GB1300142A - Improvements in and relating to resistors - Google Patents

Abstract

1300142 Voltage dependent resistors PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 28 Jan 1970 [31 Jan 1969] 4131/70 Heading H1K A voltage dependent resistor comprising semi-conductor elements having one or two rectifying metal to semi-conductor contacts is fabricated by spreading a photoconductive gallium phosphide powder doped with zinc of granular size #150 Á and energy gap >1À1eV uniformly on rubber glue on a glass substrate, from which non-adherent grains are removed. The assembly is dipped in a solution of polyurethane forming compounds, dried in air, and heated in air to partially cure the polyurethane. The foil is removed from the substrate, the glue removed by solvent, and the foil is washed in soap solution, water and alcohol, and dried. It is then etched in alcoholic KOH, washed in alcohol and deionized water, dried, and heated to cure the polyurethane. The resultant foil is clamped between perforated metal masks 2, 3 (Fig. 1) in a metal bell which after evacuation is filled with argon at low pressure, so that high voltage between masks 2, 3 and bell 4 initiates gas discharge to ionically bombard the accessible foil surfaces. After cooling the bell is evacuated, and aluminium is vapour deposited by heating helices 5, 6. Thus (Fig. 2) grains of gallium phosphide 11 are embedded in insulant foil 13 with surface aluminium contact layers 12. A current pulse is applied between the contact layers, and the resultant resistor has a characteristic (Fig. 3, not shown) with high non-linearity between 3 and 5 applied volts. Other semi-conductor materials with energy gap >1À1eV, and other thermoplastic or thermosetting insulants than polyurethane are usable. The metal contact layers may be sputtered on, and may be gold, platinum, silver or copper. Other donors and acceptors may be applied by doping to control servoconductor resistivity.