Low-Loss MIM Capacitor on Thick SiO₂ Dielectric for GaN-on-Si Substrates with Standard and Elevated Top Electrode Configurations

In this paper, Monolithic Microwave Integrated Circuits (MMICs)-compatible Si3N4-based metal-insulator-metal (MIM)-capacitors with elevated-electrode realised on thick SiO2 has been demonstrated for the first time for GaN-on-Si technology. Comparative analysis of DC and RF characteristics has also been presented with a standard MIM structure and a benchmark sample on SiC substrate. The outcomes show achievement of low-current/RF leakage and high breakdown voltage (V-BV) capabilities of the proposed capacitor. Further, analysis of RF loss in GaN-on-HR Si substrates was conducted using electromagnetic simulations and small-signal equivalent circuit models that were derived for accurate design of mm-wave integrated circuits. The developed standard and air bridged capacitors showed a V-BV exceeding 167 V and 189 V respectively. The current-density leakage (J) observed is below 1 mu A/cm(2) up to 30 V at 125 degrees C. This 13% increase in V-BV is achieved with tradeoff of low capacitance density of 68.9% attributed to the additional resistance added by the interconnects. In addition, the proposed air-bridged capacitors achieved low RF leakages of 0.4 dB up to 67 GHz which is 50% lower than the standard MIM capacitor.