A 64k pixel CMOS-DEPFET module for the soft X-rays DSSC imager operating at MHz-frame rates.

ABSTRACT

The 64k pixel DEPFET module is the key sensitive component of the DEPFET Sensor with Signal Compression (DSSC), a large area 2D hybrid detector for capturing and measuring soft X-rays at the European XFEL. The final 1-megapixel camera has to detect photons with energies between [Formula see text] and [Formula see text], and must provide a peak frame rate of [Formula see text] to cope with the unique bunch structure of the European XFEL. This work summarizes the functionalities and properties of the first modules assembled with full-format CMOS-DEPFET arrays, featuring [Formula see text] hexagonally-shaped pixels with a side length of 136 µm. The pixel sensors utilize the DEPFET technology to realize an extremely low input capacitance for excellent energy resolution and, at the same time, an intrinsic capability of signal compression without any gain switching. Each pixel of the readout ASIC includes a DEPFET-bias current cancellation circuitry, a trapezoidal-shaping filter, a 9-bit ADC and a 800-word long digital memory. The trimming, calibration and final characterization were performed in a laboratory test-bench at DESY. All detector features are assessed at [Formula see text]. An outstanding equivalent noise charge of [Formula see text]e-rms is achieved at 1.1-MHz frame rate and gain of 26.8 Analog-to-Digital Unit per keV ([Formula see text]). At [Formula see text] and [Formula see text], a noise of [Formula see text] e-rms and a dynamic range of [Formula see text] are obtained. The highest dynamic range of [Formula see text] is reached at [Formula see text] and [Formula see text]. These values can fulfill the specification of the DSSC project.