Open Resonator Technique for Measurement of Thin Dielectric Film Properties on Optically Dense Substrates
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Open Resonator Technique for Measurement of Thin Dielectric Film Properties on Optically Dense Substrates Sergey Dudorov1, Dmitri Lioubtchenko1, Juha Mallat1, Jussi Tuovinen2, Antti V. Räisänen1 1 MilliLab, Helsinki University of Technology, Radio Laboratory, P.O. Box 3000, FIN-02015 HUT, Finland 2 MilliLab, VTT Information Technology, Espoo, Finland ABSTRACT Thin dielectric films on the dielectric substrate are widely employed in millimeter and submillimeter wave device applications, so the problem of precise measurement of their properties is important. One of the most accurate technique for measurement of dielectric properties is the open resonator technique. In this work we propose the method for measurements of thin dielectric film properties on the dielectric substrate using the open semispherical resonator. A good agreement (within 1 %) was obtained in refractive index data between results obtained with direct measurements and with proposed method for thin layer of SI GaAs on a sapphire substrate. INTRODUCTION Dielectric materials are nowadays widely employed in millimeter and submillimeter wave device applications. Single-mode dielectric waveguides are promising for use in the monolithic integrated circuits, if being made of semiconductor epitaxial layers on dielectric substrates [1,2]. Therefore the precise measurement of their dielectric properties is important. One of the most accurate is the open resonator technique that has been developed by several authors mostly for bulk-type sample measurements (see e.g. [3]) and recently the structures of two relatively thick layers were studied [4]. In this work the open resonator technique was developed in application to bilayer dielectrics in which one layer is thin in comparison with a quarter of wavelength. In this case the equations were modified. The suggested method of determination of the thin film properties is to compare the resonant frequencies and quality factors of the resonator containing the substrate with and without the thin film. THEORY The semispherical resonator with two-layer tested sample is shown in figure 1. The equations used by different authors to calculate the refractive index ( n ) and loss tangent ( tan δ ) of homogeneous sample are slightly different depending on the approach being used [5-7]. However, the main equations for the resonator containing the sample are looking generally like:
AA1.7.1 Downloaded from https://www.cambridge.org/core. La Trobe University, on 21 Jun 2020 at 04:52:01, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/PROC-631-AA1.7
Figure 1. Semispherical open resonator with bi-layer dielectric. 1 tan (nkt − Φ t ) = − tan (kd − Φ d ) , n
(1)
2π is the wave number in vacuum, t λ is the thickness of the sample, d is the distance between the upper mirror and sample surface. The variations are in the calculation of the phase correction values Φt and Φd. Nevertheless, all proposed models give usually consistent results. While measuring the soft
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