Research for Mixed Signal Electronic Technologies: A Joint Initiative Between NSF and SRC - Three Dimensional Planar Device Integration for Mixed Signal Electronics

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This research effort is directed to providing a novel solution to the problems that occur with mixed-signal integration by using three-dimensional implementation of planar silicon transistors. The planned research will explore mixed signal technology's viability through research and development of device and process technology incorporating digital and analog planar transistor structures in different single-crystal device planes using techniques of single-crystal silicon layer transfer at low temperatures and by isolating the digital and analog functions with a ground-plane in between. This will be done while continuing to allow a large interconnection density in the horizontal and vertical direction for signal transmission. In order to make this feasible, transfer of thin (100's of nm) layers of single-crystal silicon on a planarized low roughness silicon dioxide surface at temperatures below 550 C has been demonstrated. Interconnections and ground planes based on doped poly-silicon and/or tungsten are incorporated in between the single-crystal silicon planes. The use of multiple planes, with oxide in between, also allows incorporation of other passive elements while limiting the increase in area together with a reduction in the loss effects of high frequencies. It is expected that this approach will reduce noise and cross-talk through the use of ground-planes and reduced coupling. This should provide additional freedom in the design of analog transistors, such as the metal-oxide semiconductor field-effect transistors in this project. This approach is also compatible with and can incorporate other developments in passive elements, such as high quality factor inductors, filters, etc., in back-end of the fabrication process. This research addresses significant issues for potential industrial applications , as analog and digital technologies can differ from each other in quite substantial ways because of the design requirements inherent to high frequency or low power. Maintaining low cost, the need for operation at low power, and the circuit and systems issues arising from interference between analog signals and digital signals are a few of these challenges.