Band-to-band tunneling induced substrate hot-electron (BBISHE) injection: a new programming mechanism for nonvolatile memory devices

A highly efficient gate current injection mechanism, band-to-band tunneling induced substrate hot electron (BBISHE) injection, is studied and demonstrated by programming experimental EPROM (electrically programmable read-only memory) devices. The gate current in the BBISHE injection is generated via impact ionization by the energetic holes which are released by the band-to-band tunneling electrons in deep depleted p-type silicon. The BBISHE injection has very high ( approximately 1%) injection efficiency, defined as I/sub G//I/sub D/, compared to channel hot electron injection (usually <10/sup -6/). With this high injection efficiency, 5-V-only EPROMs can be easily implemented. In addition, the oxide field during the BBISHE injection ( approximately 3-5 MV/cm) is much lower than that under Fowler-Nordheim tunneling ( approximately 8-10 MV/cm) at the same current density, which would greatly enhance the endurance of the thin gate oxide. Also, the BBISHE injection can be easily controlled by deeply depleting the channel region, which also favors the voltage coupling from the control gate to the floating gate. These advantages make the BBISHE injection a viable programming mechanism for nonvolatile memories.<>