Frequency Modulation–Based Infrared Detection

All existing LWIR detectors, whether they are of the cooled or uncooled variety, currently utilize amplitude modulation (AM) for the detection of changes in photocurrent, voltage, or resistance in response to light exposure. These AM-based detection methods are inherently susceptible to various forms of AM noise, including Johnson noise, flicker noise, and shot noise (Vincent, et al. Fundamentals of infrared and visible detector operation and testing. Wiley2015; Yadav, et al. Sensors Actuators A: Physical 342:113611. https://doi.org/10.1016/j.sna.2022.113611 , 2022; Donati, Photodetectors: devices, circuits and applications. Wiley, 2021). Therefore, there is a critical demand for an uncooled LWIR detector that can provide superior detectivity and an improved signal-to-noise response. Here, we introduce an LWIR detection approach based on frequency modulation (FM), utilizing an oscillating circuit integrated with a phase-change material. While traditional microbolometers operate by sensing changes in resistance due to small perturbations in material properties with LWIR light illumination, they often exhibit a positive resistance characteristic. Our proposed scheme functions through FM of the circuit. This modulation is achieved by harnessing the negative differential resistance (NDR) property change of the phase-change material with incident light, which undergoes dramatic phase transitions between insulating and metallic states. This FM-based detection scheme inherently offers robustness against noise, especially AM noises. Our room-temperature LWIR detector demonstrates a noise equivalent power (NEP) of less than 3 pW·Hz−1/2, a response time of approximately 2.96 ms, and a high detectivity (D*) on the order of 109. The performance of the FM based detection in this work can be further improved through appropriate industry-scale packaging with reduced capacitance.