Tests of a backside illuminated monolithic CMOS pixel sensor in an HPD set-up

A backside illuminated, monolithic CMOS pixel sensor for direct detection of low energy electrons has been developed and is proposed as an active element for a non-destructive hadron beam monitor. In this application, the device is used as an imager of secondary electrons emitted from an aluminium foil of sub-micrometer thick intersecting the beam and accelerated in an electrostatic field to ∼20-30 keV energy. The sensitivity to these electron energies (a few microns range in silicon) is obtained by back-thinning the detector, fabricated in the form of standard VLSI chip, down to the radiation sensitive epitaxial layer. The original thinning procedure was applied for processing of a large area, one million pixels prototype. The prototype has been tested using low-energy electrons inside an HPD structure. Tests results proving the device imaging capabilities of such a radiation are presented.