The variable threshold transistor, a new electrically-alterable, non-destructive read-only storage device

A memory element has been developed that has the structure of a typical silicon planar p-channel enhancement insulated-gate field-effect transistor (IGFET). The information is stored by setting the threshold voltage of the IGFET to a high or low value. Interrogation is accomplished by applying a gate voltage intermediate to the threshold voltage extremes. Current will flow between source and drain if the recorded threshold voltage is less negative than the interrogating gate voltage; none will flow if the recorded threshold voltage is more negative. A high (negative) threshold voltage is written by applying a pulse of -50 v or higher for a duration of 1 msec or less between gate and substrate. A low threshold voltage is similarly obtained with positive 50 v pulse. The persistence of stored information has been demonstrated for periods of at least several months.