Characterization of RF sputtered zinc oxide thin films on silicon using scanning acoustic microscopy

Zinc oxide (ZnO) thin films were grown on silicon (100) substrate using radio frequency (RF) sputtering under various processing parameters including deposition time and annealing temperature. A series of characterization techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and scanning acoustic microscopy (SAM) have been used to analyze the crystallinity and crystal orientation, structural morphology, surface roughness, and acoustic properties of these films. In particular, quantitative analysis of elastic wave propagation in ZnO thin films by scanning acoustic microscopy has been performed for the first time in the present work. It has been shown that the propagation properties of acoustic waves on the surface of ZnO thin films strongly depend on film thickness, crystallinity, and surface roughness. The dispersion properties of surface acoustic waves (SAWs) are observed as a function of ZnO film thickness. The velocities of SAWs range from 5328.3 m/s to 4245.7 m/s with increasing film thickness from 32.5 nm to 2.04 μm, while smoother surface contributes to faster propagation of SAWs.     

厚度对M型钡铁氧体薄膜结构及磁性能的影响

采用射频(RF)磁控溅射法在蓝宝石基片上制备M型钡铁氧体(Ba M)薄膜,研究了薄膜厚度对Ba M铁氧体薄膜的结构及磁性能影响。结果显示,样品的衍射峰全部为Ba M薄膜的(00l)衍射峰,表明样品都具有良好的c轴取向性。显微结构分析结果表明,在膜厚为40~90nm范围内,薄膜样品表面主要为c轴取向的片状晶粒,未出现c轴随机取向的针状晶粒;当样品厚度增加至140nm时,出现了较明显的针状晶粒;随着薄膜厚度进一步增加到190nm时,样品表面出现了大量c轴随机取向的针状晶粒,且部分针状晶粒长度达到了μm级。磁性能测试结果显示,随着薄膜厚度的增加,薄膜样品饱和磁化强度降低,垂直膜面方向矫顽力和剩磁比减小,膜厚40~90nm范围的薄膜在垂直膜面方向获得了最大剩磁比和矫顽力,表现出较好的磁晶各向异性。     

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.     

Investigation of the effects of milling ceramic targets on the optical and electrical properties of BST thin films deposited by RF sputtering

Abstract

The RF sputtering method was utilized to deposit thin films of Ba_1-xSr_xTiO₃ (BST). The targets utilized in these experiments were prepared from ceramic powders with different particle size. The goal of this work is to examine whether the particle size distribution of the target can affect the properties of the thin films fabricated by the sputtering method. The Atomic Force Microscope (AFM) was used to examine the grain size in the thin films. The composition of the thin films and the bulk materials were examined by Fourier Transform Infrared (FTIR) spectroscopy. The dielectric properties of the thin films were measured and compared to its bulk counterparts. It was found that on lattice matched electrodes of SrRuO₃ on LaAlO₃ substrates, the thin films deposited from ceramic targets manufactured from ball-milled powders had finer grain size than those deposited from targets made from unmilled powders. However, this phenomenon was not observed in the case of polycrystalline films deposited on platinized silicon wafers.     

Surface modification of stainless steel bipolar plates for PEMFC (proton exchange membrane fuel cell) application

Stainless steel 316 and 304 plates were deposited with a metallic film (top layer) and a conductive oxide film (intermediate layer) by a sputtering method and an E-beam method, respectively. The conductive oxide film was formed on the stainless steel plates in the range of thickness of 200, 400, and 600 nm. The XRD patterns of the conductive oxide films showed a typical indium-tin oxide (ITO) crystalline phase. The metallic films of 100 nm thickness were subsequently formed on the surface region of the bare stainless steel plates and the stainless steel plates deposited with ITO thin film. Surface morphologies of the stainless steel bipolar plates deposited with conductive film and metallic film were observed by AFM and FE-SEM. The metallic films on the stainless steel plates represented the microstructural morphology of the fine columnar grains of 10 nm diameter and 60 nm length. The electrical resistivity and contact angle of the stainless steel bipolar plates modified were examined as a function of the thickness of the conductive oxide film.     

Fabrication and evaluation of LaCrO3 thin film heaters

Lanthanum chromium oxide (LaCrO₃) has excellent high‐temperature properties. LaCrO₃ doped with alkaline earth metals also has high electric conductivity. The purpose of this study is to fabricate thin film heaters using LaCrO₃ doped with Ca by RF magnetron sputtering method. The crystal structure of thin films was evaluated and the surface form was studied. The results show that the thin film deposited on Si(100) single crystal and quartz glass substrates in Ar gas had a strong orientation and that its surface form was comparatively smooth. The crystal structure of the thin films deposited on Si(100) and quartz glass substrate at temperatures of 700 and 800 °C by sputtering in a mixture of Ar and O₂ gases was the same as the crystal structure of LaCrO₃. The heating characteristics of a thin film heater on Si(100) substrate with Pt electrodes were evaluated by measurement of the equilibrium temperature‐current (T–I) and resistance‐equilibrium temperature (R–T) characteristics. The maximum equilibrium heating temperature was about 1100 °C. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 139(3): 18–25, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.1156     

Dielectric characteristics investigation of (Ba0.7Sr0.3)(Ti0.9Zr0.1)O3 ferroelectric thin films

By the radio frequency (RF) magnetron sputtering methods, (Ba_0.7Sr_0.3)(Ti_0.9Zr_0.1)O₃ (BSTZ) ferroelectric thin films were deposited on the Pt/Ti/SiO₂/Si(100) substrates. The crystal structural and microstructure of these thin films were analyzed by means of the XRD, SEM, and AFM. Moreover, the dielectric characteristics were also investigated by the C-V and J-E analyses. The optimal deposition parameters for these BSTZ thin films were: RF power is 160 W, oxygen concentration is 25%, substrate temperature is 580°C, and chamber pressure is 0.075 mPa. Under these optimal deposition conditions, the (111) and (110) oriented polycrystalline of the BSTZ thin films grow easily. And under a bias voltage of 0.5 MV/cm, the dielectric constant and leakage current density of the BSTZ thin films are 191 and 3×10^?8 A/cm², respectively. In addition, under various measured temperatures (0 ～ 80°C) and frequencies (100 kHz ～ 1 MHz), all the dielectric constants remain almost unchanged. Compared to BSTZ thin films reported previously, in this study, the deposited thin films have the advantage of lower leakage current and hence are suitable for the applications of dynamic random access memory.     

退火对溶胶-凝胶法CoFe_2O_4薄膜结构与磁性的影响

采用溶胶-凝胶法在Si(001)基片上制备了CoFe_2O_4(CFO)薄膜,对样品进行不同温度的快速退火处理,并采用X射线衍射(XRD)、原子力显微镜(AFM)、振动样品磁强计(VSM)对薄膜进行微结构与磁性能分析.结果表明,薄膜退火温度在450℃及以上时生成无择尤取向的单一尖晶石相.随着退火温度上升,薄膜的晶化程度增高,Ms增大.650℃左右退火薄膜晶粒达到单畴临界尺寸,导致Hc随着退火温度的继续上升而逐渐下降.EDS分析表明,成膜后的化学计量比偏移很小.     

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.     

Structural and electrical properties of Sb-doped p-type ZnO thin films fabricated by RF magnetron sputtering

We investigated the Sb-doping effects on ZnO thin film using RF (radio frequency) magnetron sputtering and RTA (rapid thermal annealing). The structural and electrical properties of the thin films were measured by X-ray diffraction, SEM (scanning electron microscope), and Hall effect measurement. Thin films were deposited at a high temperature of 800°C in order to improve the crystal quality and were annealed for a short time of only 3 min. The structural properties of undoped and Sb-doped films were considerably improved by increasing oxygen content in the Ar-O₂ gas mixture. Sb-doping also significantly decreased the electron concentration, making the films p-type. However, the crystallinity and surface roughness of the films degraded and the mobility decreased while increasing Sb-doping content, likely as a result of the formation of smaller grain size. From this study, we observed the transition to the p-type behavior at 1.5 at.% of Sb. The thin film deposited with this doping level showed a hole concentration of 4.412?×?10¹⁷ cm^?3 and thus is considered applicable to p-type ZnO thin film.     

Fabrication and structural characterization of interdigitated thin film La1 − x Sr x CoO 3 (LSCO) electrodes

For the prospective use as micro-Solid Oxide Fuel Cell (μ-SOFC) cathodes and for the investigation of reaction kinetics, La_{1 − x}Sr_xCoO₃ (LSCO) mixed ionic electronic conducting thin films were deposited by DC and RF sputtering onto a number of different substrate materials and characterized. Standard photolithographic and wet chemical etching methods were utilized to microstructure the LSCO films and XRD, SEM, AFM, WDS, and RBS were used to characterize their structure, topography, and chemistry. Sputtering resulted in very homogeneous and smooth thin crystalline films with Sr deficiency and submicron sized grains. Hydrochloric acid was found to readily etch LSCO with the etching quality strongly dependent on substrate material. LSCO films were most easily etched when deposited directly on silicon substrates, etched at intermediate rates when deposited on Gd:CeO₂ films, and most resistant to etching after deposition onto single crystal yttria stabilized zirconia (YSZ) substrates. Imperfect etching was attributed to interface formation and the presence of impurities.     

Effects of sputtering pressure and thickness on properties of ZnO:Al films deposited on polymer substrates

Highly conducting and transparent aluminum doped zinc oxide (ZnO:Al) thin films have been deposited on polyimide substrate by r.f. magnetron sputtering at room temperature. The influence of sputter pressure and thickness on the structural, electrical, and optical properties of ZnO:Al films deposited on polyimide substrate is reported. The crystallinity and degree of orientation was increased by decreasing the sputter pressure. For higher sputtering pressures an increase on the resistivity was observed due to a decrease on the mobility and the carrier concentration. As the film thickness was increased, the crystallite sizes were increased, but the average transmittance in the wavelength range of the visible spectrum was decreased. The electrical performances of the ZnO:Al films deposited on glass substrates are slightly worse than the ones of the films deposited on polyimide substrates with same thickness. The lowest resistivity of 8.6?×?10^?4 Ω cm can be obtained for films deposited on glass substrate with the thickness of 800 nm.     

Preparation of SrBi 2 Ta 2 O 9 Ferroelectric Thin Films by RF Magnetron Sputtering

Ferroelectric SrBi 2 Ta 2 O 9 (SBT) thin films were deposited by RF magnetron sputtering on a Pt/Ti/SiO 2 /Si(100) structure. The deposition temperature of the film was varied from RT (room temperature) to 600C. It was found that the SBT films were crystallized at temperatures between 500C and 600C, which was much lower than the annealing temperature (700C to 800C) of the RT-deposited film. The maximum remnant polarization value (2Pr) of the SBT film was 15 w C/cm 2 , which was deposited at 575C.     

Effect of Thermal Treatment Temperature on the Crystallinity and Morphology of LiTaO3 Thin Films Prepared from Polymeric Precursor Method

Lithium tantalate thin films (LiTaO₃) with (50:50) stoichiometry were prepared by spin coating method using a polymeric organic solution. The films were deposited on silicon (100) substrates with 4 layers. The substrates were previously cleaned and then the solution of lithium tantalate was deposited by adjusting the speed at 5000 rpm. The thin films deposited were thermally treated from 350 to 600C for 3 hours in order to study the influence of the thermal treatment temperature on the crystallinity, microstructure, grain size and roughness of the final film. X-ray diffraction (XRD) results showed that the films are polycrystalline and secondary phases free. The thickness of films was observed by scanning electron microscopy (SEM). The atomic force microscopy (AFM) studies showed that the grain size and roughness are strongly influenced by thermal treatment.     

氮离子束能量对光伏新材料氮化碳薄膜的影响

将碳基材料应用于太阳电池半导体器件的研究已经在国内外得到重视和开展。采用离子束溅射反应沉积技术,在p型绒面硅和p型硅基片上沉积出用于制备太阳电池的氮化碳薄膜(a-C:N)。ID/IG比率,ISi/IG比率是研究氮化碳薄膜微结构的重要拉曼参数,对这些参数随氮离子束能量的变化进行了研究。能量散射光谱(EDS)和透射电子显微镜(TEM)测试显示随氮离子束能量增大,薄膜中氮原子含量下降,团簇尺寸大幅下降,非晶网络中团簇分布也趋于均匀。用真空热蒸镀工艺在氮化碳/硅异质结的氮化碳薄膜表面镀上一层半透明的铝薄膜,测得AM1.5标准光照下的开路电压随氮离子束能量的增加而增大。     

NiCr Alloy As Both Absorption Layer and Top Electrode onto Pb(Zr0.3Ti0.7)O3 Thin Films for Infrared Sensors

NiCr alloys prepared by dc magnetron sputtering are considered to apply simultaneously both the absorption layer and the top electrode on PZT thin films for infrared sensors. NiCr alloys deposited with dc powers of Ni 80 and Cr 50 W showed the most stable oxidation resistance even at 600°C in an oxygen ambient. They have a resistivity of approximately 70 μΩ-cm and a rms roughness of 2.0 nm in samples annealed at 600°C for 5 min in O₂. The NiCr/PZT/Pt capacitors showed a well-saturated hysteresis loop having a remanent polarization of 20 μC/cm². Ultra-thin NiCr alloys showed a possibility as a top electrode for infrared sensors.     

Impurity behaviors of nitrogen in W–C–N thin diffusion barriers for Cu metallization schemes

To investigate the effect of nitrogen impurities in the tungsten–carbon thin films, the electrical and structural properties of W–C–N thin films deposited with rf magnetron sputtering method were measured. Interface characteristics of W–C–N/Si were studied with resistivity and crystal structure as a function of nitrogen impurity concentrations of as-deposited and annealed state for various annealing temperature. We also investigate the interface of Cu/W–C–N/Si for various nitrogen concentration by using XRD pattern and Nomarski microscope. Our experimental results indicate that nitrogen impurity provides stuffing effect for preventing the interdiffusion between Cu and Si interface after annealing up to 800°C for 30 min, because W–C–N thin films serve as a good diffusion barrier and this may be due to the role of nitrogen and carbon inside the W–C–N film not as bonded state but impurities     

射频溅射法制备的CoFe_2O_4薄膜结构及磁性能

采用射频溅射法在Si(001)基片上制备了CoFe_2O_4 (CFO)薄膜,分别采用原子力显微镜(AFM)、X射线衍射仪(XRD)、振动样品磁强计(VSM)进行测试和分析.结果表明,随着退火温度的升高,晶粒逐渐增大,在600℃左右退火,晶粒长大受到抑制;M_s和H_c随退火温度的升高都是先增大后减小;薄膜晶粒大小和膜内晶格应力导致垂直膜面方向矫顽力大于平面方向矫顽力.在600℃退火,H_(c⊥)/H_(c∥)值达到了2.72,表明制备的CFO薄膜具有高度垂直各向异性.     

Nanoscale phenomena of gallium-doped ZnO thin films on sapphire substrates

Gallium-doped ZnO (1.2 at. %) thin films with various thicknesses were deposited on sapphire (001) substrates at 500^∘C using a pulsed laser deposition (PLD) technique. The thin films with different thicknesses (20, 40, 100, 200, 400, and 600 nm, respectively) were obtained by changing the deposition time. An x-ray diffractometer (XRD) was used to investigate the structural properties of the thin films. All of the thin films had a preferred (002) orientation. However, the thin films with 20 and 40 nm thicknesses were of low crystallinity. With increasing thickness the (002) peak increased greatly, and the full width at half maximum (FWHM) values were calculated by using omega scans. Scanning electron microscope (SEM) and atomic force microscope (AFM) were used to investigate the nanoscale phenomena and the surface morphologies of the thin films. The surface roughness increased as the thickness increased. The thin film with 20 nm thickness was very smooth, and no nucleation center could be observed. However, the thin film with thickness over 100 nm showed nucleation. The nucleation center varied with increasing thickness. A spectrometer was used to investigate the luminescent properties of the thin films. It was found that all of the thin films showed near band edge emissions and no deep-level emissions were observed. A blueshift was also observed due to the Burstein-Moss effect.     

Effect of Poling on Photovoltaic Properties in Highly Oriented BiFeO3 Thin Films

We report enhancement of photovoltaic properties of highly oriented BiFeO₃ (BFO) thin films. The single phase rhombohedral R3c space group structure was confirmed by XRD and Raman spectra in the films grown on SrTiO₃ (111) substrates using RF magnetron sputtering. The films of BFO were characterized in planar geometry with top Pt electrodes having 200μm diameter, ～40nm thickness and at a regular spacing of ～150μm deposited by DC sputtering process. For photovoltaic studies the current voltage characteristic of as grown and poled samples were studied under the white light illumination having energy density of ～1kW/m². The as grown films showed open circuit voltage (Voc) of ～3.9V which increased up to ～17.8V on poling with 200V. This enhancement in Voc by poling was attributed to increase in net polarization due to alignment of domains in the direction of applied electric field and hence potential barriers between the domains.