SAW器件用金刚石基c轴取向LiNbO3压电薄膜的制备

采用脉冲激光沉积技术,在以c轴取向ZnO作为缓冲层的金刚石/硅基底上制备出了结晶良好的高c轴取向LiNbO3薄膜。利用X射线衍射对薄膜的结晶质量和c轴取向性进行了研究,结果表明制得的LiNbO3薄膜具有高度c轴取向且结晶质量良好。采用扫描电子显微镜和原子力显微镜对薄膜的表面形貌进行了分析,发现薄膜表面光滑,晶粒尺寸均匀,薄膜表面粗糙度约为20nm。     

Correlation between domain wall properties and material parameters in amorphous SmCo-films

Amorphous Sm1-xcox-films with uniaxial in-plane anisotropy with various Co-concentrationsx (.67 leq x leq .91)and various film thicknesses d (10nm leq d leq 350nm) have been prepared by flash-evaporation of SmCo-alloy powders. The saturation magnetization decreases linearly with x in the whole concentration range, whereas the coercive field increases linearly with x down toxapprox74and then decreases. Drastic changes in all magnetic properties occur when at a given chemical composition the film thickness is reduced belowdapprox50nm. Head-on domains are separated by zig-zag walls whose amplitudes are analyzed as a function of the material parameters.     

Magnetic properties of evaporated CoCr films

Perpendicular magnetic CoCr films were prepared on glass substrates using electron beam evaporation. The magnetic properties depend strongly on the substrate temperature, Ts. The anisotropy field,H_{k}^{eff}, and the perpendicular coercivity, Hc(perp) show maximum values at Tsaround 250°C. In this case, the alignment of c-axis is optimal and the grain size is smallest. The lattice spacing of the c-planes increases wlth Tsuntil 300°C. When the films prepared below 200°C were annealed around 300°C in high vacuum, the saturation magnetization, Ms, increased. The value of Ms, however, decrease by annealing above 400°C. In spite of the decrease of Msdue to the annealing above 400°C,H_{k}^{eff}and Hc(perp) increase by annealing above 400°C. If the films were bombarded by argon ions during film growth, Msdecreased and the internal stress changed from tensile to compressive. For low substrate temperature (below 150°C),H_{k}^{eff}decreased due to ion bombardment.     

Magnetic properties and microstructure of sputtered Co-Cr films

Microscopic structural parameters of sputter-deposited Co-Cr films, such as the effective crystallite size along the thickness direction Deff(=coherent length), the strain < ε²>^1/2, and the lattice spacing d00.2have been systematically studied by means of X-ray analysis and transmission electron microscopy (TEM) in conjunction with the magnetic properties. Cross-sectional observations by TEM revealed that a number of slip bands exist in the poorly oriented films. Slip and deformation bands interrupt the coherency along the c-axis in films, giving a spread to the orientation of the c-axis across the band boundaries. The effective crystallite size Defffor such poorly oriented films was found to be less than 200 Å, which is consistent with the period of contrast observed by TEM. When a film was annealed, Deffwas found to increase and the saturation magnetization Ms decreased, implying that Cr segregation as well as slip bands decreased throughout the thickness.     

Dependence of coercivity on driving field in multilayer films of nickel

The variation in the coercivity of magnetization loops of multilayer films of nickel was investigated as function of the rate of riserin the applied magnetic field. The films were prepared by deposition of nickel and copper alternately in a vacuum of2 times 10^{-6}mm of Hg on to substrates made of thin aluminium foils. The thickness of the nickel layersLvaried in the different films from 8 to 1000 angstroms. The loops were cycled with sinusoidal or triangular waveform driving fields, with a variety of amplitudes from 1 kOe to 4 kOe, with frequencies from 0.01 to 2 c/s. The measurements were performed from room down to liquid hydrogen temperatures. It was found that the coercive force could be expressed byH_{c} = H_{o} + Q(ln r - ln r_{o})/T^{1/2}for values ofrchanging from 1 to 5 Oe/ms, whereH_{o}, Aand rovaried slightly with temperatureT. The coercive force was a very sensitive function ofLand of the thickness δ of the copper layers, having the formH_{c} = A(L + delta) exp - BLwithBnearly constant in films deposited on a substrate at room temperature. The dependence of the coercivity onLwas displayed by a nonmonotonical function showing two peaks in Hccorresponding to values ofLof about 35 and 400 angstroms. The observed dependence of Hcon the rate of rise in the applied field, as well as on the thicknesses of the layers, can be discussed on the assumption of nonuniform magnetization within the thin layers as a result of their superparamagnetic properties and of the magneto-statical coupling between neighboring layers.     

Dependence of segregated microstructure in sputter-deposited CoCr film on deposition conditions

The compositional segregation of sputter-deposited CoCr films prepared under substrate temperatures Ts of 90-160°C and Ar gas pressures PAr of 4-30 mTorr are studied by transmission electron microscopy. The segregated microstructure depends on Ts and PAr. The degree of the segregation increases as Ts increases, and is maximized at a medium PAr. Saturation magnetization increases as the degree of the segregation increases. Vertical coercivity in film with the same degree of the c-axis orientation increases as the degree of segregation increases.     

基于柱状ZnO薄膜的超低阈值电压压敏电阻

利用磁控溅射法在玻璃衬底上制备了基于柱状ZnO薄膜的Al-ZnO-Al三明治结构的超低阈值电压的压敏电阻。XRD和SEM测试结果表明,该压敏电阻中的ZnO薄膜层为结晶性能良好,并且沿ZnO的(002)晶面择优取向生长的柱状薄膜。I-V测试结果表明,这种由柱状ZnO薄膜构成的压敏电阻阈值电压仅3.2 V,为现有压敏电阻中阈值电压最低的压敏电阻。     

Synthesis of C-axis-oriented AlN thin films on high-conducting layers: Al, Mo, Ti, TiN, and Ni

Thin piezoelectric polycrystalline films such as AlN, ZnO, etc., are of great interest for the fabrication of thin film bulk/surface acoustic resonators (TFBARs or TFSARs). It is well-known that the degree of c-axis orientation of the thin films correlates directly with the electromechanical coupling. However, the degree of c-axis orientation of the piezoelectric film is, in turn, influenced by other parameters such as the structure of the substrate material, the matter of whether the c-axis is up or down (polarity), and the growth parameters used. The correlation of these three aspects with the electromechanical coupling of the AlN-thin films, is studied here. Thin AlN films, prepared in a magnetron sputtering system, have been deposited onto thin Al, Mo, Ni, Ti, and TiN films. Such thin high-conducting layers are used to form the bottom electrode of TFBAR devices as well as to define a short-circuiting plane in TFSAR devices. In both cases, they serve as a substrate for the growth of the piezoelectric film. It has been found that the degree of orientation and the surface roughness of the bottom metal layer significantly affects the texture of the AlN films, and hence its electroacoustic properties. For this reason, the surface morphology and texture of the metal layers and their influence on the growth of AlN on them has been systematically studied. Finally, FBARs with both Al and Ti electrodes have been fabricated and evaluated electroacoustically.     

MOD法制备的Bi3.25Nd0.75Ti3O12薄膜的铁电各向异性行为

采用金属有机分解法(MOD)在(111)Pt／Ti／SiO2／Si衬底上制备了含(117)成分的c轴择优取向和α轴择优取向的Bi3.25Nd0.75Ti3O12(BNT)薄膜．实验发现，BNT薄膜的品型结构主要依赖于预退火条件．电学性能测试表明，α轴择优取向的BNT薄膜具有高的剩余极化和矫顽场，较高的介电常数和介电损耗，以及较大的电容调谐率；而c轴择优取向的则相反．BNT薄膜具有同Bi4Ti3O12(BIT)薄膜相似的铁电各向异性行为．     

Morphology control of barium ferrite thin films

Hexagonal barium ferrite thin films were fabricated by spin coating of precursors obtained by sol-gel methods onto sapphire (00l) faces. Citric acid and ethylenediaminetetraacetic acid (EDTA) were used to tune the morphology of the films. The films show texture with c-axis normal to the film plane as shown by the strong x-ray diffractions from the (001) plane with full width at half maximum of the rocking curves about 0.4°. The [100] direction of the film is parallel to the [110] direction of the sapphire. With the increase of the citric acid, the percentage of the acicular crystallites increased. EDTA can be used to produce films with the best texture where faceted grains were obtained. The maximum coercive force obtained was about 302 kA/m.     

The effects of incident angle on C-axis orientation in sputtered Co-Cr films

The effects of the incident angle of the sputtered atoms on the crystallographic orientation in the Co-Cr films have been investigated in detail. Specimen films 1000 - 2000 Å thick were prepared by the Facing Targets Sputtering (FTS) system. The specially designed mask was used for collecting only the sputtered particles with the quasi-coherent incidence to the substrate. When the films are prepared at relatively low argon gas pressures, the effect of incident angle is not so apparent and the well c-axis oriented films can be obtained for the incident angle below 45°. This result indicate that the surface diffusion may be dominant over the incident angle for attaining the desired crystallographic orientation in the films when they are prepared at low working gas pressures. Owing to the unique target/substrate layout, the plasma-free FTS system with low working gas pressures may have much larger flexibilities for preparing the well c-axis oriented Co-Cr films as compared with the conventional sputtering systems or the vacuum evaporation one.     

The effects of ZnO films on surface acoustic wave properties of modified lead titanate ceramic substrates

Poly-crystal zinc oxide (ZnO) films with c-axis (002) orientation have been successfully grown on the strontium (Sr) modified lead titanate ceramic substrates with different Sr dopants by r.f. magnetron sputtering technique. Highly oriented ZnO films with c-axis normal to the substrates can be obtained under a total pressure of 10 mTorr containing 50% argon and 50% oxygen and r.f. power of 70 W for 3 hours. Crystalline structures of the films were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The phase velocity, electromechanical coupling coefficient and temperature coefficient of frequency of surface acoustic wave (SAW) devices with ZnO/IDT/PT (IDT, inter-digital transducer; PT, PbTiO3 ceramics) structure were investigated. The devices with ZnO/IDT/PT structure shows that the ZnO film effectively raise the electromechanical coupling coefficient (kappa2) from 3.8% to 9.9% of the device with the concentrations of Sr dopants of 0.15. It also improves the temperature coefficient of frequency of SAW devices.     

Effect of chelating agents on the preferred orientation of ZnO films by sol-gel process

The effect of chelating agents of ZnO precursor solutions on crystallization behavior was investigated. Two different additives, monoethanolamine (MEA) and diethanolamine (DEA), and crystalline Pt (111)/Si and amorphous SiN _x /Si substrates, were used for this study. ZnO film grown on SiN _x /Si from a DEA-chelated precursor solution shows a poorly oriented microstructure with weak crystallization peaks, while ZnO film grown on Pt(111)/Si shows a c-axis preferred orientation. In the case of ZnO films prepared with a MEA-chelated precursor solution, all films show a strong preferred orientation irrespective of substrate type. This result clearly demonstrates the role of the chelating agent on the crystallographic orientation and crystallization behavior of sol-gel processed ZnO films.     

Preferred crystal orientation of sol-gel-derived Bi4-xLaxTi3O12 thin films on silicon substrates

Polycrystalline thin films of La-substituted bismuth titanate (BLT) were formed directly on p-type Si(100) substrates by using sol-gel and spin coat methods. The BLT film and interfacial layer between BLT and Si were quantitatively investigated by the X-ray reflectivity method. Also, crystal orientations of sub-100-nm-thick BLT thin films were confirmed by X-ray diffraction using a synchrotron radiation source. The preferred c-axis orientation normal to the surface depended on the crystallization temperature. The difference in the preferred c-axis orientations of the BLT films caused the difference in the hysteresis voltage width in the capacitance-voltage characteristics of Au/BLT/p-Si structures. Furthermore, the c-axis of the Bilayered structure was preferentially oriented and aligned in the in-plane direction.     

Influence of sputtering atmosphere on crystallinity and crystal orientation of AlN thin films deposited on polycrystalline MoSi2 substrates

Highly oriented AlN thin films have been deposited on polycrystalline MoSi2 substrates by r.f. magnetron sputtering. The total sputtering pressure and the nitrogen concentration in the sputtering gas had a significant influence on the crystallinity and crystal orientation of the films. The film deposited at a sputtering pressure of 0.6 Pa and a nitrogen concentration of 20% indicated high crystallinity, high c-axis orientation (=3.1°) and very low surface roughness (Ra=0.7 nm). The crystallinity, crystal orientation, composition and morphology of the films were investigated by X-ray diffraction, X-ray photoelectron spectroscopy, and atomic force microscopy. The nitrogen concentration hardly had an effect on the composition of the films; however, it had a great influence on the shape of the fine grains constituting the films. The shape of the grains drastically changed from triangular pyramids of various sizes to uniform fine grains with increasing nitrogen concentration. © 1998 Chapman & Hall     

c轴取向PbTiO3外延生长的研究

本文研究了ＭＯＣＶＤ法淀积过程中工艺条件对ＰｂＴｉＯ３膜ｃ轴取向度的影响，探讨了ＰｂＴｉＯ３膜的生长过程，通过调节氧气流量首次在ＭｇＯ（１００）单晶衬底上淀积出ｃ轴取向的ＰｂＴｉＯ３外延膜。ＰｂＴｉＯ３外延膜的介电常数为９０，折射率为２．６４，均和单晶性能一致。     

Characteristics of (1010) and (1120) textured ZnO piezofilms for a shear mode resonator in the VHF-UHF frequency ranges

This paper reports the fabrication and characterization of ZnO piezoelectric thin films in which the crystallite c-axis is unidirectionally aligned in the plane. The films were deposited by a conventional radio frequency (RF) magnetron sputtering apparatus without epitaxy. We have measured reflection coefficient S11 of the ZnO film/glass substrate composite shear mode resonator and confirmed that the resonator excites shear wave only in the very high frequency to ultra high frequency ranges (VHF-UHF). The crystallites c-axis orientation and alignment were determined by x-ray diffraction (XRD) patterns, phi-scan pole figure analysis, omega-scan rocking curves, and atomic force microscope (AFM) measurement. The transduction of the shear wave showed good agreement with properties of the crystallite alignment in the film.     

Influence of substrate temperature on the texture and superconducting properties of thin films of YBa2Cu3O7-x on (1 0 0) YSZ substrates prepared by glow discharge sputtering

Films of c-axis textured YBa2Cu3O7-x (YBCO) were grown on (1 0 0) oriented yttria stabilized zirconia substrates by high pressure glow discharge sputtering. The influence of substrate temperature on the texture and superconducting properties of the films is reported. X-ray pole figure analysis has shown that a c-axis orientation of the film normal to the substrate surface occurs at an optimized substrate temperature of 953 K. HREM investigation revealed that the deposited material nucleates and grows as YBCO with a large amount of stacking faults and with a few Y2BaCuO5 particles. A dominant cube-to-cube orientation relationship is found between the YBCO film and the substrate. This revised version was published online in August 2006 with corrections to the Cover Date.     

Optimum permanent-magnet dimensions for repulsion applications

The repulsive force between identical right-circular-cylindrical permanent magnets is calculated, and the ratio of this force to the weight of a magnet is maximized through optimization of magnet size and shape. It is assumed that the magnets are uniformly magnetized along their axes. For magnets of thicknesstand radiusR, separated by a distance2h, the optimum dimensions areR = 3.45handt = 2.7h. For these dimensions, the repulsive magnetic force has the value2.65 mu_{0}M^{2}h^{2}newtons, with the magnetizationMin At/m andhin meters.     

氧分压对磁控溅射ZnO薄膜生长行为和光学特性的影响

采用反应射频磁控溅射方法, 在Si(001)基片上制备了具有高$c$轴择优取向的ZnO薄膜. 利用原子力显微镜、X射线衍射、透射光谱和室温光致荧光光谱等分析技术, 研究了氧分压对薄膜的表面形貌和光学特性的影响. 研究结果显示: 0.04～0.23Pa的氧分压范围内, ZnO薄膜存在三个不同的生长模式, 薄膜生长模式转变的临界氧分压分别位于0.04～0.08Pa和0.16～0.19Pa之间; 在0.16Pa以下时, ZnO薄膜的表面岛呈+c取向的竹笋状生长; 当氧分压>0.19Pa时, 薄膜的表面岛以-c取向生长为主; ZnO薄膜的折射率、光学带隙宽度以及PL光谱强度均随着氧分压的增大而增大, 氧分压为0.19Pa时, 薄膜的发光峰最窄, 其半峰宽为88meV.