MEMS 001 - Combdrive eigenmodes

In this example case, eigenmode analysis is done for a MEMS comb-drive accelerometer.

Model definition

The comb-drive CAD model is illustrated below:

Simulation setup guide

Here, you’ll find a simplified guide on setting up this simulation in Quanscient Allsolve.

Step 1 - Create the geometry

1. In the Geometry section, start by importing a .gds file for the model.

   File download link: Comb-drive_Accelerometer.gds.

2. After importing, Allsolve recognizes 6 layers in the model. Perform the layer stackup:

   • Add 5 of the 6 suggested layers in this order: 11, 1, 12, 2, 23.

   • Enter layer thicknesses:

     Layer id	Layer thickness [μm]	Layer Z-position
     23	0.10	61.25
     2	30.00	31.25
     12	0.25	31
     1	30.00	1
     11	1.00	0

     Check that layer order and Z-positions match.

   • The excluded layer 63 is a substrate on which the MEMS device is fixed. In this simulation, the substrate is replicated by clamping the bottom-most surfaces of the device. Hence, the substrate layer can be safely excluded from the geometry.

Step 2 - Define the materials

Proceed to the Physics section to define the model materials.

Pick the Gold material from the materials library 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. Pick the simple 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.