Showing papers on "Fabrication published in 2011"

Low-temperature fabrication of high-performance metal oxide thin-film electronics via combustion processing

Abstract: Solution-deposited metal oxides show great potential for large-area electronics, but they generally require high annealing temperatures, which are incompatible with flexible polymeric substrates. Combustion processing is now reported as a new low-temperature route for the deposition of diverse metal oxide films, and high-performance transistors are demonstrated using this method.

Flexible high-performance carbon nanotube integrated circuits

Abstract: Carbon nanotube thin-film transistors are expected to enable the fabrication of high-performance, flexible and transparent devices using relatively simple techniques. However, as-grown nanotube networks usually contain both metallic and semiconducting nanotubes, which leads to a trade-off between charge-carrier mobility (which increases with greater metallic tube content) and on/off ratio (which decreases). Many approaches to separating metallic nanotubes from semiconducting nanotubes have been investigated, but most lead to contamination and shortening of the nanotubes, thus reducing performance. Here, we report the fabrication of high-performance thin-film transistors and integrated circuits on flexible and transparent substrates using floating-catalyst chemical vapour deposition followed by a simple gas-phase filtration and transfer process. The resulting nanotube network has a well-controlled density and a unique morphology, consisting of long (~10 µm) nanotubes connected by low-resistance Y-shaped junctions. The transistors simultaneously demonstrate a mobility of 35 cm(2) V(-1) s(-1) and an on/off ratio of 6 × 10(6). We also demonstrate flexible integrated circuits, including a 21-stage ring oscillator and master-slave delay flip-flops that are capable of sequential logic. Our fabrication procedure should prove to be scalable, for example, by using high-throughput printing techniques.

Dye-sensitized solar cells with NiS counter electrodes electrodeposited by a potential reversal technique

Abstract: Nickel sulfides have been, for the first time, electrodeposited on transparent conductive glass by a facile periodic potential reversal (PR) technique to supersede Pt counter electrodes (CEs) of dye-sensitized solar cells (DSCs). The composition and electrochemical catalytic activity of the nickel sulfide films prepared by PR technique are different from those of the ones deposited by the commonly used potentiostatic (PS) technique. PR technique produces transparent single-component NiS, while co-deposition of Ni and NiS is found in the opaque films prepared by PS method. The nickel sulfide deposited by PR technique shows high catalytic activity for the reduction of I3− to I− in a DSC. DSC with the CE deposited by PR technique performs much better (6.82%) than that by PS method (3.22%), and is comparable to the device with conventional Pt coated CE (7.00%).

Preparation of Tunable 3D Pillared Carbon Nanotube–Graphene Networks for High-Performance Capacitance

Abstract: We have developed a rational strategy for creating the 3D pillared vertically aligned carbon nanotube (VACNT)-graphene architectures by intercalated growth of VACNTs into thermally expanded highly ordered pyrolytic graphite (HOPG). By controlling the fabrication process, the length of the VACNT pillars can be tuned. In conjunction with the electrodeposition of nickel hydroxide to introduce the pseudocapacitance, these 3D pillared VACNT–graphene architectures with a controllable nanotube length were demonstrated to show a high specific capacitance and remarkable rate capability, and they significantly outperformed many electrode materials currently used in the state-of-the-art supercapacitors.

Stretchable, Transparent Graphene Interconnects for Arrays of Microscale Inorganic Light Emitting Diodes on Rubber Substrates

Abstract: This paper describes the fabrication and design principles for using transparent graphene interconnects in stretchable arrays of microscale inorganic light emitting diodes (LEDs) on rubber substrates. We demonstrate several appealing properties of graphene for this purpose, including its ability to spontaneously conform to significant surface topography, in a manner that yields effective contacts even to deep, recessed device regions. Mechanics modeling reveals the fundamental aspects of this process, as well as the use of the same layers of graphene for interconnects designed to accommodate strains of 100% or more, in a completely reversible fashion. These attributes are compatible with conventional thin film processing and can yield high-performance devices in transparent layouts. Graphene interconnects possess attractive features for both existing and emerging applications of LEDs in information display, biomedical systems, and other environments.

System and apparatus for flowable deposition in semiconductor fabrication

Abstract: Electronic device fabrication processes, apparatuses and systems for flowable gap fill or flowable deposition techniques are described. In some implementations, a semiconductor fabrication chamber is described which is configured to maintain a semiconductor wafer at a temperature near 0° C. while maintaining most other components within the fabrication chamber at temperatures on the order of 5-10° C. or higher than the wafer temperature.

Fabrication of efficient TaON and Ta3N5 photoanodes for water splitting under visible light irradiation

Abstract: Efficient TaON and Ta3N5 photoanodes for water splitting were fabricated on conducting glass support (FTO). A necking treatment, which forms effective contacts between TaON (or Ta3N5) particles, afforded a significant increase in the photocurrent. Furthermore, loading of IrO2·nH2O nanoparticles as a cocatalyst for water oxidation improved the photocurrent of the TaON (or Ta3N5) photoanode. The incident photon to charge carrier efficiencies (IPCEs) of the TaON and Ta3N5 photoanodes were calculated to be ca. 76% at 400 nm and ca. 31% at 500 nm, respectively, at 1.15 V vs. reversible hydrogen electrode (RHE) in aqueous Na2SO4 solution. Overall water splitting into H2 and O2 under visible light was demonstrated using an IrO2·nH2O-loaded TaON (or Ta3N5) photoanode combined with a Pt electrode under an externally applied bias (TaON: > 0.6 V, Ta3N5: > 1.0 V).

3D lithium ion batteries{from fundamentals to fabrication

Abstract: 3D microbatteries are proposed as a step change in the energy and power per footprint of surface mountable rechargeable batteries for microelectromechanical systems (MEMS) and other small electronic devices. Within a battery electrode, a 3D nanoarchitecture gives mesoporosity, increasing power by reducing the length of the diffusion path; in the separator region it can form the basis of a robust but porous solid, isolating the electrodes and immobilising an otherwise fluid electrolyte. 3D microarchitecture of the whole cell allows fabrication of interdigitated or interpenetrating networks that minimise the ionic path length between the electrodes in a thick cell. This article outlines the design principles for 3D microbatteries and estimates the geometrical and physical requirements of the materials. It then gives selected examples of recent progress in the techniques available for fabrication of 3D battery structures by successive deposition of electrodes, electrolytes and current collectors onto microstructured substrates by self-assembly methods.

Laser fabrication of large-scale nanoparticle arrays for sensing applications.

Abstract: A novel method for high-speed fabrication of large scale periodic arrays of nanoparticles (diameters 40-200 nm) is developed. This method is based on a combination of nanosphere lithography and laser-induced transfer. Fabricated spherical nanoparticles are partially embedded into a polymer substrate. They are arranged into a hexagonal array and can be used for sensing applications. An optical sensor with the sensitivity of 365 nm/RIU and the figure of merit of 21.5 in the visible spectral range is demonstrated.

Strategies for the Fabrication of Porous Platinum Electrodes

Abstract: Porous platinum is of high technological importance due to its various applications in fuel cells, sensors, stimulation electrodes, mechanical actuators and catalysis in general. Based on a discussion of the general principles behind the reduction of platinum salts and corresponding deposition processes this article discusses techniques available for platinum electrode fabrication. The numerous, different strategies available to fabricate platinum electrodes are reviewed and discussed in the context of their tuning parameters, strengths and weaknesses. These strategies comprise bottom-up approaches as well as top-down approaches. In bottom-up approaches nanoparticles are synthesized in a fi rst step by chemical, photochemical or sonochemical means followed by an electrode formation step by e.g. thin fi lm technology or network formation to create a contiguous and conducting solid electrode structure. In top-down approaches fabrication starts with an already conductive electrode substrate. Corresponding strategies enable the fabrication of substrate-based electrodes by e.g. electrodeposition or the fabrication of self-supporting electrodes by dealloying. As a further top-down strategy, this review describes methods to decorate porous metals other than platinum with a surface layer of platinum. This way, fabrication methods not performable with platinum can be applied to the fabrication of platinum electrodes with the special benefit of low platinum consumption.

Direct Laser Writing of 3D scaffolds for neural tissue engineering applications

Abstract: We report on the fabrication of high resolution 3D scaffolds of polylactide-based materials using direct laser writing and we explore their use as neural tissue engineering scaffolds.

Stretchable inorganic-semiconductor electronic systems.

Abstract: Electronic and optoelectronic semiconductor components are the building blocks of modern instrumentation and equipment for sensing, computation, display, and communication. Systems incorporating these components are typically made on mechanically rigid printed circuit boards (PCBs). These systems can also be built on polymer-based fl exible PCBs, [ 1 ] which offer a bending radius of several centimeters about a single axis but are subject to fracturing from excessive bending or fatigue strain. Systems that are highly bendable (millimeter scale), stretchable, conformable to any surface topology, and mechanically insensitive to fatigue strain would greatly expand the application space of electronics. For example, in medicine there is a need for electronics to conform to and deform with the human body [ 2 ] to perform accurate diagnosis and deliver therapy. Other application spaces include renewable energy, [ 3,4 ] robotics, [ 5 ] military, [ 6 ] and lighting. [ 7 ] These applications have motivated research in fl exible and/or stretchable organic electronics [ 6 , 8–9 ] and inorganic electronics assembled on stretchable substrates. [ 2,4 , 7 , 10 ] One approach to building stretchable inorganic electronics is to connect thin electronic components together with stretchable spring-like metal interconnects and embed the entire interconnected structure into a stretchable (rubber) substrate. [ 2–3 , 7 ] Whereas prior work based on this approach used custom microfabrication of the electronic components and interconnects, here we present a process that uses commercially available electronic components and fl ip-chip bonding processes. Therefore, this fabrication process is a platform that can be used without modifi cation to create stretchable electronic systems incorporating any set of electronic components. As a demonstration, we fabricated stretchable light-emitting diode (LED) arrays containing up to 50 LEDs and show that the arrays can survive repeated stretching of 90 000 cycles and also tightly conform to a human thumb tip. The general concept behind the fabrication process is to separately manufacture the electronic components and the stretchable interconnects, then combine them using fl ip-chip bonding technology. We term this process “CINE” (combination of interconnects and electronics). Specifi cally, the process involves three steps: 1) the fabrication of metal contact pads and stretchable interconnects using standard microfabrication techniques; 2) transfer printing the contact pads and stretchable interconnects to a stretchable substrate using dissolvable adhesives as the intermediate transfer material; and 3) fl ip-chip bonding the electronic components onto the metal contact pads using anisotropic conductive fi lm (ACF). A detailed description of the fabrication process is presented in the Experimental Section. Figure 1 shows a stretchable LED array fabricated with this process. The stretchable LED array consists of ten pairs of gold contact pads, connected by serpentine-shaped metal interconnects. The interconnects are fully encapsulated in polyimide, whereas the contact pads have openings to allow electrical contact. Five blue and fi ve red LEDs were fl ip-chip bonded to the pairs of contact pads (in opposing polarities so the array can be powered with either a positive or negative voltage bias). The array was made on a silicone substrate with an elastic modulus of 10 kPa (we used the material EcoFlex made by Smooth-On Inc.). When the array is stretched, the serpentine-shaped interconnects deform to accommodate most of the strain, minimizing the strain seen by the LEDs and allowing the LEDs to maintain their optoelectronic properties (Figure 1 c,e). When the substrate is stretched, the interconnects accommodate strain via out-of-plane buckling as well as lateral deformation; this out-of-plane deformation is possible because the EcoFlex substrate is extremely compliant. We measured the resistance of individual interconnects while being stretched and found no signifi cant change in electrical resistance. To test the mechanical robustness of the arrays, we repeatedly stretched them in the length-wise direction using a mechanical actuator (additional details are provided in the Supporting Information). In the initial state, the array was without any strain, and we measured the distance between two adjacent LEDs as L 0 . When the array was fully stretched, we remeasured the distance between the two adjacent LEDs as L 1 . We defi ne the strain as ( L 1 – L 0 )/ L 0 . With a peak stretching strain of 67%, the arrays survived up to 90 000 stretching cycles (at an oscillating frequency of 1 Hz). With a peak stretching strain of 200%, the arrays survived up to 5000 cycles. We determined the failure mechanism to consistently be fracture–breakage of the serpentine interconnects near the contact pads used for powering the array. These contact pads were too large, at about 1 cm 2 in size, and created regions of high localized strain around their edges. The interconnects connecting adjacent LEDs never failed and neither did the fl ip-chip bonds made between the LEDs and the contact pads. Therefore, we expect the mechanical robustness of the arrays to dramatically increase simply by redesigning the end-most contact pads to be smaller by a factor of about four. To examine the electrical robustness, we measured the current-voltage ( I – V ) relation of an LED array prior to being stretched, after being stretched 1000 cycles, and after being stretched 10 000 cycles. We found no signifi cant variation in the I – V characteristics; the results are presented in Figure 2 a. We also measured the current fl owing through an array of 15 LEDs (arranged as three parallel sets of fi ve LEDs in-series), biased at 20 V. The current fl ow was a constant 93 mA as the

High-Sensitivity Strain Gauge Based on a Single Wire of Gold Nanoparticles Fabricated by Stop-and-Go Convective Self-Assembly

Abstract: High-sensitivity strain gauges based on single wires of close-packed 14 nm colloidal gold nanoparticles are obtained by a novel variant of convective self-assembly (CSA). This CSA mode named stop-and-go CSA enables the fabrication of nanoparticle wires only a few micrometers wide, separated by distances that can be easily tuned over tens to hundreds of micrometers. Nanoparticle wires are obtained in a single step by direct deposition of nanoparticles from suspensions onto flexible polyethylene terephthalate films, without any lithographic prepatterning. When connected between two electrodes, such single nanoparticle wires function as miniature resistive strain gauges. The high sensitivity, repeatability, and robustness demonstrated by these single-wire strain gauges make them extremely promising for integration into micro-electromechanical systems or for high-resolution strain mapping.

Room-temperature fabrication of ultrathin oxide gate dielectrics for low-voltage operation of organic field-effect transistors.

Abstract: Organic fi eld-effect transistors (OFETs) are attractive building blocks for low-cost electronic devices such as radio-frequency identifi cation (RFID) tags, sensors, electronic paper, and backplane circuits for active-matrix displays. [1–6 ] Low-voltage operation of OFETs is necessary for practical applications, hence the need to develop gate dielectrics with a high areal capacitance. [ 7 , 8 ]

A first report on the fabrication of vertically aligned anatase TiO2 nanowires by electrospinning: Preferred architecture for nanostructured solar cells

Abstract: Higher performance is expected in electronic devices that utilize metal oxide semiconductors in vertical architecture owing to the direct and effective electron transport. Producing anatase phase vertical TiO2 nanowires on conductive substrate has been challenging. Herein we demonstrate for the first time not only the facile fabrication of vertical arrays of anatase TiO2 nanowires, but also fabricating the wires by using electrospinning method. Firstly aligned nanofiberous TiO2 ribbons were produced by electrospinning and then erected to vertical nanowires after the post-treatment. As-produced vertical ceramic TiO2 nanowires possessed the area of 0.2 cm2 with wire diameter of 90 ± 30 nm, and height up to 27 μm. This approach can be a better alternative to the currently available methods like hydrothermal synthesis and template assisted fabrication as the diameter, height of the wires, and spacing between the wires can be effectively controlled by this method. With vertical nanowires of anatase phase TiO2 as photoelectrode in dye sensitized solar cells (DSSC), the solar-to-current conversion efficiency (η), short circuit current (Jsc), open circuit voltage (Voc), and fill factor (FF) were measured as 2.87% and 5.71 mA cm−2, 0.782 V, 64.2% respectively.

Innovative porous SiC-based materials: From nanoscopic understandings to tunable carriers serving catalytic needs

Abstract: Progress in developing a new class of catalyst carrier materials based on porous self-bonded silicon carbide (SiC) is reviewed. Since the demonstration of scalable economically viable β-SiC production process, innovative β-SiC-based materials with tunable physical and chemical properties were successfully synthesized. Silicon carbide has superior mechanical and thermal properties which, coupled to chemical inertness, avoids several of the problems inherent in the use of commercial oxide and carbon based supports and catalysts. High surface area SiC (35 m 2 /g) can now be easily synthesized, with unmatched mechanical properties, tailored pore size distribution (meso- and macroporous network and total pore volume up to 1 cm 3 /g) and at reasonable cost. It can be shaped directly into extrudates, (μ-) spheres, monoliths, open cell foams, 3D forms depending to the downstream applications. Furthermore, it can also be chemically modified for specific catalytic applications through the addition of promoters (oxides like Al 2 O 3 , TiO 2 , ZrO 2 , carbides and metals) rendering the fabrication simple and cost effective. In many respects, it combines the best properties of oxide and carbon based supports without suffering many of their disadvantages. New structured TiO 2 /SiC composites have been prepared and are expected to be the next photocatalytic media. The ability of the SiC material to be used as catalyst support will be illustrated in the present work by two exothermic reactions, namely the selective oxidation of trace amount of H 2 S and the Fischer–Tropsch synthesis. For this later, a direct comparison was also made with a traditional support, i.e. alumina.

Fabrication of Capacitive Micromachined Ultrasonic Transducers via Local Oxidation and Direct Wafer Bonding

Abstract: We present the successful fabrication of capacitive micromachined ultrasonic transducers (CMUTs) with an improved insulation layer structure. The goal is to improve device reliability (electrical breakdown) and device performance (reduced parasitic capacitance). The fabrication is based on consecutive thermal oxidation steps, on local oxidation of silicon (LOCOS), and on direct wafer bonding. No chemical-mechanical polishing step is required during the device fabrication. Aside from the advantages associated with direct wafer bonding for CMUT fabrication (simple fabrication, cell shape flexibility, wide gap height range, good uniformity, well-known material properties of single-crystal materials, and low intrinsic stress), the main vertical dimension (electrode separation) is determined by thermal oxidation only, which provides excellent vertical tolerance control ( <;10 nm) and unprecedented uniformity across the wafer. Thus, we successfully fabricated CMUTs with gap heights as small as 40 nm with a uniformity of ±2 nm over the entire wafer. This paper demonstrates that reliable parallel-plate electrostatic actuators and sensors with gap heights in the tens of nanometer range can be realized via consecutive thermal oxidation steps, LOCOS, and direct wafer bonding without chemical-mechanical polishing steps.

One-step maskless grayscale lithography for the fabrication of 3-dimensional structures in SU-8

Abstract: We propose a novel and simplified method to fabricate complex 3-dimensional structures in SU-8 photoresist using maskless grayscale lithography The proposed method uses a Digital Micro-mirror Device (DMD ® ) to modulate the light intensity across a single SU-8 photoresist layer Top and back-side exposure are implemented in the fabrication of original structures such as cantilevers, covered channels with embedded features and arrays of microneedles The fabrication of similar structures in SU-8 with other techniques often requires complex physical masks or the patterning of several stacked layers The effects of critical process parameters such as software mask design, exposure and developing conditions on the quality of 3-D structures are discussed A number of applications using bridges, cantilevers and micromixers fabricated using this methodology are explored

Ultrathin transparent Au electrodes for organic photovoltaics fabricated using a mixed mono-molecular nucleation layer

Abstract: A rapid, solvent free method for the fabrication of highly transparent ultrathin (similar to 8 nm) Au films on glass has been developed. This is achieved by derivatizing the glass surface with a mixed monolayer of 3-mercaptopropyl(trimethoxysilane) and 3-aminopropyl(trimethoxysilane) via co-deposition from the vapor phase, prior to Au deposition by thermal evaporation. The mixed monolayer modifies the growth kinetics, producing highly conductive films (similar to 11 Omega per square) with a remarkably low root-mean-square roughness (similar to 0.4 nm) that are exceptionally robust towards UV/O(3) treatment and ultrasonic agitation in a range of common solvents. As such, they are potentially widely applicable for a variety of large area applications, particularly where stable, chemically well-defined, ultrasmooth substrate electrodes are required, such as in organic optoelectronics and the emerging fields of nanoelectronics and nanophotonics. By integrating microsphere lithography into the fabrication process, we also demonstrate a means of tuning the transparency by incorporating a random array of circular apertures into the film. The application of these nanostructured Au electrodes is demonstrated in efficient organic photovoltaic devices where it offers a compelling alternative to indium tin oxide coated glass.

Reducing Transmission Losses in Hollow THz Waveguides

Abstract: Research on reducing material absorption in Terahertz (THz) waveguides has lead to development of guiding structures with transmission losses as low as 1 dB/m. Among waveguides that exhibit low loss at THz frequencies are the dielectric-lined hollow cylindrical metallic waveguides. Loss reduction in this waveguide is attributed to an ideal profile of the dominant hybrid HE11 mode. This mode profile also results in relatively low dispersion and very high coupling efficiency. In this contribution we overview properties of dielectric-lined hollow cylindrical metallic waveguides for THz waves, their design principles and the fabrication process. The impact of the mode profile on losses and dispersion at THz frequencies is confirmed experimentally by THz near-field imaging and THz time-domain spectroscopy and numerically by the finite element method.

Orthogonal processing: A new strategy for organic electronics

Abstract: The concept of chemical orthogonality has long been practiced in the field of inorganic semiconductor fabrication, where it is necessary to deposit and remove a layer of photoresist without damaging the underlying layers. However, these processes involving light sensitive polymers often damage organic materials, preventing the use of photolithography to pattern organic electronic devices. In this article we show that new photoresist materials that are orthogonal to organics allow the fabrication of complex devices, such as hybrid organic/inorganic circuitry and full-colour organic displays. The examples demonstrate that properly designed photoresists enable the fabrication of organic electronic devices using existing infrastructure.

Polymer microstructured optical fibers for terahertz wave guiding

Abstract: We outline the most recent technological advancements in the design, fabrication and characterization of polymer microstructured optical fibers (MOFs) for applications in the terahertz waveband. Focusing on specific experimental demonstrations, we show that polymer optical fibers provide a very flexible route towards THz wave guiding. Crucial incentives include the large variety of the low-cost and relatively low absorption loss polymers, the facile fiber preform fabrication by molding, drilling, stacking and extrusion, and finally, the simple fabrication through fiber drawing at low forming temperatures.

Zinc selenide optical fibers.

Abstract: Semiconductor waveguide fabrication for photonics applications is usually performed in a planar geometry. However, over the past decade a new field of semiconductor-based optical fiber devices has emerged. The drawing of soft chalcogenide semiconductor glasses together with low melting point metals allows for meters-long distributed photoconductive detectors, for example.[1,2] Crystalline unary semiconductors (e.g., Si, Ge) have been chemically deposited at high pressure into silica capillaries,[3,4] allowing the optical and electronic properties of these materials to be exploited for applications such as all-fiber optoelectronics.[5-7] In contrast to planar rib and ridge waveguides with rectilinear cross sections that generally give rise to polarization dependence, the cylindrical fiber waveguides have the advantage of a circular, polarization-independent cross section. Furthermore, the fiber pores, and thus the wires deposited in them, are exceptionally smooth[8] with extremely uniform diameter over their entire length. The high-pressure chemical vapor deposition (HPCVD) technique is simple, low cost, and flexible so that it can be modified to fill a range of capillaries with differing core dimensions, while high production rates can be obtained by parallel fabrication of multiple fibers in a single deposition. It can also be extended to fill the large number of micro- and nanoscale pores in microstructured optical fibers (MOFs), providing additional geometrical design flexibility to enhance the potential application base of the fiber devices.[9] Semiconductor fibers fabricated via HPCVD in silica pores also retain the inherent characteristics of silica fibers, including their robustness and compatibility with existing optical fiber infrastructure, thus presenting considerable advantages over fibers based on multicomponent soft glasses.

Solution‐Processed Organic Light‐Emitting Transistors Incorporating Conjugated Polyelectrolytes

Abstract: Improved performance of p-type organic light-emitting transistors (OLETs) is demonstrated by introducing a conjugated polyelectrolyte (CPE) layer and symmetric high work function (WF) source and drain metal electrodes. The OLET comprises a tri-layer film consisting of a hole transporting layer, an emissive layer, and a CPE layer as an electron injection layer. The thickness of the CPE layer is critical for achieving good performance and provides an important structural handle for consideration in future optimization studies. We also demonstrate for the first time, good performance solution-processed blue-emitting OLETs. These results further demonstrate the simplification of device fabrication and improved performance afforded by integrating CPE interlayers into organic optoelectronic devices.