New Version 5.0 of UFSOI Model Released in SmartSpice


The University of Florida SOI Group first released version 5.0 of UFSOI model in August 1999 and then in November 1999. To keep backward compatibility with previous versions, two model parameters (VERSION, REVISION) have been added in SmartSpice to select the desired model. By default, the value of VERSION is 5.0 and the value of REVISION is 1.0 which corresponds to the last release of November, 1999.


Global Features (prior to version 5.0)

The UFSOI NFD (Non-Fully Depleted) and FD (Fully Depleted) charge-based SOI MOSFET models have been developed from the basic modeling of thin-film devices. The principal improvements are:

  • the UFSOI NFD (Non-Fully Depleted) and FD (Fully Depleted) charge-based SOI MOSFET models are selected according to the value of the NFDMOD model parameter

  • the model for the FD SOI MOSFET, which physically accounts for the charge coupling between the front and back gates, includes a two-dimensional analysis or the subthreshold region of operation

  • the model for the NFD SOI MOSFET properly accounts for DC as well as dynamic floating-body effects in all regions of operation

  • both UFSOI models have improved quasi-2D modeling of the parasitic (coupled) BJT (current and charge), GIDL, junction tunneling, and impact-ionization currents

  • recent improvements (introduced in version 4.5) take account of polysilicon-gate depletion, energy quantization, junction tunneling, GIDL, RSCE (Reverse short Channel Effect)/halo effect and narrow-width effects

  • charge modeling has been improved

  • all terminal charges and their derivatives are now continuous for all bias conditions, as are all currents and their derivatives

  • substrate depletion charge under the source and drain regions is included as components of the source, drain and back-gate charges

  • temperature depended effects are modeled

New Features (introduced in version 5.0)

New features and improvements have been added to enhance the accuracy of the model and speed up the simulation.

Release of August [1]

  • the physical noise modeling has been expanded to account for hot-carrier effects on the channel thermal noise

  • the most noteworthy improvement is the run-time reduction for the NFD model : by switching from difference approximations to approximate analytical derivatives, DC and transient simulation times for the NFD model have been reduced by about a factor of three (Table 1)

  • bug fixes related to Iweak

  v4.5 v5.0, rev0.0 v5.0, rev1.0
FD x1 x0.73 x0.79
NFD x1 x0.33 x0.44

Table 1: Comparison of run times.

Release of November [2]
  • a physical accounting for carrier-velocity overshoot has been added (Figures 1 and 2)

  • for the NFD model, the difference approximations had to be retained for the Vbs-derivatives because of the numerical accuracy required for reliable simulation of floating body effects. The simulation time has now been reduced by a factor of 2-3 (Table 1)

  • the FD model is also valid for asymmetrical double-gate (DG) MOSFETs having one predominant channel in strong inversion

  • diffusion capacitance for Cdds has been added (needed for high Vbd)

  • dIbjt/dVds has been refined regarding Xlbjt

  • bug fixes related to Fvbjt

Figure1. Influence of the velocity overshoot with FD model

Figure 2. Influence of the velocity overshoot with NFD model

New Model Parameters

The default value of VSAT has changed to 7.0e6. VSAT should be set to its physical value (default) when the velocity-overshoot option is used (VO > 0).

Parameter Description Units Default
VERSION Version selector - 5.0
REVISION Revision selector - 1.0
VO Velocity overshoot parameter - 0.0


  1. UFSOI MOSFET MODELS (Ver. 5.0), User?s Guide, SOI Group, University of Florida, August 1999.
  2. [2] UFSOI MOSFET MODELS (Ver. 5.0), User?s Guide, SOI Group, University of Florida, November 1999.