Quantum efficiency of Si Hybrid CMOS detectors in the soft X-ray band*

X-ray sensitive Si Hybrid CMOS detectors (HCDs) will potentially replace X-ray CCDs in the focal planes of future X-ray observatories. HCDs improve on the performance of CCDs in numerous areas: faster read out time, windowed read out mode, less susceptibility to radiation {\&} micrometeoroid damage, and lower power consumption. Understanding the detector quantum efficiency (QE) is critical for estimating the sensitivity of an X-ray instrument. We report on the QE for multiple energies in the soft X-ray band of four HCDs based on the Teledyne Imaging Sensors HyViSI$^{\mathrm{TM}}$ detectors. These detectors have Al optical blocking filters deposited directly on the Si substrate; these filters vary in thickness from 180 -- 1000 {\AA}. We estimate the QE with a 1D slab absorption model and find good agreement between the model and our results across an energy range from 0.677 -- 8.05 keV.