 It was improved to +12 V by PMOS-based MNOS (metal-nitride-oxide-semiconductor) structure.By the early 1980s, polysilicon NMOS-based structures were in use with operating voltages under 20 V. By the late 1980s and early 1990s PMOS SONOS structures
were demonstrating program/erase voltages in the range of 5–12 volts.On the other hand, in 1980, Intel realized highly reliable EEPROM with double layered polysilicon structure, which is named "FLOTOX", both for erase and write cycling endurance and for data retention term.