Novel soft erase and re-fill methods for a P/sup +/-poly gate nitride trapping non-volatile memory device with excellent endurance and retention properties

Abstract

This paper proposes a soft erase which is a short negative FN (Fowler-Nordheim) channel erase that can be performed after the hot-hole sector erase. By using a P/sup +/-poly gate, the gate injection is reduced and this soft erase produces an excellent self-converging property with desirable low V/sub T/, and it recovers both the hard-to-erase and over-erased cells. Since the hard-to-erase problem is solved by this soft erase, it can be combined with low-power programming methods such as CHISEL; more than 2 MB/s programming throughput is achieved, suitable for data Flash applications. Soft erase also possesses a strong electrical annealing effect to recover the hot-hole induced damages. Moreover, a shorter version of this soft erase method can be applied to the programmed state to eradicate shallow-level electrons and replace them with deep-level electrons (re-fill). Repeated "re-filling" of electrons results in a shifting of the trapped electron energy distribution to a "bluer" spectrum. Greatly improved endurance and retention properties are demonstrated by these new methods.