Materials
The pressure sensor consists of a silicon die with an enclosed cavity. The pressure sensor is bonded onto a cylindrical steel plate during the packaging process. COMSOL Multiphysics includes a Material Library with many predefined material properties. A predefined material is used for the steel plate, but the silicon is set up as a user-defined material, as for this model isotropic material parameters are used to enable direct comparison with the results in Practical MEMS. The cavity also needs ‘material’ properties (to define the relative permittivity) and a user-defined material is used to set the relative permittivity to 1 in this region.
Material 1
1
In the Materials toolbar click Blank Material .
2
In the Settings window for Material locate the Material Contents section. In the table, enter the following settings:
Property
Name
Value
Relative permittivity
epsilonr…
11.7
Young’s modulus
E
170[GPa]
Poisson’s ratio
nu
0.06
Density
rho
2330
3
In the Label text field enter Silicon.
By default the first material is applied to all domains. Some of these selections will be overridden as other materials are added.
Steel AISI 4340 (mat 2)
1
In the Material toolbar click Add Material .
2
Go to the Add Material window. Click to expand the tree node Built-In; then select Steel AISI 4340 .
3
Click Add to Component. Then click Add Material  in the Material toolbar to close the Add Material window.
4
In the Model Builder window click Steel AISI 4340 .
5
In the Settings window for Material locate the Geometric Entity Selection section. From the Selection list, choose Steel Base.