Calibration strategy and experimental qualification of the first DEPFET pixel sensors of the DSSC camera

A novel design of the Depleted P-Channel Field Effect Transistor (DEPFET) with non-linear response is at the heart of the 1 Mpixel DSSC camera (DEPFET Sensor with Signal Compression) for ultra-fast imaging of soft X-rays at the European XFEL. The simultaneous requirement of single-photon detection down to 0.5 keV and dynamic range up to 104 photons/pixel/pulse is here solved by introducing a non-linear compression of the DEPFET transistor. The accurate calibration of a 1 Mpixel DEPFET sensor with signal compression is the key to reach the desired performances but also the major challenge. The aim of this work is to discuss the general calibration strategy, to present the experimental results of the first calibration campaigns on the first 128x512 DSSC ladder and to discuss the open issues. The achieved results validate the calibration strategy of the full DSSC camera and show achievement of noise levels below 20 electrons rms and an input range of deposited energy up to several MeV per pixel per pulse.