RESURF stepped oxide (RSO) MOSFET for 85V having a record-low specific on-resistance

A RESURF stepped oxide (RSO) transistor is presented and electrically characterised. The processed RSO MOSFET includes a trench field-plate network in the drift region that is isolated with a thick oxide layer. This trench network has a hexagonal layout that induces an improved RESURF effect at breakdown compared with the more common stripe (2D) layout. Consequently, the effective doping can be two times higher for the hexagonal layout. We have obtained a record value for the specific on-resistance (R_ds,on) of 58 mΩ.mm² at V_gs=10 V for a breakdown voltage (BV_ds,) of 85 V. These values have been obtained for devices having a 4.0 μm cell pitch and a 5 μm long drift region with a doping level of 2.10¹⁶ cm^-3. Measurements of the gate-drain charge density (Q_gd) for these devices show that Q_gd is fully dominated by the oxide capacitance of the field-plate along the drift region.