Effect of IrO₂/Pt, IrO₂, and Pt bottom electrodes on the structure and electrical properties of PZT based piezoelectric microelectromechanical system devices

In piezoelectric microelectromechanical system devices with PbZr _x Ti_1−xO₃ as the ferroelectric, the bottom electrode can provide a template for oriented PbZr _x Ti_1−xO₃ growth. IrO₂/Pt, IrO₂, and Pt bottom electrode layers were sputter deposited onto TiO₂ and were used as growth templates for oriented PbZr_0.52Ti_0.48O₃ growth. The IrO₂ and Pt were found to be {100}- and {111}-oriented, respectively, by X-ray diffraction. Scanning/transmission electron microscopy results indicate that the bottom electrodes are textured; however, the PbZr_0.52Ti_0.48O₃ layer is partially textured. The impact of the bottom electrode type on the electrical properties is investigated by dielectric, ferroelectric, and piezoelectric measurements on circular capacitors formed on blanket PbZr_0.52Ti_0.48O₃ films and unimorph cantilevers. For devices with PbZr_0.52Ti_0.48O₃ on IrO₂/Pt bottom electrodes, values for the dielectric constant of 1103 ± 28, loss tangent of 0.070 ± 0.004, maximum polarization of 0.399 ± 0.003 C/m² at 38 MV/m, and leakage current of 5.4 ± 5.8 nA at 20 MV/m were obtained. Values of normalized strain of 0.0030 ± 0.0001 at 20 MV/m, and effective piezoelectric coefficient, d_31,f, of 100 ± 25 pm/V at 15 MV/m were obtained on cantilever unimorphs with electrode area 16 µm × 123 µm and PZT area 16 µm × 125 µm. These values are comparable to results obtained for PbZr_0.52Ti_0.48O₃ on 100 nm thick Pt-only bottom electrodes.