X. Y. Zhou

ZnO-based film bulk acoustic resonator for high sensitivity biosensor applications

Zinc oxide (ZnO)-based film bulk acoustic resonator consisting of a piezoelectric element (Au∕ZnO∕Pt) and a Bragg reflector (ZnO∕Pt multilayer structure) has been fabricated by magnetron sputtering. The transmission electron microscopy and x-ray diffraction measurements revealed that all thin film layers in the device were well crystallized and highly textured. By electrical measurements, it was found that the device had a high resonant frequency (3.94GHz) and mass sensitivity (8970Hzcm2∕ng). The use of the device as a biosensor was demonstrated by comparing the resonant properties of the device with/without coatings of biospecies.

Enhanced in-plane ferroelectricity in Ba0.7Sr0.3TiO3 thin films grown on MgO (001) single-crystal substrate

Highly oriented Ba0.7Sr0.3TiO3 thin films were grown on MgO (001) single-crystal substrate using pulsed-laser deposition and the in-plane ferroelectric properties of the film were evaluated. X-ray diffraction characterization revealed a good crystallinity and tensile in-plane stress in the film. A well-defined ferroelectric hysteresis loop with Pr=9.5μC∕cm2 was observed along the (100) direction, which implied an enhanced in-plane ferroelectricity in the Ba0.7Sr0.3TiO3 thin film in comparison with the Ba0.7Sr0.3TiO3 ceramics. Curie temperature of the film was found to be ∼88°C, which is nearly 50°C higher than that of the Ba0.7Sr0.3TiO3 ceramics. The butterfly-shaped C‐V characteristic curve also evidenced the enhanced in-plane ferroelectric property in the film, and a large dielectric tunability of 69% was found at 1MHz under a moderate dc bias field. The observation of enhanced ferroelectricity along the in-plane direction in the highly oriented Ba0.7Sr0.3TiO3 thin film was explained in terms of the inc...

Microstructure and dielectric relaxor properties for Ba0.5Sr0.5TiO3/La0.67Sr0.33MnO3 heterostructure

Ferroelectric and magnetoresistance heterostructure (Ba,Sr)TiO3/(La,Sr)MnO3 (BST/LSMO) heterostructure is deposited epitaxially on SrTiO3 (001) substrate by pulse laser deposition. The phase structures of the BST/LSMO heterostructure are characterized by x-ray diffraction. Cross-sectional transmission electron microscope shows a substantial interdiffusision between BST and LSMO layers. The dielectric properties and conductivity of BST/LSMO heterostructure is measured as a function of temperature, frequency, and electric field. The dielectric constant dependence on electric field, e vs E, exhibits a strong nonlinear behavior in the temperature from 20 to 300 K, while e(E=0) vs T relation shows a dielectric relaxor characteristic. Furthermore, the dielectric constant (E=0 kV/cm) and the dielectric tunability (E=200 kV/cm) are found to be similar temperature dependencies. Last, in the temperature regime where a semiconduction-type conduction became dominate, the activation thermal energy of BST/LSMO heterost...

Fine-grained BaZr0.2Ti0.8O3 thin films for tunable device applications

A study of the structure and in-plane dielectric properties of BaZr0.2Ti0.8O3 thin film epitaxially grown on (LaAlO3)0.3(Sr2AlTaO6)0.35 (001) single-crystal substrates through pulsed-laser deposition has been carried out. X-ray diffraction measurements revealed a good crystallinity and tensile in-plane stress in the film. Fine grains with an average size of ∼20 nm were observed using atomic force microscopy. Curie temperature of the film was found to be ∼120 °C, which is 100 °C higher than that of the ceramic. Butterfly-shaped C-V curve confirmed the in-plane ferroelectric state in the film. A large dielectric tunability of ∼50% was found in the film.

Dielectric properties of (001)-oriented Ba(Zr0.25Ti0.75)o3 thin films prepared by pulsed laser deposition

Ba(Zr 0.25 Ti 0.75 )O 3 (BZT) thin film was deposited on LaAlO 3 (001) single crystal substrate using pulsed laser deposition. The X-ray diffraction examination reveals that the film is highly (001)-oriented with a pure perovskite phase. Fine grains with size of 20–30 nm in diameter were observed in atomic force microscope image. Dielectric properties of the Ba(Zr 0.25 Ti 0.75 )O 3 thin film was characterized in a broad frequency range (1 kHz–10 GHz). Curie temperature of the film was found to be ∼90°C, which is nearly 100°C higher than that of the Ba(Zr 0.25 Ti 0.75 )O 3 bulk ceramics. The relative permittivity of the film exhibits strong dependence of the dc bias field over the whole frequency range. Microwave measurements, performed between 50 MHz–1 GHz, suggest our Ba(Zr 0.25 Ti 0.75 )O 3 thin film is highly tunable (tunability up to 26.1% at 1 GHz under a dc electric field of 13.3 MV/m).

Interface characterization of SrTiO3/Sr/Si heterostructure through X-ray reflectivity

The growth of hetero-epitaxial strontium titanate (SrTiO3) on single-crystal silicon (Si) substrate is of considerable scientific interest because of its wide range application. Unlike other hetero-epitaxial systems, there exists a fairly large lattice mismatch between SrTiO3 and Si. This leads to the possibility of strain in SrTiO3 thin film. In order to prevent the formation of amorphous SiO2 phase and interdiffusion of component atoms at the interface, an ultrathin strontium (Sr) layer is deposited on the underlying Si-substrate. The X-ray diffraction (XRD) is used for characterization of hetero-structures. In this paper, we report the characterization of SrTiO3 thin film on Si (100) substrate with Sr interlayer by a variety of X-ray measurements. Based on the data obtained from SrTiO3 thin film, the growth characteristics of the sample is objectively appreciated. The sample is prepared by laser molecular beam epitaxy (L-MBE) under optimized conditions of substrate temperature and oxygen pressure. 2?/? scan indicates a high crystallization quality and epitaxial grown of SrTiO3 thin film in the nanometre scale. ?-scans have further revealed the in-plane orientation relationship between SrTiO3 and Si. The ?- and c- lattice parameters of the SrTiO3 thin film are found to be 0.3898, and 0.3901 nm, respectively, which suggests a slight elastic distortion. More detailed investigations by X-ray reflectivity have therefore been carried out, in order to get better understanding to the effect of the buried heterointerface.

Comparison of structures and properties of bst thin films grown on lao and mao substrates

ABSTRACT The crystal structure and in-plane dielectric and ferroelectric properties of Ba0.7Sr0.3TiO3 (BST 70/30) thin films epitaxially grown on LaAlO3 (LAO) and MgAl2O4(MAO) (001) single crystal substrates by PLD are compared. Through X-ray diffraction it is found that BST thin film in both heterostructures has an elongated in-plane lattice parameter, which results in a shifted Curie temperature (Tc = 70°C for BST on LAO and 78 o C for BST on MAO) and enhanced ferroelectric properties (Pr = 8.4 μ C/cm2 for BST on LAO and 7.1 μ C/cm2 for BST on MAO).

Influence of Processing Conditions on the Structure of Strontium Titanate Thin Films Grown on Si by Laser Mbe

ABSTRACT Epitaxial SrTiO3 thin films have been deposited on Si (100) substrates by laser molecular-beam epitaxy. The experiments have confirmed that the use of Sr buffer layer is essential for making high quality SrTiO3 film. Apart from this, processing parameters including the deposition temperature and time for each layer also have significant influence on the crystallinity and roughness of SrTiO3. The thin films prepared under optimized conditions were found to have a pure perovskite phase, well crystallized and epitaxially aligned. The electrical measurements indicate that the SrTiO3 film has a capacitance effective thickness of less than 16 Å.

INFLUENCE OF TEMPERATURE ON THE IN-PLANE DIELECTRIC PROPERTIES OF BARIUM STRONTIUM TITANATE THIN FILMS

ABSTRACT (Ba0.7Sr0.3)TiO3 (BST 70/30) thin films were deposited on (LaAlO3)0.3(Sr2AlTaO6)0.7 single crystal substrates by means of pulsed laser ablation. X-ray diffraction revealed that the BST 70/30 thin film was well crystallized and epitaxially aligned on the substrate. Compared with the cubic lattice structure of BST ceramics with the same composition, the lattice of BST 70/30 thin film was found to have been slightly distorted to a tetragonal symmetry. As a result of the distortion, the Curie temperature of the thin film was found to be 73°C, which is ∼ 40°C higher than that of the ceramics. The in-plane dielectric tunability of the thin film was found to be dependent on temperature. The largest tunability occurs at the Curie temperature. In the paraelectric state, the tunability is more sensitive to temperature than in the ferroelectric state.

Tuning the Resistance of La0.7Sr0.3MnO3 Thin Films by Converse Piezoelectric Effect

We have examined the effects of converse piezoelectric effect induced lattice strains on the resistance of the La 0.7 Sr 0.3 MnO 3 (LSMO) thin films grown on (001)-oriented (1-x)Pb(Mg 1/3 Nb 2/3 )O 3 -xPbTiO 3 (x∼0.3) (PMN-PT) single-crystal substrates. It has been found that the resistance of the LSMO films can be modulated by the converse piezoelectric effect of the PMN-PT substrates. Piezoelectric displacement measurements indicate that the converse piezoelectric effect induces lattice displacements in the PMN-PT substrates, which modulates the lattice strain and resistance of the LSMO films. Based on the experimental results, the relationship between the resistance of the LSMO films and the converse piezoelectric effect induced lattice strains in the PMN-PT substrates has been discussed.