Speaker
Description
The Adaptive Gain Integrating Pixel Detector (AGIPD) is a hybrid pixel, large area detector tailored to the unique beam structure of the European XFEL [1]. The development is a collaborative effort of Deutsches Elektronen-Synchrotron (DESY), the University of Hamburg, the University of Bonn and the Paul Scherrer Institute (PSI) in Switzerland, and has been in operation with silicon sensors since 2017. It is currently the main detector system of 2 scientific instruments (SPB/SFX and MID) and a very valuable tool for the High Energy Density (HED) scientific instrument.
The HED instrument aims at applications in the photon energy range of 20 to 30 keV, where silicon sensors become inadequate due to their low quantum efficiency. To address this limitation, we proposed to develop an AGIPD detector with high atomic number (high-Z) sensor materials. Compound semiconductors such as chromium-doped gallium arsenide (GaAs:Cr), cadmium telluride (CdTe) and cadmium zinc telluride (CdZnTe) were considered, and an electron-collecting version of AGIPD ASICs (ecAGIPD) was designed to leverage from the higher mobility and longer lifetime of electrons with respect to holes in such materials.
While these sensor materials have been extensively characterized by the synchrotron community, their use at XFELs has, to date, been extremely limited. While initial measurements made at LCLS using CdZnTe and GaAs:Cr LPD sensors demonstrated encouraging performance [2], these measurements were limited to pulse repetition rates of 120Hz. Their performance at the high instantaneous flux and MHz repetition rates delivered by the EU.XFEL is yet to be stablished and is the focus of this work.
Prototypes consisting of either 4 single chips or 2x2 quads where flip-chipped and mounted onto AGIPD front-end modules. After initial characterization, the 4 best-performing modules, comprising GaAs:Cr and CdZnTe of different generations and hybridization methods, were mounted side by side on a detector head. The system was tested at HED during beamtimes in November 2024 and February 2025, focusing on the characterization of the system performance and comparison of the sensor materials. A Sparta silicon module produced by X-Spectrum with AGIPD 1.1 technology was used as a reference. In the first beamtime the prototypes were exposed to powder diffraction rings at 18 and 24 keV photons, while the second used homogeneous scattering of 8 keV photons to explore higher intensity conditions.
The ecAGIPD ASICs presented a lower gain compared to AGIPD 1.1 ASICs, even after correcting by the electron-hole pair creation energy of each sensor material. The signal formation in the CdZnTe sensors was delayed by 15 to 25ns with respect to Si and GaAs:Cr, which is consistent with an enhanced small-pixel effect on such materials: while all sensors have an identical pixel pitch of 200um, CdZnTe sensors are 2mm thick, in contrast with 500um thick Si and GaAs:Cr sensors. The preliminary results indicate good linearity and residual after-pulse signal contributing less than 1% of the pulse intensity on all investigated sensor materials, up to an estimated flux of 3.5e+04 8 keV photons/mm2/pulse of 200ns.
[1] Allahgholi, A. et al. (2019). J. Synchrotron Rad. 26, 74-82.
[2] Veale, M.C. et al. (2019). J. Phys. D: Appl. Phys. 52, 085106.
| Workshop topics | Sensor materials, device processing & technologies |
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