Sending report ...FETToy Detailed Description
Toy model to simulate I-V characteristics of nanoscale double gate MOSFETs
FETToy 2.0 is a set of Matlab scripts that calculate the ballistic I-V characteristics for a conventional MOSFETs, Nanowire MOSFETs and Carbon NanoTube MOSFETs. For conventional MOSFETs, FETToy assumes either a single or double gate geometry and for a nanowire and nanotube MOSFETs it assumes a cylindrical geometry. Only the lowest subband is considered, but it is readily modifiable to include multiple subbands. The underlying theory is described in detail in A. Rahman, J. Guo, S. Datta, and M. Lundstrom, "Theory of Ballistic Nanotransistors", IEEE Transactions on Electron Devices, 50, pp. 1853-1864, 2003. This theory extends on work by Natori (J. Appl. Phys., 76, 4879-4890, 1994) by including 2D electrostatics and the so-called "quantum capacitance".
All parameters used in FETToy are in MKS units except energy, which is in eV. In addition to device specification, temperature, and bias information, FETToy needs the following three parameters:
- The "Source Fermi Level", Ef, which determines the off current. Increasing Ef increases the off current and vice versa.
- The "Gate Control Parameter", alphag (0 < alphag < 1), which describes the control of the gate electrode over the potential at the top of the barrier. Increasing this parameter decreases the subthreshold swing and vice versa. For alphag = 1, there is complete gate control, as is the case for a long channel MOSFET.
- The "Drain Control Parameter", alphad, which describes the control of the drain electrode over the potential at the top of the barrier. Increasing this parameter increases DIBL and vice versa.
Users can run FETToy 2.0 in the simulation hub, or they can download it to their own computer. The source code for simulating conventional MOSTFETs, Nanowire MOSFETs, and Carbon Nanotube MOSFETs are organized into different folders. A previous version of FETToy (version 1.0) is also included in the source download package as well as a code module that uses numerically tabulated energy bands.
In FETToy 2.0, the option of using the so-called floating boundary condition has been disabled. However, FETToy 1.0 incorporates the floating boundary condition and is included in the source download package. See Rahman et. al. for a discussion of floating boundary condition.
In addition to an output file summarizing the key results from the simulation, eight plots are produced. These are:
- Linear plot of Id vs. Vgs at low and high Vds
- Logarithmic plot of Id vs. Vgs at low and high Vds
- Plot of Id vs. Vds at different Vgs
- Linear plot of Mobile Charge vs. Vgs at low and high Vds
- Logarithmic plot of Mobile Charge vs. Vgs at low and high Vds
- Plot of Mobile Charge vs. Vds at different Vgs
- Plot of Quamtum Capacitance vs. Vgs at low and high Vds
- Plot of Injection Velocity vs. Vgs at high Vds
Four data files containing the I-V data, the self-consistent field data, the mobile charge data, and a file containing input parameters and select results are also created and can be used later to reproduce all the above plots.
The following default parameters are a good starting point for running FETToy:
| Device Type | ||
| Single Gate Silicon MOSFET: | (default) | |
| Double Gate Silicon MOSFET: | ||
| Silicon Nanowire FET: | ||
| Carbon Nanotube FET: | ||
| Device Specifications | ||
| Gate Insulator Thickness (m): | 1.5e-9 | |
| Gate Insulator Dielectric Constant: | 3.9 | |
| Transport Effective Mass: | 0.19 | |
| Valley Degeneracy: | 2 | |
| NT / NW Diameter (m): | 1.0e-9 | |
| Temperature (K): | 300 | |
| Terminal Voltage | ||
| Number of Bias Points: | 13 | |
| Voltage Range (V): | 0 to 0.6 | |
| FETToy Model Parameters | ||
| Source Fermi Level, Ef (eV): | -0.32 | |
| Gate Control Parameter, ag: | 0.88 | |
| Drain Control Parameter, ad: | 0.035 | |