Effect Of Residual Stress On The Properties Of Piezoelectric Thin Films

Piezoelectric material can transfer the following information each other: mechanical information, electric information, thermal information, et al. It has been used in many fields due to the distinct properties. However, one needs its thin film with the same properties of bulk piezoelectric material with the progress of micro-electric technology and for the age integration beyond the 1 990s into the new century. Therefore, piezoelectric thin film has attracted great interests due to its distinct properties and its wide application in many fields. Due to the structural misfit and thermal misfit of the thin films/substrate and the process from high temperature to low temperature during the preparation process of the thin films, residual stress will be produced inevitably between thin film and substrate. The residual stress exits at the interface between thin film and substrate, and may lead the degradation, or delamination or completely failure of the thin films. In this case, the study of residual stresses in piezoelectric thin film is very important. In the Introduction of the master thesis, the potential application of piezoelectric thin film material, preparation methods and the research status for piezoelectric thin film are reviewed. On the basis of the review, the research of residual stress in piezoelectric thin film material is proposed. Main contents for the thesis are also given in the Introduction. The thesis focus on the lead zirconate titanate, i.e., Pb(Zro.52Tio.48)03 (PZT) thin films. Chapter 1 is dedicated to the preparation of the films. The bulk PZT target was first prepared. The effects of some important experimental parameters such as sintering temperature, sintering time on the target properties are mainly analyzed by x-ray diffraction (XRD) and scanning electron microscopy (SEM) method. The experimental procedures about thin film preparation with pulsed laser deposition (PLD) and metalorganic deposition (MOD) method are given in detail in the Chapter. In Chapter 2, the microstructure and piezoelectric properties for PZT thin films prepared by PLD and MOD methods are studied by XRD and SEM methods. The effects of experimental parameters on the microstructure and piezoelectric properties are mainly analyzed. The main contribution in the Thesis is in Chapter 3 and Chapter 4 for the study of residual stresses in PZT thin film. In Chapter 3, the residual stress is studied by XRD. The principle and test method is first given in the Chapter. After that, the method is used to test the residual stress in PZT thin film prepared by PLD and MOD methods. It is found that the residual stresses are compressive in the films with both preparation methods. In the Chapter, a theoretical model is proposed for residual stresses formation mechanisms in PZT thin films prepared by PLD method. The effects of residual stress on piezoelectric properties, including hysteresis and c-axis orientation ratio, are discussed. In Chapter 4, the indentation fracture methods are used to measure the residual stresses in PZT thin film. In the method, two theoretical models which are GLFW model and ZCF model are used. Hardness analyzer is used to produce cracks in the film. The load, crack length are measured and the surface paragraph is taken. By using GLFW and ZCF models, the residual stresses are determined. The residual stress is also compressive. The results tested by XRD method and indentation fracture methods are compared.