Characteristics of interface-doped MNOS memory devices

The results of an investigation of the characteristics of MNOS memory devices are given in which the interface between the oxide and nitride was doped with a few monolayers of various refractory metals. In particular, write speeds of the order of microseconds could be obtained along with retention times which could be extrapolated to many decades. No temperature dependence could be found for the decay of stored charge between 77 K and 300°C, indicating that retention is normally dominated by Fowler-Nordheim back tunneling from the interface. Long time exposure to high gate voltages and write/erase cycling in excess of 1000 cycles sharply reduces the achievable memory window, and is accompanied by the copious generation of fast surface states, at least in p-channel devices.