Electric Field Gradient-Controlled Domain Switching for Size Effect-Resistant Multilevel Operations in HfO2-Based Ferroelectric Field-Effect Transistor

The ferroelectric field-effect transistor (FeFET) is a promising memory technology due to its high switching speed, low power consumption, and high capacity. Since the recent discovery of ferroelectricity in Si-doped HfO₂ thin films, HfO₂-based materials have received considerable interest for the development of FeFET, particularly considering their excellent complementary metal-oxide-semiconductor (CMOS) compatibility, relatively low permittivity, and high coercive field. However, the multilevel capability is limited by the device size, and multidomain switching tends to vanish when the channel length of the HfO₂-based FeFET approaches 30 nm. Here, multiple nonvolatile memory states are realized by tuning the electric field gradient across the Hf_0.5Zr_0.5O₂ (HZO) ferroelectric thin film along the channel direction of FeFET. The multi-step domain switching can be readily and directionally controlled in the HZO-FeFETs, with a very low variation. Moreover, multiple nonvolatile memory states or multi-step domain switching can be effectively controlled in the FeFETs with a channel length less than 20 nm. This study suggests the possibility to implement multilevel memory operations and mimic biological synapse functions in highly scaled HfO₂-based FeFETs.