LaNiO3 Buffered Si Substrates Research Articles

Lead zirconate titanate and barium titanate bi-layer ferroelectric films on Si

In this work, a novel method is proposed to integrate ferroelectric lead zirconate titanate (PZT) films on Si with highly tunable functionalities, through bi-layering with a barium titanate (BTO) film. First of all, the BTO film acts as a growth-promotion template layer which has successfully lowered the in situ deposition temperature of a ferroelectric PZT film. The PZT/BTO bilayer film deposited at 350 °C on LaNiO3-buffered Si substrate displayed a room temperature remnant polarization ∼24 μC/cm2, and its quality can be further improved via a rapid thermal annealing (RTP) process. Furthermore, by changing their thickness ratio, various ferroelectric hysteresis loops (P-E loops) can be created in the PZT/BTO films, thereby enabling a broad range of applications for this simple bi-layer structure. Examples including high performance piezoelectric energy harvesters and high energy density dielectric capacitors are demonstrated for the PZT/BTO bi-layer films.

Preparation and piezoelectric properties of self-polarized (Na,Bi)TiO3–BaTiO3 thin films on Si substrate

The c-axis oriented polycrystalline thin film of (Na,Bi)TiO3–BaTiO3 (NBT–BT) around the morphotropic phase boundary (MPB) was prepared on an LaNiO3-buffered Si substrate by rf magnetron sputtering. The NBT–BT film showed a large crystal lattice distortion in the out-of-plane direction, and a voltage shift of the hysteresis loop along the negative field axis as large as −200 kV/cm, which indicates that the film is internally biased and strongly self-polarized towards the top electrode. Owing to the large internal bias field, the NBT–BT film exhibited a linear piezoelectric response with the piezoelectric coefficient, , reaching −4.8 C/cm2 in the unipolar excitation and a low dielectric permittivity of 230. The temperature-dependent dielectric properties revealed that the permittivity maximum temperature, Tm, of the NBT–BT film was significantly enhanced to ∼550 °C from the ∼300 °C of bulk NBT–BT, accompanied by the disappearance of the depolarization temperature, Td, which is confirmed by the structural data where the crystal lattice remained unchanged up to ∼400 °C. These stable temperature properties would lead to an expansion of the temperature range of use of NBT–BT film.

Annealing effect on the bipolar resistive switching behaviors of BiFeO3 thin films on LaNiO3-buffered Si substrates

We reported the annealing effect on the electrical behaviors of BiFeO3 thin films integrated on LaNiO3 (LNO) layers buffered Si substrates by sol–gel spin-coating technique. All the BiFeO3 thin films exhibit the reversible bipolar resistive switching behaviors with Pt/BiFeO3/LNO configuration. The electrical conduction mechanism of the devices was dominated by the Ohmic conduction in the low resistance state and trap-controlled space charged limited current in the high resistance state. Good diode-like rectification property was observed in device with BiFeO3 film annealed at 500°C, but vanished in device with BiFeO3 film annealed at 600°C. This was attributed to the asymmetrical contact between top and bottom interfaces as well as the distinct oxygen vacancy density verified by XPS. Furthermore, the modification of Schottky-like barrier due to the drift of oxygen vacancies was suggested to be responsible for the resistance switching behaviors of Pt/BiFeO3/LNO devices.

Dielectric phase transition and relaxor behavior in BaTiO3/LaNiO3superlattice

(001)-oriented BaTiO3/LaNiO3 superlattices with a symmetric structure were fabricated on LaNiO3 buffered Si substrates. The formation of superlattice was confirmed by X-ray diffraction and transmission electron microscope observations. In contrast to the sharp dielectric transition of pure bulk BaTiO3, a broad dielectric anomaly with shift in dielectric maxima toward higher temperature with increasing frequency is observed, suggesting the system exhibits diffusive phase transition following the Vogel–Fulcher relationship. Furthermore, with decreasing stacking periodicity, out-of-plane lattice constant of the superlattice is increased, room temperature dielectric constant is enhanced, while phase transition temperature is decreased. The observed structure-dielectricity correlation is attributed to both strain effect of the inserted LaNiO3 layer and the interfacial Maxwell–Wagner effect.

Magnetic-electric behaviors in BiFeO3 films grown on LaNiO3-buffered Si substrate

BiFeO 3 films with different thicknesses and crystallographic orientations were grown on LaNiO3-buffered Si substrates via a modified chemical route. Remarkable size effect in ferroelectric behavior was observed with thicker films exhibiting a larger polarization value, due to combined depolarization effect and microstructure of the BiFeO3 films. High resolution transmission electron micrograph revealed a complex strain state in the BiFeO3 films, and the net magnetic moment induced by the canting of the antiparallel spins was arranged in disorder in thicker films, presenting a spin-glass state; while in the thinner BiFeO3 films, the disorder spins turned to be orderly arranged to induce a ferromagnetic behavior. Thus there exists a competition between ferroelectric and magnetic behaviors as film thickness changes. Furthermore, magnetoelectric coupling was observed in the BiFeO3 films with a magnetic-field-induced electrical voltage of around 3.5 μV/Oe.

Microstructural orientation, strain state and diffusive phase transition of pure argon sputtered BaTiO3 film

Highly (0 0 1)-oriented BaTiO3 thin film was deposited on a LaNiO3 buffered Si substrate by the pure argon sputtering method. X-ray diffraction analysis indicates that while the LaNiO3 buffer layer is slightly tensile-strained, the upper BaTiO3 layer is actually under an in-plane compressive strain state. The microstructure and crystallographic orientation of the BaTiO3 film were further analysed by transmission electron microscopy and electron diffraction observations by in situ tilting the film sample in the vacuum chamber. Temperature dependent dielectric measurements demonstrate that the ferroelectric to paraelectric phase transition temperature is lowered to 108 °C, which is attributed to the hardening of the soft mode induced by the presence of the compressive strain state. Furthermore, the observed strongly frequency dependent dielectric dispersions and the validity of the Vogel–Fulcher relationship indicate that the pure argon sputtered BaTiO3 thin film shows a diffusive ferroelectric phase transition.

Thickness dependent size effect of BiFeO3 films grown on LaNiO3-buffered Si substrates

BiFeO 3 films of different thicknesses were grown on the LaNiO3-buffered Si (100) substrate via a sol-gel spin-coating processing. X-ray diffraction and Raman spectra studies revealed a thickness dependent structural and strain state evolution. The thickness dependent size effect on ferroelectric behavior was reflected in the polarization versus electric field hysteresis loops and domain structures. Enhancement in magnetization of the thin BiFeO3 films resulted from the strain-induced canting antiferromagnetic structure, and remarkable anisotropy was observed in the 40 nm BiFeO3 film as well due to the magnetoelastic effect induced by strain. With the increase in the film thickness, the magnetic moment of BiFeO3 films decreased back to the ordinary canted antiferromagnetic state.

Dielectric response and structure of in-plane tensile strained BaTiO3 thin films grown on the LaNiO3 buffered Si substrate

Highly (001)-textured BaTiO3 films were grown epitaxially on the LaNiO3 buffered Si substrate. A strong in-plane tensile strain has been revealed by using x-ray diffraction and high resolution transmission electron microscopy. The BaTiO3 film has exhibited a small remnant polarization, indicating the presence of ca1∕ca2∕ca1∕ca2 polydomain state in the film. Temperature dependent dielectric permittivity has demonstrated that two phase transitions occurred at respective temperatures of 170 and 30°C. The result was discussed in detail based on the misfit strain-temperature phase diagrams theory.

Effect of composition and growth temperature on the dielectric properties of Pb(ScTa)1−xTixO3 (PSTT) thin films grown by MOCVD

Highly (002) textured Pb(ScTa)1−xTixO3 (PSTT) (with x = 0–0.3) thin films were grown on LaNiO3 buffered Si substrates using metal-organic chemical vapor deposition (MOCVD) technique at temperatures ranging from 600 to 685°C. Dielectric properties showed strong dependency on the growth temperature and PT content. Ti addition acted as a “Curie” temperature shifter and increased the dielectric constants. Dielectric dispersion behavior was observed, along with a diffuse phase transition, characterizing the relaxor properties of PSTT.