Investigation on Germanium Transistors with HfOx-Based Gate Stacks for CMOS Operations

Abstract

Germanium (Ge) FinFETs with HfOx-based gate stacks were fabricated to study the complementary metal oxide semiconductor (CMOS) applications. To evaluate the logic circuit operation, the associated CMOS inverters were characterized. Compared to the HfO2, Hf0.5Zr0.5Ox (HZO) gate stack provides higher drive currents and more symmetric Vth behaviors, which should be associated with the polarization effect. Through cyclic voltage transfer characteristic (VTC) operation and systematical analysis, it is found that both polarization and charge trapping in the gate stack impact the device characteristics. The HZO devices show a negative VTC shift with cycling, while the HfO2 devices reveal a positive shift. This opposite VTC behavior for both gate stack schemes indicates that the interaction of interface states and dipoles significantly influences the device operation. The results revealed in this work present a comprehensive understanding for HfOx-based device optimization.