Thin film conductive memory effects applicable to electron devices

A 2-4 orders of magnitude sustained increase in the conductivity of cadmium sulfide thin films as a result of pulsed excitation with electron beams, light or electric field has been observed. This effect appears promising as the operating principle for several types of information storage and display devices. The increased conductivity which is roughly proportional to the excitation energy is substantially undiminished for many minutes, as long as the applied field is maintained. The effect is reversible in that the momentary application of a reverse electric field or removal of the field restores the film to its pre-excited low value of conductivity. Without excitation this low value of conductivity can be maintained for many minutes, and perhaps indefinitely. Previous reports on electron beam or light induced sustained conductivity changes in cadmium sulfide crystals have indicated that to restore the crystals to their pre-excited low values of conductivity it was necessary to heat-treat them. Even this treatment did not produce complete restoration of the characteristics. Data are presented which characterize the reversible sustained electron bombardment-induced conductivity (SEBIC) effect in cadmium sulfide films. Also, a theoretical model is sketched to explain the characteristics of the conductive memory effect in these thin films. The possible application of this effect to a high resolution meshless storage tube is briefly described. This device utilizes the SEBIC effect in place of the usual separate storage and control mechanisms for exciting an electroluminescent phosphor.