Ultra-sensitive Mid-infrared Detection Using Phononic Crystal Resonator-based Oscillator

Mid-infrared (MIR) detection is essential for many applications such as chemical sensing, communications, space explorations, and national defense. Existing MIR detectors are typically categorized into two major classes: (1) semiconductor photodetectors, which offer high responsivity and fast response time but typically require cryogenic cooling, and (2) thermal-based sensors, which can operate at room temperature but suffer from low sensitivity and slow response times. In this thesis, I demonstrate room-temperature MIR detectors based on surface acoustic wave (SAW) phononic crystal (PnC) oscillators. By configuring a PnC resonator featuring high-frequency-quality-factor product into a low-noise self-oscillation system, my MIR detector achieves high sensitivity on the order of hundreds of picowatts. The SAW architecture also provides significantly higher thermal conductance than suspended thin-film structures, enabling fast thermal response. Overall, this work demonstrates a room-temperature MIR detection approach that combines high sensitivity with rapid thermal response through SAW PnC engineering, offering a pathway toward broadly applicable MIR sensing, spectroscopy, and communication technologies.