HIGH-VOLTAGE THIN-FILM TRANSISTORS MANUFACTURED WITH PHOTOLITHOGRAPHY AND WITH TA2O5 AS THE GATE OXIDE

Thin film transistors (TFTs) are usually manufactured by evaporation through masks which require frequent cleaning. This paper describes a process based on photolithography and chemical etching which avoids this interruption to manufacture. The usual gate oxide Al2O3 was replaced by anodized Ta2O5 which provided both a larger dielectric constant εr and an increased electric field strength of more than 3×105 V mm-1. Thus the TFTs operated at up to more than 100 V. The larger εr increased the transconductance. Anodization and chemical etching introduced contamination which was, however, removed by sputter etching prior to evaporation of the semiconductor CdSe. Annealing the semiconductor at 300°C for 2 h considerably improved its quality. The characteristics of the new TFTs fully meet the specifications for addressing displays. © 1979.