BE-SONOS: A bandgap engineered SONOS with excellent performance and reliability

Abstract

A bandgap engineered SONOS with greatly improved reliability properties is proposed. This concept is demonstrated by a multilayer structure of O1/N1/O2/N2/O3, where the ultra-thin "O1/N1/O2" serves as a non-trapping tunneling dielectric, N2 the high-trapping-rate charge storage layer, and O3 the blocking oxide. The ultra-thin "O1/N1/O2" provides a "modulated tunneling barrier" - it suppresses direct tunneling at low electric field during retention, while it allows efficient hole tunneling erase at high electric field due to the band offset. Therefore, this BE-SONOS offers fast hole tunneling erase, while it is immune to the retention problem of the conventional SONOS. With a N <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -poly gate, we achieve self-convergent erased Vt ~3 V, suitable for NOR flash application. On the other hand, by using a P <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -poly gate, a depletion mode device (Vt < 0) is obtained, and a very large memory window (> 6 V) is achieved, ideal for MLC-NAND application. Excellent performance and reliability for both applications are demonstrated. Furthermore, with this simple structure and no new materials BE-SONOS is readily manufacturable