Multiport-readout frame-transfer 5 megapixel CCD imaging system for TEM applications

A multiport-readout, frame-transfer charge-coupled device (CCD) digital ima ging system has been successfully developed and tested for intermediate-hig h-voltage electron microscopy (IVEM) applications up to 400 keV. The system employs a back-thinned CCD with 2560 x 1960 pixels and a pixel size of 24 mu m x 24 mu m. In the current implementation, four of the eight on-chip re adout ports are used in parallel each operating at a pixel rate of 1- or 2- MHz so that the entire CCD array can be read out in as short as 0.6 s. The frame-transfer readout functions as an electronic shutter which permits the rapid transfer of charges in the active pixels to four masked buffers wher e the charges are readout and digitized while the active area of the CCD is integrating the next frame. With a thin film-based phosphor screen and a h igh-performance lens relay, the system has a conversion factor of 2.1 digit al units per incident electron at 400 keV, and a modulation transfer functi on value of 14% at the Nyquist frequency. (C) 2000 Elsevier Science B.V. Al l rights reserved.