Use of random telegraph signal as internal probe to study program/erase charge lateral spread in a SONOS flash memory

A novel random telegraph signal (RTS) method is proposed to study the lateral spread of injected charges in program/erase of a NOR-type SONOS flash memory. The concept is to use RTS to extract an interface trap position and to detect a local potential variation near the trap due to injection of program/erase charges. By using this method, we find that CHISEL program has a broader charge distribution than CHE program. A mismatch of CHE program electrons and band-to-band erase holes is observed directly from this method.