Chunlin Fu

Structural and optical properties of BaxSr1−xTiO3 thin films on indium tin oxide/quartz substrates prepared by radio-frequency magnetron sputtering

BaxSr1−xTiO3 (x=0.6 and 0.8) thin films have been prepared on indium-doped tin oxide (ITO) coated quartz substrates using radio-frequency magnetron sputtering. Their structural properties and surface morphologies were examined by x-ray diffraction and atomic force microscopy, respectively. The BaxSr1−xTiO3 (BST) thin films with x=0.6 and 0.8 annealed at 650°C for 20min exhibit good surface morphology and well-crystallized perovskite structure. High quality BST ferroelectric thin films were further investigated by electrical measurements, showing the remnant polarization (Pr) of 6.75μC∕cm2 and the coercive field (Ec) of 43.2kV∕cm. Optical transmittance measurement indicated that the Ba concentration has an effect on the band gap energy (Eg) structure of the BaxSr1−xTiO3 thin films. The Eg decreases linearly with the increase of the Ba content. The refractive index (n) and extinction coefficient (k) of the BST films with x=0.6 and 0.8 were obtained by fitting the spectroscopic ellipsometric data using a par...

Model for dielectric nonlinearity of ferroelectrics

Dielectric nonlinearity is an important characteristic of ferroelectrics. Based on the characteristics of hysteresis loops and e-E curves in ferroelectric materials, a model for dielectric nonlinearity of ferroelectrics is established. It is verified by the data of barium strontium titanate thin films.

Effect of Samarium on the Microstructure, Dielectric and Ferroelectric Properties of Barium Titanate Ceramics

Samarium-doped barium titanate ceramics were prepared by the conventional solid-state reaction method. The microstructure, dielectric and ferroelectric properties of Sm-doped barium titanate ceramics have been investigated. The result indicates that Sm3+ ions enter the perovskite-type structure to substitute for Ba2+ ions on the A sites and lead to the change of the crystal structure from tetragonal to cubic structure. Addition of samarium can restrain the grain growth of barium titanate ceramics and lead to the fall of the Curie temperature. There is diffuse phase transition in Sm-doped barium titanate ceramics. Sm3+ ions can decrease the dielectric loss of barium titanate ceramics on the basis of the Ti-vacancy defect compensation model. The remnant polarization and the coercive field of Sm-doped barium titanate ceramics decrease monotonously with the increase of samarium content. As temperature rises, the remnant polarization and the coercive electric field of Sm-doped barium titanate ceramics decrease simultaneously. The remnant polarization and coercive electric field of barium titanate ceramics decrease with the increase of frequency. But the remnant polarization and coercive electric field of Sm-doped barium titanate ceramics have no evident change as frequency increases from 100 Hz to 1000 Hz.

Ba(Mg1/3Ta2/3)O3 substrate for BaxSr1-xTiO3 thin film used for phase shifter

Barium strontium titanate, BaxSr1-xTiO3 (BST for short), thin films are grown on the substrates of barium magnesium tantalite, Ba(Mg1/3Ta2/3)O3 (BMT for short), by pulsed laser deposition (PLD) technique. The microstructures and electric properties of Ba(Mg1/3Ta2/3)O3 ceramics and BaxSr1-xTiO3 films are investigated, and the phase shifter is fabricated. Both Ba(Mg1/3Ta2/3)O3 and BaxSr1-xTiO3 have perovskite structure and BMT ceramics has high Q0 at microwave frequency , so BMT substrate is compatible and suitable for BST films. The dielectric constant and dielectric loss of the BST films are 510 and 2% respectively , and about 50% dielectric constant tunability is achieved with an electric field bias of 3v/μm. The dielectric loss of BST films shows no obvious change with the electric fields. About 50° of phase shift has obtained with an electric field bias of 2v/μm at 5GHz .

EFFECTS OF SUBSTRATE TEMPERATURE AND TARGET-SUBSTRATE DISTANCE ON THE DIELECTRIC NON-LINEARITY OF Ba0.6Sr0.4TiO3 THIN FILM

ABSTRACT Barium strontium titanate (Ba0.6Sr0.4TiO3, short for BST) thin films were prepared by RF-magnetron sputtering. The influences of deposition conditions, such as substrate temperature and target-substrate distance, on the microstructures and non-linearities of BST thin films were investigated. The non-linearities of Ba0.6Sr0.4TiO3 thin films increase as the substrate temperature increases and/or target-substrate distance decreases.