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Photolithographic Fine Patterning of Difficult-To-Etch Metals

Copper is used as a liftoff material. A process that includes photolithography, liftoff, etching, and sputter deposition has been developed to enable the fabrication of thin, finely patterned layers of gold, platinum, and other difficultto- etch materials in advanced miniature sensors and associated electronic circuitry. Heretofore, photolithography has been used in conjunction with liftoff and etching to produce finely detailed structures in easy-to-etch materials. The present process is needed because conventional photolithography cannot be used to pattern difficult-to-etch materials and the alternative processes heretofore available for patterning difficult-to-etch materials are limited to spatial resolution of about 0.005 in. (≈0.13 mm) or coarser.

Posted in: Manufacturing & Prototyping, Briefs, TSP

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Heat Transfer Analysis for Optimizing Solar Cell Casting Equipment

Finite element analysis was used to develop a miniature furnace to cast the solar cell wafers. Solar Power Industries’ (SPI) current annual production capacity for processing polycrystalline silicon feedstock into completed solar cells has grown to 40 megawatts, with plans to increase capacity to 250 megawatts over the next several years. SPI’s solar cell manufacturing process consists of three main steps:   Ingot and Wafer Production—High-quality silicon feedstock (containing specific quantities of dopants such as boron in order to alter electrical properties) is melted and solidified inside a directional solidification furnace to cast polycrystalline silicon ingots. The ingots are cut into rectangular blocks with a square cross-section, and then the blocks are sawed into thin multicrystalline wafers. Cell Production — The wafers are etched to remove surface damage caused by sawing. The wafers are then processed in a series of steps to produce photovoltaic cells. Module Assembly — Individual cells are connected by soldering to flat wires. Strings of cells are then joined to parallel connector wires and laminated to produce a solar module.

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Fabricating Large-Area Sheets of Single-Layer Graphene by CVD

Such sheets are components for high-speed digital and RF electronics for defense and commercial communications. This innovation consists of a set of methodologies for preparing large area (>1 cm2) domains of single-atomic-layer graphite, also called graphene, in single (two-dimensional) crystal form. To fabricate a single graphene layer using chemical vapor deposition (CVD), the process begins with an atomically flat surface of an appropriate substrate and an appropriate precursor molecule containing carbon atoms attached to substituent atoms or groups. These molecules will be brought into contact with the substrate surface by being flowed over, or sprayed onto, the substrate, under CVD conditions of low pressure and elevated temperature. Upon contact with the surface, the precursor molecules will decompose. The substituent groups detach from the carbon atoms and form gas-phase species, leaving the unfunctionalized carbon atoms attached to the substrate surface. These carbon atoms will diffuse upon this surface and encounter and bond to other carbon atoms. If conditions are chosen carefully, the surface carbon atoms will arrange to form the lowest energy single-layer structure available, which is the graphene lattice that is sought.

Posted in: Manufacturing & Prototyping, Briefs, TSP

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Improved Probe for Evaluating Compaction of Mold Sand

Sand is not perturbed during switching among different measurement positions. A nominally stationary tubular probe denoted a telescopic probe has been developed as an improved alternative to a prior movable probe used to evaluate the local degree of compaction of mold sand. The prior movable probe consists mainly of a vertically oriented tube with screen vents at its lower end. The upper end is connected to a source of constant airflow equipped with a pressure gauge. The probe is inserted vertically to a desired depth in a sand-filled molding flask and the back pressure at the given rate of flow of air is recorded as a measure of the degree of partial impermeability and, hence, of the degree of compaction of sand in the vicinity of the probe tip.

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Improved Sand-Compaction Method for Lost-Foam Metal Casting

The flow of sand is redirected for better filling and compaction. An improved method of filling a molding flask with sand and compacting the sand around a refractory- coated foam mold pattern has been developed for incorporation into the lost-foam metal-casting process. In comparison with the conventional method of sand filling and compaction, this method affords more nearly complete filling of the space around the refractory-coated foam mold pattern and more thorough compaction of the sand. In so doing, this method enables the sand to better support the refractory coat under metallostatic pressure during filling of the mold with molten metal.

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Making Complex Electrically Conductive Patterns on Cloth

Circuit patterns are implemented in tightly woven cloth instead of stitched conductive thread. A method for automated fabrication of flexible, electrically conductive patterns on cloth substrates has been demonstrated. Products developed using this method, or related prior methods, are instances of a technology known as “e-textiles,” in which electrically conductive patterns are formed in, and on, textiles. For many applications, including high-speed digital circuits, antennas, and radio frequency (RF) circuits, an e-textile method should be capable of providing high surface conductivity, tight tolerances for control of characteristic impedances, and geometrically complex conductive patterns. Unlike prior methods, the present method satisfies all three of these criteria. Typical patterns can include such circuit structures as RF transmission lines, antennas, filters, and other conductive patterns equivalent to those of conventional printed circuits.

Posted in: Manufacturing & Prototyping, Briefs, TSP

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Fabricating Nanodots Using Lift-Off of a Nanopore Template

Applications include nano-scale electronic and magnetic devices. A process for fabricating a planar array of dots having characteristic dimensions of the order of several nanometers to several hundred nanometers involves the formation and use of a thin alumina nanopore template on a semiconductor substrate. The dot material is deposited in the nanopores, then the template is lifted off the substrate after the dots have been formed. This process is expected to be a basis for development of other, similar nanofabrication processes for relatively inexpensive mass production of nanometer- scale optical, optoelectronic, electronic, and magnetic devices.

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