Showing papers on "Fabrication published in 2008"

Solid freeform fabrication using a plurality of modeling materials

Abstract: A system and methods for solid freeform fabrication of an object is disclosed. The system comprises a solid freeform fabrication apparatus having a plurality of dispensing heads, a building material supply apparatus configured to supply a plurality of building materials to the fabrication apparatus, and a control unit configured for controlling the fabrication apparatus and the supply apparatus based on an operation mode selected from a plurality of predetermined operation modes.

Fabrication of low-loss photonic wires in silicon-on-insulator using hydrogen silsesquioxane electron-beam resist

Abstract: Fully etched photonic wires in silicon-on-insulator have been fabricated and propagation loss values as low as 0.92 plusmn 0.14 dB/cm have been obtained. Hydrogen silsesquioxane (HSQ) was used as an electron beam resist and as a direct mask in the dry-etch processing of the silicon core layer. The dimensional repeatability of the fabrication process was also estimated through measurements of the wavelength selection performance of nominally identical photonic wire Bragg gratings fabricated at intervals over a period of 37 days.

Effect of fabrication process on electrical properties of polymer/multi-wall carbon nanotube nanocomposites

Abstract: Polymer/carbon nanotubes nanocomposites were fabricated by an in situ polymerization process using multi-wall carbon nanotubes (MWNT) as filler in an epoxy polymer. Effects of curing process, mixing speed, mixing time, addition of ethanol, timing of hardener addition, etc., in the fabrication process on the electrical properties of nanocomposites have been investigated. In the fabrication process, the effective formation of macroscopic conducting network in matrix is most important to enhance the electrical properties of nanocomposites. It was found that the curing temperature and the mixing conditions are key factors in the fabrication process, which influence the formation of conducting network significantly. Therefore, careful design of these factors in the fabrication process is required to achieve high electrical performances of nanocomposites. The experimental percolation threshold of the resultant nanocomposites was around 0.1 wt%. Moreover, a statistical percolation model was built up to numerically investigate the percolation threshold. The experimental electrical conductivity increases from the percolation threshold following a percolation-like power law with the identified critical exponent t as 1.75.

Fabrication of Highly Ordered Silicon Oxide Dots and Stripes from Block Copolymer Thin Films

Abstract: A general route to fabricate highly ordered arrays of nanoscopic silicon oxide dots and stripes (see figure) from block copolymer thin films is described. Poly(styrene-b-4-vinylpyridine) thin films with cylindrical microdomains oriented normal and parallel to the surface were used as templates for the fabrication of nanoscopic silicon oxide, with polydimethylsiloxane as the inorganic precursor.

Trimming of silicon ring resonator by electron beam induced compaction and strain.

Abstract: Silicon is becoming the preferable platform for future integrated components, mostly due to the mature and reliable fabrication capabilities of electronics industry. Nevertheless, even the most advanced fabrication technologies suffer from non-uniformity on wafer scale and on chip scale, causing variations in the critical dimensions of fabricated components. This is an important issue since photonic circuits, and especially cavities such as ring resonators, are extremely sensitive to these variations. In this paper we present a way to circumvent these problems by trimming using electron beam induced compaction of oxide in silicon on insulator. Volume compaction of the oxide cladding causes both changes in the refractive index and creates strain in the silicon lattice. We demonstrate a resonance wavelength red shift 4.91 nm in a silicon ring resonator.

Low-temperature polysilicon thin film transistors on polyimide substrates for electronics on plastic

Abstract: In this work we show a new low-temperature polycrystalline silicon (LTPS) thin film transistor (TFT) fabrication process on polyimide (PI) layers. The PI is spun on Si-wafer used as rigid carrier, thus overcoming difficulties in handling flexible freestanding plastic substrates, eliminating the problem of plastic shrinkage with high temperature processing and allowing the use of standard semiconductor equipment. LTPS TFTs are fabricated according to a conventional non self-aligned process, with source/drain contacts formed by deposition of a highly doped Si-layer and patterned by a selective wet-etching. Laser annealing is performed providing simultaneous dopant activation and crystallization of the active layer. The maximum process temperature is kept below 350 °C. After LTPS TFTs fabrication, the PI layer is mechanically released from the rigid carrier, which can be re-used for a new fabrication process. The devices exhibit good electrical characteristics with field effect mobility up to 50 cm 2 /V s. Analysis of electrical stability and characteristics in presence of mechanical stress is also shown.

Fabrication of Free‐standing, Conductive, and Transparent Carbon Nanotube Films

Abstract: Single-walled carbon nanotubes (SWCNTs) have attracted considerable attention as a result of their remarkable strengths, elasticities, superb electrical properties, and high thermal conductivities. A major application identified for SWCNTs is to function as a coating agent to form transparent electrical conductors, which is a crucial component of many optoelectronic devices such as flat-panel displays and solar cells. When compared with commercially available flexible transparent conductors, carbon nanotube films have several advantages: (i) They have high environmental stability and flexibility. SWCNTs are generally inert to bases, humidity, and high temperatures. (ii) Bending nanotube films shows only small changes in resistance. (iii) SWCNTs have high transmittance in the visible region and the neutral color is an advantage over indium tin oxide (ITO) in display applications. (iv) SWCNT films can be fabricated at low cost by solution coating and printing as opposed to ITO, for which vacuum sputtering is typically required. These features have prompted considerable efforts and innovations directed at creating transparent SWCNT films, including vacuum filtering, drop-casting, and Langmuir–Blodgett deposition. However, it remains a challenge to fabricate high-quality free-standing, conductive, and transparent SWCNT films. To accomplish this goal, we report herein our efforts to create homogenous nanotube dispersions that are stable to slow solvent evaporation and to develop a method that allows films to be released from substrates, purified, and transferred to new substrates. A critical element of our procedure is the formation of homogenous SWCNT dispersions that are highly stable (months to years). Most commercial SWCNTs are ‘‘bundled’’ into van der Waals-induced aggregates. These aggregates can be dispersed to different degrees by ultrasonic treatment, and additives are used to create dispersions in aqueous or organic solutions. However, these suspensions usually have relatively low SWCNT concentrations and some methods require covalent bonds to the nanotube surface. In the latter case, the added defects generally lower the conductance of SWCNTs.

Nanofabricated Concentric Ring Structures by Templated Self-Assembly of a Diblock Copolymer

Abstract: The formation of well-controlled circular patterns on the nanoscale is important for the fabrication of a range of devices such as sensors, memories, lasers, transistors, and quantum devices. Concentric, smooth ring patterns with tunable dimensions have been formed from a cylinder-forming poly(styrene-b-dimethylsiloxane) (PS-PDMS) diblock copolymer under confinement in shallow circular trenches. The high etch selectivity between PS and PDMS facilitates pattern transfer, illustrated by the fabrication of arrays of ferromagnetic cobalt rings with a density of 1.1 × 109/cm2. The effects of confinement diameter and commensurability on the diameter and period of the concentric rings are analyzed using a free energy model that includes interfacial, strain, and bending energies. This work provides a simple process for the fabrication of nanoscale circular patterns with very narrow line width using a much coarser-scale template, and may facilitate the miniaturization of a variety of microelectronic devices.

Micro- and nanostructures inside sapphire by fs-laser irradiation and selective etching.

Abstract: The fabrication of microchannels and self-assembled nanostructures in the volume of sapphire was performed by femtosecond laser irradiation followed by chemical etching with aqueous solution of HF acid. Depending on the focusing conditions self-organized nanostructures or elliptical microchannels are produced. While the dimensions in two directions are on a micro- respectively nanoscale, feature lengths of up to 1 mm are achieved. This comes out to aspect ratios of more than 1000. This fabrication technique is potentially usable for photonic crystal based integrated optical elements or microfluidic devices for applications in life science, biology or chemistry.

Thin Film Stress Driven Self‐Folding of Microstructured Containers

Abstract: Lithography, the workhorse of the microelectronics industry,is routinely used to fabricate micro and nanostructures in ahighly monodisperse manner, with high accuracy and preci-sion. However, one of the central limitationsof this technologyis that it is inherently two-dimensional (2D) as a result of thewafer-based fabrication paradigm. It is extremely challengingto fabricate three-dimensional (3D) patterned structures, letalone complex structures containing encapsulated objects, onthe sub-mm scale. Thus, the parallel fabrication of such struc-tures remains a major challenge that needs to be addressed.Some solutions have emerged that enable sub-mm-scalelithographic fabrication in 3D; these include techniques suchas wafer stacking,

ZnO nanowire network transistor fabrication on a polymer substrate by low-temperature, all-inorganic nanoparticle solution process

Abstract: All-solution processed, low-temperature zinc oxide nanowire network transistor fabrication on a polymer substrate was demonstrated. This simple process can produce high resolution metal electrode transistors with inorganic semiconductor nanowire active material in a fully maskless sequence, eliminating the need for lithographic and vacuum processes. The temperature throughout the processing was under 140°C, which will enable further applications to electronics on low-cost, large-area flexible polymer substrates.

CMOS-compatible fabrication of room-temperature single-electron devices

Abstract: Single-electron devices offer many advantages over traditional devices, but it is a challenge to fabricate them in large numbers. A novel geometry in which the source and drain electrodes are vertically separated by thin dielectric films, and nanoparticles attached to the sidewall of the dielectric films act as Coulomb islands, can now be used for the CMOS-compatible fabrication of single-electron devices that operate at room temperature.

Periodic arrays of deep nanopores made in silicon with reactive ion etching and deep UV lithography

Abstract: We report on the fabrication of periodic arrays of deep nanopores with high aspect ratios in crystalline silicon. The radii and pitches of the pores were defined in a chromium mask by means of deep UV scan and step technology. The pores were etched with a reactive ion etching process with SF6, optimized for the formation of deep nanopores. We have realized structures with pitches between 440 and 750 nm, pore diameters between 310 and 515 nm, and depth to diameter aspect ratios up to 16. To the best of our knowledge, this is the highest aspect ratio ever reported for arrays of nanopores in silicon made with a reactive ion etching process. Our experimental results show that the etching rate of the nanopores is aspect-ratio-dependent, and is mostly influenced by the angular distribution of the etching ions. Furthermore we show both experimentally and theoretically that, for sub-micrometer structures, reducing the sidewall erosion is the best way to maximize the aspect ratio of the pores. Our structures have potential applications in chemical sensors, in the control of liquid wetting of surfaces, and as capacitors in high-frequency electronics. We demonstrate by means of optical reflectivity that our high-quality structures are very well suited as photonic crystals. Since the process studied is compatible with existing CMOS semiconductor fabrication, it allows for the incorporation of the etched arrays in silicon chips.

Fabrication of electrically active films based on multiple layers

Abstract: A continuous film of desired electrical characteristics is obtained by successively printing and annealing two or more dispersions of prefabricated nanoparticles.

Nanogaps with very large aspect ratios for electrical measurements

Abstract: For nanoscale electrical characterization and device fabrication, it is often desirable to fabricate planar metal electrodes separated by large aspect ratio gaps with interelectrode distances well below 100nm. We demonstrate a self-aligned process to accomplish this goal using a thin Cr film as a sacrificial etch layer. The resulting gaps can be as small as 10nm and have aspect ratios exceeding 1000, with excellent interelectrode isolation. Such Ti∕Au electrodes are demonstrated on Si substrates and are used to examine a voltage-driven transition in magnetite nanostructures. This shows the utility of this fabrication approach even with relatively reactive substrates.

Fabrication of fiber reinforced ceramic composites by chemical vapor infiltration

Abstract: Ceramic fiber-ceramic matrix composites were prepared using the chemical vapor deposition (CVD) process. Our major goal of significantly reducing the infiltration times was accomplished. We have conceived a process, fabricated hardware, and demonstrated on a laboratory scale a process which permits CVD infiltration of an SiC fibrous preform with either an Si/sub 3/N/sub 4/ or SiC matrix in 2 to 12 h. The process should be applicable to infiltration of fibrous preforms prepared by slurry molding, stacking of layers of cloth, or filament winding. Two types of composites (SiC-Si/sub 3/N/sub 4/ and SiC-SiC) have been produced at densities of about 2.0 Mg/m/sup 3/ which was near the desired range. A scheme has also been conceived whereby the new infiltration process could be used for fabrication of tubes or hollow cylinders. This is an important advance since the ability to fabricate tubes or hollow cylinders would offer the hope that the process could be used for fabrication of toughened, high-strength heat exchanger tubes, heat engine cylinder liners and valve guides. 19 references, 7 figures, 1 table.

A Nanodamascene Process for Advanced Single-Electron Transistor Fabrication

Abstract: A process design based on a nanowire structure is demonstrated with the fabrication of metallic single-electron transistors. The method is capable of subattofarad resolution resulting in transistors that exhibited Coulomb blockade up to approximately 430 K. An analysis showed that these devices have sufficient operational margin to sustain process fluctuations and still operate within the temperature limits of conventional silicon field effect transistors.

Laser micro/nano fabrication in glass with tunable-focus particle lens array.

Abstract: Based on medium-tuned optical field enhancement effect around a self-assembled particle-lens array (PLA) irradiated with a femtosecond (fs) laser source, we demonstrated that high-precision periodical array of micro/nano-structures can be readily fabricated on glass surface or inside glass in large areas in parallel without any cracks or debris. The technique has potential for rapid fabrication of three-dimensional structures in multiple layers inside glass.

Characteristics of the bond in Cu–H13 tool steel parts fabricated using SLM

Abstract: The paper is concerned with the fabrication of bi-metallic parts using a purpose-built rig and a Nd:YAG laser, the two materials being copper and H13 tool steel. Two types of bonds are identified and various characteristics of these bonds are studied. These include the microstructure using an optical and scanning electron microscopes, tensile strength and hardness of the bond. The diffusivity between copper and H13 tool steel is quantified by performing energy dispersive X-ray spectroscopy analysis. The successful fabrication of two samples, each containing both types of bonds, is described.

Fabrication of Carbon nanotube poly-methyl-methacrylate composites for nonlinear photonic devices.

Abstract: Carbon nanotubes (CNT) are an attractive material for photonic applications due to their nonlinear optical properties, such as the nonlinear saturable absorption and high third order nonlinearity. However their utilization has been hindered by the lack of flexibility on the device design which rises from the current methods of Carbon nanotube deposition within the optical system. A suitable approach to solve this problem is to embed the CNTs in an optical material from which complex devices such as optical waveguides or optical fibers can be fabricated. Here, we propose a novel method to fabricate Carbon nanotube-doped poly-methyl-methacrylate (PMMA) composites in which the Carbon nanotubes are dispersed in the methyl-methacrylate (MMA) monomer solution prior to and during the polarization process. This method allows the bundle separation and dispersion of the CNT in a liquid state without the need for solvents, hence simplifying the method and facilitating the fabrication of volume CNT-PMMA. Volume fabrication makes this technique suitable for the fabrication of CNT-doped polymer fibers. In this paper, we also analyzed the merits of adding dopants such as diphenyl sulfide (DPS) and benzyl benzoate (BEN) to the CNT-PMMA composite and we observed that DPS plays the role of CNT dispersion stabilizer that can improve the device performance. The CNT-PMMA composite was employed to implement passive mode-locked laser.

Fabrication and characterization of freestanding 3D carbon microstructures using multi-exposures and resist pyrolysis

Abstract: We present a fabrication method for freestanding complex 3D carbon microstructures utilizing a lithogaphy step and a heating step We developed two fabrication methods for multi-level 3D SU-8 microstructures, which were used as polymer precursors in a carbonization process In one method, multiple SU-8 layers were successively coated and cross-linked In the other method, aligned partial exposures were used to control the thickness of the freestanding SU-8 layer Freestyle, freestanding carbon microstructures were fabricated by heating 3D SU-8 microstructures below 1000 °C in a nitrogen atmosphere Characterization of the pyrolysis process, through measurements such as dimensional changes, roughness, hardness, elastic modulus and resistivity, was performed for positive resists AZ5214 and AZ9260 as well as SU-8 3D carbon microstructures fabricated using our methods can be utilized for various applications such as low cost resonating microsensors and microfluidics