Aluminum nitride (AlN) is a promising photonics material contributed by its wide transparency window and remarkable nonlinear optical property. Moreover, its nonlinear effect can be further enhanced by doping Scandium (Sc). Such nonlinear optical property brings potential for high efficiency in nonlinear optical generation processes, such as 2nd harmonic generation and frequency comb generation. Although the nonlinear optical property of Sc-doped AlN looks promising, its waveguide is facing challenge on loss reduction. In this work, we report Sc-doped AlN photonic integrated circuit with reduced waveguide loss of 6 dB/cm around 1550 nm. The waveguide has Sc doping concentration of 10%. Its etching process is tailored through a design of experiment (DoE) approach to achieve smooth surface. An annealing process is also applied to patterned waveguide for optical loss reduction. A loaded Q of 1.41×104 has also been reported from microring resonator on the same wafer. The reported result paves the way towards low-loss Sc-doped AlN for photonic integrated circuits.
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.
We present the optical and electrical properties of AlN-based and 12% doped ScAlN-based pyroelectric detectors fabricated on 8-inch wafers respectively. Both AlN and ScAlN materials are deposited at a temperature of ~200oC, making them potential candidates for CMOS compatible MEMS pyroelectric detectors. FTIR spectroscopy is used to measure the absorption of these pyroelectric detectors over the wavelength range of ~2–14 μm and the results show absorption improvement up to ~75% for ScAlN-based pyroelectric detectors compared to that of AlN-based pyroelectric detectors at the wavelength of 4.26 μm where CO2 gas absorption of IR radiation is anticipated. Higher output current (~3-fold increase) is also observed from ScAlN-based pyroelectric detectors. Other than pyroelectric coefficient that contributes to improved performance for ScAlN-based pyroelectric detectors, we believe that absorptivity of the device also plays a major role in the performance of pyroelectric IR detectors. The results obtained from the study of the electrical and optical properties of AlN-based and ScAlN-based CMOS compatible MEMS pyroelectric detectors will bring forth potential applications of these detectors onto multi-functional integrable and monolithic platforms.
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