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.<
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