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Resistor modelling help

Posted Nov 29, 2009, 7:45 a.m. EST 2 Replies

DEBASHIS MAJI
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Dear all,

I was doing a COMSOL modelling on joule heating of an electrical resistor in the MEMS Module using the Electro Thermal application mode. Initially I had faced some problem in meshing the structure since the thickness of my resistor is very less ( almost 0.1 micron) as compared to the length (5mm) and width (1mm) of it , however I meshed it in 2D and then extruded the mesh for 3D model. After putting the boundary conditions now I am facing some problems regarding the Solver. It is giving the following error:

Failed to find a solution:
Very ill-conditioned preconditioner. The relative residual is more than 1000 times larger than the relative tolerance.
Returned solution has not converged.

I had then tried again to model the resistor and have followed similar process as mentioned in the Prestressed Micromirror fro the meshing. I have meshed it successfully, then applied the boundary conditions where I am providing a voltage input on one end (bond pad) and ground at the other. But now i am getting this warning during solving:

Warning: Ill-conditioned preconditioner. Increase factor in error estimate to 4175.44997909695

Finally I need to get the temperature profile over the heater surface due to joule heating and the resistance.

I guess I am getting stuck in a very simple problem again and again. Kindly provide me with some tips to solve it.

Thanks
2 Replies Last Post Nov 16, 2010, 3:13 p.m. EST
COMSOL Moderator

Hello DEBASHIS MAJI

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Bao Ta
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Posted: 1 decade ago Nov 16, 2010, 11:35 a.m. EST
I am encountering similar problem.
Please help!

Bao
I am encountering similar problem. Please help! Bao
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Nov 16, 2010, 3:13 p.m. EST
Hi

meshing profles with larger than 1:1000 and worse 1:10'000 shape ratios are often very delicate. On the other side, do you expect the temperature to change much in the thickness direction ?
so do you really need several elements in the thickness ?
Even could you replace the bulk thin-film by a surface with a fictive thickness used in the equations?

These are the questions you should ask yourself.
Your model is probably far easier to solve by using a thin resistive film surface boundary condition

--
Good luck
Ivar
Hi meshing profles with larger than 1:1000 and worse 1:10'000 shape ratios are often very delicate. On the other side, do you expect the temperature to change much in the thickness direction ? so do you really need several elements in the thickness ? Even could you replace the bulk thin-film by a surface with a fictive thickness used in the equations? These are the questions you should ask yourself. Your model is probably far easier to solve by using a thin resistive film surface boundary condition -- Good luck Ivar

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