Microscale deformation behavior of amorphous/nanocrystalline multilayered pillars

Metallic glasses have recently been extended their research and application in micro-electro-mechanical systems (MEMS). However, the brittle nature of metallic glasses in the bulk and thin film forms inevitably imposes limitation. The current study applies the new idea to adopt a thin layer of nanocrystalline metal film beneath the brittle binary ZrCu thin film metallic glass (TFMG) layer. This metal film needs to be sufficiently strong in modulus and strength and needs to be deposited with the appropriate film orientation. The face-centered cubic Cu {111} film appears to be too soft, the body-centered cubic Mo {110} film behaves to be too brittle, but the hexagonal close-packed Zr {0001} film matches all above requirements. The shear bands initiated in the ZrCu thin film metallic glass layer can be absorbed and accommodated by the nanocrystalline Zr {0001} layer via the nano-twinning mechanism. The original brittle ZrCu TFMG, with the inclusion of a Zr layer beneath, can behave highly ductile with semi-uniform plastic deformation of 55%, even more ductile than most pure metals. The amorphous-crystalline interface exhibits good strain compatibility after appreciable plastic deformation. This finding can impose great impact on the TFMG/metal multilayer structures useful for MEMS design.     

Effects of Os inserted layers on the microstructures and magnetic properties of the FePt films

The microstructure and magnetic properties of multilayer [Os(t)/FePt(x)]n films on a glass substrate with a 10 nm Os buffer layer by ion beam sputtering have been studied as a function of the annealing temperatures between 300 and 800 degrees C. Here, t = 0.2, 1 or 5 nm and x varied from 10, 20, 25, 50, to 100 nm with its associated n value of 10, 5, 4, 2, and 1, respectively. No diffusion evidence was found in samples with a thin Os layer and t > or = 1 nm. The average grain size of the multilayer films can be well controlled by both annealing temperature and thickness of the FePt layer by a very thin Os space layer with t > or = 1 nm. The enhancement of H(c) can be understood from the fact that for a FePt film with an Os spacer layers, the increasing number of Os layer will inhibit the grain growth of FePt grains and enriches the grain boundary. We have experimentally demonstrated that even with a very thin 1 nm Os spacer layers, the [Os(t)/FePt(x)]n multilayer films can exhibit good hard magnetic properties and are attractive candidates for ultrahigh density magnetic recording media.     

The role of the Zn buffer layers in the structural and photoluminescence properties of ZnO films on Zn buffer layers deposited by RF magnetron sputtering

Highly c-axis oriented ZnO thin films were grown on Si (100) substrates with Zn buffer layers. Effects of the Zn buffer layer thickness on the structural and optical qualities of ZnO thin films were investigated for the ZnO films with the buffer layers 90, 110, and 130 nm thick using X-ray diffraction (XRD), photoluminescence (PL) and atomic force microscopy (AFM) analysis techniques. It was confirmed that the quality of a ZnO thin film deposited by RF magnetron sputtering was substantially improved by using a Zn buffer layer. The highest ZnO film quality was obtained with a Zn buffer layer 110 nm thick. The surface roughness of the ZnO thin film increases as the Zn buffer layer thickness increases.     

Rare earth dibenzoylmethane complexes for potential application as high-density recordable optical recording materials

Three kinds of rare earth complexes derived from dibenzoylmethane (DBM) ligand were synthesized by reacting free ligand and different rare earth ions( La³⁺, Sm³⁺and Gd³⁺). Their contents and structures were postulated based on elemental analysis, LDI-TOF-MS, FT-IR spectra and UV-Vis spectra. Smooth films on K9 glass substrates were prepared using the spin-coating method. Their solubility in organic solvents, absorption and reflection properties of thin film and thermal stability of these complexes were evaluated. These complexes would be a promising recording material for high-density digital versatile disc-recordable (HD-DVD-R) system.     

Fabrication and characterization of ZnO nanoneedle array using metal organic chemical vapor deposition

High density and vertically well-aligned ZnO nanoneedle arrays were fabricated on the ZnO thin film deposited on silicon substrates. The ZnO buffer layer and nanoneedles were synthesized by metal organic chemical vapor deposition using diethylzinc and oxygen gas. The ZnO buffer film was grown at 250 degrees C and the growth temperature of nanoneedles was in the range of 480-500 degrees C. As-grown ZnO nanoneedles showed single crystalline structure of ZnO (002). The crystalline properties of three samples (A: as-deposited ZnO buffer layer, B: annealed buffer film, C: ZnO nanoneedles) were compared using XRD and Raman spectroscopy. The synthesized ZnO nanoneedles (sample C) showed highest crystalline quality among three samples. The field emission properties of ZnO nanoneedles were investigated, which showed low turn on field of 4.8 Vmicrom(-1) and high field enhancement factor of 3.2 x 103.     

基于锆钛酸铅薄膜的变形镜微致动器

以锆钛酸铅（PZT）薄膜作为驱动材料,制备了变形镜的微致动器阵列．使用有限元软件对致动器进行了模拟仿真,得到了驱动器上电极尺寸、Si弹性层厚度等参数对致动器性能的影响,获得了最优化的致动器结构．以钙钛矿相的镍酸镧（LNO）作为PZT薄膜在Pt衬底上生长的缓冲层,增强了PZT薄膜的（100）取向,减小了PZT薄膜的内部应力,提高了致动器的驱动性能．最终制备出的1μm厚PZT薄膜驱动的变形镜微致动器,在10V直流电压的激励下,具有2．0μm的变形量．以PZT薄膜作为驱动材料制备的变形镜微致动器阵列,对变形镜致动器的微型化和系统集成度的提高具有重要意义．     

Crucial points in perpendicular recording

Since the introduction of perpendicular recording on a floppy disc by IWASAKI in 1977 and its equivalent design on a rigid disc (SPH-like sensor + double-layer medium) in 1981, many tests have been carried out on different R/W sensors. For each test the main goal was the fci record or the improvement of the magnetic layer. Seen from the recording system point of view, the head and the medium are looked at as a unit through a specification, unchanging with increasing area density. For example, a minimum of 26 dB and 70 % must be achieved for the S/N ratio and the resolution respectively. By considering the noise of the best electronic channel (with a thin film head), and ignoring mechanical and medium noises, the output signal must be at least 250 μv pop. For a 50 Kfci application, however, a sensor does not yet exist. Using a ferrite head with a 1.2 μm gap length to write on FeTbGd, the level of the signal will not be high enough to be used. It is improved with a 0.6 μm gap head but then, the field doesn't allow us to write ! Such problems exist also with thin film heads or SPH like sensors on rigid discs. To improve the R/W process, the trend is to use a double layer medium e.g. CrCo/FeNi. The results show that this direction is not necessarily the best. For example, when erasing or over-writing with the head, some domains appear in the FeNi film which create noise from the track or its edge. Another example is the fact that the optimum parameters for a medium such as CrCo are not always compatible with the characteristics of the head (i.e. Hc, the thickness, the crystallographic orientation, the bit stability compared to the write field, the signal, the noise...).     

超薄Ni81Fe19薄膜的各向异性磁电阻及磁性能

利用磁控溅射方法制备了一系列超薄Ta(5nm)/Ni81Fe19(20nm)/Ta(3nm)磁性薄膜。着重研究了基片温度、缓冲层厚度对Ni81Fe19薄膜各相异性磁电阻(AMR)及磁性能的影响。利用X射线衍射仪分析了薄膜结构、晶粒取向;用四探针技术测量了薄膜的电阻率和各向异性磁电阻;用FD-SMOKE-A表面磁光克尔效应试验系统测量了薄膜的磁滞回线。结果表明:在基片温度为400℃时制备的Ni81Fe19薄膜具有较大的各向异性磁电阻效应和较低的磁化饱和场,薄膜最大各向异性磁电阻为3.5%,最低磁化饱和场为739.67A/m。基片温度为500℃制备的薄膜,饱和磁化强度Ms值最大。随着缓冲层厚度x的增加,坡莫合金薄膜的AMR值先变大后减小,在x=5nm时达到最大值。     

Improved crystallization characteristics of ZnO thin film grown onto a-C:H film used as a buffer layer

We employed a-C:H buffer layer to improve the crystalline property of ZnO thin film for the membrane film bulk acoustic resonator (FBAR). The a-C:H film as a buffer layer is prepared by applying dc bias of 200 V and also this sample showed a smoother surface roughness, higher hardness and Young's modulus when compared to the other samples. In addition, the FWHM value was improved from 7.5 to 4.3° on a-C:H film. The fabricated FBAR device showed the resistivity of 0.73 × 10⁸ Ω when compared with no buffer layer and the frequency characteristics of the FBAR were finally confirmed to be 1.15 GHz and 21.24 dB, respectively.     

PECVD法低温淀积SiC_x薄膜的防水汽扩散性能研究

外界水汽和离子的扩散对集成电路和传感器等器件的性能及使用寿命有很大影响 ,利用无机钝化材料阻挡水汽和离子的扩散是常用的提高器件寿命和稳定性的方法。本文采用PECVD方法在较低的衬底温度条件下淀积碳化硅薄膜 ,利用各种方法研究了碳化硅薄膜的防潮性能。实验证明 ,碳化硅薄膜是一种良好的水汽扩散阻挡材料 ,其防潮能力达到甚至超过了集成电路生产中常用的氮化硅薄膜。并且 ,低温碳化硅薄膜具有非常好的化学稳定性和抗刻蚀能力 ,在各种微加工工艺中有广泛的应用前景。     

Recording on perpendicular anisotropy media with ring heads

This paper reports experimental studies directed at the application of ring head structures to a perpendicular recording system. The media tested were sputter deposited films of CoCrTa alloys. Ferrite heads were studied, but the thin film head was chosen for evaluating roll-off, overwrite, and superposition. The data presented in the paper demonstrates the potential of high density recording with a single layer medium with perpendicular magnetic anistropy and a thin film head separated by 0.20 micrometers.     

Numerical simulation of periodic cracking mechanism in microscopic surface films during roll bonding processes

The microscopic surface films existing on the top of metallic layers play an important role in the process of joining by plastic deformation. The bond formation during cold welding processes is basically associated with the fracturing of surface films to produce intimate metallic contacts. The present paper aims at providing a numerical model to describe the cracking pattern of brittle surface films bonded to the ductile substrates. A microscale finite element model is developed which takes into account the fracturing mechanisms of thin surface films in roll bonding processes. The presented model is calibrated by using the existing experimental data for an aluminum alloy covered by a thin layer of oxide film. The model is also validated against a well‐known analytical model for periodic cracking. The distribution of stresses within the fractured surface film demonstrates that the generated cracks in the surface film have essentially a periodic pattern. Moreover, it is shown that the crack spacing is highly dependent on the properties of the surface film. Finally, the obtained results for the roll bonding show that a crack density saturation takes place at the entry of the roll bite where a small surface expansion is applied to the rolled samples.     

Effect of a ZnO buffer layer on the characteristics of MgZnO thin films grown on Si (100) substrates by radio-frequency magnetron sputtering

This is a report on the effect of a ZnO buffer layer on the microstructures and optical properties of MgZnO thin films grown on Si (100) substrates by radio frequency magnetron sputtering. For the sample without the ZnO buffer layer, the microstructural analyses carried out by X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed the formation of Mg₂Si in the interface between the Si substrate and the MgZnO thin film. Mg₂Si induced the random oriented polycrystalline MgZnO thin film. For the sample with the ZnO buffer layer, a few Mg₂Si were observed. An epitaxial relationship between the Si substrate and the MgZnO thin film was formed. In both samples, the photoluminescence (PL) investigation showed a small blue shift of the emission peak, which was owing to the incorporation of Mg atoms in ZnO by co-sputtering the MgO and ZnO targets. In addition, the sample with the ZnO buffer layer showed the enhanced PL intensity, when compared with the sample without the buffer layer.     

Suppression of phase transitions in Pd thin films by insertion of a Ti buffer layer

We investigated the effects of a thin titanium (Ti) buffer layer on structural changes and electrical responses of palladium (Pd) thin films. A Ti buffer layer was inserted between a Pd film and the substrate, with varying thickness from 0.5 to 80 nm. Unlike pure Pd films, Ti-buffered Pd films showed no structural deformations after cyclic exposure to hydrogen gas, leading to a linear relationship between sensitivity and hydrogen gas concentration over the measured concentration range of 0 to 2%. This was attributed to the suppression of phase transitions from the α to the β phase in Pd films, due to the reinforced film adhesion by the inserted Ti layer. Our results highlight the practical usability of Pd thin films as reliable and sensible hydrogen sensors, enabled simply by the insertion of a thin Ti buffer layer.     

Unique aspects of a shape memory polymer as the substrate for surface wrinkling

Typical bilayer wrinkle systems employ soft elastomers as the substrates. In contrast, shape memory polymers have recently emerged as attractive alternatives. Besides the shape fixing capability, shape memory polymers distinguish from elastomers in that they are rigid at room temperature, but experience significant modulus drop upon heating. We hereby report unique aspects of shape memory polymers as the wrinkle substrate utilizing a metallic thin film as the top layer. The feasibility to create both reversible and irreversible wrinkles (and diffraction colors) on a single substrate is demonstrated. Experimental conditions are identified to create crack free wrinkles and the impact of various experimental parameters on the wrinkle wavelength and amplitude is investigated. The results suggest that the wrinkle mechanics deviate notably from the existing theories established with elastomers as the wrinkle substrates. Thus, a new theory will need to be developed in the future, taking into account of unique thermomechanical properties of the shape memory substrate and possible plastic deformation of the thin film.     

Nanophase change for data storage applications

Phase change materials are widely used for date storage. The most widespread and important applications are rewritable optical disc and Phase Change Random Access Memory (PCRAM), which utilizes the light and electric induced phase change respectively. For decades, miniaturization has been the major driving force to increase the density. Now the working unit area of the current data storage media is in the order of nano-scale. On the nano-scale, extreme dimensional and nano-structural constraints and the large proportion of interfaces will cause the deviation of the phase change behavior from that of bulk. Hence an in-depth understanding of nanophase change and the related issues has become more and more important. Nanophase change can be defined as: phase change at the scale within nano range of 100 nm, which is size-dependent, interface-dominated and surrounding materials related. Nanophase change can be classified into two groups, thin film related and structure related. Film thickness and clapping materials are key factors for thin film type, while structure shape, size and surrounding materials are critical parameters for structure type. In this paper, the recent development of nanophase change is reviewed, including crystallization of small element at nano size, thickness dependence of crystallization, effect of clapping layer on the phase change of phase change thin film and so on. The applications of nanophase change technology on data storage is introduced, including optical recording such as super lattice like optical disc, initialization free disc, near field, super-RENS, dual layer, multi level, probe storage, and PCRAM including, superlattice-like structure, side edge structure, and line type structure. Future key research issues of nanophase change are also discussed.     

Quality enhancement of AZO thin films at various thicknesses by introducing ITO buffer layer

Due to the simultaneously superior optical transmittance and low electrical resistivity, transparent conductive electrodes play a significant role in semiconductor electronics. To enhance the electrical properties of these films, one approach is thickness increment which degrades the optical properties. However, a preferred way to optimize both electrical and optical properties of these layers is to introduce a buffer layer. In this work, the effects of buffer layer and film thickness on the structural, electrical, optical and morphological properties of AZO thin films are investigated. Al-doped zinc oxide (AZO) is prepared at various thicknesses of 100 to 300 nm on the bare and 100 nm-thick indium tin oxide (ITO) coated glass substrates by radio frequency sputtering. Results demonstrate that by introducing ITO as a buffer layer, the average values of sheet resistance and strain within the film are decreased (about 76 and 3.3 times lower than films deposited on bare glasses), respectively. Furthermore, the average transmittance of ITO/AZO bilayer is improved nearly 10% regarding single AZO thin film. This indicates that bilayer thin films show better physical properties rather than conventional monolayer thin films. As the AZO film thickness increases, the interplanar spacing, d₍₀₀₂₎, strain within the film and compressive stress of the film in the hexagonal lattice, decreases indicating the higher yield of AZO crystal. Moreover, with the growth in film thickness, carrier concentration and optical band gap (E_g) of AZO film are increased from 4.62?×?10¹⁹ to 8.21?×?10¹⁹ cm^?3 and from 3.55 to 3.62 eV, respectively due to the Burstein-Moss (BM) effect. The refractive index of AZO thin film is obtained in the range of 2.24–2.26. With the presence of ITO buffer layer, the AZO thin film exhibits a resistivity as low as 6?×?10^?4 Ω cm, a sheet resistance of 15 Ω/sq and a high figure of merit (FOM) of 1.19?×?10⁴ (Ω cm)^?1 at a film thickness of 300 nm. As a result, the quality of AZO thin films deposited on ITO buffer layer is found to be superior regarding those grown on a bare glass substrate. This study has been performed over these two substrates because of their significant usage in the organic light emitting diodes and photovoltaic applications as an enhanced carrier injecting electrodes.     

Enhancement of the crystalline quality of reactively sputtered yttria-stabilized zirconia by oxidation of the metallic target surface

Yttria-stabilized zirconia (YSZ) thin films were fabricated on glass substrates by direct current magnetron reactive sputtering. We found out that the crystalline quality of the YSZ film was improved by an oxidation process of the metallic target surface prior to the sputtering deposition process. It is speculated that, at the initial stage of the sputtering, the sputtered particles from the oxidized target surface form a layer with higher degree of crystallization on the substrate, compared with those particles from the metallic target surface. This crystallized layer can enhance the crystallization of the film deposited subsequently. Other sputtering conditions such as sputtering pressure, oxygen flow rate, substrate temperature, and Y₂O₃ content in the film were investigated, for optimization of the crystalline quality of the deposited YSZ film.     

Fabrication of nanocrystal ink based superstrate-type CuInS₂ thin film solar cells

A CuInS? (CIS) nanocrystal ink was applied to thin film solar cell devices with superstrate-type configuration. Monodispersed CIS nanocrystals were synthesized by a colloidal synthetic route and re-dispersed in toluene to form an ink. A spray method was used to coat CIS films onto conducting glass substrates. Prior to CIS film deposition, TiO? and CdS thin films were also prepared as a blocking layer and a buffer layer, respectively. We found that both a TiO? blocking layer and a CdS buffer layer are necessary to generate photoresponses in superstrate-type devices. The best power conversion efficiency (～1.45%) was achieved by the CIS superstrate-type thin film solar cell device with 200 and 100 nm thick TiO? and CdS films, respectively.     

Iron thin film magnetic recording tape by vacuum deposition

A thin-film video tape was formed by sputtering a protective layer on an iron thin film evaporated at an oblique incident beam angle on a plastic base film. The reproduction characteristics show that this tape is suitable for high density digital recording, with high output at short wavelength and low modulation noise. The area packing density can be raised to more than 130 M bits/in². Since the magnetic layer is easily damaged during tape-transport on VTR equipment, its durability requires improvement for practical comsumer products.