Narrow Results

Ba(Mg${}_{1∕3}$Nb${}_{2∕3})$O₃ (BMN) doped and undoped Ba${}_{0.45}$Sr${}_{0.55}$TiO₃ (BST) thin films were deposited via radio frequency magnetron sputtering on Pt/TiO₂/SiO₂/Al₂O₃ substrates. The surface morphology and chemical state analyses of the films have shown that the BMN doped BST film has a smoother surface with reduced oxygen vacancy, resulting in an improved insulating properties of the BST film. Dielectric tunability, loss, and leakage current (LC) of the undoped and BMN doped BST thin films were studied. The BMN dopant has remarkably reduced the dielectric loss ($\sim$38%) with no significant effect on the tunability of the BST film, leading to an increase in figure of merit (FOM). This is attributed to the opposing behavior of large Mg${}^{2+}$ whose detrimental effect on tunability is partially compensated by small Nb${}^{5+}$ as the two substitute Ti${}^{4+}$ in the BST. The coupling between ${\text{Mg}}_{\mathrm{\text{Ti}}}^{″}$ and V${}_{\mathrm{\text{O}}}^{••}$ charged defects suppresses the dielectric loss in the film by cutting electrons from hopping between Ti ions. The LC of the films was investigated in the temperature range of 300–450K. A reduced LC measured for the BMN doped BST film was correlated to the formation of defect dipoles from ${\text{Mg}}_{\mathrm{\text{Ti}}}^{″}$, V${}_{\mathrm{\text{O}}}^{••}$ and Nb${}_{\mathrm{\text{Ti}}}^{•}$ charged defects. The carrier transport properties of the films were analyzed in light of Schottky thermionic emission (SE) and Poole–Frenkel (PF) emission mechanisms. The result indicated that while the carrier transport mechanism in the undoped film is interface limited (SE), the conduction in the BMN doped film was dominated by bulk processes (PF). The change of the conduction mechanism from SE to PF as a result of BMN doping is attributed to the presence of uncoupled Nb${}_{\mathrm{\text{Ti}}}^{•}$ sitting as a positive trap center at the shallow donor level of the BST.

TiO₂ thin film was deposited by a DC reactive magnetron sputtering on ZnO/soda-lime glass substrate and single crystal SiO₂ below 200 °C. ZnO layer was used as a buffer layer. Deposition was performed at Ar + O₂ gas mixture with a pressure of 1.0 Pa and oxygen with a constant pressure of 0.2 Pa. The TiO₂ / ZnO thicknesses were approximately 1000 nm and 80 nm, respectively. As-deposited films were annealed at 400 °C. The structure and morphology of deposited layers were evaluated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The transmittance of the films was measured using ultraviolet–visible light (UV–vis) spectrophotometer. Photocatalytic activities of the samples were evaluated by the degradation of 2-propanol. The microstructure of annealed films was anatase, having improved photocatalytic activity. The surface grain size of TiO₂ thin film after annealing was found about 25-35 nm and crystal size was approximately 8 nm. By using ZnO thin film as buffer layer, the photocatalytic property of TiO₂ films was improved.

Nitride doped titanium oxide (TiO_xN_y) is a photocatalytic material which acts under visible light, while conventional titanium oxide acts only in ultra violet light. In this study, we tried to make nitride doped titanium film by oxidizing of TiN film. The TiN films were deposited on the quartz substrate by DC magnetron sputtering. The film structure was analyzed by X-ray diffraction. The photocatalytic decomposing rate was measured using methylene blue solution under black light and fluorescent lamp. As a result, post annealing process after oxidizing process is unsuitable to realize a high photocatalytic activity for oxidized TiN. On the other hand, the samples oxidized in nitrogen rich atmosphere showed the obvious photocatalytic activity under visible light irradiation. This reason is that the oxidation of the film surface is controlled and nitrogen atom left in film surface by nitrogen gas supplying. In conclusion, oxidizing of TiN film in nitrogen rich atmosphere is suitable to realize a high photocatalytic activity.

Lithium niobate (LiNbO₃, LN) thin films have been extensively studied for applications in acoustic and photonic devices, due to their outstanding piezoelectric, ferroelectric and electro-optical properties. With the increasing demand for high speed and low latency wireless communication, LN thin films with high electromechanical coupling coefficients are very attractive to improve the performance of acoustic resonators for radio frequency filters. The current bottleneck for LN-based devices is the synthesis of high-quality LN thin films, which is typically fabricated by expensive and inefficient process of ion slicing and layer transfer from bulk single crystals. This review paper focuses on the direct growth of high-quality LN thin films, which has the potential to scale up and lower the cost of LN thin films. We first introduce the crystal structure and piezoelectric properties of LN, followed by an overview of the state-of-the-art LN acoustic resonators. After a summary of the challenges in the fabrication of LN thin films, we review the direct growth of LN thin films by sputtering, pulsed laser deposition, metalorganic chemical vapor deposition and molecular beam epitaxy. With the progress in optimizing the crystallinity and surface roughness, the quality of the LN thin films synthesized by direct growth has been greatly improved. As a result of the fast-growing industrial interests, we believe that the research works in direct growth of LN thin films will increase exponentially to achieve the same quality of the LN thin films as the bulk single crystals.a