Creating a Thin Film Resistor
The following is a step-by-step guide for creating a thin film resistor, assuming you do not know the thickness and the conductivity or resistivity of your thin film material. If you know these values, you can simply use the standard Conductivity or Resistivity Loss Type to specify your resistor material. However, if you do not know this information, the following procedure may be used.
Select Circuit > Settings > [Materials] : [Conductors].
Click the Add button to add a new conductor material.
Select Surface Impedance from the Loss Type drop-down menu.
The Surface Impedance Loss Type allows you to enter a surface resistance that is constant with frequency. If you know the thickness of your resistive film, you may wish to use the Sheet Resistance at DC Loss Type, which will result in a frequency-dependent surface impedance.
Enter the Rdc value for your resistor.
Rdc is the surface resistance of the resistor in ohms per square. If you know the total resistance of your resistor, R, and the number of squares, N, the Rdc value may be calculated using the following equation:
Rdc = R/N
The number of squares, N, may be calculated by dividing the length of the resistor film by its width. For example, if you need a 400 Ω resistor for a 120 by 60 micron resistor film, the number of squares is 120/60 = 2, and the Rdc value would be 400/2 = 200 ohms per square.
Click OK to save your changes and exit the Conductor Properties dialog box.
A new conductor material is added to your list of conductor materials.
In the Circuit Settings dialog box, click the [Tech Layers] category.
The Tech Layers pane is displayed.
Click the Add Planar button to create a new Tech Layer.
In the Conductor drop-down list, select the conductor material you previously created.
Fill in any additional information, such as the name and level number. For most cases, using the default Thin Metal model is sufficient.
The EM solver ignores the thickness of any Tech Layer using the Surface Impedance Loss Type. Therefore, you may leave the thickness at the default value of 0.0.
Click OK twice to exit the Tech Layer Properties window and the Circuit Settings dialog box.
The new Tech Layer is shown in the Stackup Manager.
If you do not already have a resistor polygon, create one using the new Tech Layer.
There are multiple ways to do this. For example, first click the new Tech Layer in the Stackup Manager, then select Insert > Draw Rectangle and draw the resistor.
If you already have a polygon representing your resistor, double-click your resistor polygon and assign it to the new Tech Layer.
The above technique was used to create the example res_400_thin, which may be obtained using the Example Browser.