In brief

New complementary metal-oxide-semiconductor electronic sensors use infrared light to quickly and accurately detect changes in carbon dioxide and methane gases in indoor settings.

© Unsplash

Sniffing out solutions for climate change action

2 Feb 2024

New gas sensing technologies offer improved environmental monitoring to address climate change and improve safety.

As 2023 is poised to break records as the hottest year in recorded history, the urgency for addressing climate change has never been more palpable. Doris Ng, a Research Scientist based at A*STAR’s Institute of Microelectronics (IME), said that to tackle the problem, we have to be able to accurately measure it.

“Sensing is the first step before mitigation can come into play," said Ng. "We need to monitor greenhouse gases (GHGs) and identify areas where there are increased emissions before we can come up with plans to protect the environment.”

That said, it's challenging to monitor GHGs such as carbon dioxide (CO2) and methane (CH4) accurately—they are present at very low concentrations and their atmospheric levels can vary widely based on environmental conditions, requiring advanced sensor technologies to track them consistently, Ng explained.

In some cases, Ng added, it may even be a life-or-death situation. “A lot of gases are toxic, flammable and explosive, but odourless,” said Ng. Here, detectors that use complementary metal-oxide-semiconductor (CMOS) electronics may be advantageous as they can pick up gas concentrations rapidly, work well indoors and have low energy requirements.

In their study, Ng and colleagues developed pyroelectric detector technologies using CMOS-compatible aluminium nitride (AlN) and scandium aluminium nitride (ScAlN). Pyroelectric detectors operate on the principle of pyroelectricity, where subtle changes in temperature (when infrared light passes through a sample of gas) generate warning signals.

A schematic of the nondispersive infrared (NDIR) gas sensor prototype and its configuration. The aluminium nitride (AIN) pyroelectric sensing layer can be replaced with 12% scandium AIN (ScAIN), a doped counterpart which retains its magnetic properties at higher temperatures.

© A*STAR Research

The researchers tested the ability of their AIN- and ScAIN-based sensors to monitor indoor air quality and ensure safety in environments prone to high CO2 and CH4 levels. They also integrated a compound parabolic collector into the gas sensor of the device as a means of amplifying the signal.

Testing revealed that the ScAlN detectors demonstrated superior sensitivity to the AlN-based ones, with a 40 percent increase in voltage. The detectors can respond to CO2 concentrations as low as 100 ppm and had response times of about one second, making them much faster than commercially available detectors.

CMOS-compatible pyroelectric thin films for gas sensing can make cost-effective detector technologies more widely accessible in a range of industrial settings. Additionally, the team hopes that these promising results might inspire further advancements in the field, particularly around enhancing sensitivity and shrinking detectors while maintaining high performance.

For now, Ng and team are building a prototype of their detector and working on miniaturising the sensor onto a chip. “We're looking at building multi-gas sensors, where we try to integrate sensors for multiple gases into a single sensor. We're also talking to different end users across industries to integrate our sensors into their systems,” said Ng.

The A*STAR-affiliated researchers contributing to this research are from the A*STAR’s Institute of Microelectronics (IME).

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Ng, D.K.T., Xu, L., Fu, Y.H., Chen, W., Ho, C.P., et al. CMOS AlN and ScAlN pyroelectric detectors with optical enhancement for detection of CO2 and CH4 gases. Advanced Electronic Materials 9, 2300256 (2023). | article

About the Researcher

Doris Ng received her PhD degree in Engineering from the National University of Singapore in 2008. She joined A*STAR in 2007 and moved to the Institute of Microelectronics (IME) in 2018. At IME, Doris takes a major role in developing MEMS pyroelectric detectors and building them into gas sensors. She has published >100 papers with >1000 citations. Her research interests include pyroelectric devices, and optical and thermal conductivity gas sensors using pyroelectric devices. She is currently developing CMOS-compatible pyroelectric detectors for gas sensing applications.

This article was made for A*STAR Research by Wildtype Media Group