High performance a-Si:H thin film transistors based on aluminum gate metallization

We present a systematic study of the sputter deposition conditions for aluminum thin films employed as gate metallization for high performance a-Si:H thin film transistors (TFTs). Here, we vary sputtering parameters such as deposition temperature, process pressure, and power, all of which have a strong bearing on the surface roughness of the film, including hillock generation induced by thermal processing. For example, at a low deposition temperature (30 degrees C) and a low process pressure (5 mTorr), the surface roughness appeared to be significantly reduced. Transistors with gate metallization deposited under these conditions show a low leakage current (similar to 10 fA), an ON/OFF ratio better than 10(8), and a mobility of 1.1 cm(2)/V s, in contrast, films deposited at 150 degrees C and 10 mTorr, yield a degradation in mobility to 0.77 cm(2)/V s and an increase in leakage current to 1 pA, caused by the high interface roughness of the TFT channel due to hillock formation on the Al gate. (C) 2000 Elsevier Science Ltd. All rights reserved.