Nondestructive microwave permittivity characterization of ferroelectric thin film using microstrip dual resonator

Abstract

This article presents the use of a microstrip dual resonator for nondestructive permittivity characterization of a ferroelectric thin film at microwave frequencies. The dual-resonator measurement fixture consists mainly of two capacitively coupled microstrip resonators, with the ferroelectric thin film covering the gap between the two resonators. The dielectric constant and loss tangent of the ferroelectric thin film are derived from the resonant frequencies and quality factors of the dual-resonator structure. To study the electric field dependence of the ferroelectric thin film, direct current bias voltage is applied through two electrode pads on the microstrip circuit. The temperature dependence of a ferroelectric thin film was also studied using the hermetic test fixture. The measurement uncertainty of this method comes mainly from the air gap between the microstrip circuit and the ferroelectric thin film. Calibration with a sample of known dielectric constant can be used to compensate for such an error. We demonstrated the use of this method on a piece of the Ba0.5Sr0.5TiO3 thin film deposited on a LaAlO3 substrate.