Si-substrate removal for AlGaN/GaN devices on PCB carriers
This work presents a Si-substrate removal technique for AlGaN/GaN devices on PCB carriers. The Si-removal method is explained and experimentally applied to PCB embedded AlGaN/GaN-on-Si devices. The PCB-embedding package is reopened at the thermal pad by laser-removal and the Si-substrate is removed by wet chemical etching. The paper presents a direct comparison of the electrical characteristics for devices before and after Si-removal. Different substrate related effects are observed and investigated. The pulsed drain currents degrade after Si-removal, due to the absence of the thermal substrate capacitance. Furthermore, the dynamic on-state resistance is increased by surface trapping on the exposed backside. Measurement results are discussed and physically interpreted. The on-state resistance is unaffected in the range of 175 mO before and after Si-removal. The measurements show an increase of the off-state voltage from 600 V to 1400 V for devices after Si-removal.