A novel depletion mode p-GaN island HEMT and its use in a monolithically integrated start-up circuit

In this study we present the concept and features of a novel depletion mode p-GaN island HEMT. The HEMT presented was designed and fabricated on a state-of-the-art GaN-on-Si heterojunction process. The gate of the novel transistor comprises a row of p-GaN islands, displaced in the third dimension. Depending on the gate-source bias the device may operate in three distinctive regions identified by significant changes in its on-state resistance. The edges of the three distinctive regions are defined by the two threshold voltages of the device. The first threshold voltage is negative and signifies the first turn-on of the device. By adjusting the separation of the p-GaN islands the first threshold voltage can be controlled by layout design rather than only process design. The p-GaN island HEMT in this study was designed and fabricated as both a low voltage device (30V rating) and high voltage device (650V rating). Moreover, the device was demonstrated experimentally, as a key component in a start-up circuit, monolithically integrated within a fully functional power IC for 650V applications.