Multiscale modeling of thermal transport in gallium nitride microelectronics

One of the most significant advances in GaN devices has evolved from the AlGaN/GaN high electron mobility transistor (HEMT). Technologies that incorporate such devices span the range from next generation WiMAX stations to advanced military radar applications. As a result of the large power densities being applied to these devices there can develop intense hot spots near areas of highest electric field. The hot spot phenomenon has been linked to a decrease in device reliability through a range of degradation mechanisms. In order to minimize the effect that hot spot temperatures have on device reliability a detailed understanding of relevant transport mechanisms must be developed.;This study focuses on two main aspects of phonon transport within GaN devices. The first area of focus was to establish an understanding of phonon relaxation times within bulk GaN. Relaxation times for optical modes were compared to experimental data obtain through Raman Spectroscopy measurements; acoustic phonon relaxation times were calculated to capture the bulk thermal conductivity values. This analysis gives insight into the details behind the macroscopic thermal conductivity parameter. The second area of focus was on developing a multiscale phonon transport modeling methodology to couple the Boltzmann Transport Equation and the energy equation. This coupling overcomes some computational limits and allows for nanoscale phenomena to be resolved within a macroscopic domain. Results of the transport modeling were focused on benchmarking the coupling method as well as calculating the temperature distribution within an operating 6 finger HEMT.