Multiport-Readout Frame-Transfer 5 Megapixel CCD Digital System for IVEM Applications

Abstract

A multiport-readout, frame-transfer charge coupled device (CCD) digital imaging system has been successfully constructed and tested for intermediate-high voltage electron microscopy (IVEM) applications up to 400 keV. The system employs a back-thinned CCD, made by MIT Lincoln laboratories, that comprises 2560 × 1960 pixels and a pixel size of 24 μm × 24 μm. With a frame transfer design, the imager fills nearly the entire usable area of a 100 mm-diameter silicon wafer (FIG. 1). In the current implementation, four of the eight on-chip readout ports are utilized 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 seconds. The frame-transfer readout functions as an electronic shutter which permits the rapid transfer of charges in the active pixels to four light-shielded buffers (FIG. 1) where the charges are readout and digitized while the active area of the CCD is integrating the next frame. At 2 MHz, charge transfer of 980 CCD rows will be completed in under 0.5 ms, which is much shorter than a typical exposure time of a few seconds. The camera head (FIG.2) and control electronics for CCD sensor were packaged by Photometries (Tuscon, Arizona). Two MaxVideo 200 image processing boards from Datacube (Peabody, MA) are used for high speed online imaging processing. The CCD sensor is electronically cooled to ∼ −40°C during operation.