Structural investigations of Pt∕TiOx electrode stacks for ferroelectric thin film devices

Abstract

Effects of the thermal treatment and the fabrication process of Pb͑Zr 0.3 Ti 0.7 ͒O 3 ͑PZT͒ thin films using chemical solution deposition on Pt/ TiO x electrode stacks were investigated using complementary analytical techniques including atomic force microscopy ͑AFM͒, x-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, and grazing incidence x-ray reflectivity of synchrotron radiation. The surface and interface structures of the Pt/ TiO x electrode stacks with different thermal treatments, and the PZT/ Pt/ TiO x sample were examined. The propagation of Pt hillocks on the bare Pt/ TiO x electrode stacks upon the annealing was observed. AFM observations also revealed that the upper surface of the Pt bottom electrode under PZT thin film became rougher than that of the bare Pt electrode with the same thermal history. Global structural information including the density, surface or interface root-mean-square roughness, and thickness of each constituent layer in the samples were determined using x-ray reflectivity. A density decrease of the Pt layer upon the annealing or during the fabrication of PZT thin films was found from fitting the specular reflectivity, and further confirmed by the negative shift of the Yoneda peak of Pt in the diffuse reflectivity. The formation of Pt hillocks on the bare Pt electrodes was attributed to the compressive stress during the high-temperature annealing caused by the limited incorporation of Ti and O into the Pt layer. Roughening of the PZT/Pt interface was ascribed to the interaction between the compressive stress in Pt and the indentation by the PZT crystallization and grain growth during the annealing.

Effects of Thermal Annealing on the Structure of Ferroelectric Thin Films

“…The multilayer is described as a stack of homogeneous PZT/Pt/TiO x layers on a semi‐infinite SiO 2 substrate, owing to the large thickness of the SiO 2 layer. Previously we have determined that the TiO x composition is slightly deviated from stoichiometric TiO 2 10 . Here, Ti 8 O 15 is used for the fits for approximation.…”

“…Previously we have determined that the TiO x composition is slightly deviated from stoichiometric TiO 2 . 10 Here, Ti 8 O 15 is used for the fits for approximation. From the fits, PZT densities of 7.97 and 8.01 g/cm 3 for the unannealed and annealed samples are derived, which correspond respectively to 99.3% and 99.8% of the theoretical density of 8.03 g/cm 3 calculated using the lattice parameters of bulk ceramics reported earlier.…”

Improving the fatigue endurance of lead zirconate titanate thin films through PbO interfacial modification

“…Lead zirconate titanate (PZT) is one of the most promising ferroelectric materials for memory use due to high remanent polarization (P r ) and low coercive field (E c ), etc. However, there are still some problems for metal-electroded PZT thin films such as ferroelectric fatigue, size effect and imprint effect [4][5][6][7][8]. It is generally accepted that ferroelectric fatigue of metal-electroded PZT thin films is closely related with the interface imperfections at the electrode/PZT interfaces.…”

Development of sol-gel derived lead zirconate titanate (PZT) thin films with a nonporous Pt/Ti bottom electrode

“…When annealed at a higher temperature, the residual stresses are relaxed and turn tensile, thus reducing the Pt film thickness and forming hillocks and bumps [13,14]. During a prolonged thermal annealing, the Pt hillocks population and grain size expand [15] eventually resulting in a Pt layer with high porosity and decreased density [16,17]. This might result from a strong Ti diffusion into the Pt film and followed by an oxidation in the Pt grain boundaries, which subsequently generates an additional compressive stress during the annealing [18].…”