Artificial visual systems inspired by the human visual system are gaining significant attention for their capacity to efficiently process vast visual data in neuromorphic architectures. Ferroelectric-based optoelectronic transistors with their ability to control photoconductance decay via the polarization, are particularly suited for emulating synaptic behaviors such as short-term and long-term plasticity. However, most reported devices are limited to narrow spectral responses with limited focus on the visible spectrum. Here, we present a visible-light-responsive optoelectronic synaptic transistor based on indium gallium zinc oxide (IGZO) field-effect transistors using a ferroelectric Zr-doped HfO2 (HZO) gate dielectric. The device exhibits tunable conductance under red, green, and blue light illumination, replicating both sensing and synaptic learning functions. Furthermore, by manipulating the HZO polarization state via gate voltage, we achieve dynamic control over the decay rate and retention of photocurrent, enabling transitions between short-term and long-term plasticity. Finally, logic operations such as "AND" and "OR" are also demonstrated using dual-wavelength optical inputs. These findings suggest the device's strong potential as a multifunctional platform for integrated artificial visual systems.

This study compares the effects of ultrathin Y2O3 and Al2O3 interfacial layers on the electrical properties of ZrO2 and HfO2 dielectrics deposited on Ge substrates, specifically examining the ZrO2/Y2O(3), ZrO2/Al2O3, HfO2/Y2O3, and HfO2/Al2O3 stacked structures. Reductions in both interface trap density (Dit) and leakage current were observed after five cycles of the atomic layer deposition (ALD) process for Y2O3 and Al2O3 interfacial layers. Compared with Y2O3, the Al2O3 interfacial layer was more effective in reducing the leakage current and decreasing the effective bulk trap density (Ntrap). However, this also leads to an increase in the capacitance-equivalent oxide thickness, which could be a potential drawback. The observed electrical properties are closely linked to the distinct interfacial reactions of Y2O3 and Al2O3 with Ge during ALD, resulting in similar reductions in Dit. However, the formation of a thick Al2O3 interfacial layer was more efficient in suppressing Ge out-diffusion than Y2O3, which contributed to the reduction in both the leakage current and N-trap.

A Y2O3 interfacial layer is introduced to enhance the capacitance of the blocking layer stacked with antiferroelectric (AFE)‐Hf0.2Zr0.8O2 (HZO) and Al2O3 films in charge trap flash (CTF) memories. The ultrathin Y2O3 film, with a target thickness of 2 nm, intermixes with the HZO film during the atomic layer deposition (250 °C) of HZO and promotes stabilization of the AFE tetragonal phase during postmetallization annealing (600 °C). Significant increases in the spontaneous polarization and maximum dielectric constant are achieved in the AFE‐HZO/Y2O3 structure compared with the single‐layer AFE‐HZO structure. When Si3N4‐based CTF devices are fabricated with an AFE‐HZO/Al2O3 blocking layer utilizing the capacitance‐boosting effect, the introduction of a Y2O3 interfacial layer results in performance enhancement in terms of memory window and programming efficiency. These improvements are attributed to the enhanced negative capacitance effect, which stems from the increased spontaneous polarization in the AFE‐HZO film due to Y2O3 doping.

The integration of ferroelectricity and the photoelectric effect offers substantial potential for the realization of optoelectronic-based artificial neural networks (ANNs) and biomimetic systems. Despite their potential, the application of ferroelectric field-effect transistors (FeFETs) in optoelectronic neuromorphic devices, where light regulates synaptic activation, remains largely unexplored. Here, we report InGaZnO/Zr-doped HfO2 (IGZO/HZO) artificial synapses for the emulation of optoelectronic ANNs and optogenetic-inspired neural functions. Particularly, by simultaneously optimizing the post-deposition annealing (PDA) process for the stabilization of HZO ferroelectric phase and activation of IGZO channel, high-performance FeFETs exhibiting a memory window of similar to 1 V and endurance up to 10(4) cycles were achieved. Spectroscopic analyses correlated PDA temperature-dependent dynamic transitions in electrical properties with hydrogen relocation, oxygen vacancy formation, zinc vaporization, and film densification. The IGZO/HZO synapses successfully emulated synaptic functions such as spike-amplitude and spike-duration-dependent plasticity, using both electrical (E) and optical (O) stimulation. Furthermore, dual E/O stimulus activation of IGZO/HZO synapses, combined with polarization state modulation, was employed to emulate optogenetic-inspired neural functions. We also demonstrated that dual E/O stimulus activation of artificial synapses enhanced ANN image recognition accuracy from 86 % to 90 %, outperforming the performance achieved with a single E-stimulation. We envision that these findings can provide a process protocol for IGZO/HZO FeFETs to achieve stable phasic control and realization of optoelectronic neuromorphic devices.

While B‐doped epitaxial Si1–xGex films play a crucial role in advanced semiconductor devices, the correlation between crystalline defects and the electrical properties of these films has not been extensively explored. Herein, crystalline defects are intentionally induced by varying the thicknesses of epitaxial p+–Si0.8Ge0.2 films with different B concentrations on Si. Their effects on electrical characteristics are investigated using unit devices, including p+–Si0.8Ge0.2/n–Si (p+–n) diodes and metal/p+–Si0.8Ge0.2 contacts. The characteristics of the p+–n diodes, including forward and reverse currents, ideality factors, and activation energies, are significantly influenced by the presence of strain‐induced defects in the p+–Si0.8Ge0.2 films. In particular, the ideality factor increases while the activation energy decreases with rising strain energy in the strained films and their subsequent relaxation. This behavior suggests that these parameters are highly sensitive indicators of the impact of crystalline defects in both strained and relaxed films. While the specific contact properties in metal–p+ contacts are mainly dependent on the doping concentration in strained p+–Si0.8Ge0.2 films, they also serve as an effective indicator for identifying crystalline defects in relaxed films.

Interface reactions during postdeposition annealing (PDA) of Hf0.5Zr0.5O2 (HZO) films grown on HfS2 and MoS2 crystals by atomic layer deposition are investigated for potential application in future top-gate ferroelectric transistors. Both the HZO/HfS2 and HZO/MoS2 samples experience blistering of the HZO films when annealed for ferroelectric phase formation at temperatures greater than 500 and 600 degrees C, respectively, for 1 min in an N2 atmosphere. The different critical PDA temperatures are associated with different onset temperatures for the thermal decomposition of HfS2 and MoS2 crystals, which occur because of reactions with oxygen inadvertently introduced into the N2 annealing atmosphere. In both samples, the S- and O-related byproduct gases delaminate the HZO film, forming blisters and ruptures with increasing PDA temperatures. Because of the formation of solid HfOx films on HfS2 via the diffusion of ambient oxygen through the HZO film and randomly located blisters, the HZO/HfS2 sample develops deep and irregularly shaped encroachment defects with an uneven HfS2 surface. By contrast, owing to the desorption of the volatile oxide phase (e.g., MoO3) produced during the oxidation reaction, the MoS2 crystal maintains a flat surface through its layer-by-layer decomposition as the PDA temperature increases beyond 600 degrees C.

In this study, the thermal stability of WS2 crystals during O3-based atomic layer deposition (ALD) and subsequent high-temperature post-deposition annealing (PDA) processes to form ferroelectric Hf1-xZrxO2 (HZO) films was comprehensively investigated. The oxidation of approximately one monolayer and its subsequent incorporation into the HZO film during the O3-based ALD process at 260 degrees C were confirmed through various characterization techniques, including Raman spectroscopy, photoluminescence (PL) spectroscopy, and transmission electron microscopy analyses. This phenomenon was attributed to the high oxidizing power of the O3 oxidant, as demonstrated by comparisons with density functional theory calculations and by conducting the same experiment using H2O as the oxidant in the ALD process. Unlike MoS2, which undergoes significant oxidation-induced thermal decomposition, the WS2 monolayer remained largely intact during the PDA process in the temperature range of 400-600 degrees C, with only a slight suppression of the PL peak owing to the formation of sulfur vacancies. Thermogravimetric analysis further showed that WS2 exhibits superior resistance to high-temperature oxidation compared with MoS2, even at 600 degrees C. This study provides fundamental insights into the thermal and oxidative stabilities of WS2, which are crucial for the fabrication of nanoelectronic devices that incorporate the ferroelectric properties of HZO films.

In this study, the effects of an Al2O3 interfacial layer (IL) on the characteristics of ferroelectric field-effect transistors (FeFETs) with Hf0.5Zr0.5O2 (HZO) gate dielectrics on Si substrates were investigated. FeFETs with HZO gate dielectrics have gained considerable attention owing to their compatibility with modern fabrication processes and scalability. However, during HZO deposition on Si substrates, an ultrathin metal silicate IL with a low dielectric constant is formed in an uncontrolled manner, leading to a significant voltage drop and the generation of interface traps during device operation. To address this issue, an ultrathin Al2O3 IL with a thickness less than 2 nm was introduced between the HZO film and Si substrate via in situ atomic layer deposition. The impact of this IL on a memory window (MW) and endurance characteristics was evaluated by comparing the devices with and without an intentional Al2O3 IL. The obtained results revealed that the Al2O3 IL effectively suppressed the interface trap generation, expanded the MW, and enhanced the transistor endurance characteristics. This described approach can be potentially used for improving the reliability of FeFETs fabricated on Si substrates.

AbstractA steep‐slope In‐Ga‐Zn‐O (IGZO) field‐effect transistor (FET) monolithically integrated with an Ag/Ti/Hf0.8Zr0.2O2 atomic threshold switch (ATS) device is presented, which allows switching below the Boltzmann limit of 60 mV dec−1 at room temperature (25 °C). The low‐temperature processable IGZO FET is combined with the Hf0.8Zr0.2O2‐based ATS device, which featured initialization‐free and low‐voltage switching, to achieve an ultra‐low power device solution with back‐end‐of‐line process compatibility (≤400 °C). To further assess the potential of the ATS‐IGZO FET devices for circuit applications, they are applied to logic and memory integrated circuits. Inverter ring oscillator simulations are performed to investigate the relationship between switching speed and power consumption. In addition, static random‐access memory simulations are performed to verify that ATS‐IGZO FETs can achieve a stable noise margin along with low standby power consumption. This comprehensive evaluation provides an in‐depth assessment of the applicability of ATS‐IGZO FETs for ultra‐low power logic and memory applications, highlighting their potential for substantial performance improvements.

The integration of ferroelectric HfO2 films into two-dimensional layered-material-based devices is expected to provide significant functionality for future electronics. In this study, Hf0.5Zr0.5O2 (HZO) films are directly grown on single-crystalline MoS2 flakes by atomic layer deposition (ALD) with varying deposition temperatures using H2O or O3 oxidants. According to density functional theory calculations and Raman measurements, O3-based ALD oxidizes the MoS2 surface at the atomic layer level, in contrast to the H2O-based ALD process, thus facili-tating the conformal deposition of an HZO film (10 nm) without any surface treatment of MoS2 at an elevated ALD temperature of 260 degrees C. Annealing the O3-based HZO film with a Mo capping layer at 600 degrees C significantly improves the ferroelectric properties with a symmetrical hysteresis loop on MoS2. However, distinct S out -diffusion accompanied by Hf, Zr, and O diffusion toward the Mo capping layer occurs because of the thermal dissociation of MoS2 at an additional atomic layer level, thereby leading to the subsequent reduction of weak HZO bonds by the released S atoms along the grain boundaries.

We introduced Y-O bonds in the interfacial layer between HfO2 and Si1-xGex (x = 0, 0.15, and 0.3) using two different pretreatment methods to minimize the number of interfacial defects. The pretreatments involved the application of cyclic pulses of Y(CpBut)3 and N2, which proceeded with or without the injection of an oxidizing agent (H2O) at 250 degrees C, which was the temperature used for the subsequent in situ atomic layer deposition of HfO2. Both Y pretreatments were beneficial in reducing the leakage current and positive flatband voltage shift, which were induced by an increase in the Ge concentration of the substrate. In addition, the interface state density was significantly reduced by the pretreatments, and this effect was more pronounced when the oxidizing agent injection step was skipped. However, both pretreatments increased the capacitance-equivalent oxide thickness, thereby having an adverse effect, possibly owing to a change in the composition of the interfacial layer.

The advances in modern intelligent electronic systems have a pressing need for smart electromagnetic interference (EMI) shielding capabilities in a frequency-selective manner to choose which electromagnetic waves in a certain range to be blocked. Herein, we present multilayered EMI shielding composites that can provide selective on–off characteristics for specific frequency ranges across a broad spectrum. The composites are composed of outermost dielectric layers and conductive interlayers fabricated via solution printing, wherein hexagonal boron nitride (BN) and silver-coated BN particles are embedded, respectively. The EMI shielding frequency range and on–off selectivity are controllable by varying the configuration of the composite structure in terms of the BN content and the number of composite layers, providing different interstitial spaces between the fillers and interfacial dielectric properties. Furthermore, the optimal combination of these layers permits excellent combinatorial properties of EMI shielding effectiveness (32–62 dB), thermal conductivity (7.61 W/m·K), and electrical insulation (4.03 kV/mm) in the through-plane direction. The developed composites and their synthetic pathways have enormous potential for tailored material design and flexible system integration in next-generation EMI shielding technologies.

The combined effects of the atomic-layer-deposition (ALD) temperature (220 °C–280 °C) and metal electrodes (TiN and Mo) on the ferroelectric properties of Hf 0.5 Zr 0.5 O 2 films were studied. Regardless of the metal electrode, a tetragonal–orthorhombic–monoclinic phase evolution sequence was observed with increasing ALD temperature after post-metallization annealing. However, the phase transition temperature slightly changed depending on the metal electrode, which was predetermined based on the as-deposited states. Additionally, the out-of-plane orientation of the final orthorhombic grains was highly dependent on the crystallographic alignment of the metal electrode grains, resulting in different values of the maximum remanent polarization. In terms of long-term reliability, the fatigue characteristics were highly dependent on the electrode characteristics, and the wake-up characteristics were mainly affected by the initial phase distribution determined by both the ALD temperature and metal electrode.

The endurance characteristic of Zr-doped HfO2 (HZO)-based metal–ferroelectric–metal (MFM) capacitors fabricated under various deposition/annealing temperatures in the atomic layer deposition (ALD) process was investigated. The chamber temperature in the ALD process was set to 120 °C, 200 °C, or 250 °C, and the annealing temperature was set to 400 °C, 500 °C, 600 °C, or 700 °C. For the given annealing temperature of 700 °C, the remnant polarization (2Pr) was 17.21 µC/cm2, 26.37 µC/cm2, and 31.8 µC/cm2 at the chamber temperatures of 120 °C, 200 °C, and 250 °C, respectively. For the given/identical annealing temperature, the largest remnant polarization (Pr) was achieved when using the chamber temperature of 250 °C. At a higher annealing temperature, the grain size in the HZO layer becomes smaller, and thereby, it enables to boost up Pr. It was observed that the endurance characteristics for the capacitors fabricated under various annealing/chamber temperatures were quite different. The different endurance characteristics are due to the oxygen and oxygen vacancies in ferroelectric films, which affects the wakeup/fatigue behaviors. However, in common, all the capacitors showed no breakdown for an externally applied pulse (up to 108 cycles of the pulse).

In this study, to understand the effect of sublayer thickness of doped HfO2 films with limited dopant solubility on ferroelectric phase stabilization, nanolaminated HfO2–Al2O3 films with various sublayer thicknesses were prepared through atomic layer deposition (ALD), and the phase evolution behavior of these films with increasing post-metallization annealing (PMA) temperature was investigated. A narrow optimal range of the HfO2 sublayer thickness was required to achieve facile crystallization into a tetragonal phase, followed by orthorhombic phase transformation through sufficient Al diffusion. Because the Al2O3 sublayer cannot be completely dissolved, it should be as thin as possible so that it can easily agglomerate to provide an effective connection between the HfO2 sublayers during the PMA process. When stabilizing the ferroelectric phase of HfO2 films by mixing with dopants with limited solubility, the thicknesses of the HfO2 and Al2O3 sublayers in the nanolaminated form were revealed to be more critical than the nominal doping concentration inferred from their thickness ratios (ALD cycle ratios).

To fully understand the electrical characteristics of ferroelectric field-effect transistor (especially, sub-60-mV/decade switching characteristics at 300 K), it is necessary to quantitatively figure out the physics of the negative capacitance in ferroelectric material. In this work, metal-ferroelectric-metal (MFM) and metal-insulator-ferroelectric-metal (MIFM) capacitors were fabricated with Hf0.5Zr0.5O2 (HZO) and HfO2/HZO, respectively. For various bases of the input voltage pulse across the capacitors, the charge released during the falling edge of the pulse (QD) was measured. In reality, for the given bases of the input voltage pulse, the charge (QD) boost in the ferroelectric capacitors was experimentally observed without intentionally applying imprint, as done in the prior work. It turned out that, even though the MIFM capacitor’s capacitance is lower than a fixed-value capacitor’s capacitance, QD of the MIFM capacitor was comparable to QD of the fixed-value capacitor. This clearly indicates that the charge (QD) was boosted by the negative capacitance in the ferroelectric material.

MgO films were deposited on Si via atomic layer deposition (ALD) using Mg(EtCp)2 and H2O precursors and their thermal stability was examined as a function of the post-deposition annealing (PDA) temperature. The characteristic self-limiting behavior of the ALD process was confirmed by changing several parameters, such as precursor pulsing times, deposition temperature, and number of cycles. The exceptional resulting step coverage was verified on a patterned wafer with a high aspect ratio. The band gap and dielectric constant of the as-deposited ALD-MgO film were extracted to be approximately 7.5 eV and 8.4, respectively, and were stable up to the PDA temperature of 700 degrees C. However, considerable outward diffusion of the underlying Si atoms toward MgO started to occur above 700 degrees C, and most of the MgO film was converted to an amorphous Mg-silicate phase at 900 degrees C with a thin layer of remaining MgO on top.

A two-dimension (2D) atomic-threshold-switching field-effect transistor (ATS-FET) was implemented, by connecting an AgTi/HfO2-based threshold-switching (TS) device in series to the drain electrode of the 2D baseline-FET with molybdenum disulfide (MoS2) channel material. We optimized/developed the Ag/HfO2-based TS device because its characteristic is associated to the way how to achieve high performance of the 2D ATS-FET. By reducing the effective device area of the Ag/HfO2-based TS device down to $4~\mu \text{m}^{2}$ , low threshold voltage ( $\text{V}_{\mathrm {T}} \sim 0.42$ V), low threshold current (IT, drain current at the threshold voltage, $\sim 3.79 \times 10^{-11}$ A), and low VT variation (~0.09 V) were achieved. This is because the randomly formed filaments and electric field are better controlled with the scaled effective area. Next, the titanium (Ti)-injection barrier layer was inserted between the top electrode and the switching layer, while maintaining the optimized area in the TS device. The inserted Ti-injection barrier layer prevents the migration of Ag ions into the switching layer, enabling the stable TS operation even under the compliance current of $100~\mu \text{A}$ . Additionally, it locally restricts the region where the filaments are created inside the switching layer, resulting in a 17% lower VT variation and stable IT to approximately $\sim 1.5 \times 10^{-11}$ A in 100 cycles. Due to the low off-state leakage current and low variation characteristic of the optimized AgTi/HfO2-based TS device, the 2D ATS-FET (vs. 2D baseline-FET) shows the reduction of off-state leakage current (by $\sim 10^{2}$ in sub-threshold region) and the stable switching characteristic. The proposed 2D ATS-FET shows stably steep switching characteristics, e.g., sub-threshold swing under forward bias (~19 mV/decade) and reverse bias (~26 mV/decade), because of its abruptly switching characteristics of the TS device.

Semiconducting two-dimensional (2D) materials-based devices usually exhibit inferior electrical performance compared to their theoretical predictions, which is mainly attributed to the presence of high density of interfacial defect induced trap states within the bandgap of 2D materials. It is pertinent to control the density of interface traps ( D it ) and identify their respective energy levels inside the band gap of the 2D materials to understand the tailored device performance. Here, we report the large modulation of D it by electrical gating and varying the channel thickness of tungsten diselenide (WSe 2 ) placed on ultra-clean hexagonal boron nitride (hBN) gate insulator in a metal–insulator–semiconductor structure, which is revealed by performing multi-frequency capacitance and conductance measurements. Analysis of the 2D hBN/WSe 2 interface reveals that with the increase of WSe 2 thickness, D it at the midgap of WSe 2 is reduced to 6 × 10 9 cm −2 eV −1 , which is less than D it reported for SiO 2 /Si interface (∼10 10 cm −2 eV −1 ). Furthermore, by increasing thickness and applying gate voltage, D it distribution is systematically modulated inside the WSe 2 band gap from valence band edge to mid-gap to conduction band edge, thereby changing the Fermi level of WSe 2 , and inducing versatile device polarity. Our results show that D it and its spatial energy distribution within the thickness tailored WSe 2 band gap primarily control polarity modulation in WSe 2 .

To understand the effect of H2S pre-annealing treatment on a Si1−xGex alloy film, the interfacial and electrical characteristics of atomic-layer-deposited HfO2/Si1−xGex were studied while varying the Ge concentration (x value) from 0 to 0.3.