| AVS 62nd International Symposium & Exhibition | |
| Thin Film | Tuesday Sessions |
| Session TF-TuA |
| Session: | ALD for Emerging Applications |
| Presenter: | Diana Chien, University of California at Los Angeles |
| Authors: | D. Chien, University of California at Los Angeles A. Buditama, University of California at Los Angeles L. Schelhas, University of California at Los Angeles S.H. Tolbert, University of California at Los Angeles J.P. Chang, University of California at Los Angeles |
| Correspondent: | Click to Email |
Ultra-thin, uniform, and conformal PZT films are needed to engineer nanoscale multiferroic composites with complex architectures. By coupling the piezoelectric PZT film with a magnetostrictive material (e.g. CFO), a magnetization (polarization) can be induced by an applied electric (magnetic) field via the strain-mediated magnetoelectric coupling effect, in which strain is transferred at the interface between the piezoelectric and magnetostrictive layers. Using atomic layer deposition (ALD), a surface-reaction controlled process based on alternating self-limiting surface reactions, an ultra-thin film of PZT can be synthesized with precise control of the film thickness and elemental composition (Zr/Ti = 52/48). ALD provides superior uniformity and conformality over complex surface structures with high aspect ratios.
ALD PZT thin films were synthesized by depositing alternating layers of PbO, ZrO2, and TiO2 layers using Pb(TMHD)2, Zr(TMHD)4, and Ti(O.i-Pr)2(TMHD)2 as metal precursors and H2O as the oxidant. The number of local cycles and global cycles were regulated to achieve the desired stoichiometry and thickness, respectively. ALD of PZT was studied to obtain (100) oriented Pb(Zr0.52Ti0.48)O3 on Pt (111) oriented silicon substrates. In order to attain a highly oriented PZT thin film, a (100) textured PbTiO3 seed layer was required because PZT orientation is generally governed by nucleation. The stoichiometry and crystallinity of PZT films were confirmed by XPS and XRD measurements. The conformality was confirmed over high aspect ratio structures.
By controlling the composition, thickness, and conformality of ALD PZT thin films, multiferroic nanocomposites were engineered. Specifically, ALD PZT thin films were shown to uniformly coat the walls of nanoscale templated mesoporous CFO (with neck size of 6 nm in radius) to form a complex 0D-3D nanocomposite. XPS and XRD measurements confirmed the elemental analysis and crystallinity, respectively, of the PZT/CFO nanocomposites. To study the magnetoelectric coupling effect, the nanostructure was electrically poled ex-situ and the resulting magnetic moment was measured via SQUID while sweeping in-plane and out-of-plane magnetic fields. The in-plane results show that there is no change in magnetization as a function of voltage, which is due to the effect of substrate clamping. The out-of-plane results show that the magnetization changes as a function of voltage. The mesoporous CFO coated with 3 nm thick PZT film shows a greater magnetization change than the 6 nm thick PZT film, suggesting that porosity in the templated mesoporous CFO matrix is needed for a greater magnetoelectric coupling effect.