Min Hyuk Park

Hf1–xZrxO2 (HZO) is a complementary metal–oxide–semiconductor (CMOS)-compatible ferroelectric for scaled nonvolatile memories and three-dimensional integrated electronics. However, its integration is constrained by the thermal exposure required to crystallize and retain polar orthorhombic Pca21. Building on established transformation kinetics, this Review organizes low-thermal-budget HZO processing as a path-dependent phase-selection problem. The pathway is organized into crystallization readiness, phase-selective nucleation of a metastable pseudo-cubic parent, competitive grain growth, nonpolar-to-polar conversion, suppression of monoclinic relaxation, and polar-state retention and activation. Precursor chemistry, internal interfaces, mechanics, oxygen-deficiency timing, composition, dopants, and photon- or field-assisted treatments are assessed by the bottleneck they primarily remove. Representative processes near 300 °C and within the 350–400 °C back-end-of-line window are benchmarked using deposition and annealing histories, stack geometry, pristine vs cycled response, measurement conditions, and reliability. The literature favors coupled or sequential interventions rather than a universally optimal interface, stress state, vacancy concentration, or dopant. Priorities include standardized thermal-budget reporting, phase-specific in situ characterization, quantitative descriptors of the pre-crystalline state, and predictive links from the as-deposited film to reliable device operation.

Ferroelectric hafnium zirconium oxide can increase charge density in scaled capacitors, but its high coercive field limits the low-voltage, high endurance switching required for dynamic random-access memory and embedded ferroelectric memories. Here we show that plasma-engineered (111)-textured TiN electrodes with N-rich, oxidation-resistant surfaces suppress interfacial oxidation and enable robust switching in 5 nm Hf _0.5 Zr _0.5 O ₂ capacitors. The devices exhibit saturated hysteresis at 0.6 V, with 2 P _r = 31.5 μC cm ⁻² and E _c = 0.62 MV cm ⁻¹ , and no hard electrical breakdown through 10 ¹² bipolar cycles. Their nucleation-limited switching kinetics extrapolate to sub-nanosecond polarisation reversal at DRAM-relevant capacitor areas. At 1.1 V, circuit simulations of a common plate 1T–1 C cell yield short- and long-term stand-by sensing margins of 482 and 201 mV under a 20 fF bit line load. Electrode texture and interface engineering therefore enable low-voltage, high speed switching without compromising endurance, mitigating the practical Kay–Dunn scaling penalty and the speed–endurance dilemma.

Defect‐regulated crystallization pathways govern metastable phase formation in functional oxides, yet the role of oxygen‐vacancy‐related oxygen deficiency in crystallization and ferroelectric phase stabilization in ultrathin Hf _0.5 Zr _0.5 O ₂ remains unresolved. This work combines atomic‐layer‐deposition ozone‐dose tuning with temperature‐resolved in situ grazing‐incidence wide‐angle X‐ray scattering reciprocal‐space mapping to track crystallization in 10 nm Hf _0.5 Zr _0.5 O ₂ thin films with systematically varied, X‐ray Photoelectron Spectroscopy‐inferred relative oxygen‐deficiency levels. Vacancy‐lean films crystallize at lower temperatures than vacancy‐rich films (370°C vs. 400°C) and exhibit a lower comparative apparent activation energy for crystallization (3.6 × 10 ² vs. 4.4 × 10 ² kJ mol ⁻¹ ), together with more efficient lateral crystallite growth and a larger strain‐free d‐spacing consistent with an increased orthorhombic‐phase contribution. In contrast, vacancy‐rich films show delayed crystallization, suppressed lateral coarsening, and stronger tetragonal‐phase retention. The vacancy‐lean film achieves a switchable polarization, 2P _r , of 19.9 µC cm ⁻² after annealing at 400°C, within a back‐end‐of‐line‐relevant thermal budget; higher annealing temperatures induce partial monoclinic transformation and reduce polarization. These results identify oxygen‐deficiency control as a practical route to tune crystallization pathways and low‐temperature ferroelectric phase formation in HfO ₂ ‐based thin films.

HfO ₂ ‐based ferroelectrics have attracted intensive research interest as promising candidates for next‐generation nonvolatile memory, particularly due to their excellent complementary metal‐oxide‐semiconductor (CMOS) compatibility and scalability. Unlike conventional perovskite ferroelectrics, their ferroelectricity originates from a metastable non‐centrosymmetric phase, whose stability is highly sensitive to electrical cycling, defect chemistry, and processing conditions. Consequently, the evolution of ferroelectric properties during repeated electrical operation proceeds through two distinct phenomena, wake‐up and fatigue, whose combined progression determines device endurance and reliability. This review covers the physical origins and operating mechanisms of wake‐up and fatigue in HfO ₂ ‐based ferroelectrics, including oxygen vacancy dynamics and interfacial defect chemistry. Building on these insights, we discuss experimentally demonstrated strategies for controlling these behaviors, including composition and doping engineering, process optimization, electrode and interlayer design, and multilayer structural engineering. The discussion is further extended from materials‐level mechanisms to device‐level applications, with particular emphasis on how defect redistribution, charge trapping, domain‐wall pinning, and cycling‐induced phase evolution modify finite‐pulse switching kinetics. By correlating defect/phase‐transition physics, switching dynamics, and device‐level reliability metrics, this review provides design guidelines for the development of reliable HfO ₂ ‐based ferroelectric devices.

Physical reservoir computing requires nonlinear response, fading memory, and rich transient state diversity, yet conventional nonvolatile memories often rely on explicit reset operations or long relaxation times. ZrO ₂ ‐based two‐terminal antiferroelectric tunnel junctions (AFTJs) exploit the field‐induced tetragonal‐to‐orthorhombic transition and spontaneous back‐switching of antiferroelectric ZrO ₂ . This intrinsic self‐relaxation provides reset‐free fading memory in the sub‐ms regime. An amorphous In‐Ga‐Zn oxide interlayer enlarges the dynamic range, and stoichiometric control identifies the 2:2:1‐ZrO ₂ AFTJ as the optimal composition, delivering an I _on /I _off of ∼890, a peak nonlinearity factor of ∼48.4, and a paired‐pulse facilitation index of 1.79. The enhanced memory margin and nonlinear dynamics support 16 transient current states and yield 90.4% accuracy in Modified National Institute of Standards and Technology classification with a fourfold reduction in spatiotemporal dimensionality. Temporal information processing is further assessed using an experimentally calibrated circuit‐level reservoir model, enabling waveform classification, one‐step‐ahead Hénon‐map prediction (normalized root‐mean‐square error [NRMSE] = 0.01489), and forecasting of a noisy real‐world semiconductor index time series (NRMSE = 0.12263). The fabricated 40 000 µm ² AFTJ shows a unit latency of ∼2 µs and energy consumption below 480 pJ per operation. Analytical area scaling projects show that a 100 µm ² device could achieve ∼192 ns latency and ∼115 fJ per operation.

Selector-only memory (SOM) based on ovonic threshold switches is a promising candidate for dense cross-point memory by integrating selector and memory functions in a single two-terminal device. However, the physical origins of off-state conduction and threshold voltage (V_th) modulation remain unclear. Here, we investigate these mechanisms in a Te-rich Ge-Sb-Se-Te:Sn SOM by correlating DC transport, low-frequency noise (LFN), and materials analyses. DC I-V characteristics analyzed using Poole-Frenkel (PF) emission and trap-assisted tunneling (TAT) models reveal identical trap energy levels across prefirst firing, low-V_th, and high-V_th states, indicating a common trap species with state-dependent spatial redistribution. LFN measurements distinguish PF- and TAT-dominated regimes and show consistent state-dependent noise behavior. Cross-sectional energy-dispersive X-ray spectroscopy reveals electric-field-polarity-dependent Te redistribution near the top electrode, while ab initio calculations identify Te-Te dimer defects as acceptor-like deep traps governing off-state conduction. These results provide a unified mechanism for V_th modulation in Te-based SOM devices.

Ferroelectricity in (Hf,Zr)O2 thin films is highly sensitive to bottom-electrode chemistry, as interfacial redox reactions during atomic layer deposition (ALD) and subsequent annealing can generate defective interlayers and alter oxygen-vacancy distributions. Here, we propose a stoichiometry- and lattice-tunable molybdenum nitride (MoNx) electrode platform that enables single-layer interfacial engineering through control of the Mo:N ratio. MoNx films with x = 0.00, 0.05, 0.52, and 0.79 (denoted as Mo, 05MoN, 52MoN, and 79MoN) were sputter-deposited and integrated into symmetric MoNx/Hf0.5Zr0.5O2/MoNx capacitors containing 8 nm-thick ALD Hf0.5Zr0.5O2. Structural analysis confirms a transition from Mo (110)-textured films to rock-salt-type MoNx with a (111) texture at higher N contents, while electrode-grade resistivity is maintained (≤ 200 μΩ∙cm for 52MoN). Chemical analyses reveal that increasing the N content substantially suppresses ALD-induced electrode oxidation and reduce the thickness of the oxidized interfacial-layer by 47.7% for 52MoN relative to Mo; N incorporation into the Hf0.5Zr0.5O2 (HZO) near the bottom interface is also detected. Consistently, the monoclinic phase fraction decreases from ~ 21% for Mo to < 5% for 52MoN and 79MoN. All capacitors exhibit minimal wake-up, with a ≤ 3.0% change in double remanent polarization after 104 cycles at 3 MV∙cm-1. Benchmarking against other stoichiometry-controlled electrode systems (e.g., TaNx, RuOx, and TiNx) shows that the MoNx platform maintains high pristine polarization (> 47.5 μC∙cm-2) while suppressing wake-up across a wide compositional range. Endurance improves markedly with N content, reaching ~ 108-109 cycles for high-N MoNx electrodes, depending on the cycling voltage. These results establish MoNx as a scalable, composition-engineerable electrode system that couples interfacial microstructure control with enhanced ferroelectric reliability in HZO thin films.