Every software package contains a full set of examples suitable for that version and are installed with the software. If you see examples here that are not in your installation you should consider updating to a later version of the software. These examples can be used by beginners and advanced users for product evaluation, teaching purposes, and self-training.

Required Modules

Victory Process

• 3D structure editor

Victory Mesh

• 3D Meshing

Victory Device

• 3D Simulator
• 3D Giga

This example shows how a body contact on an SOI NMOSFET can suppress a kink in the IdVd curve that is due to the effects of impact ionization. The effect of lattice heating is also shown.

This example demonstrates:

Definition of 3D SOI MOSFET structures using Victory Process

The use and effect of a body contact in a 3D MOSFET geometry

Calculation of lattice-heating effects

Simulation of impact ionization effects

The first Victory Process section in this example defines a basic SOI NMOSFET. Although the geometry of this device is essentially two-dimensional, it is here defined and simulated in 3D so that the results can be directly compared with those from a 3D MOSFET with a body contact. Using a tetrahedral mesh, the first MOSFET structure is saved to the file, from which it is imported into Victory Device.

In Victory Device, the statement ELECTRODE SUBSTRATE ensures that the substrate of this device is recognized as an electrode, which will be held at ground potential. The succeeding CONTACT statement assigns to the gate the workfunction of n-type polysilicon. The MODELS statement is used to specify the particular models to be used during the simulation. In this example, they include:

CVT: A general purpose mobility model including concentration, temperature, parallel field and transverse field dependence.

SRH: Shockley-Read-Hall recombination.

AUGER: Auger recombination.

BGN: Bandgap narrowing in the presence of heavy doping.

In addition to these models, the IMPACT SELB statement specifies that the Selberherr model for impact ionization will be used.

Now some special steps must be taken, because the MOSFET used in this example is not especially stable. That makes it difficult to obtain a consistently steady numerical solution. To facilitate this, we adjust some solver parameters by means of METHOD statements.

Once the contacts, models, and methods have been specified, the simulation begins with a SOLVE INIT to initialize the solution at zero bias. Next a small initial bias is put upon the drain, and then the gate is brought up to its operating bias of 3 V. The bias on the drain is then ramped from 0.2 V up to 4 V, and the IdVd curve saved to the logfile.

After this, the entire simulation is repeated for this structure, but this time considering lattice heating effects. The CONTACT and MATERIAL statements assign to the gate contact the workfunction, heat capacity, and thermal conductivity of n-type polysilicon. The THERMCONTACT statement here defines a thermal contact at the substrate, and specifies that it will be maintained at 300 K.

Once the gate has been biased, lattice temperature simulation is activated by the statement MODELS LAT.TEMP . The drain is then biased as before, and the IdVd curve is saved to the logfile.

The second Victory Process section defines a MOSFET with an additional body contact, beside the gate. The difference between this structure and the first one can be seen by comparing the structures in Victory visual.

As with the first structure, simulations are run with and without lattice heating effects. With the addition of the body contact (at 0 V), however, the device is much more stable. The IdVd curves are written to the log files, and all four IdVd curves generated in this example are compared in Victory visual. This comparison clearly shows that the addition of the body contact suppresses the kink in the curves, which is due to the effects of impact ionization.

In Victory Visual, you can examine the structure files to compare the impact ionization patterns for the two devices, and to compare the heat fluxes as well as other lattice heating effects.

Images