Jiuxiang Dai

Our CMOS-compatible nanoscale air channel transistor (NACT), fabricated on 4-inch silicon wafers, achieves 0.15 mV dec⁻¹ ultralow subthreshold swing via innovative gate control. Operating at 0.7V, it exhibits outstanding milliampere-level drain current and a maximum on/off ratio of 7.82×10⁶, surpassing traditional NACT limits. It maintains high stability under harsh conditions. An inverter circuit is demonstrated for the first time.

Abstract

As electronics advance toward higher performance and adaptability in extreme environments, traditional metal-oxide-semiconductor field-effect transistors (MOSFETs) face challenges due to physical constraints such as Boltzmann's law and short-channel effects. Nanoscale air channel transistors (NACTs) present a promising alternative, leveraging their vacuum-like channel and Fowler–Nordheim tunneling characteristics. In this study, a novel circular gate NACT (CG-NACT) is purposed, fabricated on a 4-inch silicon-based wafer using a CMOS-compatible process. By employing an innovative gate control mechanism, the transistors achieve an ultralow SS of only 0.15 mV dec⁻¹ and maintain the average SS remained at 1.5 mV dec⁻¹ over three decades of drain current. Additionally, our CG-NACTs deliver milliamper-level drain current at a low drain voltage of 0.7 V, with a maximum on/off ratio of 7.82×10⁶. Notably, CG-NACTs remain highly stable even at high temperatures of up to 150 °C and under irradiation. Furthermore, the practical application of CG-NACTs is successfully implemented by designing an inverter circuit for the first time.

A novel all-solid-state oxide-ion synaptic transistor is developed, based on a Bi₂V_0.9Cu_0.1O_5.35 oxide-ion conductor electrolyte and La_0.5Sr_0.5FeO_3-δ variable-resistance electrodes (channel, gate). This synaptic transistor efficiently operates at temperatures compatible with conventional electronics, exhibiting key synaptic behaviors with low energy consumption and high endurance. Integrated into an artificial neural network simulation, it achieved 96% accuracy in handwritten digit recognition, demonstrating significant potential for neuromorphic computing applications.

Abstract

Neuromorphic hardware facilitates rapid and energy-efficient training and operation of neural network models for artificial intelligence. However, existing analog in-memory computing devices, like memristors, continue to face significant challenges that impede their commercialization. These challenges include high variability due to their stochastic nature. Microfabricated electrochemical synapses offer a promising approach by functioning as an analog programmable resistor based on deterministic ion-insertion mechanisms. Here, an all-solid-state oxide-ion synaptic transistor is developed, employing Bi₂V_0.9Cu_0.1O_5.35 as a superior oxide-ion conductor electrolyte and La_0.5Sr_0.5FeO_3-δ as a variable-resistance channel able to efficiently operate at temperatures compatible with conventional electronics. This transistor exhibits essential synaptic behaviors such as long- and short-term potentiation, paired-pulse facilitation, and post-tetanic potentiation, mimicking fundamental properties of biological neural networks. Key criteria for efficient neuromorphic computing are satisfied, including excellent linear and symmetric synaptic plasticity, low energy consumption per programming pulse, and high endurance with minimal cycle-to-cycle variation. Integrated into an artificial neural network (ANN) simulation for handwritten digit recognition, the presented synaptic transistor achieved a 96% accuracy on the Modified National Institute of Standards and Technology (MNIST) dataset, illustrating the effective implementation of the device in ANNs. These findings demonstrate the potential of oxide-ion based synaptic transistors for effective implementation in analog neuromorphic computing based on iontronics.

This study unravels a self-wrinkled mechanically adaptive patterned surface (SWMAPS) by a one-step UV-curing and self-wrinkling technique. Thanks to the mechanically adaptive performance of the bionic wrinkled microstructure, the SWMAPS with both random and programmable-irradiated wrinkles can withstand more than 600 cycles of reciprocating friction, which establishes a new field of mechanically adaptive patterned surface for mechanical enhancement.

Abstract

Providing mechanically adaptive performance to surfaces is significant in preserving materials from damage in variable environments, however, it has rarely been studied. Inspired by the mechanically adaptive behaviors of the surface microstructure on the carapace of desert scorpions and bark of desert tamarisks, a self-wrinkled mechanically adaptive patterned surface (SWMAPS) using one-step UV-curing and self-wrinkling technique is reported. Because of the fluorinated polyurethane photo-initiator formed by self-assembly at the top surface, UV-induced photo-crosslinking can spontaneously generate a gradient-crosslinked structure and wrinkled patterns with different morphology. With mechanically adaptive behavior originating from self-assembled fluorinated polyurethane photo-initiators, gradient-crosslinked structures, and self-wrinkled patterns, the SWMAPS remains intact under 600 cycles of reciprocating friction with little variation in the coefficient of friction and water contact angle. The SWMAPS prepared by programmable UV irradiation maintains integral under 1800 cycles of reciprocating friction with a stable friction coefficient. Furthermore, the SWMAPS is fabricated with high efficiency, regulated morphology, good surface mechanical properties, and self-recovery performance. This strategy establishes a new field of mechanically adaptive patterned surfaces, which significantly improves durability and prolongs the service life of materials in variable environments.

A dual FeFET (ferroelectric field effect transistor) is constructed by fusing 3D ferroelectric dielectric BiFeO₃ with the 2D ferroelectric semiconductor α-In₂Se₃. This strategic integration ensures that the remanent polarization in both BiFeO₃ and α-In₂Se₃ after being programmed are harmoniously coupled. This coupling effect effectively mitigates the relaxation process of ferroelectric polarization, extending the data duration of the FeFET memory.

Abstract

Ferroelectric field-effect transistors (FeFETs) commonly utilize traditional oxide ferroelectric materials for their strong remanent polarization. Yet, integrating them with the standard complementary metal oxide semiconductor (CMOS) process is challenging due to the need for lattice matching and the high-temperature rapid thermal annealing process, which are not always compatible with CMOS fabrication. However, the advent of the ferroelectric semiconductor α-In₂Se₃ offers a compelling solution to these challenges. Its van der Waals layered structure facilitates integration with dielectric oxides, bypassing the lattice mismatch problem. Moreover, the ferroelectric polarization of α-In₂Se₃ synergizes with the polarization of the ferroelectric dielectric layer. This coupling effect significantly enhances the polarization retention and the data storage capabilities of FeFETs. Here, a dual FeFET is designed that incorporates a BiFeO₃ dielectric layer and an α-In₂Se₃ channel, showing an improvement in performance compared to FeFETs that use MoS₂ as the channel material with a BiFeO₃ dielectric, or those with an α-In₂Se₃ channel and a HfO₂ dielectric. The dual FeFET exhibits an extended retention time of up to 1000 s at 380 K. Though there is still room for further improvement in data retention capabilities, this achievement paves the way for advancements in non-volatile memory technologies.

Graphene transforms silica glass into a damage-resistant surface in water, achieving up to ≈98% friction reduction and preventing severe tribochemical wear. Nanoscale scratch tests and simulations reveal graphene's dual role in lubrication and chemical passivity, offering exceptional mechanical and chemical durability against both inert and reactive countersurfaces. This study underscores graphene's superior potential for creating durable glass coatings.

Abstract

Despite the ubiquitous use of glasses, their simultaneous susceptibility toward scratch-induced defects and atmospheric hydration deteriorates their mechanical and chemical durability. Here, it is demonstrated that the deposition of a few-layer graphene provides unprecedented wear resistance to silica glass in aqueous conditions. To this extent, nanoscale scratch tests are carried out on graphene-glass surfaces via contact-mode atomic force microscopy with chemically inert and reactive tips. It is observed that the graphene-glass exhibits up to ≈98% friction reduction and no discernable damage or material loss. This observation is in stark contrast to the behavior of bare silica glass which suffers severe tribochemical wear at equivalent contact conditions with even milder stresses. Further, through reactive molecular simulations, it is demonstrated that parallel mechanisms of lubrication and chemical passivity contribute to the enhanced damage resistance of graphene-glass surfaces against any countersurface chemistry. Altogether, the present study provides an impetus toward physically and chemically durable glass coatings exploiting the functionalities of two-dimensional materials.

2D materials are a potential candidate for beyond-silicon electronics. However, the stability is one of the key bottlenecks in the progress of 2D materials. Here, a strategy is developed that greatly improves the performance and stability of 2D materials and devices by using vitamin C. The increase in mobility is more than ten times, and the performance can be maintained in air conditions for more than 327 days.

Abstract

2D materials are promising candidates for beyond-Si electronic devices. However, their stability is a key bottleneck in their industrial applications. The instability of 2D materials is mainly attributed to their intrinsic susceptibility to O₂ and H₂O—particularly to reactive oxygen species (ROS), which have strong oxidizing properties. Inspired by the antioxidant effect of vitamin C (VC) in organisms, a strategy based on the use of VC to stabilize electron transport in 2D materials is developed, which significantly improves the performance and stability of these materials and devices. The mobility is increased by more than an order of magnitude, and excellent performance of the device is maintained in air for >327 days, which is the best reported stability for MoS₂ field-effect transistors to date. VC scavenges existing ROS via oxidation reactions and inhibits the generation of ROS by shielding excitons from oxygen quenching, which provides 2D materials lasting protection from electron trapping and oxidative damage, stabilizing electron transport. This approach, which is based on the simple utilization of readily available VC, has considerable potential for large-scale applications in the 2D material electronics industry.

Aluminum doping strategy is used to form less aggregated structural domains, creating a favorable environment for the precipitation of nanoscale polycrystalline CaSiO₃. Through the process of anomalous grain growth, the nanoscale α-CaSiO₃ crystals are fully absorbed, rearranged, and transformed into micrometer-sized single-crystalline β-CaSiO₃. The highly ordered layered structure of β-CaSiO₃ provides efficient pathways for ion and electron transport, reducing its dielectric constant, while the single-crystalline structure enhances the mechanical properties of the electronic substrate.

Abstract

β-CaSiO₃ based glass-ceramics are among the most reliable materials for electronic packaging. However, developing a CaSiO₃ glass-ceramic substrate with both high strength (>230 MPa) and low dielectric constant (<5) remains challenging due to its polycrystalline nature. The present work has succeeded in synthesizing single-crystalline β-CaSiO₃ for a high-performance glass-ceramic substrate. This is accomplished by introducing Al³⁺ into the CaO-B₂O₃-SiO₂ glass system, and by optimizing the sintering condition. Al³⁺ doping facilitates a heterogeneous network structure that energetically favors the precipitation of polycrystalline particles, including nanosized β-CaSiO₃ crystals and sub-nanosized α-CaSiO₃ crystals. As the sintering temperature increases, the nano α-CaSiO₃ crystals (2–10 nm) are gradually absorbed by the β-CaSiO₃ crystals. Through atomic rearrangement, α-CaSiO₃ crystals transform into micrometer-sized single crystal β-CaSiO₃ (1–2 µm) with layered structure. The low temperature co-fired β-CaSiO₃ glass-ceramics exhibit exceptional properties, including a low dielectric constant of 4.04, a low dielectric loss of 3.15 × 10⁻³ at 15 GHz, and a high flexural strength of 256 MPa. This work provides a new strategy for fabricating high-performance single-crystalline glass-ceramics for electronic packaging and other applications.

Wafer-scale, highly oriented (almost monocrystalline) WS₂ monolayers are synthesized on C/A-plane sapphire substrates by chemical vapor deposition. A record high saturation current density of 675 µA µm⁻¹ is achieved based on field-effect transistors made of such films, outperforming the index required for high-density integration circuits in IRDS 2025.

Abstract

2D transition-metal dichalcogenide (TMDC) semiconductors represent the most promising channel materials for post-silicon microelectronics due to their unique structure and electronic properties. However, it remains challenging to synthesize wide-bandgap TMDCs monolayers featuring large areas and high performance simultaneously. Herein, highly oriented WS₂ monolayers are reproducibly synthesized through a templated growth strategy on vicinal C/A-plane sapphire wafers. Various spectroscopic characterizations confirm the high crystallographic orientation and uniformity across the entire wafers. Electronic measurements for samples transferred onto SiO₂/Si substrates reveal high average field-effect mobilities of 62 and 180 cm²V⁻¹s⁻¹ at room temperature and 8 K, respectively. On hexagonal boron nitride substrates, these mobilities increase to 94 and 473 cm²V⁻¹s⁻¹, respectively. A record high saturation current density of 675 µA µm⁻¹ is observed, outperforming the index required for high-density integration circuits in IRDS 2025. This work paves the way for the application of wide-bandgap TMDC monolayers in post-silicon electronics.

Cobalt sulfide nanocrystals, known for their diverse structural phases and unique magnetic and conductive properties, are promising for applications in spintronics and catalysis. This study presents a method using ambient pressure chemical vapor deposition (APCVD) to synthesize phase-controllable 2D non-layered cobalt sulfide nanocrystals on insulating substrates, enabling transitions between pyrite CoS₂, cubic Co₃S₄, and hexagonal CoS by adjusting growth temperature.

Abstract

Among 2-dimensional (2D) non-layered transition-metal chalcogenides (TMCs), cobalt sulfides are highly interesting because of their diverse structural phases and unique properties. The unique magnetic properties of TMCs have generated significant interest in their potential applications in future spintronic devices. In addition, their high conductivity, large specific surface area, and abundant active sites have attracted attention in the field of catalysis. However, the synthesis of phase-controllable 2D non-layered cobalt sulfide nanocrystals remains challenging. In the present study, a method is reported in which ambient-pressure chemical vapor deposition (APCVD) is used to synthesize 2D non-layered cobalt sulfide nanocrystals on insulating substrates. By controlling the growth temperature, the transition of nanocrystal phases from pyrite-structured CoS₂ to cubic Co₃S₄ and hexagonal CoS is achieved. Magnetotransport studies revealed metallic and ferromagnetic behaviors at temperatures below the Curie temperature for CoS₂. In addition, electrical measurements of Co₃S₄- and CoS-based devices showed conventional metallic behaviors, including temperature- and magnetic field-dependent ordinary Hall effects. These findings demonstrate the potential of APCVD for synthesizing high-quality 2D non-layered cobalt sulfide nanocrystals with controllable phases, paving the way for their application in spintronics and catalysis.

Nature Electronics, Published online: 23 December 2024; doi:10.1038/s41928-024-01332-8

Based on photothermal materials, such as a detachable assembly layer, laser direct-writing (LDW) programmable dynamic aligned wrinkling is realized on arbitrary films and even on arbitrary film/substrate systems. Theoretical modeling reveals that LDW-induced localized anisotropic stress field answers for the LDW path-parallel wrinkling orientation. This dynamic oriented wrinkling has broad applications in soft photonics.

Abstract

Dynamic oriented wrinkling especially on arbitrary film materials is highly desirable yet remains a great challenge. Here, fabrication of programmable aligned wrinkling patterns on different film/substrate systems via a laser-direct-writing (LDW) method is reported, regardless of photofunctionality and transparence of the target films. The key is related to smart introduction of photothermal materials (PTMs) into compliant substrates and even as an independent attachable/detachable layer assembled underneath the film/substrate systems. Experiments and theoretical modeling reveal that with the help of the photothermal effect of PTMs, in situ LDW-induced localized dynamic anisotropic stress field is responsible for the intriguing LDW path-parallel aligned wrinkling. Furthermore, dimensional analysis is carried out and explicit solutions quantifying the connection of wrinkling morphology parameters with the LDW conditions are derived for the first time, which enables theoretical pattern designing. It is highlighted that the attachable/detachable assembly strategy for the independent PTMs layer endows arbitrary film/substrate systems with on-demand photosensitivity when needed, which has been inaccessible previously. As demonstrated, these dynamic oriented wrinkling systems have found broad applications especially in smart soft photonics, e.g., information storage, anticounterfeiting, and responsive optical devices.

Interface modulation enables an antiferroelectric-to-ferroelectric-like transition in ultrathin HZO films, driven by the superposition of depolarizing effects and built-in fields, rather than by commonly proposed phase transitions. This approach achieves robust ferroelectricity with low operating voltage, faster switching speed, and high reliability in 4 nm HZO films, offering a design space for tailoring ferroelectric properties through interface engineering.

Abstract

The development of ultrathin (≤5 nm) hafnia-based ferroelectric (FE) films is essential for achieving low operating voltages, facilitating their integration into advanced process nodes for low-power and non-volatile memory applications. However, challenges in ultrathin FE films arise from the depolarization field and interface-related issues, leading to an antiferroelectric-like (AFE-like) polarization switching behavior and more significant wake-up effects, causing operational inconvenience and reliability concerns. Here, interface-modulated ferroelectricity is reported in 4 nm Hf_0.5Zr_0.5O₂ (HZO) thin films, demonstrating excellent properties with low operating voltage, enhanced switching speed, and high reliability. Electrical and structural characterizations reveal that adjusting interface asymmetry may introduce a substantial built-in field (E _bi) and an AFE-like switching behavior can exhibit a robust FE-like characteristic. This AFE-to-FE-like transition is driven by switching kinetics rather than commonly proposed phase transitions. Furthermore, a comprehensive model is developed to elucidate the intricate physics of the modulation mechanism by asymmetric interfaces, emphasizing the critical roles of depolarizing effects and E _bi on ferroelectricity. This work underscores the importance of interfaces in engineering ferroelectricity for advanced electronic applications.

2D vdW α-In₂Se₃ is used as a ferroelectric tunneling junction in a planar structure with Au electrodes. The interface between the α-In₂Se₃ semiconductor and the Au electrode is studied to achieve a large on/off ratio by inserting a SiO₂ insulating barrier. The polarization of α-In₂Se₃ gradually changes with the applied pulses, mimicking synaptic properties and exhibiting linear LTP/LTD behavior.

Abstract

A synaptic memristor using 2D ferroelectric junctions is a promising candidate for future neuromorphic computing with ultra-low power consumption, parallel computing, and adaptive scalable computing technologies. However, its utilization is restricted due to the limited operational voltage memory window and low on/off current (I_ON/OFF) ratio of the memristor devices. Here, it is demonstrated that synaptic operations of 2D In₂Se₃ ferroelectric junctions in a planar memristor architecture can reach a voltage memory window as high as 16 V (±8 V) and I_ON/OFF ratio of 10⁸, significantly higher than the current literature values. The power consumption is 10⁻⁵ W at the on state, demonstrating low power usage while maintaining a large I_ON/OFF ratio of 10⁸ compared to other ferroelectric devices. Moreover, the developed ferroelectric junction mimicked synaptic plasticity through pulses in the pre-synapse. The nonlinearity factors are obtained 1.25 for LTP, −0.25 for LTD, respectively. The single-layer perceptron (SLP) and convolutional neural network (CNN) on-chip training results in an accuracy of up to 90%, compared to the 91% in an ideal synapse device. Furthermore, the incorporation of a 3 nm thick SiO₂ interface between the α-In₂Se₃ and the Au electrode resulted in ultrahigh performance among other 2D ferroelectric junction devices to date.

In this work, the liquid gallium is used to exfoliate bulk layered materials into 2D nanosheets at near room temperature. This method enables the production of numerous 2D nanosheets, including h-BN, graphene, layered minerals, and others, while avoiding the formation of additional defects and surfactant contamination. By adjusting the initial defect levels of the layered materials, the metallicity and/or defectiveness of 2D NSs can be customized for different applications.

Abstract

Liquid exfoliation is a scalable and effective method for synthesizing 2D nanosheets (NSs) but often induces contamination and defects. Here, liquid metal gallium (Ga) is used to exfoliate bulk layered materials into 2D NSs at near room temperature, utilizing the liquid surface tension and Ga intercalation to disrupt Van der Waals (vdW) forces. In addition, the process can transform the 2H-phase of transition metal dichalcogenides into the 1T’-phase under ambient conditions. This method produces high aspect ratio, surfactant-free 2D-NSs for more than 10 types of 2D materials that include h-BN, graphene, MoTe₂, MoSe₂, layered minerals, etc. The subsequent Ga separation via ethanol dispersion avoids the formation of additional defects and surfactant contamination. By adjusting initial defect levels of the layered materials, customize the metallicity and/or defectiveness of 2D NSs can be customized for applications such as birefringence-tunable modulators with exfoliated h-BN, and enhanced hydrogen evolution with defective MoS₂. This approach offers a strategy to optimize liquid metal/2D interfaces, preserving intrinsic properties and enabling practical applications, potentially transforming optics, energy conversion, and beyond.

A multidirectional sliding ferroelectricity in γ-InSe with a tunable bulk photovoltaic effect due to the existence of multiple polarization states is reported. The multidirectional sliding ferroelectricity is predicted by the theoretical calculations and multiple domain walls are observed experimentally. The multidirectional sliding ferroelectric polarization paves the path to explore novel optoelectronic applications like real-time imaging and neuromorphic computing.

Abstract

Through the stacking technique of 2D materials, the interfacial polarization can be switched by an interlayer sliding, known as sliding ferroelectricity, which is advantageous in ultra-thin thickness, high switching speed, and high fatigue resistance. However, uncovering the relationship between the sliding path and the polarization state in rhombohedral-stacked materials remains a challenge, which is the key to 2D sliding ferroelectricity. Here, layer-dependent multidirectional sliding ferroelectricity in rhombohedral-stacked InSe (γ-InSe) is reported via dual-frequency resonance tracking piezoresponse force microscopy and conductive atomic force microscopy. The graphene/γ-InSe/graphene tunneling device exhibits a tunable bulk photovoltaic effect with a photovoltaic current density of ≈15 mA cm⁻² due to multiple polarization states. The generation of dome-like domain walls is observed experimentally, which is attributed to the multidirectional sliding-induced domains based on the theoretical calculations. Furthermore, the ferroelectric polarization in γ-InSe ensures that the tunneling device has a high photo responsivity of ≈255 A W⁻¹ and a fast response time for real-time imaging. The work not only provides insights into the multidirectional sliding ferroelectricity of rhombohedral-stacked 2D materials but also highlights their potential for tunable photovoltaics and imaging applications.

A combination of advanced structural characterization at local and average scales and theoretical calculations reveals that the macroscopic rhombohedral-tetragonal phase coexistence of (K,Na)NbO₃-based piezoceramics is essentially an average projection of collective local disordered units exhibiting the order-disorder behavior. The field-induced polarization rotation with a change in the degree of ordering is found to play a key role in boosting the functional properties of the investigated ferroelectrics.

Abstract

Phase boundary is highly recognized for its capability in engineering various physical properties of ferroelectrics. Here, field-induced polarization rotation is reported in a high-performance (K, Na)NbO₃-based ferroelectric system at the rhombohedral-tetragonal phase boundary. First, the lattice structure is examined from both macroscopic and local scales, implementing Rietveld refinement and pair distribution function analysis, respectively. The macroscopic phase coexistence at the phase boundary can be interchangeably rationalized with an average projection of collective local disordered units, exhibiting the order–disorder nature. The structural evidence of field-induced polarization rotation is provided by the in situ synchrotron study. Theoretical studies including density functional theory calculation and molecular dynamics simulation also predict the polarization rotation mechanism. The simulation result reveals the variation of the degree of ordering during the polarization rotation as a key feature of the boosted electrical properties in the order–disorder ferroelectric system. The discovery provides meaningful insight into the design of ferroelectrics with enhanced physical properties.

Nature Protocols, Published online: 20 December 2024; doi:10.1038/s41596-024-01088-7

Nature Protocols, Published online: 20 December 2024; doi:10.1038/s41596-024-01098-5

A sustainable lithography paradigm enabled by mechanically peelable resists is demonstrated. This paradigm involves chemical-free resist stripping, and 100%-yield mechanical lift-off, and enables reliable conformal manufacturing of transient electronics. Various exemplary demonstrations indicate this technology could potentially establish a standard lift-off process for the pan-semiconductor industry and open new avenues for the mass production of transient electronics and integrated biodegradable devices.

Abstract

Lithography is critical in micro- and nanofabrication processes, enabling the development of integrated circuits, semiconductor devices, and various advanced electronic and photonic systems. However, there are challenges related to sustainability, efficiency, and yield, as well as compatibility with transient electronics. This work introduces a sustainable lithography paradigm employing mechanically peelable resists compatible with existing cleanroom processes. The resists exhibit near-zero adhesion to various substrates, facilitating efficient, cost-effective, environmentally friendly, and chemical-free mechanical stripping without observable particulate residues. The mechanical lift-off process enables scalable and 100%-yield pattern transfer using commercially available tape within seconds. Furthermore, the new paradigm supports distributed and in situ conformal manufacturing using the peelable resist as a “transferable stencil mask” to fabricate various functional devices on flexible and nonplanar surfaces, as well as ultra-thin biodegradable substrates. Overall, this work expands the potential for using lift-off as a standard process in the pan-semiconductor industry and opens new avenues for lithographic procedures aimed at the reliable mass production of transient electronics and integrated biodegradable devices, addressing growing sustainability issues caused by electronic waste.