Hi all,
I'm new in using COMSOL, but I have already worked through a bunsh of tutorials. My aim is to model a micromirror membrane which consists of many layers (in the final type at least 25 layers) with different stress characteristics. This membrane additionaly consists of a conductive layer thus electrostatic actuation with an additional counterelectrode should be possible.
To get started with this problem I reduced the problem to a two layer cantilever in 2D. The cantilever deflects due to stress in one of the two layers. This works well up to values of about 100e6 Pa for Sigma_x (Material is GaAs) in one layer. If i further increase the stress, inverted mesh elements occur and I don't really understand what's the meaning of this and how I can get rid of this problem. Nevertheless I went on in modeling with 100e6 for which the problem could be solved. I set up all the boundary conditions for the Solid Stress & Strain, Moving Mesh and Electrostatics package. I just wanted to get a feeling of the dependency between the total displacement and the applied voltage (which I set up between a counter electrode and the top surface of the cantilever). I followed the given Models in the MEMS package "comb drive 2d" and "ale cantilever beam 2d". The difference to the latter is, that I now have two layers and my material is prestressed as i already mentioned.
The curious thing now is that an increase in voltage leads to an increase of the airgap between my cantilever and the counter electrode. I would assume them to attract each other. Another point is the order of magnitude which you need to see even small effects in a change of deflection (more than 1000 V at a spacing of only 2.5-5 µm of the two electrodes and a thickness of the cantilever of only 2 µm).
I think something must be definitely wrong with the boundary conditions, but I really don't know what could be wrong. I attached the model maybe someone can help me there by having a look on it.
If I forgot some important additional information let me know.
Thanks for your help!
I'm new in using COMSOL, but I have already worked through a bunsh of tutorials. My aim is to model a micromirror membrane which consists of many layers (in the final type at least 25 layers) with different stress characteristics. This membrane additionaly consists of a conductive layer thus electrostatic actuation with an additional counterelectrode should be possible.
To get started with this problem I reduced the problem to a two layer cantilever in 2D. The cantilever deflects due to stress in one of the two layers. This works well up to values of about 100e6 Pa for Sigma_x (Material is GaAs) in one layer. If i further increase the stress, inverted mesh elements occur and I don't really understand what's the meaning of this and how I can get rid of this problem. Nevertheless I went on in modeling with 100e6 for which the problem could be solved. I set up all the boundary conditions for the Solid Stress & Strain, Moving Mesh and Electrostatics package. I just wanted to get a feeling of the dependency between the total displacement and the applied voltage (which I set up between a counter electrode and the top surface of the cantilever). I followed the given Models in the MEMS package "comb drive 2d" and "ale cantilever beam 2d". The difference to the latter is, that I now have two layers and my material is prestressed as i already mentioned.
The curious thing now is that an increase in voltage leads to an increase of the airgap between my cantilever and the counter electrode. I would assume them to attract each other. Another point is the order of magnitude which you need to see even small effects in a change of deflection (more than 1000 V at a spacing of only 2.5-5 µm of the two electrodes and a thickness of the cantilever of only 2 µm).
I think something must be definitely wrong with the boundary conditions, but I really don't know what could be wrong. I attached the model maybe someone can help me there by having a look on it.
If I forgot some important additional information let me know.
Thanks for your help!
