Characterisation of a CMOS active pixel sensor for use in the TEAM microscope

A 1M- and a 4M-pixel monolithic CMOS active pixel sensor with 9.5×9.5μm2 pixels have been developed for direct imaging in transmission electron microscopy as part of the TEAM project. We present the design and a full characterisation of the detector. Data collected with electron beams at various energies of interest in electron microscopy are used to determine the detector response. Data are compared to predictions of simulation. The line spread function measured with 80 and 300 keV electrons is (12.1±0.7)(12.1±0.7) and (7.4±0.6)μm, respectively, in good agreement with our simulation. We measure the detection quantum efficiency to be 0.78±0.040.78±0.04 at 80 keV and 0.74±0.030.74±0.03 at 300 keV. Using a new imaging technique, based on single electron reconstruction, the line spread function for 80 and 300 keV electrons becomes (6.7±0.3)(6.7±0.3) and (2.4±0.2)μm, respectively. The radiation tolerance of the pixels has been tested up to 5 Mrad and the detector is still functional with a decrease of dynamic range by ≃30%≃30%, corresponding to a reduction in full-well depth from ∼39∼39 to ∼27∼27 primary 300 keV electrons, due to leakage current increase, but identical line spread function performance.