Over the last few decades, the world of sensors has been revolutionized by exploring the disciplines of nanotechnology and sophisticated Nano-fabrication process. As a result, gas sensors have become smaller and more robust in the terms of sensitivity and accuracy. Furthermore, these sensors are able to cover a broader range of gases and volatile compounds increasing detection capabilities, allowing detection down to single ppm. However, challenges still exist in detecting certain gases, specifically ammonia. The chemical-based gas sensors for ammonia are not reliable due to several factors such as slow recovery time, sensor base-line drifting, vulnerability to degradation and false alarm [1]. On the other hand, the physical-based ammonia sensing approach has the advantage of fast response time and long-term durability [2], while the thermal conductivity detector suffers a lack of high sensitivity and selectivity.

In an effort to address these challenges, this study is designed to improve the limit of detection of a micro wire thermal conductivity gas sensor that enables the system to detect 100 parts per million for ammonia. The differential 3-Omega measurement technique uses two sensors, one as sensing sensor and the other as a reference [3,4]. It is a harmonic excitation technique that needs a sinusoidal current can produce high thermal stresses that shorten the sensor life-time. To increase the reproducibility of sensor fabrication process, the micro wire TCD sensor material is replaced with platinum. In summary, the new design of micro wire TCD includes optimized shape to bear the high thermal stresses caused by continuous current needed by 3-omega technique and higher stability of the temperature coefficient of resistance with platinum film.

[1] Azad, A. M., Akbar, S. A., Mhaisalkar, S. G., Birkefeld, L. D., & Goto, K. S. (1992). Solid‐state gas sensors: A review. Journal of the Electrochemical Society, 139(12), 3690-3704.

[2] Mahdavifar, A., Navaei, M., Hesketh, P. J., Dimandja, J. D., Stetter, J. R., & McMurray, G. (2015). Implementation of a polysilicon micro electro-thermal detector in gas chromatography system with applications in portable environmental monitoring. ECS Journal of Solid State Science and Technology, 4(10), S3062-S3066.

[3] Lotfi, A., Mahdavifar, A., Struk, D., Stetter, J. R., Navaei, M., & Hesketh, P. (2017). Ultimate Sensitivity of Physical Sensor for Ammonia Gas Detection Exploiting Full Differential 3-Omega Technique. ECS Transactions, 80(10), 1571-1578

[4] Kommandur, S., Mahdavifar, A., Hesketh, P. J., & Yee, S. (2015). A microbridge heater for low power gas sensing based on the 3-Omega technique. Sensors and Actuators A: Physical, 233, 231-238.