Secondary electron conduction (SEC) for signal amplification and storage in camera tubes

Abstract

Previous studies <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1,2</sup> of the electrical properties of thin-film low-density deposits of insulators have led us to investigate their application as electrostatic storage targets. It was found that the charge image on the target is not only established by transmitted secondary electrons but that the backward conduction of secondary electrons through the layer also contributes to the amplifying mechanism. Free electrons created by the incident primary electron which are normally not observed as emitted secondary electrons can be conducted through the voids of the low-density layer to the target signal plate under the action of an electric field. This mechanism leads to an efficient conversion of photoelectrons with several kev energy into a large number of positive charge centers on the surface of the layer which are accessible to a low-energy reading beam. The secondary electron conduction (SEC) effect provides, therefore, high target gain while solid-state time lag does not occur. The high resistivity of such layers, many orders of magnitude greater than that of insulators in bulk form, is advantageous for long-time integration and storage. The target has a large storage capacity useful not only to provide a wide dynamic range, but also to accommodate the more intense signals required for low contrast image detection. The capacity is small enough, however, to eliminate discharge lag. Compatibility of the SEC target with standard photosurfaces, such as S-11, S-20, and various ultraviolet sensitive types, has been demonstrated in sealed-off tubes. The performance of SEC vidicon tubes is reported, and it is concluded that the SEC target offers the potential of overcoming several limitations found in present day camera tubes.