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Hf0.5Zr0.5O2 (HZO)-based ferroelectric field-effect transistors (FeFETs) with HfO2 seed layer were investigated for radiation-hard nonvolatile memory applications. First, it was found that the HZO thin films grown on HfO2 seed layer showed improved crystallinity and ferroelectricity compared with those directly grown on SiO2 thin film, leading to a larger memory window (MW), better endurance, and retention properties of the HZO-based FeFETs with HfO2 seed layers. Moreover, after 1 Mrad(Si) 60Co $\gamma $ -ray irradiation, the memory properties of the HZO-based FeFETs with HfO2 seed layer were also better than those without the HfO2 seed layer. Especially, the HZO-based FeFETs with an HfO2 seed layer have a larger remaining MW (0.66 V) than that (0.29 V) of the FeFETs without an HfO2 seed layer after $1\times 10^{4}$ program/erase cycle. This work represents a first attempt to realize the high performances of radiation-hard HfO2-based FeFETs.

An amorphous ZrO2 based tunneling junction memristor (TJM) with a tunneling electroresistance (TER) ratio above 400 is demonstrated. It is attributed to the modulation of tunneling barrier width induced by the accumulation of oxygen vacancies ( $V_{O}^{+}$ ) and negative charges near the ZrO2/semiconductor interface. The ferroelectric-like behaviors attributed to the voltage-modulated switching of the dipoles consisting of $V_{O}^{+}$ and negative charges in ZrO2 are characterized by a polarization-voltage test. The ZrO2 TJM achieves a TER ratio above 400 under 2.5/–1.5 V at 100 ns write/erase pulse condition, over 104 cycles program/erase endurance, and >104 s data retention.

Exploring the high-performance non-volatile memories for realizing energy-efficient memory in complementary metal–oxide–semiconductor (CMOS) circuits, memory-in-computing, and the artificial synapse is the key to the rapid growth in data markets. One of the significant aspects is the development of non-volatile field-effect transistor (NVFET), which possesses the advantage of decoupling the “write” and “read” functions using the third terminal. In this work, building on a semiconductor channel integrated with an amorphous Al2O3 gate insulator, we report a ferroelectric-like NVFET memory and analog synapse that differ from those utilizing polycrystalline-doped HfO2 films. Switchable polarization ( ${P}$ ) is demonstrated in TaN/Al2O3/TaN, TaN/Al2O3/Si, and TaN/Al2O3/Ge stacks, which is attributed to the voltage-modulation of the oxygen vacancy and negative charge dipoles in gate insulator. A TaN/Al2O3/Ge capacitor achieves over 1010 cycles endurance of polarization-voltage measurement. A memory window (MW) of 0.85 V is obtained in the NVFET integrated with Al2O3 insulator under ±3 V at 100 ns program/erase (P/E) condition, and the P/E voltage can be reduced to ±1.6 V. A NVFET analog synapse is demonstrated to have a dynamic range above 100 [asymmetry ( $\vert \alpha _{p} - \alpha _{d} \vert $ )< 0.1] with ±2 V/100 ns potentiation/depression pulses. These results can be extended universally to other amorphous oxides and show promise for 3-D (fin-shaped) NVFETs with very small fin pitch.

Non-volatile field-effect transistor (FET) with amorphous Al2O3 dielectric is demonstrated on Si substrate, which is enabled by the voltage modulation of the oxygen vacancy and negative charge dipoles in gate insulator. Ferroelectric-like behavior in TaN/Al2O3/Si0.70Ge0.30 stacks with different thicknesses of Al2O3 is proved by polarization-voltage tests, positive-up and negative-down tests, piezoresponse force microscopy, and electrical measurements. The Al2O3 capacitors attain over 108 cycles’ endurance of polarization versus voltage measurement. A 6.5 nm-thick Al2O3 non-volatile FET achieves a memory window above 0.6 V under ±2 V at 100 ns program/erase (P/E) condition, over 104 cycles P/E endurance, and >105s data retention at room temperature.

A novel nanocrystal-embedded-insulator (NEI) ferroelectric field-effect transistor (FeFET) is demonstrated to function as a synaptic device for analog neural network (NN) applications. The NEI layer (down to 3.6 nm in thickness) comprises ferroelectric nanocrystals embedded in amorphous Al2O3, resulting in reduced operating voltages and depolarization effects as compared to conventional doped-HfO2 films. With fixed-amplitude 100 ns potentiation/depression pulses, an NEI FeFET synapse achieves weight update with small non-linearity ( $\alpha _{p}= {0.12}$ , $\alpha _{\text {d}}= -{0.09}$ ) and asymmetry factors, advantageous for analog-style NNs with online training. A convolutional NN is designed and emulated for an MNIST dataset, projecting an online training accuracy of 92%.

The mechanism of memory window (MW) degradation of Hf0.5Zr0.5O2-based ferroelectric field-effect transistors (FeFETs) with program/erase (P/E) cycling is investigated. First, the P/E cycling properties of the FeFETs are characterized at different cycling voltages. Then, the midgap voltage method is proposed to address the underlying drivers for the threshold voltage shift and MW degradation by separating the effects of oxide-trapped charges and interface-trapped charges. The mechanism for different threshold voltage evolutions between programed and erased states during P/E cycling is revealed. Moreover, the amount of MW degradation is nearly equal to the difference of midgap voltage shift values between programed and erased states, and the interface trap generation contributes to the midgap voltage shift.

Hf0.5Zr0.5O2(HZO)-based ferroelectric-field-effect transistor (FeFET) with a ZrO2 seed layer was demonstrated. It was found that the ZrO2 seed layer could effectively improve the ferroelectric properties of the (hafnium zirconium oxide) 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 ZrO2 seed layer showed wider counterclockwise 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 multilevel memory performances of ferroelectric field effect transistor (FeFET) with Hf0.5Zr0.5O2 (HZO) ferroelectric thin film are investigated. First, 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 Hf0.5Zr0.5O2 (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)/SiO2 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 104 program/erase cycles. This letter represents a first attempt to fabricate high-performance FeFET memory devices with a fully hafnium-based gate-stack.

Metal–ferroelectric–insulator–semiconductor (MFIS) structures with wide bandgap semiconductors are promising for high temperature, radiation-hard, and high-density memory applications, but the insufficient scalability of perovskite-based ferroelectric thin films and the high cost of conventional wide bandgap semiconductors are the most serious barriers for their practical applications. Here, we integrate highly scalable ferroelectric Hf0.5Zr0.5O2 (HZO) thin films on potentially low-cost bulk $\beta$ -Ga2O3substrates using an Al2O3 buffer layer to form MFIS structures and investigate the microstructural and electrical properties of the HZO thin films and TaN/HZO/Al2O3/ $\beta$ -Ga2O3(−201) MFIS structures. We find that the TaN/HZO/Al2O3/ $\beta$ -Ga2O3(−201) MFIS structure annealed at 550 °C exhibits a memory effect, which is attributed to the ferroelectricity of the HZO thin film. This letter represents the critical first step in the implementation of $\beta$ -Ga2O3in HfO2-based ferroelectric memories.

A novel nanocrystal-embedded-insulator (NEI) ferroelectric negative capacitance field-effect transistor (NCFET) is proposed and demonstrated. The NEI layer comprises orthorhombic ZrO2 nanocrystals embedded in amorphous Al2O3, as confirmed by high-resolution scanning transmission electronmicroscopy and diffraction analysis. The ferroelectric nature of NEI is proved by polarization-voltage measurements, piezoresponse force microscopy, and electrical measurements. The NEI NCFET achieves superior subthreshold swing (SS) and drive current compared with a control MOSFET with the same Al2O3 gate insulator thickness. Sub-60-mV/decade SS is also maintained through multiple DC sweeping cycles.