In recent years, highly sensitive and selective as well as cost-effective sensing and detection of bio-molecules (e.g. virus,
bacterial, DNA and protein) by MEMS/NEMS (Micro-/Nano Electro-Mechanical-System) structures have attracted extensive attention for its importance in clinical diagnostics, treatment, and various genome projects. Meanwhile, substantial research efforts have been spent on the improvement of sensitivity of BioMEMS structures. Among a variety of methods that have been investigated, surface modification by nanoparticles (NPs) turns out to be an attractive way, which provides a platform for the enhancement of the sensitivity for biosensor devices. However, conventional applications for surface modification were mostly implemented on microelectrodes. This paper is going to present the self-assembly surface binding of nano-gold particle and functional MWCNT on the cantilever sensor, which can easily facilitate biomolecular detection by resonance frequency shift. Its sensitivity can be improved due to the large binding area of probes to the targeting biomolecules. The LPCVD SiN low-stress rectangular cantilever is produced by laser micromachining and alkaline KOH
etching, which is a maskless, simple, convenient, fast-prototyping way to produce such cantilever sensor for biomolecular detection. The commercially available Atomic Force Microscopy (AFM) cantilevers are also used to verify the concept.
This paper compared the three different methods for determination of thin film modulus or MEMS applications: 1) scanning bending cantilever, 2) nanoindentation and 3) resonance frequency method. Surface profilometer was used to scan along the micro-machined cantilevers at different loads and produce the bending profile, from which the Youngss modulus can be extracted. Indentation profiled produced by Nano-indenter can deduce Young's modulus and hardness of the thin film materials. AFM vibrometer is used to detect the resonance of the thin film cantilever, from which the stiffness, and therefore the Young's modulus can be derived. The material properties of silicon nitride characterized by three methods are consistent and comparable with one another. The following MEMS materials: SiN, Ni, Ni/SiN bimorph, Nano-Diamond, SiC have been characterized and compared by using different method. Their advantages and disadvantages are also discussed.
Mechanical characterization is vital for the design of MEMS/NEMS. Many methods have been developed to measure the mechanical properties of materials; however, most of them are either too complicated, or expensive for industrial application, or not accurate. This paper describes a new characterization method to extract the mechanical properties of the materials that is simple, inexpensive and applicable to a wide range of materials. The beams of the material under tests, are patterned by laser micromachining and released by KOH etch. Surface profilometer is used to scan along μ-machined cantilevers and produce a bending profile, from which the Young’s modulus can be extracted. The errors due to initial curling and anticlastic (width) effect have been carefully studied. A new ANSYS FEA model is developed to evaluate the effects and test structure designs. SiNx, Ni, SiC and nanocrystal diamond cantilevers have been fabricated and their mechanical properties, e.g. Young’s modulus have been evaluated as 154+/-12GPa, 202+/-16GPa, 360+/-50GPa and 504+/-50GPa, respectively. These results are consistent with those measured by nano-indentation. Residual stress gradient has also been extracted by surface profilometer, which is comparable with the results inferred from Zygo interferometer measurements. It is also possible to extract plate modulus and Poisson ratio with minimal error achieved. This method can be extended to AFM or nanometer-stylus profilometer for NEMS mechanical characterization.
The in-plane motion of microelectrothermal actuator ("heatuator") has been analysed for Si-based and metallic devices. It was found that the lateral deflection of a heatuator made of a Ni-metal is about ~60% larger than that of a Si-based actuator under the same power consumption. Metals are much better for thermal actuators as they
provide a relatively large deflection and large force, for a low operating temperature, and power consumption. Electroplated Ni films were used to fabricate heatuators. The electrical and mechanical properties of electroplated Ni thin films have been investigated as a function of temperature and plating current density, and the process
conditions have been optimised to obtain stress-free films suitable for MEMS applications. Lateral thermal actuators have been successfully fabricated, and electrically tested. Microswitches and microtweezers utilising the heatuator have also been fabricated and tested.
Focused laser micromachining in an optical microscope system is used to prototype packages for optoelectronic devices and to investigate new materials with potential applications in packaging. Micromachined thin fims are proposed as mechanical components to locate fibers and other optical and electrical components on opto-assemblies. This paper reports prototype structures which are micromachined in silicon carbide to produce beams 5 μm thick by (1) laser cutting a track in a SiC coated Si wafer, (2) undercutting by anisotropic silicon etching using KOH in water, and (3) trimming if necessary with the laser system. This approach has the advantage of fast turn around and proof of concept. Mechanical test data are obtained from the prototype SiC beam package structures by testing with a stylus profilometer. The Youngs modulus obtained for chemical vapor deposited silicon carbide is 360 +/- 50 GPa indicating that it is a promising material for packaging applications.
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