Development of Novel 2D Material Based Frequency-domain Thermal Conductivity Detector (TCD)-type Gas Sensor

Abstract

The thermal conductivity detector (TCD)-type gas sensor is a physical gas sensor that converts temperature changes into electrical signals through resistance changes. Due to these characteristics, the temperature coefficient of resistance (TCR) of the sensing material directly affects the sensitivity of the sensor. In the case of metal, which is mainly used as a sensing material for TCD-type gas sensors, the TCR decreases due to surface scattering when the thickness is less than 10 nm. A thinner thickness implies a smaller heat capacity, and the lower the heat capacity of the material, the smaller the time constant, enabling faster and more sensitive temperature sensing. Therefore, existing materials, which exhibit a trade-off between heat capacity and TCR, face limitations in reducing the sensitivity of TCD-type gas sensors. In this study, a frequency domain TCD-type gas sensor based on a novel 2D material was fabricated. As the sensing material, thin MoTe2 was used, which was recently reported to have a higher TCR than metals such as platinum or palladium at the same thickness. The sensor was fabricated using a dry transfer method using nitrocellulose strips as a viscoelastic material, and the resistivity and TCR were measured. To verify the performance of the sensor, the change in the 3rd harmonic according to the thermal conductivity of the surrounding gas was measured using a frequency-based 3rd harmonic measurement method, which is a low-noise measurement method. Additionally, to determine the effect of convection heat transfer, the change in 3rd harmonic according to flow rate was measured in the same gas.