Hf0.5Zr0.5O2-Based Germanium Ferroelectric pFETs for Nonvolatile Memory Applications

Ferroelectric Field-Effect Transistors (FeFETs) with TiN/Hf_0.5Zr_0.5O₂ (HZO) gate stack on germanium p-type channel are fabricated as low voltage non-volatile memory (NVM) devices. The clean HZO/Ge interfaces and the absence of a typical passivation oxide layer resulted in stable and robust ferroelectricity without severe wake-up effect. The impact of unpassivated interfacial defect states on germanium surface on the functionality of transistors is examined. The ferroelectric field-effect is clearly observed and remains during electric field cycling at least until 5∙10⁴ cycles. With the optimum measurement conditions the memory window is MW=0.55 V. Retention measurements up to 10⁴ sec show a small reduction to 0.5 V and from data projection it is inferred that the devices are not expected to fail before 10 years. These first results of HZO-based Ge-FeFETs are promising for the realization of gate-first process and reduced total thermal budget. The lower dopant activation annealing of Ge at ~600^oC in comparison with Si at temperatures >1000^oC is compatible with the crystallization annealing of HZO, thus the two annealing processes occur simultaneously in one step.