NDIR CO2 gas sensing using CMOS compatible MEMS ScAlN-based pyroelectric detector

Ng, Doris K. T.; Ho, Chong Pei; Liang, Xu; Chen, Weiguo; Fu, Yuan Hsing; Zhang, Tantan; Siow, Li Yan; Jaafar, Norhanani Binte; Ng, Eldwin J.; Gao, Yuan; Cai, Hong; Zhang, Qingxin; Lee, Lennon Y. T.

doi:10.1016/j.snb.2021.130437

Cited by 39 publications

(33 citation statements)

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“…In addition to the detector’s absorption and gas absorbance, the pyroelectric coefficient of the detector is also a factor that determines the output signal received. In this work, we are using >20% Sc-doped AlN compared to the previously reported 3 12% Sc-doped AlN pyroelectric material. Our previous work 27 has shown that the specific detectivity of the detector increases when doped with 12% Sc, and we anticipate a further increase in specific detectivity as the Sc doping increases.…”

Section: Resultsmentioning

confidence: 99%

“…This gas channel can be cleaned by purging with N 2 gas or by isopropyl alcohol (C 3 H 8 O). The total volume of the gas channel is reduced by ∼65 times, from ∼1.96 cm 3 to ∼0.03 cm 3 .…”

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confidence: 99%

“…This will subsequently affect the absorption intensity at the same wavelength region, as absorption is calculated by subtracting the measured FTIR transmission and reflection spectra across wavelengths in the range 2−14 μm from 100%. 3,30,36 Figure 3b shows an FTIR absorption spectrum of this detector stack. The drop in absorption at around the 4 μm wavelength region is mostly due to the high reflection of the detector stack in the same wavelength region as depicted in Figure 3a.…”

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confidence: 99%

“…We try to fit the experimental data using the modified Beer− Lambert's equation: 5,54 = × CO gas response span (1 e ) lx 2 (3) where x is the CO 2 gas concentration, κ is the effective absorption coefficient of CO 2 , l is the optical path length in the gas system, which is ∼0.04 m for the small gas channel and ∼0.1 m for the bigger gas channel, and "span" is a coefficient which is an indication on the amount of IR radiation that can be absorbed. The experimental data fitted well with the equation, with coefficient of determination (R 2 ) of both gas channels >0.99 (∼0.9925 for the small gas channel and ∼0.9976 for the big gas channel).…”

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confidence: 99%

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

Liang

Chen

et al. 2022

ACS Sens.

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

Liang

Chen

et al. 2022

ACS Sens.

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“…In this context, micro-fabricated sensors are especially of great interest, as many applications allow only a small footprint. Talking about ambient gas monitoring, the market provides different solutions based on photo-acoustic (PAS) or non-dispersive infrared (NDIR) sensing, with both still facing the challenge of being miniaturized (Eberl et al, 2019;Ranacher et al, 2019;Ng et al, 2021;Lavchiev and Jakoby, 2017).…”

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confidence: 99%

Fabrication of integrated polysilicon waveguides for mid-infrared absorption sensing

Stocker

Consani

Thakkar

et al. 2022

J. Sens. Sens. Syst.

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Abstract. The increasing popularity of environments equipped with sensors for convenience and with safety features, as in, for example, smart homes, greenhouses, or the interior of modern cars, demands a variety of sensor systems. In this respect, the sensing of ambient gases in the sense of air quality monitoring or leakage detection is one of the prominent applications. However, even though there are many different systems already available, the trend goes towards smaller and rather inconspicuous sensors which are embedded in the environment. We present the fabrication and characterization of integrated waveguides, which constitute an interesting platform for absorption spectroscopy in the mid-infrared (mid-IR) using the evanescent field of guided modes interacting with the analyte, thus leading to the absorption-induced attenuation of the mode. Corresponding simulations, characterizing the efficiency of the desired interaction, predict values for the confinement factor Γ and the intrinsic damping D for a waveguide geometry, which is then characterized by measurements. Furthermore, we discuss how these waveguides could be part of an integrated, non-dispersive, mid-IR sensor system fully integrated on a single chip. In this context, we present a way to maintain the quality of waveguides throughout the entire workflow needed to integrate a pyroelectric IR detector based on aluminum nitride (AlN).

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Rapidly Modulated Wide‐Spectrum Infrared Source Made of Super Aligned Carbon Nanotube Film for Greenhouse Gas Monitoring

Lai

Liu

Zhou

et al. 2022

Adv Funct Materials

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Non‐dispersive infrared (NDIR) gas monitoring has advantages of environment stability, convenient operation and maintenance, wide detection range, and multi‐gas‐detection capability. However, the conventional IR sources for NDIR gas monitoring, such as miniature lamps, microelectromechanical system (MEMS) light sources, and light‐emitting diodes (LEDs), can only work at narrow modulation frequency and spectral range, or require complicated design and fabrication, because of the constraint of materials and work principle. These issues cause low data acquisition rate, poor anti‐interference ability and limited gas compatibility to NDIR. Here, the super‐aligned carbon nanotube (SACNT) film is developed as an IR source in NDIR gas monitoring system. It has a wide spectral range (0.2–334 µm), a facile fabrication method, and can work up to a high frequency ≈150 kHz. A mechanical‐chopper‐free and wide‐concentration‐range monitoring equipment for CO2 and CH4 greenhouse gases is demonstrated with SACNT film IR source. The concentration ranges for CO2 and CH4 investigated in this paper are 0.0195–20.10% (v/v) and 0.10–17.11% (v/v), respectively. It can be easily applied to monitor other kinds of gases as well.

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NDIR CO2 gas sensing using CMOS compatible MEMS ScAlN-based pyroelectric detector

Cited by 39 publications

References 30 publications

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

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

Fabrication of integrated polysilicon waveguides for mid-infrared absorption sensing

Rapidly Modulated Wide‐Spectrum Infrared Source Made of Super Aligned Carbon Nanotube Film for Greenhouse Gas Monitoring

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NDIR CO2 gas sensing using CMOS compatible MEMS ScAlN-based pyroelectric detector

Cited by 39 publications

References 30 publications

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

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

Fabrication of integrated polysilicon waveguides for mid-infrared absorption sensing

Rapidly Modulated Wide‐Spectrum Infrared Source Made of Super Aligned Carbon Nanotube Film for Greenhouse Gas Monitoring

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

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