Silicon Integrated HBV Frequency Multipliers for THz Applications

Abstract: This thesis deals with integrated varactor diode circuits for terahertz (THz) applications. In particular hybrid, monolithic microwave integrated circuits (MMICs), and heterogeneous integration are explored for frequency multiplier applications. Each of these techniques addresses different requirements for high power and high frequency electronic circuits. Namely: high thermal conductivity (κ) of substrates for enhanced power capabilities, process reproducibility of small diode and circuit component dimensions, and finally machining properties for enhanced robustness and functionality. A fixed tuned 175 GHz frequency quintupler with a flip-chip assembled Heterostructure Barrier Varactor (HBV) diode was demonstrated. The microstrip circuit was fabricated on AlN substrate - a material with high thermal conductivity. The device delivers 60 mW of output power corresponding to 6.3 % conversion efficiency. The heteregeneous integration of In0.53Ga0.47As/Al0.48Ga0.52As HBV material structure onto silicon and silicon-on-insulator (SOI) substrate was done in a process employing low temperature plasma assisted wafer bonding. Using this technology a frequency tripler (×3) for W-band (75-110 GHz) and frequency quintupler (×5) for 474 GHz were fabricated. The performance of the W-band frequency tripler delivering more than 180 mW of output power is comparable to the identical design in InP MMIC technology. The 474 GHz frequency quintupler circuit was fabricated on SOI substrate, hence robust and unform 20 μm thick circuits were achieved. This multiplier delivers 2.8 mW of output power, and it represents the highest frequency of operation for HBV-based frequency multipliers. By enabling the integration of compound semiconductors onto a silicon substrate, an increase in the performance and functionality of the device is achieved. Moreover, due to good thermal and mechanical properties of silicon, as well as established process technology for this material, a new generation of THz monolithic integrated circuits is predicted.