An erase model for FAMOS EPROM devices

A physical model is presented which explains the various features of the UV erase process in FAMOS EPROM devices. An erase sensitivity factor is defined in this model, and correlated with experimental results. The erase sensitivity factor was found to be proportional to the floating-gate photoinjecting area, and inversely proportional to oxide thickness and total capacitance of the floating gate. Photoinjection of electrons from thin strips on the floating-gate edges are shown to be responsible for the charge removal from the floating gate. Quantum yields in the order of 10^-4were measured for this erase process and correlated with values found in the literature. In addition, theI-Vand spectral characteristics of photoinjected currents as low as 10^-15A from poly-Si to SiO2in FAMOS devices were measured and compared to data from Si-SiO2structures. Special features pertaining to the erase of a fully covered floating-gate FAMOS cell were investigated: the decrease in erase rate at lowDelta V_{t}is discussed, as well as the optical access to the floating gate in these devices. Based on experimental and theoretical grounds, hole injection is discounted as a possible erase mechanism in the structures investigated.