Tensile testing of microfabricated thin films

 Mechanical properties of titanium thin films of 0.5 μm thickness and aluminum thin films of 1.0 μm thickness, microfabricated by magnetron sputtering, were measured by using a novel tensile machine. These thin films are difficult to handle because they are fragile, so the thin film specimens were fabricated by using semiconductor manufacturing technology in a silicon frame to protect them. The test section of these specimens was 300 μm in width and 1400 μm in gauge length. By gripping the thin film specimen with a new device using a micrometer, it could be mounted on the tensile machine easily. The stress-strain diagrams of both thin films were measured continuously in the atmosphere at room temperature. The experimental results indicated that the titanium thin film and the aluminum thin film had a smaller breaking elongation although they had a larger tensile strength than bulk pure titanium and bulk pure aluminum, respectively. Received: 31.10.96/Accepted: 14.11.96     

A visual mold with variotherm system for weld line study in micro injection molding

In order to study the weld line developing process and its influence on mechanical properties in micro injection molding, a visual mold with variotherm system mold was designed and fabricated. In this mold, a visualization design and a rapid heating/cooling system were integrated, and specimens with different cross section shape and micro dimensions could be molded for weld line study. The building process for the visual and variotherm mold was presented and the experiments were executed. The specimens for weld line study of micro injection molding were produced applying different processing parameters. A problem of flash in molded specimens needs to be solved.     

Reinforcement of micro injection molded weld line strength with ultrasonic oscillation

Weld lines are the unfavorable defect not only in normal injection molding process but in micro injection molding process. In this study, polypropylene (PP) was chosen as the processing material and a micro dog-bone tensile test sample was selected as the objective part. The micro tensile part was prepared by the double gate injection mold. An ultrasonic generator was integrated in this mold in order to investigate the effect of ultrasonic oscillation on the micro injection molded weld line strength. The experiments were carried out for studying how the ultrasonic output power and the oscillation inducing time affect the weld line strength. Three output power levels (400, 600 and 800 W) and two inducing mode (Mode 1. the oscillation is induced from injecting moment to ejection moment; Mode 2. the oscillation is induced from injecting moment to packing procedure finishing) were set. The results show that ultrasonic oscillation has obvious influence on the weld line strength; Mode 2 always has better performance than Mode 1 for reinforcing the weld line strength; and when output power is 400 W the weld line strength is the highest. The mechanism of ultrasonic oscillation affecting the micro injection molded weld line was also analyzed by AFM (atomic force microscope) and polarized microscope.     

A mechanism influencing micro injection molded weld lines of hybrid nano filled polypropylene

Nano fillers reinforced polymer composites have been widely applied in microsystem technologies. As one popular micro fabrication technology, micro injection molding is playing the key role in manufacturing micro scale parts made of nano thermoplastics composites. As a defect in micro injection molding parts hard to avoid, the weld line causes detrimental mechanical and physical properties, particularly in case of nano filled composites. In this study, the hybrid carbon nanofibers (CNFs)/TiO₂ nano particles (1:1) filled polypropylene (PP) was prepared by inner melts mixing process with various weight contents(10, 20, 30 and 35 wt%). Micro tensile samples with weld lines for all composites were formed by micro injection molding process at constant processing conditions. Mechanical properties of micro weld lines were tested by tensile test characterizing method. The results show that comparison with neat PP, the samples with weld lines made of hybrid nano PP composites are showing lower tensile strength and elongation percent, but higher E modulus. As increasing nano filler contents, the tensile strength and elongation of micro weld line samples are decreasing, while the E modulus is improved considerably.     

Effect of micro tensile sample’s cross section shape on the strength of weld line in micro injection molding process

As a suitable mass and cost efficiency fabrication method, micro injection molding is doing a very good performance in micro plastic parts production. The mold design is an important part affecting micro parts properties. In this study, a micro injection mold with multi cavities of micro tensile bar is used. These micro cavities are fabricated by a micro milling process in different cross section shapes (semicircle R = 0.5 mm, equilateral triangle D = 0.3 mm, and trapezoid D = 0.336 mm t = 0.2 mm bottom angle = 95°). With an Arburg^® 320C injection molding machine, micro tensile test sample are prepared in different processing parameters so that a correlation between the cross section shapes with micro weld line strength in different conditions could be investigated by tensile test. Final results show that when the cross section shape is different, their corresponding weld line strength is also different. Equilateral triangle cross section is leading to strongest weld line, and then followed by trapezoid, semi-circle is the last. By analysis of these tensile test results, the quantitative factor a is defined as the ratio of perimeter to area of cross section shape, and higher a value is corresponding stronger weld line. After weld line strength comparison in different processing conditions, the results show that higher injection pressure induced to lower weld line strength whatever the cross section shape is. By higher mold and melt temperature, equilateral triangle cross section gives improved weld line strength. But mold and melt temperature affect weld line strength negative for other cross section shapes.     

Influence of processing parameters on micro injection molded weld line mechanical properties of polypropylene (PP)

As a hot fabrication technology for micro scale parts, micro injection molding is receiving increasing market attention. Improving mechanical properties of micro parts should be an important issue in the micro injection molding process. The relation between weld line strength in micro injection molding parts and processing parameters is investigated. A visual mold with variotherm unit is designed and constructed, in which the micro tensile specimen with weld line are prepared. Polypropylene (PP) is used as the research material in this study, and six processing parameters were chosen as investigating factors, which were melt temperature, mold temperature, injection pressure, packing pressure, ejection temperature and injection speed. In order to achieve optimized processing parameters and their order of significance, Taguchi experiment method was applied in this presented study. The prediction formulation of the strength of micro weld line was built up by multiple regression analysis based on Chebyshev orthogonal polynomial. The results showed the influencing significance order of parameters from strong to week separately are mold temperature, melt temperature, injection speed, ejection temperature, packing pressure and injection pressure. And the tolerance of micro weld line prediction formulation was found to be lower than 21% through confirmation experiments.     

模流分析在汽车注塑件设计中的应用

鉴于越来越多的注塑部件应用于汽车设计,而注塑产品的熔接线通常是强度最薄弱的区域,因此对熔接线的预测和优化非常重要。以某汽车前端模块为实例,阐述借助Moldflow快速找到改善熔接线质量的解决方案。经Moldflow分析发现,当浇口位置和数量不变时,优化产品的局部料厚可以明显提高熔接线的质量。     

基于鼓膜法的薄膜力学性能测试研究

采用自行研制的鼓膜实验装置,结合迈克尔逊激光干涉位移测量技术,获取薄膜的变形值与压力值之间的关系曲线,以实现薄膜试样力学性能的测试.对鼓膜法测试薄膜力学性能的现状做了评述;对实验原理以及装置设计进行论述;进行实验测量,并对实验结果进行有限元分析与仿真.对纯铝薄膜(纯度99.9％,厚为210 μm)进行鼓膜实验,测得其弹性模量E为68.3 GPa,与资料结果基本一致,说明研制的鼓膜实验装置测量薄膜力学性能方法切实可行.实验装置对于在微/纳机电系统(MEMS/NEMS)中广泛应用的薄膜材料的力学性能表征具有十分重要的意义.     

Low temperature deposited titanium boride thin films and their application to surface engineering of microscale mold inserts

Titanium boride thin films were deposited at low temperatures by balanced magnetron sputtering and inductively coupled plasma (ICP) assisted balanced magnetron sputtering. The chemical composition, surface morphology, structure, and mechanical properties of titanium boride thin films were characterized by X-ray photoelectron spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy, and instrumented nanoindentation. As compared to titanium boride films deposited by balanced magnetron sputtering, the increase in plasma density surrounding the substrate surface during film growth afforded by the ICP assist causes significant film densification and mechanical property improvement. The morphology of titanium boride thin films deposited onto microscale non-flat Ta substrates and their effectiveness as barrier coatings for microscale compression molding of Al was characterized by focused ion beam sectioning and SEM. The present results show the potential of low-temperature deposited, conformal, titanium boride thin films for engineering surfaces of microscale mold inserts for microscale pattern replication in reactive metals by compression molding.     

Development of AFM tensile test technique for evaluating mechanical properties of sub-micron thick DLC films

This paper describes mechanical properties of submicron thick diamond-like carbon (DLC) films used for surface modification in MEMS devices. A new compact tensile tester operating under an atomic force microscope (AFM) is developed to measure Young's modulus, Poisson's ratio and fracture strength of single crystal silicon (SCS) and DLC coated SCS (DLC/SCS) specimens. DLC films with a thickness ranging from 0.11 /spl mu/m to 0.58 /spl mu/m are deposited on 19-/spl mu/m-thick SCS substrate by plasma-enhanced chemical vapor deposition using a hot cathode penning ionization gauge discharge. Young's moduli of the DLC films deposited at bias voltages of -100 V and -300 V are found to be constant at 102 GPa and 121 GPa, respectively, regardless of film thickness. Poisson's ratio of DLC film is also independent of film thickness, whereas fracture strength of DLC/SCS specimens is inversely proportional to thickness. Raman spectroscopy analyses are performed to examine the effect of hydrogen content in DLC films on elastic properties. Raman spectra reveal that a reduction in hydrogen content in the films leads to better elastic properties. Finally, the proposed evaluation techniques are shown to be applicable to sub-micron thick DLC films by finite element analyses.     

薄膜热膨胀系数测试技术研究

热膨胀系数是薄膜的重要热学性能参数,也是薄膜热应力和残余应力计算分析过程中的关键数据.文章基于热诱导弯曲原理,分别采用单基片法和双基片法对氮化钛(TiN)和铝(Al)薄膜的热膨胀系数进行测试,并着重对双基片法的测试误差和适用性进行了分析.研究结果表明,薄膜在不同材质基底上弹性模量的差异是影响双基片法薄膜热膨胀系数测试精度的重要因素.当不同材质基片上薄膜弹性模量差异较小时,双基片法测得的热膨胀系数与单基片法所获结果基本一致;而当不同材质基片上薄膜弹性模量相差较大时,双基片法将不再适用.此外,文章结合薄膜的形貌、结构和残余应力表征测试,对TiN和Al薄膜热膨胀系数与其块体材料的差异进行了分析,结果显示残余压应力会导致薄膜热膨胀系数增大,而残余拉应力则具有相反的效果.     

Control of properties in injection molding by neural networks

Adequate control of product properties in injection molded plastics requires very accurate predictions. The problem is that the mechanical properties of these plastics, such as tensile modulus, are highly non-linear with the process variables, hence they are tough to predict. Consequently, up to date, injection molding machines include only closed loop control of process variables. Control of product properties is virtually non-existent.

We show here for the first time, that mechanical properties, such as tensile modulus values, can be predicted using Artificial Neural Networks quite accurately within a reasonable time. This is a major step towards an integrated self-taught control mechanism for the injection molded plastics industry.     

A study of the effect of the fabrication process on diffusion in a layered thin film

 A diffusion layer that is likely to be formed at the interfaces of the multi-layered thin film would affect its overall mechanical properties; the thinner the thin film, the more significant would be the effect. We measure the distribution of atoms and estimate the thickness of the diffusion layer at the vicinity of the interfaces among thin films of Al and SiO₂ and silicon wafer with the aid of Auger electron spectroscopy (AES). The effect of heat treatment after fabrication of the thin films on the diffusion is also investigated. Received: 28 December 1998/Accepted: 4 January 1999     

Optical micro-paddle beam deflection measurement for electrostatic mechanical testing of nano-scale thin film application to MEMS

The authors describe their design for a paddle-like cantilever beam sample to relieve non-uniform stress distribution in beam-bending tests of the mechanical properties of thin film applications to MEMS. We added the sample to a custom-designed system equipped with an electrostatic panel and optical interferometer. The system overcomes problems associated with using nano-indentation for testing, and reduces errors tied to the amount of contact force required to bend the beam. Accurate paddle cantilever beam deflection was obtained using a four-step phase-shifting process with a Michelson interferometer. Film strain was determined using a simple force equilibrium equation. Residual stresses were measured at −41.3 MPa for 150 nm silver film, −3.2 MPa for 150 nm gold film, and −16.8 MPa for 150 nm copper film. We observed residual stresses for copper films at different thicknesses. The results indicate high tensile stress forms during the early deposition stage for thin copper film due to grain coalescence, and a decrease in stress with an increase in film thickness. In copper films with thicknesses greater than 153 nm, lattice relaxation associated with the surface mobility of metallic atoms changed residual stress from tension to compression.     

A micro strain gauge with mechanical amplifier

A passive micro strain gauge with a mechanical amplifier has been designed, analyzed, and tested. The mechanical amplifier provides a high gain such that residual strain in thin films can be directly measured under an optical microscope. This strain gauge can be in situ fabricated with active micro sensors or actuators for monitoring residual strain effects, and both tensile and compressive residual strains can be measured via the strain gauge. It is shown that a very fine resolution of 0.001% strain readouts can be achieved for a micro strain gauge with a 500 μm-long indicator beam. Beam theories have been used to analyze the strain gauge with a mechanical amplifier, and the results were verified by a finite-element analysis. Experimental measurements of both polysilicon and silicon-riched silicon-nitride thin films fabricated by surface micromachining processes are presented     

Photo-lithographic patterning of biomimetic molecularly imprinted polymer thin films onto silicon wafers

This investigation describes the design and synthesis of molecularly imprinted polymers (MIPs) as patterned thin films, based on molecular modelling of functional monomer-template interactions and validation by NMR-spectroscopy. Several MIP thin films were prepared from a solution containing the template N-boc-l-phenylalanine and functional acrylic monomers at varying ratios with a cross-linker and initiator in a porogenic solvent. This solution was then spin-coated onto 3-(trimethoxysilyl)propyl methacrylate-functionalised silicon wafers and subsequently the film was photo-polymerised. After template extraction, the film thickness and topography of a methacrylic acid MIP was characterised with atomic force microscopy. A 4-vinylpyridine-MIP thin film was then made by depositing the pre-polymerisation solution on top of the methacrylic acid MIP by spin-coating. Photo-lithographic etching through a gold grid and extraction of non-polymerised solution from under the gold mask yielded a grid-patterned surface, in which two different MIPs alternate with dimensionality at the micro- or submicro-meter scale. Selectivity differences between the two MIP surfaces towards fluorescent template analogue N-dansyl-l-phenylalanine were documented using fluorescence microscopy. This side-by-side comparison on the same thin film allows fast and cost-effective assessment of the two very different MIP selectivities towards various biomolecules.     

MEMS中Ni-W合金薄膜力学性能的研究

研究了柠檬酸胺-1-羟基乙烷二膦酸（HEDP）镀液体系中Ni-W的力学性能。通过紫外曝光的光刻、电铸和注塑（UV—LIGA）技术制备出微拉伸试样和单轴微拉伸测试系统进行拉伸试验。结果表明：在Ni-W薄膜试样尺寸为5μm×50μm×100μm条件下,其杨氏模量约为100．4GPa,抗拉强度为1．96GPa,应变约为3．6％。     

Design and development of a novel paddle test structure for the mechanical behavior measurement of thin films application for MEMS

A new technique was developed for studying the mechanical behavior of thin films on substrate applications for micro-electro-mechanical system (MEMS). The test structure was designed on novel “paddle” cantilever beam coated thin film specimens with dimensions of a few hundred to 50 nm. This beam has a triangle shape that provides a uniform plane strain distribution. Standard clean room processing was used to prepare the paddle sample. The experiment can be operated using the electrostatic force to deflect the “paddle” cantilever beam and measure the mechanical response of the sample with surface deposited thin film. A capacitance measurement is used to observe the deflection of the cantilever plate on the other side of the sample with respect to the electrostatic force on the one side. The measured strain was then converted through this capacitance measurement to conduct mechanical behavior studies on the coated thin film. Both system performance experiments and calculations were studied to verify the design concepts. The residual thin film stress measurements were performed and compared with the calculated results from three different forces exerted on the “paddle” cantilever beam, including the force due to the film, compliance force, and electrostatic force.     

Interference Shaders of Thin Films

This paper presents a systematic study of light interferences at single thin films. Based on Fresnel's law, we have derived generic expressions of reflectance and transmittance for film interference, as well as specific expressions for free thin films and films coated on transparent or opaque objects. By combining film interference and volume absorption, we have obtained the reflectances and transmittances of film‐coated thin objects such as ribbons. Illumination models for all interference cases of single thin films are presented, and they have been implemented and tested for various structures and materials.     

Transparent thin thermoplastic biochip by injection-moulding and laser transmission welding

Recently microfluidic devices have emerged as a viable technology for the miniaturization of high throughput tools for analytical tasks related to structural biology such as screening of crystallization conditions and structural analysis. This work reports the manufacture of microfluidic chips in transparent thermoplastic polymers [poly(methylmethacrylate) (PMMA), and cyclic olefin copolymer (COC)] using two complementary technologies, injection moulding for the fabrication of the fluidic level and laser transmission welding for the sealing of the cover. A steel mould insert was produced by laser micro caving using a solid state laser radiation source (Nd:YAG, wavelength 1,064 nm). Fluidic chips of ~670 μm thickness comprising channels of 50 μm depth and width down to 50 μm were injection moulded in PMMA and COC. Joining of transparent thin cover film to the micro-injected fluidic level was performed by laser transmission welding using high power diode laser radiation (wavelength 940 nm) and an intermediate thin absorbing layer with a thickness of about several nanometers.