Internal charge injection for the calibration of DEPFETs with non-linear amplification

Within the DSSC (DEPFET Sensor with Signal Compression) project a new active pixel sensor based on a Depleted P-Channel Field Effect Transistor (DEPFET) has been developed for the use at the European X-ray Free Electron Laser (EuXFEL). A DEPFET is an integrated detector amplifier combining internal amplification, full sensitivity over the whole bulk thickness, analog data storage, readout on demand, low serial noise, and absence of reset noise. To cope with the EuXFEL detector requirements the new developed DSSC-DEPFET has a non-linear amplification, i.e. a high gain for small signals in order to provide single photon resolution of low energy X-rays and a reduced gain for large signals to have a high dynamic range of several thousand photons per pixel and frame. For a pixel by pixel calibration of the final DSSC system the new feature of internal charge injection in every pixel has been introduced and investigated in detail using existing DSSC-prototype structures. This paper illustrates the principle of the injection mechanism and demonstrates its capability for calibration purposes.