Broadband dielectric metrology for polymer composite films

We evaluated the dielectric permittivity and relaxation in polymer composite films filled with ferroelectric ceramics. Such materials are currently being developed for power-ground decoupling in electronic circuits operating at microwave frequencies. In order to extend the measurements to the microwave range, we developed an appropriate expression for the input admittance of a thin film capacitance terminating a coaxial line. The theoretical model treats the capacitance as a distributed network and correlates the network scattering parameter with complex permittivity of the specimen. The method eliminates the systematic uncertainties of the lumped element approximations and is suitable for high frequency characterization of low impedance substrates with high value of the dielectric constant. The complex permittivity was measured at frequencies of 100 Hz to 10 GHz for films 100 /spl mu/m thick, having the dielectric constant of 4 to 40, and was fitted to a dielectric model expressed as a combination of Havriliak-Negami functions. An intrinsic high frequency relaxation process has been identified. It was found that the position of the loss peak depends on the relaxation of polymer matrix, while its magnitude is amplified by the permittivity of the ferroelectric component.

Introduction

To advance miniaturization and improve functional performance of high-speed electronics, there is growing need for dielectric films with high permittivity. Such materials can be used to construct integrated passive devices embedded within chip substrates and printed circuit sub-assemblies. Recently, high dielectric constant polymer-ferroelectric ceramic composites have shown promise for embedded decoupling capacitance and power planes with desirable, low impedance characteristics over a broad frequency range, including the microwave [1]. However, the dielectric relaxation behavior and the origin of the high frequency dispersion in polymer-ceramic composites is still poorly understood [2] and typically attributed to the domain structure of the ceramic component [3].