Effect of the annealing temperature on structural and piezoelectric properties of the sol–gel Pb(Zr 0.56Ti 0.44) 0.90(Mg 1/3Nb 2/3) 0.10O 3 films

Abstract

Sol–gel Pb(Zr 0.56Ti 0.44) 0.90(Mg 1/3Nb 2/3) 0.10O 3 (PZT–PMN) films 1 μm thick were prepared onto the Ti/Pt/Ti bottom electrodes by six layer spin-coatings. After the first triple layer coatings, a pre-annealing was carried out by rapid thermal process (RTP) with a step pattern of 600°C/5 min to 725°C/1 min. Finally, after the later triple layer coatings, the films were heat-treated by RTP with a step pattern of 650°C/5 min to 900°C/1 min (low-temperature annealing) or 650°C/5 min to 1050°C/1 min (high-temperature annealing). The structural and piezoelectric properties of the films were investigated by scanning electron microscopy (SEM), cross-sectional transmission electron microscopy (XTEM), and by measuring the piezoelectric charge constant d 31, the piezoelectric voltage constant g 31 as well as the relative permittivity ε. The films retain the tetragonal perovskite structure independent of the final annealing temperature. The interlayer caused at the middle depth of the film by the pre-annealing prevents the columnar grain growth through the film. Many fine grains are grown in the interlayer to be rich in Zr and deficient in Pb. The fine grains rich in Zr and deficient in Pb are also formed on the surface of the film. The growth of such the Zr-rich and Pb-deficient phase is effectively suppressed at the low temperature annealing rather than at the high temperature annealing. Thus, the piezoelectric films 1 μm thick with high d 31, g 31 and ε are successfully obtained with the low- temperature annealing.