Anjan Chakravorty

In this brief, we propose a step-by-step strategy to accurately estimate the finger temperature in a silicon-based multifinger bipolar transistor structure from conventional measurements. First we extract the nearly zero-power self-heating resistances (Rth,ii (Ta)) and thermal coupling factors (cij (Ta)) at a given ambient temperature. Now, by applying the superposition principle on these variables at nearly zero-power, where the linearity of the heat diffusion equation is preserved, we estimate an effective thermal resistance (Rth,i (Ta)) and the corresponding revised finger temperature Ti (Ta). Finally, the Kirchhoff's transformation on Ti (Ta) yields the true temperature at each finger (Ti (Ta,Pd)). The proposed extraction technique automatically includes the effects of back-end-of-line metal layers and different types of trenches present within the transistor structure. The technique is first validated against 3-D TCAD simulation results of bipolar transistors with different emitter dimensions and then applied on actual measured data obtained from the state-of-the-art multifinger SiGe HBT from STMicroelectronics B5T technology. It is observed that the superposition of raw measured data at around 40 mW power underestimates the true finger temperature by around 10%.

A prior estimate of the impact of thermal resistance from the back-end-of-line (BEOL) metallization layers is crucial for an accurate circuit design and thermally aware device design. This article presents a robust technique to extract the thermal resistance component originating from the BEOL metal layers in silicon germanium heterojunction bipolar transistors (SiGe HBTs). The proposed technique is first tested on data generated using analytical equations and later validated with 3-D TCAD simulation. The results clearly show that the exact contribution of the BEOL to the overall thermal resistance is captured in the proposed approach. Finally, we verified the method using measured data obtained from fabricated SiGe HBT structures using Infineon B11HFC technology. The extracted parameters show reasonable accuracy and consistency across different emitter dimensions and BEOL configurations.