Characterization of a 256 × 256 pixel DEPFET detector for the WFI of Athena

The Wide Field Imager (WFI) instrument is one of two complementary focal plane cameras on ESA's next large class X-ray astronomy mission Athena. It is coupled to a high performance X-ray mirror to provide an unprecedented survey power by combining a large field of view with an excellent count rate capability. The required spectral performance, sensitive area and readout timing necessitated the development of specific DEFPET detectors. In the course of the technology development phase of the project, different options of prototype detectors were fabricated and investigated. As a result, a new generation of spectroscopic X-ray DEPFET detectors was developed for the flight production. Those detectors will feature a linear gate layout, thin gate oxide fabrication technology and a drain current readout. In this paper, we present the detailed characterization of a prototype detector covering a large sensitive area of 256 × 256 pixels. Due to the progress in the detector development an energy resolution as low as 128 eV FWHM at 6 keV was obtained.