A Charge Storage Target for Electron Image Sensing

Abstract

A charge storage target consisting of a dense array of silicon photodiodes has been described as the image-sensing element in a vidicon type of camera tube for the Picturephone® station set. The target stores a spatially distributed charge pattern corresponding to an optical image in the form of a partial discharge of the reverse-bias voltage of the diodes. The discharge results from leakage current associated with hole-electron pairs created in the silicon substrate by incident photons during the raster interval. Recharging of the diodes to the full reverse-bias voltage along a prescribed raster by the scanning, low energy, electron beam creates the desired video signal. This paper describes creation of the hole-electron pairs in the silicon substrate by impinging high energy electrons. Since these electrons, incident from the side opposite the diode array, create a multiplicity of pairs, charge gain results. As in photon sensing, the discreteness of the array allows preservation of detail in the spatial distribution of impinging electrons. Measurements of charge gain as a function of electron energy and target resolution are presented. Applications in scan conversion, low light level TV, X-ray image intensification, and electron microscopy are indicated.