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 HfO 2 thin films, HfO 2 -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 HfO 2 -based FeFET approaches 30 nm. Here, multiple nonvolatile memory states are realized by tuning the electric field gradient across the Hf 0.5 Zr 0.5 O 2 (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 HfO 2 -based FeFETs.

The highly scalable ferroelectric hafnia‐based thin films can be easily integrated into ferroelectric field‐effect transistors (FeFETs) by existing Si technology, which are regarded as one of the promising candidates for fast read/write, energy‐efficient, and high‐density nonvolatile memories. However, device‐to‐device variation in threshold voltage (VTH) caused by non‐uniformity of ferroelectric properties is a serious challenge for implementing hafnia‐based FeFETs in high‐density nonvolatile memories. Here, the substrate‐orientation independent growth of Hf0.5Zr0.5O2 (HZO) thin films is realized with uniform ferroelectricity by using HfO2 seed layers. The HfO2 seed layers are beneficial to improving the ferroelectric polarization of HZO thin films grown on differently oriented Si substrates and reducing the variation in ferroelectric properties. Moreover, device simulation confirms that the proposed scheme contributes to realizing uniform memory properties in 3D vertical HZO‐based FeFETs. This study suggests the possibility to implement hafnia‐based FeFETs into 3D vertical high‐density memory.

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The ferroelectric field-effect transistors (FeFETs) with HfO 2 -based ferroelectric layers in the gate stacks are emerging as one of the most promising candidates for the next-generation nonvolatile memory devices due to their scalability and compatibility with conventional Si technology. Moreover, owing to the high radiation hardness of the HfO 2 -based ferroelectric thin films, HfO 2 -based FeFETs have attracted great interest in the fields of radiation-hard (rad-hard) memory. However, the reliability of their memory states under irradiation, which represents the validity of the stored information, has not been investigated. Here, we focus on the impact of the total ionizing dose (TID) on erased and programmed states of HfO 2 -based FeFETs. The TID radiation (Xray) characteristics of erased and programmed HfO 2 -based FeFETs are characterized using an on-site read operation. Both the erased and programmed states show robust stability under irradiation at a dose rate of 90 rad(Si)/s, and even at 230 rad(Si)/s, only the erased state shows a slight variation. The possible factors contributing to memory state degradation are discussed. Through the analysis of the threshold voltage shift and subthreshold swing evolution, as well as studies of ferroelectric polarization stability under radiation, it is revealed that the erased state degradation is caused by oxidetrapped charges rather than interface degradation or polarization switching. The physical mechanism of the difference in radiationinduced oxide-trapped charges buildup in programmed and erased FeFETs is analyzed to explain different TID radiation characteristics between them. Our work suggests that the HfO 2 -based FeFETs have great potential in radiation environment applications.