The reproducibility of cadmium selenide TFT's and their use in driver circuits

TFTs (thin-film transistors) based on cadmium selenide with silicon dioxide as the dielectric have been prepared by a relatively simple process with a maximum temperature of 400 degrees C. The devices have switching ratios of >10/sup 8/ for a 12-V gate swing with off currents of 10/sup -15/ A/ Square Operator of device which do not change with increasing negative gate voltage. The distribution of electrical properties of devices with channel lengths ranging from 5 to 20 mu m deposited over an area of 6 cm*6 cm has been measured. The devices can be operated with drain voltages in excess of 150 V. Their properties are shown to be reproducible from run to run, and to the first approximation independent of channel length and width, with mobilities in excess of 200 cm/sup 2/-V/sup -1/-s/sup -1/ and a threshold voltage between 3 and 4 V. Preliminary work has commenced on simple circuit elements which have been designed without the benefit of device modeling or circuit simulation, using 8- and 12- mu m channel length devices. Oscillators having an 8- mu m channel length ring have been fabricated which operate at 50 ns per stage. Shift registers with a pull-up to pull-down ratio of 1:5 and 12- mu m channel length have a large amplitude output waveform at a clock rate of 5 MHz.