Application of a Buffer Layer for the Dielectric Measurement of Thin Polymer Films
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Application of a Buffer Layer for the Dielectric Measurement of Thin Polymer Films C. K. Chiang and Wataru Sakai Polymers Division, National Institute of Standards and Technology Gaithersburg, MD 20899-8541 ABSTRACT A buffered dielectric measurement method is described. We added a thin buffer polymer layer to a polymer film before depositing aluminum electrodes. This is a modification to conventional parallel plate dielectric constant measurement method. It still has well-defined geometric factor for determining the dielectric constant. We designed the buffer layer using a simple RC model. It was determined that the buffer layer should be a high dielectric constant polymer. Two high dielectric constant polymers were selected to be buffer layers. Layered samples with structures ABA and ABC were discussed, where A is the buffer layer. We show that the method not only provides a way to preserve the structure of special polymer films, but also is able to adjust its electrical characterization to a convenient level.
INTRODUCTION The dielectric electrical characterization for thin polymer films is not only of fundamental interest, but also is critically important to their electronic application. To have a well-defined geometric factor, conventional dielectric constant measurement technique uses the parallel plate method. It is often performed depositing a metal electrode onto the thin film directly. This MPM (metal-polymer-metal) structure is simple, direct and reliable. However, increasingly, the direct metal deposition method is undesirable due to decreasing film thickness, or in studying of materials such as biopolymers. We have attempted to develop a buffer layer method by adding an additional layer on the top of the thin-film. The method is not only for the protection of ultra thin film, but also for adjustment of the electrical characterization of the sample to a frequency range that is convenient for specific instrument level. The studies of dielectric data of the layered materials are available in literature. [1] However, we approached the problem from methodology point of view. In this paper, we presented a preliminary attempt to use buffer layer to create layered samples. We first analyzed the electrical requirement for the buffer layer. We illustrate the discussion with structures of ABA and ABC, where A is the selected buffering layer polymer. One of the sample films was down to nanometer range.
EXPERIMENTAL Polymer thin films used in this experimental are assumed to be typical samples with typical dielectric constants as discussed. Polyvinylidenedifloride (PVDF) and cyanoresin (CRS) were R7.1.1
used as buffer layer materials. Dielectric constant of PVDF and CRS are 12 and 20, respectively. Aluminum electrodes were vacuum deposited on the top of the buffer layer. Dielectric measurements were performed with Hewlett-Packard 4194A Analyzer for the frequency from 100 Hz to 107 Hz, and with Gamry Instrument from 5000 Hz to 0.001 Hz. All measurements were done at ambient temperature. The data from the frequency-
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