Virtual Phase Charge Coupled Device Imager Operated In Frontside Electron-Bombarded Mode

Abstract

The Texas Instruments virtual phase CCD imager has been successfully operated in the frontside electron-bombarded mode. The entire active area of the imager was covered with 130 nm of thermally grown gate oxide while only the clocked half of each pixel was additionally covered with a 500 nm polysilicon electrode. No protective overcoat was grown over the imager. A 20 kV electron beam was focused onto the imager to a total dose in excess of 120,000 primary electrons per pixel. Both the parallel and serial clocks were operated between -15 V and +2 V throughout, and no adjustment in any of the operating parameters was required. However, flat band shifts on the order of 2 V were detected. Single primary electron events were clearly detected with a signal-to-noise ratio exceeding 10. In excess of 90% of the secondary charge generated by a primary event was collected in a single pixel. The standard virtual phase imager with only the protective overcoat deleted can be used with a photocathode in the electron-bombarded mode for observing low to moderate light levels and can act as a true photon counter.