Sub-micron thermal transport modeling by phonon Boltzmann Transport with anisotropic relaxation times

In recent years, a variety of models based on phonon Boltzmann transport (BTE) has been developed to model sub-micron heat conduction. A recent BTE model, called the full-scattering model, was developed incorporating direct calculation of three-phonon scattering terms. Though this model accurately represents resistive processes, it is computationally very expensive. In this paper, a new BTE model called the anisotropic relaxation time model is developed which significantly reduces the computational time involved, while retaining reasonable accuracy. The new model invokes the single-mode relaxation time approximation, and computes the anisotropic three-phonon relaxation times from a detailed consideration of energy and momentum conservation rules. However, unlike the full-scattering model, the relaxation-time approximation allows a one-time computation of relaxation times as a pre-processing step, significantly reducing the computational load. The model is validated against available experiments and used to compute thermal transport in a bulk metal-oxide semiconductor devices. Its predictions are compared with those of the full scattering BTE model.