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poor convergence in MEMS electromechanical switch
Posted Apr 23, 2015, 4:57 p.m. EDT MEMS & Nanotechnology, MEMS & Piezoelectric Devices, Studies & Solvers Version 5.0 2 Replies
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Greetings:
This is a grossly simplified form of a 3D model I'm doing of an electromechanical switch using the MEMS module.
There's a cantilever which is at zero bias, a "gate" electrode which is biased to a non-zero voltage, and a contact (which for purposed here is at a zero charge state). With a nonzero bias the cantilever is attracted to the gate electrode, bending, but then it makes physical contact with the contact electrode and the gap remains finite, preventing full collapse. If the bias were ramped further, eventually the gap at the gate electrode would also collapse, but this would take very high force.
In any case, I don't get anywhere close to this. I can ramp the bias up to on order 0.1 volts, and then it fails to converge.
I have two approaches. One is a standard "stationary" study in which the gate voltage is specified directly. The other is where the voltage is ramped up proportional to the square of the ramping parameter.
There is a 20 nm gap between the cantilever and the contact electrode but the total deflection at the tip maxes out at 3.6 pm (or milli-nm, if you prefer). So any geometric complexities are still minimal at this point.
I've tried to get this working for days and I'm afraid I'm missing something silly.
Anyone else have experience with these structures?
Link: www.dropbox.com/s/uvkue4m2xqv526j/Comsol_22Apr2015_ComsolGeometry_2d_clean.mph?dl=0
The electrostatics, which converge only at low bias, are shown here:
i.imgur.com/IKKxXG6.png
This is a grossly simplified form of a 3D model I'm doing of an electromechanical switch using the MEMS module.
There's a cantilever which is at zero bias, a "gate" electrode which is biased to a non-zero voltage, and a contact (which for purposed here is at a zero charge state). With a nonzero bias the cantilever is attracted to the gate electrode, bending, but then it makes physical contact with the contact electrode and the gap remains finite, preventing full collapse. If the bias were ramped further, eventually the gap at the gate electrode would also collapse, but this would take very high force.
In any case, I don't get anywhere close to this. I can ramp the bias up to on order 0.1 volts, and then it fails to converge.
I have two approaches. One is a standard "stationary" study in which the gate voltage is specified directly. The other is where the voltage is ramped up proportional to the square of the ramping parameter.
There is a 20 nm gap between the cantilever and the contact electrode but the total deflection at the tip maxes out at 3.6 pm (or milli-nm, if you prefer). So any geometric complexities are still minimal at this point.
I've tried to get this working for days and I'm afraid I'm missing something silly.
Anyone else have experience with these structures?
Link: www.dropbox.com/s/uvkue4m2xqv526j/Comsol_22Apr2015_ComsolGeometry_2d_clean.mph?dl=0
The electrostatics, which converge only at low bias, are shown here:
i.imgur.com/IKKxXG6.png
2 Replies Last Post Apr 29, 2015, 4:38 p.m. EDT
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Posted:
10 years ago
One comment: I seem on this example to get better convergence (still poor) with the direct solver versus the iterative solver, but the direct solver is more memory-intensive, and therefore doesn't scale as well to a 3-d structure.
I can suppress the mechanical solution by applying a fixed zero displacement on all domains. Then the electrostatics solve very quickly.
I rounded the corners on all linear elastic materials in order to avoid electric field singularities. The mesh engine seems to handle the curved boundaries very well: the mesh looks good, and potential profiles look exceptionally smooth, as do electric field magnitude profiles.
I can suppress the mechanical solution by applying a fixed zero displacement on all domains. Then the electrostatics solve very quickly.
I rounded the corners on all linear elastic materials in order to avoid electric field singularities. The mesh engine seems to handle the curved boundaries very well: the mesh looks good, and potential profiles look exceptionally smooth, as do electric field magnitude profiles.
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Posted:
10 years ago
Here's a simplified simplified version with the following changes:
1. the electrostatic domain was converted to a rectangle only including the region directly between the gate electrode and the cantilever
2. the gap between the gate electrode and the cantilever was increased to reduce coupling between electrostatics and mechanics
3. I modified the tip so physical contact between the cantilever and the contact electrode is just a point
4. I reduced the gap between the cantilever and the contact electrode so deflection is less at the point of contact.
It's very simple now but still doesn't work well.
I'm attaching the file. There may have been an issue with my previous mph file. having to do with an incorrect installation beyond my control, which I hopefully fixed.
www.dropbox.com/s/fbquj86z6mkqrlz/Comsol_28Apr2015_ComsolGeometry_2d_simple.mph
1. the electrostatic domain was converted to a rectangle only including the region directly between the gate electrode and the cantilever
2. the gap between the gate electrode and the cantilever was increased to reduce coupling between electrostatics and mechanics
3. I modified the tip so physical contact between the cantilever and the contact electrode is just a point
4. I reduced the gap between the cantilever and the contact electrode so deflection is less at the point of contact.
It's very simple now but still doesn't work well.
I'm attaching the file. There may have been an issue with my previous mph file. having to do with an incorrect installation beyond my control, which I hopefully fixed.
www.dropbox.com/s/fbquj86z6mkqrlz/Comsol_28Apr2015_ComsolGeometry_2d_simple.mph