A NOVEL PROGRAMMING METHOD FOR HIGH-SPEED, LOW-VOLTAGE FLASH E(2)PROMCELLS

A novel flash E(2)PROM cell structure programmed by hot electron injec tion from the source and drain sides of a MOSFET is presented. The hot electrons are generated by Zener/avalanche breakdown of heavily doped reverse biased p(+)n(+) junctions at the source and drain. Two-dimens ional device simulations were used to investigate the effect of the p( +)n(+) doping concentrations on the programming time, and the required supply voltages. The cell performance was experimentally verified on test devices fabricated using a standard CMOS process how in which the n(-)LDD step was replaced with a p(+) boron implant with a doping lev el of similar to 1.8 x 10(18) cm(-3). A programming time of 6 mu s was obtained on test devices with a gate length of 3 mu m. With appropria te p(+) doping concentrations and submicron gate lengths, it is possib le to achieve a 3.3 V flash E(2)PROM cell with a programming time in t he order of 150 ns. The superior programming speed and low operating v oltages of the proposed flash E(2)PROM cell makes it suitable for a va riety of portable applications. Copyright (C) 1996 Elsevier Science Lt d.