| AVS 61st International Symposium & Exhibition | |
| Thin Film | Tuesday Sessions |
| Session TF+PS-TuM |
| Session: | ALD for Emerging Applications |
| Presenter: | Diana Chien, UCLA |
| Authors: | D. Chien, UCLA T. Kim, UCLA J.P. Chang, UCLA |
| Correspondent: | Click to Email |
As one of the best dielectric, piezoelectric, and ferroelectric materials, PZT is a promising material to engineer nanoscale multiferroic composites. The magnetoelectric (ME) effect occurs indirectly through strain at the interface. Using atomic layer deposition (ALD), a surface-reaction controlled process based on alternating self-limiting surface reactions, a thin film of PZT can be synthesized with precise control of the elemental composition (Zr/Ti = 52/48) and film thickness. ALD provides much superior uniformity and conformality over complex surface structures with high aspect ratios.
In this work, 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 platinized 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 hollow Si3N4 cylinders with aspect ratio of 2.2.
By controlling the composition, thickness, and conformality of ALD PZT thin films, the properties of PZT can be exploited to increase the ME coefficient. Specifically, PZT was coupled with MgO/CoFeB to fabricate magnetic tunnel junction for memory applications. With co-mediated effects from higher dielectric constant and strain transfer via the interface, the voltage-controlled magnetic anisotropy effect is expected to increase, thereby realizing magnetic anisotropy energy per area per electric field greater than 37 fJ/(V.m) (Zhu, J. et al., Phys Rev Lett., 108, 2012). ALD PZT thin films were shown to uniformly coat the walls of nanoscale porous CFO template to form a 3-D composite and a larger ME coefficient is expected due to an increase in surface area to volume ratio.