During the cooling from the growth temperature, the PZT thin film undergoes a ferroelectric phase transition from a cubic phase to a tetragonal phase at 4900C. Consequently, a high stress field is induced in the film. The stress in the film can be relieved by a domain formation. The phenomenon is similar to the formation of coherent alternating twins in martensities. The phase transition stress can be expressed as, 0 0 f f 0 0 f f tr a [c(T) a ] 1 E a [a(T) a ] 1 E (1 P) − −ν +α − −ν σ = − (10) where a(T) and c(T) are a-axis and c-axis lattice parameters of tetragonal PZT at transition temperature and a0 is the lattice parameter of cubic phase. the a-axis and c-axis lattice parameters of tetragonal structure (before annealing). The a-axis lattice parameters are, respectively, 4.030A0, 4.030A0 and 4.017 A0 for the film thickness of 0.05µm,0.5µm and 1.0µm. The c-axis lattice parameters are, respectively, 4.0958A0, 4.0861A0 and 4.0817A0 for the film thickness of 0.05µm,0.5µm and 1.0µm. The contribution of phase transition stress to residual stress is shown in figure 4. It is obvious the phase transition stress has greatly contribution to the total residual stress. It is shown that the theoretical results and the experimental results for residual stress in PZT thin film are relatively consistent. Observing the results for ferroelectric properties shown in figure 1, c-axis orientation ratio shown in figure 2 and residual stress shown in figure 4, one can see that there is a relationship of ferroelectric properties with residual stress. When the film is thin, the compressive residual stress is high and in this case, remnant polarization Pr and c-axis orientation ratio are both low. When the film is thick, the compressive residual stress is low and in this case, remnant polarization Pr and c-axis orientation ratio are both high. One can have the conclusion that the high compressive residual stress will result in the low values of remnant polarization Pr and c-axis orientation ratio. During the PZT thin film deposition, when the residual stress was gradually eliminated, crystal particles were ease to grow and the spontaneity polarization would be easy to progress. CONCLUSIONS In the investigation, the piezoelectric thin film Pb(ZrxTi1-x)O3(PZT) was prepared by a pulse laser deposition method. The residual stress in piezoelectric thin film was tested by x-ray diffractometer (XRD). The relation of properties such as microstructures, piezoelectric response with residual stress was investigated. A theoretical model for residual stress formed mechanism is proposed. The model is based on the combined effects of the difference of thermal mismatch between substrate and thin film, the phase transformation and the different of lattice constant between thin film and substrate. Remnant polarization Pr linearly increases with increasing film thickness and the coercive field gradually decreases with increasing film thickness at the same electric field. The residual stress has a great effect on ferroelectric properties of PZT thin films. Remnant polarization Pr decreases with increasing residual stress. The coercive field gradually increases with increasing residual stress. ACKNOWLEDGMENTS Support for this research program was provided partly by the NNSF of China (No. 10072052). REFERENCES 1. Haertling, G. H. (1999) J. Am. Ceram. Soc., 82, 797. 2. Noyan, I. C., Cohen, J. B., (1987) Residual Stress-Measurement by Diffraction and Interpretation, Springer-Verlag, New York. 3. Luo, H., Zheng, X. J. and Zhou, Y. C., (2000) J.Chinese Laser, (in press) 4. Foster, C. M., Li, Z., Buckett, M., et al.(1995) J. Appl. Phys., 78, 2607.
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