Patent GB-837651-A (GB)
Title: High power field-effect transistor
IPC: H01L23/40
Filed: 1957-12-09
Abstract: 837,651. Transistors. TESZNER, S. Dec. 9, 1957 [Dec. 10, 1956; Nov. 30, 1957], No. 38244/57. Class 37. A high-power field effect transistor comprises a semi-conductor body of one conductivity type with a base region from which extends perpendicularly a plurality of rods, one electrode being ohmically connected to the base region, a second electrode being ohmically connected to the ends of all the rods and a gate electrode connected to at least a circular section of the wall of each rod either by a rectifying contact or through a thin insulating layer. Fig. 3 shows a section through a germanium body 1 in which ohmic contacts are facilitated by the production of dart-shaped strongly doped regions 3 and 4 by masking and gaseous diffusion of acceptors for a P-type body or donors for an N-type body. Electrolytic etching using for example a bath of sulphuric acid or caustic potash of one face of the body, suitable regions of which are protected by varnish or masking, is employed to produce a plurality of rods 2 projecting from a base region. The etching may be facilitated by illuminating the etched area with light of the wavelength which is absorbed by the semiconductor. An insulating layer 6 of for example silicone varnish is then applied to the recesses between the rods which is covered with a layer 5 of aluminium or Woods metal to form the gate electrodes. Alternatively, a metallic layer may be directly applied to the semi-conductor without the insulating layer, in a manner which provides a rectifying contact with the body. This may be achieved by using a solution of indium sulphate and sulphuric acid for the etching process, and then reversing the direction of current to deposit indium on the semi-conduc. tor. Fig. 4 shows the completed device in which bronze or nickel electrodes 7 and 8 with a multitude of points contact the dart-shaped doped regions of the semi-conductor to form source and drain electrodes, and gate electrode 15 contacts the deposited metal layer 5. Cooling fins 10 and 11 are associated with the electrodes. The unit is sealed by insulating material 12 which may consist of polyethylene, polyvinyl chloride or epoxy resin. Fig. 6 shows an alternative arrangement in which a zone of opposite conductivity type comprising projection 19 is produced to provide the rods 2, the gate connection 15 to the rods being made in this case via the PN junction 19. Fig. 7 shows a transistor unit 19 mounted on a metal base 20 with cooling fin 21. The base 20 is sealed by means of a glass rim 22 to a metal ring 22 to which is soldered a cover 27. The glass rim supports leads 24 and 25 which are connected to the other ohmic electrode and the gate electrode of the transistor. In a further modification the metal deposit for the gate electrode is applied only to the middle portion of each rod which is thinned to lower the input capacity of the device. The shaping of the semi-conductor body may be effected by an ultrasonic vibration process instead of electrolytic etching. The semi-conductor may consist of germanium, silicon, or an Am Bv compound. Specification 808,734 is referred to.