Thermal conductivity detector (TCD)-type gas sensor based on a batch-fabricated 1D nanoheater for ultra-low power consumption

Abstract

Thermal conductivity detectors (TCDs) are widely used to detect high-concentration gases or identify low-concentration gases in chromatography, owing to their fast response and recovery time for a wide range of gases. However, conventional TCD devices require large power consumption because of their relatively large sizes, which limits their applicability, specifically in IoT. In this study, an ultralow-power TCD was implemented for use as a gas sensor by manufacturing a suspended nanoheater via cost-effective wafer-level microfabrication technology (i.e., carbon-microelectromechanical systems). The aspect ratio of the nanoheater was optimized for a fixed minimum section area (width = 200–300 nm, thickness = 300–400 nm) using simulations and experiments. The small size, high aspect ratio (~ 270, corresponding to a nanoheater length of 80 µm), and suspended architecture allowed the nanoheater-based gas sensor to operate with high sensitivity and ultrafast response/recovery (time constant of less than 1 μs). This fast response enabled the sensor to operate with pulse-width modulation, reducing the power by 1/1000 (240 nW). The nanoheater-based gas sensor exhibited a linear gas response for various high-concentration gases (H2: 1–20 %, Ar: 1–100 %, He: 1–5 %). Moreover, the nanoheater was fabricated using only wafer-level microfabrication processes, ensuring cost-effective sensor manufacturing. Thus, nanoheater-based gas sensors are expected to be used in various portable IoT devices.