Showing papers on "Fabrication published in 1996"

Fabrication of high frequency nanometer scale mechanical resonators from bulk Si crystals

Abstract: We report on a method to fabricate nanometer scale mechanical structures from bulk, single-crystal Si substrates. A technique developed previously required more complex fabrication methods and an undercut step using wet chemical processing. Our method does not require low pressure chemical vapor deposition of intermediate masking layers, and the final step in the processing uses a dry etch technique, avoiding the difficulties encountered from surface tension effects when wet processing mechanically delicate or large aspect ratio structures. Using this technique, we demonstrate fabrication of a mechanical resonator with a fundamental resonance frequency of 70.72 MHz and a quality factor of 2 x 10^(4).

Structure and fabrication process for an aluminum alloy junction self-aligned back contact silicon solar cell

Abstract: An improved solar cell design and method of fabrication that primarily uses two materials, n-type doped silicon and aluminum to form a p-n alloy junction back contact solar cell. The aluminum alloy junctions are placed on the back (unilluminated) side of the cell, thereby combining the desirable features of aluminum (as a dopant, contact metal and light reflector), with the advantages of a back contact cell. The cell design and method of fabrication includes such features as surface texturing, front and back surface field minority carrier mirrors, surface passivation using oxidation layers, use of Al contacts as light reflectors, intrinsic protection against reverse bias due to contiguous n + and p + regions, and an improved bus bar contact design suitable for interconnecting cells using a surface mount technology. An improved method of ohmic contact formation uses a self-alignment technique for forming the ohmic contacts.

Single‐atom point contact devices fabricated with an atomic force microscope

Abstract: The fabrication of atomic point contacts by using anodic oxidation of thin Al films with an atomic force microscope is reported. In situ electrical measurements were used as feedback to control the fabrication of Al nanowires that were subsequently anodized through their cross section to form point contacts. When the conductance of a point contact is reduced below ∼5×10−4 S it starts to decrease in discrete steps of ∼2e2/h. In some devices we are able to stabilize the conductance at a value near 2e2/h which corresponds to a single, atomic‐sized conducting channel.

Free form fabrication of metallic components using laser engineered net shaping (LENS{trademark})

Abstract: Solid free form fabrication is one of the fastest growing automated manufacturing technologies that has significantly impacted the length of time between initial concept and actual part fabrication. Starting with CAD renditions of new components, several techniques such as stereolithography and selective laser sintering are being used to fabricate highly accurate complex three-dimensional concept models using polymeric materials. Coupled with investment casting techniques, sacrificial polymeric objects are used to minimize costs and time to fabricate tooling used to make complex metal castings. This paper will describe recent developments in a new technology, known as LENS{sup {trademark}} (Laser Engineered Net Shaping), to fabricate metal components directly from CAD solid models and thus further reduce the lead times for metal part fabrication. In a manner analogous to stereolithography or selective sintering, the LENS{sup {trademark}} process builds metal parts line by line and layer by layer. Metal particles are injected into a laser beam, where they are melted and deposited onto a substrate as a miniature weld pool. The trace of the laser beam on the substrate is driven by the definition of CAD models until the desired net-shaped densified metal component is produced.

High responsitivity intrinsic photoconductors based on AlxGa1−xN

Abstract: This letter reports on the fabrication and characterization of visible‐blind ultraviolet photoconductors using single‐crystal AlxGa1−xN layers deposited on basal plane sapphire substrates. With aluminum mole fractions ranging from 5% to 61%, the long‐wavelength cutoff can be varied from 350 to 240 nm. Photoresponsitivities as high as several hundred amperes per watt were measured with 10 μm interelectrode spacing.

Multilayer high vertical aspect ratio thin film structures

Abstract: This invention relates to the area of microelectromechanical systems in which electronic circuits and mechanical devices are integrated on the same silicon chip. The method taught herein allows the fabrication of thin film structures (2) in excess of 150 microns in height using thin film deposition processes. Wafers may be employed as reusable molds for efficient production of such structures. Various material properties may be varied within the structures to produce electrical, mechanical or electromechanical devices.

Electrochemical Patterning of Self-Assembled Monolayers onto Microscopic Arrays of Gold Electrodes Fabricated by Laser Ablation

Abstract: This report demonstrates proof-of-concept application of two established electrochemical techniques affecting self-assembled monolayersthe thermodynamic control of monolayer assembly at gold and the electrochemical desorption of self-assembled monolayers from goldto pattern monolayers onto gold microelectrodes. When combined with a simple laser-based microfabrication technique, using commercially available microscope adaptations, to form arrays of individually-addressable gold microelectrodes from continuous thin gold films on glass, two new patterning methodologies result that enable fabrication of monolayer-based affinity arrays for potential use in chemical and biosensors. The described microfabrication technique is central to the success of these patterning methodologies because it allows SAM patterning of metal arrays immediately after their fabrication, so as to avoid problems associated with forming SAMs on commercially-supplied arrays. In this paper, each patterning methodology is used to fabricat...

Fabrication of a pencil-shaped fiber probe for near-field optics by selective chemical etching

Abstract: We propose a novel method by chemical etching using hydrofluoric (HF) acid and a buffered HF solution (BHF) to fabricate a pencil-shaped fiber probe for near-field optics. We succeeded in producing such probes with high reproducibility using a dispersion-compensating fiber having the high GeO/sub 2/ doped core. The method involves tapering of the cladding, then sharpening of the core. The fabricated probe has a conical tip with a cone angle of 20/spl deg/ and an apex diameter of less than 10 nm.

Photovoltaic element and fabrication process thereof

Abstract: Provided are a photovoltaic element suitable for practical use, low in cost, high in reliability, and high in photoelectric conversion efficiency, and a fabrication process thereof. In the photovoltaic element having stacked layers of non-single-crystal semiconductors, at least an i-type semiconductor layer and a second conductivity type semiconductor layer are stacked on a first conductivity type semiconductor layer, and the second conduction type semiconductor layer has a layer A formed by exposing the surface of the i-type semiconductor layer to a plasma containing a valence electron controlling agent and a layer B deposited on the layer A by a CVD process using at least the valence electron controlling agent and the main constituent elements of the i-type semiconductor layer.

Radio‐frequency‐magnetron‐sputtered CdS/CdTe solar cells on soda‐lime glass

Abstract: We report the fabrication of an 11.6% efficient, polycrystalline thin‐film CdS/CdTe solar cell in which both semiconductor layers were deposited by planar‐magnetron‐radio‐frequency sputtering at 380 °C on commercially available soda‐lime float‐glass substrates coated with SnO2:F. We show that the magnetron magnetic field is critical to obtaining high cell efficiency. Much stronger photoluminescence and higher electrical conductivity are found in films and cells grown with unbalanced‐field magnetrons. The magnetic field dependence is interpreted as arising from the enhanced electron and ion bombardment of the film growth interface when unbalanced magnetrons are used.

Intrinsic Sol−Gel Clad Fiber-Optic Sensors with Time-Resolved Detection

Abstract: Sol−gel clad fiber-optic waveguides are investigated as intrinsic distributed fiber-optic chemical sensors. The porous sol−gel cladding allows diffusion of analytes into the evanescent field region close to the fiber-optic core. Pulsed optical excitation (0.5 ns) and time-resolved emission detection can be used to simultaneously monitor several multiplexed sensor clad regions along a single optical fiber. Time-resolved detection is also demonstrated as a means of resolving both the spatial location and the fluorescence kinetics of intrinsic sensor chromophores along the fiber-optic waveguide. Narrow band excitation and spectrally resolved emission provide additional experimental means for discriminating between specific sensor clad regions. A fluorescein-doped silica xerogel clad pH sensor and an undoped aluminosilica xerogel clad quinone sensor are demonstrated as intrinsic sol−gel clad fiber-optic sensors.

General aspheric refractive micro‐optics fabricated by optical lithography using a high energy beam sensitive glass gray‐level mask

Abstract: General aspheric refractive microlens arrays with an almost 100% fill factor are useful in a wide range of applications ranging from display, optoelectronic interconnections, or improving the efficiency of detector arrays to lithography techniques utilizing microlens arrays. In this article a technique will be discussed which allows the microlithographic fabrication of general aspheric non rotationally symmetric refractive lenses with a 100% fill factor. A gray‐level mask based on high energy beam sensitive (HEBS) glass is used to pattern a thick (4–5 micron) photoresist layer. After development, the refractive structure is transferred into the substrate material using a chemically assisted ion beam etching (CAIBE) process. The HEBS‐glass gray‐level mask is generated by a electron‐beam writer, allowing for complete freedom in terms of the shape and location of the lenses.

Fabrication of arrays of large step‐free regions on Si(001)

Abstract: In this letter we describe a method for producing large areas of Si(001) surfaces which are (i) free of atomic steps and (ii) arranged in regular patterns on the wafer. The first step is the fabrication of a two‐dimensional grating structure using e‐beam lithography and reactive ion etching. This grating is then annealed within the appropriate temperature window in ultrahigh vacuum to produce the desired array of (001) step‐free regions. We illustrate the success of the method through the use of low‐energy electron microscopy for a few repeat spacings on test structures each extending over a 3×3 mm2 area. Alternative processing steps are discussed as well as application to submicron device technology.

Surface micromachining by sacrificial aluminium etching

Abstract: Sacrificial aluminium etching enables micromechanical structures integrated with circuitry to be fabricated using standard IC processes followed by simple post-processing. In this paper, the etching characteristics of CMOS aluminium in four etch solutions are reported. The solutions are (A) a commercially available aluminium etchant, (B) Krumm etch, (C) diluted hydrochloric acid, and (D) diluted hydrochloric acid with hydrogen peroxide. The etching of narrow channels is studied as a function of time and temperature. Initially, the etching process is reaction-rate controlled and then crosses over to a diffusion-controlled regime with reduced etch rate. Underetching distances larger than are readily achieved with etchants `A', `B', and `D'. The commercially available aluminium etchant has a low initial underetch rate of at but offers best control. The initial etch rate of hydrochloric acid with hydrogen peroxide is at . However, irregular etch fronts are obtained. Reliable protection of aluminium pads against etchants `A', `B', and `D' is guaranteed by Shipley's photoresist S1828 spun at 3000 rpm and hardbaked at .

Thin film semiconductor device and method for producing the same

Abstract: In order to fabricate a high performance thin film semiconductor device using a temperature process in which it is possible to use inexpensive glass substrates, a highly crystalline mixed-crystallinity semiconductor film is deposited by means of PECVD using a silane as the source gas and argon as the dilution gas, then the crystallinity of this film is improved by such means as laser irradiation. Thin film semiconductor devices fabricated in this way are used in the manufacture of such things as liquid crystal displays and electronic devices. In applying the present invention to the fabrication of an active matrix liquid crystal display, it is possible to both easily and reliably fabricate a large, high-quality liquid crystal display. Additionally, in applying the present invention to the fabrication of other electronic circuits as well, it is possible to both easily and reliably fabricate high-quality electronic circuits.

Cleaning thin-film diamond surfaces for device fabrication: An Auger electron spectroscopic study

Abstract: Auger electron spectroscopy was used to analyze polycrystalline thin‐film diamond surfaces following the use of differing methods for the removal of unwanted nondiamond carbon. Exposing the film to a hydrogen plasma at the termination of the growth process is effective for producing a surface that gives an Auger spectrum typical of diamond with little contamination. Strongly oxidizing solutions involving sulfuric acid generate low concentrations of surface sulfur together with an oxide phase. However, in the case of an ammonium persulfate–sulfuric acid etchant solution, the Auger features associated with the diamond more closely resemble those of single crystal material suggesting that this treatment may offer better performance when used during the fabrication of thin‐film diamond electronic devices.

Fabrication of InP-based freestanding microstructures by selective surface micromachining

Abstract: InP-based microstructuring methods are presented with a view to develop micro opto electro mechanical systems (MOEMS). Fabrication parameters and dimensions of the freestanding structures are determined for specific technological constraints (etching selectivities, anisotropy, sticking phenomena). thick InGaAs deformable cantilevers, bridges and membranes have been fabricated by elimination of around -thick InAlAs sacrificial layers. Showing high aspect ratio, smooth surfaces and high accuracy in thicknesses, these microstructures are perfectly suitable for optical applications.

Fabrication, characterization, and potential application of carbon fiber cone nanometer-size electrodes.

Abstract: A novel method has been developed for the fabrication of carbon fiber cone nanometer-size ultramicroelectrodes (nanoelectrodes) with overall tip dimensions as small as 50 nm in diameter. In this method, carbon fibers were initially etched by an argon ion beam thinner. Afterward, a single etched carbon fiber was inserted into a glass capillary, which was then sealed by heating the glass/fiber interface in a vacuum; thus, no epoxy resin is involved. The success rate of our fabrication route for the electrodes with overall tip diameters of up to 500 nm was about 80%; for those with tip diameters of up to 100 nm, it was about 50%. The fabricated carbon fiber cone nanoelectrodes (CFCNEs) were inspected by optical and scanning electron microscopy. Their electrochemical behavior was examined by cyclic and linear sweep voltammetric measurements of ferricyanide and ferrocene ions in aqueous and nonaqueous media. The potential analytical applicability of the CFCNEs was tested by differential pulse voltammetric meas...

Fabrication of SOI wafers with buried cavities using silicon fusion bonding and electrochemical etchback

Abstract: This paper describes a new technique for batch fabrication of silicon-on-insulator (SOI) wafers for microelectromechanical systems (MEMS) applications by silicon wafer bonding techniques. The process permits the inclusion of buried cavities in the SOI wafers, providing a useful tool for sensor and actuator fabrication using the resulting wafers. A low-cost electrochemical etchback step is used to define accurately the thickness of the remaining single-crystal material even though the two wafers are bonded with an intermediate insulating oxide layer. The results presented include guidelines for backside contact definition which maximize the useful silicon area as a function of doping level. The final single-crystal silicon thickness is uniform to within 0.05 μm (standard deviation) and does not require any costly high-accuracy polishing steps.

A New Fabrication Method for Ultra Small Tunnel Junctions

Abstract: We have developed a new method for fabrication of microstructures. Using a Si3N4 membrane with small windows as a mask, a metal film with fine structure is vacuum deposited directly onto a substrate. By means of piezoelectric actuators which slide the mask on the substrate, we have fabricated an array of Al/AlOx /Al small tunnel junctions. This method has the important advantage that the lift-off process after vacuum deposition is not necessary. The use of rf plasma oxidation to form the tunnel barrier is another advantage of this method. We have fabricated a Ni/NiO/Fe small junction array with a junction area of 0.01 µ m2 using plasma oxidation and double-angle evaporation.

Principles of the development of a silica dielectric for microelectronics packaging

Abstract: Recognizing that speed, size, reliability, and cost are the principal driving forces for advanced electronic packages, this review article describes the much needed development of a new, phase transformation-free, single-phase silica dielectric with a dielectric constant (k) of about 4, the lowest among the inorganic oxides, and a coefficient of thermal expansion (CTE) of about 3 ppm/°C, similar to that of Si. This dielectric, consisting largely of SiO2, represents a gain in media speed by about 50% over alumina dielectric, combined with an improvement in reliability of the package by a factor of about 1000. The feature size and system cost can also be drastically reduced by using this dielectric. It is made from a mixture of binary borosilicate glasses that normally exhibit an undesirable characteristic of precipitating cristobalite during sintering that severely weakens the structure. The most important aspect of this article is the design and development of a strategy that prevents the cristobalite growth by incorporating a crystal growth inhibitor in the binary mixture of glasses. Since kinetics, not thermodynamics, are shown to be the key to success of this strategy, the roles of rate-controlling parameters are deliberately emphasized. A working model is delineated to identify compositions that yield a cristobalite-free silica dielectric with values of CTE that match those of Si and GaAs. Critical issues of co-firing between metals and this dielectric are addressed within the context of multilayer packaging fabrication. Finally, a list of measured properties is presented that clearly shows new opportunities for this silica dielectric.

Electroless plating of nickel on silicon for fabrication of high-aspect-ratio microstructures

Abstract: An electroless plating process for the fabrication of nickel micromechanical structures on a silicon substrate has been investigated. Appropriate chemical roughening of the silicon surface is found to be critical for good adhesion of the nickel to the silicon substrate. The optimum temperature and pH of the elecroless plating solution for smooth nickel films (e.g., R a of 23 A) with practical plating rates (e.g., 15 μm h −1 ) are determined. Electroless plating is shown to be a suitable process for the fabrication of micromechanical structures.

Laser-ablation deposition and characterization of ferroelectric capacitors for nonvolatile memories

Abstract: An intense worldwide research-and-development effort has been undertaken during the last seven years with the objective of developing thin-film deposition techniques and materials-integration and processing strategies capable of realizing a commercially viable solid-state nonvolatile-ferroelectric-random-access-memory (NVFRAM) technology. Many laboratories around the world have focused their work on developing strategies for integrating submicron thin-film ferroelectric capacitors with the mature silicon-based transistor technology to yield capacitor-transistor-based memory architectures as schematically illustrated in Figure 1. This figure also shows the perovskite unit cell of a capacitor, based on a ferroelectric Pb(ZrxTi 1−xO3 (PZT) layer, and the variety of structural, chemical, electronic, and ionic interfaces that arise during the fabrication and integration of these metal-oxide hetero-structure capacitors on a Si substrate. Nonvolatile ferroelectric random-access memories exploit the capacity of the ferroelectric layer to be polarized in two opposite directions, which are used as the 0 and 1 binary stable states.

Design and fabrication of a thermal infrared emitter

Abstract: In this paper a thermal infrared (IR) emitter is described. It is part of a non-dispersive infrared (NDIR) gas-analysing system. The system is planned for multi-gas analysis. In particular, CO 2 should be detected from 100 ppm to 10%. The thermal heater is integrated with a Fresnel zone plate. The zone plate is a diffractive lens with dispersive properties. The number of components of the system is reduced by integration. A combination of surface and bulk micromachining is used for fabrication of the emitter. The cavity of the heating structure is made by direct bonding of two structured wafers. A new method for sealing the cavity by aluminium sputtering is used. Aluminium has bifunctional properties. Beside the metallization, it is used for sealing the cavity. The sputtering is carried out at a pressure below 6 mtorr so that the cavity is simultanously evacuated. An analytical model is developed to calculate the emitted power of the radiating structure and the thermal strain. For a 30 μm × 10 μm thermal emitter an emitted power of 430 nW at a maximum heating temperature of 1500 K has been calculated. The results are compared with finite-element method (FEM) analysis.