Enhancement of the surface and structural properties of ZnO epitaxial films grown on Al2O3 substrates utilizing annealed ZnO buffer layers

ZnO films were grown on Al₂O₃ (1000) substrates without and with ZnO buffer layers by using radio-frequency magnetron sputtering. Atomic force microscopy images showed that the surface roughness of the ZnO films grown on ZnO buffer layers annealed in a vacuum was decreased, indicative of an improvement in the ZnO surfaces. X-ray diffraction patterns showed that the crystallinity of the ZnO thin films was enhanced by using the annealed ZnO buffer layer in comparison with the film grown on without a buffer layer. The improvement of the surface and structural properties of the ZnO films might be attributed to the formation of the Zn-face ZnO buffers due to annealing in a vacuum. These results indicate that the surface and structural properties of ZnO films grown on Al₂O₃ substrates are improved by using ZnO buffer layers annealed in a vacuum.     

Effects of ZnO on the piezoelectric properties of Pb(Mn1/3Sb2/3)O3-Pb(Zr,Ti)O3 ceramics

Perovskite-type 0.05 Pb(Mn_1/3Sb_2/3)O₃-0.95 Pb(Zr_0.5Ti_0.5)O₃ (PMS-PZT) was synthesized by conventional bulk ceramic processing technique. ZnO as a dopant up to 0.5 mol% was incorporated into the PMS-PZT system, and the effects on piezoelectric properties were investigated. Pyrochlore phase was not detected to form during the synthesis of the PMS-PZT system with 0∼0.5 mol% ZnO addition. The highest density of 7.92 g/cm³ was obtained when sintered at 1200°C for 2 hrs. Piezoelectric properties as a function of ZnO content were evaluated using a gain phase analyzer. Piezoelectric charge constant (d₃₁) and piezoelectric voltage output coefficient (g₃₁) increased up to −130 pC/N and −24.9 × 10³Vm/N, respectively, with increasing ZnO content. Mechanical quality factor (Q _m) was shown to reduce considerably with increasing ZnO content. When 0.3 mol% of ZnO was added into the system, electromechanical coupling factor (k _p) and relative dielectric constant () reached to the maximum of 56% and 1,727, respectively.     

Effects of ZnO on the piezoelectric properties of Pb (Mn1/3 Sb 2/3 )O 3 -Pb(Zr,Ti)O 3 Ceramics

Perovskite-types 0.05Pb(Mn_1/3Sb_2/3)O₂-0.95Pb- (Zr_0.5Ti_0.5)O₃ (PMS-PZT) was synthesized by conventional bulk ceramic processing technique. ZnO as a dopant up to 0.5 mol% was incorporated into the PMS-PZT system, and the effects on piezoelectric properties were investigated. Pyrochlore phase was not detected to form during the synthesis of the PMS-PZT system with 0–0.5 mol% ZnO addition. The highest density of 7.92 g/cm³ was obtained when sintered at 1200^∘C for 2 h. Piezoelectric properties as a function of ZnO content were evaluated using a gain phase analyzer. Piezoelectric charge constant (d ₃₁) and piezoelectric voltage output coefficient (g ₃₁) increased up to −130 pC/N and −24.9 × 10³Vm/N, respectively, with increasing ZnO content. Mechanical quality factor (Q _m) was shown to reduce considerably with increasing ZnO content. When 0.3 mol% of ZnO was added into the system, electromechanical coupling factor (k _p) and relative dielectric constant (ε₃₃ ^T /ε_o) reached to the maximum of 56% and 1727, respectively.     

Al2O3掺杂ZnO压敏电阻在不同烧结温度下的电气特性研究

在不同烧结温度下制备了氧化铝(Al₂O₃)掺杂的氧化锌(ZnO)压敏电阻,并对其进行扫描电子显微镜、X射线衍射、电流-电压、电容-电压测试以研究ZnO压敏电阻的微观结构和电气特性。结果表明:随着烧结温度的升高,Al₂O₃掺杂的ZnO压敏电阻泄漏电流得到了明显的抑制,这是由于施主密度和界面态密度不断增大,提高了晶界的势垒高度。而Al³⁺随着烧结温度的升高会不断地固溶入ZnO晶粒中,降低了晶粒电阻率,从而降低ZnO压敏电阻在通过大电流时的残压比。当烧结温度为1 150℃时,ZnO压敏电阻的电气特性最佳,电压梯度为418.70 V/mm,泄漏电流为0.74,残压比为1.68,非线性系数为67.5,有助于提高ZnO避雷器的保护性能,实现深度限制电力系统,特别是特高压系统的过电压。     

Effects of the O2/Ar gas flow ratio on the electrical and transmittance properties of ZnO:Al films deposited by RF magnetron sputtering

ZnO:Al thin films for transparent conductors were deposited on sapphire (0001) substrates by using an RF magnetron sputtering technique. Effects of the O₂/Ar flow ratio in the sputtering process on the crystallinity, carrier concentration, carrier mobility, and transmittance of the films were investigated. The FWHM of the (002) XRD intensity peak is minimal at the O₂/Ar flow ratio of 0.5. According to the Hall measurement results the carrier concentration and mobility of the film decrease and thus the resistivity increases as the O₂/Ar flow ratio increases. The transmittance of the ZnO:Al film deposited on the glass substrate is characteristic of standing wave. The transmittance increases as the O₂/Ar flow ratio in-RF magnetron sputtering increases up to 0.5. Considering the effects of the the O₂/Ar flow ratio on the electrical resistivity and transmittance of the ZnO:Al film the optimum O₂/Ar flow ratio is 0.5 in the RF magnetron sputter deposition of the ZnO:Al film.     

Growth and characterization of device quality ZnO on Si(111) and c-sapphire using a conventional rf magnetron sputtering

In this article, it is shown that high quality ZnO films were grown on Si(111) and Al₂O₃(0001) substrates using a conventional rf magnetron sputtering. High-resolution X-ray diffractometry (HR-XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and photoluminescence (PL) investigations clearly confirmed that the ZnO films grown on Al₂O₃ (0001) at substrate temperatures above 650^∘C are single crystal as well as high optical quality. It is also estimated in both cases grown on Si and Al₂O₃ that an introduction of template pre-grown at 500^∘C can induce a homogeneous interface and improvement of emission characteristic by relaxing the strain caused by large lattice and thermal mismatch between the film and substrate and by reducing defect density in interface region.     

Negative thermal quenching in undoped ZnO and Ga-doped ZnO film grown on c-Al2O3 (0001) by plasma-assisted molecular beam epitaxy

Negative thermal quenching (NTQ) was observed in bound exciton emission line in undoped ZnO and the donor-to-valence-band emission in heavily Ga-doped ZnO thin films grown on c-Al₂O₃ (1000) through low temperature photoluminescence spectra. In both cases, the enhanced feature of PL peak intensity occurred in the temperature range of 35–45 K corresponding to the energies of either excitation to the vibrational/rotational resonance states or the involvement of B-valence band considering the activation energy of about 5 meV.     

Studies of ZnO Thin Films On Sapphire (0001) Substrates Deposited by Pulsed Laser Deposition

ZnO thin films are deposited on sapphire (0001) substrates at different temperatures in the pulsed laser deposition (PLD) system. By measurements of X-ray diffraction (XRD), atomic force microscopy (AFM), and Photoluminescence (PL) at room temperature, fabrication temperatures higher than 400C is found to be the optimum condition for the structural and optical properties of ZnO thin films. With the increase of the fabrication temperature, the grain size becomes bigger and the thin film becomes more homogeneous. In order to get the high-quality ZnO thin film at low temperature, ZnO thin films are deposited at room temperature and annealed in a rapid thermal annealing (RTA) system. It is found that the optical property of the thin film can be greatly improved by annealing in RTA system.     

Growth and electrical properties of Pb(Zr,Ti)O3 thin films by sputtering using an alloy target

Abstract

Pb(Zr_x,Ti_1?x)O₃ thin films were deposited on Pt/SiO₂/Si substrates by the rf magnetron sputtering using an alloy target consisting of Zr-Ti alloy and Pb metal. The dependence of electrical properties on film thickness and sputtering gas pressure was investigated. The dielectric constant and the remanent polarization decreased and the coercive field increased with the decrease of the film thickness. In the dependence of gas pressure, the relative dielectric constant of the film with only a perovskite phase were in the range of 235–280, which were higher than those of the film with only a pyrochlore phase, 20. The asymmetry of hysteresis loops increased with the decrease of the gas pressure.     

Growth and characterization of epitaxial SrBi2Ta2O9 films on (110) SrTiO3 substrates

Abstract

SrBi₂Ta₂O₉ (SBT) is an attractive material for nonvolatile ferroelectric memory applications. In this paper we report on the deposition of highly epitaxial and smooth SrBi₂Ta₂O₉ films on (110) SrTiO₃substrates. The films were grown by pulsed laser deposition at temperatures ranging from 600 to 800°C and at various laser fluences from a Bi-excess SBT target. The background oxygen pressure was maintained at 28 Pa during the film deposition. Structural characterization of the films was performed by x-ray diffraction. Atomic force microscopy was used to investigate morphology and growth of the films. The films grew with preferred (115) or (116) orientation. The roughness was of the order of unit cell height. The films display a growth pattern resulting in corrugated film morphology.     

Microstructural and electrical properties of multicomponent varistor ceramics with PbO–ZnO–B2O3 glass addition

Zinc oxide based ceramics are widely used materials in varistors because of their excellent nonlinearity. Traditionally these ceramics are sintered at high temperatures (about 1,100–1,300°C). In this work a novel zinc oxide-based material with a low sintering temperature (900–1,000°C) was investigated. This material can be used in varistors consisting of several ceramic layers with embedded silver/palladium thick-film electrodes. This paper explains the research procedure employed with this novel varistor material, including the effect of sintering aid addition on the final electrical properties and fired microstructure. The electrical properties achieved are compared to the values measured from the original zinc oxide composition without sintering aid addition. Especially the I–V characteristics, nonlinearity coefficient α, breakdown voltage V _bk and leakage current density J _L are investigated. The sintering properties are also reported. It was found that by adding 10 wt.% of glass and using a 900 °C sintering temperature, the material had good varistor characteristics, as V _bk = 378 V/mm, α = 33 and J _L  = 15 μA/cm². The investigated varistor material can be applied to protect electrical circuits against surges.     

Electrophoretic deposition of SrBi4Ti4O15 thick films on Al2O3 substrate

Electrophoretic deposition (EPD) is a powerful route to obtain thick films onto conductive substrate. In this work, ferroelectric SrBi₄Ti₄O₁₅ films up to 15 μm were prepared by EPD using submicrometer SrBi₄Ti₄O₁₅ (SBT) powders. The ethanol was used as the solvent with addition of HCl and PVB (dispersant). The zeta potential of SBT powder in ethanol is low compared to some other ceramics such as PZT, so it tends to flocculate and is more difficult to be deposited. With addition of PVB, the suspension was then stabilized. The deposition kinetics and the effect of additives were observed and discussed using DLVO theory. From SEM and XRD observation, the films obtained were crack-free and grain-oriented.     

Effects of PbTiO 3 Seed Layer on the Characteristics of RF-Sputtered Pb(Zr 0.5 ,Ti 0.5 )O 3 Thin Films

The effects of seed layers on the characteristics of rf-sputtered lead zirconium titanate thin films were investigated. Prior to sputtering, PbTiO 3 seed layers (100 nm) were deposited onto the Pt/Ti/Si and Pt/Si substrates by sol-gel (spin coating) processing method. Structure-property relation was studied as functions of substrate temperature and sputtering conditions. Special efforts were given in optimizing the deposition parameters to prepare the films in the perovskite phase without post deposition annealing. Dielectric constant and loss tangent of the films were in the range 800-950 and 0.04 -0.06, respectively. Remanent polarization and coercive field were 23.1 w C/cm 2 and 75kV/cm, respectively, for the films without PbTiO 3 seed layer, where as the corresponding quantities for in situ -deposited perovskite Pb(Zr, Ti)O 3 films on PbTiO 3 seed layer were 28 w C/cm 2 and 65 kV/cm, respectively.     

ZnO表面包覆In(OH)_3的制备及电化学性能

通过直接沉淀的方法成功地在氧化锌的表面包覆一层In(OH)_3.X射线衍射光谱法(XRD)和透射电子显微镜法(TEM)测试证明,ZnO表面包覆的为纳米级In(OH)_3.通过充放电循环、循环伏安以及交流阻抗等电化学方法研究了表面包覆纳米In(OH)_3的ZnO的电化学性能,与纯ZnO以及混入In(OH)_3的ZnO相比,表面包覆纳米In(OH)_3的ZnO具有较高的放电容量、较低的容量衰减率、较低的充电电压以及较稳定的中值电压.XRD测试表明,ZnO表面包覆的In(OH)_3在充电的过程中转变成了单质铟.     

表面修饰In(OH)_3后ZnO的电化学性能

用化学沉淀法在ZnO颗粒表面修饰了In(OH)3层.粉末XRD和TEM测试的结果表明,In(OH)3颗粒的尺寸约为10～30 nm.随着In(OH),负载量的增加,ZnO的放电比容量、利用率和电荷转移电阻逐渐增大,而充放电电压逐渐降低.In(OH)3负载量为12.5%的ZnO与纯ZnO前150次循环的平均放电比容量分别为552 mAh/g和286 mAh/g;ZnO的平均利用率分别为84.2%和44.7%;电荷转移电阻分别为0.82Ω和0.24Ω;平均充放电电压降低24 mV和40 mV.     

Preparation of SrBi2(Ta,Nb)2O9 thin films by rf sputtering for ferroelectric memory production

Abstract

Ferroelectric SrBi₂(Ta, Nb)₂O₉ (SBTN) thin films were prepared by rf magnetron sputtering utilizing a multi-chamber type production tool (ULVAC CERAUS ZX1000). Accurate and dynamic compositional control results in excellent ferroelectric performances such as large 2Pr up to 15μC/cm², fatigue free at least 10⁹ cycles as well as good uniformity and process repeatability. These results indicate that the SBTN sputtering process is promising for ferroelectric memory production.     

Effects of Al2O3 on the piezoelectric properties of Pb(Mn1/3Nb2/3)O3-PbZrO3-PbTiO3 ceramics

Piezoelectric properties of Al₂O₃-doped Pb(Mn_1/3Nb_2/3)O₃-PbZrO₃-PbTiO₃ ceramics were investigated. The constituent phases, microstructure, electromechanical coupling factor, dielectric constant, piezoelectric charge and voltage constants were analyzed. Diffraction peaks for (002) and (200) planes were identified by X-ray diffractometer for all the specimens doped with Al₂O₃. The highest sintered density of 7.8 g/cm³ was obtained for 0.2 wt% Al₂O₃-doped specimen. Grain size increased by doping Al₂O₃ up to 0.3 wt%, and it decreased by more doping. Electromechanical coupling factor, dielectric constant, piezoelectric charge and voltage constants increased by doping Al₂O₃ up to 0.2 wt%, and it decreased by more doping. This might result from the formation of oxygen vacancies due to defects in O^{2 −} ion sites and the substitution of Al³⁺ ions.     

Al2O3不同掺杂方式对钛酸钡介电性能的影响

采用固相法制备了掺杂1 mol%Al2O3和1mol%Al2O3-2mol%BaO两组钛酸钡陶瓷样品。结果表明:Al2O3两种掺杂方式对钛酸钡的作用效果存在差异,其中Al2O3-2BaO共掺杂的作用效果较强,这与不同掺杂方式所引起的钛酸钡陶瓷的晶格变化差异有关。两种掺杂方式均使钛酸钡陶瓷的εmax减小,居里温度降低,介质损耗降低,同时伴有介温峰展宽,且由于弥散相变的存在其室温介电常数呈增大之势。     

Growth and characterization of non-c-axis-oriented SrBi2Ta2O9 epitaxial thin films on Si(100) substrates with SrRuO3 bottom electrodes

Abstract

We have successfully grown non-c-axis-oriented epitaxial ferroelectric SrBi₂Ta₂O₉ (SBT) films with (116) and (103) orientations on Si(100) substrates using epitaxial (110)- and (111)-oriented SrRuO₃ (SRO) bottom electrodes, respectively. The SRO orientations have been induced by coating the Si(100) substrates with epitaxial YSZ(100) and MgO(111)/ YSZ(100) buffer layers, respectively. All films were sequentially grown by pulsed laser deposition. Specific in-plane orientations of the epitaxial SBT films were found, which are in turn determined by specific in-plane orientations of the epitaxial SRO bottom electrodes. These include a diagonal rectangle-on-cube epitaxy of SRO(110) on YSZ(100) and a triangle-on-triangle epitaxy of SRO(111) on MgO(111).     

Effect of Sb2O3 addition on the varistor characteristics of ZnO-Bi2O3-ZrO2-MtrO (Mtr = Mn, Co)

Effect of Sb₂O₃ addition on the varistor characteristics of pyrochlore-free ZnO-Bi₂O₃-ZrO₂-M_trO (M_tr = Mn, Co) system previously proposed has been studied. With Sb₂O₃ up to 0.1 mol%, a gradual enhancement of densification and the grain growth inhibition were seen in the system sintered between 900 and 1200^∘C. In X-ray diffraction patterns, small amount of pyrochlore appeared in the specimens doped with Sb₂O₃ (>0.06 mol%), which is thought responsible for the sintering behavior. Enhanced values of non linear coefficient (α) were obtained in ZnO-Bi₂O₃-ZrO₂ (ZBZ) doped with 0.001 mol% Sb₂O₃, but was leveled off at higher concentrations. In ZBZ added with M_trO (M_tr = Mn, Co), significant increase of nonlinear coefficient (α > 30) along with low leakage current (I _L ≪ 100 μA/cm²) was attained. The α-enhancement effect of Sb₂O₃, however, was not observed in high-α ZBZ added with M_trO. As for degradation, addition of a trace amount (0.001 mol%) of Sb₂O₃ to ZBZM_tr was efficient, especially in I _L.