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Research Papers

Thermally Actuated Microswitches: Computation of Power Requirements for Alternate Heating Configurations

[+] Author and Article Information
Elham Maghsoudi

e-mail: emaghs1@lsu.edu

Michael James Martin

Department of Mechanical Engineering,
Louisiana State University,
Baton Rouge, LA 70803

Contributed by the Electronic and Photonic Packaging Division of ASME for publication in the JOURNAL OF ELECTRONIC PACKAGING. Manuscript received August 2, 2012; final manuscript received March 7, 2013; published online April 12, 2013. Assoc. Editor: Gamal Refai-Ahmed.

J. Electron. Packag 135(2), 021011 (Apr 12, 2013) (7 pages) Paper No: EP-12-1075; doi: 10.1115/1.4024012 History: Received August 02, 2012; Revised March 07, 2013

Steady state behavior of a thermally actuated RF MEMS switch in the open and closed positions is simulated using the governing thermal and structural equations. The switch is a bridge with a length of 250 microns, a width of 50 microns, and a thickness of 1 micron, in air with a pressure of 5 kPa. Simulations are performed for two different materials: silicon and silicon nitride. Three heating configurations are used: uniformly distributed heat, concentrated heat at the center of the top surface, and concentrated heat at the sides of the top surface. The steady state results show that the displacement at the center of the bridge is a linear function of the heat addition. This can be used to define a switch efficiency coefficient η*. In the uniformly distributed heat configuration, for a specific center displacement, a closed switch needs less heat at the top than an open switch. Adding concentrated heat at the center of the top surface yields a larger center displacement per unit heat addition than adding heat to the sides. When the heating is changed to a concentrated heat load at the center, the required heat is an order of magnitude less than heat added to the sides. Changing the contact length shows that variation in the length of the contact results in negligible changes in required heat to achieve a given displacement.

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Figures

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Fig. 1

The geometry and boundary conditions: (a) distributed heat in open switch; (b) concentrated heat at the center of the top surface in open switch; (c) concentrated heat at the sides of the top surface in open switch; (d) distributed heat in closed switch

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Fig. 2

The switch behavior schematic

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Fig. 3

Thermal steady state displacement versus heating rate for silicon and silicon nitride (open switch)

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Fig. 4

Thermal steady state displacement variations by heating rate for open and closed switch (silicon nitride)

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Fig. 5

Thermal steady state displacement for various heating configurations: (a) open-switch model; (b) closed-switch model

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Fig. 6

Midplane cross section along the x axis

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Fig. 7

Temperature distribution in the midplane: (a) distributed heat configuration open-switch model; (b) distributed heat configuration closed-switch model; (c) center-heating configuration open-switch model; (d) center-heating configuration closed-switch model; (e) side-heating configuration open-switch model; (f) side-heating configuration closed-switch model

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Fig. 8

Efficiency coefficient variation by the heating length

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Fig. 9

Midplane temperature difference distribution: (a) Tc = 295; (b) Tc = 305

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