Research InterestCommercial ferroelectric thin film devices are rapidly approaching the same nanoscale dimensions as individual grains, yet little is known about the influence of grain boundaries and local texture on ferroelectric properties. Accordingly, several complementary experimental and theoretical techniques are being developed to assess the local ferroelectric response. By combining quantitative piezoelectric force microscopy (PFM), electron backscattering diffraction (EBSD), and two-dimensional object oriented finite-element modeling (OOF), various individual crystallographic distributions with either beneficial or detrimental effects can be identified and eventually predicted. Crystallographic orientation can now be determined with nanometer scale lateral resolution using the newly installed electron backscattering diffraction system (EBSD), allowing the orientation of individual ferroelectric grains to be mapped as indicated in Figure 1a.
Recent advances in two-dimensional (2-d) object oriented finite element modeling (OOF) have made it possible to predict the piezoelectric response of a polycrystalline thin film with full consideration of the sample texture as determined by EBSD. Figure 1b demonstrates the strain normal to the surface for an applied bias of 1 V across a 100 nm thick film using a 100 nm diameter electrode, where the electrode is positioned across multiple grains of differing orientations. The local response is strongly dependent on texture, in some cases oppositely oriented. Piezoelectric force microscopy (PFM) was employed to determine experimentally the ferroelectric properties of the same grain and grain boundary regions considered by EBSD and OOF. This AFM-based technique is widely used, but can be significantly hindered by several instrumental artifacts that were identified and overcome during this work. The area of piezoelectric hysteresis loops determined using the newly developed quantitative methods is indicated in Figure 2 for several distinct grains and boundaries. The measured hysteresis variations correlate with grains and grain boundaries of differing misorientation as measured by EBSD and correlates with strains calculated by OOF. Key accomplishments and conclusions include:
- Novel methods for identifying and overcoming artifacts in piezoelectric force microscopy to allow quantitative local piezoelectric hysteresis measurements;
- Unique 2-d simulations of converse-piezo actuation with complete incorporation of true thin-film texture;
- The importance of uniform texture for optimal ferroelectric properties when device dimensions approach the lateral grain size; and
- The likelihood of domain pinning or even crack initiation at certain grain boundaries and intersections as a result of local orientation.
- “Equilibrium Shape of Internal Cavities in Ruby and the Effect of Surface Energy Anisotropy on the Equilibrium Shape”, J.-H. Choi, D.-Y. Kim, B.J. Hockey, S.M. Wiederhorn, J.E. Blendell and C.A. Handwerker, J. Amer. Ceram. Soc., 85 1841-4, 2002.
- “Modeling of Anisotropic Shrinkage During Sintering of Low Temperature Cofired Ceramic Tapes”, J.E. Blendell, M.R. Locatelli, J.S. Wallace and B.J. Hockey, IMAPS Advanced Technology Workshop on Ceramic Applications for Microwave and Photonic Packaging, Providence, RI, 2002.
- “Grain Growth and Twin Formation in 0.74 PMN – 0.26 PT”, J.S. Wallace, J-M. Huh, J.E. Blendell and C.A. Handwerker, J. Amer. Ceram. Soc. 851581-4, 2002.
- “Singular Grain Boundaries In Alumina and Their Roughening Transition”, C.-W. Park, D.-Y. Yoon, J.E. Blendell And C.A. Handwerker, J. Amer. Ceram. Soc. 86 603-11, 2003.
- “Structure of Sapphire Bicrystal Grain Boundaries Produced by Liquid Phase Sintering”, B.J. Hockey, S.M. Wiederhorn, J.E. Blendell, J.-S. Lee and M.-K. Kang, J. Amer. Ceram. Soc., 86 612-22, 2003.
- “Crystallographic Orientation Dependent Dissolution Behavior of Sapphire in Anorthite Liquid Containing Cr2O3”, J.-K. Park, D.-Y. Kim, H.-Y. Lee, J.E. Blendell and C.A. Handwerker, J. Amer. Ceram. Soc. 86 1014-8, 2003.
- “Atomic Force Microscopy Observations of Domains in Fine Grain Bulk Lead Zirconate Titanate Ceramics”, Z. Wang, J.E. Blendell, G.S. White and Q. Jiang, Smart Materials and Structures, 12 (2003) 217-22.
- “The Importance of Distributed Loading and Cantilever Angle in Piezo-Force Microscopy”, B. D. Huey, C. Ramanujan, M. Bobji, J.E. Blendell, G.S. White, R. Szoszkiewicz, A. Kulik, Journal of Electroceramics, 13, 287-291, 2004.