Electrostatic Actuators with Intrinsic Stress Gradient

Chinthakindi, A.; Bhusari, D. M.; Dusch, B.; Musolf, J.; Willemsen, Balam A.; Prophet, Eric; Roberson, Mark W.; Kohl, Paul A.

doi:10.1149/1.1486454

Cited by 24 publications

(22 citation statements)

References 18 publications

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“…14 It was observed that as the length of the beam increases, the second-order polynomial description of the beam curvature becomes less accurate and deviations from the stress gradient model become more severe. 14 The movable electrodes with large intrinsic stress gradients created by the deposition of 0.2 and 0.3 m of hard gold have shown an initial curvature of polynomial order greater than 2. The hard gold thickness variation along the length of the movable electrode during electroplating would result in nonuniform stress gradient along the length leading to the curved beam with higher order curvature.…”

Section: Discussionmentioning

confidence: 99%

“…A model for calculating the deflection of the beam after release due to relief of the residual stress was presented in Part I of this study. 14 The initial curvature of the cantilever beam with a built-in stress gradient can also be modeled by assuming the beam to be made of two different materials. 13 An internal stress gradient can be created by using two materials with dissimilar coefficient of thermal expansion ͑CTE͒.…”

Section: Theorymentioning

confidence: 99%

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Electrostatic Actuators with Intrinsic Stress Gradient

Chinthakindi

Kohl

2002

J. Electrochem. Soc.

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Electrostatic actuators are used as voltage-controlled oscillators or resonators in high frequency applications. The change in deflection of a cantilever beam due to an applied voltage leads to change in capacitance between the plates of the beam. However, the range of operation of these devices is limited due to the nonlinear nature of the applied electrostatic forces as the cantilever beam moves. The pull-down instability of the beam limits the travel distance of elastically suspended parallel-plate electrostatic actuators to about one-third of the initial gap distance. The movement of curved actuators under application of an electrostatic force is investigated. The initial curvature of the movable electrode was established by using a built-in stress gradient in the metallic cantilever-beam. A two-dimensional, semi-analytical, finite difference model was used to simulate the behavior of the devices. Three-dimensional modeling was also performed to understand the movement of the cantilever beams. The pull-down voltage of the beams was studied as a function of initial tip deflection, shape of the movable electrode, and anchor type. The stable range of operation of these cantilever beams before pull-down was found to be smaller than one third of the tip deflection. After pull-down, the movable electrode was found to ''uncurl'' upon further application of voltage. This was attributed to the higher order curvature of the movable electrode with large built-in stress gradient.Microelectromechanical systems ͑MEMS͒ is a technology which leverages the existing state-of-the art integrated circuit ͑IC͒ fabrication technology and enables the batch fabrication of miniature mechanical structures, devices, and systems. 1-5 This technology exhibits advantages such as cost reduction through batch fabrication, device-to-device consistency, and performance advancements from dimensional downscaling leading to size and weight reduction. Several MEMS devices, which have been successfully commercialized, include microsensors, micro-optics, pressure sensors, accelerometers, and ink-jet nozzles. 2-4 Emerging applications for MEMS are in the areas of optics, microfluidics, and wireless communications. 2 Most of the MEMS designs use electrostatic, piezoelectric, thermal, pneumatic, or magnetic actuation to move the micromachined parts. 2,3 Due to the availability of large electrostatic forces and high energy densities, electrostatic actuation has advantages as compared to other actuation mechanisms. In most electrostatic actuators, the balance between the electrostatic force and the mechanical restoring force controls the deflection of the electrodes. Upon application of the voltage, a continuous movement of the electrodes is desirable for tuning applications. 6-10 Unfortunately, the range of continuous motion of the electrostatically actuated beam is limited due to the presence of nonlinear electrostatic forces. This leads to the well-known ''pull-down'' instability in these devices, which prevents the stable positioning of the electrode...

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Section: Discussionmentioning

confidence: 99%

Section: Theorymentioning

confidence: 99%

Electrostatic Actuators with Intrinsic Stress Gradient

Chinthakindi

Kohl

2002

J. Electrochem. Soc.

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“…The total intrinsic stress in the beam can be divided into a constant mean stress σ 0 and a gradient stress σ 1 . Assuming a linear stress profile within the beam, σ 0 and σ 1 can be expressed as [12,13]…”

Section: Analysis Of the Intrinsic Stressmentioning

confidence: 99%

Characterization and optimization of dry releasing for the fabrication of RF MEMS capacitive switches

Liu

Oberhammer

et al. 2007

J. Micromech. Microeng.

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This paper discusses fabrication aspects of photoresist sacrificial layers for fabricating metal bridges of capacitive radio frequency (RF) microelectromechanical systems (MEMS) switches. First, reflow of the photoresist layer after lithography is investigated for reducing mechanical fracture of the metal layer by smoothing the edges of the sacrificial layer. Second, the dry-etch releasing process of the structures in an O 2 plasma has been investigated by identifying suitable etching parameters. The findings in this paper reveal that the mechanical performance of the released bridges strongly depends on the etch parameters. It is shown that especially the etching power affects the mean stress and the stress gradient in the bridge, which results in buckling and deformed bridge shape for an etching power above 500 W, drastically increasing the actuation voltage and reducing the down-state capacitance. Finally, the paper presents a suitable parameter set for the release etching of capacitive MEMS metal bridges.

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“…The assumption of linear stress distribution, i.e. constant stress gradient, is frequently employed in the literature [10,14,[16][17][18], which is especially proper for very thin films such as the 1-lm-thick nickel film of this study:…”

Section: Residual Stress Gradients and Their Characterizationmentioning

confidence: 99%