Combination of guided mode and photometric optical metrology methods for precise determination of refractive index dispersion: application to polymer blend and ceramic thin films for gas sensors

Abstract

Two optical techniques, m-lines and spectroscopic ellipsometry, arecompared for their suitability for obtaining the wavelength and thetemperature dispersion of the refractive index of thin-film layers usedin gas detector devices. Two types of materials that are oftenintegrated into gas sensors are studied: a polymer organic-inorganicblend deposited by spin coating typically used in near-infraredwaveguides and the ceramic semiconductor SrTi(1-x)FexO(3) (strontiumtitanate) doped with iron at concentrations x 0.075 and 0.1 deposited byelectron beam deposition. The refractive index dispersion obtained bym-lines and ellipsometry is compared, and the differences between themeasured parameters for the two materials are discussed. The chromaticdispersion will be represented by a three-term Cauchy law. An intuitivemethod for verifying the measured indices using an integrating sphereand reflexion coefficient modeling techniques are also demonstrated.Thermo-optic coefficients in the order of -1 x 10(-4)/ K for bothmaterials are reported, and very low chromatic dispersions are alsomeasured, thanks to the high sensitivity of the m-lines technique. Theuniaxial anisotropic properties of the polymerblend films are measuredand discussed in the case of the semiconductor films. (C) 2013 Societyof Photo-Optical Instrumentation Engineers (SPIE)