NDIR CO₂ gas sensing using CMOS compatible MEMS ScAlN-based pyroelectric detector

We demonstrate NDIR CO₂ gas sensing using CMOS compatible MEMS ScAlN-based pyroelectric detectors. The ScAlN-based pyroelectric detectors are fabricated using 8-inch wafer level technology with 12 % Sc-doped AlN deposited at a temperature of ∼200 °C. Together with a blackbody thermal emitter, a 10 cm long enclosed gas channel with only inlet and outlet holes connected to tubings, and testing using 2 different reference gases (N₂ and synthetic air), measurements show voltage signal drop due to CO₂ gas absorption at the 4.26 μm wavelength at CO₂ gas concentrations ranging from 5000 ppm down to 25 ppm. The signal change due to the CO₂ gas response ranges from ∼2% at 100 ppm CO₂ concentration to ∼40 % at 5000 ppm CO₂ gas concentration for both CO₂ gas measured in N₂ and in synthetic air. CO₂ gas response times are also measured for CO₂ gas in N₂ and in synthetic air at concentrations of 5000 ppm, 1000 ppm and 400 ppm. The gas response times measured around 2 s and lower. Introduction of humidity show some minor effect (<3%) to the CO₂ gas response and seems most perturbed at 10 % relative humidity. To the best of our knowledge, this is the first demonstration using ScAlN-based pyroelectric detectors in NDIR CO₂ gas sensing, towards practical sensor applications. The results obtained show promise in using CMOS-compatible MEMS ScAlN-based pyroelectric detectors for NDIR gas sensing, opening up possibilities for low cost, wafer-level, monolithic NDIR gas sensors with small footprint integrated with CMOS circuits.