In the scope of the Electron DETector project, a DEPFET-based camera system for direct electron imaging in a TEM (Transmission Electron Microscopy) environment, the so-called EDET80k (abbr. for 80 kHz Framerate), is being developed. This project is done in collaboration with the Max-Planck-Institute for structure and dynamics of matter in Hamburg, Karlsruhe Institute of Technology and University of Bonn. The key feature of this system is the fast imaging rate of 80 kHz, i.e. 13 μs per frame, for 1024 x 1024 pixels. In the TEM system, which has an electron source capable of providing a primary electron beam with corresponding structure in time, the DH80k camera system will allow observing dynamic processes with unprecedented time resolution. Due to the high data rate, the recording of frames takes place in bursts of 60 images, which are acquired completely, followed by a break, in which the data is being transferred to the peripheral readout electronics. The overall instrument’s duty cycle is targeted to be 1:10.
Different window modes with reduced image size are also possible allowing even faster readout sequences.
The focal plane is composed of 4 tiles of 512 x 512 pixels each, which are arranged in a clover-like geometry with minimal sensitivity gaps at the edges of adjoining tiles. The entire focal plane assembly is mounted inside the TEM vacuum vessel, where the available space is very limited, so the entire system needs to be designed in a maximally compact way. To reduce the instruments potential downtime in case of problems and to allow for easy replacements and repairs, the system is set up in a modular way.
The technology of the tile modules is based on the All-Silicon-Module (ASM) technology on Silicon-On-Insulator (SOI) material developed in the pace of the BELLE vertex tracker development. To keep the influence of multiple scattering of electrons (and the according deterioration of the line spread function) inside the sensitive volume of the detector as low as possible, the decision was made to thin the detector sensitive volume (the part of the SOI wafer below the actual DEPFET matrix) down to 50 μm or even 30 μm for some, more experimental wafers. In the peripheral parts of the ASM, the silicon remains at its original thickness of ~500 μm.
EDET80k all silicon module
CAD view of EDET DH80k focal plane.
Block schematic of a tile module and its system components.
Overview over the complete EDET system
Results of imaging measurements