## 3.16 `M`: MOSFET

### 3.16.1 Syntax

`M` xxxxxxx nd ng ns nb mname {args}
`M` xxxxxxx nd ng ns nb mname {width`/`length} {args}
`.MOSfet` label nd ng ns nb mname {args}
`.MOSfet` label nd ng ns nb mname {width`/`length} {args}

### 3.16.2 Purpose

MOSFET.

### 3.16.3 Comments

Nd, ng, ns, and nb are the drain, gate, source, and bulk (substrate) nodes, respectively. Mname is the model name.
Length and width are the drawn channel length and width, in microns. Note that the notation W/L has units of microns, but the same parameters, in the argument list (`W` and `L`) have units of meters. All other dimensions are in meters.
The options `rstray` and `norstray` determines whether or not series resistances are included. `rstray` is the default. Experience has shown that the effect of series resistance is often not significant, it can significantly degrade the simulation time, and it often increases roundoff errors. `rstray` is the default for Spice compatibility, and because it usually is significant for the BJT model. `Norstray` is the equivalent of setting the model parameters `rd`, `rs`, and `rsh` all to zero.
Entering a parameter value of 0 is not the same as not specifying it. This behavior is not compatible with SPICE. In SPICE, a value of 0 is often interpreted as not specified, with the result being to calculate it some other way. If you want it to be calculated, don't specify it.
Another subtle difference from SPICE is that Gnucap may omit some unnecessary parts of the model, which may affect some reported values. It should not affect any voltages or currents. For example, if the gate and drain are tied, Cgs will be omitted from the model, so the printed value for Cgdovl and Cgd will be 0, which will disagree with SPICE. It doesn't matter because a shorted capacitor can store no charge.
Levels 1, 2, 3, 4, 5, 6, 7 are implemented.

### 3.16.4 Element Parameters

#### Basic Spice compatible parameters

`L` = x
  Drawn channel length. (Default = `DEFL` parameter from `options`. `DEFL default = 100μ`)
`W` = x
  Drawn channel width. (Default = `DEFW` parameter from `options`. `DEFW default = 100μ`)
`AD` = x
  Area of drain diffusion. (Default = `DEFAD` parameter from `options`. `DEFAD default = 0`)
`AS` = x
  Area of source diffusion. (Default = `DEFAS` parameter from `options`. `DEFAS default = 0`)
`PD` = x
  Perimeter of drain junction. (Default = 0.)
`PS` = x
  Perimeter of source junction. (Default = 0.)
`NRD` = x
  Number of squares of drain diffusion. (Default = 1.)
`NRS` = x
  Number of squares of source diffusion. (Default = 1.)

### 3.16.5 Model Parameters

#### Basic selection – required for all models

`LEVEL` = x
  Model index. (Default = 1) Selects which of several models to use. The choices supported are 1-7, corresponding to Spice 3f5.

#### Extended control (not in Spice) – all models

`CMODEL` = x
  Capacitance model selector (Default = 1 for level 4,5,7. Default = 2 for level 1,2,3. Default = 3 for level 6.) The only valid values are 1, 2 and 3. 2 selects Meyer capacitance calculations compatible with Spice 2. 3 selects Meyer's model compatible with Spice 3. 1 selects not to use Meyer's model.

#### Binning (not in Spice) – all models

Gnucap supports “binning”. You can specify any number of models as a family. These models must have the selection parameters `WMAX`, `WMIN`, `LMAX`, and `LMIN`.
To use “binning”, define a set of models with the same name, except for a numeric extension, beginning at 1. The models must be numbered consecutively. For example, you might have a set of models: `NM3U.1`, `NM3U.2`, `NM3U.3`, `NM3U.4`, `NM3U.5`, `NM3U.6`. For the device, you would specify the model `NM3U`. The first model meeting the requirements that length is between `LMIN` and `LMAX`, and width is between `WMIN` and `WMAX` will be used. They will be tried in numerical order.
If there is a gap in the numbering, only those below the gap will be used. If you want a specific model from a set, disabling binning, you can specify its full name.

`WMAX` = x
  Maximum width. (Default = Infinity.) The maximum device width that may be used with this model.
`WMIN` = x
  Maximum width. (Default = 0.) The minimum device width that may be used with this model.
`LMAX` = x
  Maximum length. (Default = Infinity.) The maximum device length that may be used with this model.
`LMIN` = x
  Maximum length. (Default = 0.) The minimum device length that may be used with this model.

#### Substrate coupling – all models

`IS` = x
  Bulk junction saturation current. If not input, it is calculated from `JS`. If both are input, a warning is issued, and the calculated value (from `JS`) is used, if `AD` and `AS` are also input. If neither `IS` or `JS` is input, a default value of 1e-14 is used.
`JS` = x
  Bulk junction saturation current per square-meter of junction area. May be used to calculate `IS`. If a conflict exists, a warning is issued.
`FC` = x
  Coefficient for forward bias depletion capacitance formula. (Default = 0.5)
`PB` = x
  Bulk junction potential. (Default = 0.8)
`CJ` = x
  Zero bias bulk junction bottom capacitance per square-meter of junction area. If not input, but `NSUB` is, it is calculated, otherwise a default value of 0 is used.
`MJ` = x
  Bulk junction bottom grading coefficient. (Default = 0.5)
`PBSW` = x
  Sidewall Bulk junction potential. (Default = PB)
`CJSW` = x
  Zero bias bulk junction sidewall capacitance per meter of junction perimeter. (Default = 0.)
`MJSW` = x
  Bulk junction sidewall grading coefficient. (Default = 0.33)

#### Strays – all models

`RSH` = x
  Drain and source diffusion sheet resistance. If not input, use `RS` and `RD` directly. If a conflict exists, a warning is issued. The resistance is only used if the option `rstray` is set.
`RD` = x
  Drain ohmic resistance (unscaled). If `RS` is input, the default value of `RD` is 0. If `RD` and `RS` are both not input, and `RSH` is input, they are calculated from `RSH`. If any conflict exists, a warning is issued, indicating the action taken, which is believed to be compatible with SPICE. The resistance is only used if the option `rstray` is set.
`RS` = x
  Source ohmic resistance (unscaled). If `RD` is input, the default value of `RS` is 0. If `RD` and `RS` are both not input, and `RSH` is input, they are calculated from `RSH`. If any conflict exists, a warning is issued, indicating the action taken, which is believed to be compatible with SPICE. The resistance is only used if the option `rstray` is set.
`CBD` = x
  Zero bias B-D junction capacitance (unscaled). If `CBD` is not specified, it is calculated from `CJ`.
`CBS` = x
  Zero bias B-S junction capacitance (unscaled). If `CBS` is not specified, it is calculated from `CJ`.
`CGSO` = x
  Gate-source overlap capacitance, per channel width. (Default = 0.)
`CGDO` = x
  Gate-drain overlap capacitance, per channel width. (Default = 0.)
`CGBO` = x
  Gate-bulk overlap capacitance, per channel length. (Default = 0.)

#### Accepted and ignored – all models

`KF` = x
  Flicker noise coefficient. SPICE parameter accepted but not implemented.
`AF` = x
  Flicker noise exponent. SPICE parameter accepted but not implemented.

#### Level 1,2,3,6 shared parameters

`VTO` = x
  Zero bias threshold voltage. If not input, but `NSUB` is, it is calculated, otherwise a default value of 0 is used.
`KP` = x
  Transconductance parameter. If not input, it is calculated by `UO` * `COX`.
`GAMMA` = x
  Bulk threshold parameter. If not input, but `NSUB` is, it is calculated, otherwise a default value of 0 is used.
`PHI` = x
  Surface potential. If not input, but `NSUB` is, it is calculated, otherwise a default value of 0.6 is used. A warning is issued if the calculated value is less than 0.1, in which case 0.1 is used.
`LAMBDA` = x
  Channel length modulation. If not input, it is calculated dynamically during simulation. If the value input is larger than 0.2, a warning is issued, but no correction is made. (accepted but ignored for level 3)
`TOX` = x
  Oxide thickness. (meters) (Default = 1e-7)
`NSUB` = x
  Substrate doping. (atoms / cm3) Used in calculation of `VTO`, `GAMMA`, `PHI`, and `CJ`. If not input, default values are used.
`NSS` = x
  Surface state density. (atoms / cm2) (Default = 0.) Used, with `NSUB` in calculation of `VTO`.
`XJ` = x
  Metallurgical junction depth. (meters) Used to calculate short channel effects. If not input, do not model short channel effects, effectively defaults to 0.
`LD` = x
  Lateral diffusion. (Default = 0.) Effective channel length is reduced by 2 * `LD`.
`UO` = x
  Surface mobility. (cm2/V-s) (Default = 600.)
`DELTA` = x
  Width effect on threshold voltage. (Default = 0.) (Level 2 and 3 only.)
`TPG` = x
  Type of gate material. (Default = 1.) +1 opposite to substrate
  –1 same as substrate
  0 Aluminum

#### Level 1

The Level 1 model has no additional parameters.

#### Level 2

`NFS` = x
  Fast surface state density. (atoms / cm2) Used in modeling sub-threshold effects. If not input, do not model sub-threshold effects.
`VMAX` = x
  Maximum drift velocity of carriers. (m/s) Used in calculating vdsat, and lambda. If not input, use a different method. `VMAX` does not always work, if the method fails, the alternate method is used and the warning “Baum's theory rejected” is issued if the error threshold is set to `debug` or worse.
`NEFF` = x
  Total channel charge (fixed and mobile) coefficient. (Default = 1.) Used in internal calculation of lambda.
`UCRIT` = x
  Critical field for mobility degradation. (V/cm) (Default = 1e4)
`UEXP` = x
  Critical field exponent in mobility degradation. If not input, do not model mobility degradation, effectively defaulting to 0.
`UTRA` = x
  Transverse field coefficient. SPICE parameter accepted but not implemented. It is also not implemented in most versions of SPICE.

#### Level 3

`NFS` = x
  Fast surface state density. (atoms / cm2) Same as Level 2.
`VMAX` = x
  Maximum drift velocity of carriers. (m/s) Used in calculating vdsat. If not input, use a different method.
`THETA` = x
  Mobility modulation.
`ETA` = x
  Static feedback.
`KAPPA` = x
  Saturation field vector.

#### Level 6

`KV` = x
  Saturation voltage factor.
`NV` = x
  Saturation voltage coefficient.
`KC` = x
  Saturation current factor.
`NC` = x
  Saturation current coefficient.
`NVTH` = x
  Threshold voltage coefficient.
`PS` = x
  Sat. current modification par.
`GAMMA1` = x
  Bulk threshold parameter 1.
`SIGMA` = x
  Static feedback effect par.
`LAMBDA1` = x
  Channel length modulation parameter. 1.

#### Level 4, 5, 7, 8 (BSIM models) general comments

The BSIM models have additional parameters for length, width, and product (length * width) dependency. To get the name, prefix the listed parameter with L, W, or P, respectively. Spice supports the “P” parameter only for BSIM3, but Gnucap supports it for all 3 models. For example, VFB is the basic parameter with units of Volts, and LVFB, WVFB, and PVFB also exist. The units of LVFB and WVFB are Volts * micron. The units of PVFB are Volts * micron * micron. The real parameter is calculated by P = P0 + PL / L + PW / W + PP / (L*W), where L and W are the effective length and width in microns.
The parameter s are not listed here, but they are the same as Spice 3f5, with the same defaults.
The “levels” are the same as Spice.

`4`
  BSIM 1.
`5`
  BSIM 2.
`7`
  BSIM 3v3.1.

The following are reserved for future use:

`8`
  BSIM 3v3.2.
`9`
  BSIM-SOI.
`10`
  BSIM 4.

### 3.16.6 Probes

`VDS`
  Drain-source voltage.
`VGS`
  Gate-source voltage.
`VBS`
  Bulk-source voltage.
`VDSInt`
  Drain-source internal voltage.
`VGSInt`
  Gate-source internal voltage.
`VBSInt`
  Bulk-source internal voltage.
`VGD`
  Gate-drain voltage.
`VBD`
  Bulk-drain voltage.
`VSD`
  Source-drain voltage.
`VDM`
  Drain-midpoint voltage.
`VGM`
  Gate-midpoint voltage.
`VBM`
  Bulk-midpoint voltage.
`VSM`
  Source-midpoint voltage.
`VDG`
  Drain-gate voltage.
`VBG`
  Bulk-gate voltage.
`VSG`
  Source-gate voltage.
`VDB`
  Drain-bulk voltage.
`VGB`
  Gate-bulk voltage.
`VSB`
  Source-bulk voltage.
`VD`
  Drain-ground voltage.
`VG`
  Gate-ground voltage.
`VB`
  Bulk-ground voltage.
`VS`
  Source-ground voltage.
`Id`
  Drain current.
`IS`
  Source current.
`IG`
  Gate current.
`IB`
  Bulk current.
`CGSO`
  Gate-source overlap capacitance.
`CGDO`
  Gate-drain overlap capacitance.
`CGBO`
  Gate-bulk overlap capacitance.
`CGSm`
  Gate-source Meyer capacitance.
`CGDm`
  Gate-drain Meyer capacitance.
`CGBm`
  Gate-bulk Meyer capacitance.
`CGST`
  Gate-source total capacitance.
`CGDT`
  Gate-drain total capacitance.
`CGBT`
  Gate-bulk total capacitance.
`CBD`
  Bulk-drain junction capacitance.
`CBS`
  Bulk-source junction capacitance.
`CGATE`
  Nominal gate capacitance.
`GM`
  Transconductance.
`GDS`
  Drain-source conductance.
`GMB`
  Body effect transconductance.
`VDSAT`
  Saturation voltage.
`VTH`
  Threshold voltage.
`IDS`
  Drain-source current, not including strays.
`IDSTray`
  Drain current due to strays.
`IError`
  Estimated drain current error bound.
`P`
  Power.
`PD`
  Power dissipated. The power dissipated as heat. It is always positive and does not include power sourced. It should be the same as P because the mosfet cannot generate energy.
`PS`
  Power sourced. The power sourced by the part. It is always positive and does not consider its own dissipation. It should be 0 because the mosfet cannot generate energy.
`REgion`
  Region code. A numeric code that represents the region it is operating in. The number is the sum of several factors. A negative code indicates the source and drain are reversed.
    1 Active. (Not cut off.)
    2 Not sub-threshold.
    4 Saturated.
    10 Source to bulk is forward biased.
    20 Drain to bulk is forward biased.
    40 Punch through.

All parameters of the internal elements (Ids, Gmr, Gmf, Yds, Gmbr, Gmbf, Cgb, Cgd, Cgs, Dsb, Ddb, Rd, Rs) are available. To access them, concatenate the labels for the internal element with this device, separated by a dot. Cgd.M6 is the gate to drain capacitance of M6.
In this release, there are no probes available in AC analysis except for the internal elements.