Patent ID: 6552387
Filing Date: 2003-04-22
Classification: G11C,H01L

Abstract:
A method of programming, reading, and erasing an electrically erasable programmable read only memory (EEPROM) cell, said memory cell having a source and a drain with a channel therebetween and a gate above said channel but separated therefrom by a non conducting charge trapping material sandwiched between first and second silicon dioxide layers, said method comprising:programming in a forward direction by injecting electrical charge into said charge trapping material utilizing hot electron injection for a sufficient time that an amount of electrical charge becomes trapped asymmetrically in a charge trapping region of said charge trapping material close to said drain, said electrical charge being injected until the threshold voltage of said cell reaches a predetermined level when said memory cell is read in a direction opposite from which it was programmed, said amount of charge being small enough to be generally fully erased during an erase operation, said injecting being caused by applying programming voltages to said drain and said gate and grounding said source; reading in said direction opposite from which it was programmed by applying read voltages to said source and said gate and grounding said drain, and subsequently sensing whether or not current flows between said memory cell source and drain; and erasing said memory cell by applying erasing voltages to said gate and said drain so as to cause electrons to be removed from said charge trapping region.