Low temperature CO2 laser annealing of PZT thin films on stainless steel substrates

• Main Authors: Ke-heng Lai, 賴科亨
• Other Authors: C.C. Chou
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/78625348073859860358

碩士 === 國立臺灣科技大學 === 機械工程系 === 96 === In this study, Pb(Zr0.52Ti0.48)O3(PZT) and La0.7Sr0.3MnO3 (LSMO) ferroelectric thin films were coated on stainless steel substrates of planar and micro wire shaped using sol-gel process, spin coating and sputtering technques. The phase structure of the films was successfully transformed from pyrochlore to perovskite phase using low temperature CO2 laser annealing. The interfacial property between different components was significantly improved using laser annealing process in order to develop flexible components. Microstructural analysis reveals that the furnace annealed films causes to generate oxide elements on the surface due to high temperature annealing. The growth of oxide elements started from the surface of the substrate and grown upto the surface of LSMO by which the adhesion between LSMO and PZT is reduced. Hence the leakage current increased to maximum. This resulted in degrading the film quality and ferroelectric property. Furnace annealed PZT film coating on planar stainless steel substrate showed ferroelectric remanent polarization of 4.3μC/cm2 and coercive field of 288.3kV/cm. The remanent polarization and coercive fields were improved significantly to 17.9μC/cm2 and 126.3kV/cm by using low temperature CO2 laser annealing. This might be due to decrease in leakage current from 10-6 to 10-9 A/cm2 and enhanced interfacial property between different components. Similar behavior is observed in the case of PZT films coated on wire shaped stainless steel substrate. The remanent polarization increased from 2.9 to 9.8μC/cm2 and coercive field decreased from 290 to 165kV/cm. Moreover, the improvement in leakage current density is from 10-5 to 10-7 A/cm2. The microstructure of the wire shaped stainless steel substrate surface showed the pores, grown oxides and defects. Hence, a new process was used to overcome the defects and surface property. Electropolishing technique was carried out to improve the surface property as well as interfacial property between substrate and buffer layer. The surface condition was enhanced by applying voltage of 2V for 150 sec in electropolishing process. The ferroelectric hysteresis loop of PZT films with wire shaped stainless steel substrates after electropolishing show remanent polarization of 12.9μC/cm2 and coercive field of 146.5kV/cm. In addition the leakage current also decreased to 10-8A/cm2. This result is closer to the ferroelectric property obtained for the films with planar shaped stainless steel substrates. Hence it can be concluded that the surface property and interfacial condition has a major role in increasing the property. Finally, the flexible characteristic was tested using the bending property of the wire. When the wire is bent into the curve of radius 20mm, the surface structure is found stable without any macro cracks. But, cracks were observed by increasing the bending strength upto the radius of curvature to 0.7mm. This indicates that the bending upto the radius of curvature 20mm is an appropriate condition to meet the requirements for flexible device.