Patent GB-1158923-A (GB)
Title: Improvements in and relating to methods of manufacturing Monograin Layer Devices
IPC: H05B33/20
Filed: 1966-08-01
Abstract: 1,158,923. Uses of luminescence. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. 1 Aug., 1966 [4 Aug., 1965], No. 34354/66. Heading C4S. [Also in Division H1] A monogram layer e.g. a flat or cylindrical layer of semi-conducting material 1 such as 30 micron grains of cadmium sulphide activated with 10<SP>-4</SP> per cent by wt. of Cu and equal amounts of Ga and halogens or cadmium telluride with phophorus dopant, or zinc selenide (grains of less than 50 micron size instanced) is embedded in an insulating filler 2, and electrode layers are applied to at least one face of the layer. The fabrication involves embedding one face of the layer of grains 1 in a photoresist and exposing to radiation from the opposite face, the photoresist on the grains 1 being shielded by the grains 1, and remaining soluble to a developer. The intervening regions of photoresist are exposed and hardened. Application of conducting layer 8, e.g. of vapour deposited copper 100 Š thick provides contact to the protruding grain regions 7 . A second electrode layer 11, e.g. of indium 0À3 micron thick, may be deposited on the opposite face, and a flexible support layer 9, e.g. of radiation-permeable epoxy resin (e.g. 100 microns thick) applied over layer 8. In the form shown the grain layer is made by embedding the grains 1 in a thin layer (4), Fig. 1 (not shown), of adhesive on transparent support (3) (of glass for instance) and applying a coating (2) of negative photoresist to cover the grains (1). On illumination (5), regions (6) of the photoresist remain unexposed, and may be dissolved to allow deposition of the upper electrode. The resulting coherent layer is removed from the support (3) by dissolution of adhesive (4) (of an aqueous solution of saccharose and glucose or polyvinyl alcohol or non- aqueous nitrocellulose acetate in butane for instance). A layer of a material which decreases the adhesion of the layer (4) to the support (3) may be provided between the layer (4) and support (3) to facilitate removal of the grain layer from the support. Alternatively a transparent electrode (14), e.g. indium oxide 0À3 microns thick, Fig. 3 (not shown) may be provided on the support (3). In a further embodiment each grain has a core (21), Figs. 6-9 (not shown), surrounded by an outer region (22) of different electrical properties ; e.g. a core of n-type cadmium telluride with a p-type phosphorus-diffused layer (1 micron thick), or both the core and the outer region may be of the same material, but with differing conductivity, providing a rectifying contact. The grains are embedded in a negative photoresist (23), and exposed surface (24) of outer region (22) of each grain is etched to the core (21). A layer of negative photoresist (25, 26) is applied, and after illumination (32) through the support (3) the portions (26) of this layer on the grains are dissolved away. The exposed junction region of the grain parts (21, 22) remain covered and application of an electrode layer (28) and a flexible support layer (9), removal of the system from its support (3), and deposition of the opposite electrode (30) (e.g. of gold 100 Š thick) proceed as for the first embodiment. Applications instanced are as radiation detectors for corpuscular or e.m. radiation, as photo-diodes (with the p-n junction(s) located in one single crystal or in a powder of monocrystalline grains), photo-resistors, solar batteries, variable capacitors, or as converters of electrical to radiation energy, e.g. injectionluminescence by recombination radiation. One or both electrodes may be replaced by a stream of charged particles e.g. ions or electrons. Radiation impermeable electrodes are also mentioned and also electrodes in two or more parts exposing the underlying grain layer.