Highly c-axis oriented monocrystalline Pb(Zr, Ti)O3 based thin film on Si wafer by sputter deposition with fast cooling process

We have successfully obtained a highly c-axis oriented epitaxial Pb(Zr, Ti)O₃ (PZT) based thin film, 0.06Pb(Mn_1/3, Nb_2/3)O₃-0.94Pb(Zr_0.5, Ti_0.5)O₃ (PMnN-PZT), on a (100) Si substrate by fast cooling of the substrate just after sputter deposition. The Si substrates were covered with SrRuO₃//La_0.5Sr_0.5CoO₃//CeO₂//yttria-stabilized zirconia buffer layers. It is found that c-axis orientation ratio of the PMnN-PZT thin film has reached more than 75% owing to the fast cooling (~-180°C/min) although a-axis orientation is normally predominant on a Si substrate in a conventional sputtering process. A piezoelectric unimorph microcantilever utilizing the PMnN-PZT thin film was fabricated for characterizing the dielectric and piezoelectric properties. No damage was observed after the microfabrication process. As a result, 1~4-μm-thick PMnN-PZT thin films exhibited a piezoelectric coefficient as large as e_31,f = ~-14 C/m² with a small dielectric constant of ε_r = ~270. These unique properties can provide an excellent figure of merit, (e_31,f)²/ε₀ε_r = ~80 GPa, for piezoelectric microelectromechanical systems (MEMS) sensors such as piezoelectric gyroscope. The present piezoelectric thin films are expected to be used for a variety of high-performance piezoelectric MEMS devices.