Gate and Drain Currents in Off-State Buried-Type p-Channel LDD MOSFET's

The buried-type p-channel LDD MOSFET's biased at high positive gate voltage exhibit new characteristics: 1) the ratio of the drain to gate currents is about 1 x 10 -3 to 5 x 10 -3; and 2) the gate and drain currents both are functions of only the gate voltage minus the n-well bias. Such characteristics are addressed based on the formation of the surface n+ inversion layer due to the punchthrough of the buried channel to the underlying shallow p-n junction. The measured gate current is due to the Fowler-Nordheim tunneling of electrons from this inversion layer surface and the holes generated within the high-field oxide constitute the drain current. The n + inversion layer surface potential is found to be equal to the n-well bias plus 0.55 V. As a result, not only the oxide field but also the gate and drain currents are independent of drain voltage.