Quantum Efficiency of the CIS115 in a Radiation Environment

An optical bench setup for quantum efficiency (QE) measurements across the 350 nm to 1100 nm range has been developed at the Open University's Centre for Electronic Imaging (CEI). Here we use it to measure the performance of a monolithic silicon CMOS image sensor (CIS), the CIS115. This sensor was selected for the JANUS camera, due to launch on board ESA's JUpiter ICy moons Explorer (JUICE) spacecraft in 2022. The CIS115 sensors tested here have high quantum efficiency (QE) over the optical band, due to their backside illumination and multi-layer anti-reflective coating. Here we validate the QE measurements against manufacturer reported performance and compare the QE for unirradiated (beginning of life) and gamma-irradiated devices, indicating that no significant change in performance should be expected after a total ionizing dose (TID) of 200 krad(Si). This is important for the JANUS application, where the sensor is predicted to accumulate up to 44 krad(Si) TID. We also demonstrate that the measurement setup has excellent repeatability. We conclude by discussing the limitations of the setup, including the key systematic error sources that have been understood and investigated. Optional improvement to the setup for reducing these errors are presented and will be considered for follow-on activities.