Charge Defects in Low Temperature Silicon Nitride/Silicon Interfaces for Application in Computational Clothing and Electronic Textiles
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Date
2002-07-26
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Abstract
The purpose of this research has been to 1) explore materials prepared using plasma enhanced chemical vapor deposition (PECVD) for amorphous silicon thin film transistors (TFTs) fabricated on large area flexible polyimide substrates, and 2) develop new concepts to make smart fabrics for computational clothing using the flexible TFTs.
For item 1), silicon nitride films, as gate dielectric of TFTs, were deposited using various processing gases having different NH3/SiH4 gas ratio with constant temperature and various temperature at constant processing gas ratio. It was shown that as NH3/SH4 ratio increases, NH/SiH ratio increases. Apparent leakage current decreased but the flat band voltage was shifted with increasing NH/SiH in the films. It was proposed that the decrease in apparent leakage current with increasing NH/SiH ratio was related to charge screening effect as well as film improved insulating quality. The interface charge and bulk charge densities for SiNx films with different processing gas composition have been calculated. The interface charge density increases with increasing NH/SiH causing flatband shift and increasing total charge density. It was believed that the interface charge is generated by stress build up at Si/SiNx interface and increases with NH/SiH ratio. We found that as substrate temperature increases the NH/SiH ratio remains constant, the apparent leakage current increases and the flat band voltage shifts. Because the net total charge is compensated as substrate temperature changes, charge screening effects were believed to be less important than effects of composition change under the conditions studied. Interface charge density increased also with temperature. This was consistent with flat band voltage shift with temperature.
For item 2), amorphous silicon TFTs were formed successfully on large area polyimide substrate using back channel inverted staggered structure and novel masks design. Linear and saturation mobility are 0.026 and 0.059 cm2/V•s, respectively. To address TFTs into clothing, conductive thread contact was investigated. Finally, using novel method, we attempted to form an electronic NOR gate using thin film transistors on polyimide, woven directly into a cotton fabric.
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Keywords
Silicon Nitride, Interface charge, Thin film transistor, Electronic textile
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Degree
MS
Discipline
Chemical Engineering
