TiNi-based thin films for MEMS applications

In this paper, some critical issues and problems in the development of TiNi thin films were discussed, including preparation and characterization considerations, residual stress and adhesion, frequency improvement, fatigue and stability, as well as functionally graded or composite thin film design. Different types of MEMS applications were reviewed and the prospects for future advances in fabrication process and device development were discussed.Singapore-MIT Alliance (SMA

Nanocomposite Thin Films for both Mechanical and Functional Applications

The design methodology and realization of nanocomposite films aiming for mechanical (superhardness, toughness) and functional (optical, microelectronic) properties were discussed in this paper. Superhard TiCrCN and nc-TiN/a-SiNx films and super-tough nc-TiC/a-C(Al) films were prepared through co-sputtering method by optimal design of microstructure. The nanocrystalline silicon (nc-Si) passivated with a matrix of thermally grown silicon dioxide were prepared using implantation of Si into SiO₂ film, and showed improved photoluminescence and optical properties. Also discussed is the nano-composite design of thin film resistor with optimized temperature coefficient of resistivity.Singapore-MIT Alliance (SMA

Preparation and characterization of ZnO microcantilever for nanoactuation

Zinc oxide [ZnO] thin films are deposited using a radiofrequency magnetron sputtering method under room temperature. Its crystalline quality, surface morphology, and composition purity are characterized by X-ray diffraction [XRD], atomic force microscopy [AFM], field-emission scanning electron microscopy [FE-SEM], and energy-dispersive X-ray spectroscopy [EDS]. XRD pattern of the ZnO thin film shows that it has a high c-axis-preferring orientation, which is confirmed by a FE-SEM cross-sectional image of the film. The EDS analysis indicates that only Zn and O elements are contained in the ZnO film. The AFM image shows that the film's surface is very smooth and dense, and the surface roughness is 5.899 nm. The microcantilever (Au/Ti/ZnO/Au/Ti/SiO2/Si) based on the ZnO thin film is fabricated by micromachining techniques. The dynamic characterizations of the cantilever using a laser Doppler vibrometer show that the amplitude of the cantilever tip is linear with the driving voltage, and the amplitude of this microcantilever's tip increased from 2.1 to 13.6 nm when the driving voltage increased from 0.05 to 0.3 Vrms. The calculated transverse piezoelectric constant d31 of the ZnO thin film is -3.27 pC/N. This d31 is high compared with other published results. This ZnO thin film will be used in smart slider in hard disk drives to do nanoactuation in the future

HfB2-SiC-MoSi2 oxidation resistance coating fabricated through in-situ synthesis for SiC coated C/C composites

A brand new HfB2-SiC-MoSi2 coating was fabricated to protect carbon/carbon (C/C) composites with inner SiC coating from oxidation, which was prepared by in-situ synthesis. In this paper, the C/C substrate with the protection of the HfB2-SiC-MoSi2/SiC coating could resist oxidation in 1773 K air for 408 h. The double coating also presented expected oxidation protection performance at dynamic oxidation environment. In the test process, the surface coating was oxidized to form a self-sealing silicate glass layer containing HfO2 and HfSiO4, which could hinder crack propagation in coating

Microwave-assisted rapid preparation of hollow carbon nanospheres@TiN nanoparticles for lithium-sulfur batteries

Highly conductive titanium nitride (TiN) has a strong anchoring ability for lithium polysulfides (LiPSs). However, the complexity and high cost of fabrication limit their practical applications. Herein, a typical structure of hollow carbon nanospheres@TiN nanoparticles (HCNs@TiN) was designed and successfully synthesized via a microwave reduction method with the advantages of economy and efficiency. With unique structural and outstanding functional behavior, HCN@TiN-S hybrid electrodes display not only a high initial discharge capacity of 1097.8 mA h g−1 at 0.1C, but also excellent rate performance and cycling stability. After 200 cycles, a reversible capacity of 812.6 mA h g−1 is still retained, corresponding to 74% capacity retention of the original capacity and 0.13% decay rate per cycle, which are much better than those of HCNs-S electrodes

Probing resistive switching in HfO2/Al2O3 bilayer oxides using in-situ transmission electron microscopy

In this work, we investigate the resistive switching in hafnium dioxide (HfO2) and aluminum oxide (Al2O3) bilayered stacks using in-situ transmission electron microscopy and X-ray energy dispersive spectroscopy. Conductance of the HfO2/Al2O3 stack changes gradually upon electrical stressing which is related to the formation of extended nanoscale physical defects at the HfO2/Al2O3 interface and the migration and re-crystallization of Al into the oxide bulk. The results suggest two competing physical mechanisms including the redistribution of oxygen ions and the migration of Al species from the Al electrode during the switching process. While the HfO2/Al2O3 bilayered stack appears to be a good candidate for RRAM technology, the low diffusion barrier of the active Al electrode causes severe Al migration in the bi-layered oxides leading to the device to fail in resetting, and thereby, largely limiting the overall switching performance and material reliability

Effect of the surface morphology of solidified droplet on remelting between neighboring aluminum droplets

Good metallurgical bonding between neighboring droplets is essential in droplet-based 3D printing. However, although the mechanism of remelting has clearly been mastered, cold laps are still common internal defects of formed parts in uniform aluminum droplets deposition manufacturing, which is due to the overlook of the surface morphologies of solidified droplets. Here, for the first time, the blocking effect of ripples and solidification angles on the fusion between droplets is revealed. To investigate the detailed process of remelting, a 3D numerical model was developed, basing on the volume of fluid (VOF) method. Experiments and simulations show that the remelting process between neighboring droplets can be divided into two stages according to the transient contact between the second droplet and the substrate. In the first stage, a non-intuitive result is observed that cold laps can also be formed even if the remelting conditions are satisfied in theory. Ripples on the surface of previously-deposited droplet block its direct contact with the new-coming droplet. In the second stage, cold laps on bottom surface are formed due to incomplete filling of liquid metal when the solidification angle is greater than 90°. Furthermore, these cold laps are difficult to be completely avoided by improving the temperature parameters. To address this problem, a novel strategy of decreasing the thermal conductivity coefficient of the substrate is proposed. This method effectively promotes remelting between droplets by eliminating ripples and decreasing solidification angles

Geometry control of closed contour forming in uniform micro metal droplet deposition manufacturing

Micro metal droplet deposition manufacturing shows great potential applications in many industrial areas such as micro circuits printing, thin-wall metal parts, porous metal parts, and heterogeneous material parts. However, excessive overlapping of metal droplets in corners deteriorates the quality of printed parts. To solve this problem, the droplet center-to-center distance must always keep uniform and be in an ideal range. First, reasons of excessive overlapping in corners are analyzed and a mathematical model is proposed. Then droplet center-to-center distance is optimized and compensated according to corner angle of contour lines and number total of droplets so that the distance between adjacent droplets is proper. The coordinate of rearranged droplets is obtained by calculation. To verify this method, uniform solder droplets were ejected and deposited on a flat substrate. A series of deposition experiments were carried out. Some triangle contours were formed. The results show that quality of the formed parts had been significantly improved by using the proposed method