New writing mechanism for reliable SONOS embedded memories with thick tunnel oxide

This paper describes a new low-cost non-volatile embedded memory option for sub-100 nm CMOS processes, based on the SONOS (silicon-oxide-nitride-oxide-silicon) concept. The retention issue inherent to SONOS memories was solved by increasing the thickness of the tunnel oxide from 2 nm to 4-6 nm which is sufficient for operation temperatures up to 100degC. Because of the thicker tunnel oxide, the conventional way of erasing SONOS memory cells by means of hole tunneling can not be used anymore; therefore, a new writing mechanism, punch-through assisted hot hole injection, was developed. This mechanism has a high write speed (~100 mus) at moderate voltages (absolute biases are below 5-6 V). Thanks to these low operation voltages, no dedicated high-voltage transistors are needed, thus reducing the integration costs of the memory significantly.