In recent years, β-phase gallium oxide (Ga~2~O~3~) has attracted extensive attention of device engineers due to its promising electrical and optical properties. The ultra-wide bandgap (\~4.8 eV) and the extremely large breakdown field (E~br~) (\~8 MV/cm) are favorable for high-power switching. Furthermore, the availability of high-quality and low-cost native substrates renders Ga~2~O~3~ as a candidate suitable for electric vehicle motor inverters and envelope tracking power supplies. However, the low thermal conductivity of Ga~2~O~3~ (\<20 W/mK) raises significant thermal challenges for Ga~2~O~3­~-based power electronics. Device performance and reliability will be severely compromised unless heat can be effectively removed from the device active region. Integrating Ga~2­~O~3~ thin films with high thermal conductivity materials such as 4H-SiC is a potential route to alleviate the undesired device self-heating. However, it is difficult to characterize thermal transport across the interface between Ga~2~O~3~ and the heat sinking substrate via current experimental techniques; for example, frequency- and time-domain thermoreflectance methods are unable to measure the interfacial thermal boundary resistance (TBR) between several micrometer thick Ga2O3 films and non-native substrates due to the shallow thermal penetration depth of the pump laser.

In this study, a novel differential steady-state thermoreflectance (SSTR) technique was developed. This technique enables simultaneous measurement of the Ga~2~O~3~ film thermal conductivity and the interfacial TBR. Ga~2~O~3~ heterostructures formed via wafer bonding and heteroepitaxial growth were characterized. The microstructure and film thickness dependences of the Ga~2~O~3~ film thermal conductivity and the interfacial thermal transport across the Ga2O3 layer and non-native substrates were studied via SSTR, x-ray diffraction (XRD), and scanning transmission electron microscopy (STEM). These results provide key insight for the electro-thermal co-design of Ga~2~O~3~ devices and the development of package-level thermal management solutions.


Thermal Characterization of Gallium Oxide Heterostructures

Division / Sponsors: 
Electronic & Photonic Packaging Division (EPPD)

Paper Proceedings: https://asmedigitalcollection.asme.org/InterPACK/InterPACK2020/volume/84041

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