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

Germanium (Ge) FinFETs with HfOx-based gate stacks are fabricated to study the CMOS applications. To evaluate the logic circuit operation, the associated CMOS inverters are characterized. Compared to the HfO2, the Hf0.5Zr0.5Ox (HZO) gate stack provides higher drive currents and more symmetric V-th 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 of HfOx-based device optimization.