MEMS 002 - Combdrive static deflection

What you’ll learn

• How to extend the combdrive model from MEMS 001 with an air box and couple Solid mechanics, Electrostatics, and Mesh deformation for electrostatic actuation.
• How to apply large displacement coupling, run a voltage sweep, and visualize displacement and electric field results.

Prerequisites: complete MEMS 001 — Combdrive eigenmodes first — this example extends that model with an air box and electrostatic actuation.

In this example case, static deflection is simulated in a MEMS comb-drive accelerometer.

Model definition

The same model is used for the comb-drive as in MEMS 001 - Combdrive EigenModes. Here, an air box is added around the comb-drive:

Simulation setup guide

Step 1 - Build the geometry

1. Import the comb-drive model exactly as in MEMS 001 - Combdrive EigenModes.

2. After the comb-drive model is imported, build the air box around it:

   Name	Element type	Center point	Size	Rotation
   box	Box	X: 0	X: 1250e-6	X: 0
   		Y: 100e-6	Y: 750e-6	Y: 0
   		Z: 30.65e-6	Z: 111.5e-6	Z: 0

Step 2 - Define variables and materials

1. Go to the Common sidebar.

2. Define a variable:

   Name	Description	Expression
   voltage	voltage applied to the fixed comb	20

3. Proceed to the Physics section.

4. Assign the Air material to the air box.

5. Assign Gold to the square top plate.

6. Assign Silicon dioxide to the thin silicon dioxide layers:

   

7. Assign Monocrystalline silicon to the thick monocrystalline silicon layers:

   

Step 3 - Define the physics

Proceed to the Physics section to define the physics.

For static deflection, the Solid mechanics, Electrostatics and Mesh deformation physics are required.

Physics 1 - Solid mechanics

• As solid mechanics target, select all volumes except the air box.
  • Add the target as a region with name Solid domain.
• Add Clamp.
  • As target, select the bottom silicon dioxide layers.
• Add Large displacement.
• Add Electric force.

Physics 2 - Electrostatics

• Leave the electrostatics target as empty, letting it default to all volumes.
• Add Constraint, and name it as Voltage.
  • As target, select the fixed comb volumes.
  • Set constraint value to voltage.
• Add Constraint, and name it as Ground.
  • As target, select the movable comb and top plate volumes.
  • Set constraint value to 0.
• Add Large displacement.

Physics 3 - Mesh deformation

• As mesh deformation target, select the region Electric domain.
• Add Constraint.
  • As target, select the region Solid domain.
  • As value, use expressions as in the image below.
    • 

Your simulation physics are now defined.

Step 4 - Generate the mesh

Proceed to the Simulations section to generate the mesh:

• Create a new mesh.
• Set Autorefine to Disabled.
• Under Customizations, add Mesh extrusion with all volumes as target.
• Set the sublayer counts as necessary.
• Click Apply & mesh.

Step 5 - Simulate

In the Simulations section, create a new simulation:

• Analysis type
  • Static
• Solver mode
  • Iterative solver
• Relative residual tolerance
  • 1e-6
• Mesh
  • Select the mesh you created in Step 4.
• Input
  • Add voltage sweep with override expression linspace(0, 1, 10).
• Output
  • Add u field output.
  • Add v field output.
  • Add E field output.

Run the simulation.

Step 6 - Visualize

In the Simulations section, add visualizations to see field output results.

To see u field results, for example:

• Add a visualization.
• On the visualization, add u (real).
• On u, add Warp.
• Set warp scale factor to 1e-3.