A. L. Ding

Preparation and characterization of highly (111)-oriented (Pb, La)(Zr, Ti)O3 thin films by sol-gel processing

Abstract Lanthanum modified lead zirconate titanate (Pb0.91La0.09)(Zr0.65Ti0.35)O3 (PLZT) ferroelectric thin films were grown on Pt/Ti/SiO2/Si(1xa00xa00) and fused quartz substrates using a sol–gel method with rapid thermal annealing processing. The results showed that the highly (1xa01xa01)-oriented pervoskite PLZT thin film growth on Pt/Ti/SiO2/Si(1xa00xa00) substrates. The electrical measurements were conducted on PLZT films in metal–ferroelectric-metal capacitor configuration. The PLZT thin films annealed at 600 °C showed well-saturated hysteresis loops with remanent polarization and coercive electric field values were 10.3 μC/cm2 and 36 kV/cm, respectively, at an applied field of 300 kV/cm. At 100 kHz, the dielectric constant and dielectric loss of the film are 682 and 0.021, respectively. The PLZT thin film on fused quartz substrate, annealed at 600 °C, exhibited good optical transmittance, the band gap of optical direct transitions is 3.89 eV.

Microstructure and optical properties of amorphous and crystalline PbZrO3 thin films grown on Si(100) substrates by a sol-gel process

Abstract Amorphous and crystalline PbZrO3 thin films deposited on Si(100) substrate have been prepared by a sol–gel process. The crystal structure and surface morphologies of the thin films have been studied by X-ray diffraction and atomic force microscopy. The crystalline PbZrO3 film on Si(100) substrate is a pseudocubic structure with a (111) orientation. The refractive index n and extinction coefficient k of the amorphous and crystalline thin films were obtained by spectroscopic ellipsometry as a function of the photon energy in the range from 2.0 to 5.4xa0eV. The absorption edges for amorphous and crystalline PbZrO3 thin films are 4.07 and 3.63xa0eV, respectively. The absorption edge of the amorphous PbZrO3 film shift to high energy is mainly due to the quantum-size effect.

Synthesis and dielectric characteristic of Ba1-xSrxTiO3 thin films-based strontium-barium alkoxides derivatives

Abstract Homogeneous Ba1−xSrxTiO3 (BST) sols have been synthesized using barium, strontium acetate, and titanium tetra-n-butoxide as starting materials. Acetic acid and ethylene glycol were selected as solvents. The formamide was selected as an additive to adjust the solution viscosity in order to reduce the crack of the BST thin films. The structure and thermal decomposition process of BST gel powders and thin films, which were prepared from a precursor of strontium-barium titanate alkoxides, were investigated by means of differential thermal/thermogravimetric analyses (DTA/TGA) and X-ray diffraction measurements. DTA/TGA technique was used to determine the temperature of decomposition and crystallization. The BST thin films were prepared by a spin-on sol–gel process on Pt/Ti/SiO2/Si (1xa00xa00) substrates. The thin films were crystallized above 600°C, and formed completed perovskite structure around 700°C. The capacitance–voltage curve shows that the polarization and capacitance vary non-linearly with an applied field due to the domain structure. A tunability of dielectric constant about 29.3% and a figure of merit, K=6.5, were obtained with an electric field of 150xa0kVxa0cm−1.

Electrical properties of (Pb0.76Ca0.24)TiO3 thin films on LaNiO3 coated Si and fused quartz substrates prepared by a sol–gel process

Abstract Ferroelectric (Pb 0.76 Ca 0.24 )TiO 3 (PCT) thin films were grown on LaNiO 3 (LNO) coated Si(1xa01xa01) and fused quartz substrates by using a sol–gel process. The highly (1xa00xa00)-oriented PCT films on LNO coated Si(1xa01xa01) substrates, and random oriented pervoskite PCT thin films on fused quartz substrates have been obtained, respectively. Atomic force microscopy (AFM) revealed that the surface morphology smooth. PCT films on LNO coated Si(1xa01xa01) and fused quartz substrates, the grain sizes were about 60–120 and 40–60xa0nm, respectively. The PCT thin films on LNO coated Si(1xa01xa01) and fused quartz substrates annealed at 600xa0°C have the remanent polarization ( P r ) and coercive electric field ( E c ) values were 9.3xa0μC/cm 2 and 64xa0kV/cm, 1.4xa0μC/cm 2 and 28xa0kV/cm, respectively. At 100xa0kHz, the dielectric content and dielectric loss of the PCT films on LNO coated Si(1xa01xa01) and fused quartz substrates were 231 and 0.045, 160 and 0.061, respectively.

Synthesis and analyses of thermal decomposition and microstructure of Sr-doped barium titanate alkoxide derived precipitates and thin films

Abstract The structure and thermal decomposition process of Ba 0.8 Sr 0.2 TiO 3 (BST) powders and thin films, which were prepared from a precursor of Sr-doped barium titanate alkoxides, were investigated by means of differential thermal/thermogravimetric analyses (DTA/TGA), X-ray diffractometer (XRD), AFM, and Fourier transform infrared spectroscopy (FTIR) measurements. From the FTIR spectra, it has been possible to observe that gel powders pyrolyzed and crystallized by analyzing the bands of organic functional groups and inorganic oxides. For further determination of the temperature of decomposition and crystallization, DTA/TGA technique was used. The thin films of Ba 0.8 Sr 0.2 TiO 3 were prepared by spin-on sol–gel process on Si (1xa00xa00) substrates, the films were crystallized above 600°C, and formed complete perovskite structure around 700°C. The morphology was investigated by atomic force microscope.

Synthesis and characteristics of strontium-barium titanate graded thin films at low temperature using a sol-gel technique

Abstract Thin films (∼400xa0nm) of Ba x Sr 1− x TiO 3 (BST) with gradients in composition were formed on Si(100) and fused quartz substrates by a modified sol–gel technique. A special heating treatment procedure was employed in this study to form the uniform composition gradients at below 750°C. The results of Auger depth profiling indicate that the special process produces smooth, linear composition gradients. XRD diffraction clearly shows the formation of the perovskite structure. The (200) peaks of the BaTiO 3 , SrTiO 3 , and the graded BST films were analyzed; the peak from the graded film is broad and centered at 46.4°, while the intensity is slightly weaker than those of BaTiO 3 and SrTiO 3 . The index of refraction and the band gap were determined at room temperature in the wavelength 200–900xa0nm from spectrophotometric measurements of the transmittance. The average value of the refractive index is found to be 2.45 for the graded BST films in the wavelength 400–800xa0nm; the higher values near ultraviolet are associated with the fundamental band gap absorption. The variation of the refractive index of the graded films is smaller than that of the other films. The direct band gap energy is found to be 3.73xa0eV.

Effect of compositionally graded configuration on the optical properties of BaxSr1-xTiO3 thin films derived from a solution deposition route

Abstract BaxSr1−xTiO3 (BST) thin films with gradients in composition were deposited on Si(1xa00xa00) and fused quartz substrates by a modified sol–gel technique. A special heating treatment procedure was employed in this study to form the uniform composition gradients at below 750xa0°C. XRD diffraction clearly shows that the perovskite structure of the graded films formed around 730xa0°C. The (2xa00xa00) peaks of the BST (10/90), BST (50/50), and the graded BST films were analyzed, the peak from the graded film is broad and centered at 46.3°. The optical band-gap energy and the absorption coefficient were determined at room temperature in the wavelength range of 200–900xa0nm from spectrophotometer measurements of the transmittance. The optical band-gap energy (Egap) decreases from 4.29 to 3.68xa0eV with an increase of annealing temperatures from 350 to 730xa0°C. The refractive index dispersion curves rise rapidly toward shorter wavelengths and a smaller variation of the refractive index was found in graded film than the single-composition samples. There are two distinct absorption bands found about 3.15 and 2.78xa0eV corresponding to the impurities absorption.

Surface morphology and chemical states of highly oriented PbZrO3 thin films prepared by a sol–gel process

Abstract Antiferroelectric PbZrO 3 thin films have been prepared on Pt/Ti/SiO 2 /Si(1xa00xa00) substrates by a simple sol–gel process. The structure and surface morphology evolution were investigated by an X-ray diffraction (XRD) and an atomic force microscopy (AFM), and a scanning electron microscopy (SEM), respectively. The results shows that the films grown on Pt/Ti/SiO 2 /Si (1xa00xa00) substrates have a pseudocubic perovskite structure with high (1xa00xa00) oriention, and the surface morphology evolution of the thin film depends on annealing temperature. The films have three dimensional island growth. The chemical states and chemical composition of the film was also determined by X-ray photoelectron spectroscopy (XPS), near the film surface. Pb and Zr exist mainly in the forms of PbZrO 3 .

The effect of thickness on the dielectric properties of highly (111) oriented Pb(Zr 0.53 Ti 0.47 )O 3 thin films prepared by a simple sol-gel route

Lead zirconate titanate Pb(Zr0.53Ti0.47)O3 (PZT) ferroelectric thin films of various thicknesses were grown on Pt(111)/Ti/SiO2/Si(100) substrates by a simple sol-gel process, without reflux or high temperature distillation to remove water. The thin films were annealed at 550-600 °C in an oxygen atmosphere by rapid thermal annealing (RTA), and highly (111)-oriented PZT thin films have been obtained. The microstructure and surface morphologies of the thin films have studied by X-ray diffraction (XRD) and atomic force microscopy (AFM). AFM images shown that the highly (111) oriented PZT thin films on Pt/Ti/SiO2/Si substrates with grain sizes of 0.2-0.3 and 2-3 µm, and root mean square roughnesses of 0.92 and 34 nm, for PZT films with thicknesses of 0.3 and 0.56 µm, respectively. The remanent polarization (Pr) and coercive electric field (Ec) values were 32.2 µC/cm2 and 79.9 kV/cm, 27.7 µC/cm2 and 54.4 kV/cm; at 100 kHz, the dielectric constant and dissipation factor were 539 and 0.066, 821 and 0.029, respectively, for PZT films with thicknesses of 0.3 and 0.56 µm.

Processing effects on the microstructure and ferroelectric properties of Pb(Zr,Ti)O3 thin films prepared by sol–gel process

Abstract Lead zirconate titanate Pb(Zr 0.53 Ti 0.47 )O 3 (PZT) thin films grown on Pt(1xa01xa01)/Ti/SiO 2 /Si(1xa00xa00) substrates by a simple sol–gel process use various thermally decompose temperatures from 320 to 400 °C. Then PZT films were annealed at various temperatures from 550 to 600 °C in oxygen atmosphere by a rapid thermal annealing process, and highly (1xa01xa01)-oriented PZT thin films have been obtained. The microstructure and surface morphologies, and root mean square (RMS) roughness of the thin films were studied by X-ray diffraction and atomic force microscopy (AFM). AFM images shown that the higher (1xa01xa01) orientation present in the PZT thin films, the smaller grain size, and the lower RMS roughness. PZT films on Pt/Ti/SiO 2 /Si substrates were initially heated at 400 and 320 °C, then annealed at 550 °C, the remanent polarization ( P r ) and coercive electric field ( E c ) were 16.1 μC/cm 2 and 105 kV/cm, 32.2 μC/cm 2 and 79.9 kV/cm; at 100 kHz, the dielectric constant and dissipation factor were 331 and 0.045, 539 and 0.066, respectively. The highly (1xa01xa01) oriented PZT films, have smooth surface, good ferroelectric and dielectric properties.