Effect of metallization on RF properties of PZT-based transmission lines

This paper describes the material parameters which affect high frequency transmission lines built on ferroelectric lead zirconate titanate (PZT) thin films. The electrical characteristics of two transmission line (TL) structures, namely microstrip (MS) and coplanar waveguide (CPW), were studied over 1 to 20 GHz using electromagnetic simulation and verified through measurement. The characteristics were studied by simulating the insertion loss of the lines using four different types of metals namely Pt, Au, Ni and W. The effect of metallization on rf properties was due to metal conductivity and skin effect. The length of the line was set constant at 100 μm and the electrode thickness 0.1 μm, the PZT thickness was 0.5 μm. The relative permittivities of PZT used for MS and CPW were 87 and 112 respectively. The dielectric properties of the PZT films were obtained from previous capacitance measurements over the said frequency range. Results of this study show that the structures exhibit similar performance, with Pt showing the lowest loss for all given electrodes. These results suggest Pt as the preferred conductor for building transmission lines and circuit elements on PZT-based microwave integrated circuits (MIC).