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Stress on Silicon Wafer

Posted Jun 12, 2020, 11:49 a.m. EDT Structural & Acoustics, MEMS & Piezoelectric Devices, Materials Version 5.5 6 Replies

Marc Malek
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I have a model of a silicon wafer with a labyrinth to thermally isolate the center from a section of the outside. I am wanting to know how strong the wafer will be. I initially set up a 3d model by importing a CAD file, but the degrees of freedom were too massive so i have switched to a 2D model so I could do calculations faster. However, it seems any mass placed on the chip center whatsoever causes a huge displacement, which I think has something to do with the dimensional units but I can't find out where I have gone wrong. Furthermore, the chip center is displacing in the direction opposite of where is should be (up instead of down). I am a self-taught COMSOL user and will try to answer questions as best I can, and I understand this is a simple problem so thank you for your time.

Marc

6 Replies Last Post Jun 18, 2020, 11:39 a.m. EDT
Dave Greve Certified Consultant
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Posted: 4 years ago Jun 12, 2020, 2:17 p.m. EDT

I don't see what you say you see. I see plausible displacements due to gravity in the right direction.

Try using the gravity node or try exerting point forces.

Be sure to activate geometric nonlinearity.

I don't see what you say you see. I see plausible displacements due to gravity in the right direction. Try using the gravity node or try exerting point forces. Be sure to activate geometric nonlinearity.
Marc Malek
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Posted: 4 years ago Jun 12, 2020, 5:00 p.m. EDT

That is strange, because when i plot the maximum and minimum displacement, is around 3 meters in the positive z direction, and I would expect the movement to be in the negative z direction. I have attached an image of my results.

Thank you again for your time, Marc

That is strange, because when i plot the maximum and minimum displacement, is around 3 meters in the positive z direction, and I would expect the movement to be in the negative z direction. I have attached an image of my results. Thank you again for your time, Marc
Jeff Hiller COMSOL Employee

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Posted: 4 years ago Jun 12, 2020, 5:23 p.m. EDT

Hi Marc,

I don't have the software here to open your file, but I am going to guess that you're looking at modes, so that magnitude and orientation have no meaning.

Best,

Jeff

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Jeff Hiller
Hi Marc, I don't have the software here to open your file, but I am going to guess that you're looking at modes, so that magnitude and orientation have no meaning. Best, Jeff
Dave Greve Certified Consultant
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Posted: 4 years ago Jun 12, 2020, 8:43 p.m. EDT

I only ran the static analysis, which makes perfect sense. The weird things are in the linear buckling analysis, which I have not had occasion to use.

I only ran the static analysis, which makes perfect sense. The weird things are in the linear buckling analysis, which I have not had occasion to use.
Marc Malek
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Posted: 4 years ago Jun 18, 2020, 11:35 a.m. EDT

When I run the static analysis (assuming that is the stationary step), the displacement I get is 0. Is this study step just using the intial values, and can I change that?

When I run the static analysis (assuming that is the stationary step), the displacement I get is 0. Is this study step just using the intial values, and can I change that?
Marc Malek
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Posted: 4 years ago Jun 18, 2020, 11:39 a.m. EDT

Using the gravity node does not have this issue, so I will just avoid using the added mass domain condition.

Thank you, Marc

Using the gravity node does not have this issue, so I will just avoid using the added mass domain condition. Thank you, Marc

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