![]() ![]() In addition to reducing its cost, the size of each sensor is also of importance, as a bulky sensor will make mass deployment difficult, not to mention that material cost might increase for a sensor with a bigger form factor. In general, there are many factors when considering the cost of a CO 2 sensor. At the same time, functional flexibility of these CO 2 sensors should also be considered, whether they can be modified with minimum cost or involve change to sense different gases. Other than the cost of manufacturing the sensor, the operational cost such as the power required to operate the sensor and the temperature at which the sensor operates could also add to the cost. If these sensors are high cost, the number of sensors that can be deployed for air quality monitoring will be limited by the sensor price. Cost is an important factor, as CO 2 gas sensors which are low cost can enable more sensors to be deployed for more accurate real-time CO 2 level monitoring within a certain area. ![]() This would become more of a reality if the CO 2 gas sensors are low cost and miniature. With the presence of CO 2 sensors, one would be able to monitor in real-time the quality of air, raising awareness on the quality of the air we breathe in. (1) Specifically, elevated levels of CO 2 (>1000 ppm of CO 2 gas concentration) in enclosed spaces will result in sick building syndrome (SBS), (2) with occupants experiencing drowsiness, headaches, and difficulties in concentrating. Even before the COVID-19 pandemic, there were reports on the detrimental effects to human health with extended exposure to high concentrations of CO 2. The need for well ventilated spaces is especially important these days to ensure good air quality, so as to reduce the transmission of SARS-CoV-2/COVID-19 (severe acute respiratory syndrome coronavirus-2/coronavirus disease 2019). ![]() 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.Ĭarbon dioxide (CO 2) sensors have been of interest in recent years to monitor air quality in enclosed crowded spaces. 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. 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 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. CO 2 gas responses are measured for 20% ScAlN-based pyroelectric detectors in both 10-cm-long and 4-cm-long gas channels, respectively. While keeping the temperature variation constant at 2 ☌, we note that the pyroelectric coefficient seems to increase with background temperature. The pyroelectric coefficient of these 20% ScAlN with abnormally oriented grains shows, in general, a higher value compared to that for 12% ScAlN. 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. Cross-sectional TEM images show the presence of abnormally oriented grains in the 20% ScAlN sensing layer in the pyroelectric detector stack. wafers, allowing cost reduction leveraging on semiconductor manufacturing. The CMOS-compatible 20% ScAlN-based pyroelectric detectors are fabricated over 8-in. 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. 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. ![]()
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