MEMS 001 - Combdrive EigenModes

Model definition

Eigenmode analysis of a MEMS comb-drive accelerometer is considered. Below is an image of the comb-drive CAD model from above.

Simulation setup guide

Step 1 - Create the geometry

In the Model section, import the accelerometer.gds file and perform the layer stackup. The file can be downloaded here (add download location here). After importing, Allsolve should recognize 6 separate layers in the model.

• Add 5 of the 6 suggested layers in this order: 11, 1, 12, 2 and 23 (exclude layer 63).
• Next, check that the layers are in the same order as in the image below.
• Then, set the Thickness for each layer as in the image below.
• Check that Units are in Micrometer (μm).
• Click Confirm model changes.

Step 2 - Define the materials

Proceed to the Properties section to define the model materials.

Pick the Gold material from the materials database and assign it to volume 10. Click Apply.

Next, pick the Silicon dioxide material from the materials database. As the target, select volumes 1, 2, 3, 7 and 8. Click Apply.

Finally, pick the Monocrystalline silicon material from the materials database. As the target, select volumes 4, 5, 6 and 9. Click Apply.

At this point, your model should look like in the image below (Translucent model with Silicon dioxide volumes highlighted in red).

Step 3 - Define the physics

Proceed to the Physics section to define the physics.

For eigenmode analysis, Solid mechanics is the only physics required. Under Solid mechanics, add Clamp. As the clamp target, select volumes 1, 2 and 3. Click Apply.

Step 4 - Set up the mesh

Proceed to the Simulations section to set up the mesh:

• Create a new mesh with Mesh quality set to Expert settings.
• Set Used mesher as Basic and scale factor as 0.25.
• Scroll down and click + next to Mesh extrusion. As target volume, click Select all to select all volumes. Now, the mesh extrusion tool should recognize five separate layers.
• Set the sublayer counts as in the image below.
• Click Apply & mesh.

Step 5 - Simulate

In the Simulations section, create a new simulation with the following options:

• Set Analysis type as Eigenmode.
• Set Number of requested modes as 5.
• Set Target eigenfrequency as 0.
• Set Solver mode as Iterative solver and set Relative residual tolerance as 1e-6.
• As the Mesh, select the mesh you just created.
• Next to Output, click + and add Displacement field u as a Field output.
  • Let the u field target default to the whole geometry.
  • Under Parameters, enable Skin only. This should drastically reduce visualization loading times.

Run the simulation by clicking Not Run.

Tip: Skin only

Enabling Skin only for an output field forces the field to be generated only on the outer skin surfaces of the volumes, instead of the whole mesh. This can reduce visualization loading times.

Step 6 - Visualize

In the Simulations section, add a visualization to see u field results:

• Under Results, next to Visualizations, click +.
• On the visualization, add u (real) and Warp.
• Set the warp Scale factor to 1e-3.
• Click Apply.

You can step through the different eigenmodes in the top-right corner of Model view. Below is eigenmode 6 post-processed as a gif.