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.     

Comparative analysis for the crystalline and ferroelectric properties of Pb(Zr,Ti)O3 thin films deposited on metallic LaNiO3 and Pt electrodes

The crystalline quality and ferroelectricity of the Pb(Zr,Ti)O₃ (PZT) films deposited on the metallic LaNiO₃ (LNO) and Pt electrodes were comparatively analyzed to investigate the possibility for their application to non-volatile memory devices. LNO thin films were successfully deposited on various substrates by using r.f. magnetron sputtering even at a low temperature ranging from 250 to 500 °C, and the ferroelectric PZT thin films were spin-coated onto the LNO and Pt bottom electrodes. Metallic LNO thin films exhibited [100] orientation irrespective of the substrate species and PZT films coated onto LNO films had highly a- and c-axis orientations, while those with Pt bottom electrode were polycrystalline. PZT films with LNO bottom electrode had smaller grain size and larger dielectric constant compared to those grown on the Pt electrode. The ferroelectric thin films fabricated on LNO bottom electrode displayed an asymmetric D–E hysteresis loop, which was explained by the defect effects formed at the interface. Especially, the LNO/PZT/LNO capacitor was found to significantly improve the polarization fatigue and the effects of the LNO electrodes to the fatigue were discussed.     

Sol–gel derived PZT films doped with vanadium pentoxide

The present research investigated the sol–gel preparation, dielectric and ferroelectric properties of PZT films doped with 5 mol% vanadium oxide. Stable PZTV sols can be readily formed, and homogeneous, micrometer thick and pinhole-free PZTV films were obtained by using spin coating followed with rapid annealing. The X-ray diffraction patterns revealed that no parasitic or secondary phases were formed in the sol–gel PZT films with the addition of vanadium oxide. The material doped with vanadium pentoxide showed enhanced dielectric constant and remanent polarization with reduced loss tangent and coercive field.     

Total dose radiation effects of Au/PbZr0.52Ti0.48O3/YBa2Cu3O7-δ capacitors

PbZr_0.52Ti_0.48O₃/YBa₂Cu₃O₇₋δ (PZT/YBCO) thin films have been fabricated on Y₂O₃ stabilized zirconate (YSZ) substrates by a pulsed excimer laser deposition (PLD) method. In order to investigate total dose radiation effects on the Au/PZT/YBCO ferroelectric capacitor, the capacitance–voltage (C–V) curves and the retained polarization property of the capacitor have been measured before and after γ-ray irradiation. The results showed that, with an increased total dose, the retained polarization and the dielectric constant decreased, but the coercive field drifted towards positive voltage direction. This is caused by charges trapped by defects in the PZT capacitor during irradiation.     

Thickness dependence of electrical properties of PZT films deposited on metal substrates by laser-assisted aerosol deposition

Dependence of electrical properties-dielectric, ferroelectric, and piezoelectric properties-on film thickness was studied for lead-zirconate-titanate (PZT) thick films directly deposited onto stainless-steel (SUS) substrates in actuator devices by using a carbon dioxide (CO₂), laser-assisted aerosol deposition technique. Optical spectroscopic analysis data and laser irradiation experiments revealed that absorption at a given wavelength by the film increased with increasing film thickness. Dielectric constant epsiv, remanent polarization value P_r, and coercive field strength E_c of PZT films directly deposited onto a SUS-based piezoelectric actuator substrate annealed by CO₂ laser irradiation at 850degC improved with increasing film thickness, and for films thicker than 25 mum, e > 800, Pr > 40 muC/cm², and E_c < 45 kV/cm. In contrast, the displacement of the SUS-based actuator with the laser-annealed PZT thick film decreased with increasing film thickness.     

Thickness effect on electrical properties of Pb(Zr0.52Ti0.48)O3 thick films embedded with ZnO nanowhiskers prepared by a hybrid sol-gel route

Silicon-based lead zirconate titanate thick films embedded with zinc oxide nanowhiskers (ZnO_w-PZT) were prepared by a hybrid sol-gel route. ZnO_w-PZT films with thickness from 1.5 μm to 4 μm are perovskite structure and have smooth surface without any cracks. As the thickness increases, the remanent polarization and dielectric constant increase, but the coercive field and tetragonality decrease. Compared with PZT films, the ZnO_w-PZT film has the close tetragonality and electrical properties which are different from those of bulk PZT-based ceramic doped with ZnO powder. The thickness dependences of the ferroelectric and dielectric properties are attributed to the relaxation of internal stress.     

Fabrication and characterization of (1−x)SrBi2Ta2O9–xBi3TaTiO9 layered structure solid solution thin films for ferroelectric random access memory (FRAM) applications

We report on the properties of (1−x)SrBi₂Ta₂O₉–xBi₃TaTiO₉ solid solution thin films for ferroelectric non-volatile memory applications. The solid solution thin films fabricated by modified metalorganic solution deposition technique showed much improved properties compared to SrBi₂Ta₂O₉. A pyrochlore free crystalline phase was obtained at a low annealing temperature of 600°C and grain size was found to be considerably increased for the solid solution compositions. The film properties were found to be strongly dependent on the composition and annealing temperatures. The measured dielectric constant of the solid solution thin films was in the range 180–225 for films with 10–50% of Bi₃TaTiO₉ content in the solid solution. Ferroelectric properties of (1−x)SrBi₂Ta₂O₉–xBi₃TaTiO₉ thin films were significantly improved compared to SrBi₂Ta₂O₉. For example, the observed remanent polarization (2P_r) and coercive field (E_c) values for films with 0.7SrBi₂Ta₂O₉–0.3Bi₃TaTiO₉ composition, annealed at 650°C, were 12.4 μC/cm² and 80 kV/cm, respectively. The solid solution thin films showed less than 5% decay of the polarization charge after 10¹⁰ switching cycles and good memory retention characteristics after about 10⁶ s of memory retention. The improved microstructural and ferroelectric properties of (1−x)SrBi₂Ta₂O₉–xBi₃TaTiO₉ thin films compared to SrBi₂Ta₂O₉, especially at lower annealing temperatures, suggest their suitability for high density FRAM applications.     

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.     

PZT95/5铁电陶瓷的掺杂改性研究

采用固相烧结法制备锆钛酸铅95/5(PZT95/5)材料,以“相同化合价,不同原子半径;相近原子半径,不同化合价”的原则,选择了碱金属族、碱土金属族元素的碳酸盐以及Fe₂O₃、SiO₂、Nb₂O₅、WO₃等作为掺杂物分别对其进行掺杂改性.研究了掺杂对材料介电性能、极化性能和低温-高温铁电相的相变温度的影响.发现受主掺杂使得材料的介电常数降低,施主掺杂使得材料的介电常数提高;剩余极化随着掺杂离子的化合价增大而增大;制备得到了低温-高温铁电相相变在15℃的铁电材料,在实际应用上有重要意义.     

新型Sol-Gel技术PZT铁电厚膜的制备及电学性能研究

采用新型ｓｏｌ－ｇｅｌ技术在 Ｐｔ／Ｔｉ／ＳiO2/Si基片上制备出了厚度为 ２～６０μｍ的ＰＺＴ铁 电厚膜材料;研究了ＰＺＴ厚膜的结构及其介电、铁电性能．ＸＲＤ谱分析显示,ＰＺＴ厚膜 呈现出纯钙钛矿相结构,无焦绿石相存在．ＳＥＭ电镜照片显示,ＰＺＴ膜厚均匀一致,无裂 纹、高致密．厚度为５０μｍ的ＰＺＴ厚膜的介电常数为８６０,介电损耗为０.０３,剩余极化强度 是２５μＣ／ｃｍ^２．矫顽场是４０ｋＶ／ｃｍ.     

Electric characterization of HfO2 thin films prepared by chemical solution deposition

Hafnium dioxide (HfO₂) thin films were prepared on Si substrates using the chemical solution deposition (CSD) method. The Au/HfO₂/n-Si/Ag structures were characterized by X-ray diffraction (XRD), C–V curves and leakage current measurements. A relative dielectric constant of about 13.5 was obtained for the 65 nm HfO₂ film. Atomic force microscopy (AFM) measurements show uniform surfaces of the films. C–V hysteresis was found for the metal-oxide-semiconductor (MOS) structures with HfO₂ films of 52 and 65 nm thick. It is found that the width of C–V windows is related with the thickness of the HfO₂ films. Furthermore, the C–V hysteresis reveals the possibility of stress-effect, suggesting that it is possible to use HfO₂ to build an MOS structure with controllable C–V windows for memory devices. The leakage current decreases as the film thickness increases and a relatively low leakage current density has been achieved with the HfO₂ film of 65 nm.     

Electrical properties of sol-gel processed barium titanate films

The sol-gel technique has been used to prepare ferroelectric barium titanate (BaTiO₃) films. The electrical properties of the films have been investigated systematically. The room temperature dielectric constant (ε) and loss tangent (tanδ) at 1 kHz were respectively found to be 370 and 0.012. Both ε and tanδ showed anomaly peaks at 125°C. The room temperature remanant polarization (P_r) and coercive field (E_c) were found to be 3.2 μC/cm² and 30 kV/cm, respectively. The capacitance–voltage (C–V) and conductance–voltage (G–V) characteristics also showed hysteresis effect. The temperature variation of C–V and G–V characteristics also confirms the ferroelectric to paraelectric phase transition at 125°C.     

Influence of thickness and growth temperature on the properties of zirconium oxide films grown by atomic layer deposition on silicon

ZrO₂ films of thicknesses varied in the range of 3–30 nm were atomic layer deposited from ZrI₄ and H₂O–H₂O₂ on p-Si(100) substrates. The effects of film thickness and deposition temperature on the structure and dielectric properties of ZrO₂ were investigated. At 272 and 325 °C, the growth of ZrO₂ started with the formation of the cubic polymorph and continued with the formation of the tetragonal polymorph. The ratio between the lattice parameters increased with the film thickness and growth temperature. The effective permittivity, determined from the accumulation capacitance of Hg/ZrO₂/Si capacitors, increased with the film thickness, reaching 15–17 in 25-nm-thick films. The permittivity decreased with the increasing growth temperature. The hysteresis of the capacitance–voltage curves was the narrowest for the films deposited at 325 °C, and increased towards both lower and higher deposition temperatures.     

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.     

Micromachined high frequency ferroelectric sonar transducers

Millimeter-sized ferroelectric monomorph sonar transducers have been built using sol-gel PZT on micromachined silicon wafers. First generation transducer arrays with diaphragms varying in size from 0.2 to 2 mm were tested. Second generation 8×8 arrays have also been built and tested in water in the frequency range of 0.3 to 2 MHz. Improvements to the sol-gel process have yielded high-quality, crack-free PZT films up to 12 μm in thickness, which leads directly to higher sensitivity and figure of merit for acoustic transducers. The longitudinal piezoelectric coefficient d₃₃ is 140 to 240 pC/N, measured through a double beam laser interferometer. Remanent polarization of 28 μC/cm², a coercive field of 30 kV/cm, and dielectric constant of 1400 were measured on 4-μm thick films. Test results are presented, including frequency response, beam patterns, and sensitivity. High-resolution acoustic images have been generated using these transducers and a four-element underwater acoustic lens. Potential applications for these transducers include high-frequency imaging sonars, medical ultrasound, ultrasonic communication links, and flaw detection (NDT)     

Gd掺杂对PZT薄膜介电性能及极化行为的影响

采用sol-gel法在Pt/Ti/SiO₂/Si衬底上制备出高度(100)择优取向的Gd掺杂PZT薄膜(简写为PGZT); 介电测试结果表明, 1mol%Gd掺杂的PZT薄膜介电常数最大, 2mol%Gd掺杂PZT薄膜与未掺杂薄膜的介电常数相差不大, Gd掺入量>2mol%时, 薄膜的介电常数下降; 薄膜的不可逆极化值呈现与介电常数相同的变化趋势, 而可逆极化值变化较小. 在弱电场下(低于矫顽场E_c), 用瑞利定律分析薄膜介电常数随电场强度的变化规律, 1mol%Gd掺杂的薄膜瑞利系数α最大, 说明薄膜中缺陷的浓度最低. 1mol%Gd掺杂的薄膜介电和铁电性能的改善与Gd³⁺在PZT晶格中的占位情况有关.     

Characterization of Cat-CVD grown Si–C and Si–C–O dielectric films for ULSI applications

Si–C films with the Si compositions ranging from 40 to 70% have been grown by Cat-CVD using dimethylsilane [DMSi, Si(CH₃)₂H₂] compounds. Tetraethoxysilane [TEOS, Si(OC₂H₅)₄] and dimethyldimethoxysilane [DMDMOS, Si(CH₃)₂(OCH₃)₂] gas source gave us Si–C–O (C-doped SiO_x) films with wide ternary alloy compositions. The dielectric constant of a Si–C film has been evaluated by C–V measurements (at 1 MHz) using Al/Si–C/n-Si(001)/Cu MIS structure. The relative dielectric constant value of a Si–C film was estimated to be 3.0. The resistivity of the Si–C layer with 1 mm diameter and 0.24 μm thickness was estimated to be more than 24.5 Gohm·cm. These results gave us promising characteristics of Si–C and Si–C–O films grown by alkylsilane- and alcoxysilane-based Cat-CVD.     

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.     

Spray deposition of lanthanum selenide (La2Se3) thin films from non-aqueous medium and their characterizations

The spray pyrolysis technique was employed to prepare lanthanum selenide (La₂Se₃) thin films on ordinary glass and fluorine doped tin oxide (FTO) coated glass substrates under optimized conditions. The preparative parameters are optimized to get good quality of La₂Se₃ thin films. X-ray diffraction (XRD) study reveals that only cubic La₂Se₃ is formed with a grain size of about 42 nm. The direct optical band gap is estimated to be 2.6 eV. The dispersions of dielectric constant and dielectric loss are studied with the variation of frequency. The room temperature electrical resistivity of the films is found to be of the order of 10⁵ Ω cm. The film is found to be a p-type semiconductor.     

Orientation controlling of Pb(Zr<Subscript>0.53</Subscript>Ti<Subscript>0.47</Subscript>)O<Subscript>3</Subscript> thin films prepared on silicon substrates with the thickness of La<Subscript>0.5</Subscript>Sr<Subscript>0.5</Subscript>CoO<Subscript>3</Subscript> electrodes

Pb(Zr_0.53Ti_0.47)O₃ (PZT) thin films were prepared on La_0.5Sr_0.5CoO₃ (LSCO) coated Si substrates by a sol–gel route. The thickness of LSCO electrode was found to modify the preferential orientation of PZT thin films, which consequently affected the dielectric and ferroelectric properties. (100) textured PZT films with dense columnar structure could be obtained on the top of (110) textured LSCO with thickness of 230 nm. PZT thin films prepared on the optimized LSCO films exhibit the enhanced dielectric constant and remnant polarization of 980 and 20 μC/cm², respectively.