GB845213A - Improvements in or relating to electroluminescent display devices - Google Patents

Abstract

845,213. Electroluminescence. GENERAL ELECTRIC CO. Ltd. May 29, 1958 [May 29, 1957], No. 17060/57. Class 39(1). [Also in Group XXXVI] An electroluminescent device for use in displaying television images or the results from a computing machine, comprising two sets 2, 5 of mutually insulated conducting elements lying in substantially parallel surfaces with the elements of one set transverse to those of the other set and with a layer of electroluminescent material 3 sandwiched between the two sets at least at their regions of intersection so as to provide a multiplicity of individual electroluminescent cells, has between the electroluminescent layer and at least one set of conducting elements a layer of semi-conducting material 4 having a non-linear resistance characteristic such that the current through the layer between opposite faces increases at an increasing rate as the voltage is increased. The use of the semi-conducting layer is stated to avoid the " cross-effect " of illumination. The semi-conducting material can be such that the current through it is proportional to the nth power of the voltage where n is greater than unity and preferably greater than 3, e.g. approximately 4. The semi-conducting material can consist of powdered germanium, silicon or silicon carbide, or of cadmium sulphide, with a suitable chloride impurity concentration, which can be in an insulating binder such as ethyl cellulose. The cadmium sulphide semi-conducting layer can be made slightly photo-conductive by incorporating a small quantity of activator. The semi-conducting layer can consist of a series of strips each associated with and extending parallel to a respective conducting element of one set of elements, or of a multiplicity of individual deposits located at the regions of intersection of the conducting elements with each deposit shielded from the adjoining electroluminescent cells. The device can be operated on an A.C. supply or on a D.C. supply particularly where the electroluminescent material is in the form of single crystals. In the construction shown in the drawings a glass plate 1 is provided with a series of transparent conducting strips 2 of stannic oxide formed by contacting the glass plate, whilst it is heated to about 500‹C, with the vapour of stannic chloride in the presence of moisture through a suitable mask. Alternatively the strips 2 can be formed by applying a continuous film of stannic oxide to the glass plate and cutting a series of gaps in the film. Over the strips 2 extends a thin layer of electroluminescent material 3 of powdered copper-activated zinc sulphide in an insulating binder such as nitro-cellulose in butyl acetate formed by a flushing and settling process. Over the layer 3 extends a semi-conducting layer 4 of cadmium sulphide in an insulating binder such as ethyl cellulose formed by a settling process. Over the layer 4 is provided a further series of conducting strips 5 extending perpendicularly to the strips 2 and formed by spraying or painting the surface of the layer 4 with silver paint through a mask. An insulating layer 6, such as a glass plate, extends over the strips 5. One end of each of the strips 2, 5 is provided with a terminal 7, 8 respectively for connection to a corresponding contact 9 of the switching means 10 or a contact 11 of a switching means 12. The switching means 10, 12 are connected to opposite ends of the secondary 15 of a transformer 16, the centre point of the secondary being earthed.