Modeling Short Channel MOSFETs Using the BSIM3 and Philips Level 9 Models in UTMOST

Introduction

The need for improved sub-micron MOSFET models for analog and mixed analog-digital design applications has long been recognized and is well documented [1]. Traditionally, MOSFET models have been adequate for digital design purposes but have failed to meet the needs of analog designers. Typical limitations of some of the commonly used MOSFET models include poor modeling of weak-inversion and moderate-inversion currents, inaccurate predictions of device output conductance and transconductances, non-scalability, non-physical parameters, poor predictions and discontinuities in the modeling of the transition regions between different modes of device operation, poor high frequency performance, difficulty with parameter extraction, inadequate temperature modeling, and unnecessarily large numbers of parameters. Two recently proposed models claim to address the needs of designers involved in the design of analog circuits using sub-micron devices. These models are the BSIM3 [2] and Philips Level 9 [3] MOSFET models. Both of these models are now supported by Silvaco's parameter extraction package, UTMOST, and Silvaco's circuit simulator, SmartSpice.

 

UTMOST also now offers a completely new local optimization parameter extraction environment. Local optimization within UTMOST allows the user full flexibility in the development of quick and accurate parameter extraction techniques for any supported model. Parameters can be extracted in any sequence from very specific regions of device operation which means that the physical nature of certain model parameters will not be compromised. UTMOST's local optimization facility has a multi-geometry capability and optimization targets may include device currents and/or conductances. Local optimization techniques are easy to implement and are much faster than the more traditional global optimization procedures. The speed, repeatability, and accuracy of UTMOST's local optimization option ensures that model parameters can be realistically gathered from many wafer sites. Such parametric information is imperative if reliable "worst-case" models are to be generated.

 

Example

Table 1 details basic, single geometry, local optimization procedures which were developed and implemented in UTMOST for the extraction of BSIM3 and Philips Level 9 MOSFET parameters for an n-channel device with a W/L of 20µm/0.65µm. Figures 1 and 2 show some measured and simulated device characteristics which resulted from the execution of these local optimization procedures. The success of the extraction procedure is evident from the data presented in Figures 1 and 2. More complicated multi-stage and multi-geometry local optimization procedures allow accurate scalable models to be extracted. Details and examples of such parameter extraction techniques will appear in future issues of the Simulation Standard. Local optimization procedures are also applicable to any other device models supported by UTMOST and are not limited to MOSFET models.

 

Table 1. Basic single geometry local optimization procedures for the BSIM3 and Philips Level 9 MOSFET.

 



Figure 1. Measured and simulated characteristics for a N-channel 20/0.65µm device
using the BSIM3 MOSFET model and basic local optimization strategies.

 

 

Figure 2. Measured and simulated characteristics for an N-channel 20/0.65µm
device using the Philips Level 9 MOSFET model and basic local optimization strategies.

 

 

Acknowledgment

Silvaco would like to thank Dick Klaassen of Philips Research, The Netherlands, Jian-hui Huang, Mansun Chan, and Kelvin Hui of UC Berkeley, and Chris Lyons of Analog Devices, Boston for their helpful contributions.

 

References

[1] Yannis P. Tsividis, "MOSFET Modeling for Analog Circuit CAD: Problems and Prospects," IEEE Journal of Solid-State Circuits, Vol. 29, No.3, pp. 210-216, March 1994.

[2] J.H. Huang, Z.H. Liu. M.C. Jeng, K. Hui, M. Chen, P.K. Ko, and C. Hu, BSIM3 Manual (version 2.0), University of California, Berkeley, March 1994.

[3] R.M.D.A. Velghe, D.B.M. Klaassen, and F.M. Klaassen, MOS MODEL 9, Unclassified Report NL-UR 003/94, Philips Electronics N.V., 1994.