Theoretical and experimental investigation of advanced SiGe HBTs under extreme operating conditions and compact model development
Zusammenfassung der Projektergebnisse
Silicon-based BiCMOS technologies offering Silicon-Germanium (SiGe) bipolar transistor operating speed well beyond 200GHz enable implementation of high-frequency (h.f.) applications such as 60GHz WLAN, 40/80/160Gb/s fiber-optic systems or 24/77GHz collision radar. Present experience shows, that cost and design of h.f frontend circuit modules represent a significant bottleneck for the implementation ofthe overall system, even at today's fairly low frequencies of 2..lOGHz. Furthermore, considering skyrocketing mask cost, a reduction of design cycles is of utmost importance, which requires very accurate models for circuit simulation (so-called compact models). The main goal of this project was to provide physics-based geometry-scalable compact transistor models that are suited for h.f analog circuit design related aspects, including circuit optimization. The focus has been on modeling Si/SiGe heterojunction bipolar transistors (HBTs) operating in, e.g., power amplifiers (PAs) and under extreme conditions that affect or limit the existing model accuracy as well as the device performance itself This project addressed the most critical modeling challenges for advanced HBTs. • A methodology for generating distributed electrothermal compact models was developed that allows to accurately describe inter-device thermal coupling. The method is based on a Green's function approach for solving the heat equation and can be applied to multi-finger transistors as well as multi-transistor arrays enclosed by either deep trench or junction isolation. • Generating accurate distributed compact models requires to partition the entire device in appropriate subcells. The latter are then represented by compact models that are properly coupled electrically and thermally to each other. Improved geometry scalable formulations have been developed for the substrate coupling network elements using conformal mapping techniques and also for the base resistance. The equations cover the large variety of contact configurations found in advanced HBTs. • In advanced SiGe technologies lateral variations ofthe doping profile under the emitter have been observed, which can not be captured by the existing standard scaling method. Hence, a "non-standard" scaling approach has been developed and verified for profile variations typically occurring in advanced SiGe HBT process technologies. • At medium and high injection, the electric field distribution in the collector region determines the current dependent avalanche multiplication factor, base-collector capacitance, and transit time. An analytical formulation for the field was derived and employed for a compact analytical description ofthe base-collector depletion capacitance and the non-local avalanche multiplication factor. The new formulations have been implemented in a preliminary version of HICUM/L2 and have been verified through single- and two-tone analyses as well as load-pull operation with data from both measurements and mixed-mode device/circuit simulation. Employing the latter was necessary since, unfortunately, the requested funding for a special test chip dedicated to this project had not been approved. Hence, the experimental verification was only possible on less suitable transistor structures that did not always allow to demonstrate the full potential ofthe new model. Therefore, additional verification is still required before releasing a new production-type HICUM version.
Projektbezogene Publikationen (Auswahl)
- "Non-standard geometry scaling effects in high-frequency SiGe bipolar transistors", Proc. of WCM, International NanoTech Meeting, Santa Clara, pp. 603-608, 2007
M. Schröter, S. Lehmann, D. Celi
- "The rectangular bipolar transistor tetrode structure and its application", Proc. of ICMTS, Tokyo, pp. 1397-1402, 2007
M. Schröter and S. Lehmann
- "Compact Layout and Bias-Dependent Base-Resistance Modeling for Advanced SiGe HBTs", IEEE Trans, on Electron Devices, Vol. 55, pp. 1693-1701,2008
M. Schröter, J. Krause, S. Lehmann, D. Celi
- "Improved layout dependent modeling ofthe base resistance in advanced HBTs", Proc. of WCM, International NanoTech Meeting, Santa Clara, pp. 603-608, 2008
S. Lehmann, M. Schröter
- "Modeling of SiGe HBT operation in extreme temperature environment" Abstracts of Swedish national symposium "GH2008", Göteborg, p. 9i, 5-6 March, 2008
P. Sakalas, M. Ramonas, M. Schröter, A. Kittlaus, H. Geissler, C. Jungemann, A. Shimukovitch
- "Status of DFG Project "High-Frequency Power Bipolar Transistor Modeling (HF-BTM)" ", HICUM-Workshop, Böblingen, 2008
S. Lehmann, M. Schröter and Y. Zimmermann
- "A HICUM extension for medium current densities", HI-CUM Workshop, Würzburg, 2009
A. Pawlak, M. Schröter, J. Krause
- "Schwarz-Christoffel Mapping for LDMOS and Bipolar Transistor Modeling", IEEE Semiconductor Conference Dresden, Dresden, Germany, April 29-30, 2009
K.E. Moebus, Y. Zimmermann, M. Schröter
- „TRADICA - an integrated modeling tool linking process and circuit design", IEEE Semiconductor Conference Dresden, Dresden, Germany, April 29-30, 4 pages, 2009
Y. Zimmermann, K.E. Moebus, H. Wittkopf, M. Schröter
