T. Arakawa et al., IMPACT OF TUNNEL FILM OXYNITRIDATION ON BAND-TO-BAND TUNNELING CURRENT AND ELECTRON INJECTION IN FLASH MEMORY, JPN J A P 1, 36(3B), 1997, pp. 1351-1354
The impact of the use of oxynitride tunnel film on write, erase and re
ad operations of flash memories was investigated. We found that during
electron ejection from a floating gate into a drain, band-to-band tun
neling currents of flash memory cells with tunnel films having a high
degree of nitridation are two orders of magnitude smaller than that of
flash memory cells with oxide tunnel films. Consequently, higher-nitr
idation tunnel films improve the endurance characteristics of flash me
mory. However, during electron injection from a channel into the float
ing gate, Fowler-Nordheim tunneling gate currents of flash memory cell
s with higher-nitridation tunnel films are two orders of magnitude sma
ller than that of flash memory cells with oxide tunnel films. Moreover
, the threshold voltage of flash memory cells with oxynitride tunnel f
ilms is 0.24-0.48 V smaller than that of flash memory cells with oxide
tunnel films in read operations. These results can be explained by th
e modification of the electric field under oxynitride tunnel films due
to the formation of donor layers, which is induced by nitridation of
tunnel oxide films.