Showing papers on "Fabrication published in 1997"

Critical Review: Adhesion in surface micromechanical structures

Abstract: We present a review on the state of knowledge of surface phenomena behind adhesion in surface micromechanical structures. After introducing the problem of release-related and in-use adhesion, a theoretical framework for understanding the various surface forces that cause strong adhesion of micromechanical structures is presented. Various approaches are described for reducing the work of adhesion. These include surface roughening and chemical modification of polycrystalline silicon surfaces. The constraints that fabrication processes such as release, drying, assembly, and packaging place on surface treatments are described in general. Finally, we briefly outline some of the important scientific and technological issues in adhesion and friction phenomena in micromechanical structures that remain to be clarified.

Design and fabrication of compliant micromechanisms and structures with negative Poisson's ratio

Abstract: This paper describes a new way to design and fabricate compliant micromechanisms and material structures with negative Poisson's ratio (NPR). The design of compliant mechanisms and material structures is accomplished in an automated way using a numerical topology optimization method, The procedure allows the user to specify the elastic properties of materials or the mechanical advantages (MA's) or geometrical advantages (GA's) of compliant mechanisms and returns the optimal structures. The topologies obtained by the numerical procedure require practically no interaction by the engineer before they can be transferred to the fabrication unit. Fabrication is carried out by patterning a sputtered silicon on a plasma-enhanced chemical vapor deposition (PECVD) glass with a laser micromachining setup. Subsequently, the structures are etched into the underlying PECVD glass, and the glass is underetched, all in one two-step reactive ion etching (RIE) process. The components are tested using a probe placed on an x-y stage. This fast prototyping allows newly developed topologies to be fabricated and tested within the same day.

Design and fabrication of double-chirped mirrors

Abstract: We present an analytic design method for the reproducible fabrication of double-chirped mirrors to achieve simultaneously a high reflectivity and dispersion compensation over an extended bandwidth compared with those of standard quarter-wave Bragg mirrors. The mirrors are fabricated by ion beam sputtering. Use of these mirrors in a Ti:sapphire laser leads to 6.5-fs pulses directly out of the laser. The method can also be applied to the design of chirped-fiber gratings and general optical filters.

A very large integrated pH-ISFET sensor array chip compatible with standard CMOS processes

Abstract: The development and preliminary evaluation of a very large pH-sensitive ISFET sensor array chip is reported in this paper. The sensor array chip boasts a 15×16 array of pH-ISFETs with on-chip control and readout circuits. It was designed and fabricated using a novel process which is compatible with standard CMOS technology. This process only required four new mask layers in the design stage and four extra standard processing steps in the fabrication stage. A novel signal processing technique was also employed.

Fabrication and Characterization of Glassy Carbon MEMS

Abstract: This paper describes the fabrication of free-standing high-carbon microstructures by soft-lithographic techniques; these structures ranged in complexity from simple beams to complex, suspended defl...

Fabrication of submicrometre 3D periodic structures composed of Si/SiO2

Abstract: The successful fabrication of 3D periodic structures composed of two transparent materials in the submicrometre range is reported for the first time. The material system comprises a-Si (n=3.26) and SiO/sub 2/ (n=1.46), and sputter-etching leads to 'high-fidelity' layer-to-layer propagation of a concave-convex pattern.

Fabrication of Nanocrystalline Silicon with Small Spread of Particle Size by Pulsed Gas Plasma ( Quantum Dot Structures)

Abstract: We have investigated the formation of nanocrystalline Si (nc-Si) in SiH4 plasma using a pulsed-H2 gas supply by very-high-frequency (VHF; 144 MHz) excitation. Nanocrystalline Si is formed in the gas phase of a SiH4 plasma cell by the coalescence of radicals. The particle size of nc-Si is determined by the growth time of nc-Si in the plasma cell. Supplying H2 into SiH4 plasma enhances nucleation of nc-Si. When the H2 gas supply is turned off, nucleated nc-Si particles grow larger in SiH4 plasma. In the next cycle of H2 gas supply, nc-Si particles grown in the previous cycle are pushed out of the cell into the deposition chamber. Using this method, fabrication of nc-Si with a diameter around 8 nm and a narrow spread (±1 nm) of particle size was realized.

Using soft lithography to fabricate GaAs/AlGaAs heterostructure field effect transistors

Abstract: This letter describes the fabrication of functional GaAs/AlGaAs field effect transistors using micromolding in capillaries—a representative soft lithographic technique. The fabrication process involved three soft lithographic steps and two registration steps. Room temperature characteristics of these transistors resemble those of field effect transistors fabricated by photolithography. The fabrication of functional microelectronic devices using multilayer soft lithography establishes the compatibility of these techniques with the processing methods used in device fabrication, and opens the door for their development as a technique in this area.

New fabrication techniques for high quality photonic crystals

Abstract: We have developed new methods for the fabrication of high quality two-dimensional (2D) and three-dimensional (3D) photonic crystals. These techniques involve anisotropic etching and steam oxidation of AlAs mask layers. We have made manufacturable 2D photonic crystals with high aspect ratios for use as micropolarizers and have measured extinction ratios larger than 800 to 1 between TE and TM modes transmitted through these structures. The new Al2O3 mask fabrication technique also allows us to fabricate 3D structures with up to six repeating layers in depth and over 90% attenuation in the band gap region. Here, we show the fabrication details and performance of 2D and 3D photonic crystals.

Fabrication of glassy carbon microstructures by pyrolysis of microfabricated polymeric precursors

Abstract: Communications formed with this method is limited by the resolution of the microcontact printing (-0.2 pm)J2] by the ability to set the angle and position of the stamp relative to the object to be patterned (-0.01\", and-2 Fm for our apparatus))'] and by uncertainties in the dimensions of the curved support. The composition of these parts is limited to materials that can be electrodeposited. We believe that our method offers a simple means for fabrication of complex three-dimensional microstructures that will be a valuable complement to other means for microfabrication. Many applications in biotechnology and MEMS should be found. This paper describes a method of fabricating microstruc-tures of glassy carbon and other high-carbon solids. This method uses micromolding of polymers to form precursors to these structures, and pyrolysis of these polymeric micro-structures to form the carbon solids. These microstructures are stiff and can be either electrically insulating or conducting , depending on their thermal history. In addition, carbon structures can be very stable thermally, and the surface of carbon is readily functionalized.[',21 We are developing carbon microstructures as components in microelectromecha-nical systems (MEMS), microreactors, and other systems in which thermal stability, chemical inertness, engineered surface properties, and electrical conductivity are useful characteristics. The mechanical, electrical, and chemical properties of high-carbon solids can be controlled over wide ranges by the temperature at which these solids are prepared.'1231 The range of electrical properties that can be achieved is especially interesting: the conductivity of a phenol-formalde-hyde resin can be controlled over a range of-10L9!x' cm-' by pyrolysis. Insulating, semiconducting, and semimetallic behaviors have been observed for pyrolyzed novolac photoresists, depending on the pyrolysis conditions.[42s1 Glassy carbon is often produced by carbonization of organic polymeric precursors; resins of furfuryl alcohol, phenol -formaldehyde, acetone-furfural, or furfuryl alcohol-phenol copolymers are among those commonly used for this purpose.'*] In this work, copolymers of phenol-formal-dehyde or furfuryl alcohol-phenol were formed in patterns on appropriate substrates (silica, Si/Si02, glassy carbon) using micro-molding in capillaries (MIMIC)[6-s1 and micro-transfer molding (pTM).I9' The resulting polymeric structures were carbonized at high temperatures in vacuum (600-1100 \"C, 10-6-10-7 torr) or in an inert atmosphere (ar-gon), either on the substrate or after being lifted from the surface, to yield high-carbon structures having micron-scale dimensions. Supported structures of a phenol-formaldehyde resin and of a furfuryl alcohol-modified phenolic resin were prepared by MIMIC, using a patterned poly(dimethylsi1oxane)

Chemical Solid Free-Form Fabrication: Making Shapes without Molds

Abstract: Solid free-form fabrication methods are surveyed. This approach of making objects by depositing material layer by layer lends itself to the direct conversion of fluid reactants to a solid part, as opposed to the production of a material and its subsequent processing. Examples are given of the formation of ceramics, metals, thermoplastics, thermosets, and composites. In principle, mobile products can be removed from the layers as they form, allowing a much wider range of reactions to be used. Since the composition may be varied as the object is built up, it is also possible to combine several materials into a monolithic piece.

Method for formation of thin film transistors on plastic substrates

Abstract: A process for formation of thin film transistors (TFTs) on plastic substrates (10) replaces standard thin film transistor fabrication techniques, and uses sufficiently low processing temperatures so that inexpensive plastic substrates may be used in place of standard glass, quartz and silicon wafer-based substrates. The process relies on techniques for depositing semiconductors (20), dielectrics (11, 24) and metals (21, 22, 23) at low temperatures; crystallizing and doping semiconductor layers (20) in the TFT with a pulsed energy source; and creating top-gate self-aligned as well as back-gate TFT structures. The process enables the fabrication of amorphous and polycrystalline channel silicon TFTs at temperatures sufficiently low to prevent damage to plastic substrates. The process has use in large area low cost electronics, such as flat panel displays and portable electronics.

Fabrication process of high aspect ratio elastic structures for piezoelectric motor applications

Abstract: Briefly reports on advances in the fabrication technology of components for millimeter size ultrasonic piezoelectric motors. A very large height to width aspect ratio with good lateral patterning resolution is required for the active component in acoustic mode conversion. A new fabrication process using a thick epoxy-based material (SU-8) and the electroplating of nickel is demonstrated. The main advantages over past fabrication methods are better flexibility in the design, simplicity of the fabrication process and the combination of metallic materials (Ni) with polymeric materials (SU-8). The mechanical properties of SU-8 have been measured using free cantilever beam structures.

Fabrication of an S-shaped microactuator

Abstract: We have developed a new fabrication process for electrostatic actuators having an S-shaped film element, which we previously invented for such applications as gas valves. The developed process allows batch fabrication of the actuator whose S-shaped structure height, which is equal to the amount of vertical film displacement, is of the order of a few hundred micrometers. The microactuators are fabricated by stacking three wafers. The middle wafer contains the sputtered Ni film strip which is buckled into an S-shape during the stacking process. The length of film necessary for the S-bend profile has a folded structure which is stretched after stacking. The size of the fabricated chip was 5 mm/spl times/5 mm, and the vertical film displacement was 220 /spl mu/m. The actuator was operated by electrostatic force when the applied voltage was more than 70 V.

Fabrication method for reduced-dimension FET devices

Abstract: Pre-amorphization of a surface layer of crystalline silicon to an ultra-shallow (e.g., less than 100 nm) depth provides a solution to fabrication problems including (1) high thermal conduction in crystalline silicon and (2) shadowing and diffraction-interference effects by an already fabricated gate of a field-effect transistor on incident laser radiation. Such problems, in the past, have prevented prior-art projection gas immersion laser doping from being effectively employed in the fabrication of integrated circuits comprising MOS field-effect transistors employing 100 nm and shallower junction technology.

Writing FIB implantation and subsequent anisotropic wet chemical etching for fabrication of 3D structures in silicon

Abstract: The further miniaturization of silicon micromechanical structures in combination with the highly developed microelectronic technology at the micrometre and sub-micrometre level will lead to a new generation of microdevices. A modern technique to fabricate three-dimensional micromechanical structures is the combination of high-concentration p′ -doping by writing ion implantation using a focused ion beam (FIB) and subsequent anisotropic and selective wet chemical etching. FIB-patterned and chemically etched 3D Si structures with nanoscale thickness have been fabricated using 35 keV Ga + ion implantation and subsequent anisotropic etching in KOH/H 2 O solution. Design and fabrication considerations to achieve freestanding Si structures are discussed and some typical structures are shown.

Nanofabrication with proximal probes

Abstract: In this paper, we describe the use of proximal probes, such as the atomic force microscope (AFM) and the scanning tunneling microscope (STM), for nanofabrication. A resistless proximal probe-based lithographic technique has been developed that uses the local electric field of an STM or conductive AFM tip that is operated in air to selectively oxidize regions of a sample surface. The resulting oxide, typically 1-10 nm thick, can be used either as a mask for selective etching or to directly modify device properties by patterning insulating oxides on thin conducting layers. In addition to this resistless approach, we also describe the use of the STM/AFM to modify the chemical functionality of self-assembling monolayer films. Such modified films are used as a template for the selective electroless plating of metal films. The above processes are fast simple to perform, and well suited for device fabrication. We apply the anodic oxidation process to the fabrication of both semiconductor and metal-oxide devices. In these latter structures, sub-10 nm-sized device features are easily achieved, and we describe the fabrication of the smallest possible device, a single, atomic-sized metallic point contact by using in situ-controlled AFM oxidation.

Novel, Organically Doped, Sol–Gel‐Derived Materials for Photonics: Multiphasic Nanostructured Composite Monoliths and Optical Fibers

Abstract: Sol-gel-processed organic-inorganic hybrid materials combine the merits of inorganic glass and organic molecules, and are therefore a class of materials with good potential for photonics. In this review, two approaches which have shown promising results for producing useful materials for photonics are described: (i) a novel way to fabricate organically doped, multiphasic nanostructured composite monoliths and (ii) a method of fabrication of organically doped, sol-gel-derived optical fibers. For each approach, the preparation process is presented, together with selected applications such as multidye solid-state tunable laser, multiphasic optical power limiter, a micron-scale chemical-sensing and biosensing fibers and solid-state dye-doped fiber lasers.

Angular micropositioner for disk drives

Abstract: Rotary electrostatic microactuators suitable for use in a two-stage servo system for magnetic disk drives have been fabricated using the HexSil process. A 2.6 mm diameter device is shown to be capable of producing 0.17 mN-mm of output torque, corresponding to a predicted actuation bandwidth of 1.6 kHz. The structures are formed from LPCVD polysilicon deposited into deep trenches etched into a silicon mold wafer. Upon release, these structures are transferred to a target wafer using a solder bond. The solder bonding process will provide easy integration of mechanical structures with integrated circuits, allowing separate optimization of the circuit and structure fabrication processes. An advantage of HexSil is that once the mold wafer has undergone the initial plasma etching, it may be re-used for subsequent polysilicon depositions, amortizing the cost of the deep trench etching over many structural runs and thereby significantly reducing the cost of finished actuators. Further, 100 /spl mu/m high structures may be made from a 3 /spl mu/m deposition of polysilicon, increasing overall fabrication speed.

Method of fabricating a high-density dynamic random-access memory

Abstract: The invention relates to a high-density DRAM fabrication technique for forming a source/drain contact between word lines in a self-alignment manner, with the offset length between a source region and a drain region of a peripheral transistor maintained at an adequate value. After gate electrodes (i.e. word lines) are formed, a first insulating layer, which is thin enough not to block up space defined between the word lines, is deposited. The source/drain contact is etched as deep as the first insulating layer is thick to form an extraction electrode made of polycrystalline silicon. A second insulating layer is deposited until a spacer thickness (i.e. the sum of the film thickness of the second insulating layer and the film thickness of the first insulating layer) for determining the offset length is obtained. The first and second insulating layers are etched back for a distance corresponding to the sum of the film thickness of the second insulating layer and the film thickness of the first insulating layer so that a spacer (i.e. the residue of the insulating layers) is left on the side walls of the gate electrode. An implantation of highlevel impurities is performed to form heavily doped source and drain regions of a peripheral transistor. In-cell self-align contact is made possible while maintaining the offset length of the heavily doped source and drain regions

Recent developments in freeform fabrication of dense ceramics from slurry deposition

Abstract: A freeform fabrication technique for dense ceramics and composites has been developed. The technique requires less than 2 volume percent of organic additives and relies on the principle of layerwise deposition of highly loaded colloidal slurries. Components can be manufactured into complex geometries with thick solid sections as well as with thin-walled sections with high aspect ratios. Process feasibility and quality is dependent on the processing parameters of solids loading, slurry rheology, deposition rate, and drying rate. These interrelated parameters must be controlled so that sintering defects are prevented and shape tolerance is maintained. A review of this freeform fabrication technique, called robocasting, will be discussed for fabrication of aluminum oxide parts. Recent developments for a finite element analysis technique for modeling the drying process will also be presented.

New Fabrication Techniques for High-Quality Photonic Crystals

Abstract: We have developed new methods for the fabrication of high quality two-dimensional (2D) and three-dimensional (3D) photonic crystals. These techniques involve anisotropic etching and steam oxidation of AlAs mask layers. We have made manufacturable 2D photonic crystals with high aspect ratios for use as micropolarizers and have measured extinction ratios larger than 800 to 1 between TE and TM modes transmitted through these structures. The new Al2O3 mask fabrication technique also allows us to fabricate 3D structures with up to six repeating layers in depth and over 90% attenuation in the band gap region. Here, we show the fabrication details and performance of 2D and 3D photonic crystals.

Fabrication of a side-polished fiber polarizer with a birefringent polymer overlay

Abstract: The fabrication of an in-line fiber polarizer consisting of a side-polished fiber (SPF) with a birefringent polymer thin-film overlay, polyvinyl carbazole, is described. Typical devices had <0.5-dB insertion loss and extinction ratios of ∼36 dB. A weakly coupled waveguide model that accurately describes these SPF–thin-film overlay devices and guides in their fabrication is also presented.

Optimized aluminum back surface field techniques for silicon solar cells

Abstract: Screen-printed Al and rapid thermal alloying have been combined in order to achieve an Al back surface field (Al-BSF) which lowers the effective back surface recombination velocity to 200 cm/s on 2.3 /spl Omega/cm Si. This Al-BSF process has been integrated into a high-efficiency, laboratory fabrication sequence as well as a high-throughput, industrial-type process in order to achieve solar cell efficiencies in excess of 19.0% and 17.0%, respectively, on 2.3 /spl Omega/cm FZ Si. For both process sequences, the efficiency values are 1-2 absolute percentage points higher than cells made with unoptimized Al-BSFs. The critical process requirements for optimal Al-BSF formation are: (1) the use of a fast ramp rate to reach the alloying temperature; and (2) thick film Al deposition prior to alloying.

A new sacrificial layer process for the fabrication of micromechanical systems

Abstract: A new process using photoresists as sacrificial layers has been developed to fabricate micromechanical components and systems. Commonly used photoresists are spun on a substrate as a sacrificial layer and patterned by a mask aligner. Free-standing metal structures are built by patterning a second layer of thick photoresist and electroplating on top of the photoresist sacrificial layer. Electrostatic microactuators and micromotors have been fabricated using the new photoresist sacrificial layer technique. Compared with all the existing sacrificial layer techniques, the photoresists used in the new process are easy to coat, easy to dissolve and less process steps are involved. The process is compatible with most of the materials and processes used in existing microfabrication technology. The fabrication of micromechanical systems becomes much simpler and cheaper with the use of a photoresist as a sacrificial layer.

Diffractive optical elements

Abstract: A method for the replication of diffractive optical elements (32) using audio/video disc manufacturing equipment and processes. The audio/video disc manufacturing process and mold mastering tooling create diffractive optical elements (32) using a mold plate (14). The diffractive optic design and photomasks are first fabricated then replicated using compact disc industry mold mastering techniques. The surface relief pattern is produced centered in the plate using ion milling or refractive ion etching photolithographic fabrication techniques. Once patterned, the mold master plate (14) is punched into a circular form consistent with standard compact or video disc mold bases - typically eight inches for a compact disc. After molding, each element (32) can be cut out of the disc (30) using blade, shear, waterjet or laser cutting.