Sripriya Das


Scaling of CMOS technology to 100 nm & below and the endless pursuit of higher operating frequencies drive the need to accurately model effects that dominate at those feature sizes and frequencies. Current modeling techniques are frequency limited and require different models for different frequency ranges in order to achieve accuracy goals. In the foundry world, high frequency models are typically empirical in nature and significantly lag their low frequency counterparts in terms of availability. This tends to slow the adoption of new foundry technologies for high performance applications such as extremely high data rate serializer/deserializer transceiver cores. However, design cycle time and time to market while transitioning between technology nodes can be reduced by incorporating a reusable, industry-standard model. This work proposes such a model for device gate impedance that is simulator-friendly, compact, frequencyindependent, and relatively portable across technology nodes. This semi-empirical gate impedance model is based on depletion in the poly-silicon gate electrode. The effect of device length and single-leg width on the input impedance is studied with the aid of extensive measured data obtained from devices built in 110 nm and 180 nm technologies in the 1-20GHz frequency range. The measured data illustrates that the device input impedance has a non-linear frequency dependency. This variation in input impedance is the result of gate poly-silicon depletion, which can be modeled by an external RC network connected at the gate of the device. Excellent agreement between the simulation results and the measured data validates the model in the device active region for 1-20GHz frequency range. The gate impedance model is further modified by incorporating parasitic effects, extending its range to 200MHz-20GHz. This model performs accurately for 180 run, 110 nm and 90 nm technologies at different bias conditions and dimensions. The model and model parameter behavior are consistent across technology nodes thereby enabling re-usability and portability. The accuracy of this new gate impedance model is demonstrated in various applications: to validate the model extraction techniques for different device configurations, to assess the input data run-length variations on CML buffer performance and to estimate the jitter in ring oscillators.

Library of Congress Subject Headings

Metal oxide semiconductor field-effect transistors--Design and construction; Metal oxide semiconductor field-effect transistors--Mathematical models

Publication Date


Document Type


Student Type


Degree Name

Microsystems Engineering (Ph.D.)

Department, Program, or Center

Microsystems Engineering (KGCOE)


P.R. Mukund

Advisor/Committee Member

J.E. Moon

Advisor/Committee Member

R. Pearson


Physical copy available from RIT's Wallace Library at TK7871.99.M44 D37 2007


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