Dielectric and Pulsed Spectroscopy of Shear Mode PZT Microactuator
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Dielectric and Pulsed Spectroscopy of Shear Mode PZT Microactuator Jürgen Brünahl, Alex Grishin and Sergey Khartsev Department of Condensed Matter Physics, Royal Institute of Technology, S-100 44 Stockholm, Sweden ABSTRACT Ferroelectric lead zirconate titanate (PZT) is the main industrial product in piezoelectric ceramic materials used for sensor and actuator applications. High precision in manufacturing of microelectromechanical systems is essential to get demanded performance accuracy. An adequate and preferably non-destructive measurement technique is desired to characterize the materials properties at various stages of device fabrication as well as to find correlation between the processing parameters, microstructure and functional properties. We report on a new pulsed technique, which has been employed to characterize all relevant properties of special machined array of PZT channels quickly, reliably and reproducibly: dielectric constant, loss factor tan δ, electromechanical coupling coefficient, resonance frequency and mechanical quality factor Q as well as temperature dependencies of these parameters. INTRODUCTION Ferroelectric ceramics used to convert electrical energy into mechanical and vice versa are important in industrial applications such as igniters, transducers and actuators [1]. Actuators for piezoelectric ink jet printing [2-3] with their complex channel structure are typical examples for micro-electromechanical systems. Several production steps as e.g. sawing, metallization or polishing are necessary to build such microsystems. Each of these processes influences the properties of the initial ceramics due to local heating, vibrations and mechanical stress. To control the processes and to characterize the properties of the materials in early stages of the production is therefore essential get best performance of the actuator. Different techniques are used to characterize specially machined bulk ceramics, including commercial instruments as Fluke 6304 RCL-meter and HP 4194A Impedance Analyser, both with the option to measure dielectric permittivity and dielectric losses as a function of frequency and temperature and the new employed pulsed technique. The principle of the pulsed technique is based on recording the transient current as response on a short voltage pulse applied to the ferroelectric acoustic element (later FAE). Since the investigated PZT ceramic has a high coupling coefficient k15, an electric field applied perpendicular to the polarization will cause a shear motion of FAE. If a voltage pulse with fast rise time is high enough in amplitude to animate the element, then it will act like a tuning fork and oscillate at resonant frequencies. Because of the piezoelectric effect the mechanical oscillations of the actuating element can be seen as oscillations of the transient current. EXPERIMENT Polarised Pb(ZrxTi1-x)O3 (PZT) bulk ceramics with Zr/Ti=53/47 are used to demonstrate capability of the new pulsed technique. Table I shows main characteristics of the investigated ceramics. An array of
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