Modelling of advanced silicon-based substrates for RF and mm-wave applications
(2021)
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Details
- Authors
- Supervisors
- Raskin, Jean-Pierre
- Abstract
- At high frequency, the accurate modelling of parasitic elements is crucial to IC design. Substrate behavior is a significant contributor to such parasitics, and its modelling is a challenge, not only under small-signal conditions due to strongly non-uniform resistivity profiles in semiconductor materials, but especially under large-amplitude excitations. In this work, substrate impact on a variety of pertinent integrated devices is studied, under both small- and large-signal conditions. To do so, the effective resistivity and linearity parameters are defined as RF substrate figures of merit, and their extraction procedures are described. These figures of merit serve as reliable indicators of substrate loss, coupling, and induced signal distortion. It is required that such considerations be kept under careful control in front-end circuitry for advanced telecommunication applications that have stringent spectral cross-contamination specifications between adjacent communication bands. In this thesis, both small- and large-signal modelling approaches are developed to account for such substrate effects. The developed models are heavily based in material semiconductor physics, and, in this work, the physical charge-balance interplay is rigorously studied, shedding light on the inner workings of a wide range of silicon-based substrates under both quasistatic and strong non-equilibrium transient conditions. In particular, the developed large-signal modelling scheme is demonstrated to be stable, i.e. to converge in both space and time, and to correlate well to a wide set of measurement data from over 20 different silicon-based substrates. The impact of each considered parameter, be it a material parameter (traps, doping, interface charge, etc.), an excitation parameter (signal amplitude, frequency, etc.), or an environment parameter (temperature, dimensions/layout of the structure, etc.), is not only well captured by the model, but beyond that the data trends can be fully explained thanks to the deep physical understanding developed throughout this text, based on a set of key concepts such as Fermi-level pinning, finite carrier inertia, drift and recombination time constants, partial equilibrium, available free carriers, etc. After applying the physical analyses to the most widespread flavors of RF substrate solutions, i.e. high-resistivity-types and trap-rich-types of wafers (commercial 300 mm samples from Soitec and university-fabricated samples), the models are used to develop and optimize novel RF substrates. Two novel interface passivation schemes of HR-Si are presented, the first based on P and N surface implants, and the second on substrate interface potential control through the field-effect. Furthermore, two bulk passivation schemes are presented, the first based on the introduction of deep-level traps in all silicon regions by doping with Gold (Au) atoms, and the second based on the porosification of the silicon bulk. All four of schemes are demonstrated as being viable through simulations and by measurements of fabricated prototype wafers. Beyond being of use for developing RF substrate solutions at the material level, the simulation approach is relevant to the design of RF and mm-wave circuits and systems. As of yet, no satisfactory large-signal modelling tool is available that can capture substrate-induced signal distortion effects. The combination of the model outputs with a full-wave EM simulator is proposed as a perspective to this work in the final chapter as a potential design flow to be of practical use to the RFIC design community.
- Affiliations
Citations
Rack, M. (2021). Modelling of advanced silicon-based substrates for RF and mm-wave applications. https://hdl.handle.net/2078.5/240311