Effects of AlN film thickness and operating frequency on sensing output of CO2 pyroelectric-based non-dispersive infrared gas sensor

Effects of AlN film thickness and operating frequency on sensing output of CO2 pyroelectric-based non-dispersive infrared gas sensor

Terahertz, RF, Millimeter, and Submillimeter-Wave Technology and Applications XVIII

10.1117/12.3043055

https://doi.org/10.1117/12.3043055

Doris Keh Ting Ng, Kristel Pei Xuan Wee, Md Hazwani Khairy, Landobasa Tobing, Wing Wai Chung, Isaac Siyuan Ling, Norhanani Jaafar, Jia Sheng Goh, Linfang Xu, Weiguo Chen, Qingxin Zhang

20 March 2025

Ng, D. K. T., Wee, K. P. X., Khairy, M. H., Tobing, L., Chung, W. W., Ling, I. S., Jaafar, N., Goh, J. S., Xu, L., Chen, W., Zhang, Q., & Li, N. (2025). Effects of AlN film thickness and operating frequency on sensing output of CO2 pyroelectric-based non-dispersive infrared gas sensor. In L. P. Sadwick & T. Yang (Eds.), Terahertz, RF, Millimeter, and Submillimeter-Wave Technology and Applications XVIII (p. 26). SPIE. https://doi.org/10.1117/12.3043055

CMOS compatible AlN-based pyroelectric detectors of different thicknesses (500 nm and 1 μm respectively) are examined by measuring their responses to different concentrations of CO2 gas in an NDIR gas sensing system. We note up to ~55% improvement in signal when AlN thickness reduces from 1 μm to 500 nm. In addition, we design our AlN-based pyroelectric detectors similar to 2 capacitors connected in series and 4 capacitors connected in series while keeping the total pyroelectric sensing layer constant. CO2 sensing responses of both designs with AlN thicknesses of 500 nm and 1 μm are measured in the NDIR gas sensing system and the 2-capacitor design with 500 nm thick AlN in general gives a more sensitive response. The LOD for CO2 sensing when using this detector is extracted based on Beer-Lambert law and we obtain an LOD of ~53ppm. As pyroelectric detectors are known to operate at lower frequencies (~tens of hertz), we also operate the detectors at different modulating frequencies (7 Hz, 11 Hz and 17.4 Hz) and observe their effects on the gas sensing signal. Comparing the 4 different detectors in NDIR gas sensing, the AlN-based pyroelectric detector with 500 nm thick AlN and of 2-capacitor design presents the best performance in CO2 gas sensing. This work shows effects of AlN film thickness change and variation in operating frequency on pyroelectric-based NDIR CO2 gas sensing. The results will provide more understanding on characteristics of AlN-based pyroelectric detectors and their behaviours in NDIR gas sensing.

Publisher Copyright

This research / project is supported by the National Research Foundation, Singapore, and A*STAR (Agency for Science, Technology and Research), Singapore - Low-Carbon Energy Research (LCER) Funding Initiative (FI)
Grant Reference no. : U2102d2012

This research / project is supported by the National Research Foundation, Singapore, and A*STAR (Agency for Science, Technology and Research), Singapore - Low-Carbon Energy Research (LCER) Phase 2
Grant Reference no. : U2303D4001

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https://oar.a-star.edu.sg/communities-collections/articles/21676

10.1117/12.3043055

Institute of Microelectronics