24 Mars – Thesis defense - Mathieu Jaoul

10 h Amphi Jean-Paul Dom - laboratory IMS / building A31 (Talence campus)

Study of HBT operation beyond breakdown voltage. Definition of a Safe Operating Area in this operation regime including the aging laws

The development of new BiCMOS technology will be possible, thanks to the SiGe:C HBTs technological improvements to reach dynamic performance beyond 0.5 THz. An important aspect to be investigated is the Safe Operating Area (SOA) beyond the traditional BVCEO. In fact, due to the complexity of future architectures of HBTs (like the B55X from STMicroelectronics) and their nanoscale size, an increase of the wear-out mechanisms occurring in these transistors is expected. In addition, because of the increasing dependence of circuit design on software tools, it is expected that additional efforts will be required to develop more predictive compact models. Thus, the SOA sub-project is designed to describe the functional safety area of nanoscale SiGe:C HBTs allowing the compact model to take into account critical aspects.
After a short introduction, a precise description of the transistor operations beyond the breakdown voltage is detailed in the second chapter. The compact model HICUM is improved to account for the mechanisms occurring in this region to accurately model the avalanche regime and the pinch-in effect. This new model is validated on TCAD simulations and through electrical measurements on different devices, architecture, geometries and temperatures.
In the third chapter, the investigation is deepen towards the device border’s operation. A study of the pinch-in effect and the snapback behavior is therefore realized to understand
the operation limitations at high currents and voltages and a stable operation regime is introduced.
In the fourth chapter, accelerated aging tests are carried out at the boundaries of the safe operating area to submit the transistor to thermal and hot carriers stresses during its
operation. An aging model is developed to account for the wear-out mechanism occurring in that regime.
To conclude, this work allowed to increase the modeling of SiGe HBTs at high voltages and currents accounting for the wear-out mechanisms occurring in that operation regime.

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