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

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 250 eV and 6 keV, and must provide a peak frame rate of 4.5MHz 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 512 x 128 hexagonally-shaped pixels with a side length of 136 mu m. 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 testbench at DESY. All detector features are assessed at 18 degrees C. An outstanding equivalent noise charge of 9.8e-rms is achieved at 1.1-MHz frame rate and gain of 26.8 Analog-to-Digital Unit per keV ( ADU/ keV). At 4.5MHz and 3.1 ADU/ keV, a noise of 25.5 e(-)rms and a dynamic range of 26 ke(-) are obtained. The highest dynamic range of 1.345Me(-) is reached at 2.25MHz and 1.6ADU/ keV. These values can fulfill the specification of the DSSC project.

Automated summary

This paper summarizes the functionality and properties of the 64k pixel DEPFET module, a key sensitive component of the DEPFET Sensor with Signal Compression (DSSC) used for capturing and measuring soft X-rays at the European XFEL. The module features low input capacitance and signal compression capability, and has been calibrated and evaluated in a laboratory testbench. The pixel sensors provide excellent energy resolution and can meet the specifications of the DSSC project.