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 ultra-violet spectrograph for solar physics studies on ESA's Solar
Orbiter. Our route to EUV sensitivity relies on adapting the back-thinning and back-illumination techniques first
developed for CCD sensors. Our first large-format sensor consists of 4kx3k 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 2kx2k 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 512x512 10 μm pixels. Each
of the arrays has been given a different pixel design to allow verification of our models and progress towards optimising
a design for minimal system readout noise and maximum dynamic range. These sensors will also be back-thinned for
characterisation at EUV wavelengths.