The DEPFET detector-amplifier structure for spectroscopic imaging in astronomy and for experiments at free electron lasers

Abstract

The DEPFET detector-amplifier structure possesses several unique properties which make it extremely useful as readout element in semiconductor detectors and in particular as building block of semiconductor pixel detectors. Variations of DEPFETs can be tuned to specific requirements as to be sensitive only in predetermined time intervals, to measure signal charge with sub-electron precision, dead-time-free readout and with signal compression. These devices have been shown to work in simulations and in prototypes. Recently the first two fully developed detector systems have been finished and installed in the MIXS (Mercury Image X-ray Spectrometer) instrument of the Mercury Planetary Orbiter scheduled to be launched in 2017. A further DEPFET detector system under development is the DSSC (Depfet Sensor with Signal Compression) that will be installed in one of the beam-lines of XFEL. The requirements of the two projects are rather different. While the MIXS sensors are supposed to measure precisely the energy and position of single photons down to very low energies but at moderate rates, the DSSC has to measure the number of photons arriving in each pixel within a time interval of 220ns. Here the challenge is the capability of detecting single X-ray photons in one pixel simultaneously with up to 10,000 photons in some other pixels. Device functioning has been verified with sensors produced in a research laboratory. Now process and design have been adapted to an industrial type production line, allowing additional improvements.