Layout options of spectroscopic X-ray DEPFETs

Abstract

The demanding requirements on large area silicon detectors of recent experiments in X-ray astrophysics promoted the development of DEPFET (depleted field effect transistor) active pixel sensors. Those sensors provide an excellent time resolution and noise behavior due to an intrinsic signal amplification, implemented for each pixel. A new generation of spectroscopic prototype X-ray detectors was recently developed for the Wide Field Imager of ESA's (European space agency) next X-ray observatory Athena. For this reason, a dedicated prototype production of DEPFET sensors, comprising different fabrication technologies, pixel layouts and readout modes was fabricated and assembled to detector modules. In this paper we compare different layout options and study their impact on the spectroscopic performance of 64 × 64 pixel detectors. The main difference concern the shape of the transistor gate and the size of the clear structures. Different gate dimensions determine the noise and gain, whereas the size of the clear and source regions mainly effects the charge collection and removal process. In particular DEPFET specific properties like the clear behaviour, short channel effects or the impact of the depletion state on the charge collection are analysed. The comparison of different layouts considers results of the spectral operation complemented by an electrical characterization.