Improving PZT Thin Film Texture Through Pt Metallization and Seed Layers
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Improving PZT Thin Film Texture Through Pt Metallization and Seed Layers L.M. Sanchez1,3, D.M. Potrepka1, G.R. Fox2, I. Takeuchi3, R.G. Polcawich1 1
U.S. Army Research Laboratory, 2800 Powder Mill Road, Adelphi, Maryland 20783
2
Fox Materials Consulting LLC, 7145 Baker Road, Colorado Spring, CO 80908
3
Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742, USA
ABSTRACT Leveraging past research activities in orientation control of lead zirconate titanate (PZT) thin films [1,2], this work attempts to optimize those research results using the fabrication equipment at the U.S. Army Research Laboratory so as to achieve a high degree of {001}texture and improved piezoelectric properties. Initial experiments examined the influence of Ti/Pt and TiO2/Pt thins films used as the base-electrode for chemical solution deposition PZT thin film growth. In all cases, the starting silicon substrates used a 500 nm thermally grown silicon dioxide. The Pt films were sputter deposited onto highly textured titanium dioxide films grown by a thermal oxidation process of a sputtered Ti film [3]. The second objective targeted was to achieve highly {001}-textured PZT using a seed layer of PbTiO3 (PT). A comparative study was performed between Ti/Pt and TiO2/Pt bottom electrodes. The results indicate that the use of a highly oriented TiO2 led to highly {111}-textured Pt, which in turn improved both the PT and PZT orientations. Both PZT (52/48) and (45/55) thin films with and without PT seed layers were deposited and examined via x-ray diffraction methods (XRD) as a function of annealing temperature. As expected, the PT seed layer provides significant improvement in the PZT {001}-texture while suppressing the {111}-texture of the PZT. Improvements in the Lotgering factor (f) were observed upon comparison of the original Ti/Pt/PZT process (f=0.66) with samples using the PT seed layer as a template, Ti/Pt/PT/PZT (f=0.87), and with films deposited onto the improved Pt electrodes, TiO2/Pt/PT/PZT (f=0.96). INTRODUCTION Lead zirconium titanate (PZT) exhibits superior piezoelectric properties for many types of microelectromechanical systems (MEMS) and is one of the most economical piezoelectric ceramics, making it cost effective for mass production. It also exhibits a high piezoelectric coefficient [4] compared with other common piezoelectric materials such as ZnO and AlN, thus allowing for the use of lower operating voltages while still achieving the same actuator performance metrics. The highest magnitude piezoelectric coefficients are observed at the PZT morphotropic phase boundary, where the crystal structure changes abruptly between the tetragonal and rhombohedral symmetry [5]. The morphotropic phase boundary (MPB) is located around the PbZr0.52Ti0.48O3, or PZT (52/48), composition. At the MPB, high dielectric permittivity and piezoelectric coefficient are observed. At the Army Research Laboratory (ARL) in Adelphi MD, efforts are focused on achieving highly {001}-textured PZT (52/48). Proper co
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