Dr. Alexander Klös
Research Project
PREDICTMOS – Structure Oriented 2D Compact Modelling of MOS devices
Existing device models for circuit simulation of submicron MOSFETs tend to lack physical
insight. In their model equations, a large number of numerical fitting parameters have been
introduced, which strongly depend on process and layout data in a widely unpredictable way. A
common approach for featuring the scalability of a compact model is the introduction of
empirically motivated equations, again with numerical fitting parameters without any physical
meaning. Often, the range of gate geometries is split up into several subregions (“binning”);
each subregion possesses its own specific MOS model parameter set.
In the field of predictive device modelling, the application of such compact models is very
limited. While the accuracy of these models and their coverage of parasitical effects is quite
high, if they are used for standardized transistor structures, an estimation of the influence of
process or layout data variation on system performance or even a single device’s behaviour is
hardly possible. Extensive numerical device simulations followed by a sensitivity analysis would
have to be carried out, providing data for a fit of the compact model’s many numerical
parameters which are necessary for its scalability. Furthermore, in the view of a more and more
fabless design industry, the compact model of a MOS device is the major link between foundry
and design house. But when a model contains very little physical basis, it is difficult for a
designer to conduct statistical analysis or to describe matching behaviour.
Our research project:
In our research project, we developed PREDICTMOS (Predictive compact model for simulation
of submicron MOSFETs). It is a physics-based compact model, which is not only useful for
keeping physical insight during circuit simulation. It offers an effective way to investigate the
influence of process and layout data and their tolerances on system performance. The model
equations of PREDICTMOS were derived from an approach, which maintains a strong link to
process and layout data. The main intention of PREDICTMOS is to feature an acceptable
accuracy over a wide range of device geometries and process data together with the ability to
predict electrical device parameters as e.g. the threshold voltage or output conductance.
Although the accuracy obtained by numerical device simulations is expected to be higher, in the
field of device scaling calculations an analytical model is more useful to get a first coarse
estimation of system performance and to maintain physical insight hereby. PREDICTMOS
bridges the gap between very accurate, but time-consuming numerical device simulations of
MOSFETs and device structure oriented, predictive circuit simulations. For this purpose,
PREDICTMOS requires a minimum number of model parameters, which all have a strong link to
device physics.
The first release of our model was implemented in the ELDO circuit simulator via its CFAS
interface. Starting with Version 1.3R1, the UDM (User Definable Model) interface of the same
framework is used for implementation. With this, it is possible to link PREDICTMOS to the
simulator in a very common way. The model can easily be chosen via the LEVEL parameter in
the net list. The designer can make use of the standard SPICE commands for source/drain area
and parasitic resistance. Therefore, the application of PREDICTMOS is much simplified and
enables for its use in the simulation of complex circuits.
The current version of PREDICTMOS can be downloaded for testing:
http://homepages.fh-giessen.de/kloes/predictmos
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Next steps:
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Transfer of the modelling technique on new device structures as e.g. Double-Gate-FETs,
FinFET.
Extension of the 2D modelling approach to the strong inversion regime of operation.
In cooperation with:
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EU Network of Excellence SINANO ( www.sinano.org )
Darmstadt University of Technology, Solid-State Electronics Laboratory
University Graduate Center Kjeller, Norway
Universitat Rovira i Virgili, Spain
References:
[1]
A. Kloes and A. Kostka, “A fully 2D, analytical model for the geometry and voltage
dependence of threshold voltage in submicron MOSFET’s,” in Simulation of
Semiconductor Devices and Processes, Vol. 6 (H. Ryssel and P. Pichler, eds.), pp. 218–
221, Springer-Verlag, 1995.
[2]
A. Kloes and A. Kostka, “A new analytical method of solving 2D poisson’s equation in
MOS devices applied to threshold voltage and subthreshold modeling,” Solid-State
Electron., Vol. 39, 1996, pp. 1761–1775.
[3]
A. Kloes and A. Kostka, “A physics-based, analytical model for the threshold voltage in
MOSFET’s using a unified approach to account for short- and narrow-channel effects,” in
1996 International Electron Devices and Materials Symposia, Symposium A/D, pp. 285–
288, National Tsing Hua University, Hsinchu, Taiwan, R.O.C., 1996.
[4]
A. Kloes and A. Kostka, “A new physics-based, predictive compact model for small
geometry MOSFETs including two-dimensional calculations with a close link to process
and layout data,” in IEDM Technical Digest, pp. 147–150, 1996.
[5]
Kloes, A., Freund, D., Kostka, A.: Physics-based, predictive compact modeling of lateral
bipolar transistors and short-channel MOSFET´s by conformal mappings, GMM
Fachbericht 17: Mikroelektronik ´97, VDE-Verlag GmbH, Berlin, 1997.
[6]
A. Kloes and A. Kostka, “PREDICTMOS – a predictive compact model of small geometry
MOSFETs for circuit simulation and device scaling calculations,” Solid-State Electron.,
Vol. 44, 2000, pp. 1145–1156.
[7]
Kloes, A., Kostka, A.: PREDICTMOS – a contribution to performance assessment of SoC
with regard to process technology, Workshop “Heterogeneous reconfigurable systems on
chip,” Hamburg, 2002.
[8]
Kloes, A.: Unified current equation for predictive modeling of submicron MOSFETs, SolidState Electron., Vol. 49, No. 1, pp. 85–95, 2005.
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