Thermal Studies of 3-D Stacked InGaAs HEMTs and Mitigation Strategy of Self-Heating Effect Using Buried Metal Insertion

Heterogenous and monolithic 3-D (M3D) integration of III-V RF devices on Si CMOS is a very attractive technology for future wireless communication systems. However, the self-heating effect, caused by limited heat dissipation, remains a significant bottleneck in implementing M3D integrated platforms. In this study, we fabricated both conventional 2-D planar InGaAs HEMTs and 3-D stacked InGaAs HEMTs to investigate and compare their respective self-heating characteristics using thermoreflectance microscopy (TRM). Our results revealed that 3-D stacked InGaAs HEMTs exhibit 40.2% higher thermal resistivity than 2-D planar InGaAs HEMTs. To address this issue, we proposed a back metal insertion, an M3D integration-compatible process. We fabricated 3-D stacked InGaAs HEMTs with back metal using three different layout options (without back metal, with local back metal, and with global back metal) to analyze the effectiveness of the back metal in providing a heat dissipation path. Our experiments demonstrated the effectiveness of a back metal structure in greatly reducing the self-heating of 3-D stacked devices. These results provide valuable guidance for enhancing the heat management of the M3D RF platform by providing information on the self-heating characteristics in the 3-D stacked devices.