This section describes the LEVEL 5 IDS model parameters and equations.
The LEVEL 5 model parameters follow.
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Implant channel mobility temperature exponent (depletion model only) |
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The LEVEL 5 MOSFET model has been expanded to include two modes: enhancement and depletion. These two modes are accessed by the flag mode parameter, ZENH.
The Star-Hspice enhancement and depletion models are basically identical to the AMI models. However, certain aspects have been revised to enhance performance. Using the Star-Hspice enhancement and depletion models provides access to Star-Hspice features as described below.
The Star-Hspice version of the enhancement and depletion models allows the choice of either SPICE-style or ASPEC-style temperature compensation. For LEVEL 5, the default is TLEV=1, invoking ASPEC style temperature compensation. Setting TLEV=0 invokes SPICE-style temperature compensation.
CAPOP=6 represents AMI Gate Capacitance in Star-Hspice. CAPOP=6 is the default setting for LEVEL 5 only. The LEVEL 5 models can also use CAPOP =1, 2, 3.
The parameter ACM defaults to 0 in LEVEL 5, invoking SPICE-style parasitics. ACM also can be set to 1 (ASPEC) or to 2 (Star-Hspice). All MOSFET models follow this convention.
The Star-Hspice option SCALE can be used with the LEVEL 5 model; however, option SCALM cannot be used due to the difference in units.
You must specify the following parameters for MOS LEVEL 5: VTO (VT), TOX, UO (UB), FRC, and NSUB (DNB).
The LEVEL 5 IDS equations follow.
(See Subthreshold Current, Ids)
and gate oxide capacitances per unit area are calculated by:
The effective channel length and width in the LEVEL 5 model is determined as follows.
The model parameter VTO is an extrapolated zero-bias threshold voltage of a large device. The effective threshold voltage, including the device size effects and the terminal voltages, is given by:
using DNB and ignores the GAMMA model parameter.
The effective body effect 
,
including the device size effects, is computed as follows.
The saturation voltage due to channel pinch-off at the drain side is computed by:
If ECV is not equal to 1000, then the program modifies vsat to include carrier velocity saturation effect:
The mobility degradation effect in the LEVEL 5 model is computed by:
The channel length modulation effect 
is defined in the following section.
The LEVEL 5 model includes the channel length modulation effect by modifying the I
The 
is in microns, assuming XJ is in microns and DNB is in cm
This region of operation is characterized by the Fast Surface State (FSS) if it is greater than 1e10. Then the effective threshold voltage, separating the strong inversion region from the weak inversion region, is determined as follows:
and vt is the thermal voltage.
The LEVEL 5 MOS model uses depletion mode devices as the load element in contemporary standard n-channel technologies
This implanted layer also causes the formation of an additional channel, offering a conductive pathway through the bulk silicon, as well as through the surface channel. This second pathway can cause difficulties when trying to model a depletion device with existing MOS models. The bulk channel is partially shielded from the oxide interface by the surface channel, and the mobility of the bulk silicon can be substantially higher. Yet with all the differences, a depletion model still can share the same theoretical basis as the Ihantola and Moll gradual channel model.
The depletion model differs from the Ihantola and Moll model as follows:
In the depletion model, the gain is lower at low gate voltages and higher at high gate voltages. This variation in gain is the reason the enhancement models cannot generate an accurate representation for a depletion device. The physical model for a depletion device is basically the same as an enhancement model, except that the depletion implant is approximated by a one-step profile with a depth DP.
Due to the implant profile, the drain current equation must be calculated by region. MOSFET device model LEVEL 5 has three regions: depletion, enhancement, and partial enhancement.
The low gate voltage region is dominated by the bulk channel.
The region is defined by high gate voltage and low drain voltage. In the enhancement region, both channels are fully turned on.
The region has high gate and drain voltages, resulting in the surface region being partially turned on and the bulk region being fully turned on.
The IDS equations for a LEVEL 5 depletion model follow.
The saturation voltage, threshold voltage, and effective 
are described in the following sections.
The model parameter VTO is an extrapolated zero-bias threshold voltage for a large device. The effective threshold voltage, including the device size effects and the terminal voltages, is calculated as follows:
The effective 
, including small device size effects, is computed as follows:
The saturation voltage (vsat) is determined as:
IF ECV is not equal to 1000 (V/µm), Star-Hspice modifies vsat to include the carrier velocity saturation effect.
The surface mobility (UB) is dependent upon terminal voltages as follows:
The channel length modulation effect 
is defined next.
The channel length modulation effect is included by modifying the I
The 
parameter is in microns, assuming XJ is in microns and na1 is in cm
When device leakage currents become important for operation near or below the normal threshold voltage, the subthreshold characteristics are considered. The Star-Hspice LEVEL 5 model uses the subthreshold model only if the number of fast surface states (that is, the FSS) is greater than 1e10. An effective threshold voltage (von) is then determined:
If von < vinth, then vinth is substituted for von.
vde > 0FILE ML5IV.SP HSPICE LEVEL 5 MODEL EXAMPLES
*OUTPUT CHARACTERISTICS FOR ENHANCEMENT & DEPLETION MODE
+ VT=.7 TOX=292 FRC=2.739E-2 DNB=2.423E16 UB=642.8
+ OXETCH=-.98 XJ=.29 LATD=.34 ECV=4 VST=5.595E7
+ FSB=7.095E-5 SCM=.4 FSS=2.2E11 NWM=.93 PHI=.61
+ TCV=1.45E-3 PTC=9E-5 BEX=1.8
.MODEL MODDP NMOS LEVEL=5 ZENH=0.
+ VT=-4.0 FRC=.03 TOX=800 DNB=6E14 XJ=0.8 LATD=0.7
+ DEL=0.4 CJ=0.1E-3 PHI=0.6 EXA=0.5 EXP=0.5 FSB=3E-5
+ ECV=5 VST=4E7 UB=850 SCM=0.5 NI=5.5E11 DP=0.7 UH=1200
Star-Hspice Manual - Release 2001.2 - June 2001
linear region
saturation region
Linear region
Saturation region
