Showing papers on "Fabrication published in 1992"

Flexible light-emitting diodes made from soluble conducting polymers

Abstract: THE recent fabrication of light-emitting diodes (LEDs) from conjugated polymers1,2demonstrates the technological potential of this class of electronic materials. A variety of colours are possible, because the wavelength of luminescence emission can be chemically tuned during synthesis1–4. In addition, the mechanical properties of polymers suggest that light-emitting structures can be made that are more flexible than their inorganic counterparts, provided appropriate materials can be found for the substrate and electrodes. Here we report the fabrication of a fully flexible LED using poly(ethylene terephthalate) as the substrate, soluble poly-aniline as the hole-injecting electrode, a substituted poly(1,4-phenylene-vinylene) as the electroluminescent layer and calcium as the electron-injecting top contract. The structure is mechanically robust and may be sharply bent without failure. The LED is easily visible under room lighting and has an external quantum efficiency of about 1%. With a turn-on voltage for light emission of 2–3 V, the 'plastic' LED demonstrates that this unique combination of optical, electrical and mechanical properties can be used to make novel structures that are compatible with conventional devices.

Quantum Wire Fabrication by E-Beam Elithography Using High-Resolution and High-Sensitivity E-Beam Resist ZEP-520

Abstract: We have evaluated the resolution of the positive electron-beam (E-beam) resist ZEP-520 using finely focused E-beam exposure for the application of quantum wire fabrication in a large area. Compared with the poly-methylmethacrylate (PMMA) resist conventionally used for nanofabrication, ZEP resist shows almost the same resolution under sensitivity improvement of one order of magnitude, and the throughput is increased by a factor of more than 100 by introducing a highly bright Zr/O/W thermal field emitter as an E-beam source. Other excellent performance characteristics, such as high dry-etching durability and process stability, allow us to apply ZEP resist for larger-area, high-density quantum wire fabrication. By both wet chemical etching and dry-etching combined with CBE selective growth, InGaAs nanostructures as small as 15 nm can be obtained with a pitch of 70 nm over several hundred µm squares.

Processing and Fabrication of Advanced Materials for High Temperature Applications

Abstract: This volume is divided into the following sections: (1) processing and fabrication of intermetallics; (2) intermetallic and metal matrix composites; (3) ceramics and SHS processing; (4) carbon-carbon composites and high temperature coatings; and (5) novel processing routes. Separate abstracts were prepared for 43 papers in this volume.

Fabrication of high depth-to-width aspect ratio microstructures

Abstract: It is reported that a 3-D fabrication process, based on sputtering of a thin-film plating base, on conventional UV lithography, and on electrochemical deposition of gold, makes microstructures of considerable height and resolution possible. The thin-film formation and the lithographic process are outlined, particular attention being paid to layer deposition and structure printing. The present resolution limit is about 4.5 mu m for a 30- mu m-thick resist. Much thicker layers (80 mu m) can be printed with reduced resolution. The results are discussed and process characteristics relevant in various applications are considered. >

Microtip-controlled nanostructure fabrication and multi-tipped field-emission tool for parallel-process nanostructure fabrication

Abstract: Fabrication of crystalline or molecular nanostructures with dimensions less than or equal to 1000Å on a substrate surface is achieved by the indirect and/or direct action of a highly-localized field-emission current, which causes atoms of molecular gases introduced into a vacuum chamber to deposit or etch at surface atomic sites that are fixed by the emission-tip location. The tip is shaped to maintain control of the emitting region and is typically about 10Å above the structure. The tip position is stepped in a programmed sequence, with each step taken on detecting the current increase induced by an atomic deposition below the tip. Gas sequences or mixtures can also be programmed, and microstructures of typically 10 2 -10 8 atoms are thereby formed with exact control of the positions and types of atomic constituents. The multi-tipped tool consists of a large array of field-emitting nanostructure probe tip extensions on the end of a metal probe. The nanostructures are spaced in a prescribed, repeating pattern with typical spacings on the order of 400Å. The probe voltage, current and position, as well as CVD or etching gas pressures, are sequentially adjusted to fabricate nanostructures on a nearby substrate, which is typically 10-30Å below the termination points of the probe tip extensions.

Micromotor fabrication

Abstract: Micromotor fabrication and related issues are discussed. The micromotors under study are of the variable-capacitance side-drive type with salient-pole and wobble (harmonic) designs. Polysilicon surface micromachining forms the basis of the micromotor fabrication process. In this process, LPCVD heavily phosphorus-doped polysilicon is used for the structural parts, LPCVD silicon nitride is used for electrical isolation, and CVD low-temperature oxide is used to as the sacrificial material. The fabrication process affects the performance characteristics of the micromotor through the reproduction accuracy of the design geometry and through the modification of the characteristics of contacting surfaces. Pattern definition and delineation are among the most critical steps of the micromotor fabrication process because of the increasing surface topography during fabrication and the large film thicknesses utilized. The release and testing process can affect the frictional characteristics of the micromotor significantly, determining success or failure of operation by dielectric excitation. >

Electrical feedthrough structure and fabrication method

Abstract: In an electrical via structure and fabrication method that is particularly suited to coplanar contact solar cells, an initial opening (38,48a,48b,64) through the substrate is coated and substantially closed with a dielectric material (42,52,80). An inner opening (44) is then formed through the dielectric, and the via is provided with a conductive coating (46,54). The dielectric is initially applied in a liquid state and is thereafter cured to a solid. The need for strong chemical etchants to smooth the via opening prior to application of the dielectric and metallization is eliminated, and a polyimide dielectric on a GaAs/Ge solar cell has resulted in a substantial improvement in leakage resistance and cell efficiency.

Crystallization of fibres inside a matrix: a new way of fabrication of composites

Abstract: Fibrous composites are normally fabricated by inserting premade fibres into a matrix and trying to tailor mechanical or physical properties of the material by a proper choice of fibre arrangement, fibre volume fraction, structure and properties of interface, etc. As a rule, this method satisfies all the needs fairly well. But in many cases, particularly when heat-resistant composites are involved, it leads to complications which cause composite experts to refrain from being involved in technically very attractive projects. So the need for alternative methods of composite fabrication obviously exists. The process described here is an example of such an alternative. It is based on the fibres growing from the melt within the volume of the matrix. The matrix should have prefabricated continuous cylindrical channels to be filled with the melt of the fibre material. The process is described using as a model a composite with a molybdenum matrix and single crystalline sapphire fibres. It is shown that the productivity of oxide fibre fabrication based on the process described can be some orders of magnitude higher than that based on the well known Czochralsky's and Stepanov's methods. The strength of the single-crystalline sapphire fibres obtained has been studied, as well as the high-temperature creep strength of composites containing such fibres. Some of the results of these experiments are reported here.

Fabrication of microchannels by laser machining and anisotropic etching of silicon

Abstract: Micromechanical structures in silicon are usually fabricated by photolithography and anisotropic etching. While the shape and the size of the pattern on the wafer surface are defined by a masking layer, the dimension of the microstructures perpendicular to the wafer surface depends mainly on the crystallographic orientation of the wafer. Our work presents a method for the fabrication of new types of microstructures with high aspect ratio. This technique is based on the local destruction of limiting {111} crystal planes by laser melting and anisotropic etching of the molten zones. Although the shape and the size of the microchannels are lithographically predetermined, their aspect ratio can be modified by the parameters of the laser beam. The partially closed form of these microchannels is suitable for precise positioning of fibers in hybrid microoptical devices and transport systems for gases and liquids.

A precision capacitor sensor

Abstract: A precision, low cost, capacitor sensor comprised of two parallel plates, with an air dielectric, with preferably both substrates comprised of vitreous materials and electrically conductive coating, but with at least one of the substrates and coating being transparent. The coatings are preferably of identical material, thickness and pattern to offset stress distortion of the sensor plates from thermal expansion and contraction. Uniform spacing between the plates is provided by means of glass fibers of uniform diameter, dispersed in a matrix of adhesive and bonded under pressure, deposited between the plates as two thin semicircular seal rings surrounding the dielectric and separated by a diametrical gap, allowing entrance or escape of air dielectric. A novel feature, provided by at least one plate and coating being transparent, is use of optical measuring techniques during fabrication to verify acceptability of the manufacturing process and uniformity of the sensor product. This permits easy, rapid, efficient and economical grading and process control of the sensors during fabrication with resulting improved precision performance of the product and economical cost to manufacture. As an option, three or more of the four faces of the two substrates will bear conductive coatings, for structural stability, to minimize distortion in capacitance due to changes in temperature.

Preparation and Characterization of CuInSe2 Thin Films by Molecular-Beam Deposition Method

Abstract: Polycrystalline CuInSe2 films were prepared by coevaporation of the elements under an ultrahigh vacuum by a molecular-beam deposition method. The composition of the film was controlled by changing the In molecular-beam flux intensity while the other elements remained at a constant value. It is shown, at the substrate temperature of 500°C, that there is a critical In molecular-beam flux intensity for the fabrication of stoichiometric films. At the In molecular-beam intensities higher than the critical value, single-phase CuInSe2 films with nearly constant compositions are obtained as a result of the removal effects of excess In. It is shown that the present coevaporation process is suitable for the fabrication of stoichiometric or slightly In-rich composition films. Furthermore, the structural and electrical properties of the films were investigated and discussed in relation to film composition.

Simple technologies for fabrication of low-loss silica waveguides

Abstract: A simple and reproducible technology is developed for the fabrication of low-loss silica waveguides on silicon substrates. The guiding layer is formed by changing the Si-O ratio composition of the SiO/sub 2/ layer. The waveguides can be made to have a good match to either optical fibres or guided-wave devices in III-V compound semiconductors.

Slow-wave electrode for use in compound semiconductor electrooptic modulators

Abstract: A slow-wave electrode structure for integrated optic traveling-wave modulators in which the microwave's effective refractive index is matched to the optical wave's effective refractive index is described. The electrode structure is a capacitively loaded coplanar strip waveguide which can be formed in a single layer of metallization. Fabrication can be accomplished by a single photo-resist patterning, followed by an etching and a standard lift-off technique. Based on the use of gallium arsenide substrates and modern lithographic techniques allowing fabrication with micron scale resolution, slow-wave electrodes having a microwave effective refractive index of 3.5, as well as 50 and 75 Omega characteristic impedances are proposed. The theory of slow-wave electrodes is developed, and slow-wave electrodes have been designed, fabricated, and tested to verify the theory. Measurement results are found to agree well with the theory. >

Deep three‐dimensional microstructure fabrication for infrared binary optics

Abstract: Anisotropic reactive ion etching of deep Si structures (≥8 μm), planarization of deeply stepped topographies, and multilayer resist processes have been developed for fabrication of silicon IR binary optics devices. The effect of adding O2 and C2F6 to the SF6 feed gas on sidewall profile and etch selectivity (Si:photoresist) has been determined. Vertical profiles, without mask undercutting or surface texturing, and high etch selectivity (≥5:1) have been obtained with a 74% SF6–26% O2 mixture. We have successfully fabricated 8‐μm deep Si optics with 16 phase levels and eight‐level structures with a total depth of 14 μm in Si.

Micron-sized, high aspect ratio bulk silicon micromechanical devices

Abstract: The fabrication of high-aspect-ratio microstructures having widths of approximately=1 mu m and thicknesses exceeding 10 mu m for application in a variety of microsensors and microactuators is reported. The fabrication process utilizes deep etching of fine features into boron-diffused bulk silicon wafers using chlorine- and fluorine-based reactive ion etching techniques. These wafers are then electrostatically bonded to glass wafers which have been previously patterned with metal interconnect. The wafers are finally etched in an ethylenediamine pyrocatechol solution that frees the microstructures. The process requires a total of three masking steps (two for silicon and one for glass), is single-sided, and has high yield. Structures with thickness-to-width ratios greater than 10:1 have been fabricated using this process. Electrical measurements have shown that very large deflections (>7 mu m) are possible at voltages as low as 25 V. >

Powder processing technique for development of zirconia-nickel functionally gradient materials

Abstract: A powder processing technique is developed for the fabrication of tetragonal zirconia-nickel functionally gradient materials. The powder volume fraction, the linear shrinkage during drying, and the pore radius of monolithic zirconia-nickel green compacts with various zirconia/nickel volume ratios were measured. A multilayer zirconia-nickel green compact with a step-wise compositional gradient was formed by slip casting and then pressureless-sintered. The key to successful fabrication is to avoid the fracture of green compact during drying process in an ambient atmosphere. In conclusion, it is desirable to minimize differences in permeability and pore radius between neighboring layers in a multilayer green compact.

Facet modulation selective epitaxy–a technique for quantum-well wire doublet fabrication

Abstract: The technique of facet modulation selective epitaxy and its application to quantum-well wire doublet fabrication are described. Successful fabrication of wire doublets in the AlxGa1–xAs material system is achieved. The smallest wire fabricated has a crescent cross section less than 140 A thick and less than 1400 A wide. Backscattered electron images, transmission electron micrographs, cathodoluminescence spectra, and spectrally resolved cathodoluminescence images of the wire doublets are presented.

Single‐crystal thin film InP: Fabrication and absorption measurements

Abstract: A new process for separating high quality single‐crystal InP thin films from the growth substrate is reported. These thin films were used for transmission measurements to determine InP absorption coefficients above the band edge. Photoluminescence measurements performed on these films before and after the fabrication process verified that the high quality of the separated thin film was not affected by the fabrication process. Two n‐type InP thin films, one with a doping concentration of 1.4×1017 cm−3 (1 μm thick) and the other with a doping concentration of 3.2×1018 cm−3 (2.5 μm thick), were grown and subsequently separated from the substrate. Using these separated films, the first direct transmission measurements of above band edge absorption coefficients in doped InP films are reported in this letter.

Low Temperature Fabrication of poly-Si TFTs Using in-Situ Chemically Cleaning Method

Abstract: Thin film transistors were fabricated using polycrystalline silicon (poly-Si) film which were directly deposited on Corning 7059 glass substrates by plasma chemical vapor deposition method at very low temperature of 450°C. No annealing procedure was carried out in the fabrication process. The dependences of the crystallinity and the electrical properties on the poly-Si film thickness were investigated for three kinds of films deposited under different conditions. These dependences on the film thickness were found to be strongly influenced by the deposition condition, especially the reaction gas pressure. By choosing optimum poly-Si deposition condition carefully, high performance TFTs have been fabricated by this novel method.

CBiCMOS fabrication method using sacrificial gate poly

Abstract: A complementary bipolar CMOS fabrication method uses a common deposition for both the CMOS gate contacts, and as a sacrificial layer for patterning bipolar devices. The deposition is removed from the bipolar devices and, after implanting base and emitter regions, is replaced with a separate emitter contact. Prior to its removal the sacrificial layer is coated with an oxidation resistant layer that imparts a desirable rounded shape to the edge of a thermal oxide layer that is grown around the bipolar emitter area. Common mask and implant steps are also used to fabricate lightly doped CMOS drains together with bipolar base-link regions, and CMOS source/drain regions together with bipolar external base regions. The fabrication technique also facilitates the fabrication of capacitors with no additional steps required, and includes an improved NiCr resistor contact method.

Application of x‐ray lithography with a single‐layer resist process to subquartermicron large scale integrated circuit fabrication

Abstract: The applicability of synchrotron radiation x‐ray lithography to future ultralarge scale integrated circuit fabrication processes is demonstrated by the test fabrication of subquartermicron bipolar‐ complementary metaloxide semiconductor devices (SRAM, gate arrays, and several test element groups) with a total size of two‐million transistors. Synchrotron radiation lithography is used at four critical levels: gate poly, first metal, via hole, and second metal. Both negative and positive chemically amplified resists are used with a single‐layer resist system to simplify the resist process. An overview of the lithography process is presented with emphasis on patterning and overlay performance.

New Fabrication Technology for Polymer Optical Waveguides

Abstract: Polymeric materials are very promising for a substantial cost reduction in the fabrication of guided wave devices, since mass fabrication technologies like molding, injection molding or casting may be applied. One of the greatest advantages of these technologies lies in the fact that the optical waveguide structures may be manufactured simultaneously together with fibre alignment grooves in one fabrication process.

Fabrication and characterization of a silicon microvalve

Abstract: The fabrication of a unidirectional micro-valve in silicon is reported. Pressure/flow characteristics between 0–1 bar for water were measured. Practically no leakage was observed (less than 1 nL min−1) when the valve was pressurized in the backward direction. A nonlinear pressure-flow relation, believed to be due to the particular design of the closing cantilever beam, was observed in the forward direction. Some of the merits of the construction are discussed.

Digital pressure switch and method of fabrication

Abstract: A micromachined pressure switch and method of fabrication from silicon wafers using aligned fusion bonding. Pattern etched thermally grown silicon dioxide insulating pads are used to determine the size of silicon pressure membranes on an upper silicon wafer, with the desired switch gap set by the oxide thickness. The silicon membranes are formed by controlled thinning the upper silicon wafers. V-shaped vent grooves are pattern etched into a bottom silicon wafer to form electrodes to which the insulating pads are fusion bonded. The area between the electrodes and the membrane forms wells of specified sizes into which the membranes deflect upon application of pressure. The pressure switch operates when the membrane is deflected to contact the electrodes in the bottom wafer, and closes at the desired pressure threshold for both directions of pressure change with negligible hysteresis. The method of fabrication applies to a single element pressure switch as well as to an array of pressure switches.