Platinum Thin Films

Temperature Sensitivity

The relationship between electrical resistance and temperature in high-purity metals is highly linear and reproducible over hundreds of degrees. In platinum thin films, the temperature coefficient of resistance dictates the sensitivity and accuracy of the temperature measurement. To achieve the standard value of zero point zero zero three eight five per degree Celsius, the crystalline structure must be highly oriented and free of impurities that scatter electrons and reduce the temperature coefficient.

Deposition Control

Physical vapor deposition processes under high vacuum determine the microstructure and adhesion of the metallic layer. Sputtering parameters used to grow platinum thin films must be carefully controlled to optimize grain size and minimize internal stress. Because platinum does not adhere well to oxide substrates, a thin adhesion layer of titanium or chromium is typically deposited prior to the platinum growth to prevent delamination during subsequent thermal processing.

Mechanical Reliability

Thermal expansion mismatches between the metallic layer and the ceramic substrate generate mechanical stress during thermal cycling. In platinum thin films, this stress can lead to plastic deformation or grain growth, which cause irreversible shifts in electrical resistance. Annealing the deposited films at temperatures above their operating range relieves these stresses and stabilizes the grain structure, ensuring that the sensor maintains its baseline resistance during subsequent thermal exposure.

This thermal treatment is critical because it prevents the metal from recrystallizing during field use, which would otherwise lead to a slow, continuous drift in the sensor’s temperature readings.