Substrate and Gate Current Extraction

mos1ex06.in : Substrate and Gate Current Extraction

Requires: SSuprem 4/DevEdit/S-Pisces
Minimum Versions: Athena 5.22.1.R, Atlas 5.22.1.R

This is a MOS Athena/DevEdit/Atlas interface example simulating substrate and gate current versus gate bias using energy balance and impact ionization models. This example demonstrates:

  • Process simulation of a MOS transistor in Athena
  • Process parameter extraction (eg. oxide thicknesses)
  • Autointerface between Athena and DevEdit
  • Remeshing using DevEdit
  • Autointerface between DevEdit and Atlas
  • Solution for a Vgs ramp with Vds=3.3V
  • Parameter extraction for maximum gate and substrate currents

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

The grid requirements for Atlas simulation of impact ionization effects are more stringent than for the low electric field cases described earlier. DevEdit is used to remesh the Athena structure before proceeding to Atlas. DevEdit has two modes. The graphical mode allows users to draw and interactively edit regions and impurities. The batch mode used here executes structure and mesh commands similar to these. The syntax used by DevEdit is described in the DevEdit manual. It can be constructed from the DeckBuild Command menu, or most commonly mesh edits made during a graphical session can be saved as a 'command file' from the SAVE menu of DevEdit.

The imp.refine commands specify regrids on impurities. Here a regrid on net doping is performed. The constr.mesh command defines the base mesh. The refine commands specify mesh refinements inside boxes specified by the coordinates in each statement.

The Atlas simulation contains similar syntax to the simple examples described earlier in this section. The solution of the energy balance equations for electrons is specified by the parameter hcte.el The parameter hei specifies the hot carrier injection model, which gives the gate current. The equivalent hcte.ho and hhi exist for holes but is not required in NMOS simulation.

The impact ionization model is selected on the impact statement. The parameter lrel.el sets the relaxation time for electrons in this model. Although the hei model is directly responsible for the gate current, there is no 'special' model required to simulate substrate current. Running this sweep of gate voltage with a high drain bias and including impact ionization and energy balance supplies all the necessary physics. The substrate current can simply be plotted from the log file in a similar manner to the drain current. No special extraction of substrate current is needed.

The extract statements used in this run extract the peak value and position of the substrate and gate currents. The value of the peak current is measured first. This result is then used in a current search to find the gate voltage where this current is measured.

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.