Atmos—An electrically reprogrammable read-only memory device

An adjustable threshold MOS (Atmos) transistor is described that can be used as an electrically reprogrammable read-only memory by changing the charge content of a floating polysilicon gate. This floating gate is charged negatively (write) by means of a nonavalanche mechanism and charged positively (erase) by the avalanche breakdown of source or drain junction and subsequent hole injection into the oxide. The write time is between 10 and 100 ms, the erase time on the order of 1 s. The charge retention of the floating gate is about 90 percent after storage for 1000 h at 125°C.