CO2Gas Sensing By Cmos-Mems Scaln-Based Pyroelectric Detector Based on MID-IR Absorption

Chen

et al. 2022

ACS Sens.

Self Cite

NDIR CO 2 gas sensors using a 10-cm-long gas channel and CMOS-compatible 12% doped ScAlN pyroelectric detector have previously demonstrated detection limits down to 25 ppm and fast response time of ∼2 s. Here, we increase the doping concentration of Sc to 20% in our ScAlN-based pyroelectric detector and miniaturize the gas channel by ∼65× volume with length reduction from 10 to 4 cm and diameter reduction from 5 to 1 mm. The CMOS-compatible 20% ScAlN-based pyroelectric detectors are fabricated over 8-in. wafers, allowing cost reduction leveraging on semiconductor manufacturing. Cross-sectional TEM images show the presence of abnormally oriented grains in the 20% ScAlN sensing layer in the pyroelectric detector stack. Optically, the absorption spectrum of the pyroelectric detector stack across the mid-infrared wavelength region shows ∼50% absorption at the CO 2 absorption wavelength of 4.26 μm. The pyroelectric coefficient of these 20% ScAlN with abnormally oriented grains shows, in general, a higher value compared to that for 12% ScAlN. While keeping the temperature variation constant at 2 °C, we note that the pyroelectric coefficient seems to increase with background temperature. CO 2 gas responses are measured for 20% ScAlN-based pyroelectric detectors in both 10-cm-long and 4-cm-long gas channels, respectively. The results show that for the miniaturized CO 2 gas sensor, we are able to measure the gas response from 5000 ppm down to 100 ppm of CO 2 gas concentration with CO 2 gas response time of ∼5 s, sufficient for practical applications as the average outdoor CO 2 level is ∼400 ppm. The selectivity of this miniaturized CO 2 gas sensor is also tested by mixing CO 2 with nitrogen and 49% sulfur hexafluoride, respectively. The results show high selectivity to CO 2 with nitrogen and 49% sulfur hexafluoride each causing a minimum ∼0.39% and ∼0.36% signal voltage change, respectively. These results bring promise to compact and miniature low cost CO 2 gas sensors based on pyroelectric detectors, which could possibly be integrated with consumer electronics for real-time air quality monitoring.

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confidence: 99%

Miniaturized CO₂ Gas Sensor Using 20% ScAlN-Based Pyroelectric Detector

Chen

et al. 2022

ACS Sens.

Self Cite

“…Pyroelectric coefficients (Figure S2, Supporting Information) have shown that 12% ScAlN demonstrates ≈3× increase in pyroelectric coefficient as compared to AlN. Fourier transform infrared spectra have also reported higher absorption from 12% ScAlN-based pyroelectric detector stack [14,55,58,59] compared to AlN-based pyroelectric detector stack. [38,58] Although the pyroelectric coefficient shows ≈3× improvement for 12% ScAlN-based pyroelectric detector compared to AlN-based pyroelectric detector, absorptivity of both detector stacks at specified gas absorption wavelength also need to be considered and both factors will affect the final output gas sensing signal.…”

Section: Aln-and 12% Scaln-based Pyroelectric Detectors Gas Sensing R...mentioning

confidence: 99%

“…To the best of our knowledge, we have not found any reports on the gas sensing properties from AlN‐based pyroelectric detectors, though many have reported on electrical properties of AlN pyroelectric detectors [ 40,52–54 ] and limited reports on gas sensing responses using ScAlN‐based pyroelectric detectors. [ 14,15,55 ]…”

Section: Introductionmentioning

confidence: 99%

“…To the best of our knowledge, we have not found any reports on the gas sensing properties from AlN-based pyroelectric detectors, though many have reported on electrical properties of AlN pyroelectric detectors [40,[52][53][54] and limited reports on gas sensing responses using ScAlN-based pyroelectric detectors. [14,15,55] Herein, we would like to examine AlN and ScAlN CMOS compatible pyroelectric sensing materials in CO 2 and CH 4 gas sensing based on NDIR technique at room temperature operation. These pyroelectric detectors have two terminals connected to the top and bottom electrodes respectively and no bias (no extra power) is required to be applied during operation, which helps in further saving energy and cost.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

CMOS AlN and ScAlN Pyroelectric Detectors with Optical Enhancement for Detection of CO₂ and CH₄ Gases

et al. 2023

Adv Elect Materials

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Gassensors are useful for monitoring of greenhouse gases. As the move toward complementary metal-oxide-semiconductor (CMOS) compatible pyroelectric room temperature detectors is gaining traction due to its scalability to 8-in./12-in. wafer area and integrable with CMOS electronics, CMOS compatible aluminum nitride (AlN)-and scandium aluminum nitride (ScAlN)-based pyroelectric detectors are developed for sensing of CO 2 and CH 4 gases, which are two of the greenhouse gases that contribute significantly to global warming. Leveraging gas absorption at respective mid-infrared (IR) wavelengths, CO 2 and CH 4 gases are detected at various concentrations with fast response time ≈1 s. A compound parabolic collector (CPC) is designed and integrated into the gas sensor to enhance the optical flux received by the detector, which demonstrates ≈10× signal improvement in its presence. Further factors such as the effect of sensing area reduction and response to random gas concentrations are also tested on AlN-and ScAlN-based pyroelectric detectors respectively to observe the gas sensing behaviors of both detectors. The results obtained provide further understanding of the behavior of CMOS AlN-and ScAlN-based pyroelectric detectors as IR gas sensors, which can potentially inspire new design and design selection for various gas sensing applications.

“…They are compact and can function at room temperature without the need for liquid nitrogen (N2) cooling, unlike photon detectors which usually require cooling. 4 Their thermal sensing capability is widely used for a number of applications including gas sensing, [5][6][7] temperature sensing, [8][9][10] ultraviolet/ infrared (UV/ IR) light detection, [11][12][13][14][15] thermal imaging [16][17] etc. When considering using pyroelectric detectors in contactless button system, they could potentially replace the traditional way contactless button works.…”

Section: Introductionmentioning

confidence: 99%

Low-power contactless button system based on MEMS ScAlN pyroelectric detector

MOEMS and Miniaturized Systems XXII

Ng²,

Chen³

et al. 2023

Self Cite

We demonstrate a system-level low-power contactless button using MEMS ScAlN-based pyroelectric detector. As pyroelectric detectors can sense instantaneous temperature change, the human finger can act as a thermal source to activate the button. Using our in-house fabricated ScAlN-based pyroelectric detector which does not require any IR source, we package it into a contactless button system designed with electrical read-out circuits and signal processing. This contactless button system could detect the presence of a finger at a center distance measured up to ~4 cm away, ~2 cm radius circle area, suitable for application as contactless elevator button. Our contactless button system using ScAlN-based pyroelectric effect is characterized, tested and compared with a commercial contactless button. The power consumed is measured ~3.5× lower than that of commercial contactless button. The results obtained provide a potential solution towards energy efficient low-power contactless button system.