ACS Applied Electronic Materials最新文献

In the context of developing and encouraging flexible energy storage applications and optoelectronic devices, the influence of multiwalled carbon nanotubes (MWCNTs) on structural, optical, dielectric, and electrical characteristics of polyethylene glycol/poly(vinyl alcohol) (PEG/PVA) blends has been studied. TEM imaging confirms that MWCNTs are elongated nanotubes with multiple concentric graphene layers, typically 20–22 nm in diameter. XRD studies showed that, after MWCNTs were added , the crystallinity of the polymeric matrix decreased, whereas the amorphous content increased, ensuring significant optimization of electrical conductivity. Strong interactions between MWCNTs and the polymer matrix have also been detected by FTIR spectroscopic analysis through the shifting of absorption bands and the variation in the intensity of functional groups. Optical characterization exhibited tunable absorption properties and narrowed band gap, while the increased concentration of MWCNTs facilitated the formation of charge-transfer complexes, which enhanced electronic conductivity of the present samples. This is evidenced by the reductions in both the indirect and direct optical band gaps. For the pure PEG/PVA matrix, the indirect and direct optical band gaps were 4.24 and 4.88 eV, respectively. However, with the addition of 1.2 wt % MWCNTs these optical band gaps decreased significantly to 3.05 eV (indirect) and 4.36 eV (direct). Dielectric studies showed an improvement in electrical permittivity with reduced interfacial polarization losses. The maximum AC conductivity was observed at 1.2 wt % MWCNTs, reaching a value of 1.45 × 10^–6 S/cm at room temperature. This enhancement in conductivity is attributed to the formation of interconnected MWCNT networks within the polymer matrix, which effectively lowers the energy barriers for charge transport and promotes efficient electron mobility. Impedance spectroscopy and Nyquist plots showed a considerable reduction in bulk resistance, reflecting the increased conductivity and energy storage potential. An electrical equivalent circuit was presented for each sample based on the fitting curves of the impedance spectroscopy data. Specific research findings indicated that the PEG/PVA/MWCNTs nanocomposites exhibited promising properties for the next generation of flexible electronics, storage, and optoelectronic appliances. This work provided a deep understanding of how MWCNTs doping inherently influences polymer nanocomposites and could be of great importance to designers in engineering modern advanced functional material systems.

Flexible pressure sensing arrays exhibit broad application prospects in many emerging fields. Challenges remain in fabricating crosstalk-free, stabilized, and large-area pressure sensing arrays through scalable and low-cost methods. Herein, a facile strategy is proposed for preparing an electrically isolated flexible pressure sensing array (EIFPSA) by simply rubbing a Au-sprayed thermoplastic polyurethane substrate surface with inverted micropyramids. The inverted micropyramids on the rubbed sensing substrate are electronically isolated from each other, and the nonconductive ridges can prevent the current flow across adjacent sensing units. This enables the EIFPSA to have crosstalk-free performance in both flat and bent states and accurately identify the spatial pressure distribution of an object. Meanwhile, the sensing units in the EIFPSA exhibit a low zero drift without pressure and good signal stability and repeatability to respond to both static and dynamic pressures. The sensing units also exhibit good durability and sensitivity retention during cyclic compression/release testing. Specifically, there is only a slight reduction in the sensitivity after 10,000 cycles. As a proof of concept, a flexible Braille reader consisting of a data acquisition system and machine learning model is constructed to demonstrate a successful application of the EIFPSA in tactile sensing systems with a multipoint recognition capability without crosstalk.

Brain-inspired neuromorphic systems have recently garnered significant interest owing to their ability to effectively overcome the von Neumann bottleneck to increase computing and energy efficiency in the era of the rapid development of artificial intelligence. A hardware artificial neuron with a rectified linear unit (ReLU) activation function is highly desired for introducing a nonlinear activation function and resolving the vanishing gradient problem. In this work, we developed a ReLU artificial neuron based on a threshold switching memristor (TSM) device of Pt/Ag/Al₂O₃/HfO₂/Ag-NIs/Pt structure with an ultralow threshold voltage. This artificial neuron realizes the ReLU activation function by correlating the amplitude of the output spike with the amplitude of the input voltage, which is reported for the first time. To mitigate the potential “dying ReLU” problem that can arise when the ReLU activation function is applied to deep spiking neural networks (SNNs), we developed a LeakyReLU artificial neuron. Experimental results showed that we successfully developed a high-integration and low-power ReLU artificial neuron and its variant, the LeakyReLU artificial neuron, and realized a digital recognition function in a simulated single-layer fully connected SNN, which is of great significance for the construction of large-scale SNNs in the future.

The scaling limitations in traditional semiconductor technologies have accelerated the demand for advanced nonvolatile memory devices. Ferroelectric HfO₂-based thin films, particularly Zr-doped HfO₂ (HZO), have gained prominence due to their ability to support ferroelectricity at reduced dimensions, offering a path toward high-density and low-power memory solutions. However, reliability issues such as wake-up and imprint phenomena still hinder the commercialization of HZO-based devices. In this study, we propose a N₂/H₂ pretreatment for Mo electrodes in metal-ferroelectric-metal (MFM) capacitors to enhance device performance and mitigate interfacial degradation. The pretreatment reduces the MoO_x interfacial layer, lowers the oxidation state, and minimizes work function differences between electrodes, thus improving ferroelectric properties. XPS analysis shows a 10% reduction in Mo⁶⁺, while GAXRD results reveal enhanced stabilization of the ferroelectric orthorhombic phase. Electrical characterization demonstrates increased remanent polarization and a reduced imprint field, with negligible wake-up effects up to 10⁶ cycles. These findings highlight the effectiveness of N₂/H₂ pretreatment in improving the reliability of HZO-based MFM capacitors and promoting their potential for next-generation memory applications.

Optimizing an organic light-emitting diode (OLED) structure for high efficiency typically requires extensive efforts in tuning layer thicknesses and conducting photometric analyses. While computational simulations can shorten the optimization process, applying them to solution-processed OLEDs (s-OLEDs) is challenging since ink concentration affects both the thickness and morphology of films, complicating the simulation substantially. To address this, we employed machine learning (ML), specifically Gaussian Process Regression (GPR), to optimize s-OLED ink concentrations without the need to calibrate material- or thickness-dependent properties typically required in conventional simulations. The GPR model efficiently suggested optimal ink concentrations for the hole transport layer (c_HTL) and electron transport layer (c_ETL) to maximize the current efficiency (CE). Using a data set of ink concentrations (2.5–17.5 g/L) as input and CE measured at 100, 1000, and 10,000 cd/m² as output, the model was trained to propose viable combinations of c_HTL and c_ETL. The GPR model successfully identified three distinct optimal ink concentration pairs within just three experimental iterations. By integrating GPR with spectral analysis, we also uncovered the interplay among ink concentration, recombination zone dynamics, and CE. Based on these findings, we proposed a mechanism explaining why distinct ink concentration pairs yield higher efficiency at different luminance levels. This study highlights the potential of ML techniques not only in streamlining s-OLED optimization but also in providing deeper insights into the relationships among the s-OLED structure, charge carrier dynamics, and performance.

Soft three-axis strain sensors detect normal strains perpendicular to the interface and shear strains parallel to the interface, having potential applications in actuators and human motion monitoring. However, in the measurement process of three-axis strain sensors, issues like cross-coupling errors, nonlinear errors, and noise interference often arise. The issues originate from imperfections in the structural design of the sensor, inadequate sensor sensitivity, and the absence of a mathematical decoupling model. Consequently, the sensor faces significant challenges in accomplishing the decoupling of three-axis strain. In order to fulfill the objective of three-axis strain decoupling, this study presents a flexible capacitive three-axis strain sensor fabricated based on liquid metal elastomer foam (LMEF). Leveraging LMEF, the sensor attains enhanced sensitivity, and the nonlinear errors as well as noise interference in the measurement are diminished. By designing the cross-axis overlapping areas of the three capacitive electrodes, one capacitor is only sensitive to normal strain, while the other two capacitors are sensitive to both normal and shear strains simultaneously. By employing a capacitor that is solely sensitive to the normal strain in the Z-direction, it becomes feasible to decouple the capacitors for shear strains in the X and Y directions from the normal strain in the Z-direction. This enables a completely crosstalk-free three-axis strain measurement. Through theoretical analysis and finite element simulation, the operating principle of the sensor was thoroughly explored, and a three-axis strain decoupling model was established. As a result, the sensor has successfully achieved the decoupling of three-axis strain. Moreover, the feasibility of the sensor’s applications in object grasping and human gait monitoring has been demonstrated.

As gallium nitride (GaN) devices are scaled for higher-frequency performance, their advancement is increasingly limited by parasitic delays due to elevated Ohmic contact resistance. To mitigate this, selective-area growth n-type doped GaN (n⁺-GaN) with titanium (Ti) as the Ohmic contact metal has been widely used, achieving specific contact resistivity in the range of 1 × 10^–7 Ω·cm². However, further reductions of Ti/n⁺-GaN interfacial specific contact resistivity are constrained by the Fermi-level pinning (FLP) effect that originated from the metal-induced gap states and interfacial dangling bonding states. In this study, we propose an approach to relieve the FLP effect and achieve ultralow contact resistivity by forming an approximately 2 nm gallium oxide passivation layer at the Ti/n⁺-GaN interface through air annealing of the n⁺-GaN surface. This passivation method yields 0.24 eV Schottky barrier height and a low specific contact resistivity of 3 × 10^–8 Ω·cm² for GaN Ohmic contact. Atomic force microscopy (AFM), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDX) confirm the formation of various oxide layers under different annealing conditions. This study demonstrates an effective strategy for reducing Ohmic contact resistance, addressing parasitic resistance, and enabling further scaling of GaN devices for enhanced performance.

Ferrimagnets have the potential to play a key role in spintronics due to their high stability, low energy consumption, and rapid magnetic state switching. These characteristics are typically observed in ferrimagnetic materials near magnetic or angular compensation states. Near the magnetic compensation point, an external field can disrupt the collinearity between the sublattices, leading to aligned magnetic projections. In this work, a violation of antiferromagnetic ordering is detected by a change in the direction of the effective field induced by spin–orbit torque, without altering the dominance type. In the studied W/Co₇₀Tb₃₀/Ru structure, the canted phase region is observed near room temperature under external fields of approximately 0.1 T. Using macrospin simulations and analytical derivations, a correlation is established between anisotropy, interlattice exchange interaction, and the presence of the canted phase region.

Small-size In–Ga–Zn–O thin-film transistors (IGZO TFTs) exhibit significant potential for high-end display and memory applications; however, contact resistance remains a critical parameter limiting their miniaturization. To address this challenge, we designed a IGZO TFT with low contact resistance using Al-induced microstructure regularization technique. The contact resistance of the Al-TFT is 4 ± 2 KΩ·μm, which is significantly better than that of the ITO-TFT ((5 ± 4)×10³ KΩ·μm) and Mo-TFT ((1 ± 1)×10³ KΩ·μm). This is due to the different interfacial properties of Al/IGZO compared to Mo/IGZO and ITO/IGZO, with unique nanocrystalline structures, generation of metal oxide layers, and significant changes in In and Zn contents. Measurements of the contact potential difference also indicate that the ohmic contacts formed at the Al/IGZO contact interface are different from the Schottky contacts formed by Mo/IGZO and ITO/IGZO. These findings highlight the effectiveness of the Al-induced microstructure regularization technique in reducing contact resistance through microstructural changes.

In this work, we report the synthesis and fabrication of a fully wearable piezoelectric nanogenerator based on hydrothermally grown tungsten disulfide (WS₂) quantum dots and dip-coated conductive polyaniline (PANI) on cotton fabrics. WS₂ quantum dots with a hexagonal crystal structure and an average diameter of 7–8 nm were confirmed by X-ray diffraction and a high-resolution transmission electron microscope. A fully wearable nanogenerator was constructed using a poly(methacrylic acid methyl ester) (PMMA) matrix for WS₂ QDs and conductive PANI deposited on the cotton fabric. Conductive PANI coated on cotton fabric was used as the top and bottom electrodes. Functional group and distribution of the WS₂QDs inside PMMA were confirmed through the Fourier transform infrared spectroscopy (FT-IR) and field emission scanning electron microscopy techniques. A fully wearable WS₂ QDs-PMMA-cotton, PANI-based nanogenerator generated a very high output voltage of 60 V and a current density of 302 nA/cm² under vertical mechanical strain. Interestingly, the WS₂ QDs-PMMA-cotton based nanocomposite showed a very dielectric constant (έ) of 799 at 1.5 kHz. The wearable nanogenerator based on the WS₂ QDs-PANI fabric-based nanocomposite exhibits a high power density. Moreover, the device shows a high tensile strength of 60.25 MPa, confirming robust performance of the wearable nanogenerator. The output performance of the wearable WS₂ QDs-PANI nanogenerator is measured under various humid conditions, and a stable output performance was observed even up to 60% relative humidity. Such a stable output performance is due to the hydrophobic nature of the device, and a large water contact angle of 141° is obtained. A real time application of the wearable WS₂QDs-PANI nanocomposite nanogenerator as a piezoelectric touch sensor was also demonstrated under various human body movements.