Thick Pb(Zr,Ti)O 3 films fabricated by inducing residual compressive stress during the annealing process
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The effects of residual stress induced during the annealing process on the microstructural evolution and electrical properties of Pb(Zr,Ti)O3 (PZT) films were investigated. PZT films were deposited on platinized silicon substrates by the radio frequency magnetron sputtering method using a single oxide target. Compressive stress was induced in the film by bending the silicon substrate during sputtering using a specially designed substrate holder and subsequently annealing the film without the holder. Without the residual stress, the PZT film was severely cracked when it was thicker than 2 m due to the thermal expansion mismatch between the PZT and the Si substrate. On the other hand, when the residual stress was applied, no cracks were detected in the film for thicknesses of up to 4 m. The suppression of crack formation was attributed to the residual compressive stress that compensated for the tensile stress generated during and/or after the annealing process. The electrical properties of the PZT film with the residual stress were improved compared to those of the PZT film without the residual stress.
Dense and crack-free piezoelectric thick films integrated on a silicon substrate have been the subject of considerable attention in recent years for their potential application in micro-electromechanical systems (MEMS). The desired thickness of the piezoelectric films is typically in the range of 0.5–10 m for MEMS and microactuators with a relatively large generative force.1 For the fabrication of piezoelectric thick films, tapecasting2 and screen-printing technologies3 have traditionally been used. However, these techniques require a processing temperature that is too high for the processing of Si. 2,3 Pb(Zr,Ti)O 3 (PZT) films suitable for lowtemperature processing have been fabricated by the solgel or sputtering method. However, the films fabricated by these processes are very prone to crack formation because of the tensile stress arising during or after the annealing process required for the fabrication of thick PZT films. Many studies have been conducted in an attempt to overcome the tensile stress which develops during and/or after annealing.4–6 Tuttle et al.4 reported that PZT films deposited on sapphire had compressive stress and exhibited superior ferroelectric properties as compared to films deposited on silicon substrates. Qin et al.5 investigated
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2005.0383 2898
http://journals.cambridge.org
J. Mater. Res., Vol. 20, No. 11, Nov 2005 Downloaded: 18 Mar 2015
the orientation of PZT films induced by external stress during the annealing procedure. They reported that PZT films subjected to compressive stress during annealing exhibited (100) orientation, whereas PZT films subjected to tensile stress during annealing exhibited (111) orientation. Studies have also been performed to investigate the effect of stress on the ferroelectric properties of the film, and it was found in this case that films under compressive stress
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