NEW POLYSILICON-OXIDE-NITRIDE-OXIDE-SILICON ELECTRICALLY ERASABLE PROGRAMMABLE READ-ONLY MEMORY DEVICE APPROACH FOR ELIMINATING OFF-CELL LEAKAGE CURRENT

Abstract

A new polysilicon-oxide-nitride-oxide-silicon (SONOS) electrically erasable programmable read-only memory (EEPROM) device, which eliminated off-cell leakage current, has been described and fabricated. The leakage current is easily encountered in metal-nitride-oxide-silicon (MNOS)-type EEPROMs. Two parasitic transistors, which are in parallel with the desired variable V(t) cell, are responsible for the leakage current. We demonstrated that the parasitic transistors are caused either by the nearly constant-threshold-voltage parasitic transistors surrounding the active region or by the ''fringing effect'' in poly-Si gate edges. The on-state and off-state I-V curves of the cell are shown and compared with those of two other different devices. The results reveal that the off-cell leakage current, which is observed in the other two devices, is completely eliminated in the proposed cell.