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

Germanium (Ge) FinFETs with HfO_x-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 Hf_0.5Zr_0.5O_x (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 HfO_x-based device optimization.