Design and analysis of general and travelling dielectrophoresis

This paper presents the simulation of general and travelling dielectrophoretic forces, as well as the movement of the particles in a sandwich structure micro-device. The electrode geometry of the micro device used for simulation is an interdigitated bar electrode. The simulation method used to solve the equations is based on the least square finite difference method (LSFD). The simulation first calculates all forces acting at any place in the chamber, with these forces the trajectory of a particle can now be proposed. All of the particles parameters like radius, voltage, initial height, etc can easily be changed and the simulation can be redone. With this continuous trial we receive different behavior of the particles and examine the relevancy of the different changes made. This detailed information about the influences of the parameters on the procedure in the micro-device can be used for the development of further micro-devices

Encapsulation for flexible electronic devices

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Design rules for IGZO logic gates on plastic foil enabling operation at bending radii of 3.5 mm

Findings obtained from bending experiments with mechanically flexible InGaZnO-based thin-film transistors are used to derive design rules for flexible InGaZnO-based n-channel metal-oxide-semiconductor logic circuits. Based on the developed design rules, flexible NAND gates, inverters, and five-stage ring oscillators are fabricated directly on free-standing plastic foils at temperatures ≤ 150 °C. Geometrically well-designed circuits operated at a supply voltage of 5 V are exposed to tensile mechanical strains, induced by bending, up to 0.72% without performance degradation. This corresponds to a bending radius of 3.5 mm. At the same time, increases in the rise time by a factor of ca 2 and reductions in the high and low output voltage levels by ca 10% and 50% have been observed for circuits with disadvantageous geometrical design. Ring oscillators designed to be operated under strain show an increase in oscillation frequency from 22.9 kHz (flat substrate) to 23.32 kHz (bending radius: 3.5 mm). This demonstrates the held-effect mobility increase in a-IGZO-based circuits under tensile mechanical strain. Long-term reliability is evaluated with 20000 cycles of repeated bending and reflattering without circuit failure

Crack prevention of highly bent metal thin films in woven electronic textiles

Recent smart textile fabrication methods that are aimed at increasing the integration of electronics with textiles have involved fabricating micro-electronic components directly at the yarn level. Our approach to creating smart textiles is to fabricate thin-film devices and interconnects on plastic strips to create ‘e-fibers’ and weave them into a textile using a commercial weaving machine. e-Fibers are exposed to bending radii as small as 165 μm during weaving. If patterned interconnect lines and device layers on the surface of the e-fiber are not designed correctly, they will crack due to the high strain and lose their electronic functionality. Brittle sensor and transistor device layers may be protected locally using rigid encapsulation materials, but cracking remains an issue for long metal interconnect lines which require flexibility. We investigated two strain-control methods to prevent the thin-film interconnect lines from cracking during weaving: (1) patterning the metal interconnect lines with a geometric design to slow propagation and merging of cracks and (2) encapsulation of interconnect lines to shift the deposited films to the neutral plain of the substrate. The mechanical behavior of interconnect lines exposed to tensile bending was studied by measuring the change in interconnect resistance versus bending radii ranging from 5 mm to 50 μm. The critical bending radius, XC, defined as the radius at which the normalized interconnect resistance changes to 1.1 (indicating the onset of film rupturing) was 150 μm for standard interconnect lines. Patterned interconnect lines had a radius XC of 115 μm while encapsulated interconnect lines never reached this critical bending radius and showed a maximum resistance change of 1.02 at 100 μm. These results show that it is possible to design interconnect lines with reduced cracking behavior when exposed to high strain during commercial weaving

Combining electronics on flexible plastic strips with textiles

Electronic textiles are an enabling technology for a variety of applications in health care, rehabilitation or sports. In this paper, three methods to combine flexible plastic strips with textiles are discussed. Flexible plastic strips serve as carriers for electronic devices. The first approach uses a roving frame to wrap flexible plastic strips with cotton fibers. For the second method, flexible plastic strips are woven into textiles using a narrow fabric loom and a rapier loom. In the third approach, flexible plastic strips are embroidered on a shuttle embroidery machine. Due to the flexible plastic strips, electronic devices mounted on the strips are exposed to strain with the potential to damage the electronics. For the three presented methods, strain on the surface of a flexible plastic strip is investigated: roving causes strain >25%, embroidery approximately 6% and weaving 15%. Weaving flexible plastic strips is investigated in more detail because it offers possibilities to embed thin-film devices, surface mount devices and integrated circuits into textiles. Conductive yarns within the textile are used to contact the electronics. Weaving flexible plastic strips is first applied to fabricate a textile patch with woven flexible plastic strips carrying thin-film temperature sensors. In a second textile patch, a flexible plastic strip carrying an accelerometer is woven in the weft direction and connected with conductive yarns in the warp direction. The textile-integrated accelerometer can have an angular deviation of up to 10° from the textile surface. Nevertheless, applications in rehabilitation and health care can benefit from textile-integrated accelerometers. © 2013, SAGE Publications. All rights reserved

Integration method for electronics in woven textiles

This paper presents a technology to integrate electronics at the thread level in woven textiles. Flexible plastic substrates are cut into stripes and serve as carriers for electronics, including ICs, thin-film devices, interconnect lines, and contact pads. These functionalized plastic stripes, called e-stripes, are woven into textiles. Conductive threads perpendicular to the e-stripes electrically interconnect the devices on the individual e-stripes. The integration of e-stripes and conductive threads into the woven textiles is compatible with commercial weaving processes and suitable for large-scale manufacturing. We demonstrate the technology with a woven textile containing five e-stripes with digital temperature sensors. Conductive threads interconnect the e-stripes among each other to form a bus topology. We show that the contacts between the conductive threads and the pads on e-stripes as well as the contacts between the temperature sensors and e-stripes withstand shear forces of at least 20 N. The integration of the temperature sensors into the textile increases the bending rigidity of the textile by 30%; however, it is still possible to obtain a textile-bending radii of <;1 mm. This technology seamlessly integrates electronics into textiles, thus advancing the field of smart textiles and wearable computing

Theoretical and experimental study of the bending influence on the capacitance of interdigitated micro-electrodes patterned on flexible substrates

Interdigitated electrodes are common structures in the fields of microelectronics and MEMS. Recent developments in flexible electronics compel an understanding of such structures under bending constraints. In this work, the behavior of interdigitated micro-electrodes when subjected to circular bending has been theoretically and experimentally studied through changes in capacitance. An analytical model has been developed to calculate the expected variation in capacitance of such structures while undergoing outward and inward bending along the direction perpendicular to the electrodes. The model combines conformal mapping techniques to account for the electric field redistribution and fundamental aspects of solid mechanics in order to define the geometrical deformation of the electrodes while bending. To experimentally verify our theoretical predictions, several interdigitated electrode structures with different geometries were fabricated on polymeric substrates by means of photolithography. The samples, placed in a customized bending setup, were bent to controlled radii of curvature while measuring their capacitance. A maximum variation in capacitance of less than 3% was observed at a minimum radius of curvature of 2.5mm for all the devices tested with very thin electrodes whereas changes of up to 7% were found on stiffer, plated electrodes. Larger or smaller variations would be possible, in theory, by adjusting the geometry of the device. This work establishes a useful predictive tool for the design and evaluation of truly flexible/bendable electronics consisting of interdigitated structures, allowing one to tune the bending influence on the capacitance value through geometrical design. (c) 2013 AIP Publishing LLC

Flexible self-aligned amorphous InGaZnO thin-film transistors with submicrometer channel length and a transit frequency of 135 MHz

Flexible large area electronics promise to enable new devices such as rollable displays and electronic skins. Radio frequency (RF) applications demand circuits operating in the megahertz regime, which is hard to achieve for electronics fabricated on amorphous and temperature sensitive plastic substrates. Here, we present self-aligned amorphous indium-gallium-zinc oxide-based thin-film transistors (TFTs) fabricated on free-standing plastic foil using fabrication temperatures . Self-alignment by backside illumination between gate and source/drain electrodes was used to realize flexible transistors with a channel length of 0.5 μm and reduced parasitic capacities. The flexible TFTs exhibit a transit frequency of 135 MHz when operated at 2 V. The device performance is maintained when the TFTs are bent to a tensile radius of 3.5 mm, which makes this technology suitable for flexible RFID tags and AM radios