Enhancement of hot-electron currents in graded-gate-oxide (GGO)-MOSFETs

Graded-Gate-Oxide(GGO)-MOSFETs with various degrees of gate-drain(source) overlap (and grading thickness of the gate oxide near the polysilicon-gate edge) have been investigated for hot-electron generation. Compared with a conventional MOSFET, the GGO-MOSFET exhibits higher substrate and gate currents when the gate voltage is raised above a critical value(Vgc). Vgc is found to be dependent on the drain voltage. It is also a smooth function of the degree of gate-drain(source) overlap which can be controlled by the fabrication process. These experimental findings are supported by results obtained from the two-dimensional analysis of a similar device structure. Implications of the GGO phenomena on MOS technologies are discussed. Possible use of the GGO-MOSFET in EPROM is proposed.