Degradation of tunnel-oxide floating-gate EEPROM devices and the correlation with high field-current-induced degradation of thin gate oxides

摘要

In the past it has been assumed that the behavior of MOS transistors and thin-oxide floating-gate memory cells during high field stress can be predicted using experimental results obtained on capacitors. Here, it is shown that, due to incorrect extrapolation of the results, important memory degradation phenomena, such as window opening, are prone to misinterpretation. The results of a study on the degradation of tunnel-oxide floating-gate EEPROM devices, making use of the charge-pumping technique in combination with threshold voltage window degradation measurements, are reported. Contacted floating-gate transistors were used to study the effect of Fowler-Nordheim tunneling on thin-oxide gate dielectrics. Different types of floating-gate transistors were subjected to different degradation conditions. By comparing the experimental results with those of a theoretical study of the influence of trapped oxide charges on injection current and threshold voltage, it is possible to explain all measured degradation characteristics unambiguously.