Id/Vgs and Threshold Voltage Extraction : Id/Vgs and Threshold Voltage Extraction

Requires: SSuprem 4/S-Pisces
Minimum Versions: Athena 5.22.3.R, Atlas 5.24.1.R

This is a basic MOS Athena to Atlas interface example simulating an Id/Vgs curve and extracting threshold voltage and other SPICE parameters. No advanced features are used in this example so as to demonstrate simple functionality. This example demonstrates:

  • Process simulation of a MOS transistor in Athena
  • Process parameter extraction (eg. oxide thicknesses)
  • Autointerface between Athena and Atlas
  • Simple Id/Vgs curve generation with Vds=-0.1V
  • IV Curve parameter extraction for Vt, Beta and Theta

The process simulation, process parameter extraction and electrode definition for this example are exactly as described in the first example in this section.

The unique feature of this example is the IV data simulated and the extraction syntax used. The model, interface and contact statements in Atlas are also as in the previous example.

The sequence of SOLVE statements is set to ramp the gate bias with the drain voltage at -0.1V. Solutions are obtained at -0.25V intervals up to -3.0V. All terminal characteristics are saved to the file mos1ex02_1.log as specified in the LOG statement.

The extract statement at the end of the file are used to measure the threshold voltage and other SPICE parameters. The results from the extract statements are printed in the run-time output, saved to a file called, and optionally used in the optimizer or VWF automation tools. The syntax used in these statements is freely composed of operators such as maximum value (max) and simulation results such as drain current (i."drain"). One operator of particular use in PMOS device extraction is abs() . This takes the absolute value of a variable and can be used to make all PMOS and NMOS extractions equivalent.

The name parameter specifies a user-defined label. The routines are not hard-coded to these names. Thus the first extraction statement reads: extract the value called pvt found by taking the x intercept of the maximum slope to the curve of drain voltage vs. drain current and subtracting half the drain voltage. This is just one definition of threshold voltage. Current search methods are also possible and are described under the DIBL example later in this section. The VWF interactive tools manual has details of the EXTRACT syntax.

The second extract statement measures the gain (or Beta). This is defined as the value of the steepest slope to the Id/Vgs curve divided by the drain voltage. The final extraction is for the SPICE level 3 mobility roll-off parameter (or Theta). This syntax shows the use of the syntax: $"pvt" and $"pbeta" . This tells DeckBuild to use the previously extracted values of threshold and beta in the equation.

To load and run this example, select the Load button in DeckBuild > Examples. This will copy the input file and any support files to your current working directory. Select the Run button in DeckBuild to execute the example.