IGBT Transient Latch-up with Lattice Heating

powerex03.in : IGBT Transient Latch-up with Lattice Heating

Requires: S-Pisces/Giga
Minimum Versions: Atlas 5.22.1.R

In this example the non-isothermal latchup of an IGBT device is simulated. The latchup is produced in the transient or switching mode. The currents during latchup in this device are high and significant local heating occurs. Therefore, the solution of lattice temperature and heat flow must be included. This example shows:

  • The definition of the IGBT structure using Atlas
  • How to enable Giga non-isothermal simulation
  • IGBT collector steady state solution at 300V
  • Transient gate voltage ramp to produce latchup

The Atlas simulation begins with the definition of the IGBT structure. A fine rectangular mesh is first defined. Next, the materials are assigned to specific regions using the region command. The electrodes and doping profiles are then defined. Additionally, specific characteristics of these materials, their electrodes and the charge carriers within can be modified. The material statement is used to define the electron and hole recombination lifetimes in the semiconductor. The contact statement defines the workfunction of the polysilicon electrode, in this case, that of degenerately doped n-type polysilicon. This completes the IGBT structure definition.

For any Atlas device simulation, the physical transport models must be enabled using the model statement. In this case, they reflect the different physical effects important to the IGBT device. They are analytic: analytic concentration dependent mobility, fldmob: lateral electric field dependent mobility, surfmob: surface mobility degradation, srh: Shockley-Read-Hall recombination, and auger: recombination accounting for high level injection effects.

The steady-state characteristics of the IGBT are now solved. As with most Atlas simulations, an initial solution is performed at zero bias using the statement solve init . This gives the Atlas solvers a good starting point. The subsequent solve statements ramp the IGBT collector up to 300V in several stages . Each additional stage uses the previous solution as an initial guess. Other initial guess strategies are available however. Consult the Atlas User's manual for more details. If an electrode bias is not specified, it remains at its previous value, in this case, zero volts. After the solution is obtained at 300V, the solution is saved. It will be used as the initial solution in the transient mode latchup simulation which follows.

Three additional items are added for the IGBT transient mode simulation: thermal contacts, heat flow, and impact ionization. Thermal boundary conditions are a very important part of any non-isothermal simulation and must be specified. For the IGBT, a constant temperature along the collector contact is specified in the thermcontact statement. All other contacts and surfaces are assumed to be in thermal isolation. The lat.temp lattice temperature model is added to the model statement to include heat flow. This means that the heat flow equation is solved in addition to the semiconductor equations and all physical parameters become temperature dependent. In addition to heat flow, impact ionization plays an important role in IGBT transient mode latchup. The Selberherr impact ionization model is added using the impact statement with the selb option.

An IGBT gate transient is now simulated. The previous solution at the collector bias of 300V is loaded and used as an initial guess for the latchup simulation. The output statement is used to add additional solution quantities to the standard output variables. The gate voltage is ramped from 0 to 10 V in 100 nano seconds to cause the IGBT latchup. The gate will then be held at the 10 V level until the time reaches 1 micro second. These conditions are set on the solve statement. The output results are saved in the log file. Using TonyPlot, it is possible to observe the latchup by plotting the collector current and maximum temperature in the device versus time. The structure and solution at the final time point is saved and all output variables can be observed using TonyPlot.

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.