Heterogeneous wafer bonding of ultra-wide bandgap Ga2O3: A review

Gallium oxide (Ga2O3), with its ultra-wide bandgap (similar to 4.8 eV) and high theoretical breakdown field (8 MV/cm), holds significant research value and promising application in power electronics and microwave radio-frequency (RF) devices. However, the extremely low thermal conductivity of Ga2O3 severely impedes the fabrication of complicated structures and the optimization of device performance. The wafer bonding technology, as a method to fabricate heterogeneous structures materials, newly applied on Ga2O3 to fabricate Ga2O3 hybrid materials. This paper reviews the wafer bonding technology for ultra-wide bandgap Ga2O3 material based on plasma activation and room-temperature surface activation, as well as the heterogeneous integration with silicon (Si), silicon carbide (SiC), and diamond. The effects of various wafer bonding methods on the bonding quality, thermal, and electrical properties are systematically summarized. Finally, the advancements of Ga2O3-based heterogeneous structures in the applications of power, RF, and optoelectronic devices are summarized. This review aims to address the key challenges in Ga2O3 material through an understanding of principles and development of bonding technology, thereby facilitating the practical application of Ga2O3-based devices.