Optimizing SiGe HBTs technology using small-signal and high frequency noise device's modeling
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B6.2.1
Optimizing SiGe HBTs technology using small-signal and high frequency noise device’s modeling J.G Tartarin 1, G. Cibiel 1, A. Monroy 2, V. Le Goascoz 2, J. Graffeuil 1 1 LAAS-CNRS and Paul Sabatier University, 07 av. Col. Roche, 31077 Toulouse cedex 4, France 2 ST-microelectronics, Crolles, France ABSTRACT The rapid expansion of SiGe technologies during the last decade essentially due to civil telecommunication’s applications have led Si/SiGe based heterojunction bipolar transistors (HBTs) to excellent performance levels, allowing high frequency low noise circuit designs such as linear low noise amplifiers( RF noise) or also low-phase noise oscillators (LF noise). Among these technologies, the SiGe BiCMOS one integrates digital and RF functions on the same chip. Fast improvements of the technological process have been performed thanks to large efforts allowed to characterization and modeling of the devices. We have investigated on the influence of technological parameters such as Germanium profile, doping level and thickness of the base layer (5 different wafers) on the dynamic and high frequency noise performances to converge towards the optimum technological process (now available with the BiCMOS6G processed by ST microelectronics). We made use of scattering parameters [S] measurements on the devices to extract the electrical parameters of our small signal model. The high frequency noise parameters based on the electrical model (with noise sources added to the junction, resistances) are simulated and compared with the measured noise parameters of the devices. The four noise parameters (Fmin, Rn, and complex Γopt) measurements have been performed from 1 GHz to 12 GHz, and the dynamic S parameters measurements have been realized in the 40 MHz-40 GHz range. These models have been used to enable the identification of the limiting parameters on the dynamic performances and on the high frequency noise parameters. INTRODUCTION The process under the scope of this study for technological improvement is the BiCMOS6G, a 0.35µm SiGe HBT/CMOS process supplied by ST-microelectronics. This process, providing transition frequency Ft and maximum oscillation frequency Fmax respectively of 45GHz and 60GHz, is suitable for system-on-chip applications up to the X-band. The base layer is known to be the critical point for high frequency low noise applications, and the optimization of the layer thickness, doping level and doping profile of the base are presented. Electrical model with noise sources stands as a good tool to give interpretations about the differences revealed by dynamic (and noise) measurements between several wafers featuring variations in their technological processes. In the first paragraph, a small signal model (with its high frequency noise sources) is introduced. The next paragraph is dedicated to the study of the optimum base’s thickness and base’s doping level. Finally, the last paragraph is dedicated to the doping Ge profile influence on the dynamic and noise performances.
B6.2.2
SMALL SIGNAL AND NOISE
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