Discussion Forum

Hi James,

Looks like we are in the same boat. I am also currently working on simulation for piezoresistive diaphragm pressure sensor.

Here is my thought. According to literature, the change in resistance is equal to piezoresistive coefficient (longitudinal) multiply with mechanical stress (MPa). We can obtain the mechanical stress from the Comsol simulation but not the piezoresistive coefficient. (Please correct me if I am wrong)

There are two papers you can refer to obtain the piezoresistive coefficient which are:
Smith, C.S. "Piezoresistance Effect in Germanium and Silicon." Physical Review 94, no. 1, 42-49, (April 1954)
Kanda. Y., "A Graphical Representation of the Piezoresistance Coefficients in Silicon, IEEE Transactions on Electron Devices, 1982. However you need to know what is the doping concentration, p type or n type, of your piezoresistors in order to get the correct piezoresistive coefficient value.

Here are things that we can do on Comsol. We can modify the resistivity of the silicon resistor to your desired doping level. Then we have to modify the electrical conductivity of the silicon in order to consider the conductivity change with the stress due to the piezoresistivity property of silicon: S=1e2[S/m]/(1+piezoresistive coefficient[Pa^-1]*solid.sz[Pa]. This equation is adopted from the recent published paper: Hs Saboonchi and D. Ozevin,"Optimization of Design Parameters of a Novel MEMS Strain Sensor Used for Structural Health Monitoring of Highway Bridges", Proceedings of the 2011 COMSOL Conference in Boston.

Hope to hear from you.

Best Regards,
Tan

The new version of the MEMS Module has 3 new dedicated user interfaces for piezoresistivity. Please see:
www.comsol.com/products/4.3/#mems
for more information.

Hello Tan,

I am still struggling with adding this Kanda factors to my model of piezoresistive pressure sensor.

Did you succeed to do it? and how?

thanks in advance,
Mohamed

Dear Mohamed,

I suppose it is a lot difficult to simulate piezoresistive effect in COMSOL version earlier than 4.3.
Once you upgraded beyond 4.3 version, you will find a new piezoresistive model available for your simulation.

I have done some piezoresistive simulation recently which was published in the COMSOL Rotterdam 2013 conference. Here is the link for more information:

www.br.comsol.com/paper/a-computational-approach-for-simulating-p-type-silicon-piezoresistor-using-four--15421

Hope this helps.

Best regards,
Tan

Dear Tan,

thanks for your fast reply. i will go through the paper.

is it possible to send me this publication too on mob@melexis.com


Evaluation of the piezoresistance properties of p-type silicon. / Tan, Teng ; McNeill, David ; Baine, Paul ; Montgomery, John ; Mitchell, Neil ; Wadsworth, Haydn; Strahan, Sam; Bailie, Ivan.

2012. Poster session presented at 23rd Micromechanics and Microsystems Europe, Ilmenau, Germany.

Thanks once more,
Mohamed

Hi,

I am new to COMSOL and am trying to obtain the resistance of a similar structure (a cylinder). Can you please tell me how I can obtain the resistance?