Thin film filter having negative temperature drift coefficient
View Patent ↗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.
1. A structure of a film filter comprising a plurality of film layers made of a film stack material and a substrate wafer which said film layers are deposited on and retained to, wherein said substrate wafer has a coefficient of thermal expansion greater than that of the film stack material, and both said substrate wafer and said film layers commonly define a convex configuration under a condition that said substrate wafer is located closer to a center of said convex configuration than said filter layers.
2. The structure of the film filter as described in claim 1 , wherein the film layers have a substantially compressive stress generated therein at room temperature.
3. A structure of a film filter comprising 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 are retained to after being cooled to the room temperature;
wherein said substrate wafer has a coefficient of thermal expansion greater than that of the film stack material so as to generate compressive stress in the associated film layers, thus resulting in a negative temperature drift coefficient of said film filter;
said substrate wafer and said film layers commonly define a convex configuration under a condition that said substrate wafer is located closer to a center of said convex configuration than said filter layers.