26 Octobre – Thesis defense - Bishwadeep Saha

13 h30 Visio

Investigation and modeling of high frequency - Effects in SiGe HBTs.

The demand for increased functionality and speed of modern communication systems drive the rapid development of the silicon germanium heterojunction bipolar transistors (SiGe HBTs). In this thesis high-frequency behavior of SiGe HBTs has been analyzed and subsequently developed models have been presented from three different perspectives.
First, we investigate the maximum oscillation frequency (fMAX) which is an important figure-of-merit being used to evaluate a particular process technology. It is observed that the conventional way of extracting fMAX by directly using Mason’s gain formula onto the measured data yields highly uncertain results, which effectively delays an appropriate evaluation of promising technology nodes. It has been shown that a simple y-parameter model solves this long-standing pressing problem of fast technology evaluation. Secondly, it is found that the substrate geometry and parasitic capacitance distribution play a vital role in determining the
high frequency s-parameter characteristics of modern SiGe HBTs. Since successful designs of radio-frequency circuits demand highly accurate models for small-signal s-parameters, appropriate models to cater the distributed collector-substrate effects in modern transistor structures are necessary. After reviewing the existing state-of-the-art model, the proposed correction, its implementation and results have been discussed. Finally, detailed and comprehensive TCAD and SPICE modeling frameworks for SiGe HBTs are presented with a focus to understand the high-frequency behavior of such transistors. High-frequency related parameters extraction, their sensitivity analysis and modeling results till 500 GHz have been presented and compared against the measured data obtained from modern high performance SiGe HBTs fabricated in STMicroelectronics B55 process.

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