Partially Depleted SOI - Vt and Subthreshold Slope : Partially Depleted SOI - Vt and Subthreshold Slope

Requires: S-Pisces
Minimum Versions: Atlas 5.22.1.R

This example simulates the Ids/Vgs characteristics of a thick film SOI MOSFET and from these results extracts the threshold voltage and subthreshold slope. These are two key parameters involved in the design of any SOI MOSFET. It demonstrates:

  • Basic SOI structure definition using Atlas syntax
  • Setting transport models including impact ionization
  • Generating an Ids/Vgs curve with Vds=0.1V
  • Extracting threshold voltage and subthreshold slope from the results
  • Plotting output curves and structures.

The SOI device is a partially depleted device composed of a 0.2 micron layer of silicon on a 0.4 micron silicon dioxide substrate. The device has a 17 nm thick gate oxide and a gate length of 1.0 microns. For simplicity there is no silicon below the back oxide. Other examples in this section do include a silicon substrate.

The device mesh, region specification and electrode definition are performed using the mesh, region and electrode statements at the start of the input file. The doping is added as simple analytical functions. The channel doping in this simple example is presumed a constant. Gaussian source and drain profiles are used. No LDD or spacer is considered in this case.

After the structure description, the interface statement is used to define fixed oxide charges on both silicon - silicon dioxide interfaces. Next the contact statement is used to specify the workfunction on the poly-silicon gate.

The model statement is used to specify a reasonable set of physical models for SOI simulation. In this case, concentration dependent mobility, SRH recombination, Auger recombination, band-gap narrowing, and parallel electric field dependent mobility are specified.

After the initial solution, a negative gate voltage is applied followed by solutions at drain biases of 0.05 and 0.1 volts are obtained. Next, the log statement is used to specify a file for collection of the Id/Vgs characteristics of the SOI device. These characteristics are captured with the following solve statement where the gate bias is ramped in 0.1 volt increments from -0.2 volts up to 1.5 volt.

After the voltages have been solved extract statements are used to find the threshold voltage and the subthreshold slope of the SOI MOSFET.

Finally, the resultant Id/Vgs curve is plotted using TonyPlot.

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