Patent ID: 7642585

Claim:
A memory cell having a threshold voltage dependent on charge trapped in a dielectric charge storage layer, comprising: a semiconductor substrate having a channel region with a valence band energy level, a gate and a data storage structure between the channel and the gate, the data storage structure including 1) a tunnel dielectric structure contacting the channel region; 2) said dielectric charge storage layer contacting the tunnel dielectric structure having a valence band energy level; and 3) a blocking dielectric layer contacting the dielectric charge storage layer; and wherein the tunnel dielectric structure consists of a combination of materials including at least a first material having a first characteristic valence band energy level and a second material having a second characteristic valence band energy level, respective materials in the combination of materials having concentrations which vary with distance from the substrate so that the tunnel dielectric structure has a valence band that varies in energy level along a line between the substrate and the dielectric charge storage layer, so that the valence band has a first energy level lower than the valence band energy level of the channel in a first location near the channel, a second energy level in a second location spaced away from the channel by less than 2 nm that under no bias is between the first energy level and the valence band energy level of the channel, and a third energy level in a third location between the second location and the dielectric charge storage layer that under no bias is lower than the valence band energy level of the channel and lower than the valence band energy level of the dielectric charge storage layer; and wherein said data storage structure is capable of use in an operating mode in which hole tunneling current between the substrate and the dielectric charge storage layer is used to lower the threshold voltage from a target threshold voltage by at least 2 volts in less than 100 msec.