Optimization of Program Threshold Window from Understanding of Novel Fast Charge Loss in Nonvolatile Memory

This paper describes and discusses intensively the charge loss characteristics in the stacked-gate memory device with interpoly oxide-nitride-oxide (ONO) dielectric at elevated temperatures. There exist two distinct phases in the charge loss characteristics. The dominant mechanism in the first phase can be described as the charge transport in the nitride layer. The second phase is dominated by effective thermionic emission effect from the stacked gate system. A linearly proportional relationship is also observed between normalized charge loss in the first phase and initial threshold voltage shift. Due to the fast charge loss rate, the charge loss in the first phase governs the threshold instability of the stacked-gate device. A method to determine the programming window for better threshold voltage stability based on charge loss in first phase is proposed.