Transient 3D CMOS Latch-Up

latchex04.in : Transient 3D CMOS Latch-Up

Requires: DevEdit 3D/Device 3D
Minimum Versions: Atlas 5.22.1.R

This example demonstrates transient latch-up in a three-dimensional npnp structure typical of CMOS processes. The stages of this examples are:

  • Definition of npnp structure in DEVEDIT3D
  • Setting of a transient negative voltage pulse on the Vss contact to trigger latch-up

The npnp structure defined by DEVEDIT3D is a three dimensional one. The n+ and p+ contacts do not fall in one 2D plane as in the previous examples. They are arranged in a rectangle. The DEVICE3D module of Atlas is required to simulate latch-up in this structure.

The structure is created using DEVEDIT3D either graphically or using the command menus in DeckBuild. The most common technique is to form the structure graphically, then save an input file containing all the commands required to reproduce this structure. This input file can be loaded into DeckBuild, and Atlas runs can be appended to it to create a file similar to this one.

In Atlas, no special syntax is required to enter the DEVICE3D module as opposed to 2D SPISCES. On reading a mesh file, Atlas will automatically detect if it is two or three dimensional. The syntax for specifying bipolar models and setting up the initial bias state are identical to the two-dimensional cases described in the previous examples.

The command method halfimpl chooses the half-implicit scheme for transient simulation. This scheme significantly reduces the simulation time for many 3D transient problems. In difficult cases more robust but slower methods might be required. The transient pulse applied to the n+ contact in the pwell is similar to the first example in this section.

Results from the log file show latch-up occurs as the device does not return to its initial state after the pulse is over. The current is still increasing at the end of the simulation which will eventually cause device failure. It is possible to repeat this experiment varying the the parameter t.final in the statement:
solve v4=-2.0 tfinal=4.5e-9 tstep=10.e-12
If the voltage is held at -2.0V for shorter times latch-up may not occur.

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.