Achieving the best thermal performance for GaN-on-diamond

GaN-based RF transistors offer impressive power densities, although to achieve the maximum potential offered by GaN, thermal management must be improved beyond the current GaN-on-SiC devices. By using diamond, rather than SiC substrates, transistor thermal resistance can be significantly reduced. It is important to experimentally verify thermal resistance, rather than relying solely on simulation expectations, using measurement results to aid further optimization. The novel thermal characterization methodology presented here combines Raman thermography and simulation to determine the substrate thermal conductivity and GaN/substrate thermal resistance in GaN-on-diamond devices. Measured GaN-on-diamond interfacial thermal resistance is similar to reported values for GaN-on-SiC, whereas the diamond substrate thermal conductivity is substantially higher, resulting in a significantly improved thermal resistance with respect to GaN-on-SiC, with great potential for further improvement.