Improvement of the RON- BV Tradeoff in Field-Plate MOSFETs by Localized Fixed Charges in the Trench Oxide

With the increasing demand for low-voltage power MOSFETs in applications such as data centers, the need to reduce power losses is also growing. Aiming to decrease conduction loss, we investigate a method for improving the tradeoff between the on-resistance
$(R_{\text{ON}})$
and breakdown voltage (BV) of field-plate (FP) MOSFETs by using localized and fixed positive charges (LFCs) in the trench oxide. The simulation results show that BV is improved when the LFC density peak is at the trench-bottom oxide because the LFCs relax the trench-bottom electric field. In addition, the LFCs contribute to the reduction in RON because the electrons accumulate on the
$\text{Si}/\text{SiO}_{2}$
surface, and the spreading resistance is reduced. A gradient LFC profile was realized in the experiment by applying proton irradiation, which enabled some of the oxygen vacancies in
$\text{SiO}_{2}$
to act as positive fixed charges. The experimental results imply that the gradient LFC is useful in the trench oxide for improving the
$R_{\text{ON}}-BV$
tradeoff, particularly without any disruption of the charge balance.