CMOS Latch-Up By Negative Voltage on Vss : CMOS Latch-Up By Negative Voltage on Vss

Requires: MaskViews/SSuprem 4/S-Pisces
Minimum Versions: Athena 5.22.3.R, Atlas 5.28.1.R

This example demonstrates a latch-up caused by a DC ramp in an npnp structure typical of CMOS processes . The stages of this examples are:

  • Definition of a CMOS layout to include a parasitic npnp structure
  • Interface of the layout information to Athena
  • Process simulation of the npnp structure
  • Interface of the structure to Atlas with automatic electrode specification
  • Negative ramp of Vss to cause latch-up using curve tracing algorithm.

The parasitic npnp device used is identical to the device in the previous example. The use of MASKVIEWS and Athena to create this structure is given in the description of that example. The initial part of the Atlas run is also identical.

This file differs only in the manner of triggering the latch-up. A DC ramp of the n+ contact in the p-well (named Vss) is used as the trigger. Once the voltage on Vss becomes less than the 0.0V on the pwell, the n+/p-well junction is forward biased and latch-up may be triggered.

To allow the complete holding voltage and current to be extracted simply, the curve tracing algorithm in Atlas is used. The key command is the curvetrace statement coupled with 'solve curvetrace'. The parameters on the trace statement are used to set initial conditions and limits on the curve tracing. In particular the step.init parameter is given as a negative voltage step. This is all that is required to select the polarity of the voltage sweep. A detailed description of the use of this technique in tracing IV curves with turning points can be found in the description of the MOS snapback example.

The latch-up characteristic can be seen in the stored log file. It is important to plot the current versus vss int. bias rather then 'vss bias', since the former is the voltage actually applied to the semiconductor and the latter includes the effect of the load line used during the curve trace.

To load and run this example, select the Load button in DeckBuild. This will copy the input file and any support files to your current working directory. You cannot run this file until the cross-section file is loaded. To do this go to the DeckBuild menu Tools->MaskViews->Cutlines Then select the name of the cross-section file from the list. The name will be <file>.sec where <file> is the name of this example. Then press Load on this Cutline menu. Once the cross-section file is loaded, select run in DeckBuild to execute the example.