Integrated circuits incorporating thin-film active and passive elements

The thin-film field-effect transistor (TFT) provides the active element for complex integrated circuits deposited upon an insulating substrate. N-type transistors are obtained with evaporated layers of cadmium sulfide or selenide and p-type transistors with evaporated tellurium. Switching speeds of less than 4 nsec and gain-bandwidth products of greater than 30 Mc are observed with polycrystalline films of cadmium sulfide. Oscillations at frequencies up to 74 Mc have been noted. Significant improvements in the life and stability of the coplanar-electrode TFT have been obtained by encapsulation. A 30-stage completely integrated thin-film scan generator incorporating 60 TFT's, 30 diodes, 60 resistors and 30 capacitors has been designed. The novel circuit, whose operating characteristics resemble those of a shift register, is deposited by evaporation using movable metal masks controlled from outside the vacuum system. In one unit 28 consecutive stages were operated for nearly 700 hours. Laboratory models of the scan generator are being used to drive the address strips in experimental solid-state image-sensor panels.