Access resistor modelling for EEPROM’s retention test vehicle

• Access resistor models explain maximum drain-source current in a CAST test vehicle.
• The threshold voltage shift is explained by the sub-threshold slope.
• Gate access resistor should have no effect on reading or programming.
• Model is helpful to quantify the extrinsic cells in retention tests.
• Memory lines inside array should not be longer than thousand cells per line.

The electrical characteristic of EEPROM’s retention test vehicle presents two unexplained abnormalities in comparison with an individual cell’s measurement: the maximum drain–source current value and threshold voltage shift. We propose a simple electrical model based on access resistors in order to explain this behaviour. The model is presented, an extraction process is proposed and simulation results are compared with measurements. Then the model is used in order to predict the effect of a sector programmed inside an all erased memory array in order to simulate the threshold voltage shift observed with extrinsic cells during retention tests.