Comb drive

QuickField simulation example

Comb-drive is a MEMS device that utilize electrostatic forces acting between two electrically conductive combs connected to the voltage source.

Engineering question
How to find electrostatic force in MEMS comb drives?

Engineering answer
Set up a 3D QuickField Electrostatics problem for a MEMS comb drive structure and evaluate electrostatic force from computed field results.

Typical applications
MEMS comb actuators, electrostatic microdrives, micro-positioning structures

• Download simulation files (files may be viewed using any QuickField Edition).

Problem Type electrostatics.

Geometry 3D extrusion.
Comb thickness L_z = 40 um.
Gap between fingers d = 2.5 um.

Given
Relative permittivity of air ε = 1,
Relative permittivity of comb ε = 10,
Potential difference ΔU = 40 V

Task
Find the attraction force per tooth width and compare with 2D analytical solution:^*
f = 0.5 · εε₀ · n·L_z · U² / d,
where n is number of air gaps.

Solution
The simulation model includes only one pair of teeth (two air gaps, n=2). The Dn=0 boundary condition is applied on the plane of symmetry.

Results
Analytical solution (force per one pair of electrodes, n=2):
f = 0.5 · 1 · 8.854e-12 · 2·40e-6 · 40² / 2.5e-6 = 2.27e-7 N.

^* Comb drive, from Wikipedia, the free encyclopedia.

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