In a longstanding effort to overcome limits of film and the charge coupled device (CCD) systems in electron microscopy, we have developed a radiation-tolerant system that can withstand direct electron bombardment. A prototype Direct Detection Device (DDD) detector based on an Active Pixel Sensor (APS) has delivered unprecedented performance with an excellent signal-to-noise ratio (approximately 5/1 for a single incident electron in the range of 200-400 keV) and a very high spatial resolution. This intermediate size prototype features a 512×550 pixel format of 5&mgr;m pitch. The detector response to uniform beam illumination and to single electron hits is reported. Radiation tolerance with high-energy electron exposure is also impressive, especially with cooling to -15 °C. Stable performance has been demonstrated, even after a total dose of 3.3×10<sup>6</sup> electrons/pixel. The characteristics of this new detector have exciting implications for transmission electron microscopy, especially for cryo-EM as applied to biological macromolecules.
High resolution electron imaging is very important in nanotechnology and biotechnology fields. For example, Cryogenic Electron-Microscopy is a promising method to obtain 3-D structures of large protein complexes and viruses. We report on the design and measurements of a new CMOS direct-detection camera system for electron imaging. The
active pixel sensor array that we report on includes 512 by 550 pixels, each 5 by 5 μm in size, with an ~8 μm epitaxial layer to achieve an effective fill factor of 100%. Spatial resolution of 2.3 μm for a single incident e- has been measured. Electron microscope tests have been performed with 200 and 300 keV beams, and the first recorded Electron Microscope image is presented.