Degradation study of AIGaN/GaN HEMT through electro-thermo-mechanical calculations and thermo-reflectance measurements

Abstract

During the last few years, AIGaN/GaN high electron mobility transistors (HEMTs) have been intensively studied for high frequency high power applications. In spite of this great interest, device reliability is still an important challenge for the wide deployment of AIGaN/GaN HEMT technology. To fully understand reliability in these devices, it is necessary to consider the electrical, mechanical and thermal properties of the operating AIGaN/GaN transistors. Since AIGaN and GaN are both piezoelectric materials, the coupling among electric field, lattice heating and mechanical characteristics gives rise to large changes in strain field and elastic energy density in the transistors under the pinch-off conditions. Most previous work have studied the inverse piezoelectric effect on device degradations, however, quantitative analysis of this failure mechanism is still needed. In this thesis, we have developed the first fully-coupled electro-thermo-mechanical simulation of AIGaN/GaN HEMTs to study the correlation between the critical voltages of the gate current degradation and the lattice temperature distributions of these devices under the reverse-gate-bias reliability testing. In addition, we have compared the numerical results of our simulations with DC measurements and high resolution thermo-reflectance images, obtaining excellent agreement for both of them. Moreover, our studies suggest a covenient and low-cost way to obtain the reliability characteristics of AIGaN/GaN HEMTs by using the thermo-reflectance measurements of the lattice temperature distributions for those devices.