Pushing away the silicon limits of ESD protection structures: Exploration of crystallographic orientation

Improving the ESD robustness of integrated protection structures to cope with the constraints of severe environments such as the automotive one is a real challenge. Getting a deep understanding of the involved high injection physics during an ESD stress helps defining specific design guidelines. The grounded-base NPN bipolar transistor is a popular and efficient protection device. In this paper, we explore the impact of crystal orientation on the electrical characteristics and the robustness of this device. It is shown for the first time that orienting the structure 45deg with respect to the wafer flat allows significantly improving its on-resistance. A 30% improvement is measured on the device under study.