Failure mechanism of GaN-on-Si device in high-frequency RF operation

In 5G telecommunication, high free-space pass loss puts a high-power delivery demand for transmitters. The GaN high electron mobility transistor (HEMT) with its high output power density suits power amplifier application in 5G RF transmitters. High current density and breakdown voltage are pillars of high output power density. Imec has demonstrated GaN HEMTs on 8” Si wafers for high-frequency power amplifier applications. The GaN-on-Si HEMT is a cost-efficient solution that attracts strong industrial interests. But because of a large GaN-to-Si lattice mismatch, the GaN-on-Si HEMT has two major weaknesses of relatively high self-heating and dislocation density. The associated high operation temperature and trapping effects would both compromise breakdown voltage of GaN-on-Si HEMT. A particular research focus for GaN-on-Si RF transistor would be comprehension of the failure mechanism behind the interplay of three factors—a high field, high dislocation density, and high temperature. A complex and dynamic bias voltage history of HEMTs as a power amplifier makes their failure mechanism a systematics HEMT device physics exploration.

In this PhD topic, you will comprehend the physical mechanism behind GaN-on-Si HEMT failure. You will not only construct robust reliability test methods but carry out physical characterizations to detect weak/failure spots in HEMTs. You will reveal the limitations caused by increased dislocation density and self-heating with GaN-on-Si and propose compensation solutions. You will begin with DC failure mechanism exploration and proceed to comprehending RF failure mechanism. The GaN-on-Si transistors with various flavors will be fabricated in imec 200mm production line with teamwork. You will communicate frequently with different experts in integration, epitaxy, device physics and reliability domains. You will contribute your insights to improving reliability especially breakdown voltage of GaN RF HEMTs.