GB1173444A - Improvements in and relating to Semiconductor Resistors - Google Patents

Abstract

1,173,444. Semi-conductor devices. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. 6 June, 1967 [9 June, 1966], No. 26981/67. Heading H1K. A semi-conductor resistor comprises a body of semi-conductor material of substantially prismatic shape with one side face bevelled near one end face which is constituted by a surface of fracture of the material, the bevelled face and an oppositely located face being provided with electrodes in the form of metal coatings extending up to the edge of the surface of fracture. The resistor may be a phototransistor, a thermistor, or a varistor. The electrical characteristics of the devices are mainly determined by the semi-conductor material at the fractured surface, this being the shortest distance between the electrodes, which is relatively uncontaminated by electrode material. A plurality of devices may be simultaneously produced by forming a wafer (53) of semiconductor material having a groove (55) extending along one surface by compressing finely divided material in a mould and sintering, Fig. 3 (not shown), vapour depositing layers (57, 59) of gold on the major surfaces, Fig. 4 (not shown), breaking the wafer perpendicularly to the groove (55) to form a plurality of bars as shown in Fig. 5, and then breaking each bar along the line 63. A resistor for mounting directly on a printed circuit board has two opposed side surfaces bevelled, the electrodes extending from the bevelled surfaces to the opposite end of the body where they are soldered to the conductors on the board, Fig. 1 (not shown). The device may be a temperature-sensitive resistor made of sintered lanthanum-doped barium titanate with electrodes of vapour deposited nickelchromium. Alternatively the device may be a photo-sensitive resistor comprising a body of cadmium sulphide activated with copper and gallium. A plurality of photo-conductive resistors may be assembled in individual apertures in a thick plate (33) of light-absorbing insulating material to form a matrix, Fig. 2 (not shown). Each resistor may comprise a body of sintered copper- and gallium-activated cadmium sulphide with one bevelled surface and having vapour deposited gold electrodes. Connections to the resistors are provided by metal strips (39, 41) secured to the gold films by electrically conductive cement. The metal strips (39) connected to the flat sides of each resistor extend forward of the fractured ends of the bodies, and have their ends bent over and secured with electrically conductive cement to a conductive silver lacquer layer (47) provided on the upper surface of the mounting plate (33). The metal strips (41) connected to the bevelled sides of each resistor extend in the opposite direction and terminate in tags (45) which protrude into and are dip soldered to metal eyelets (50) in a thin insulating plate (49).