Detailed observation of small leak current in flash memories with thin tunnel oxides

This paper describes a method for measuring the small current through the oxides on the order of 10/sup -20/ A or less using a floating gate MOSFET and the application results on flash memories with thin tunnel oxides. The method is based on an accurate measurement of the threshold voltage of a floating gate MOSFET with no charge in the floating gate. We applied this method to flash memories to investigate the leak current behavior through thin tunnel oxides with very small areas (<0.16 /spl mu/m/sup 2/), and found some anomalous phenomena which cannot be observed from SILC measurements if we use large capacitors. We also discuss possible mechanisms to explain the phenomena.