Design of a High Signal to Noise Balanced Platinum Thermal Conductivity Detector

Thermal Conductivity Detector (TCD) is one of the universal gas sensors which often is used in the Gas Chromatography (GC) systems. The principle behind TCD sensor is joule heating. TCD sensor heats the surrounding gas which results in change of thermal-physical properties of the sensor. The focus of this work is to improve the Signal to Noise Ratio (SNR) of the Thermal Conductivity Detector (TCD) by the separating the heating and sensing elements of the sensor. Although the TCD sensor has several advantages over chemical sensors: short response time, no base-line drift, and high corrosion resistance, the shortcoming of this sensor is the limit of detection (LOD) [1-3]. The conventional TCD sensor uses a single layer of thin film for both heating and sensing and even though it simplifies the fabrication process, degrades the TCD SNR. Here we propose a new design in which a thin layer of Atomic Layer Deposition (ALD) of Al 2 O 3 is sandwiched between two layers of platinum film. In order to enhance the performance of the TCD at the operating temperature of 700˚ K [1, 4], the heating layer of the sensor needs to be thick enough to be able to pass a sufficiently high current. On the contrary, for the sensing layer to be sensitive to the change of temperature, it needs to be thin enough to have a high resistance value. In this study a lumped model was used to study the High SNR (HSNR) balanced TCD design which revealed that the sensing layer can follow the TCD heater’s temperature with a delay less than 0.3 ns while the HSNR balanced TCD’s response time is 6 µs. Therefore, by comparing the delay time between the two layers, and the response time of the sensor, it can be concluded that the sensing layer resistance represents the real-time temperature of the TCD. The sensor design schematic has been represented in Figure 1. The new design has a higher precision and accuracy which enhances the Limit of Detection (LOD) of the TCD sensor. This was achieved by separating the sensing and heating elements. Lotfi, A., et al., Ultimate Sensitivity of Physical Sensor for Ammonia Gas Detection Exploiting Full Differential 3-Omega Technique. ECS Transactions, 2017. 80 (10): p. 1571-1578. Mahdavifar, A., et al., Simulation and Fabrication of an Ultra-Low Power Miniature Microbridge Thermal Conductivity Gas Sensor. Journal of The Electrochemical Society, 2014. 161 (4): p. B55-B61. Kommandur, S., et al., A microbridge heater for low power gas sensing based on the 3-Omega tech