Radiation response of floating gate EEPROM memory cells

The effect of radiation on a floating-gate EEPROM (electrically erasable and programmable read-only memory) nonvolatile memory cell is determined experimentally and modeled analytically. The proposed model predicts the threshold voltage change resulting from radiation. A screen based on the initial `1´ state (excess electron) threshold voltage is shown to be necessary to assure data retention during irradiation. Techniques to increase radiation hardness are described. The hardness of floating-gate cells is shown to be limited to less than 100 krad(Si) for a fixed-reference sense amplifier. The use of a differential sense amplifier can increase this limit. Therefore, floating-gate memories should be useful for applications requiring low total doses