Abstract
We present a miniaturised thermal acoustic gas sensor, fabricated using a CMOS microhotplate and MEMS microphone. The sensing mechanism is based on the detection of changes in the thermal acoustic conversion efficiency which is dependent on the physical properties of the gas. An active sensing element, consisting of a MEMS microphone, is used to detect the target gas while a reference element is used for acoustic noise compensation. Compared to current photoacoustic gas sensors, our sensor requires neither the use of gas-encapsulated microphones, nor that of optical filters. In addition, it has all the benefits of CMOS technology, including production scalability, low cost and miniaturization. Here we demonstrate its application for CO_2 gas detection. The sensor could be used for gas leak detection, for example, in an industrial plant.
Highlights
Gas sensors play an increasingly important role in environmental monitoring due to elevated levels of atmospheric pollutants in urban areas, or the need for the safety monitoring of numerous industrial p rocesses[1,2]
We describe a miniaturised thermal acoustic sensor which utilizes a CMOS-based microhotplate chip and MEMS microphone and demonstrate its application for CO2 gas sensing
The membrane is formed by deep reactive ion etching (DRIE) and thermally isolates the heater from the Si substrate
Summary
Gas sensors play an increasingly important role in environmental monitoring due to elevated levels of atmospheric pollutants in urban areas, or the need for the safety monitoring of numerous industrial p rocesses[1,2]. A widely used sensing technology is the chemiresistor which utilises changes in the electrical conductivity of a semiconducting metal oxide (MOx) layer when it is exposed to an oxidising or reducing gas. These types of sensors are commonly used in low-cost, low-power applications, including portable air conditioning u nits[3]. Optical sensors (including photoacoustic) can address some of these limitations, and are the tool of choice for monitoring CO2 , as well as a range of other gases[5] Their operating mechanism is typically based on the detection of absorption lines in the mid-infrared (MIR) spectrum. An early example of such a device is the thermophone, developed in 1917 by H
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