GB1267107A - - Google Patents

Abstract

1,267,107. Thermistors. STANDARD TELEPHONES & CABLES Ltd. 19 Nov., 1970 [25 Nov., 1969], No. 57626/69. Heading HlK. A thin film thermistor is formed by first depositing on a clean insulating substrate 1 (Fig. 1) a pair of spaced apart contact pads 2, 3 and an elongate base electrode 5 which contacts one and is spaced from the other pad, then sputtering a thermistor material 6 to cover the electrode except where it abuts its contact pad, and finally depositing by sublimation or evaporation an elongate top electrode 7 which crosses the base electrode and extends to the other contact pad 2. In the example the substrate is of glass or alumina, the low resistance pads 2, 3 of chromium below and gold above, electrode 5 of chromium or manganese below and silver, gold or nickel above, and electrode 7 of pure silver. Layer 6 may be deposited by triode sputtering in argon, possibly containing a trace of hydrogen or oxygen, as described in Specification 1,104,770 using a target consisting of a 5 : 1 Mn 2 O 3 : NiO mixture and is subsequently stabilized by heating in vacuo or air. A protective layer of silicon monoxide is finally deposited to leave only the bonding areas exposed. In an alternative construction the lower electrode is comb-shaped (Fig. 2, not shown) or of serpentine form to allow adjustment of the thermistor resistance by cutting to isolate one or more of the teeth of the comb or limbs of the serpentine. Adjustment may instead be effected by microengraving to eliminate parts of the upper electrode. The contact pads and higher resistance electrodes are deposited in any sequence by evaporation or sputtering through masking so as to overlap at their ends.