Electromagnetic Investigation of Substrate Coupling for Monolithic Microwave Integrated Circuits in GaN-on-Si Technology

In this work, we present electromagnetic (EM) investigation into the substrate coupling in monolithic microwave integrated circuits (MMICs) in GaN-on-Si technology for high signal frequency up to 25 GHz. By numerically solving Maxwell's equations based on finite element method (FEM), the electric field distribution and then the electromagnetic (EM) coupling are determined in the GaN-on-Si device structures. The S-parameter results disclose that |S₂₁| increases sharply to about - 10 dB for multi-gigahertz signals over a physical separation distance of 700 μ m. Such poor signal isolation remains more or less the same extending to 25 GHz. The computed electric field intensity distribution reveals the EM coupling through the GaN buffer layer rather than the resistive silicon (Si) substrate. These results pose important implications for the implementation of GaN-on-Si MMICs to avoid serious crosstalk and noise coupling among nearby devices and circuits operating at gigahertz frequencies. Effective isolation trench structures or alike would be necessary for suppressing the substrate coupling in GaN-on-Si MMICs.