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

Ferroelectric field-effect transistors (FeFETs) with a TiN/Hf 0.5 Zr 0.5 O 2 (HZO) gate stack on a germanium p-type channel are fabricated as low-voltage nonvolatile memory (NVM) devices. The clean HZO/Ge interfaces and the absence of a typical passivation oxide layer resulted in stable and robust ferroelectricity without a severe wake-up effect. The impact of unpassivated interfacial defect states on a 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 × 10 4 cycles. With the optimum measurement conditions the memory window is 0.55 V. Retention measurements up to 10 4 s 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 a gate-first process and reduced total thermal budget. The lower dopant activation annealing of Ge at ∼600 °C in comparison with Si at temperatures greater than 1000 °C is compatible with the crystallization annealing of HZO, and thus the two annealing processes occur simultaneously in one step.