Quality factor (Q-factor) is important parameter for surface ion trap. To improve the Q-factor, isolation dielectric thickness was increased from 2μm to 3μm, Si trench concept was applied in this study. To reduce Si substrate RF loss, glass substrate was used for surface ion trap metal plates fabrication. We report the results obtained from determining the Q-factor of the fabricated devices at room temperature and cryogenic temperatures.
SF6 gas sensor is developed to measure SF6 gas at different concentrations mixed with N2 based on mid-IR absorption of SF6 at a wavelength of ~10.6 μm. An optical bandpass filter of ~10.6 μm is put in front of a thermal emitter source to allow light of this wavelength to pass through. A CMOS compatible pyroelectric detector is put on the other end of the gas channel to measure the voltage change due to presence of SF6 gas. Here, we use AlN-based and 12% ScAlN-based pyroelectric detectors respectively. The results show for 100% SF6 gas sensing, 12% ScAlN-based pyroelectric detector gives ~73% higher response compared to when using AlN-based pyroelectric detector. The voltage drop between reference N2 gas and different SF6 gas concentrations is also higher (up to 2x) when using 12% ScAlN-based pyroelectric detector. Based on the measured SF6 gas responses, we try to estimate the lower limit of detection of our gas sensors when using AlN- and ScAlN- based pyroelectric detectors respectively. Response times taken for both detectors to detect SF6 concentrations are measured to be ~6.26 s for AlN-based pyroelectric detector and ~1.99 s for 12% ScAlNbased pyroelectric detector. Finally, both pyroelectric detectors’ electrical responses across different frequencies are measured and their 3-dB frequency cutoffs are extracted to be ~13.5 Hz and ~12.6 Hz for AlN- and 12% ScAlN- based pyroelectric detector respectively. The results provide more understanding on characteristics of pyroelectric detectors in SF6 greenhouse gas sensing based on mid-IR absorption.
A demonstration of an on-chip CO2 gas sensor is reported. It is constructed by the integration of a MEMS-based thermal emitter, a scandium-doped aluminum nitride (ScAlN) based pyroelectric detector, and a sensing channel built on Si substrate. The integrated sensor has a small footprint of 13mm × 3mm (L×W), achieved by the replacement of bulky bench-top mid-IR source and detectors with MEMS-based thermal emitter and ScAlN-based pyroelectric detector, with their footprints occupying 3.15 mm × 3 mm and 3.45 mm × 3 mm, respectively. In addition, the performance of the integrated sensor in detecting CO2 of various concentrations in N2 ambient is also studied. The results indicate that the pyroelectric detector responds linearly to the CO2 concentration. The integration of MEMS emitter, thermal pathway substrate, and pyroelectric detector, realized through CMOS compatible process, shows the potential for massdeployment of gas sensors in environmental sensing networks.
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