Patent GB-1109102-A (GB)
Title: Improvements in or relating to condition responsive control systems
IPC: H01L45/00
Filed: 1965-04-09
Abstract: 1,109,102. Semi-conductor devices. ENERGY CONVERSION DEVICES Inc. 9 April, 1965 [10 April, 1964 (2)], No. 15085/65. Addition to 1,070,412. Heading H1K. [Also in Division H2] Bidirectional threshold solid-state switches used in the circuits described in Division H2 comprise a block or a thin layer of semi-conductor material provided with a pair of electrodes. When the amplitude of the applied alternating voltage exceeds an upper threshold value it switches to a conductive state which is maintained until the RMS value of the applied voltage falls below a lower threshold value, though reversion to the non-conducting state occurs during a part of each half-cycle the duration of which decreases as the difference between the applied and lower threshold voltages falls. The upper and lower threshold levels decrease with increasing temperature pressure, light intensity or moisture content. Suitable semi-conductor materials include specified mixtures of arsenic tellurium and germanium with or without silicon; arsenic, tellurium and gallium with or without germanium or lead sulphide; tellurium, silicon, and germanium; selenium and arsenic; tellurium, selenium and aluminium; aluminium telluride and the telluride of indium or gallium; and tellurium with one of aluminium, germanium, silicon, indium antimonide, gallium arsenide, arsenic or gallium. The light sensitivity of the mixtures not already including selenium or lead sulphide may be enhanced by the addition of cadmium sulphide, silver telluride, or the selenide of lead, cadmium or zinc. To improve the moisture response the oxide, fluoride, hydroxide, carbonate, orthophosphate, metaborate, ortho- or meta-silicate, acetate, or sulphate, of lithium may be added to the mixtures. A block of material is made by mixing the ground constituents and, after firing, casting the material into heated moulds or allowing it to solidify and then machining it to shape. The entire block or its surface may be produced in the blocking state by inclusion in the relevant parts of impurities such as oxygen, nitric or hydrofluoric acid, chlorine, sulphur, carbon, gold, nickel, iron or manganese, or compounds of alkali or alkaline earth metals. Alternatively it is treated afterwards by machining, sand blasting, bending, impacting, etching, ultrasonic vibration, heating and quenching, bombarding with α, # or γ particles, or current pulsing. Layers of the materials may be formed by vapour depositing the components sequentially and then heating to combine them. Electrodes which may be pressed in or fused or soldered to the blocks or layers or applied by vapour deposition are suitably of tantalum, graphite, niobium, tungsten or molybdenum. Typical multiple devices comprise a conducting electrode block with layers and associated electrodes on opposed faces or with a layer on one face with a pair of spaced electrodes thereon. Light and moisture sensitive elements preferably consist of a layer of semi-conductor bridging two electrodes deposited on an insulated substrate. Pressure sensitive elements may be mounted in a housing (Fig. 13, not shown) consisting of two parts separated by a diaphragm through which fluid pressure in one part is communicated to the element in the other part. The heat-responsive elements may be associated with an auxiliary heater for use as a power relay.