A new route to macroelectronic backplanes, polycrystalline silicon on steel substrates: Materials, devices, circuits, and processing

Macroelectronics stands for microelectronics fabricated on large-area substrates and with low-cost processes. It is a fast growing field dealing with the interfaces between humans and machines, such as information displays, sensor arrays, etc. The conventional backplanes in these applications only contain the amorphous silicon addressing matrices, and drivers have to be fabricated separately, posing a barrier to further lowering of the cost.; This thesis describes a new route to macroelectronics backplane fabrication: polycrystalline silicon-on-steel. By utilizing the high temperature tolerance of steel, polysilicon thin film transistors and circuits can be fabricated on flexible and non-breakable steel with the uniform high performance required for drivers and switching matrices over large areas, and the polysilicon can be formed in very short time to fulfill the manufacturing speed requirement. Furthermore, the flexibility of steel makes it a potential candidate for roll-to-roll manufacturing, which is a low-cost process to substitute for today's one-plate manufacturing tools.; The polysilicon-on-steel process is explored starting with an investigation of substrate preparation, continuing with crystallization techniques to form polysilicon, the device fabrication process, and finishing with the fabrication of complementary metal-oxide-semiconductor polysilicon circuits.; The substrates were 0.2-mm thick steel foil coated with 0.5-μm thick SiO₂. We employed silicon crystallization times ranging from 6 hours (at 600°C) to 20 seconds (at 950°C). Thin film transistors (TFTs) were made in either self-aligned or non-self-aligned geometries. The gate dielectric was SiO₂ made by thermal oxidation or from deposited SiO₂. The field-effect mobilities reach 64 cm2/Vs for electrons and 22 cm2/Vs for holes. Complementary metal-oxide-silicon circuits were fabricated with self-aligned TFT geometries, and exhibit ring oscillator frequencies of 1 MHz. These results lay the groundwork for polycrystalline silicon circuitry on flexible substrates for large-area electronic backplanes.; This thesis also extends to the discussion and demonstration of some front-end macroelectronic concepts including electronics on curved surfaces and electronic textiles. Electronics on curved surfaces can be used for fabricating high-performance super compact detector arrays. Electronic textiles are promising approach to make sensitive skin, which will give machinery the intelligent ability to deal with unpredictable environments.; Finally, we propose some future work to improve the performance of polysilicon-on-steel transistors. The integration of frontplanes and backplanes is also proposed to show the feasibility of flexible displays based on polysilicon-on-steel process. We conclude by summarizing some key results from this research.