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Microcantilevers fabricated by microelectromechanical system processes were used to study the residual stresses in the film/substrate systems. Aluminum films were deposited on silicon nitride substrates by thermal evaporation at room and elevated temperatures, and residual stresses were characterized from the deflection profiles of the Al/SiNx microcantilevers. The Al/SiNx microcantilever beam made of room-temperature-deposited Al film was found to deflect toward the substrate side, which in turn resulted in compressive residual stress in the film. In contrary, the microcantilever of Al film deposited at 105 °C was found to deflect toward the side of Al film when the thickness ratio of film to substrate was greater than 0.31 and the residual film stresses were tensile. The axes with zero bending strain component and zero stresses, i.e., the bending and the neutral axes in the film/substrate system were also investigated. The results can be applied to the arm of the atomic force microscope to characterize its deflection and stresses.
This study presents the mechanical and electrical properties (including elastic modulus, yield strength and electrical resistance) of PDMS/CNTs nanocomposites. The elastic modulus and yield strength were determined from tensile tests. In addition, a high resistance meter was used to measure the electrical resistances of the PDMS/CNTs nanocomposites. The test specimens of nanocomposites were manufactured using the thermoforming method. There were two recipes used during the thermoforming process: 100 °C for 1 hour, and 150 °C for 15 minutes. The mixtures of PDMS and CNTs were stirred by ultrasonic instrument to prevent polymerization. A feeler gap was used to define the thickness of the specimens. Therefore, the thickness could be controlled within the range of ∼100 μm. Four different kinds of specimens were investigated, including pure PDMS, 1.0 wt%, 2.0 wt% and 4.0 wt% CNTs polymeric composites. As for the l00°C recipe, the elastic modulus of pure PDMS, 1.0 wt%, 2.0 wt%, and 4.0 wt% CNTs were 1.05MPa, 1.17MPa, 1.10MPa and 1.35MPa, respectively. A for the l50°C recipe, the elastic modulus of pure PDMS, 1.0 wt%, 2.0 wt% and 4.0 wt% CNTs were 1.32MPa, 1.42MPa, 1.43MPa, and 1.54MPa. The differences of electrical resistance of PDMS/CNTs nanocomposites at two different conditions and the microstructures composed of the mixtures are also described in this article.
This study has successfully demonstrated a novel tensile testing approach to mount the thin film test specimen onto the MEMS instrument using microfabrication process. The MEMS instrument consists of thermal actuator, differential capacitance sensor, supporting spring. The thermal actuator applies tensile load on the test specimen to characterize the Young's modulus and the residual stress of thin films. As compare with the existing approaches, the problems and difficulties resulting from the alignment and assembly of thin film test specimens with the testing instrument can be prevented. Furthermore, the parylene passivation technique of MEMS fabrication process allows the changing of testing film materials easily. In application, the present approach has been employed to determine the Young's modulus and the residual stress of Al films.
The mechanical properties of thin film are very critical for the performance of MEMS devices. Since Poly-silicon film is of great use in MEMS, this study investigates the surface modification by various plasma treatments to finely tune the chemical and mechanical properties of poly-silicon film. Various plasma treatments, including H2, O2, and NH3, were implemented to modify the original Si-Si film bonding, Young's modulus, and hardness of poly-silicon film. These were significant Si-O, Si-OH/Si-H and Si-NH2/Si-N bonds formed after O2, H2 and NH3 plasma treatment, respectively. According to the H analysis from SIMS depth profile of, the thickness of surface modified layer would be ranged from 50 to 120 nm. In summary, the surface modification with H2 plasma can reduce the elastic modulus of poly-silicon film for about 32.3%; moreover, the following vacuum annealing will further reduce the elastic modulus for about 60.2%. Therefore, surface modification with an adequate plasma treatment would be an effective method to change the chemical and mechanical properties of poly-silicon film.
This study reported a novel method for tuning thin film mechanical properties by means of plasma surface modification. In order to demonstrate the feasibility of this approach, various plasma treatments, including O2, H2, NH3 atmospheres, were implemented to tune the Young's modulus and residual stress of SiO2 film. Without plasma treatment, the static tip deflection of 200μm long SiO2 cantilever was 9.01μm. After treatment with H2, O2, and NH3 plasma, the tip deformation of the treated cantilevers became 10.22μm, 8.28μm, and -6.84μm respectively. The Young's modulus of the SiO2 cantilever without plasma treatment was 76.3GPa. After treated with H2, O2, NH3 plasma, the Young's modului of those treated cantilevers became 70.8 GPa, 74.7 GPa, and 71.4 GPa, respectively. Hence, after H2 and NH3 plasma treatment, the equivalent elastic modulus of SiO2 cantilever could be reduced about 7%.
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