A Nonvolatile Memory Overview

By Jitu J.Makmawa, Dr Deiter K.Schroder – Full Paper

Memory devices can be split into two main categories; volatile and nonvolatile. A nonvolatile memory device is a MOS transistor having a source, drain, control and floating gates. Nonvolatile memory cell can be further divided into floating gate Floating Gate Device and charge trapping. Floating gate structure is the most widely used structure in current memory device technology i.e EPROM, EEPROM and Flash.

In both floating gate and charge-trapping memories, the charges needed to program the memory cell, in order to change the memory state or the charge contents of NVM. Two main mechanism is widely used; FN tunneling and Channel Hot Electron Injection. There are two models that can be used to describe the gate current due to hot-electron injection. They are the lucky electron model and the effective electron temperature model.

In FN tunneling, tunnel oxide thickness have to be less than 12 nm whereas in the case of CHEI, the tunnel oxide thickness is not critical.

For the erasing, two commonly used methods are UV emission and FN tunneling. UV emission is currently used for erasing EPROM memory contents while FN tunneling commonly used in EEPROM’s and Flash’s.