Model and Simulation of GaN-Based Pressure Sensors for High Temperature Applications—Part I: Physics Based Compact Modeling

In this work, physical compact modelling of Gallium Nitride High Electron Mobility Transistor (GaN HEMT) based pressure sensor for high temperature applications is presented. The model builds around device placement at arbitrary positions on circular membranes, which itself acts as a transducer between pressure and surface strain. The presented model is integrated with the compact Advanced SPICE Model for High Electron Mobility Transistors (ASM-HEMT), as the core HEMT model. In this part, the effects of internal strain, external strain and temperature on the HEMT characteristic pinch-off voltage is modelled as a function of epitaxial design (barrier design, device dimensions, substrate type and thickness). In addition, the device response to pressure as a function of position on the membrane is also modelled. The analytical equations to describe the mechanical strain situation at the wafer surface, was integrated in the compact model on basis of Finite Element Method (FEM) simulations. Lattice-related effects like thermal expansion and elastic constants degradation with temperature is also modelled, based on physical equations fitted to experimental published data. The model was verified against experimental C- V measurements and published experimental data of GaN HEMTs used as pressure sensors, with different substrates (Si, sapphire), different epitaxial design, and different sensor geometry. The presented compact model allows the simulation of GaN based pressure sensors as a part of a compact circuit simulation. The model developed here is used in Part II to propose an optimized design of temperature-insensitive GaN-based pressure sensor, for high temperature applications.