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Texture Control of PbTiO3 Thin Films for Ferroelectric Storage Media

Texture Control of PbTiO3 Thin Films for Ferroelectric Storage Media
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Ferroelectric materials have been explored as storage media in next-generation ultrahigh-density recording systems. As high-density recording media, ferroelectric materials are considered to be superior to the ferromagnetic materials widely used at present because the domain wall thickness of typical ferroelectric materials is of the order of a few lattice spaces, far less than that of ferromagnetic materials.We used pulsed laser deposition (PLD) to fabricate epitaxial PbTiO3 film on SrRuO3(001)/SrTiO3(001) substrate. This thin film had a stronger switching signal and a very smooth surface than randomly-oriented PbTiO3 thin film. The bit size can be easily and reliably controlled by applying voltage pulses to the film, and the obtained minimum single bit size of the sample was 20 nm, which corresponds to a recording density of 1.7 Tbit/in2. Therefore, use of epitaxial ferroelectric thin films on single crystal substrates next generation storage media is feasible. However, commercialization of this epitaxial structure difficult due to size limitations and the high cost of their single crystal substrates. In contrast, if a ferroelectric recording medium is manufactured on a glass substrate, it is possible to obtain a medium with price competitiveness. Therefore, we attempted to prepare PbTiO3 thin film on glass substrates for the storage media by using thermal annealing of a multilayer film composed of binary oxide layers of PbO and TiO2. The binary oxides were deposited using RF magnetron sputtering. The PbTiO3 thin film had random orientation and showed clear switching behavior.However, the PbTiO3 thin film grown on a glass substrate was randomly-oriented and had weaker ferroelectric property than does epitaxial PbTiO3 thin film deposited on a single crystal substrate. Ferroelectric thin films with preferred orientation have better switching signals and lower operation voltages than randomly-oriented ferroelectric thin films. Therefore, preferentially-oriented PbTiO3 thin film was grown on a glass substrate using a texture-controlled Pt electrode layer. Preferentially (111)-oriented PbTiO3 film was highly crystalline and had a smooth surface with root mean square (RMS) roughness of 1.5 nm. The minimum bit size of this film was 22 nm, which corresponds to a potential recording density of 1.3 Tbit/in2. These results indicate that use of (111)-oriented PbTiO3 thin film on glass as a storage medium for commercial ferroelectric hard disc drive (FeHDD) should be feasible and that this technique should be useful to obtain high recording density and to reduce production costs.
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