Interfacial Oxide Layer Scavenging in Ferroelectric Hf_0.5Zr_0.5O₂-Based MOS Structures With Ge Channel for Reduced Write Voltages

Strategies to reduce the interfacial oxide layer thickness in ferroelectric (FE) Hf0.5Zr0.5O2 (HZO) metal-oxide-semiconductor capacitor (FE-MOS) structures on Ge and Si substrates were investigated by electrode engineering, as means to reduce the write voltage in FE field-effect transistors (FEFETs). When the gate metal in Ge FE-MOS capacitors is changed from W (control) to Pt/Ti, the coercive voltage is reduced from similar to 2.5 to similar to 0.9 V (a 66% reduction) along with a 64% increase in the capacitance consistent with an interfacial layer (IL) thinning. High-resolution scanning transmission electron microscopy (HR-STEM) reveals no visible IL with Pt/Ti electrodes in Ge FE-MOS, suggest-ing the scavenging of oxygen from the GeOx IL by the Pt/Ti electrode. However, a much smaller reduction of the coercive voltage was observed on Si FE-MOS structures with Pt/Ti electrodes. In this study, it is demonstrated that IL thinning might provide a pathway to reduce the write voltage in FEFETs based on conventional semiconductor channel materials down to a logic-compatible level.