GB1300096A - Voltage-dependent resistors - Google Patents

Abstract

1300096 Voltage dependent resistors PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 29 Jan 1970 [1 Feb 1969] 4358/70 Heading H1K A voltage dependent resistor comprises a one grain thick layer 1 (Fig. 3) of zinc doped gallium phosphide in a polyurethane binder 3; the grains projecting in either side of the binder and layers 4, 5 of aluminium being applied to contact the projecting parts. The electrode layers 4, 5 (Figs. 1, 2) each comprise two rows of islands 4A, 4B, to 4F, 5A, 5B to 5F located on opposed sides of the grain layer; each island 4B to 4F partially overlapping consecutive islands 5A to 5F and vice versa. Islands 4A, 5F have aluminium layer or wire conductors 6, 7 attached thereto, between which two sequences of series connected sections 8 of the grain layer interposed between the overlapping parts of islands 4A to 5F are connected in parallel. The current/voltage characteristics (a) between conductors 6/7 and (b), between opposite islands over a single region 8, are given (Fig. 4, not shown) and non-linearity is obtained from the non-linear metal/semi-conductor contact junctions between the electrode layers and the grains. A selected intermediate island 4 (Fig. 1) has a metallic layer tapping 9 connected to a further voltage dependent resistor formed by electrode 10, the grain layer, and an opposed electrode 11. The grains may be of N-type conductive silicon, and the granular layer may be ionically bombarded; after which the aluminium layers are vapour deposited over a mask and the contact formed by a short initial current pulse between the layers. In a modification (Fig. 5, not shown) the non-linear characteristic is obtained by PN junctions in silicon grains having a highly doped P-type core partially surrounded by an N-type layer and a P-type layer; the electrode layers respectively constituting ohmic contacts with the core and with the outer P-layer. A single coherent electrode layer on each side of the granular layer provides an asymmetric characteristic, while a series combination for even number of regions provides a symmetric characteristic. Other semi-conductor grains and electrode materials may be used.