Thin film filter having negative temperature drift coefficient

摘要

A structure of a film filter includes a plurality of film layers made of a film stack material and a substrate wafer which said film layers are deposited on at a temperature substantially higher than a room temperature and retained to after being cooled to the room temperature. The substrate wafer has a coefficient of thermal expansion greater than that of the film stack material so as to generate compressive forces upon the associated film layers, thus resulting in the film filter having a negative temperature drift coefficient.