Search

Solid-state reactions between Er and Ge (001) under different processing conditions were investigated. Under normal rapid thermal processing (RTP) in high-purity N2 ambience, the Er–Ge film formation was Fcontaminated_ with Er2O3 even at low temperature annealing. Ti capping of Er films before RTP delayed Er2O3 formation with the Ti cap acting as a sacrificial layer for the Er underneath. Vacuum annealing of Er films significantly reduced Er2O3 formation even after higher temperature annealing. High quality Er–Ge films can thus be formed through solid-state reaction of Er and Ge if oxygen contamination from annealing ambient during RTP is controlled. The Er–Ge phase had low sheet resistance values averaging 3 to 4 V/sq. ErGe1.8 was formed from the solid-state reaction between Er and Ge(001) in vacuum. D 2005 Elsevier B.V. All rights reserved.

A process to stabilise the formation of NiGe using Zr alloying engineering approach was investigated. The NiGe film maintained continuity up to 600 °C with NiGe phase stable up to 700 °C. Secondary ion mass spectroscopy and transmission electron microscopy characterisations showed that a thin ZrO x layer was formed on top of NiGe. The ZrO x layer acted as a capping layer to NiGe. As a result, the morphology and phase formation of NiGe were stabilised. We propose Ni(Zr) alloy as a promising material for germanides metallisation contacts in metal-oxide-semiconductor field-effect transistors (MOSFETs).

Intermetallic compounds (IMCs) are present in microelectronic solder interconnects as a result of interfacial reaction between the solder and the metallization materials. Their mechanical properties are of great interest for the prediction of joint reliability of electronic packages. In this work, thin film Ni 3 Sn 4 IMCs were formed by co-sputtering of Sn and Ni, followed by annealing at different temperatures. Elasticity modulus and hardness of the films were investigated by nano-indentation. It was found that measured hardness decreased with increasing residual tensile stress in the film. The elasticity modulus of the Ni 3 Sn 4 thin films was measured to be around 134 GPa by nano-indentation. The fracture toughness of these Ni 3 Sn 4 thin films varied considerably with the annealing temperature. It ranged from 2.11 ± 0.15 MPa m 1/2 for 100 °C annealing to 5.75 ± 0.25 MPa m 1/2 for 200 °C annealing. Densification during annealing is believed to be the cause of the increase in toughness.

We studied the charge mobility characteristics of a series of new poly (p-phenylenevinylene) PPV derivatives, with different substituents (CF3, OCH3, F) on their biphenylyl side chains, using a conventional time of flight (TOF) photoconductivity technique. The TOF hole transients at 295 K showed a non dispersive nature of transport and the dependence of hole mobility with applied electric field follows Pool–Frenkel relation. The present results indicate that the charge mobility characteristics can be fine-tuned by varying the size of the substitutents on the biphenylyl side chains, which is in good agreement with the PLED device performance.

The failure mechanisms of SnAgCu solder on Al/Ni(V)/Cu thin-film, underbump metallurgy (UBM) were investigated after multiple reflows and high-temperature storage using a ball shear test, fracture-surface analysis, and cross-sectional microstructure examination. The results were also compared with those of eutectic SnPb solder. The Al/Ni (V)/Cu thin-film UBM was found to be robust enough to resist multiple reflows and thermal aging at conditions used for normal production purposes in both SnAgCu and eutectic SnPb systems. It was found that, in the SnAgCu system, the failure mode changed with the number of reflows, relating to the consumption of the thin-film UBM because of the severe interfacial reaction between the solder and the UBM layer. After high-temperature storage, the solder joints failed inside the solder ball in a ductile manner in both SnAgCu and SnPb systems. Very fine Ag3Sn particles were formed during multiple reflows in the SnAgCu system. They were found to be able to strengthen the bulk solder. The dispersion-strengthening effect of Ag3Sn was lost after a short period of thermal aging, caused by the rapid coarsening of these fine particles.

The commercial application of rare earth magnets has been in part held back by their poor corrosion resistance. As part of e!orts to overcome this problem two types of nickel coatings were electroplated on the surface of Nd 2 Fe 14 B substrates, one from an acidic plating solution and the other from an alkaline solution. The corrosion characteristics of both coatings were evaluated both by electrochemical potentiodynamic polarisation and by physical exposure to high-humidity environments. The results showed that both coatings enhanced the corrosion resistance of substrate. However, both the degree of protection a!orded by the coating and the strength of its adhesion to the substrate strongly depended on the chemical composition of the original plating solution. The coating plated from the acidic solution provided a high degree of protection against both aqueous and atmospheric corrosion, whilst that plated from the alkaline solution behaved only marginally better than the bare substrate. It was postulated that the poor performance of the coatings plated from the alkaline bath could have been due to the spontaneous formation of a passive oxide "lm between the Nd 2 Fe 14 B substrate and the nickel coating. ( 2001 Elsevier Science B.V. All rights reserved.

All-polymer dielectric elastomer actuators have been microfabricated using a high aspect ratio molding process. The actuators are multilayer beams of 3 conductive and 2 dielectric elastomer layers. By applying an electrical potential between two of the neighboring conductive electrodes, a stress is generated. This leads to an asymetric stress in the beam and, therefore, bending. Bidirectional actuation is possible by changing which electrodes the potential is applied across. A 1000 µm long actuator demonstrated a tip displacement as high as 350 µm at 1 kV with a static electrical power consumption of 10 µW.

We elucidate the reason for preferential bending along the long edge in thin rectangular bilayers in which one of the layers is isotropically strained. While this preference has been observed previously, the physical basis for this preference has not been understood. We find that the bending direction is determined by the existence of doubly curved regions at the curled edges, which lower the energy. This energy difference between "spiral" and "cigar" shapes increases with aspect ratio.

Dielectric elastomer actuators (DEAs) have been demonstrated for meso- and macro-scale applications, but only a few devices have been shown at the micro-scale, the most common of which have been diaphragms that bulge out of the plane of the wafer. Microscale DEAs would be of value in a wide range of small devices, including micro-robots, micropumps, and micro-optical systems. An additional advantage of miniaturizing is a reduction in the required driving voltage from kilovolts to tens of volts because the layers are thinner. However, fabrication of micro-scale DEAs remains challenging, due in part to the fact that the vast majority of macro-scale materials and/or fabrication methods cannot be adapted to the micro-scale. On the micro-scale, the elastomers must be deposited as thin films, they must be patternable, and they must be compatible with the other materials used during fabrication, such as sacrificial layers. The realization of compliant electrodes must also be handled in a new way. To fully realize the potential of micro-DEAs, it would also be desirable to develop fabrication procedures for integrating the micro-scale DEAS with complementary metal-oxidesemiconductor (CMOS) driver circuits and other micro-electro-mechanical systems (MEMS). This article addresses the progress that has been made thus far in making microfabricated DEAs, as well as the challenges and the key areas in which additional research needs to be pursued.

The effects of layer thickness and stiffness on multilayer bending actuator performance were investigated with an analytical mechanical model. Performance was evaluated in terms of curvature, blocked force, and work. Multilayer device designs corresponding to dielectric elastomer actuator, ionic polymer metal composite, and conjugated polymer structures were examined. Normalized plots of the performance metrics as functions of relative layer thickness and stiffness are presented that should allow initial, starting-point estimates for designs for particular applications. The results show that to achieve high curvature, layer thickness and stiffness may need to be set above or below particular bounds, or varied together, depending on the device configuration; often there is a broad plateau of combinations that work equally well. There is a conflict between achieving high bending and high force: the former requires the device to behave as much as possible like a simple bilayer with optimal ratios of thickness and modulus, while the latter requires thicker layers and shows little dependence on their moduli. Finally, to maximize work there are areas in the thickness-modulus plane that should be avoided, these areas varying with the configuration in sometimes surprising ways.

The solid-state reaction between Ti-capped Er thin film and Ge(001) was investigated. The germanide film formed had a smooth morphology with the phase identified as ErGe1.5. The film is highly textured with ErGe1.5 (1100) //Ge(001). ErGe1.5 has a resistivity value ~18 muOmega.cm. The Ti cap was able to delay the erbium oxide formation to higher temperature.

Intermetallic compounds (IMC) in a solder joint play an important role in the joint reliability for electronic packages. Experimental observation shows there is a clear trend of intermetallic fracture when the layer thickness increases. However there has been so far not much work carried out on the direct measurement of IMC fracture toughness in the thinfilm form. The main reason is that the thickness of these intermetallic compounds at solder joints is only of the order of micra, which makes the direct measurement very difficult. Conventional shear test or butt pull test on a solder joint could not reveal the fracture strength of intermetallics because the fracture path is often very complicated involving more than one fracture mechanism. The current work employed a new testing approach of directly measuring the fracture strain and fracture toughness of around one micron thick Sn-Cu intermetallic compounds by controlled buckling test. Single phase Cu& or Cu’Sn was prepared by co-sputtering Cu and Sn of the right atomic ratio followed by appropriate annealing. The substrates used were polymeric thin plates. During experiment the thin film intermetallics fractured by channeling cracks at the maximum strain site. By monitoring the formation of channeling, critical strain at which the cracking initiates can be calculated by large displacement beam theory. Based on the critical fracture strain, the mode I fracture toughness of the intermetallic compounds can be calculated. It was found that the toughness of the two.types of thin film intermetallics between Cu and Sn is around 55-65 Jim'. This new approach is also applicable to the fracture toughness measurement of other types of brittle thin films.

Intermetallic compounds (IMCs) are formed as a result of interaction between solder and metallization to form joints in electronic packaging. These joints provide mechanical and electrical contacts between components. The knowledge of fracture strength of the IMCs will facilitate predicting the overall joint property, as it is more disposed to failure at the joint compared to the solder because of its brittle characteristics. The salient feature of this paper is the measurement of the fracture toughness and the critical energy-release rate of Cu3Sn and Cu6Sn5 intermetallic thin films, which is the result of the interaction between Sn from the solder and Cu from the metallization. To achieve the objective, a controlled buckling test was used. A buckling test in the current work refers to one that displays large transverse displacement caused by axial compressive loading on a slender beam. The stress and strain along the beam can be easily calculated by the applied displacement. Fracture-toughness values of Cu3Sn and Cu6Sn5 are 2.85 MPa √m ± 0.17 MPa √m and 2.36 MPa √m ± 0.15 MPa √m, respectively. Corresponding critical energy-release rate values are 65.5 J/m2 ± 8.0 J/m2 and 55.9 J/m2 ± 7.3 J/m2, respectively. The values obtained were much higher than the ones measured in bulk intermetallic samples but correlated well with those values obtained from conventional fracture-toughness specimens when fracture was confined within the intermetallic layers. Hence, the controlled buckling test is a promising fast and effective way to elucidate mechanical properties of thin films. Accepted version

All-polymer dielectric elastomer actuators have been manufactured using a micro-molding fabrication process. The actuators are multilayer beams made of three conductive and two dielectric elastomer layers. By applying an electrical potential between two of the neighboring conductive electrodes, a stress is generated, which leads to an asymmetric axial strain and, therefore, bending. Bidirectional actuation is achieved by changing the pair of electrodes across which the potential is applied. A 100??m wide, 40??m thick, and 1000??m long actuator demonstrated tip displacement as high as 318??m at 1.1?kV with an electrical power consumption of 10??W. Experimental results validate a two-dimensional ANSYS model that is also used to explore the effects of further decreasing layer thickness and relative electrode thickness on DEA performance.

Meandering beams, crenellated surfaces, and zigzag-shaped electrodes are employed as compliant elements in microscale applications ranging from springs attached to proof masses in microelectromechanical systems (MEMS) to stretchable electrodes in flexible electronics and dielectric elastomer actuators. An understanding of how the meander shape affects the stiffness of these structures would permit preliminary design without the necessity of fabricating or running simulations on each case. In this paper, we present general guidelines for designing meandering cantilevers, showing how the amplitude, angle, length, and thickness affect both the axial and bending stiffnesses. Simple analytical expressions are derived, and the results are compared with those from numerical simulations and experimental measurements. The more complex case of a stiff thin film overlying a crenellated elastomer is also simulated.

PDMS films of 10 μm thickness can be patterned within 30 min by combining dry etching to achieve substantially vertical sidewalls with wet etching to achieve high etch rates and to protect the underlying substrate from attack. Dry etching alone would have taken 5 h, and wet etching alone would produce severe undercutting. In addition, using either technique alone produces undesirable surface morphologies. The mask used during etching is critical to a successful patterning outcome. E-beam evaporated Al was found to work well, adhering strongly to oxygen-plasma-treated PDMS and holding up well during both dry and wet etching. To prevent wrinkling of the PDMS, a fast deposition rate should be used. (Some figures in this article are in colour only in the electronic version)

The phase and texture of of Er-germanide formed on Ge(001) through a solid-state reaction between Er thin films and Ge(001) via rapid thermal annealing (300-600°C) were investigated. It was found that amorphous ErGe 1.2 forms at 300°C, followed by the formation of AlB 2 hexagonal ErGe 1.5 at 400-500°C and then orthorhombic ErGe 1.8 at 600°C. X-ray diffraction pole figure measurement revealed that the ErGe 1.5 5 films formed at 400-500°C consist predominantly of epitaxial grains with an orientation relationship of ErGe 1.5 (1100)[0001]//Ge(001)[011], although the presence of a considerable amount of epitaxial grains with an orientation relationship of ErGe 1.5 (1012)[0110]//Ge(001)[010] was also observed in the film formed at 400°C. The germanide film formed at 600°C was found to consist of randomly orientated orthorhombic ErGe 1.8 grains. Among the three different germanide phases, ErGe 1.5 showed minimum resistivity values as low as ∼ 19 μΩ cm.

Texture of NiGe on Ge(001) and its evolution with formation temperature have been investigated. Pole figure investigation showed that NiGe formed by rapid thermal annealing of Ni(35nm)∕Ge(001) largely consists of epitaxial grains with orientation relationships: NiGe(111)[01¯1]∕∕Ge(001)[110],NiGe(020)[001]∕∕Ge(001)[100],NiGe(201)[102¯]∕∕Ge(001)[110],NiGe(211)[011¯]∕∕Ge(001)[110],NiGe(112)[201¯]∕∕Ge(001)[110], and NiGe(210)[001]∕∕Ge(001)[100]. For NiGe formed at 400 °C, NiGe(111)[01¯1]∕∕Ge(001)[110],NiGe(020)[001]∕∕Ge(001)[100],NiGe(201)[102¯]∕∕Ge(001)[110], and NiGe(211)[011¯]∕∕Ge(001)[110] were found to be the preferred orientations, while NiGe formed at 600 °C was dominated by NiGe grains with NiGe(111)[01¯1]∕∕Ge(001)[110] orientation. The increasing dominance of the grains with NiGe(111)[01¯1]∕∕Ge(001)[110] orientation is attributed to the minimum lattice mismatch with this orientation.

We report near-field scanning optical microscopy (NSOM) studies of 300‐nm-wide ZnO nanopatterns fabricated by micromolding in capillary technique using a sol-gel route. Atomic force microscopy and scanning electron microscopy show that the patterns are continuous with uniform linewidths. Simultaneous topography and optical signal collected in NSOM scans exhibit nanoscale photoluminescence intensity distribution in the ZnO nanopatterns. The nanoscale spectral mapping shows very broad defect-induced green-yellow-red luminescence bands, at room temperature, when excited with a 514.5‐nm Ar-ion laser. Our analyses demonstrate that spatially resolved ZnO luminescence features with an optical resolution of ⩽300nm can be obtained with NSOM while operating in collection mode, and underscore the need to couple nanoscale physical characterization with functional properties at the same scale.

Data Storage Institute, National Universityof Singapore, Singapore 119260For high density magnetic recording, it is necessary to protect the magnetic layer from wear and corrosion with a thin carbonovercoat. On ultrasmooth disk substrates, magnetron sputtering is still the preferred technique because it can provide protectivecarbon layers as thin as 4 nm. Degradation of the magnetic layer occurs in the atmosphere and during hard disk operation; thus,the carbon-based overcoat functions as an indispensable component in protecting the essential magnetic layer. Moreover, carbonovercoat quality plays a vital role in the strong demand to reduce the flying height between a disk and read/write head, which inturn enhances the density of recording. The impact of sputtering conditions on the quality of deposited amorphous hydrogenatedand nitrogenated carbon was assessed by the electrochemical measurement of the linear polarization resistance. The film’spolarization resistance was correlated to its porosity, and a statistical method was developed to allow easy comparison of resultsin the data analysis. The results obtained suggest that the best overcoats are formed with a substrate voltage bias of 2120 V, avery low deposition pressure of 0.9 mTorr, a dc magnetron sputtering power of 2.8 W/cm

Air humidity as well as various gases present in the environment or evolved from the hard disk file has a detrimental effect on the lifetime of the hard disk. The corrosion properties of unprotected Co Cr Pt magnetic layer and covered by a carbon 78 12 10 overcoat have been studied using a three-electrode electrochemical corrosion test. Potentiodynamic scanning and direct current (DC) polarization resistance techniques have been used with 0.1 M NaCl solution at different pH values. Time-of-flight secondary ion mass spectroscopy (TOF-SIMS) and scanning electron microscopy (SEM) imaging of the corrosion sites revealed development of corrosion products along the scratch lines originating from the previous surface polishing and texturing step. Capillary retention of water vapor along the scratch valleys enhances creation of corrosion sites. The SEM images showed the build-up of hillocks formed by migrated Co and its hydroxide and chloride compounds on the carbon surface. A lower solubility and decrease in corrosion potential of Co were observed when the pH of the electrolyte was increased from 5.5 to 11. The void structure of the carbon overcoat enables the penetration of water vapor and dissolution of Co in the magnetic layer. A driving force for the Co ion migration through the porous structure of a carbon film is a galvanic electrochemical reaction between the Co alloy and the carbon overcoat. The carbon overcoat slows down the lateral growth of the Co corrosion products. The provoked corrosion of the magnetic layer had not led to a macroscopic change in the film magnetic properties, measured by vibrating sample magnetometer. 2002 Elsevier Science B.V. All rights reserved.