Sol-Gel Derived PZT Thick Films with Nano-Sized Microstructure
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Sol-Gel Derived PZT Thick Films with Nano-Sized Microstructure C. L. Zhao, Z. H. Wang, W. Zhu*, O. K. Tan, and H. H. Hng Microelectronics Center, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798 ABSTRACT Lead zirconate titanate (PZT) films are promising for acoustic micro-devices applications because of their extremely high electromechanical coupling coefficients and excellent piezoelectric response. Thicker PZT films are crucial for these acoustic applications. A hybrid sol-gel technology has been developed as a new approach to realize simple and cost-effective fabrication of high quality PZT thick films. In this paper, PZT53/47 thick films with a thickness of 5-50 µm are successfully deposited on Pt-coated silicon wafer by using the hybrid sol-gel technology. The obtained PZT thick films are dense, crack-free, and have a nano-sized microstructure. The processing parameters of this technology have been evaluated. The microstructure of the film has been observed using field-emission scanning electron microscopy and the crystallization process has been monitored by the X-ray diffraction. The thick films thus made are good candidates for fabrication of piezoelectric diaphragm which will be an essential element of microspeaker and microphone arrays.
INTRODUCTION Lead zirconate titanate (PZT) piezoelectric materials have opened a wide variety of applications in the field of capacitors, memories, sensors and actuator because of its excellent piezoelectric effect. PZT piezoelectric film has been extensively investigated in its thin film form (thickness less than 1 µm) in order to minimize the operating voltage of devices. The introduction of micromaching process into the fabrication of piezoelectric devices, which has the advantages of reducing device size and the capability of integrating the devices with on-chip circuit at low cost, has provided a potential application of the PZT in micro-acoustic devices, including microspeaker and microphone [1, 2]. The primary and simplest structure for these applications is a multilayer diaphragm with piezoelectric actuating layer on an elastic membrane. The piezoelectric actuating layer is often employed as dense micro-patterned films with a thickness of 1~50 µm and geometry of mm2 in order to produce large displacement and generative force. Therefore, during the fabrication of this piezoelectric diaphragm, deposition of the piezoelectric films and patterning of the actuating element are two key points. One of the challenges in the research on PZT piezoelectric films deposition is to obtain crack-free films with certain thickness at a temperature compatible with silicon process. Some fabrication processes have been proposed to deposit PZT thick films on Pt-coated substrate, such as sol-gel, aerosol deposition and arc-discharged reactive ion plating [3-5]. Among them the sol-gel process is much preferred because of its simplicity and feasibility to deposit crack free PZT thick films. It has attracted a great deal of attent
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