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Main >> Applications >> Sample problems

MEMS thermal actuator - QuickField simulation example

The MEMS thermal actuator is made of polysilicon.

Engineering question

How to calculate displacement of a MEMS thermal actuator from Joule heating?

Answer
Calculate current and Joule losses with DC conduction, transfer the losses to heat transfer for the temperature field, then transfer thermal expansion to stress analysis for the actuator displacement.

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Typical applications
MEMS thermal actuators, electrothermal microactuators, polysilicon actuator structures

MEMS thermal actuator

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Simulation problem

Problem Type
Plane-parallel problem of DC conduction, heat transfer and stress analyses.

Geometry
Foil thickness is 1 micron.
MEMS thermal actuator Microelectromechanical system thermal actuator is made of polysilicon Cold arm Hot arm GND V+ 470 μm 495 μm 30 μm 2 μm 10 motion

Given
Voltage applied: V+ = 5 V
Electrical resistivity: 2.3*10-5 Ohm*m
Thermal conductivity: 150 W/(m*K)
Thermal expansion coefficient: 2.9*10-6 1/K
Young's modulus: 169 GPa, Poisson's ratio: 0.22.

Task
Calculate the electric current and Joule heat losses distribution, temperature and linear mechanical displacement.

Solution
To calculate the electric current and Joule losses distribution the DC conduction problem is simulated. Then the results are used in the thermal analysis study to calculate the temperature distribution. Finally, the stress analysis problem is simulated to calculate the related thermal deformation.

Results

Electric potential distribution
mems thermal actuator voltage

Electric current distribution
mems thermal actuator current

Joule heat losses distribution
mems thermal actuator losses

Temperature distribution
mems thermal actuator temperature

The actuator mechanical displacement is 17 um
mems thermal actuator displacement

* Reference: Marin Hristov Hristov, Tihomir Borisov Takov, Ivelina Nikolaeva Cholakova, Krassimir Hristov Denishev, Vladimir Emilov Grozdanov, Dobromir Georgiev Gaydazhiev, Design and investigation of a thermal actuator, ELECTRONICS 2008, 24-26 September, Sozopol, BULGARIA

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