  In this work, we propose a new Stepped Oxide Hetero-Material Trench (SOHMT)
power MOSFET with three sections in the trench gate (an N+ poly gate sandwiched
between two P+ poly gates) and having different gate oxide thicknesses
(increasing from source side to drain side). The different gate oxide thickness
serves the purpose of simultaneously achieving (i) a good gate control on the
channel charge and (ii) a lesser gate to drain capacitance. As a result, we
obtain higher transconductance as well as reduced switching delays, making the
proposed device suitable for both RF amplification and high speed switching
applications. In addition, the sandwiched gate with different work function
gate materials modifies the electric field profile in the channel resulting in
an improved breakdown voltage. Using two-dimensional simulations, we have shown
that the proposed device structure exhibits about 32% enhancement in breakdown
voltage, 25% reduction in switching delays, 20% enhancement in peak
transconductance and 10% reduction in figure of merit (product of ON-resistance
and gate charge) as compared to the conventional trench gate MOSFET.
