NMOS Snapback

mos2ex07.in : NMOS Snapback

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

This example demonstrates the curve tracing algorithm in Atlas to simulate the snapback of a MOSFET. The example shows:

  • Creation of a N-channel MOSFET in Athena
  • Remesh by DEVEDIT,
  • The Atlas curve tracing algorithm is used to trace MOS snapback.

A standard NMOS device is constructed, remeshed and loaded into Atlas. The process simulation, interface to DEVEDIT and initial setup in Atlas are described in the previous section under MOS examples.

The initial syntax in Atlas sets all the required contact, interface and model setting used for MOS simulation. These settings are described in earlier example descriptions. Calculation of impact ionization is necessary for breakdown and snapback simulation. The impact statement is used to activate the Selberherr impact ionization model.

Curve tracing is an algorithm for choosing the boundary conditions for a simulation to trace out an IV curve. It is typically used on curves such as snapback or latchup with many turning points.

For curve tracing simulations the key statement is : curvetrace end.val=1.e-3 contr.name=drain curr.cont mincur=1e-10 nextst.ratio=1.3. It is used to initialize parameters for the curve tracing algorithm. The contr.name parameter specifies the name of electrode for which the load line technique will be applied. Here this is the 'drain'. The curr.cont parameter sets that value of current will be monitored. The simulation will stop when the current exceeds the value specified by end.val parameter. The mincur parameter defines the minimum current value after which the load line technique will be actually be applied. Before that, pure voltage boundary conditions are used. The nextst.ratio parameter defines the factor which is used to increase voltage step on parts of the IV curve away from the turning points. The main place this is used is in the pre-breakdown voltage ramp. solve curvetrace is used to activate the curve tracing algorithm.

The final snapback curve can be plotted using TonyPlot. To plot the drain voltage actually applied to the device, the x-axis should be set to drain int. bias and not drain bias. 'drain int. bias' is the voltage on the drain contact/semiconductor interface. The value of drain bias should be disregarded since it includes the effect of the load line algorithm used for the curve trace.

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.