Chapter 2 - Electrothermal Characterization, TCAD Simulations, and Physical Modeling of Advanced SiGe HBTs

Abstract

Abstract This chapter analyzes electrothermal effects in advanced SiGe heterojunction bipolar transistors (HBTs), which are affected by critical thermal issues that seriously impact and degrade their performances; in these devices, a deep insight into the mechanisms of heat generation and diffusion, as well as an accurate characterization and modeling of these phenomena are mandatory, in order to allow realistic circuit simulations during the design phase. The measurement techniques adopted for the characterization of static and dynamic electrothermal effects are presented, with particular attention to the extraction of the thermal resistance and impedance and to two-tones large signal operation. Special transistor test structures designed in a state-of-the art BiCMOS technology node from Infineon Technologies have been analyzed. For these test structures, the electrothermal impact of the back-end-of-line (BEOL) metallization is analyzed and a compact modeling approach is described and validated in the time and frequency domain. It is demonstrated that performance improvements are possible with a careful design of metal heat spreaders placed above the transistors. The measured thermal parameters are compared to the results of thermal 3D TCAD simulations, and the concept of thermal penetration depth is introduced and its implications on the device operation are discussed.