Showing papers on "Fabrication published in 2004"

A three-dimensional optical photonic crystal with designed point defects.

Abstract: Photonic crystals1,2,3 offer unprecedented opportunities for miniaturization and integration of optical devices. They also exhibit a variety of new physical phenomena, including suppression or enhancement of spontaneous emission, low-threshold lasing, and quantum information processing4. Various techniques for the fabrication of three-dimensional (3D) photonic crystals—such as silicon micromachining5, wafer fusion bonding6, holographic lithography7, self-assembly8,9, angled-etching10, micromanipulation11, glancing-angle deposition12 and auto-cloning13,14—have been proposed and demonstrated with different levels of success. However, a critical step towards the fabrication of functional 3D devices, that is, the incorporation of microcavities or waveguides in a controllable way, has not been achieved at optical wavelengths. Here we present the fabrication of 3D photonic crystals that are particularly suited for optical device integration using a lithographic layer-by-layer approach15. Point-defect microcavities are introduced during the fabrication process and optical measurements show they have resonant signatures around telecommunications wavelengths (1.3–1.5 µm). Measurements of reflectance and transmittance at near-infrared are in good agreement with numerical simulations.

Fabrication of high-aspect ratio, micro-fluidic channels and tunnels using femtosecond laser pulses and chemical etching

Abstract: We present novel results obtained in the fabrication of high-aspect ratio micro-fluidic microstructures chemically etched from fused silica substrates locally exposed to femtosecond laser radiation. A volume sampling method to generate three-dimensional patterns is proposed and a systematic SEM-based analysis of the microstructure is presented. The results obtained gives new insights toward a better understanding of the femtosecond laser interaction with fused silica glass (a-SiO2).

Fabrication of woodpile structures by two-photon polymerization and investigation of their optical properties.

Abstract: Two-photon polymerization (2PP) is a powerful technique for the fabrication of 3D micro- and submicro-structures. By applying laser powers that are only slightly above the polymerization threshold, 3D structuring of photosensitive materials with a resolution down to 100 nm can be realized. Here we report on woodpile photonic crystal structures fabricated in organic-inorganic hybrid polymers (Ormocers) and investigation of their optical properties. The fabricated crystals possess a photonic band gap in the near infrared spectral region. The polymeric woodpile structures can be used as templates for the fabrication of highly refractive TiO2 replicas. First results in this direction are presented.

All-sputtered 14% CdS/CdTe thin-film solar cell with ZnO:Al transparent conducting oxide

Abstract: Radio-frequency (rf)-sputtered Al-doped ZnO was used as the transparent front contact in the fabrication of high efficiency superstrate configuration CdS∕CdTe thin-film solar cells. These cells had CdS and CdTe layers also deposited by rf sputtering at 250°C with the highest processing temperature of 387°C reached during a post-deposition treatment. The devices were tested at National Renewable Energy Laboratory and yielded an efficiency of 14.0%, which is excellent for a CdTe cell using ZnO and also for any sputtered CdTe solar cell. The low-temperature deposition process using sputtering for all semiconductor layers facilitates the use of ZnO and conveys significant advantages for the fabrication of more complex multiple layers needed for the fabrication of tandem polycrystalline solar cells and for cells on polymer materials.

Nanometric superlattices: non-lithographic fabrication, materials, and prospects

Abstract: A non-lithographic technique that utilizes the self-organized, highly ordered anodized aluminum oxide (AAO) porous membrane as a template is employed as a general fabrication means for the formation of vastly different two-dimensional lateral nanometric superlattices. The fact that material systems as different as metals, semiconductors, and carbon nanotubes (CNT) can be treated with the same ease attests to the generality of this nano-fabrication approach. The original alumina nanopore membranes determine the uniformity, packing density, and size of the nanostructures. The flexibility of using a variety of materials, the accurate control over fabrication process, and the command over the alumina template attributes give us the freedom of engineering various physical properties determined by the shape, size, composition, and doping of the nanostructures. The novel nanomaterial platform realized by this unique technique is powerfully enabling for a broad range of applications as well as for uncovering new physical phenomena such as the collective behavior of arrays of nano-elements that may not be intrinsic to individual nano-elements.

Novel three-dimensional embedded SU-8 microchannels fabricated using a low temperature full wafer adhesive bonding

Abstract: This paper describes a novel fabrication method for the manufacture of three-dimensional (3D) interconnected microchannels. The fabrication is based on a full wafer polymer bonding process, using SU-8 polymer epoxy photoresist as a structural material. The technology development includes an improvement of the SU-8 photolithography process in order to produce high uniformity films with good adhesive properties. Hence, 3D embedded microchannels are fabricated by a low temperature adhesive bonding of the SU-8 photopatterned thick films. The bonding occurs at temperatures (100–120 °C) lower than those usually applied in bonding technology. The bonding process parameters have been chosen in order to achieve a strong and void-free bond. High bond strengths, up to 8 MPa, have been obtained. Several examples using this new technology are shown, including bonding between different combinations of silicon and Pyrex wafers. This method also allows us to bond wafers with previously surface micromachined structures. Interconnected microchannels with vertical smooth walls and aspect ratios up to five have been obtained. Channels from 40 to 60 µm depth and from 10 to 250 µm width have been achieved. Liquid has been introduced at different levels into the microchannels, verifying good sealing of the 3D interconnected microchannels. The fabrication procedure described in this paper is fast, reproducible, CMOS compatible and easily implementable using standard photolithography and bonding equipment.

Fabrication and characterization of a nanowire/polymer-based nanocomposite for a prototype thermoelectric device

Abstract: This paper discusses the design, fabrication and testing of a novel thermoelectric device comprised of arrays of silicon nanowires embedded in a polymer matrix. By exploiting the low-thermal conductivity of the composite and presumably high-power factor of the nanowires, a thermoelectric figure of merit, higher than the corresponding bulk value, should result. Arrays were first synthesized using a vapor-liquid-solid (VLS) process leading to one-dimensional (1-D) growth of single-crystalline nanowires. To provide structural support while maintaining thermal isolation between nanowires, parylene, a low thermal conductivity and extremely conformal polymer, was embedded within the arrays. Mechanical polishing and oxygen plasma etching techniques were used to expose the nanowire tips and a metal contact was deposited on the top surface. Scanning electron micrographs (SEMs) illustrate the results of the fabrication processes. Using a modification of the 3/spl omega/ technique, the effective thermal conductivity of the nanowire matrix was measured and 1 V characteristics were also demonstrated. An assessment of the suitability of this nanocomposite for high thermoelectric performance devices is given.

Microstructure fabrication with a CO2 laser system

Abstract: In this paper, we investigate the use of a commercial CO2 laser system for fabrication of microfluidic systems in polymers. We discuss the cutting process with the laser system and present a straightforward model for the channel depth of microchannels dependent on the fabrication parameters. In particular, we examine the influence of the cutting sequence, the number of cut passes, the laser beam velocity and the laser radiant flux. The model allows the prediction of microchannel depths within a maximum deviation of 8 µm for channels that are up to 210 µm in depths. It was shown that, at constant channel depth, the channel width could be varied by 27% by using different cutting parameters. The optimum cutting sequence for the production of a channel -junction is also presented in the paper. The laser system is shown to be a flexible and rapid tool for the production of polymer microfluidic prototypes.

Toward Atomic-Scale Device Fabrication in Silicon Using Scanning Probe Microscopy

Abstract: We present a complete fabrication process for the creation of robust nano-and atomic-scale devices in silicon using a scanning tunneling microscope (STM). In particular we develop registration markers which, in combination with a custom-designed STM-scanning electron microscope (SEM) system, solve one of the key fabrication problems - connecting the STM-patterned buried phosphorus-doped devices, fabricated in the ultrahigh vacuum environment, to the outside world. The first devices demonstrate the feasibility of this technology and confirm the presence of quantum confinement in devices as electron propagation is laterally constricted by STM patterning.

Femtosecond laser fabrication of tubular waveguides in poly(methyl methacrylate)

Abstract: Femtosecond laser direct writing is employed for the fabrication of buried tubular waveguides in bulk poly(methyl methacrylate). A novel technique using selective chemical etching is presented to resolve the two-dimensional refractive-index profile of the fabrication structures. End-to-end coupling in the waveguides reveals a near-field intensity distribution that results from the superimposition of several propagating modes with different azimuthal symmetries. Mode analysis of the tubular waveguides is performed using the finite-difference method, and the possible propagating mode profiles are compared with the experimental data.

Fabrication of Carbon Nanotube Reinforced Alumina Matrix Nanocomposite by Sol-gel Process

Abstract: Abstract Carbon nanotube reinforced alumina matrix nanocomposite was fabricated by sol–gel process and followed by spark plasma sintering process. Homogeneous distribution of carbon nanotubes within alumina matrix can be obtained by mixing the carbon nanotubes with alumina sol and followed by condensation into gel. The mixed gel, consisting of alumina and carbon nanotubes, was dried and calcinated into carbon nanotube/alumina composite powders. The composite powders were spark plasma sintered into carbon nanotube reinforced alumina matrix nanocomposite. The hardness of carbon nanotube reinforced alumina matrix nanocomposite was enhanced due to an enhanced load sharing of homogeneously distributed carbon nanotubes. At the same time, the fracture toughness of carbon nanotube reinforced alumina matrix nanocomposite was enhanced due to a bridging effect of carbon nanotubes during crack propagation.

A simple and cost-effective approach to fabrication of dense ceramic membranes on porous substrates

Abstract: A simple and elegant approach to fabrication of dense ceramic membranes on porous substrates, a traditional dry pressing of foam powders, has been developed to reduce the cost of fabrication. Gd-doped ceria (GDC, Gd0.1Ce0.9O1.95) electrolyte membranes as thin as 8 μm are obtained by dry-pressing highly porous GDC powders. The membrane thickness can be readily controlled by the amount of powder. The electrolyte membranes are studied in a solid-oxide fuel cell (SOFC) with air as oxidant and humidified hydrogen (3% H2O) as fuel. Open-circuit voltages of about 1.0 V are observed, implying that the permeability of the membranes to molecular gases is insignificant. Power densities of 140 and 380 mW/cm2 are demonstrated at 500° and 600°C, respectively, representing a significant progress in developing low-temperature SOFCs.

Liquid crystal display device and fabrication method thereof

Abstract: The present invention provides a novel photolithography processes using photoresist pattern having at least two areas which has different thickness from each other for a fabrication method for a liquid crystal display device having reversed staggered and channel-etched type thin film transistors, reduce a number of photolithography processes required for whole of the fabrication process of the liquid crystal display device, and improve brightness of the liquid crystal display device.

Low temperature fabrication of immersion capacitive micromachined ultrasonic transducers on silicon and dielectric substrates

Abstract: A maximum processing temperature of 250/spl deg/C is used to fabricate capacitive micromachined ultrasonic transducers (CMUTs) on silicon and quartz substrates for immersion applications. Fabrication on silicon provides a means for electronics integration via post-complementary metal oxide semiconductor (CMOS) processing without sacrificing device performance. Fabrication on quartz reduces parasitic capacitance and allows the use of optical displacement detection methods for CMUTs. The simple, low-temperature process uses metals both as the sacrificial layer for improved dimensional control, and as the bottom electrode for good electrical conductivity and optical reflectivity. This, combined with local sealing of the vacuum cavity by plasma-enhanced chemical-vapor deposition of silicon nitride, provides excellent control of lateral and vertical dimensions of the CMUTs for optimal device performance. In this paper, the fabrication process is described in detail, including process recipes and material characterization results. The CMUTs fabricated for intravascular ultrasound (IVUS) imaging in the 10-20 MHz range and interdigital CMUTs for microfluidic applications in the 5-20 MHz range are presented as device examples. Intra-array and wafer-to-wafer process uniformity is evaluated via electrical impedance measurements on 64-element ring annular IVUS imaging arrays fabricated on silicon and quartz wafers. The resonance frequency in air and collapse voltage variations are measured to be within 1% and 5%, respectively, for both cases. Acoustic pressure and pulse echo measurements also have been performed on 128 /spl mu/m/spl times/32 /spl mu/m IVUS array elements in water, which reveal a performance suitable for forward-looking IVUS imaging at about 16 MHz.

Fabrication of poly(methyl methacrylate) microfluidic chips by atmospheric molding.

Abstract: A greatly simplified method for fabricating poly(methyl methacrylate) (PMMA) separation microchips is introduced. The new protocol relies on UV-initiated polymerization of the monomer solution in an open mold under ambient pressure. Silicon microstructures are transferred to the polymer substrate by molding a methyl methacrylate solution in a sandwich (silicon master/Teflon spacer/glass plate) mold. The chips are subsequently assembled by thermal sealing of the channel and cover plates. The new fabrication method obviates the need for specialized replication equipment and reduces the complexity of prototyping and manufacturing. Variables of the fabrication process were assessed and optimized. The new method compares favorably with common fabrication techniques, yielding high-quality devices with well-defined channel and injection-cross structures, and highly smoothed surfaces. Nearly 100 PMMA chips were replicated using a single silicon master, with high chip-to-chip reproducibility (relative standard deviations of 1.5 and 4.7% for the widths and depths of the replicated channels, respectively). The relatively high EOF value of the new chips (2.12 x 10(-4) cm(2) x V(-1) x s(-1)) indicates that the UV polymerization process increases the surface charge and hence enhances the fluidic transport. The attractive performance of the new CE microchips has been demonstrated in connection with end-column amperometric and contactless-conductivity detection schemes. While the new approach is demonstrated in connection with PMMA microchips, it could be applied to other materials that undergo light-initiated polymerization. The new approach brings significant simplification of the process of fabricating PMMA devices and should lead to a widespread low-cost production of high-quality separation microchips.

Atom chips: Fabrication and thermal properties

Abstract: Neutral atoms can be trapped and manipulated with surface mounted microscopic current carrying and charged structures. We present a lithographic fabrication process for such atom chips based on evaporated metal films. The size limit of this process is below 1 μm. At room temperature, thin wires can carry current densities of more than 107A∕cm2 and voltages of more than 500 V. Extensive test measurements for different substrates and metal thicknesses (up to 5 μm) are compared to models for the heating characteristics of the microscopic wires. Among the materials tested, we find that Si is the best suited substrate for atom chips.

A rapid prototyping technique for the fabrication of solvent-resistant structures

Abstract: We demonstrate a rapid prototyping technique for the fabrication of solvent-resistant channels up to and exceeding one millimeter in height. The fabrication of channels with such dimensions by conventional lithography would be both challenging and time consuming. Furthermore, we show that this technology can be used to fabricate channels with a depth that varies linearly with distance. This technique requires only a long-wavelength ultraviolet source, a mask made by a desktop printer and a commercially available optical adhesive. We demonstrate two lithographic methods: one that fabricates channels sealed between glass plates (close-faced) and one that fabricates structures on a single plate (open-faced). The latter is fully compatible with silicon replication techniques to make fluid handling devices.

Transparent Ferroelectric Glass-Ceramics

Abstract: In recent years, there has been a resurgence of interest in transparent ferroelectric glass-ceramics (TFGCs), which are a special class of glass-ceramic composites that combine the low cost of fabrication and forming of transparent glass with the superior nonlinear optical and electro-optical properties of ferroelectric crystals. In this paper, we present a review of the current status, focusing on the challenges of fabrication and opportunities for selectively creating nonlinear optical structures, which will be useful in realizing integrated optical devices. A successful fabrication of TFGC requires the nucleation and growth of crystallites that are too small to scatter light, yet large enough to have ferroelectric response. Early experiments on silica based glasses containing common ferroelectric oxides indicated that although the preparation of TFGC is feasible, such a balance of crystallite size is difficult to achieve. However, later studies have demonstrated successful fabrication of TFGCs with com...

Fabrication of high aspect ratio 100nm metallic stamps for nanoimprint lithography using proton beam writing

Abstract: We report a way of fabricating high-quality void-free high-aspect-ratio metallic stamps of 100nm width and 2μm depth, using the technique of proton beam writing coupled with electroplating using a nickel sulfamate solution. Proton beam writing is a one-step direct-write process with the ability to fabricate nanostructures with high-aspect-ratio vertical walls and smooth sides, and as such has ideal characteristics for three-dimensional (3D) stamp fabrication. Nanoindentation and atomic force microscopy measurements of the nickel surfaces of the fabricated stamp show a hardness and side-wall roughness of 5GPa and 7nm, respectively. The fabricated 100nm 3D stamps have been used to transfer test patterns into poly(methylmethacrylate) films, spin coated onto a silicon substrate. Proton beam writing coupled with electroplating offers a process of high potential for the fabrication of high quality metallic 3D nanostamps.

Rendering SU-8 hydrophilic to facilitate use in micro channel fabrication

Abstract: A simple method is presented to reduce the contact angle of the photo-resist SU-8. A low contact angle is valuable in micro total analysis systems for the fabrication of micro channels where the capillary pressure is linearly related to the cosine of the contact angle, θ. If the surface of the channel is hydrophilic, the capillary pressure can be used as the only means to direct the liquid through the channels and the need for external pumps can be avoided. This is very useful, especially in the fabrication of devices for 'lab-on-a-chip' where it is important to keep the design as simple as possible. A commonly used technique for releasing structures fabricated on Si wafers is to use a sacrificial Cr layer. It is shown that the contact angle of SU-8 decreases by 40° after etching this layer. A further reduction in contact angle is desirable and can be achieved by treating the sample with ethanolamine at 50 °C for only 10 min. The resulting contact angle is 23° ± 7°. Using a wet chemical treatment, a selective change in contact angle between different areas of a micro channel system can be achieved, without the need to involve different materials in the fabrication process.

Fabrication of Single-Channel Catalytic Microburners: Effect of Confinement on the Oxidation of Hydrogen/Air Mixtures

Abstract: A protocol for the inexpensive fabrication of catalytic microburners with integrated thermocouples is introduced. Experimental data for the oxidation of hydrogen/air mixtures over platinum/alumina ...

High Performance Low Temperature Polycrystalline Silicon Thin Film Transistors on Non-alkaline Glass Produced Using Diode Pumped Solid State Continuous Wave Laser Lateral Crystallization

Abstract: High performance low temperature polycrystalline silicon (poly-Si) thin film transistors (TFTs) with large grains were created using diode pumped solid state (DPSS) continuous wave (CW) laser lateral crystallization (CLC), employing fabrication processes at 450°C. Field-effect mobilities of 566 cm2/Vs for the n-channel and 200 cm2/Vs for the p-channel were obtained for a thick Si film (100–150 nm) on a 300×300 mm non-alkaline glass substrate. The high performance of the TFTs is attributed to the predominantly (100)-oriented very large grains. With a decreasing Si-film thickness, the grain size decreases, and the surface orientation of the grain changes from (100) to other orientations. These effects lead to reduced field-effect mobility with decreasing Si-film thickness, but it is easy to obtain a high field-effect mobility of over 300 cm2/Vs, even with a 50 nm thick Si film, without special processing techniques. A complementary metal oxide semiconductor (CMOS) ring oscillator was fabricated using a thin Si film 65 nm thick to demonstrate the high circuit performance of CLC poly-Si TFTs by applying the simplest CMOS process technology. A delay of 400 ps/stage at a gate length of 1.5 µm and a supply voltage of Vdd=5.0 (V) was produced on a large non-alkaline glass substrate utilizing a fabrication temperature of 450°C. This crystallization method will lead to the fabrication of high-performance and cheap Si-LSI circuits on large non-alkaline glass substrates.