Investigation of Substrate Current Effects and Modeling of Substrate Resistance Network for RFCMOS
J.C. Lee, R.B. Anna, S.L. Sweeney, L.H. Pan and K.M. Newton
IBM Corporation, US
substrate, RFCMOS, noise, modeling, investigation
RF device models focus on device performance in the high frequency region, with a reasonable DC model. The substrate current (Isub) is often regarded as unimportant in the DC model and thus ignored because the magnitude of Isub is much smaller than the channel current (Idch). However, the low frequency region of the S22 and Y22 characteristics of a FET is determined by the total output conductance (Gdsout), which is sensitive to the Isub variation. The S22 behavior at medium to high frequency is accordingly impacted by Isub variation. To our knowledge, no prior studies have been done on the relationship between substrate current and RF performance. Accuracy in predicting S22 cannot be achieved without a reliable substrate resistance (Rsub) network in addition to the Isub model. An accurate, compact and scalable Rsub network comprised of three components is proposed in this paper, which is physically consistent with the device layout configuration. It works well with BSIM3v3 for a 0.24um RFCMOS technology up to a frequency of 25GHz. We also investigate the bias dependence of noise coefficient, gamma, within the BSIM3v3 model and the de-embedding of NFmin data.
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Nanotech 2006 Conference Program Abstract