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) Ti1-x O-3 as the ferroelectric, the bottom electrode can provide a template for oriented PbZr (x) Ti1-x O-3 growth. IrO2/Pt, IrO2, and Pt bottom electrode layers were sputter deposited onto TiO2 and were used as growth templates for oriented PbZr0.52Ti0.48O3 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 PbZr0.52Ti0.48O3 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 PbZr0.52Ti0.48O3 films and unimorph cantilevers. For devices with PbZr0.52Ti0.48O3 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/m(2) 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 A mu m x 123 A mu m and PZT area 16 A mu m x 125 A mu m. These values are comparable to results obtained for PbZr0.52Ti0.48O3 on 100 nm thick Pt-only bottom electrodes.