NDIR CO₂ 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 CO₂ 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. CO₂ 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 CO₂ gas sensor, we are able to measure the gas response from 5000 ppm down to 100 ppm of CO₂ gas concentration with CO₂ gas response time of ∼5 s, sufficient for practical applications as the average outdoor CO₂ level is ∼400 ppm. The selectivity of this miniaturized CO₂ gas sensor is also tested by mixing CO₂ with nitrogen and 49% sulfur hexafluoride, respectively. The results show high selectivity to CO₂ 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 CO₂ gas sensors based on pyroelectric detectors, which could possibly be integrated with consumer electronics for real-time air quality monitoring.

中文翻译：

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使用 20% ScAlN 基热释电探测器的小型 CO2 气体传感器

NDIR CO ₂使用 10 厘米长的气体通道和 CMOS 兼容的 12% 掺杂 ScAlN 热释电探测器的气体传感器之前已证明检测限低至 25 ppm，快速响应时间约为 2 秒。在这里，我们在基于 ScAlN 的热释电探测器中将 Sc 的掺杂浓度提高到 20%，并将气体通道的体积缩小 65 倍，长度从 10 减小到 4 厘米，直径从 5 减小到 1 毫米。CMOS 兼容的 20% 基于 ScAlN 的热释电探测器的制造尺寸超过 8 英寸。晶圆，允许利用半导体制造降低成本。横截面 TEM 图像显示热释电探测器堆栈中的 20% ScAlN 传感层中存在异常取向的晶粒。光学上，₂吸收波长为4.26 μm。与 12% ScAlN 相比，这些具有异常取向晶粒的 20% ScAlN 的热释电系数通常显示出更高的值。在将温度变化保持在 2°C 的同时，我们注意到热释电系数似乎随着背景温度的增加而增加。分别在 10 厘米长和 4 厘米长的气体通道中测量了 20% ScAlN 基热释电探测器的CO _{2气体响应。}结果表明，对于小型化的 CO ₂气体传感器，我们能够测量从 5000 ppm 到 100 ppm 的 CO ₂气体浓度的气体响应，CO ₂气体响应时间约为 5 s，足以满足实际应用的平均需求。户外一氧化碳₂级为～400 ppm。_{还通过将 CO 2}与氮气和 49% 的六氟化硫分别混合来测试这种小型化 CO ₂气体传感器的选择性。结果显示对CO ₂具有高选择性，氮和49% 的六氟化硫分别引起最小的~0.39% 和~0.36% 的信号电压变化。这些结果为基于热释电探测器的紧凑型和微型低成本 CO ₂气体传感器带来了希望，该传感器可能与消费电子产品集成以进行实时空气质量监测。