Spectroscopic ellipsometry study of spin coated P(VDF-TrFE-CTFE) thin films and P(VDF-TrFE-CTFE)/PMMA blends

Abstract

The optical properties of spin coated P(VDF-TrFE-CTFE) electrostrictive polymer films and films of a novel blend of P(VDF-TrFE-CTFE) with Poly(methyl methacrylate) (PMMA) were studied by means of Variable Angle Spectroscopic Ellipsometry (VASE) in the wavelength range of 200-1000nm and at 65°–75° incident angles using Cauchy and Sellmeier dispersion models. Such polymers are used as building blocks for polymer microelectromechanical systems (MEMS) and their integration with conventional processing requires an accurate and reproducible monitoring of their thickness and optical properties. The films were also characterized electrically and their breakdown fields were 1.20MV/cm for the P(VDF-TrFE-CTFE) films and 1.76MV/cm, for the P(VDF-TrFE-CTFE)/PMMA blend films. We report on significant changes in film texture between the two types of films. Our main finding is that optical anisotropy appears in both films and we have characterized this anisotropy for both electroactive polymers. The blend films display a higher refractive index in the plane of the film while the homogenous P(VDF-TrFE-CTFE) display a higher refractive index in the direction perpendicular to the plane. Depolarization and scattering were analyzed with the Mueller-Stokes formalism and a depolarization correction method was implemented decoupling thickness related non-uniformity from scattering effects. It is concluded that in-line, non-destructive characterization tools presented here are useful for both the industrialization of P(VDF-TrFE-CTFE) based micro-electro-mechanical systems and for probing the correlation between surface morphology and optical properties using VASE.