Recent improvements on high-speed DEPFET detectors for x-ray astronomy

Sensors that are based on active pixels enable a flexible adaption to the needs of a scientific instrument. The DEPFET,∗ a p-channel field effect transistor implemented on a fully depleted silicon bulk, contains a so-called internal gate that serves as potential minimum for collected charge carriers generated by incident photons.¹ The potentially collected electrons induce mirror charges in the FET channel and change its conductivity. It changes the current through the DEPFET or – for a fixed current – the source potential proportionally to the collected charge carriers and, therefore, to the energy of the incident photon. By the integration of a storage into each pixel, the accuracy of the energy measurement can be improved, especially for high frame rates in the order of the readout time of one pixel. One implementation of such a concept is the so-called Infinipix.² It is composed of two sub-pixels that share their source node in the center. The functional principle was already demonstrated on single pixel³ and matrix scale⁴ but enhancements are still necessary to improve the robustness of the devices. In this paper we present variations in the processing technology and the layout that enhance the reliability of the DEPFETs with integrated storage. Adaptions in the technology help to increase the operation voltages for the charge suppression at the insensitive sub-pixel which is demonstrated with measurements. A layout variation combines the advantages of existing layout variants. It was tested with 3D TCAD† simulations and is in fabrication to be available for measurements.