A SV/3.3V-compatible Flash E2PROM cell with a 4OOns/7Ops programming time for embedded memory applications

Flash E2PROM devices which use an enhanced hotelectron injection mechanism for programming, have gained a lot of interest during the last few years [I-31. Indeed, these fast-programmable devices are viable candidates for SV-only and 3.3V-only applications. Most of these concepts however add considerable complexity to the processing technology through the inclusion of a third polysilicon layer [1,2] or a buried injector [3], which makes these devices unsuited for low cost Flash technology as required in embedded memory applications. The recently reported High Injection MOS (HIMOS) device [4,5] however combines fast SV-only programming features with a low development entry cost through the combination of a split-gate structure and a coupling capacitor which increases the channel hot-electron (CHE) injection efficiency by several orders of magnitude [6]. Additionally, the HIMOS concept exhibits an inherent immunity to soft-write and overerase effects. These unique features make this device into a very attractive candidate for embedded memory applications. The purpose of this paper is to show that submicrosecond 5Vonly programming can even be obtained for a minimum cell area of 16pm2 in a 0.7pn technology. To accomplish this, a virtual ground array (VGA) architecture is proposed. Moreover, the possibility for 3.3V-only HIMOS operation can already be considered as well in 0.7~ technology. 1. Device structure and operation