Structural and electrical properties of polycrystalline PbZr0.5Ti0.5O3 films deposited on La0.5Sr0.5CoO3 coated silicon by sol-gel process

La_0.5Sr_0.5CoO₃ (LSCO) films have been grown on Si (100) by a metalorganic chemical liquid deposition (MOCLD) technique using lanthanum acetate, strontium acetate and cobalt acetate as the starting materials. Subsequent PbZr_0.5Ti_0.5O₃ (PZT) films were deposited onto LSCO films by a modified sol-gel method. Field-emission scanning electron microscopy and X-ray diffraction analysis show that PZT and LSCO films are polycrystalline and entirely perovskite phase. At an applied electric field of 250 kV/cm, the Pt/PZT/LSCO capacitor shows no polarization fatigue after 3×10⁹ switching cycles and an internal electric field; the remnant polarization P_r and the coercive field E_c are about 22 μC/cm² and 73 kV/cm, respectively. The dielectric constant of PZT films is 650 at a frequency of 1 kHz. Received: 20 February 2001 / Accepted: 6 June 2001 / Published online: 30 August 2001     

Spray pyrolysis deposition of YSZ and YSZ-Pt composite films

In the present paper procedures are described for spray pyrolysis deposition of YSZ films (0.1-30 μm in thickness) with 8 or 15 mole % of YO_1.5 on different substrates. Aqueous or ethylene glycol solutions of Y-Zr-citrates were used as starting material and O₂ as carrier gas. The crystal structure and the morphology of the films were studied.The optimal deposition and post-deposition annealing conditions were defined, taking into account the desired film thickness and characteristics. Substrate temperatures of 250 °C during the deposition followed by heating for 10 min to 400 °C after every spraying and to 590 °C after every three sprayings with final annealing at 590 °C for 2 h in static air atmosphere were found to be suitable for the production of dense, uniform and cracks-free films.     

Superhydrophilic stability enhancement of RF co-sputtered TixSi1−xO2 thin films in dark

Ti_xSi_1−xO₂ compound thin-film systems were deposited by reactive RF magnetron co-sputtering technique. The effect of Ti concentration on the hydrophilicity of Ti_xSi_1−xO₂ compound thin films was studied and it was shown that the films with Ti_0.6Si_0.4O₂ composition possess the best hydrophilic property among all the grown samples. Surface ratio and average roughness of the thin films were measured by atomic force microscopy (AFM). Surface chemical states and stoichiometry of the films were determined by X-ray photoelectron spectroscopy (XPS). In addition, XPS revealed that the amount of Ti-O-Si bonds in nanometer depth from the surface of the Ti_0.6Si_0.4O₂ films was the maximum, which resulted in the most stable superhydrophilic property. According to XRD data analysis for the pure TiO₂ films, the polycrystalline anatase phase was formed with an average grain size of about 15 nm. Moreover, amorphous phase was also formed for the Ti_xSi_1−xO₂ compound systems due to presence of silicon in the films. Finally, optical properties of the films such as transmission, reflection and band gap energy were investigated using UV-vis spectrophotometry. It was found that the transmittance of the films was decreased with increasing Ti concentration in the films.     

Deposition and characterization of La2Ti2O7 thin films via spray pyrolysis process

Thin films of La₂Ti₂O₇ have been deposited on fused silica and Si substrates by a spray pyrolysis method using ethylene glycol solution of La(III)-Ti(IV)-citrate complexes as starting material and O₂ as a carrier gas. The composition, crystal structure and morphology of the films are studied.     

Dielectric relaxations in Tb0.91Yb1.38Bi0.71Fe5O12 ceramics

Dielectric relaxations of Tb_0.91Yb_1.38Bi_0.71Fe₅O₁₂ ceramics were investigated. A Debye-type relaxation was observed in the temperature range of 125-620 K with an activation energy of 0.29 eV. This activation energy agreed well with that of carriers hopping between Fe²⁺ and Fe³⁺, indicating that this relaxation might be a dipolar-type relaxation associated with the hopping carries. A high relaxorlike dielectric peak with a very strong frequency dispersion in the high temperature range of 400-620 K might be originate from the oxygen vacancies related dielectric relaxation.     

Comparative study of K0.5Bi0.5TiO3 nanoparticles derived from sol-gel-hydrothermal and sol-gel routes

A kind of novel lead-free ferroelectrics, potassium bismuth titanate, K_0.5Bi_0.5TiO₃ (KBT), has been prepared by sol-gel-hydrothermal and sol-gel routes, respectively, and the structural characters of as-synthesized powders were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The results indicated that sol-gel-hydrothermal route led to the formation of KBT nanowhiskers with diameters of 20 nm and lengths of 1 μm, and the processing temperature was as low as 160 °C, but the normal sol-gel route tended to form KBT cubic particles of about 100-200 nm, and the processing temperature was higher than 700 °C. It is believed that the gel precursor and hydrothermal environment play an important role in the formation of the nanowhiskers at low temperature. Due to the good sinterability of nanowhiskers, the ferroelectric and dielectric properties of KBT ceramics prepared by sol-gel-hydrothermal route were super to that prepared by sol-gel route.     

Structure, dielectric and ferroelectric properties of highly (1 0 0)-oriented BaTiO3 grown under low-temperature conditions

The highly (1 0 0)-oriented BaTiO₃ thin films were fabricated on LaNiO₃(1 0 0)/Pt/Ti/SiO₂/Si substrates under low-temperature conditions. Substrate temperatures throughout the fabrication process remained at or below 400 °C, which allows this process to be compatible with many materials commonly used in integrated circuit manufacturing. X-ray diffraction data provided the evidence for single BaTiO₃ phase. Field-emission scanning electron microscopy was used to study the columnar structure of the films. The dielectric properties as a function of frequency in the range of 1 kHz to 1 MHz was obtained. The room temperature remanent polarization (2P_r) and coercive field were found to be ∼5 μC/cm² and 50 kV/cm, respectively. The BTO film maintains an excellent fatigue-free character even after 10⁹ switching cycles.     

Sol-gel-derived pyroelectric barium strontium titanate thin films for infrared detector applications

Quality pyroelectric Ba_0.8Sr_0.2TiO₃ films have been successfully fabricated by a sol-gel processing using a highly diluted precursor solution. The remnant polarization of the films decreases with the temperature increasing, which results in a large pyroelectric coefficient at room temperature. Infrared response measured using a 500-K chopped blackbody at room temperature exhibits a typical pyroelectric response waveform. Frequency dependence of the infrared response measurement for a pixel with area of 2.5×10^-3 cm² showed that the maximum response output voltage of 3.2 mV was obtained at 6 Hz. Better infrared response can be expected by the improvement in thermal isolation of the pixels and electrode materials. Received: 26 April 2000 / Accepted: 9 May 2000 / Published online: 9 August 2000     

Realization of MMI Power Splitter by UV-light Imprinting Technique Using Hybrid Sol-Gel SiO2 Materials

An efficient fabrication scheme of buried ridge waveguide devices is demonstrated by UV-light imprinting technique using organic-inorganic hybrid sol-gel Zr-doped SiO2 materials. The refractive indices of a guiding layer and a cladding layer for the buried ridge waveguide structure are 1.537 and 1.492 measured at 1550nm, respectively. The tested results show more circular mode profiles due to existence of the cladding layer. A buried ridge single-mode waveguide operating at 1550 nm has a low propagation loss （0.088 dB/cm） and the 1× 2 MMI power splitter exhibits uniform outputs, with a very iow splitting loss of 0.029 dB at 1549nm.     

Fabrication and electrical properties of sol-gel-derived Ba0.8Sr0.2TiO3 ferroelectric films from a 0.05-M spin-on solution

Barium strontium titanate (Ba_0.8Sr_0.2TiO₃) films with good ferroelectricity have been obtained by a developed sol-gel processing, using a 0.05-M spin-on solution. X-ray diffraction and Raman spectroscopy investigations showed that the Ba_0.8Sr_0.2TiO₃ film exhibited a tetragonal structure at room temperature. Field-emission scanning electron microscopy measurements revealed that large columnar grains with the size of 100 to 200 nm in the film were formed from the highly dilute spin-on solution with layer-by-layer homoepitaxy. Electrical measurements for the prepared Ba_0.8Sr_0.2TiO₃ film showed a remnant polarization of 3.5 μC/cm², a coercive field of 53 kV/cm, two distinctive phase transitions, lower dissipation factor, and good insulating properties. These results indicate the sol-gel-derived Ba_0.8Sr_0.2TiO₃ film from a 0.05-M solution is suitable for uncooled infrared detector applications. Received: 19 August 1999 / Accepted: 11 October 1999 / Published online: 1 March 2000     

On the spray-drying deposition of TiO2 photocatalytic films

The photocatalytic activity of TiO₂ films deposited on different substrates by the spray-drying method using suspensions of commercially available TiO₂ (Degussa P25 or Tronox) as starting material was studied. The influence of the type of the initial TiO₂, preparation conditions (temperature of the substrate during the film deposition, temperature of the post-deposition annealing), substrate material (glass, fused silica, stainless steel and graphite), the presence of additives in the spraying suspension (polyethylene glycol, ethylene glycol and acetylacetone) and its sonication before spraying on the morphology, size of crystallites and phase composition (rutile/anatase ratio) was studied. Optimal conditions for spray deposition of the films are suggested.     

Preparation and characterisation of compositionally graded BaxSr1-xTiO3 thin films

Ba_xSr_1-xTiO₃ thin films with a compositional gradient of x=0.3 to 1 (in 0.1 mole fraction increments) were fabricated on Pt/Ti/SiO₂/Si substrates using a modified sol–gel technique. The graded film crystallised in a perovskite structure and consists of a uniform microstructure with comparatively larger grains. The room-temperature relative dielectric constant (ε_r) and dielectric loss (cosδ) at 100 kHz were found to be 305 and 0.03 respectively. Dielectric peaks were not observed in the temperature range from -20 °C to 120 °C. The dielectric constant and dielectric loss were almost independent of temperature. Polarisation–electric field measurements at room temperature revealed a saturated but slim hysteresis loop with a remanent polarisation (P_r) of 0.6 μC/cm² and a coercive field (E_c) of 2.4 kV/mm. The graded film behaves as a stack of Ba_xSr_1-xTiO₃ capacitors connected in series and hence the dielectric Curie peaks are removed. Received: 4 October 2001 / Accepted: 17 October 2001 / Published online: 23 January 2002     

Characterization of piezoelectric materials with large piezoelectric and electromechanical coupling coefficients

The relaxor based ferroelectric (1-x)Pb(Zn(1/3)Nb(2/3))O(3)-xPbTiO(3) and (1-x)Pb(Mg(1/3)Nb(2/3))O(3)-xPbTiO(3) single crystals provided new challenges in property characterization because their extraordinarily large piezoelectric coefficients and electromechanical coupling coefficients. Large errors may occur in some of the derived material constants using conventional characterization techniques. This paper will analyze the inadequacy of the traditional characterization methods and provide some basic guidelines for properly characterizing piezoelectric materials with extremely high piezoelectric and electromechanical coupling coefficients.     

Lead zirconate titanate–barium titanate by mechanical activation of mixed oxides

For the first time, the perovskite phase in 0.9Pb (Zr_0.52Ti_0.48)O₃-0.1BaTiO₃(0.9PZT-0.1BT) is triggered to form in an oxide matrix consisting of PbO, ZrO₂, BaO, and TiO₂. Unlike in the solid-state reaction activated by calcination at an intermediate temperature, intermediate phases, such as PbTiO₃, were not observed with increasing degree of mechanical activation prior to the formation of perovskite 0.9Pb(Zr_0.52Ti_0.48)O₃-0.1BaTiO₃ phase. This suggests that the nucleation and subsequent growth of perovskite crystallites in the activated oxide composition are not a result of the interfacial reactions that normally occur in the temperature-driven solid-state reaction. The mechanical activation-derived powders can be sintered to a relative density of >97% theoretical at 1100 °C. Sintered 0.9Pb(Zr_0.52Ti_0.48)O₃-0.1BaTiO₃ derived from mechanical activation of constituent oxides exhibits a maximum dielectric constant of 775 and a minimum dielectric loss of <2% at room temperature when measured at 1.0 kHz. Received: 3 December 1998 / Accepted: 18 March 1999 / Published online: 24 June 1999     

Optical properties of GdTaO4:Eu thick films prepared from a PVP-containing solution

Transparent GdTaO₄:Eu³⁺ thick films were prepared from the inorganic salt and 2-methoxyethanol solution containing polyvinylpyrrolidone (PVP) via sol-gel technique. The critical thickness of the film, i.e. the maximum thickness achievable without crack formation via non-repetitive deposition, was 0.8 μm. The effect of PVP on the morphology, crystallization behavior and optical property of the GdTaO₄:Eu³⁺ thick film was investigated. The results indicated that PVP could play an important role in the formation of transparent GdTaO₄:Eu³⁺ thick films, suppressing the stress evolution, adjusting the sol viscosity, ameliorating the crystallinity, and strengthening the covalency of Eu-O bonds. The GdTaO₄:Eu³⁺ thick films prepared with PVP exhibited a superior photoluminescence and X-ray exited luminescence, which implies that it will have promising applications in high-spatial-resolution X-ray imaging and flat panel display devices.     

Sol-gel preparation and photoluminescence property of YBO3:Eu/Tb nanocrystalline thin films

YBO₃:Eu³⁺/Tb³⁺ nanocrystalline thin films were successfully deposited onto quartz glass substrates by Pechini sol-gel dip-coating method, using rare-earth nitrates and boric acid as starting materials. The crystal structure, morphology, chemical composition and photoluminescence property of the films were investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy and fluorescence spectrophotometer. The results of XRD, AFM, XPS and FTIR revealed that the films were composed of spherical YBO₃:Eu³⁺/Tb³⁺ nanocrystals with average grain size of 80 nm. The YBO₃:Eu³⁺ film exhibited strong orange emission at 595 nm and red emission at 615 nm, which were, respectively ascribed to the (⁵D₀→⁷F₁) and (⁵D₀→⁷F₂) transitions of Eu³⁺. The YBO₃:Tb³⁺ film showed dominant green emission at 545 nm due to the ⁵D₄-⁷F₅ transition of Tb³⁺.     

Structural and optical properties of Bi<Subscript>3.25</Subscript>La<Subscript>0.75</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> ferroelectric thin films prepared by chemical solution methods

Ferroelectric Bi_3.25La_0.75Ti₃O₁₂ (BLT) thin films have been grown on Pt/Ti/SiO₂/Si substrates by chemical solution methods. X-ray diffraction analysis shows that BLT thin films are polycrystalline with (171)-preferential orientation. Atomic force microscopy investigation shows that they have large grains about 120 nm in size. A Pt/BLT/Pt capacitor has been fabricated and showed excellent ferroelectricity, with a remnant polarization and coercive field of 24 μC/cm² and 116 kV/cm, respectively. The capacitor shows no polarization fatigue up to 10⁹ switching cycles. The optical constants (n,k) of the BLT thin films in the wavelength range 0.35–1.7 μm were obtained by spectroscopic ellipsometry measurements, and the band-gap energy was found to be about 3.25 eV. Received: 16 October 2001 / Accepted: 6 January 2002 / Published online: 3 June 2002 RID="*" ID="*"Corresponding author. Fax: +86-21/65830-734, E-mail: gswang@mail.sitp.ac.cn     

In vitro degradation of AZ31 magnesium alloy coated with nano TiO2 film by sol-gel method

A nano TiO₂ film was coated on AZ31 alloy substrate by sol-gel method. The TiO₂ film was characterized by X-ray diffractometry (XRD), differential scanning calorimetry-thermogravimetric analysis (DSC-TG), field emission scanning electron microscopy (FE-SEM) and energy dispersion spectroscopy (EDS). The degradation of the nano-TiO₂ coated alloy was evaluated by immersion test and electrochemical measurement. An attempt was made to relate corrosion of coated alloys with the annealing treatment and resultant structural evolution.     

Effect of Pyrolysis Atmosphere on Ferroelectric Properties of Bi3.25La0.75Ti3O12 Films Prepared by Sol-Gel Method

The effect of pyrolysis atmosphere is investigated for Bi3.25 La0.75 Ti3O12 （BLT） films prepared on Pt/TiO2/SiO2/p-Si（100substrates by sol-gel processes. The pyrolysis is carried out at 400℃ for 20 min under air or O2 atmosphere and the successive anneal is performed at 700℃ for 30min under O2 atmosphere. The pyrolysis under O2 is enough for complete removal of organic species, however after pyrolysis under air, carbon and hydrogen atomic species as organic fragment are partly remained in the film. This incomplete removal of organic fragments affects the grain growth and cause more defects in the film or between interfaces during the annealing for the crystallization of BLT film. The growth direction and grain size of the BLT film is revealed to affect ferroelectric properties. The remanent polarization PTfor the BLT films of pyrolysis in O2 and air are measured to be 18.85μC/cm^2 and 12.56μC/cm^2,respectively. The defects degrade the fatigue property dramatically for the film of pyrolysis in air. It can be concluded that the pyrolysis is an important procedure to control ferroeleetrie properties.     

The characteristics of surface acoustic waves on AlN/LiNbO3 substrates

The characteristics of surface-acoustic-wave (SAW) devices on various substrates were measured by a network analyzer in the temperature range from 0 to 80 °C. Based on the structure of IDT/AlN/LiNbO₃, it was revealed that the magnitude of the temperature coefficient of frequency (TCF) of a SAW on a LiNbO₃ substrate was significantly decreased due to the thickness increase of AlN thin film deposited on the LiNbO₃ substrate. The TCF of a SAW on an AlN/LiNbO₃ device was measured to be about -51 ppm/°C at h/λ=0.1, where h is the thickness of the AlN film and λ is the wavelength of the SAW. This indicates that the deposition of an AlN film on a LiNbO₃ substrate could improve the temperature stability, as compared with that of a SAW on a LiNbO₃ substrate (-73 ppm/°C). The SAW device on the ST-X quartz is shown to have a positive TCF as the AlN thin film is deposited on the surface of the ST-X quartz. In addition, the phase velocity (V_p) of the SAW on an AlN/LiNbO₃ substrate was significantly increased by the increase of AlN thickness (h/λ). Received: 14 October 2002 / Accepted: 15 October 2002 / Published online: 29 January 2003 RID="*" ID="*"Corresponding author. Fax: +886-7/525-4199, E-mail: ycc@ee.nsysu.edu.tw