NPN - BVCEO Breakdown Voltage

bjtex05.in : NPN - BVCEO Breakdown Voltage

Requires: S-Pisces
Minimum Versions: Atlas 5.28.1.R

This example calculates the BVCEO breakdown voltage in an NPN transistor. It shows:

  • Formation of an NPN BJT using Atlas syntax
  • Selection of the correct models and methods for breakdown simulation
  • Setting of current boundary conditions to force an open base contact
  • Ic extraction versus Vce with an open base contact

In the first part of the input file the device is described, including mesh, electrodes location, and doping distribution. The device geometry and doping are as used in the previous example.

The {bold} impact statement is used to specify the Selberherr impact ionization model required for breakdown analysis.

For increased stability which is typically needed for such kind of simulation with zero base current, the solution with small value of base current Ib=3.e-15 A/um is obtained at the first stage of simulation. Then the collector voltage is ramped until the collector current reaches the value 5.e-11 A/um.

To set the open base contact, it is necessary to define zero current passing through the base electrode. This is done by setting current boundary conditions on the base using contact name=base current . Then throughout the breakdown simulation Ib is held at zero. This is the most effective approach for BVCEO simulation.

The ramp of collector voltage is set on the final solve statement. The ramp continues up to 10V. However a compliance limit on the collector current is set using the parameters compl=<num> cname=collector . The <num> specifies the value of the compliance limit in A/um, whilst the cname indicates which contact the complaince current should be measured on. Once the simulated collector current exceeds the complaince value the simulation steps on to the next line of syntax. Here that line is to plot the results in TonyPlot.

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