A new method to extract gate coupling ratio and oxide trapped charge in flash memory cell

Abstract

A new method to obtain the gate coupling ratio ( α g) and oxide trapped charge ( Q ox) as a result of cycling in flash memory cells is described here. Three cells with an equivalent physical structure but different erase characteristics are measured. The threshold changes versus erase times are fitted to the charge removal rate calculated based on Fowler–Nordheim (FN) tunneling and the capacitive relations among all nodes. The extracted α g is independent of technologies and this method is particular useful when the profile of the floating gate is not traditionally rectangular owing to advanced processes such as trapezoidal poly etch or a poly-spacer addition on the floating gate sidewall. The Q ox can also be determined once α g is extracted.