Characterization of SONOS oxynitride nonvolatile semiconductor memory devices

Abstract

We present results on scaled silicon–oxide–nitride–oxide–silicon (SONOS) nonvolatile semiconductor memory devices with oxygen-rich ‘oxynitride’ charge storage layers. SONOS devices are designed specifically for high-density EEPROMs operating at high temperatures. We describe scaling considerations and process optimization to achieve low-voltage operation (+7 V write for 2.5 ms/−7 V erase for 7.5 ms) with 10-year retention at 150 °C. Memory transistors are programmed, erased, and read at elevated temperatures in order to observe thermal excitation of electrons from traps in oxynitride charge storage layers. The density of traps in the oxynitride is extracted using charge decay rates of programmed transistors at elevated temperatures. Trap density profiles for oxynitride films are compared with trap density profiles for silicon-rich nitride films.