NPN Gummel Plot and fT Extraction : NPN Gummel Plot and fT Extraction

Requires: SSuprem 4/DevEdit/S-Pisces
Minimum Versions: Athena 5.22.1.R, Atlas 5.24.1.R

This example demonstrates the processing, remeshing and electrical test of a poly silicon emitter NPN bipolar transistor. Design parameters are finally extracted from the IV Curve, including fT and Gain. This example demonstrates the use of:

  • Process simulation of a polysilicon emitter bipolar device
  • Re-meshing of the structure in DevEdit
  • DC ramp of Vbe with fixed Vce
  • Simultaneous AC simulation during Vbe ramp
  • Extraction of peak gain and fT

The file starts with the definition of the process flow for an NPN bipolar transistor in Athena. The first boron implant forms the intrinsic base region. A second boron implant is self-aligned to the polysilicon emitter region to form a connection between the intrinsic base and p+ base contact regions. Spacer-like structures are used on the side of the poly emitter to space the p+ base contact and provide self-alignment. During the simulation, the relax statement is used to reduce the mesh density in the deep regions of the structure. Only half of the full device is simulated. Mirroring of this half device into a full structure is performed with structure mirror left . The final stage of the Athena syntax defines the electrode positions. In this example only one base contact is used. A subsequent example describes how two base contacts can be specified and linked together.

Often a mesh that is used for process simulation is not optimal for use with device simulation. In this example, the mesh generation tool DevEdit is used to recreate a mesh that has zero obtuse triangles in the semiconductor region. It is then refined as a function of a number of solution quantities on the mesh (eg: boron conc).

Popup windows under the DeckBuild Command window were used to create this set of commands to control DevEdit. To switch to DevEdit Commands, select the current simulator to DevEdit from the Main Control window. Further use of DevEdit in more advanced applications is shown in later examples.

In Atlas the solution procedure starts with a solution for a collector bias of 2V. Next, the log statement is used to specify a file for collection of Gummel plot data. The Gummel data is collected by applying a bias ramp on the base electrode up to 0.9. The parameter ac on the solve statement sets the ac analysis on. The frequency of this signal is set to 1MHz. Once the bias ramp is completed the data is plotted using TonyPlot.

Finally, the extract statement is used to extract the maximum gain, "maxgain", and the maximum ft, "maxft", for the BJT. The extracted parameters may be used as optimization targets for simulator tuning.

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.