Patent GB-950593-A (GB)
Title: Improvements in or relating to solid-state image intensifiers
IPC: H01L31/14
Filed: 1960-02-19
Abstract: A solid state image intensifier incorporates a layer of 70-90, preferably 80%, by volume of finely divided, photo-conductive cadmium sulphide or selenide and 10-30% by volume of electret material which constitutes a binder. The electret material can be a lead-free, lithium containing glass enamel.  A suitable composition for the enamel is in mol. per cent: Li2O-15, K2O-7.5, CaO-10.5, SrO-4.5, ZnO-10.3, TiO2-2.8, Al2O3-2.3, SiO2-18.8, B2O3-28.3. The layer is formed by spreading over ridges in the intensifier a thin coating of a suspension of the photo-conductive grains and the powdered glass enamel in an organic liquid such as butyl acetate and heating to about 600 DEG  C. for about 3 minutes.ALSO:A solid-state image intensifier comprises electric field sensitive luminescent elements, radiation-sensitive impedance-variable elements and electrodes for applying an alternating voltage, so arranged that in operation the part of the supply voltage appearing across any luminescent element is controlled by a group consisting of at least two radiation-sensitive elements electrically associated with that luminescent element, the radiation-sensitive elements consisting of a finely divided photo-conductive material and an electret material polarized in such a manner that the group of radiation-sensitive elements electrically associated with the same luminescent element comprises at least one element polarized in one direction with respect thereto and at least one polarized in the opposite direction. As shown <PICT:0950593/C3/1> in Fig. 1, the intensifier may comprise a transparent base 1, a transparent electrode 2, an electroluminescent layer 3, an opaque layer 4, auxiliary electrode elements 5 defining elements 11 in the electroluminescent layer 3, and insulating V-section ridges 6 surmounted by electrodes 8 and covered by a photo-conductive layer 10 extending into the valleys between the ridges to contact the electrodes 5.  The electroluminescent layer 3 is 50-100 microns thick and comprises 20% by volume of copper and aluminium activated zinc sulphide and 80% by volume of lead-free glass enamel. The photo-conductive layer comprises 70-90% by volume of finely divided photo-conductive copper or gallium activated cadmium sulphide or cadmium selenide or cadmium telluride and 10-30% of electret material also acting as a binder. The electret material is preferably a lead-free lithium-containing glass enamel, e.g. Li2O 15%; K2O 7.5%; CuO 10.5%; SrO 4.5%, ZnO 10.3%; TiO2 10.8%; Al2O3 2.3%; SiO2 18.8%; B2O3 28.3% in terms of mol. per cent The electret material is polarized in the required direction by application of a direct voltage of about 650 v. from source 15 with a simultaneous exposure to white light of intensity about 20 lux for 5-10 seconds.  The intensifier operates with A.C. from source 14 applied across electrode layer 2 and the electrodes 8, commoned as shown, the photo conductive elements 12, 13 associated with the electroluminescent "element" 11 being oppositely polarized. In another embodiment neighbouring "elements" of the photo-conductive layer are oppositely polarized by two successive exposures to light through an element-defining mask, the applied D.C. being reversed between the two exposures. In a further embodiment wherein after assembly, electrodes to polarize or re-polarize the electret material are inaccessible from outside, this material is contacted by insulating strips which may be rendered temporarily conductive, e.g. by irradiation or heat, to enable a polarizing voltage to be applied.