Design Considerations for 4H-SiC Lateral BJTs for High Temperature Logic Applications

Abstract

4H-silicon carbide (SiC)-based bipolar integrated circuits (ICs) are suitable alternatives to silicon (Si)-based ICs in high temperature applications, owing to superior properties of 4H-SiC and the robust performance of SiC bipolar junction transistors (BJTs). However, cost, size, and manufacturability of 4H-SiC ICs remains inferior to the prevalent Si-based ICs, due to large footprint and high number of epilayers in conventional SiC BJTs. An alternative to overcome these limitations is to use lateral BJTs (LBJTs). Though Si LBJTs have been demonstrated, this is the first time they are explored in 4H-SiC. This paper proposes a symmetric, self-aligned 4H-SiC LBJT design, which is relatively easier and cheaper to manufacture, has fewer epilayers, and is >90% smaller than existing structures. Extensive device simulations and optimization is performed to achieve optimal current gains, at a range of temperatures (27 °C–500 °C). The results suggest current gains of over 100 in devices with base width of 1 $\mu \text{m}$ , at room temperature. The applicability of the structure is validated by designing a 4H-SiC LBJT-based emitter-coupled logic inverter, which shows stable operation and good speeds (~3 ns) up to 500 °C, while having high integration density and lower cost.