Considerations for an 8-inch Wafer-Level CMOS Compatible AlN Pyroelectric 5–14 μm Wavelength IR Detector Towards Miniature Integrated Photonics Gas Sensors

Abstract

CMOS compatibility and 8-inch manufacturability have been highly desired in MEMS technology. In this article, we demonstrate a MEMS pyroelectric IR detector using CMOS compatible AlN and 8-inch semiconductor wafer technology. This AlN pyroelectric detector detects IR over wavelength ranging from 5 µm to 14 µm. In addition, this detector is designed to have added mechanical stiffness for improved device integrity. The detectors are fabricated with different sensing area dimensions to compare their performance. The best performing detector has an NEP ∼ 8.87 × 10-9 W/ √ Hz and D * ∼ 6.04 × 10 6 cm √ Hz/W. These pyroelectric detectors are designed and built with the consideration to enable ease of monolithic integration with other components to form an integrated gas sensor system. This includes enabling detection of illumination from the front side and using an absorber stack that consists of CMOS dielectric layers. Subsequently, they will form a crucial part of the architectures for miniature photonics-based gas sensors. Their performance is a first step towards 8-inch wafer level CMOS-compatible manufacturable photonics gas sensors.

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

“…The absorption of ∼50% for the 20% ScAlN-based pyroelectric detector with AOGs is lower than that of the 12% ScAlN-based pyroelectric detector previously reported with absorption ∼75% 3 , 29 , 36 but higher than that of AlN-based pyroelectric detector which reports absorption ∼25%. 30 , 36 The high reflection at the ∼4 μm wavelength region which causes lower absorption in the same wavelength region could be caused by the rougher surface 37 of the detector stack (as observed from Figure 2 b previously) mainly attributed by the AOGs in the 20% ScAlN layer that induces the rough interface between the ScAlN layer and TiN (as observed from Figure 2 c and d previously).…”

“…Aluminum (Al) is used for the metal contact layers for the top and bottom electrodes. Beneath the bottom Mo electrode is a layer of silicon dioxide (SiO 2 ) patterned with waffle-like structures , to help increase mechanical stiffness of the pyroelectric detector membrane stack and act as a damper to reduce microphonic effects.…”

“…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.…”

Integrated Nanophotonic Waveguide-Based Devices for IR and Raman Gas Spectroscopy

“…The recent trend in the integrated detector domain has moved toward MEMS-based IR detectors, such as thermopiles, microbolometers, and pyroelectrics, which can work even at room temperatures and have detection capabilities across a longer wavelength range [124][125][126]. However, they still lag behind photodetectors in terms of sensitivity and have slower response times.…”

2020 Index Journal of Microelectromechanical Systems Vol. 29

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