2007 NSTI Nanotechnology Conference and Trade Show - Nanotech 2007 - 10th Annual

LINFET: A BSIM class FET model with smooth derivatives at Vds=0

L. Wagner and C.M. Olsen
IBM Systems Technology Group, US

Keywords:
compact modeling, bulk mos, distortion, bsim

Abstract:
The linearity of compact transistor models near Vds=0 is important for designing RF circuits. Currently compact models such as BSIM3/4 have problems around this bias point due to discontinuities in the derivatives. Recently, the PSP model was released which resolves the discontinuities. However, it may not be cost effective to extract parameters for older MOSFET technologies. Thus, the singularity problem is likely to remain in older technologies. We propose a method of getting around this problem by linearizing the BSIM equations and we denote this model LINFET. The advantage of this, and the motivation of this work, is that the already existing parameter set can be reused and that only a simple and inexpensive recentering may be required. We adopt the basic framework of the BSIM model and show how the discontinuities arise as various approximations and physical effects are added. In LINFET the drain current is composed of two opposing current contributions. There are two mobilities and two threshold voltages; one for the drain side and one for the source side. We also fixed the CV-model discontinuities. We editted an existing BSIM3.2 0.18um BiCMOS FET model and performed a simple recentering. The simulated DC derivatives and intermodulation distortion around Vds=0 are in reasonable agreement with measurements.

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