Hf0.5Zr0.5O2 (HZO) based ferroelectric-field-effect transistor (FeFET) with a ZrO2seed layer was demonstrated. It was found that the ZrO2seed layer could effectively improve ferroelectric properties of the HZO thin film. The remanent polarization and the coercive voltage of the metal-ferroelectric-insulator-semiconductor (MFIS) structure with the ZrO2-seed layer were larger than those without the seed layer. Moreover, the FeFET with the ZrO2seed layer showed wider counter-clockwise hysteresis loops in the transfer characteristics than that without the seed layer, achieving a large memory window of about 2.8 V. These results validate the advantages of the ZrO2 seed layer in promotion of FeFET performance and thus warrant further study.

The HfO2-based ferroelectric field effect transistor (FeFET) with a metal/ferroelectric/insulator/semiconductor (MFIS) gate stack is currently being considered as a possible candidate for high-density and fast write speed non-volatile memory. Although the retention performance of the HfO2-based FeFET with a MFIS gate stack could satisfy the requirements for practical applications, its memory window (MW) and reliability with respect to endurance should be further improved. This work investigates the advantage of employing ZrO2 seed layers on the MW, retention, and endurance of the Hf0.5Zr0.5O2 (HZO)-based FeFETs with MFIS gate stacks, by using fast voltage pulse measurements. It is found that the HZO-based FeFET with a ZrO2 seed layer shows a larger initial and 10-year extrapolated MW, as well as improved endurance performance compared with the HZO-based FeFET without the ZrO2 seed layer. The results indicate that employing of a direct crystalline high-k/Si gate stack would further improve the MW and reliability of the HfO2-based FeFETs.

We demonstrate for the first time ZrO2 ferroelectric field-effect transistors (FeFETs) for em-bedded non-volatile memory applications. Multiple sweeps of polarization vs. voltage measurement demonstrate that a metal/ZrO2/Ge capacitor is entirely free of wake-up effect and has significantly improved fatigue characteristics compared to a HfZrOx control device. Thanks to relatively small remnant polariza-tion and a high-quality ZrO2/Ge interface, up to 107 cycles program/erase endurance, 10 ns program/erase speed, and >10-year data retention at 85°C are achieved.

HfO₂-ZrO₂ superlattice (SL) ferroelectric (FE) ultrathin films exhibit significant improvement in endurance performance compared with solid-solution Hf_xZr_1−xO₂ (HZO). Despite the experimental evidence, the underlying microscopic mechanisms of the enhanced reliability of SL remain elusive. This Letter explores the mechanism by performing first-principle calculations on SL and HZO systems. The enhanced endurance in the SL can be well explained by higher oxygen vacancy (Vo) migration energy barriers along the FE polarization direction, which slow down the increase in Vo. The suppression of Vo increase will potentially help maintain the stability of the FE phase and alleviate the fatigue. Based on this mechanism, we suggest that doping materials with higher Vo migration barriers can further improve the endurance of HfO₂-based FE devices. This work facilitates the future development of HfO₂-based FE devices with enhanced endurance and reliability.

Hf _0.5 Zr _0.5 O ₂ (HZO)-based ferroelectric field-effect transistors (FeFETs) with HfO ₂ seed layer were investigated for radiation-hard nonvolatile memory applications. First, it was found that the HZO thin films grown on HfO ₂ seed layer showed improved crystallinity and ferroelectricity compared with those directly grown on SiO ₂ thin film, leading to a larger memory window (MW), better endurance, and retention properties of the HZO-based FeFETs with HfO ₂ seed layers. Moreover, after 1 Mrad(Si) ⁶⁰ Co γ-ray irradiation, the memory properties of the HZO-based FeFETs with HfO ₂ seed layer were also better than those without the HfO ₂ seed layer. Especially, the HZO-based FeFETs with an HfO ₂ seed layer have a larger remaining MW (0.66 V) than that (0.29 V) of the FeFETs without an HfO ₂ seed layer after 1×10 ⁴ program/erase cycle. This work represents a first attempt to realize the high performances of radiation-hard HfO ₂ -based FeFETs.