Stress induced leakage current limiting to scale down EEPROM tunnel oxide thickness

Abstract

The effects of thinning the FLOTEX EEPROM tunnel oxide on its reliability are investigated using capacitors and cell structures with oxide thickness ranging from 47 to 100 AA. A low-electric-field oxide leakage current is induced by charge injection stressing, and it increases with decreasing oxide thickness. Its conduction mechanism is found to be different from that caused by positive charge accumulation in that it has the opposite thickness dependence. A corresponding increase of charge loss in a write/erase (W/E)-cycled EEPROM cell is observed with decreasing oxide thickness in a room-temperature retention test. When oxide thickness is decreased, the maximum number of W/E cycles to tunnel-oxide breakdown decreases with the decrease in charge to breakdown of the negatively biased gate. For scaling down the EEPROM tunnel oxide, the most serious limiting factor is oxide leakage current induced by W/E cycling stress, resulting in data-retention degradation. >