Ultra-Fast Device Simulation with Monte Carlo
Tuned Transport Models in FastBlaze

FastBlaze is a fast physical device simulator for MESFETs and HEMTs optimized to provide interactive TCAD for modern III-V FET devices. It incorporates device-specific techniques to allow 1000x to 10000x simulation speeds compared to conventional device simulation. FastBlaze is the first simulator in the FastATLAS framework and covers III-V material models for isothermal DC and RF simulation of FETs.


Sophisticated Physical Models

FastBlaze does not compromise in the accuracy of the physical models in order to obtain fast simulations. In practice the speed of FastBlaze allows use of the most complex and advanced models without the huge speed penalty seen in conventional device simulation. Highlights of the physical models in FastBlaze are:

  • Monte Carlo Generated Material Parameters
    The Monte Carlo simulator Mocasim was used to derive carrier velocity characteristics for common III-V materials. Models are derived as a function of field, doping, mole fraction and temperature. Figure 1 shows the electron velocity as a function of doping and field for GaAs. Figure 2 shows the function for different materials.
  • Energy Balance Simulation
    FastBlaze uses energy balance simulation by default. The energy and momentum relaxation times as a function of carrier energy, doping, mole fraction and temperature are also obtained from Mocasim. These provide the most accurate representation of velocity overshoot and non-local transport possible.
  • Quantum Mechanics
    FastBlaze provides quantum statistics for describing carrier distributions in quantized channel regions. A Schrodinger solver is used to calculate and plot the quantized energy levels at any bias. Figure 3 shows the conduction band of a InGaAs HEMT with the first eleven bound-state energy levels.
  • Multi-Layer Transport
    FastBlaze uses a true multi-layer transport scheme where material parameters are layer dependent. This is important for HEMTs and also for devices with complex impurity and trap distributions. (See Figure 4)
  • Bulk and Interface Traps
    Typically the trap densities in III-V FETs can greatly affect the device performance. FastBlaze allows definition of multiple trap states both for bulk traps such as EL2 and interface surface states. Figure 5 shows the trap distribution in a typical FET structure in FastBlaze.

 

Figure 1. Monte Carlo generated electron velocity as a function of doping and field. This data is used by FastBlaze for accurate carrier transport simulation.

 

Figure 2. Velocity-field characteristics for various III-V materials.

 

Figure 3. Quantized states in a pHEMT.

 

Figure 4. Comparison of HEMT Id-Vd using correct multi-layer transport models.
The AlGaAs transport parameters are derived from Mocasim.

 

Figure 5. Effect of incomplete ionization on dopant and carrier densities.
Both traps and dopant impurities have several occupation statistic models.

 

Interactive TCAD

FastBlaze was written entirely in-house at Silvaco to meet commercial development standards. For the average user it is important to marry the sophisticated physics with a simulator that is easy to use and is well supported. Important features that move towards interactive use of TCAD have been included in the development. Seamless integration is done with the VWF framework and the interactive tools DeckBuild and TonyPlot. In addition the following key features make FastBlaze easy to use for non-TCAD experts:

  • FastATLAS specific GUI
    A dedicated GUI as part of DeckBuild allows rapid prototyping of FET structures including epitaxy and doping definition. The interface supports the definition of complex multi-recess structures with multiple impurity and trap doping profiles. Figure 6 shows the GUI used to define a pHEMT.
  • Interactive Graphics
    FastBlaze interfaces both I-V data and 2D electrical distributions of physical parameters to TonyPlot. Full 2D plots of potential, field and current density can be obtained. TonyPlot supports both polar plots and Smith charts for analyzing RF parameter data.
  • Automated, adaptive meshing
    The user does not need to do any mesh definition or refinement when using FastBlaze. The automatic mesh algorithm applies a very high mesh density to critical areas of the FET structure. Although the typical simulation time in FastBlaze is less than 1 minute the number of mesh points is around 7000 node points.
  • Parameter Variations and Experimentation
    With such fast simulation speeds the ability to run many device structure variations becomes very attractive for device development or characterization. Figure 7 shows an experiment with various recess depths.

 


Figure 6. The FastBlaze GUI is called from DeckBuild and allows easy definition of complex III-V FET structures for FastBlaze.

 

Figure 7. Experimentation using FastBlaze is quick and simple. Here the transconductance is shown as a function or recess depth.

 

Summary

FastBlaze brings together sophisticated device physics tuned using Monte Carlo simulation with user-oriented operation. The solution techniques used allow most simulations of I-V families or RF characteristics to be run in less than 1 minute. This means that experimentation with device structures can be run much more efficiently and accurately than in conventional device simulation or circuit simulators.