ALN thin-films as heat spreaders in III–V photonics devices Part 2: Simulations

Abstract

In the paper, we aim to solve the thermal problems appearing in integrated silicon photonics by using high thermal conductivity Aluminium Nitride (ALN) as a thermal spreading layer located around the ridge of a hybrid III-V laser on silicon in comparison to the existing encapsulation material benzocyclobutene (BCB). Here, to facilitate the design of reliable hybrid semiconductor lasers, we first develop and implement a multiphysics electro-thermo-mechanical model within a finite element environment COMSOL. A phenomenological model of laser operation is used to numerically capture all the thermal and electrical characteristics of the lasers. In terms of the hybrid devices, the simulated thermal resistance agrees well with our device measurements presented in Part 1 of this work. We also demonstrate that the use of the ALN heat spreader can significantly reduce the thermal resistance. Moreover, a linear elastic model is employed for a mechanical analysis of the entire laser structure. The maximum allowable stress is estimated using the Christensen criterion. We find that the process-dependent residual stress dictates the device stress field. In the current design, the BCB encapsulation layer is at risk of failure around the InP waveguide. For AlN spreaders, lower film processing temperatures are key to reduce the stress in the deposited film. We further perform a parametric study on Tref to determine the maximum allowable deposition temperature of AlN/BCB. The simulations suggest that Tref should not exceed 59 °C and 69 °C for ALN and BCB respectively to avoid mechanical failure in the devices.