High Temperature Dielectric Properties of Sol-Gel Derived Thick PZT thin Films with Different Zr/Ti Atom Ratios
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High temperature dielectric properties of sol-gel derived thick PZT thin films with different Zr/Ti atom ratios Jinrong Cheng, Wenyi Zhu, Nan Li and L.Eric Cross Material Research Laboratory, The Pennsylvania State University University Park, PA 16802 ABSTRACT PZT thin films of different thicknesses and Zr/Ti ratios of 60/40, 52/48 and 45/55 were coated onto platinized silicon substrates by using 2 methoxyethanol (2-MOE) based sol-gel spinon technique and crystallized with a rapid thermal annealing (RTA) process. XRD analysis revealed that thin PZT films exhibit random texture, while the thicker ones exhibit (100) texture, which was independent of composition. Dielectric constants and dissipation factors of PZT thin films were measured at elevated temperatures and as a function of frequency. For films with a thickness of ~ 4 µm, the Curie points are at 350, 375 and 422°C for Zr/Ti ratios of 60/40, 52/48 and 45/55, respectively. All these films exhibit a high remnant polarization. A remnant polarization of 35 µC/cm2 had been achieved for the 60/40 films. No enhancement of the dielectric constant was observed in films with a composition close to MPB. The higher dielectric constant observed in films with the highest Zr content was explained by the concept of domain engineering.
INTRODUCTION Pb(ZrxTi1-x)O3 (PZT) bulk ceramics are well known and widely used piezoelectric materials. There is a morphotropic phase boundary (MPB) in the PZT system at a Zr/Ti ratio of 52/48. Both the dielectric constant and piezoelectric effect near the MPB are enhanced [1-3]. The reason behind this enhancement is that the metastable coexistence of tetragonal and rhombohedral phase results in maximum poling efficiency and electromechanical activity. Such properties have motivated the study of PZT thin films for various applications, such as nonvolatile memories, micro sensors and actuators, and infrared detectors. A great difference in microstructure and properties was observed between PZT thin films and bulk ceramics due to the effect of a substrate and fine grain size in films. The effect of Zr/Ti ratios on the dielectric, ferroelectric and piezoelectric properties in PZT thin films has been investigated [4-6]. However, there are no consistent conclusions regarding the MPB composition, the texture, and even the Curie temperature due to the extreme sensitivity of film properties to even subtle variations in processing conditions. The control of the texture and the film thickness is also of a great interest in thin film studies. A further benefit of texture may be enhancing process integration of ferroelectric thin films and semiconductor technologies. Because of the improved reproducibility and self-poling effect of textured films, the efficiency of the integration process should be increased. Thick films are needed for the fabrication of film capacitors for decoupling and bypassing, and microactuators for the ultrasonic motor and accelerometer to withstand high operating voltages and provide a large driving force. In this paper, (100) orie
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