DEPFET active pixel sensor with non-linear amplification

One of the X-ray imaging detectors in development for the European XFEL (X-ray Free Electron Laser) is the DSSC (DEPFET Sensor with Signal Compression). The DSSC sensor array will have a format of 1024 × 1024 pixels with a pixel size in the order of 200 μm. It is optimized for the detection of low-energy X-ray photons and designed to operate at frame rates up to 4.5 MHz with a dynamic range of several thousand photons per pixel and frame and single photon resolution at small photon numbers. The DSSC system´s core component is an active pixel sensor based on the DEPFET (DEpleted P-channel Field Effect Transistor) structure. 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. For the DSSC-adaptation of the DEPFET principle the new feature of signal compression has been added, i.e. the device has a high gain at small signals and a reduced gain at large signals. With this strongly non-linear response the DSSC-DEPFET provides the required high charge handling capacity with simultaneous single photon resolution for low-energy X-rays. This paper presents the concept of the DSSC-DEPFET. Its functionality is demonstrated by measurements of a first series of prototypes.