Electrostatically-tunable infrared filter that uses etched thin Si plates

Abstract

We fabricated infrared Fabry-Perot filters by stacking two wet-etched Si plates. When an electric voltage was applied between the plates, the spacing between the plates changed due to an electrostatic force, which caused a shift of interference peaks. The Si plates were etched in a KOH solution to 34-μm thickness in order to reduce the driving voltage. When the voltage was raised from 0 to 20 V, an interference peak shifted from 7.9- to 5.5-μm wavelength, corresponding to the decrease in the spacing from 7.9 to 5.5 μm. The peak transmittance increased to 91% by an antireflection coating on the outer surface of the filter. This coating was effective to suppress the interference inside the Si plates that created a complicated spectrum.