Effect of IrO_2/Pt, IrO_2, and Pt bottom electrodes on the structure and electrical properties of PZT based piezoelectric microelectromechanical system devices

摘要

In piezoelectric microelectromechanical system devices with PbZr~( x )Ti~(1− x )O~(3)as the ferroelectric, the bottom electrode can provide a template for oriented PbZr~( x )Ti~(1− x )O~(3)growth. IrO~(2)/Pt, IrO~(2), and Pt bottom electrode layers were sputter deposited onto TiO~(2)and were used as growth templates for oriented PbZr~(0.52)Ti~(0.48)O~(3)growth. The IrO~(2)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~(0.52)Ti~(0.48)O~(3)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~(0.52)Ti~(0.48)O~(3)films and unimorph cantilevers. For devices with PbZr~(0.52)Ti~(0.48)O~(3)on IrO~(2)/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 µm × 123 µm and PZT area 16 µm × 125 µm. These values are comparable to results obtained for PbZr~(0.52)Ti~(0.48)O~(3)on 100 nm thick Pt-only bottom electrodes.