BSIM4v4

Industry Standard Sub-0.13 Micron MOSFET Model

Advanced Model Technology for Sub-0.13 Micron and RF High-Speed CMOS Design

Until now the physical MOSFET device model named BSIM3 version 3.2 and developed at UC Berkeley was considered as the industry standard model for deep sub-micron CMOS circuit design. It was rapidly adopted by IC companies and foundries for modeling devices down to 0.25 µm with a good accuracy. For device scale down to 0.10 µm, some physical mechanisms need to be better characterized. These mechanisms include:

  • The velocity overshoot
  • Better modeling of weak inversion charges
  • Gate bias dependent source and drain series resistance of LDD MOSFETs
  • More physical investigation of narrow width effects
  • Carrier quantization of MOSFET inversion layers

Basically, BSIM4v4 is developed to explicitly address the following issues, for which BSIM3v3.2 was found lacking and inaccurate:

  • Accurate modeling of sub-0.13 micron MOSFET devices
  • Accuracy in RF, high-frequency analog and high-speed digital CMOS circuit simulation
  • Model functionality (geometry-dependent parasitics model)

As a public domain model BSIM4v4 (like BSIM3v3) is a mean of communication, simplifying technology sharing and improving productivity.

BSIM4v4 Fundamental Improvements Over BSIM3v3

Like BSIM3v3, BSIM4v4 accounts for major physical effects:

  • Short-Narrow channel effects on threshold voltage
  • Non-uniform doping effects
  • Mobility reduction due to vertical field
  • Bulk charge effect
  • Carrier velocity saturation
  • Drain induced barrier lowering
  • Channel length modulation
  • Source/Drain parasitic resistances
  • Substrate current induced body effect
  • Quantum mechanic charge thickness model
  • Unified flicker noise model

BSIM4v4 has the following major improvements and additions over BSIM3v3.2:

  • Accurate model of the intrinsic input resistance for both RF, high-frequency analog and high-speed digital applications
  • Flexible substrate resistance network for RF modeling
  • New accurate channel thermal noise model and noise partition model for the induced gate noise
  • Non-quasi-static (NQS) model, consistent with the Rg-based RF model and consistent AC model, accounting for the NQS effect in both transconductances and capacitances
  • Accurate gate direct tunneling model
  • Comprehensive geometry-dependent parasitics model for various source/drain connections and multi-finger devices
  • Improved model for steep vertical retrograde doping profiles
  • Better model for pocket-implanted devices in Vth, bulk charge effect, and Rout equations
  • Asymmetrical and bias-dependent source/drain resistance, either internal or external to the intrinsic MOSFET
  • Acceptance of either the electrical or physical gate
  • Oxide thickness as the model input at the user’s choice in a physically accurate manner
  • Quantum mechanical charge-layer-thickness model for both IV and CV
  • More accurate mobility model for predictive modeling
  • Gate-induced drain leakage (GIDL) current model, available in BSIM for the first time
  • Improved unified flicker (1/f) noise model, smooth over all bias regions and accounting for the bulk charge effect
  • Different diode IV and CV charateristics for source and drain junctions
  • Junction diode breakdown with or without current limiting
  • Gate dielectric constant defined as a model parameter

 

Overview of Advanced Physics-Based Model Equations

Basic Current-Voltage (IV) Model

Including:

  • A new threshold voltage model for pocket/retrograde technologies
  • A Vgsteff formulation, re-derived to achieve better accuracy of gm, gm/Id and gm2/Id in the moderate inversion region
  • A bulk charge model, with a new formulation of Abulk to consider its strong effect on doping profile
  • Three mobility models, MOBMOD=0 and 1 coming from BSIM3v3.2 and the new MOBMOD=2 corresponding to a universal and more accurate model
  • A new output resistance model, especially suitable for long-channel and pocket-implanted devices
  • A Gate-Induced-Drain-Leakage (GIDL) current model, introduced in BSIM4
  • Two bias-dependent Rds model, corresponding to the BSIM3v3.2 model (internal) or to a new asymmetric model (external), which is more accurate for RF CMOS circuit simulation
  • A quantum-mechanical inversion-layer thickness and high-k gate dielectrics model, accounted for in both IV and CV
  • Trap-assisted tunneling and recombination current model to account for halo-doping technology
  • Scalable stress effect model for process induced stress (STI). Device performance varies with active area geometry and location of the device in the active area

 

RF and High-Speed Model

Including:

  • Four options for modeling electrode gate (bias-independent) and intrinsic input (bias-dependent) resistances, also working with multi-finger devices (fig.1)
  • Two different switches to turn on and off the charge-deficit Non-Quasi-Static (NQS) model in transient and in AC analysis, both AC and transient NQS models based on the same fundamental physics
  • A flexible built-in substrate resistance network accounting for the high frequency coupling through the substrate
  • A gate dielectric tunneling current model accounting for a current flowing between gate and substrate and a current flowing between gate and channel region, which is partitioned between the source and the drain terminals

 

Figure 1. Main DC characteristics

 

Charge-Voltage (CV) Model

BSIM4 provides three options for selecting intrinsic and overlap/ fringing capacitance models, all coming from BSIM3v3.2. The following table maps these models in BSIM4 to those in BSIM3v3.2:

CAPMOD in BSIM4 Matched Intrinsic CAPMOD in BSIM3v3.2.2 Matched Intrinsic Overlap/ fringing CAPMOD in BSIM3v3.2.2
0 0 0
1 2 2
2 (default) 3 2

Figure 2. A complete plot of all intrinsic capacitances

 

Parasitics Modeling

  • A comprehensive and versatile geometry-dependent parasitics model, providing series and multi-finger device layout modeling capabilities
  • Three asymmetrical source/drain junction diode IV models: resistance-free and breakdown-free models coming from BSIM3v3.2 and a new breakdown-and-resistance model

Noise Modeling

  • Flicker noise: a simplified model and a unified physical model are available, both coming from BSIM3v3.2 with several improvements in the unified formulation
  • Thermal noise: a long-channel model (coming from BSIM3v3.2) and a new holistic model are available

Silvaco Implementation

  • BSIM4 MOSFET model can be accessed within SmartSpice or Utmost as level 14. Older versions, 0.0, 1.0, 2.0, 2.1 and 3.0, previously released by UC-Berkeley are also supported and are accessible using the model parameter VERSION
  • The implementation is fully compatible with the most recent model description issued on March 4, 2004 by UC-Berkeley
  • Further speed improvements can be gained through the VZERO option and the multi-threading capabilities
  • The diagnostics option EXPERT is supported in BSIM4 to help the designer find convergence problems
  • Three selectable STI models : TSMC and Berkeley beta-version models are available in addition to the latest Berkeley model, using the STIMOD selector

Rev. 012114_06