Cost-effective fabrication of RF AlGaN/GaN HEMTs on surface activated bonding-bonded SiC-SiC substrate

High cost of high-purity semi-insulating (HPSI) SiC is a significant barrier to its widespread industrial use as a substrate for RF GaN transistors. This study presents a cost-effective 6 in. SiC-on-SiC (SOS) composite substrate. This novel substrate is created by bonding an HPSI-SiC film onto a more affordable supporting SiC wafer using smart cut and surface activated bonding technologies. This approach not only allows multiple transfers of HPSI-SiC films but also enables the reuse of the supporting substrate, potentially reducing costs by over 60%. The epitaxial AlGaN/GaN heterostructure grown on the SOS substrate exhibited excellent high-resistance properties with minimal RF loss, measuring less than 0.04 dB/mm across frequencies from 30 MHz to 40 GHz. The RF loss characteristics were analyzed using a small signal model, revealing detailed capacitance and resistance behavior. Additionally, an AlGaN/GaN RF device, developed using a 0.12 μm process on the SOS substrate, achieved good electric performance with an output current of 1.3 A/mm and ft/fmax values of 63.3/173.4 GHz. The SOS substrate offers a cost-effective alternative to traditional GaN substrates while maintaining the high standards required for advanced RF electronic devices.