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.

The multilevel memory performances of ferroelectric field effect transistor (FeFET) with Hf₀ٜ₅Zr₀ٜ₅O₂ (HZO) ferroelectric thin film are investigated. Firstly, similar retention characteristics are observed for intermediate and saturated polarization states of HZO ferroelectric thin film, which enables memories for multi-bit data storage. And then, 2-bit/cell operation of HZO based FeFET is demonstrated utilizing two NAND architecture compatible write schemes of varying program pulse amplitude and width. Low cycle-to-cycle variability, long retention to extrapolation of 10 years at 85°C, and endurance of 500 cycles are achieved for the both schemes. Moreover, the mechanism for multilevel memory operations of the FeFET is illustrated based on the polarization switching dynamics of HZO ferroelectric thin film.

Compatibility of hafnium nitride (HfN) electrodes with Hf _0.5 Zr _0.5 O ₂ (HZO) ferroelectric thin films was investigated for ferroelectric field-effect transistor (FeFET) applications. It was found that HZO thin films capped by HfN top electrodes offer improved ferroelectric properties and lower leakage current densities compared to HZO thin films capped by TiN top electrodes. Moreover, FeFETs with HfN/HZO (10 nm)/SiO ₂ gate-stacks showed a fast write speed of 100 ns, a large 10-year extrapolated memory window (MW) of 0.92 V, and a moderate MW of 0.5 V after 10 ⁴ program/erase cycles. This letter represents a first attempt to fabricate high-performance FeFET memory devices with a fully hafnium-based gate-stack.