Data storage in NOS: lifetime and carrier-to-noise measurements

Charge trapping in thin films of silicon nitride has long been studied for use as a nonvolatile semiconductor memory. Recently, this technology has been combined with scanned probe technologies with the sharp probe tip serving as the upper electrode in a Si₃N₄-SiO₂-Si (NOS) structure. By applying a voltage pulse between the tip and silicon substrate, charge carriers can be made to tunnel through the oxide and be trapped in the nitride. It has been proposed that such a system could be used as a high density data storage device. We have explored some of the issues related to such an application, including data lifetime and data rates. In high temperature aging studies, no sign of charge spreading was seen after 9 months at 150°C. From the logarithmic nature of the charge decay, we predict that the initial written charge should have a lifetime in excess of 30 years at 150°C. At a data rate of 500 kHz, a carrier-to-noise ratio (CNR) of approximately 60 dB in a 5-kHz bandwidth was demonstrated. A model based on the presence of trapped charge in oxide or nitride is used to explain a 45-dB discrepancy between the calculated and measured CNR