Investigation on the Isolation Approaches for High-Voltage GaN-on-Sapphire Monolithic Power Integrated Circuits

Gallium Nitride (GaN) fabricated on an insulated sapphire substrate achieves a higher rated voltage of monolithic power integrated circuits compared to that fabricated on a conductive silicon substrate. In this paper, the effectiveness of isolation approaches considering substrate bias and crosstalk effects between adjacent devices in GaN-on-Sapphire monolithic power integrated circuits is investigated. It is demonstrated that the substrate bias and crosstalk effects between high-side and low-side power devices are effectively suppressed regardless of substrate termination with the implantation isolation approach. Thanks to the ultrathin buffer upon an insulated sapphire substrate, the ion implantation can also isolate the adjacent high-voltage (power) and low-voltage (logic) devices. However, a weak crosstalk effect that is caused by capacitive coupling is still observed between high-voltage devices and low-voltage devices with the implantation approach; the degradation rate is calculated to be up to 3%. Experimental results prove that a shallow trench isolation structure in the implantation region can be adopted to mitigate the crosstalk effects, to further improve the stability of integrated logic circuits and drivers under dynamic high-voltage switching conditions.