1,721,038 research outputs found
A systematic approach to process selection in MEMS
Full text linkA systematic approach is developed to select manufacturing Process Chains for the generic elements of a MEMS device. A database of MEMS Process Chains and their attendant process attributes is developed from an extensive review of the literature, and used to construct Process Attribute charts. The performance requirements of MEMS beams and trenches are translated into the same set of Process Attributes. This allows for a screening of the Process Chains to obtain a list of candidate manufacturing methods. This method is illustrated in a brief design example
MEMS actuators and sensors: observations on their performance and selection for purpose
No full textThis paper presents an exercise in comparing the performance of microelectromechanical systems (MEMS) actuators and sensors as a function of operating principle. Data have been obtained from the literature for the mechanical performance characteristics of actuators, force sensors and displacement sensors. On-chip and off-chip actuators and sensors are each sub-grouped into families, classes and members according to their principle of operation. The performance of MEMS sharing common operating principles is compared with each other and with equivalent macroscopic devices. The data are used to construct performance maps showing the capability of existing actuators and sensors in terms of maximum force and displacement capability, resolution and frequency. These can also be used as a preliminary design tool, as shown in a case study on the design of an on-chip tensile test machine for materials in thin-film form
Comparison of microtweezers based on three lateral thermal actuator configurations
No full textThermal actuator-based microtweezers with three different driving configurations have been designed, fabricated and characterized. Finite element analysis has been used to model the device performance. It was found that one configuration of microtweezer, based on two lateral bimorph thermal actuators, has a small displacement (tip opening of the tweezers) and a very limited operating power range. An alternative configuration consisting of two horizontal hot bars with separated beams as the arms can deliver a larger displacement with a much-extended operating power range. This structure can withstand a higher temperature due to the wider beams used, and has flexible arms for increased displacement. Microtweezers driven by a number of chevron structures in parallel have similar maximum displacements but at a cost of higher power consumption. The measured temperature of the devices confirms that the device with the chevron structure can deliver the largest displacement for a given working temperature, while the bimorph thermal actuator design has the highest operating temperature at the same power due to its thin hot arm, and is prone to structural failure
Modelling and fabrication of microspring thermal actuator
No full textA new spring type microelectrothermal actuator with greatly enhanced displacement is proposed. Instead of using a single long chevron actuator, several chevrons are folded into a number of sections to become a spring-like actuator. Insulating beams with a very low thermal expansion coefficient are used to form cross-linkages thereby avoiding displacement in the x-direction. As the actuator is heated up under bias, thermal expansion of the material leads to displacement in the y-direction only. FEMLAB simulation shows that for each device, the displacement linearly increases with increasing arm length. By introducing folded arms, the device size is substantially decreased whilst still delivering a large displacement, which is proportional to the number of arms. Hence the displacement that can be achieved by thermal actuation is significantly increased. For instead, the displacement for chevron with l=400µm is ~17µm and the size of ~800_50µm. A spring actuator consists of four chevrons with l=100um, it delivers a 12.5µm displacement with a size of only ~220_100µm. As comparing with a single chevron actuator with l=100µm, the folded spring delivers almost 4 times the displacement. A 2-mask stages process is used to fabricate the device. A freestanding electroplated Ni spring arms without the cross-linkages has already been fabricated
Young's modulus of electroplated Ni thin film for MEMS applications
No full textThe Young's modulus of an electroplated nickel (Ni) thin film suitable for microelectromechanical applications has been investigated as a function of process variables: the plating temperature and current density. It was found that the Young's modulus is approximately 205 GPa at plating temperatures less than 60 °C, close to that of bulk Ni, but drastically drops to approximately 100 GPa at 80 °C. The inclusion of ammonium and sulphate ions by hydrolysis is believed to be responsible for the sharp drop. The Young's modulus of 205 GPa is for a Ni film plated at J=2 mA/cm2 and it decreases to 85 GPa as the plating current density is increased to 30 mA/cm2. The results imply that at low current density, the plating speed is slow and there is sufficient time for the as-plated Ni atoms to rearrange to form a dense coating. At high currents, the plating speed is high, and the limited mass transport of Ni ions leads to a less dense coating
Three types of planar structure microspring electro-thermal actuators with insulating beam constraints
No full textA new concept of using an electrically insulating beam as a constraint is proposed to construct planar spring-like electro-thermal actuators with large displacements. On the basis of this concept, three types of microspring actuators with multi-chevron structures and constraint beams are introduced. The constraint beams in one type (the spring) of these devices are horizontally positioned to restrict the expansion of the active arms in the x-direction, and to produce a displacement in the y-direction only. In the other two types of actuators (the deflector and the contractor), the constraint beams are positioned parallel to the active arms. When the constraint beams are on the inner side of the active arms, the actuator produces an outward deflection in the y-direction. When they are on the outside of the active arms, the actuator produces an inward contraction. Finite-element analysis was used to model the performances. The simulation shows that the displacements of these microspring actuators are all proportional to the number of the chevron sections in series, thus achieving superior displacements to alternative actuators. The displacement of a spring actuator strongly depends on the beam angle, and decreases with increasing the beam angle, the deflector is insensitive to the beam angle, while the displacement of a contractor actuator increases with the beam angle
Uniformity control of Ni thin film microstructures deposited by through-mask plating
No full textThe thickness uniformity within a specimen and the cross-sectional profiles of electroplated individual Ni microstructures have been investigated as a function of the electroplating conditions. It was found that the uniformity and profiles of microstructures could be controlled by varying the process conditions. A uniform thickness distribution and microstructures with flat profiles could be obtained at optimal plating conditions of 8 mA/cm2 and 60°C. Above this optimal plating current density, the microstructure has a rabbit-ears profile, and the thickness of a narrow microstructure is thicker than that of wide ones. Below this current density, the microstructure has a cap-like cross-sectional profile, and a narrow structure is thinner than wide ones. Increasing the plating temperature enhances the nonuniformity, whereas other process parameters have insignificant effects on it. The current crowding observed in patterned specimens is responsible for the rabbit-ears profile of individual microstructures, while a combination of the fluidic friction on the sidewall of the photoresist and the electrophoresis of the ions in the solution are believed to be responsible for the abnormal cap-like profile of individual microstructures and the thinning effect on narrow microstructures
Effects of process conditions on properties of electroplated Ni thin films for microsystem applications
No full textThe properties of electroplated Ni thin films have been systematically investigated as a function of plating temperature and current density. The resistivity and its temperature coefficient remain unchanged on varying the process conditions, though the values of these properties are approximately three times and one-half of those of bulk Ni material, respectively. Optimal conditions of J = 2 mA/cm(2) and 60 degrees C were found for stress-free Ni thin films. The modulus of elasticity of the Ni films is as high as that of bulk Ni (210 GPa) when plated at high temperature and low current density, and then decreases linearly with increasing plating current density, down to 85 GPa at a plating current density of 30 mA/cm(2). It is believed that higher plating rates produced fine-grained structures of low density, leading to a high tensile stress and low modulus of elasticity, while lower plating rates produced a dense material with a modulus of elasticity close to that of bulk Ni and a compressive residual stress. A clear correlation between modulus of elasticity and the stress exists, which reveals that a material under high tensile stress may posses a low modulus of elasticity, and is not suitable for fabrication of microelectromechanical systems devices
Normally closed microgrippers using a highly stressed diamond-like carbon and Ni bimorph structure
No full textA normally closed microgripper with a radius of curvature of 18–50 µm using a diamond-like carbon (DLC) and stress free electroplated Ni bimorph structure has been demonstrated. The large curvature in the fingers of the microgrippers is due to the high compressive stress of the DLC layer. The radius of curvature of the figures can be adjusted by the thickness ratio, and the closure of the devices can also be adjusted by varying the finger length. This device works much more efficiently than other bimorph structures due to the large difference in thermal expansion coefficients between the DLC and the Ni layers. Preliminary electrical tests have shown these microgrippers can be opened by 60°–90° at an applied power of <20 mW
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