Patent GB-1070411-A (GB)
Title: Improvements in or relating to symmetrical current controlling devices
IPC: H01L21/00
Filed: 1963-09-20
Abstract: 1,070,411. Semi-conductor switches. ENERGY CONVERSION DEVICES INCORPORATED. Sept. 20, 1963 [Sept. 28, 1962; Jan. 18, 1963 (3); June 17, 1963], No. 37137/63. Heading H1K. [Also in Divisions H2 and H3] A symmetrical switch comprises a semi-conductor material between ohmic electrodes the material being switchable from a generally amorphous high-resistance blocking state to a crystalline conductive state. It may be switched to. the conductive state by application of a direct voltage above a threshold value and is capable under certain conditions of remaining in this state while the current is reduced to zero but can be switched back to the blocking state by a current pulse above a threshold value. Three types of device, referred to as the HILO, CIRCUIT BREAKER and MECHANISM WITH MEMORY devices respectively are described. The first two may also be rendered conductive by an alternating voltage above a threshold value and remain so when the current is removed but can be rendered blocking again when the applied voltage is below the threshold by a pulse current above a certain value. In the case of the circuit breaker reversion to the blocking state occurs even if the current is slowly raised to such a value. Response of the mechanism devices with memory to alternating currents is different. They switch on when the alternating voltage peak exceeds a threshold but switch off momentarily during the low-current parts of each cycle and switch off altogether when the applied voltage falls to a lower threshold value. In all cases the threshold values are temperature variable. The same physical constructions are used for all three types of device. Typically the semi-conductor material is in the form of a body with electrodes on opposed faces or on the same face. Alternatively it is a layer on one face of a conductive or insulating block. Where the block is conductive it may constitute one electrode of one device or the common electrode of two series-connected devices. In each case further control electrodes may be provided on the body or layer. In a particular form of device the body is necked and insulated control electrodes are provided on the necked region between the main electrodes. The semi-conductor material may alternatively be a coating on one or both of two wires which may be in contact side by side or crossing one another or twisted together. Lead sulphide and specified mixtures of tellurium and germanium which may contain vanadium pentoxide, magnetic particles, or gallium arsenide and iron as additives, of tellurium and antimony, gallium antimonide, nickel, silicon or indium antimonide, and of selenium and germanium are suitable materials for use in HILO devices. Various treatments and methods of providing electrodes to such materials are discussed. HILO devices may alternatively consist of aluminium or tellurium between layers of tellurium oxide each provided with an electrode or of surface oxidized copper, iron or aluminium wires twisted together. Circuit breakers may consist of specified mixtures of tellurium and germanium with or without silicon, caesium, or gallium arsenide and iron, bodies of selenium-germanium, or bodies of tellurium-germanium coated with a mixture of tellurium, arsenic, gallium and lead sulphide. The alloy materials are prepared by grinding up the components, melting in a sealed vessel and grinding or casting the resulting material to the required form. Alternatively they may be vapour deposited on a substrate. It is stated that the materials may be improved and stabilized by additions of arsenic, sulphur, phosphorus, antimony, arsenides, sulphides, phosphides and antimonides, gold, carbon, chlorine, oxygen, nickel, iron, manganese, aluminium, caesium and other alkali or alkaline earth metals, by electroforming, and by various mechanical and heat treatments, etching and radiation bombardment. The theory of operation of the devices is discussed in the Specification.