A 180-stage integrated thin-film scan generator

Experimental models of a 180-stage, thin-film scan generator suitable for digital scanning of an array of elements have been produced by evaporation of all components upon a glass substrate. The generator is a modified shift register, comprising 360-thin-film transistors (CdSe TFT's), 180 field-effect diodes, 360 resistors, and 180 capacitors. Output voltage pulses of two to four volts are obtained, with clock frequencies ranging from 12 kc/s up to 2 Mc/s. The complete circuit, including all active and passive elements, was deposited during one pump-down of the vacuum system. A wire grill having 480 wires per inch was used in combination with movable masks to define the patterns. Reproducibility of fabrication under laboratory conditions has been excellent. Seven out of eighteen recent experimental units were operable throughout all 180 stages. Units have been operated continuously on life test for more than 5000 hours at 85°C without failure of any stages. Successful operation of the entire generator requires all 1080 thin-film components to be free of short circuits and have operating characteristics within the range of tolerance of the circuit.