Surface Mobilities in Laser-Processed Polysilicon Films

Abstract

ABSTRACTSurface mobilities in laser-processed polysilicon films were measured using silicon-gate n-channel thin-film transistors of varying dimensions. The apparent surface mobility inferred from transconductance measurements was found to be a decreasing function of channel length. For very short (~0.3/µm) channels, this mobility approaches the surface mobility of identical devices fabricated on bulk silicon. Furthermore, the temperature dependence of the surface mobilities in polycrystalline and bulk films was found to be identical.A novel EBIC technique was employed to examine the surface potential of transistors in operation. These measurements indicate a high degree of spatial nonuniformity in the inversion layer of polycrystalline films arising from the grain boundary region. A simple model of the transistors is presented which explains the geometry dependent surface mobility and its temperature dependence.