A New Disturb Free Programming Scheme in Scaled NAND Flash Memory

Abstract

New programming scheme is proposed to improve the program disturb characteristics in NAND Flash memory named Program Disturb Free Scheme (PDFS), which is executed by removing excess electrons from the channel and source/drain into bit line or source line using drift-diffusion mechanism, and also by recombining electrons in the surface states with accumulated holes before programming. Thus, no excess electron exists in the program inhibit cell string during programming, thereby program disturb can be suppressed drastically. By measuring 8Gbit NAND Flash memory with 50nm technology node, almost no Vt shift was observed even applying 30 times over programming (partial programming) in 2bit/cell operation. This universally applicable innovation is independent from generation of design rule. Therefore, new operation has broken new ground for the cell device engineering, especially for sub-30nm NAND which has seriously narrowed program operation margin.