POLYCRYSTALLINE SILICON THIN-FILM TRANSISTORS

During the past decade there has been a rapid growth of interest in po ly-Si for the active device layer in thin film transistors (TFTS) for active matrix flat-panel displays. Whilst the early work, demonstratin g the high carrier mobility of these devices, employed processing temp eratures of similar to 1000 degrees C and quartz substrates, this was soon followed by the investigation of lower-temperature processes whic h were compatible with the use of glass substrates. Some of the key as pects of this work are reviewed in this article: the preparation of th e material by direct deposition and by crystallization from a-Si precu rsors, the characterization of the defect-induced trapping states with in the material and their passivation, and the present understanding o f the TFT leakage current mechanisms. This work is put into the contex t of the requirements for active matrix liquid-crystal displays, and, with the understanding and control of poly-Si which has been achieved to date, its application in this area can be expected to increase rapi dly in the coming years.