifting mask, it is difficult to expose the resist on the wafer into a desired shape.
(3) Disadvantage Caused By Remaining Defects
In some cases, during patterning of chromium film 705a shown in FIGS. 50 and 51, a remaining defect 705b is generated as shown in FIG. 75. Such a remaining defect 705b can be repaired by the above-described laser blow or the like. However, this does not mean that all of generated remaining defects 705b cannot be sensed and repaired. Also, it is sometimes desired to omit a step of repairing for the sake of simplifying of a manufacturing process. In such a case, some remaining defects 705b are still left.
In the manufacturing method of the conventional phase shifting mask, the trench is formed on the surface of quartz substrate 701 by anisotropic etching in the steps shown in FIGS. 52 and 53. However, if anisotropic etching is carried out with remaining defect 705b being generated, an unetched region (a region indicated by D.sub.6 in the figure) which should have been etched is generated as shown in FIG. 76.
Referring to FIG. 77, the phases of the beams of exposure light transmitted through adjacent light transmitting portions are not converted by 180.degree. in the thus formed phase shifting mask. More particularly, the exposure light transmitted through light transmitting portion 701a and the exposure light transmitted through a light transmitting portion 701ab have the same phase. Accordingly, the exposure light transmitted through both transmitting portions 701a and 701ab will be intensified in a portion where those beams of light are overlapped. Consequently, a difference of light intensity between the exposed region and the light-shielded region on the wafer becomes small, so that the resolution is degraded, and formation of a desired pattern cannot be achieved.
Additionally, as shown in FIG. 78, if region 701ab which is not etched due to the remaining defect is generated partially at the light transmitting portion, the shape of transfer pattern will be deformed.
More particularly, phases of exposure light transmitted through unetched region 70lab and a region 701bb which is removed by etching are reverse. Accordingly, at an interface P between unetched region 701ab and etched region 701bb, a portion having the light intensity of zero is generated due to canceling of exposure light.
The resist on the wafer cannot be exposed with light at such portion having the light intensity of zero. In other words, a region where exposure should have been carried out is generated on the resist, so that a resist pattern having a desired shape cannot be obtained. If patterning of the underlying layer is carried out by using such a resist pattern, an insufficient pattern is formed.
Specially, when a negative type resist in which a portion shielded from light is removed by a developing solution is used, resist will not be left at a portion having the light intensity of zero (region P). That is, a region wherein resist should have been left is generated. When an interconnection layer, for example, is formed by patterning with using such a resist pattern, the interconnection will be cut off at region P having the light intensity of zero, as shown in FIG. 79.
Thus, in addition to deterioration of the resolution, the pattern shape will be deformed when the remaining defects are generated.

Phase shifting mask, manufacturing method thereof, and exposure method using such a phase shifting mask


A construction technique, for example for residential, light commercial and multifamily building construction, involving pre-fabricated elements. The elements include prefabricated structural components and prefabricated surface components. A technique of incremental building includes assembling a building structure using these pre-fabricated elements.

Conventional construction techniques used in residential, light commercial and multifamily buildings can be laborious, expensive and, to some extent, limited in architectural style. Typical construction involves layering of systems and parts in a way that supports many independent trades, which is inherently complicated, time consuming and expensive.
In recent decades, there has been a move towards more environmentally-friendly building, including the net zero building. Low energy standards, such as the Passive House standard, add sophisticated technology based on new building science to create more energy conservative buildings. Such standards include low energy metrics, for example involving mechanical ventilation, air tight windows and doors, air barriers and vapor barriers, and high insulation. However, these requirements add cost, complications and time to the building process.
Prefabricated buildings typically involve the same process as is used in conventional on-site building construction, albeit with some improvements in efficiency by virtue of factory production. Conventional construction of a high standard, regardless of whether it is performed in the factory or on the job site, can involve as many as nine or more construction layers, for example a natural lime plaster interior layer, a drywall layer, a high density cellulose layer, a plywood layer, an air barrier layer, joists, thermal barriers, rain screens, and siding.
Combining conventional construction with low energy directives and technology creates further difficulties in design and construction. Deviations from the Passive House standard are often used for architectural reasons, making Passive House construction difficult to implement.
There is, therefore, a need for a new structural solution for construction of residential, light commercial, multifamily and other buildings that is less expensive and labor intensive than conventional techniques and promotes flexibility in architectural design.