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Abstract The unique characteristics of an anti‐ambipolar switch (AAS) device exhibit Λ‐shaped transfer responses (namely delta conductance) and present unique opportunities to overcome the limit of silicon‐based, complementary metal‐oxide‐semiconductor (CMOS) logic circuits. It is crucial because a device that only turns on under a certain bias range can be utilized to simplify the logic circuit and reduce the device count and circuit area required to perform logic functions. In this study, a physically scalable AAS device is investigated using ZnO and dinaphtho[2,3‐b:2′,3′‐f]thieno[3,2‐b]thiophene as heterojunction structures to reduce the operating voltage and enhance the peak current and peak‐to‐valley ratio of the AAS device. Moreover, novel logic circuits for AND, OR, XOR, DEMUX, and half‐adder functions are demonstrated using AAS devices. AAS device‐based logic circuits exhibit power‐efficiency characteristics (≈49 times lower than that of the 90‐nm silicon‐based CMOS inverter) and reduce the transistor count and the circuit area by ≈67% and ≈70%, respectively. These results indicate that the use of AAS device‐based logic circuits can be a promising approach to overcome the physical scaling limit of current CMOS technology.

Feedback field-effect transistors (FBFETs) have been studied to obtain near-zero subthreshold swings at 300 K with a high on/off current ratio ~1010. However, their structural complexity, such as an epitaxy process after an etch process for a Si channel with a thickness of several nanometers, has limited broader research. We demonstrated a FBFET using in-plane WSe2 p−n homojunction. The WSe2 FBFET exhibited a minimum subthreshold swing of 153 mV/dec with 30 nm gate dielectric. Our modeling-based projection indicates that the swing of this device can be reduced to 14 mV/dec with 1 nm EOT. Also, the gain of the inverter using the WSe2 FBFET can be improved by up to 1.53 times compared to a silicon CMOS inverter, and power consumption can be reduced by up to 11.9%.

Abstract In this study, the domain switching mechanism of ferroelectric HZO thin films is investigated by analyzing the bulk charge of a graphene field‐effect transistor with an HZO dielectric device by using a pulsed IV measurement method. The domain switching speed, which is generally difficult to observe from a typical DC‐IV analysis of metal‐oxide‐semiconductor field‐effect transistors using a parameter analyzer, is investigated via the fast pulsed IV analysis method. Based on the measurements, most of the ferroelectric HZO domains are fast switched within 100 ns; however, domains that require a longer switching time in the order of 1 ms are also identified. Short pulses can be continuously applied to minimize the influence of other domains that are not switched by the switched domain. The feasibility of partial switching of the domains, which can be utilized for the multi‐functional operation of ferroelectric HZO devices, is observed. The results suggest that further investigation of the physical properties of slow‐switching domains is necessary to develop future synaptic array applications.

Abstract A p-type ternary logic device with a stack-channel structure is demonstrated using an organic p-type semiconductor, dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT). A photolithography-based patterning process is developed to fabricate scaled electronic devices with complex organic semiconductor channel structures. Two layers of thin DNTT with a separation layer are fabricated via the low-temperature deposition process, and for the first time, p-type ternary logic switching characteristics exhibiting zero differential conductance in the intermediate current state are demonstrated. The stability of the DNTT stack-channel ternary logic switch device is confirmed by implementing a resistive-load ternary logic inverter circuit.

Abstract P-type ternary switch devices are crucial elements for the practical implementation of complementary ternary circuits. This report demonstrates a p-type ternary device showing three distinct electrical output states with controllable threshold voltage values using a dual-channel dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]-thiophene–graphene barristor structure. To obtain transfer characteristics with distinctively separated ternary states, novel structures called contact-resistive and contact-doping layers were developed. The feasibility of a complementary standard ternary inverter design around 1 V was demonstrated using the experimentally calibrated ternary device model.

The authors present a novel all-in-one optoelectronic logic gates based on the bipolar spectral photo-response characteristics of self-powered perovskite photodetector. Five representative logic gates are demonstrated with only a single detector via photocurrent polarity control.

The oxidation degradation by unsaturated metal atoms or dangling bonds at MXene edges and defects severely hinders the practical application of MXene. Herein, a passivation scheme for Ti3C2Tx MXene is demonstrated by utilizing a sulfhydryl‐containing molecule, β‐mercaptoethanol (BME), which can significantly suppress the Ti3C2Tx oxidation in various environments, including long‐term storage of Ti3C2Tx aqueous dispersions (2 m), single‐layer Ti3C2Tx‐based devices in humid air (2 m), and high‐temperature environment (12 h). Notably, the nonionic BME does not cause aggregation but maintains the 2D morphology of Ti3C2Tx. A comprehensive investigation of the protection mechanism through density functional theory (DFT) calculations and experimental characterizations reveals that BME is adsorbed especially at the edges and surface defects of MXene (binding energy −1.70 and −1.05 eV), where the degradation starts. Further, the electron‐donating effect of sulfhydryl groups tunes the work function of Ti3C2Tx from 4.70 to 4.39 eV, resulting in improved carrier‐transport performances in MoS2 field‐effect transistors owing to band alignment, where BME–Ti3C2Tx serves as the source electrode. The described methodology can largely contribute to the ultralong service life of 2D Ti3C2Tx without affecting its excellent properties, thereby promoting the practical application of this emerging material.

Abstract Van der Waals (vdW) heterostructures, consisting of a variety of low-dimensional materials, have great potential use in the design of a wide range of functional devices thanks to their atomically thin body and strong electrostatic tunability. Here, we demonstrate multi-functional indium selenide (InSe)/black phosphorous (BP) heterostructures encapsulated by hexagonal boron nitride. At a positive drain bias (V D), applied on the BP while the InSe is grounded, our heterostructures show an intermediate gate voltage (V BG) regime where the current hardly changes, working as a ternary transistor. By contrast, at a negative V D, the device shows strong negative differential transconductance characteristics; the peak current increases up to ~5 μA and the peak-to-valley current ratio reaches 1600 at V D = −2 V. Four-terminal measurements were performed on each layer, allowing us to separate the contributions of contact resistances and channel resistance. Moreover, multiple devices with different device structures and contacts were investigated, providing insight into the operation principle and performance optimization. We systematically investigated the influence of contact resistances, heterojunction resistance, channel resistance, and the thickness of BP on the detailed operational characteristics at different V D and V BG regimes.

Abstract Here, we demonstrate the fabrication of a Cu-graphene heterostructure interconnect by the direct synthesis of graphene on a Cu interconnect with an enhanced performance. Multilayer graphene films were synthesized on Cu interconnect patterns using a liquid benzene or pyridine source at 400 °C by atmospheric pressure chemical vapor deposition (APCVD). The graphene-capped Cu interconnects showed lower resistivity, higher breakdown current density, and improved reliability compared with those of pure Cu interconnects. In addition, an increase in the carrier density of graphene by doping drastically enhanced the reliability of the graphene-capped interconnect with a mean time to failure of >106 s at 100 °C under a continuous DC stress of 3 MA cm−2. Furthermore, the graphene-capped Cu heterostructure exhibited enhanced electrical properties and reliability even if it was a damascene-patterned structure, which indicates compatibility with practical applications such as next-generation interconnect materials in CMOS back-end-of-line (BEOL).

A reconfigurable passive device that can manipulate its resonant frequency by controlling its quantum capacitance value without requiring complicated equipment has been experimentally investigated by modifying the Fermi level of large-area graphene using an external electric field. When the total capacitance change, caused by the gate bias in the passive graphene device, was increased to 60% compared to the initial state, a 6% shift in the resonant frequency could be achieved. While the signal characteristics of the graphene antenna are somewhat inferior compared to the conventional metal antenna, simplifying the device structure allowed reconfigurable characteristics to be implemented by using only the gate bias change.

Barrier height ( $\phi _{b}$ ), trap state, bandgap ( $E_{g}$ ), and band alignment information of the metal–ZrO2–metal capacitor have been extracted using internal photoemission (IPE) system. By correlating the IPE analysis with I-V and C-V characteristics obtained before and after rapid thermal annealing, origin and transformation of defect states have been successfully investigated. Our analysis revealed that deep-level defects originating from oxygen vacancies near the top electrode are causing of leakage current in MIM capacitor and these defects can be effectively reduced by a proper thermal annealing.

In this paper, we improved the performance of a near-infrared graphene/germanium heterojunction photodetector at atmospheric pressure and at room temperature. We applied graphene with p-type chemical doping (doping chemical: polyacrylic acid) to lower the graphene Fermi level and increase the Schottky barrier formed at the junction with Ge. The responsivity at 1550 nm is improved from 0.87 to 1.27 A/W after the doping process. At the same time, the dark current is reduced by 20 times and the detectivity of the optimized device is improved to 9.6 × 109 Jones, which is 540% improvement compared to the undoped graphene device. With the result of improving performance through this simple process, it will be able to contribute to the fabrication of highly reactive graphene/semiconductor based photodetectors and the development of near-infrared sensors.

Designing multi-value logic transistors with stable and reliable intermediate states remains a challenge. Here, the authors report the mobility edge quantization phenomenon via resonant hybridization of ZnO QDs embedded in amorphous ZnO domains to enable adjustable multi-value intermediate states.

Abstract There has been growing interest in developing nanoelectronic devices based on graphene because of its superior electrical properties. In particular, patterning graphene into a nanoribbon can open a bandgap that can be tuned by changing the ribbon width, imparting semiconducting properties. In this study, we report the effect of ribbon width on electrical transport properties of graphene nanoribbons (GNRs). Monolayer graphene sheets and Si nanowires (NWs) were prepared by chemical vapor deposition and a combination of nanosphere lithography and metal-assisted electroless etching from a Si wafer, respectively. Back-gated GNR field-effect transistors were fabricated on a heavily p-doped Si substrate coated with a 300 nm-thick SiO2 layer, by O2 reactive ion etching of graphene sheets using etch masks based on Si NWs aligned on the graphene between the two electrodes by a dielectrophoresis method. This resulted in GNRs with various widths in a highly controllable manner, where the on/off current ratio was inversely proportional to ribbon width. The field-effect mobility decreased with decreasing GNR widths due to carrier scattering at the GNR edges. These results demonstrate the formation of a bandgap in GNRs due to enhanced carrier confinement in the transverse direction and edge effects when the GNR width is reduced.

The transition metal dichalcogenides (TMDCs) have been extensively investigated for various applications such as logic, memory and optical devices, and sensors. The pressing challenge in the research of TMDCs is the electrical performance limited by the high contact resistance. We report more than 5000 times reduction in the contact resistance of WS2 field-effect transistor (FET) with Ti contact (81 MΩ μm to 14.6 kΩ μm) by high-pressure hydrogen annealing. Schottky barrier height reduction appears to play a major role in the reduction of the contact resistance. This process can be used to reduce the contact resistance even further by combining with a doping technique for TMDCs and a contact metal optimization for TMDC FETs.

The electronic properties of single-layer, CVD-grown graphene were modulated by deep ultraviolet (DUV) light irradiation in different radiation environments. The graphene field-effect transistors (GFETs), exposed to DUV in air and pure O2, exhibited p-type doping behavior, whereas those exposed in vacuum and pure N2 gas showed n-type doping. The degree of doping increased with DUV exposure time. However, n-type doping by DUV in vacuum reached saturation after 60 min of DUV irradiation. The p-type doping by DUV in air was observed to be quite stable over a long period in a laboratory environment and at higher temperatures, with little change in charge carrier mobility. The p-doping in pure O2 showed ~15% de-doping over 4 months. The n-type doping in pure N2 exhibited a high doping effect but was highly unstable over time in a laboratory environment, with very marked de-doping towards a pristine condition. A lateral pn-junction of graphene was successfully implemented by controlling the radiation environment of the DUV. First, graphene was doped to n-type by DUV in vacuum. Then the n-type graphene was converted to p-type by exposure again to DUV in air. The n-type region of the pn-junction was protected from DUV by a thick double-coated PMMA layer. The photocurrent response as a function of Vg was investigated to study possible applications in optoelectronics.

Tunable DC voltage control circuit based on a half-wave rectifier was developed using a graphene–germanium barristor. The output DC voltage level could be modulated at 30–100% of the peak voltage by controlling the Schottky barrier height between graphene and germanium using a gate bias. Owing to the simple and low-temperature integration process, this device can be used for a variable DC power supply in monolithically integrated circuits or flexible devices.

A graphene photodetector decorated with Bi2Te3 nanowires (NWs) with a high gain of up to 3 × 104 and wide bandwidth window (400–2200 nm) has been demonstrated. The photoconductive gain was improved by two orders of magnitude compared to the gain of a photodetector using a graphene/Bi2Te3 nanoplate junction. Additionally, the position of photocurrent generation was investigated at the graphene/Bi2Te3 NWs junction. Eventually, with low bandgap Bi2Te3 NWs and a graphene junction, the photoresponsivity improved by 200% at 2200 nm (~0.09 mA/W).

The fabrication of smart textiles is currently relying on the printing of ultrathin electronics on fabric, which is subject to the poor adhesion between electronics and textile. Here, Yoon et al. propose the use of cilia-like structure to improve adhesion in addition to release mechanical stress.

An enhancement-mode AlGaN/GaN metal-insulator-semiconductor high-electron- mobility-transistor was fabricated using a recess gate and CF4 plasma treatment to investigate its reliable applicability to high-power devices and circuits. The fluorinated-gate device showed hysteresis during the DC current-voltage measurement, and the polarity and magnitude of hysteresis depend on the drain voltage. The hysteresis phenomenon is due to the electron trapping at the Al2O3/AlGaN interface and charging times longer than milliseconds were obtained by pulse I-V measurement. In addition, the subthreshold slope of the fluorinated-gate device was increased after the positive gate bias stress because of the two-dimensional electron gas reduction by ionized fluorine. Our systematic observation revealed that the effect of fluorine ions should be considered for the design of AlGaN/GaN power circuits.

The electrical characteristics of Zinc oxide (ZnO) thin-film transistors are analyzed to apprehend the effects of oxygen vacancies after vacuum treatment. The energy level of the oxygen vacancies was found to be located near the conduction band of ZnO, which contributed to the increase in drain current (ID) via trap-assisted tunneling when the gate voltage (VG) is lower than the specific voltage associated with the trap level. The oxygen vacancies were successfully passivated after the annealing of ZnO in oxygen ambient. We determined that the trap-induced Schottky barrier lowering reduced a drain barrier when the drain was subjected to negative bias stress. Consequentially, the field effect mobility increased from 8.5 m2 V−1·s−1 to 8.9 m2 V−1·s−1 and on-current increased by ~13%.

Persistent PMMA residue formed during a graphene transfer has been a culprit in the optimization of graphene device performance. We demonstrated a facile process to remove the PMMA residue using pulsed KrF laser annealing system at H2/Ar ambient. 10min laser annealing at 248nm could remove the PMMA residue as well as the methoxy and carboxyl function groups without causing noticeable damage to the graphene.

Graphene–ZnO:N Schottky junction barristors are fabricated on a flexible polyethylene naphthalate substrate utilizing a low thermal budget integration process with a maximum process temperature below 200 °C. An on/off ratio of over 104 is obtained with a 0.1 A/cm2 drive current density at Vd = 0.5 V. The transmittance, degraded by the device stack, was 2.5–3% in the visible wavelength range, and a high on/off ratio was maintained after 600 bending cycles at a 0.6% strain (bending radius = 10 mm).

We have investigated the effects of metal decoration on the gas-sensing properties of a device with two-dimensional (2D) molybdenum disulfide (MoS2) flake channels and graphene electrodes. The 2D hybrid-structure device sensitively detected NO2 gas molecules (>1.2 ppm) as well as NH3 (>10 ppm). Metal nanoparticles (NPs) could tune the electronic properties of the 2D graphene/MoS2 device, increasing sensitivity to a specific gas molecule. For instance, palladium NPs accumulate hole carriers of graphene/MoS2, electronically sensitizing NH3 gas molecules. Contrarily, aluminum NPs deplete hole carriers, enhancing NO2 sensitivity. The synergistic combination of metal NPs and 2D hybrid layers could be also applied to a flexible gas sensor. There was no serious degradation in the sensing performance of metal-decorated MoS2 flexible devices before/after 5000 bending cycles. Thus, highly sensitive and endurable gas sensor could be achieved through the metal-decorated 2D hybrid-structure, offering a useful route to wearable electronic sensing platforms.

Memcapacitor model based on its one possible physical realization is developed and simulated in order to know its limitation before making a real device. The proposed device structure consists of vertically stacked dielectric layer and MoS2 monolayer between two external metal plates. The Metal Insulator Transition (MIT) phenomenon of MoS2 monolayer is represented in terms of percolation probabilty which is used as the system state. Cluster based site percolation theory is used to mimic the MIT of MoS2 which shows slight discontinuous change in MoS2 monolayer conductivity. The metal to insulator transition switches the capacitance of the device in hysterical way. An Ioffe Regel criterion is used to determine the MIT state of MoS2 monolayer. A good control of MIT time in the range of psec is also achieved by changing a single parameter in the model. The model shows memcapacitive behavior with an edge of fast switching (in psec range) over the previous general models. The model is then extended into vertical cascaded version which behaves like a ternary device instead of binary.

The electrical characteristics and operation mechanism of a molybdenum disulfide/black phosphorus (MoS2/BP) heterojunction device are investigated herein. Even though this device showed a high on-off ratio of over 1 × 107, with a lower subthreshold swing of ~54 mV/dec and a 1fA level off current, its operating mechanism is closer to a junction field-effect transistor (FET) than a tunneling FET. The off-current of this device is governed by the depletion region in the BP layer, and the band-to-band tunneling current does not contribute to the rapid turn-on and extremely low off-current.