Electronic Devices on Plastic Substrates

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In recent years. new applications such as large area conformal displays, multi-color organic displays. fault-tolerant terra-byte memories, large area solar cells, conformal electronic sensors for biological applications etc. have demanded that active electronic devices be grown on plastic films. With the exception of organic LED's, almost all such devices use amorphous Si as the active materiaL However, a-Si material suffers from low carricr mobilities, and poor stability. Therefore, the ability to grow thin film electronic devices in cri stalline Si-based materials on plastic substrates may provide both better performance and greater stability in these applications. Such a development would also allow one to grow c-Si devices on polyimide layers, which are widely used as planarizing insulators in standard c-Si wafer-based device technology, and thereby allow three dimensional device architecture. The development of thin film crystalline devices would be very useful for efficient integration of organic LED's with driver circuits on a polymer substrate. It is the objective of this proposal to develop hi2h performance crystalline Si- based electronic devices on plastic substrates.The proposed work is based on our recent success, under a NSF SGER grant, in being able to deposit high quality c-Si films on polyimide. and making proof-of-concept c-Si solar cells in them. We plan a comprehensive research project to improve the electronic properties of the film and to make novel TFT devices in thcse films. The project embraces the following tasks:o Control of crystallinity of the films by using reactive ion beams of H, Cl and F during growth in a novel, well-controlled ECR reactor.o Systematic investigation of structural properties by using Raman, TEM. SEM and x-ray diffraction.o Systematic investigation of electronic properties by using DLTS, Hall measurements and capacitance spectroscopy of defect levels.o Study of growth of stable field-oxides (gate insulators in MOS devices) by controlled plasma-oxidation with F and 0 and study of oxide/semiconductor interfaces, using capacitance and conductance techniques.o Fabrication of horizontal TFT devices.o Measurement of properties of these devices, including channel mobility and stability after charge pumping and charge injection.o Fabrication of novel proottof. concept vertical TFT which may not be affected by grain boundaries.The effort relies on using our past experience in material growth, material analysis, device fabrication and device design and analysis. The facilities exist to carry out this work. A significant educational component is planned, including graduate student and undergraduate student involvement. The undergraduate students will be drawn from our on-going NSF-REU site program. A significant minority student research experience is also planned. Women students, particularly at the high school level, will also participate in the program. The program will lead to development of new courses in this area, thereby integrating research and education. The project has a potentially significant impact on industry. We have planned a strong collaboration with a company, Micron technologies, which is expected to provide a cash grant for supporting additional graduate students in this research area.