Top Electrode Area Dependence on Displacement Property of Lead Zirconate Titanate Films Prepared by Chemical Solution De
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Top Electrode Area Dependence on Displacement Property of Lead Zirconate Titanate Films Prepared by Chemical Solution Deposition Process
Takashi Iijima, Sachiko Ito and Hirofumi Matsuda Smart Structure Research Center, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 2, 1-1-1 Umezono, Tsukuba 305-8568, Japan
ABSTRACT Effects on ferroelectric and piezoelectric properties of top-electrode diameter variance from 80 to 8 µm were investigated using an AFM probing system connected with a ferroelectric test system with bipolar and unipolar signals at 5 Hz. The Pt and 1.2-µm-thick PZT layers were etched off to prepare Pt top electrode etched samples or Pt/PZT stack etched samples. In the case of bipolar measurement, the top electrode diameter did not affect ferroelectric properties, while the maximum displacement of the butterfly-shaped hysteresis curve, related with piezoelectric response, increased with decreasing top-electrode diameter. On the other hand, the longitudinal piezoelectric constant, AFM d33, calculated from the strain curve slope at 5 Hz, +5 V, increased with decreasing top-electrode diameter. The average value of the Pt/PZT stack-etched AFM d33 almost equals that of Pt-etched AFM d33. Average AFM d33 of the 8-µm-diameter Pt-etched and Pt/PZT stack-etched samples are 129 and 135 pm/V, respectively.
INTRODUCTION
A combination of preparation techniques for ferroelectric films and micro machining of Si is considered effective for fabricating microelectromechanical systems (MEMS) such as piezoelectric micro-actuator devices for applications in electrical and medical fields [1, 2]. Precise evaluation of piezoelectric constants, d33 and d31, is required to design mechanical structures for such devices. One common means to evaluate d33 is with a double-beam laser interferometer [3]. Moreover, the combination of an atomic force microscope (AFM) and a lock-in amplifier was applied to evaluate the miniscule longitudinal displacement of ferroelectric thin films [4, 5]. For this system, samples were driven by a high frequency AC signal at about 1 kHz as a function of large DC bias voltage; then, displacement was evaluated with a bend signal of the AFM cantilever. Therefore, force curve calibration of the cantilever using a standard sample, like quartz, is required. In contrast, we use an AFM probing system connected with a ferroelectric test system to measure the polarization hysteresis (P-E) curve and longitudinal displacement properties simultaneously with low frequency AC drive voltage. We evaluated longitudinal displacement using a Z-feedback signal of the AFM cantilever at 5 Hz. Advantages of this measuring system include dynamic evaluation of longitudinal displacement and direct comparison of ferroelectric and piezoelectric properties. We have reported the butterfly-shaped displacement hysteresis curve of PZT films while varying the top electrode diameter from 500 to 30 µm [6]. Displacement curves for 500 to 300-µm-diameter top electrodes showed opposite directi
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