Towards a model linking tunnel oxide degradation to programming window closure in EEPROM cells

摘要

One of the main reliability problem in electrically erasable programmable read only memory (EEPROM) devices is the progressive closure of the programming window as the number of applied write/erase cycles is increased. This closure is qualitatively attributed to the build-up of fixed negative charge in the tunnel oxide during Fowler-Nordheim (FN) electron injection. Electron trapping induces FN current voltage shifts and consequently variations of the charge accumulated into the floating gate during one programming operation. In this work, we present an analytical quantitative model linking these shifts representative of oxide charging, to EEPROM cells threshold voltages in programmed states. This model is based on a simple electrical equivalent circuit and predicts a linear relationship between threshold and FN injection voltages shifts. The proportional constant is only dependent on the control gate-floating gate capacitive coupling ratio. Using a specific EEPROM-like test structure, the proposed model has been experimentally validated. (C) 2003 Published by Elsevier B.V. [References: 6]