Platinum Metals Rev., 1965, 9, (3), 82
High-Stability Fixed Resistors
Noble Metal Films in Glass Tubes
A new type of noble metal film resistor, now in quantity production by Siemens and Halske, is described by Werner Kugelstadt (Siemens Zeitschrift, 1965, 39, (2), 145-149).
The resistors comprise a thin 80:20 gold-platinum diffusion alloy film applied to the inside of high insulating toughened glass tubes, and helically grooved to obtain the required values.
The alloy film is deposited and fired on to the substrate by a ceramic decorating technique using a solution containing organic compounds of gold and platinum, and small amounts of other metals to promote adhesion, which are controlled to provide a film sufficiently soft to be mechanically grooved without stressing. The thickness of the film is controlled within the range 0.01 to 5.0μ in which maximum stability is obtained with a specific resistance of about 40μΩcm.
Use of the relatively soft elastic noble metal alloy film of stable structure is claimed to eliminate corrosion and irreversible changes in resistance during temperature cycling due to differences in thermal expansion between the film and the substrate. It is also claimed to provide a positive temperature coefficient of resistance of about 300 × 10−6 per °C constant between − 70 and + 200°C, and to give exceptionally low noise in operation.
The resistors have a maximum continuous operating temperature of 165°C. Two main types are available, for power loadings of 0.5 and 1.0 watt with values between 1Ω and 240 K Ω, and 2Ω and 510 KΩ respectively. The author discusses in detail factors governing the performance of metal film resistors, and gives data on electrical properties, dimensions, and conformity of the resistors to German and United States specifications.