Development of a thinned back-illuminated CMOS active pixel sensor for extreme ultraviolet spectroscopy and imaging in space science

We describe our programme to develop a large-format, science-grade, monolithic CMOS active pixel sensor for future space science missions, and in particular an extreme ultraviolet (EUV) spectrograph for solar physics studies on ESAʹs Solar Orbiter. Our route to EUV sensitivity relies on adapting the back-thinning and rear-illumination techniques first developed for CCD sensors. Our first large-format sensor consists of 4k×3k 5 μm pixels fabricated on a 0.25 μm CMOS imager process. Wafer samples of these sensors have been thinned by e2v technologies with the aim of obtaining good sensitivity at EUV wavelengths. We present results from both front- and back-illuminated versions of this sensor. We also present our plans to develop a new sensor of 2k×2k 10 μm pixels, which will be fabricated on a 0.35 μm CMOS process. In progress towards this goal, we have designed a test-structure consisting of six arrays of 512×512 10 μm pixels. Each of the arrays has been given a different pixel design to allow verification of our models, and our progress towards optimizing a design for minimal system readout noise and maximum dynamic range. These sensors will also be back-thinned for characterization at EUV wavelengths.