Model Behavior
Posted date : Jul 26, 2010

Leti has compact models ready for FD-SOI SPICE simulations.

A critical link in the move to FD-SOI is the availability of robust compact models. Compact models of transistors and other elementary devices are used to predict the behavior of a design.  As such, they are embedded in simulations like SPICE that designers run before actual manufacturing.

Extremely thin FD-SOI (ETSOI) technologies offer an excellent alternative to bulk thanks to great electrostatic control and low variability.  Naturally, the transistors have different characteristics than current generations of bulk or partially depleted (PD) SOI, so new models are necessary.

This example of parameter extraction results illustrates some comparisons between measurements and simulations with this compact model. (Courtesy: Leti)

To support these technologies from an IC design point of view, Leti has developed an FD-SOI compact model.  It is based on the same approach as the new, industry-standard surface potential PSP model, which is now used by the major foundries for bulk technologies at and below the 45nm node.

The code was developed using the Verilog-A language and is compatible with most all IC simulators. This new model takes into account all standard parasitic effects plus specific effects of ETSOI MOS devices such as the interface coupling.  It is specifically tuned for ultra-thin (<10nm) undoped silicon films.  Furthermore, it is perfectly compatible with ultra-thin buried oxide (UTBOX) technologies.

The core of the model is fully based on physics, which is the best choice for modeling variability.  Every step was validated using TCAD simulations and/or measurements.

New analytical expressions of surface potentials, drain currents and charges are specifically computed for FD-SOI transistors. In addition, the mean parasitic effects, such as short channel effects, stress effects, self heating effects, gate leakage currents, gate induced drain/source leakages, etc. are included in the model code.
As with bulk PSP models, the concept of local-global parameters is preserved. For the designer, this means that there is no difference in design flow between bulk and FD-SOI simulations.

The models have also been included in Leti’s Process Design Kit (PDK), which is available to external partners.

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