 Chen of Fairchild Camera and Instrument published a paper detailing the invention of SONOS, a MOSFET technology with far less demanding program and erase conditions and longer charge storage.This improvement led to manufacturable EEPROM devices based on charge-trapping SONOS in the 1980s.In 1991, Japanese NEC researchers including N. Kodama, K. Oyama and Hiroki Shirai developed a type of flash memory that incorporated a charge trap method.