Thin Film Ferroelectric–Photoconductor Memory Device

The ferroelectric–photoconductor (FE–PC) device consists of a transparent electrode on a photoconductor covering a ferroelectric layer on a conductive substrate. When light is directed onto a spot on the photoconductor while a voltage is applied, the photocurrent will switch the corresponding spot of the ferroelectric into an information storage state determined by the polarity of the applied voltage. Binary information has been stored in such devices for days at densities approaching a million bits per square inch with switching speeds of a few tens of microseconds at light exposures only an order of magnitude greater than required by AMU standard microfilm. To achieve this performance, the photoconductor and ferroelectric must be about 1 μm thin and Schottky barriers must exist on both surfaces of the photoconductor film. These barriers prevent the disturbing of stored information by space-charge-limited currents in the unilluminated region of the device while permitting pulsed photocurrents with gain greater than unity at the light-addressed spot.