Effect of electron trapping on IGFET characteristics

Abstract

At large applied voltages, electrons flowing from the source to the drain of a n-channel insulated-gate field-effect transistor (IGFET) may gain sufficient energy from the high-field region near the drain to be emitted into the gate insulator layer near the drain junction. The trapping of these hot electrons in the gate insulator results in transconductance degradation and/or threshold voltage shift. There is also evidence of surface-state generation resulting from hot-electron emission into the SiO2 layer. The extent of the resultant transconductance degradation and/or threshold shift depends strongly on the electron trapping characteristics of the gate insulator. For devices having SiO2/Si3N4 as gate insulator, electron trapping is completely dominated by the Si3N4 layer. In this case, channel hot-electron effect results in threshold shift alone. For devices having SiO2 as gate insulator, the trapping characteristics depend on its positive oxide-charge concentration. In this case, channel hot-electron effect results in a combination of transconductance degradation and threshold shift.