BSIM3SOI Version 3.0 Model Released in SmartSpice

Introduction

BSIM3SOI version 3.0 model was released on May 2002 by UC Berkeley. This model includes both Partially depleted and Fully depelted models. This model is now implemented in SmartSpice and can be selected according to LEVEL selector.

LEVEL=33 selects          BSIM3SOI v3.0 model.

A new full-depletion (FD) module has been included to provide better fitting to FD SOI devices. This can be invoked setting the model parameter SOIMOD=1.

The partially-depletion (PD) module is by default identical to lastest version of BSIM3SOI PD version 2.2.3 (also supported in SmartSpice with previous versions setting LEVEL=29). This can be invoked setting the model parameter SOIMOD=0.

New Gate-to-Channel curent (Igc) and new Gate-to-Source/Drain currents (Igs and Igd) compo-nents have been added in BSIM3SOI v3.0. By default, these currents are set to 0 in order to stay compatible with previous version but can be accounted turning on the new selector IGCMOD.

Gate-to-Body tunneling current was taken into account in BSIM3SOI v2 PD (LEVEL=29) model turning on IGMOD selector. In BSIM3SOI v3.0, identical expressions are used for the calculation of this gate tunneling current component but the selector is named IGBMOD now.

A minor bug has been fixed in the self-heating algorithm.

 

Implementation

The present section provides all the information needed to understand and use the BSIM3SOI v3.0 model.

The SmartSpice implementation of the BSIM3SOI v3.0 model is close but not identical to UC Berkeley release. The SmartSpice implementation provides a number of improvements and additional parameters currently unsupported in Berkeley’s BSIM3SOI v3.0 model.

In the SmartSpice implementation of the BSIM3SOI v3.0 model, enhanced convergence is obtained by properly handling GMIN and DCGMIN control options during transient and DC analysis. The GMIN option connects a conductance in parallel with the bulk diodes and between drain and source.

The option VZERO defines the Modified Nodal Analysis (MNA) formulation. The VZERO = 2 option is recommended when simulating in the time domain relatively large circuits with hundreds or thousands of transistors. It accelerates simulation and increases the accuracy of simulation results.

The option CAPDC=1 allows the user to see charge and capacitances in DC (see output variables).

The parameter checking procedure initially used for BSIM3v3 and BSIM4 has been extended to BSIM3SOI v3.0. This checking procedure verifies some critical parameters values, and output warnings and/or errors to the screen or to a logfile.

BSIM3SOI v3.0 model has been optimized to take avantage of the multi-processor machines. The simulation is speed up when SmartSpice is run on paralel architectures without influence on the accuracy.

 

Major Features

BSIM3SOI v3.0 has the following new features relative to BSIM3SOI PD v2 [1]:

  • Real floating body simulation in both C-V and I-V. The body potential is determined by the balance of all the body current components
  • Enhancements in the threshold voltage and bulk charge formulation of the high positive body bias regime
  • An improved parasitic bipolar current model. This includes enhancements in the various diode leakage components, second order effects (high-level injection & early effect), diffusion charge equation and temperature dependence of the diode junction capacitance
  • An improved impact ionization current model. The contribution from BJT current is also modeled by the parameter FBJTII
  • Instance parameters (PDBCP, PSBCP, AGBCP, AEBCP, NBC) are provided to model the parasitics of devices with various body-contact and isolation structures
  • An external body node (the 6th node) and other improvements are introduced to facilitate the modeling of distributed body-resistance
  • Self-heating: an external temperature node (the 7th node) is supported to facilitate the simulation of thermal coupling among neighboring devices
  • A unique SOI low frequency noise model, including a new excess noise resulting from the floating body effect
  • Width dependence of the body effect is modeled by parameters (K1, K1W1, K1W2)
  • Improved history dependence of the body charges with two new parameters (FBODY, DLCB)
  • An instance parameter vbsusr is provided for users to set the transient initial condition of the body potential;
  • The new-charge thickness capacitance model introduced in BSIM3v3.2, CAPMOD3, is included
  • Gate-to-Body tunneling current
  • A body halo sheet resistnce
  • A minimum width fro thermal resistance calculation
  • A higher limit for exponetial functions

BSIM3SOI v3.0 has the following new features relative to BSIM3SOI FD v2 [2]:

  • Supports external body bias and backgate bias: a total of 5 external nodes
  • Improved self-heating implementation
  • New depletion charge model (EBCI) introduced for better accuracy in capacitive coupling prediction
  • Single I-V expression to guarantee continuities of Ids, Gm, and Gds and their derivatives for all bias conditions

New version BSIM3SOI v3.0 includes the binning feature to enhance the model flexibility and fixes some bugs found in the previous BSIM3SOI PD v2.2.3.

New features have been added in BSIM3SOI v3.0 model:

  • Gate-to-Channel current component Igc splitted into two components Igcs and Igcd
  • Gate-to-Source/Drain tunneling currents (Igs and Igd) between the gate and the source/drain diffusion regions
  • Gate-to-Body tunneling current (Igb)

For more details concerning the physical expressions of BSIM3SOI v3.0 model, please refer to SmartSpice Modelling Manual Volume 3 [3].

 

Model Parameters

BSIM3SOIv3 model LEVEL=33 supports all model paramters of BSIM3SOI Partially depleted LEVEL=29 and Fully depleted LEVEL=26 models. The additional parameters listed in Table 1 correspond to BSIM3SOIv3 model released by UC Berkeleyin May 2002 only.

Parameter Description Units Default
SOIMOD SOI model selector (0 for BSIMPD and 1 for BSIMFD)
-
0
VBSA Offset voltage due to non-idealities
V
0.0
NOFFFD Smoothing parameter in FD module
-
1.0
VOFFFD Smoothing parameter in FD module
V
0.0
K1B First backgate body effect parameter
-
1.0
K2B Second backgate body effect parameterfor short channel effect
-
0.0
DK2B Third backgate body effect parameter for short channel effect
-
0.0
DVBD0 First short channel effect parameter in FD module
-
0.0
DVBD1 Second short channel effect parameter in FD module
-
0.0
MOINFD Gate bias dependence coefficient of surface potential in FD module
-
1.0E+3
IGCMOD Global model selector for Igs, Igd, Igcs, Igcd
-
0
IGBMOD Global model selector for Igb
-
0
AIGC Parameter for Igs, Igd, Igcs, Igcd
(F.s^2/g)^.5.
m^-1

0.43 (NMOS)
0.31 (PMOS)

BIGC Parameter for Igcs and Igcd
(F.s^2/ g)^.5.
mV^-1

0.054 (NMOS)
0.024 (PMOS)

CIGC Parameter for Igcs and Igcd
V^-1

0.075 (NMOS)
0.03 (PMOS)

AIGSD Parameter for Igs and Igd
(F.s^2/ g)^.5.
m^-1

0.43 (NMOS)
0.31 (PMOS)

BIGSD Parameter for Igs and Igd
(F.s^2/g)^.5.
mV^-1

0.054 (NMOS)
0.024 (PMOS)

CIGSD Parameter for Igs and Igd
V^-1

0.075 (NMOS)
0.03 (PMOS)

DLCIG Parameter for Igs and Igd
V^-1

0.075 (NMOS)
0.03 (PMOS)

DLCIG S/D overlap length for Igs/Igd   LINT
NIGC Parameter for Igs, Igd, Igcs, Igcd   1.0
POXEDGE Factor for the gate oxide thichness in the dource/drain overlap regions
-
1.0
NTOX Exponent for the TOX ratio
-
1.0
TOXREF Targert oxide tickness in gate tunnelling
m
2.5e-9
TOXQM Equivalent oxide tickness in gate tunnelling
m
TOX

Table 1. Additional parameters to BSIM3SOI v2 PD and FD for BSIM3SOI v3.0 model

 

Silvaco Improvements

Options
The option VZERO=2 allows faster runtime when large circuits are used.

The EXPERT option can be specified to detect possible problems in models, before and during simulation, such as:

  • negative conductances GM, GDS and GMBS
  • negative gate capacitances

The feature summary of the parameter checking in BSIM3SOI3 v3.0 is provided below:

  • To read warnings on screen, set the EXPERT option to 777
  • To perform all possible tests, add PARAMCHK=1 to the model card.
  • To avoid writting any logfile, add PARAMCHK=-1 in the model card.

In order to control the checking procedure, two values are used :

  • The EXPERT option : if equal to 777, non-fatal warnings will be displayed on screen. The fatal warnings are always sent to screen.
  • The PARAMCHK model parameter : if equal to 1 or true, a full parameter testing will be performed, issuing warnings when suspicious parameters values are found

The logfile contains the warnings concerning models and devices, as well as the number of fatal errors and clipped parameters. It is created when PARAMCHK > 0. If the logfile cannot be created (lack of disk space, no write permissions, etc...), warnings will be sent to screen.

If it is created, the logfile is named after the netlist’s filename, appended with the model’s type, and the extension chk. For example : netlist1.bsim3soi_v2.chk

Fatal errors are always displayed on screen, and make the simulation stop. A summary is also always displayed on screen, giving the number of fatal errors and clipped parameters.

SmartSpice includes two algorithms for the BYPASS option which can be invoked setting BYPASS=1 and BYPASS=2. In the best case, the performance of simulations has been improved of 30%.

New Model Parameters
New model parameters are listed in Table 2.

Parameter Description Units Default
VERSION Version selector
-
3.0
SMART Improvement selector
-
2
LMIN Minimum length for binning
m
0.0
LMAX Maximum length for binning
m
1.0
WMIN Minimun width for binning
m
0.0
WMAX Maximun width for binning
m
1.0
TMIN Minimum temperature for binning
degC
0.0
TMAX Maximum temperature for binning
degC
0.0
BULK Default body (bulk) node name
-
“not given”
BACKGATE Default backgate (substrate) node name
-
“not given”

Table 2. SmartSpice Specific parameters.

 

The four model parameters (LMIN, LMAX, WMIN and WMAX) are used for binning to select a model. Moreover, a temperature binning capability has been added (TMIN and TMAX). For the bin-ning, Silvaco has also added new binned model parameters shown in Table 3.

AT GAMMA1 GAMMA2 VBM VBX XT KT1
KT1L KT2 UA1 UB1 UC1 UTE RTH0
PRT CGDL CGSL CKAPPA CF CLC CLE
XJ RBODY CSDMIN CTH0 ASD CSDESW CJSWG
PBSWG MJSWG TT XBJT XDIF XREC XTUN
LN NDIF LDIF0 TCJSWG TPBSWG NTRECF NTRECR

Table 3. New binning model parameters.

 

The SMART model parameter allows to switch on Silvaco improvements which are not compatible with original Berkeley model. SMART model parameter has been created as follows :

  • if SMART = 0: the original Berkeley model is used with its different versions
  • if SMART > 0: Silvaco’s ACM common equations are used (geometry, bulk diodes and drain/source series resistances)

 

BSIM3SOI v3.0 Model Characteristics

Figure 1. Selfheating effect on output characteristics (SOIMOD=0)

 

Figure 2. Gate tunneling currents (SOIMOD=0).

 

Figure 3. Ring oscillator (SOIMOD=0).

References

  1. BSIM3SOI PD v2.2 User’s Manual, 1999, Department of EECS, University of California, Berkeley
  2. BSIM3SOI FD v2.1 User’s Manual, 1999, Department of EECS, University of California, Berkeley
  3. SmartSpice Modelling Manual Volume 3