Electrical Contacts to Vertically Oriented Silicon Nano and Microdevices for Applications in Flexible Systems
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Electrical Contacts to Vertically Oriented Silicon Nano and Microdevices for Applications in Flexible Systems Mark Triplett, 1 2 3
2,1
Hideki Nishimura,
1,3
1
Matthew Ombaba, M. Saif Islam
1
Department of Electrical and Computer Engineering, University of California, Davis Department of Physics, University of California, Davis, California 95616, USA Microelectronic Device Science Laboratory, Nara Institute of Science and Technology, Japan
ABSTRACT Flexible devices utilizing crystalline semiconductor nano or microstructures materials are attractive for many applications. However, these materials are fabricated or grown in unusable forms for flexible systems due to their rigid crystalline mother substrates. We demonstrate a transfer printing technique for transferring vertical arrays of one-dimensional (1D) materials from mother substrates to flexible substrates with subsequent device fabrication steps to create flexible devices from these arrays. The transfer printing technique is based on vertical embossing of arrays of 1D materials into thermoplastic (Poly (methyl methacrylate) (PMMA)) transfer layers, while the device fabrication steps rely on encapsulation with insulating polymers and contact deposition. We investigated the use of flexible insulating layers like polydimethylsiloxane (PDMS) and polyurethane (PU) which are shown to be effective for encapsulation and contact isolation. Representative flexible resistive devices were created from these transferred arrays and insulating layers which showed a reversible tactile characteristic. Electronic characterization and flexibility testing was carried out to show the potential of these methods for enabling large-scale integrations of nano and microstructures into vertical and flexible packages. INTRODUCTION Flexible electronic devices incorporating crystalline semiconductors have been gaining considerable research attention owing to the popularity of nano- and micro-scale semiconductor materials. Devices in these flexible packages may enable many new applications where flexibility is a key characteristic including bio-compatible electronics, conformable sensors, or low-cost solar applications.[1] Crystalline semiconductor materials are the best active material option for electronics and solar applications, which has been widely demonstrated for decades by industry and the research communities. However, crystalline semiconductor materials are grown/etched on/from rigid substrates requiring a method to remove the materials from the growth substrate and transfer them to a flexible substrate. Many flexible device architectures have been demonstrated, both horizontal (2D) and vertical (3D), with vertical devices having distinct advantages, particularly for optical applications, due to the larger available absorption path.[1-4] Flexible devices pose a challenge for contact formation as the contacts must be formed either during or after a transfer method and these contacts must be robust during flexing,
twisting, bending and compression. A significant roadblock
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