Ba(Zr0.15Ti0.85)O3厚膜的介电与铁电性能研究

本研究采用流延法制备Ba(Zr_0.15Ti_0.85)O₃(BZT)厚膜样品。采用扫描电子显微镜分析样品形貌; 采用LCR测试仪和Sawyer-Tower电路法测量样品的介电与铁电性能。结果表明, BZT厚膜具有明显的介电弛豫特征, 击穿电场强度可达60 kV/cm以上, 饱和极化强度可达58.1 μC/ cm², 剩余极化强度(Pr)为20.9 μC/ cm²。     

Contribution to the comprehension of dissipation phenomena in lead zirconate titanate: aliovalent doping effect

By the solid reaction method, undoped, potassium doped and niobium doped lead zirconate titanate (PZT) are elaborated. The mechanical losses measured in the range of the Hz as a function of temperature shows two peaks R₁ and R₂, and a ferroelectric transition peak P₁ between ferroelectric and para-electric states on the undoped PZT—Pb(Zr_0.54Ti_0.46)O₃—noted PZT54/46. Potassium doped PZT—Pb_1−xK_x(Zr_0.54Ti_0.46)O₃—shortly called PKZT 100x/54/46 shows an increase in the height of both the peaks at a doping content, x, less than 0.5 at.% but an opposite effect is observed above this value. Niobium doped PZT—Pb[(Zr_0.54Ti_0.46)_1−yNb_y]O₃—shortly called PNZT 100y/54/46, shows the vanish of the R₂ peak and the decrease of the height of the R₁ peak when the doping content increases.     

Fabrication of One-Transistor-Capacitor Structure of Nonvolatile TFT Ferroelectric RAM Devices Using Ba(Zr 0.1Ti 0.9)O 3 Gated Oxide Film

In this study, the Ba(Zr_0.1Ti_0.9)O₃ (BZ1T9) thin films have been well deposited on the Pt/Ti/SiO₂/Si substrate. The optimum radio frequency (RF) deposition parameters are developed, and the BZ1T9 thin films deposition at the optimum parameters have the maximum capacitance and dielectric constant of 4.4 nF and 190. As the applied voltage is increased to 8 V, the remnant polarization and coercive field of BZ1T9 thin films are about 4.5 muC/cm² and 80 kV/cm. The counterclockwise current hysteresis and memory window of n-channel thin-film transistor property are observed, and that can be used to indicate the switching of ferroelectric polarization of BZ1T9 thin films. One-transistor-capacitor (1TC) structure of BZ1T9 ferroelectric random access memory device using bottom-gate amorphous silicon thin-film transistor was desirable because of the smaller size and better sensitivity. The BZ1T9 ferroelectric RAM devices with channel width = 40 mum and channel length = 8 mum has been successfully fabricated and the I_D-V_G transfer characteristics also are investigated in this study.     

Ferroelectrics: new wide-gap materials for UV detection

Photoconductive properties of some sol-gel deposited, ferroelectric thin films are investigated in the ultraviolet (UV) domain. The investigated materials are: Bi₄Ti₃O₁₂ (BiT)_; SrBi₂Ta₂O₉ (SBT) and Pb(Zr_0.45Ti_0.55)O₃ (PZT). It was found that all these materials exhibit pronounced photoconductivity in the 250–500 nm domain. The best current responsivity was obtained for Bi₄Ti₃O₁₂ (BiT) films.     

Structure and electrical properties of (100)-oriented Pb(Zn1/3Nb2/3)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 thin films on La0.7Sr0.3MnO3 electrode by chemical solution deposition

(100)-oriented 0.462Pb(Zn_1/3Nb_2/3)O₃–0.308Pb(Mg_1/3Nb_2/3)O₃–0.23PbTiO₃ (PZN-PMN-PT) perovskite ferroelectric thin films were prepared on La_0.7Sr_0.3MnO₃/LaAlO₃ (LSMO/LAO) substrate via a chemical solution deposition route. The perovskite LSMO electrode was found to effectively suppress the pyrochlore phase while promote the growth of the perovskite phase in the PZN-PMN-PT film. The film annealed at 700 °C exhibited a high dielectric constant of 2130 at 1 kHz, a remnant polarization, 2P_r, of 29.8 μC/cm², and a low leakage current density of 7.2 × 10^− 7 A/cm² at an applied field of 200 kV/cm. The ferroelectric polarization was fatigue-free at least up to 10¹⁰ cycles. Piezoelectric coefficient, d₃₃, of 48 pm/V was also demonstrated. The results showed that much superior properties could be achieved with the PZN-PMN-PT thin films on the solution derived LSMO electrode than on Pt electrode by sputtering.     

Conduction analysis of Li2O doped 0.2[Pb(Mg1/3Nb2/3)]–0.8[PbTiO3–PbZrO3] ceramics fabricated by columbite precursor method

We have fabricated 0.2Pb(Mg_1/3Nb_2/3)O₃–0.8Pb(Zr_0.475Ti_0.525)O₃ [PMN–PZT] ceramics doped with various amounts of Li₂O (0, 0.05, 0.1, 0.2, 0.3 wt.%) using the columbite precursor method. The effects of Li-doping on the conduction behavior of PMN–PZT ceramics are discussed in relation to the low frequency dielectric dispersion and frequency domain measurement. The Li-doped PMN–PZT ceramics sintered at 950 °C showed a sufficient densification with large dielectric constant and low dielectric loss. The incorporation of Li⁺ ion in PMN–PZT ceramics led to an appreciable reduction in electrical conductivity and further enhanced the ferroelectric and piezoelectric properties. The activation energies of PMN–PZT + xLi₂O (x = 0, 0.05, 0.1, 0.2, 0.3 wt.%) ceramics calculated from ac conductivity measurement using the Arrhenius relation were 1.05, 1.25, 1.27, 1.38 and 1.41 eV, respectively. The conduction behavior is examined in the low frequency and high temperature region and the results are discussed in detail through crystal defect mechanism.     

Crystallization behavior and domain structure in textured Pb(Zr0.52Ti0.48)O3 thin films by different annealing processes

Amorphous Pb(Zr_0.52Ti_0.48)O₃ (PZT) thin films were prepared on the Pt/Ti/SiO₂/Si substrates by radio-frequency magnetron sputtering at room temperature. After rapid thermal annealing (RTA) and conventional furnace annealing (CFA) at different temperatures, the films were transformed into polycrystalline PZT thin films with (111) and (100) orientation, respectively. The phase formation and ferroelectric domains correlated with different orientation were systematically investigated by X-ray diffraction and piezoresponse force microscopy. The results showed that the perovskite PZT crystal with [111] orientation hetero-nucleated preferentially on top of the PtPb intermetallic phase at the PZT/Pt interface during RTA process. It is of interest to find that the domain self-organized into a structure with rounded shape at the early stage of crystallization. While the nucleation of the films treated by CFA dominantly homo-nucleated, thus the (100) orientation grains with minimum surface energy were easy to grow. The texture effects on ferroelectric properties of PZT films were also discussed in relation to the domain structure.     

Piezoelectric and dielectric properties of PZT–PZN–PMS ceramics prepared by molten salt synthesis method

Piezoelectric powders and ceramics with the composition of Pb_0.95Sr_0.05(Zr_0.52Ti_0.48)O₃–Pb(Zn_1/3Nb_2/3)O₃–Pb(Mn_1/3Sb_2/3)O₃ (PZT–PZN–PMS) were prepared by molten salt synthesis (MSS) and conventional mixed-oxide (CMO) methods, respectively. The influence of synthesis process on the properties of powders and ceramics were investigated in detail. The results show that the MSS method significantly improved the sinterability of PZT–PZN–PMS ceramics, resulting in an improvement of dielectric and piezoelectric properties compared to the CMO method. The optimum values of MSS samples are as follows: _r = 1773; tan δ = 0.0040; T_c = 280 °C; d₃₃ = 455 pC/N; k_p = 0.70; Q_m = 888; E_c = 10.3 kV/cm; and P_r = 28.2 μC/cm², at calcination of 800 °C and sintering of 1120 °C temperature.     

Fabrication of robust Bi3.25La0.75Ti3O12 thin film resistant to hydrogen damage

Ferroelectric bismuth lanthanum titanate (Bi_3.25La_0.75Ti₃O₁₂; BLT) thin films were deposited on Pt/TiO₂/SiO₂/Si substrate by chemical solution deposition method. The films were crystallized in the temperature range of 600–700 °C. The spontaneous polarization (P_s) and the switching polarization (2P_r) of BLT film annealed at 700 °C for 30 min were 22.6 μC/cm² and 29.1 μC/cm², respectively. Moreover, the BLT capacitor did not show any significant reduction of hysteresis for 90 min at 300 °C in the forming gas atmosphere.     

Polycrystalline silicon prepared by metal induced crystallization

Growth of large-grain polycrystalline silicon has been demonstrated using silicide-mediated crystallization of amorphous silicon (a-Si) by a pulsed rapid thermal annealing (RTA). The Ni atoms in concentration of 4.6×10¹²/cm² on the a-Si surface were heated at 700 °C in the RTA system for 10 s, ten times with 60 s intervals between the heat pulses. The Ni atoms on a-Si aggregate together, forming NiSi₂ precipitates. The crystallization proceeds from the NiSi₂ nuclei until the neighboring crystallites collide and forms distinct grain boundaries. It was found that 3.6×10⁷ Ni atoms form a seed for metal induced crystallization and the grain size was 40 μm when the Ni density was 4.6×10¹²/cm² on the a-Si. The grain size increases with decreasing metal density on a-Si.     

Optical Properties of Pb(Zr,Ti)O/sub 3/Films Prepared by Aerosol Deposition

The optical properties and related band structure of ferroelectric lead zirconate titanate [PZT, Pb(Zr_0.6Ti_0.4)O₃] films prepared on glass substrates at room temperature by aerosol deposition were investigated. The reflectance and transmittance of the PZT films were measured in the wavelength range from UV to near-infrared. The measured optical spectra were analyzed using dielectric function models that describe optical transitions in the band gap region. Optical absorption of the as-deposited PZT films was found to be larger than that of the annealed PZT films in the near-infrared wavelength range. The analyzed results indicated that post-deposition annealing increased the band gap energy of the PZT films, corresponding to a decrease in optical absorption.     

Infrared optical properties of Bi2Ti2O7 thin films by spectroscopic ellipsometry

Bi₂Ti₂O₇ thin films have been grown directly on n-type GaAs (1 0 0) by the chemical solution decomposition technique. X-ray diffraction analysis shows that the Bi₂Ti₂O₇ thin films are polycrystalline. The optical properties of the thin films are investigated using infrared spectroscopic ellipsometry (3.0–12.5 μm). By fitting the measured ellipsometric parameter (Ψ and Δ) data with a three-phase model (air/Bi₂Ti₂O₇/GaAs), and Lorentz–Drude dispersion relation, the optical constants and thickness of the thin films have been obtained simultaneously. The refractive index and extinction coefficient increase with increasing wavelength. The fitted plasma frequency ω_p is 1.64×10¹⁴ Hz, and the electron collision frequency γ is 1.05×10¹⁴ Hz, and it states that the electron average scattering time is 0.95×10⁻¹⁴ s. The absorption coefficient variation with respect to increasing wavelength has been obtained.     

The influence of fabrication processing on domain structure and polarization switching in PZN-based ferroelectric ceramics

Lead zinc niobate (Pb(Zn_1/3Nb_2/3)O₃, PZN) based ceramics are prepared by using conventional mixing oxide and complex phase reaction-sintering ceramic techniques. From the results of X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), it is clear that these two fabrication processing routes produce different microstructures and ferroelectric domains in the same Pb(Zn_1/3Nb_2/3)O₃–BaTiO₃–Pb(Zr_0.4Ti_0.6)O₃ composition. Furthermore, different phase transitions are observed for the temperature dependence of the dielectric permittivity that can be confirmed by differential scanning calorimetry (DSC). Different polarization switching characteristics are also examined by using high field-induced strain and ferroelectric hysteresis loop. It is suggested that the distribution of the inner stress and domain configuration should be related with the fabrication processing of ferroelectric ceramics.     

Linear and nonlinear optical response of bismuth and antimony implanted fused silica: annealing effects

We report the linear and nonlinear optical response of bismuth and antimony implanted fused silica with doses of 6 × 10¹⁶ ions/cm². The nonlinear refractive index, n₂, was measured using a Z-scan technique with a mode locked Ti:sapphire laser operating in 140 fs pulse duration at 770 nm wavelength. It is found that the nonlinear refractive index n₂ of as-implanted samples is large, in the order of 10⁻¹⁰ cm²/W and the n₂ value of Bi as-implanted sample is about 2.4 times lager than that of Sb as-implanted sample. The large n₂ response is attributed to the presence of nanosized metal particles in the implanted layer observed by transmission electron microscopy. We also report the changes of linear and nonlinear optical response when implanted samples were subsequently annealed at temperatures from 500 to 1000 C in argon and oxygen atmospheres. The annealing effect on optical properties is found to be strongly dependent on the annealing atmospheres. Our results indicate that annealing treatment in O₂ affects the local environment of the implanted metal ions and hence the linear and nonlinear optical properties of the metal-dielectric composite. We suggest that a new phase of metal-oxygen-silicate was formed during annealing in O₂ atmosphere.     

Characteristics of relaxor-based piezoelectric single crystals forultrasonic transducers

For ultrasonic transducers, piezoelectric ceramics offer a range of dielectric constants (K~1000-5000), large piezoelectric coefficients (d_ij~200-700 pC/N), and high electromechanical coupling (k _t≃50%, k₃₃≃75%). For several decades, the material of choice has been polycrystalline ceramics based on the solid solution Pb(Zr_1-xB_2x)O₃ (PZT), compositionally engineered near the morphotropic phase boundary (MPB). The search for alternative MPB systems has led researchers to revisit relaxor-based materials with the general formula, Pb(B₁,B₂)O₃ (B₁:Zn²⁺ , Mg²⁺, Sc³⁺, Ni²⁺..., B₂ :Nb⁵⁺ Ta⁵⁺...). There are some claims of superior dielectric and piezoelectric performance compared to that of PZT materials. However, when the properties are examined relative to transition temperature (T₃), these differences are not significant. In the single crystal form, however, Relaxor-PT materials, represented by Pb(Zn_1/3Nb_2/3)O₃-PbTiO ₃ (PZN-PT), Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PMN-PT) have been found to exhibit longitudinal coupling coefficients (k₃₃)>90%, thickness coupling (k_t)>83%, dielectric constants ranging from 1000 to 5000 with low dielectric loss <1%, and exceptional piezoelectric coefficients d₃₃>2000 pC/N, the later promising for high energy density actuators. For single crystal piezoelectrics to become the next generation material of ultrasonic transducers, further investigation in crystal growth, device fabrication and testing are required     

Growth and spectroscopy of Dy doped in ZnWO4 crystal

Single-crystal ZnWO₄:Dy³⁺ was grown by Czochralski technique. The XRD, absorption spectra as well as fluorescence spectrum are investigated and the Judd–Ofelt intensity parameters Ω₂, Ω₄, Ω₆ are obtained to be 7.76 × 10⁻²⁰ cm², 0.57 × 10⁻²⁰ cm², 0.31 × 10⁻²⁰ cm², respectively. Calculated radiative transition rate, branching ratios and radiative lifetime for different transition levels of ZnWO₄:Dy³⁺ crystals are presented. Fluorescence lifetime of ⁴F_9/2 level is 158 μs and quantum efficiency is 66%.The most intense fluorescence line at 575 nm correlative with transition ⁴F_9/2 → ⁶H_13/2 is potentially for application of yellow lasers.     

Effect of the microwave oven on structural, morphological and electrical properties of SrBi4Ti4O15 thin films grown on Pt/Ti/SiO2/Si substrates by a soft chemical method

Thin films of SrBi₄Ti₄O₁₅ (SBTi), a prototype of the Bi-layered-ferroelectric oxide family, were obtained by a soft chemical method and crystallized in a domestic microwave oven. For comparison, films were also crystallized in a conventional method at 700 °C for 2 h. Structural and morphological characterization of the SBTi thin films were investigated by X-ray diffraction (XRD) and atomic force microscopy (AFM), respectively. Using platinum coated silicon substrates, the ferroelectric properties of the films were determined. Remanent polarization P_r and a coercive field E_c values of 5.1 μC/cm² and 135 kV/cm for the film thermally treated in the microwave oven and 5.4 μC/cm² and 85 kV/cm for the film thermally treated in conventional furnace were found. The films thermally treated in the conventional furnace exhibited excellent fatigue-free characteristics up to 10¹⁰ switching cycles indicating that SBTi thin films are a promising material for use in non-volatile memories.     

Drying temperature effects on microstructure, electrical properties and electro-optic coefficients of sol-gel derived PZT thin films

Transparent lead zirconium titanate (PZT) thin film is suitable for a variety of electro-optic application, and the increasing of the electro-optic coefficient of PZT film is one of the important factors for this application. In this study, the main processing variable for improving an electro-optic coefficient was the drying temperature: 300, 350, 450 and 500°C in sol-gel derived PZT thin films. The highest linear electro-optic coefficient (1.65×10⁻¹⁰ (m/V)) was observed in PZT film dried at 450°C. The PZT film showed the highest perovskite content, polarization (P_max=49.58 μC/cm², P_r=24.8 μC/cm²) and dielectric constant (532). A new two-beam polarization (TBP) interferometer with a reflection configuration was used for electro-optic testing of PZT thin films which allows measurement of the linear electro-optic coefficient of thin film with strong Fabry–Perot (FP) effect usually present in PZT thin film.     

Investigation of stress behaviors and mechanism of void formation in sputtered TiSix films

We have investigated the stress behaviors and a mechanism of void formation in TiSi_x films during annealing. TiSi_x thin films were prepared by DC magnetron sputtering using a TiSi_2.1 target in the substrate temperature range of 200–500 °C. The as-deposited TiSi_x films at low substrate temperature (<300 °C) have an amorphous structure with low stress of 1×10⁸ dynes/cm². When the substrate temperature increases to 500 °C, the as-deposited TiSi_x film has a mixture of C49 and C54 TiSi₂ phase with stress of 8×10⁹ dynes/cm². No void was observed in the as-deposited TiSi_x film. Amorphous TiSi_x film transforms to C54 TiSi₂ phase with a random orientation of (311) and (040) after annealing at 750 °C. The C49 and C54 TiSi₂ mixture phase transforms to (040) preferred C54 TiSi₂ phase after annealing over 650 °C. By increasing substrate temperature, the transformation temperature for C54 TiSi₂ can be reduced, resulting in relieved stress of TiSi₂ film. The easy nucleation of the C54 phase was attributed to an avoidance of amorphous TiSi_x phase. We found that amorphous TiSi_x→C54 TiSi₂ transformation caused higher tensile stress of 2×10¹⁰ dynes/cm², resulting in more voids in the films, than C49→C54 transformation. It was observed that void formation was increased with thermal treatment. The high tensile stress caused by volume decreases in the silicide must be relieved to retard voids and cracks during C54 TiSi₂ formation.     

复合掺杂BCZT陶瓷的介电弛豫行为研究

采用固相法制备了Ba_0.9175Ca_0.08Nd_0.0025(Zr_0.18Ti_0.8175-xY_xMn_0.0025)O₃ (BCZT-Y, x=0、0.5mol%、0.75mol%、1.0mol%、 1.5mol% 、2.0mol%)铁电陶瓷, 研究了不同Y³⁺掺杂量对该铁电陶瓷结构与介电性能的影响。结果表明: 随着Y³⁺掺杂量增加, Y³⁺进入晶格, BCZT-Y陶瓷的密度从4.029 g/cm³增加到6.058 g/cm³; 同时介电峰压低并展宽, 居里温度向低温方向移动, 表现出明显的铁电体弛豫特征, 采用Lorenz型公式对该实验结果进行拟合验证,发现随着Y³⁺掺杂量增加, 电滞回线变窄变斜、回线面积大幅减小, 剩余极化强度和矫顽电场降低。