ACS Applied Electronic Materials最新文献

The epitaxial growth and semiconductor functionality of δ-Ga₂O₃ thin films were demonstrated using mist chemical vapor deposition. A high-quality δ-Ga₂O₃ film was grown on YSZ(111) substrate utilizing a β-Fe₂O₃ buffer layer on a bcc-ITO electrode. X-ray diffraction analysis revealed the formation of a single-phase δ-Ga₂O₃ with a bixbyite structure, as evidenced by clear 222 diffraction peaks at 33.6°. The epitaxial relationships and sharp interfaces between layers were further validated by transmission electron microscopy, with selected area electron diffraction patterns definitively establishing the bixbyite crystal structure. Photoluminescence excitation spectroscopy revealed an absorption edge at 4.5 eV with a peak near 4.9 eV. We demonstrated the first semiconductor functionality of δ-Ga₂O₃ through a vertical Schottky barrier photodiode structure. This structure exhibited photoresponsivity in the deep UV region, with a maximum value of 1.25 mA/W at approximately 5.1 eV. These results validate the presence of δ-Ga₂O₃ while highlighting its potential in deep UV optoelectronics.

The development of memristors for neuromorphic computing has gained attention due to their ability to mimic biological neurons. Among the various switching mechanisms, volatile electrochemical metallization (ECM)-threshold switching (TS) memristors show promise for artificial neural networks due to their simple structure and low operating voltages. However, ECM TS memristors often suffer from poor switching uniformity, limiting practical applications. In this work, we demonstrate a highly uniform switching Ag-based TS memristor with a nanoporous-Pt (np-Pt) cation limiter. The device achieves ultralow leakage current (<1 pA), high selectivity (>10⁷), and high endurance (>10⁶ cycles). The np-Pt cation limiter also enhances the device’s stability by reducing variability in the operating voltages (V_th and V_hold) and enabling operations at higher current compliance levels (∼10 μA). In addition, the Ag/np-Pt TS device exhibits self-oscillation behavior at low voltage (<1 V), with oscillation frequency increasing with the applied voltage. The insertion of the np-Pt cation limiter provides a simplistic technique of metal ions manipulation in ECM TS devices, enhancing their performance for artificial neural network applications.

Manipulating and designing the interfaces between two-dimensional (2D) van der Waals materials serves as a fundamental approach for achieving technologically significant effects and tailoring material characteristics. The exchange bias effect exhibited in 2D van der Waals magnetic heterostructures has garnered significant attention in the realm of spintronics research owing to its intriguing physics and promising prospects for practical applications. Herein, we have, for the first time, constructed the CrCl₃/Fe₃GeTe₂/CrCl₃ heterostructure and employed the anomalous Hall method to precisely measure its unique characteristics. Interestingly, distinct double-shifted hysteresis loops observed in the anomalous Hall effect curve are attributed to the emergence of multiple domains within the Fe₃GeTe₂ layer induced by the CrCl₃/Fe₃GeTe₂ interfaces. In contrast to the pure Fe₃GeTe₂ few-layer structures, the CrCl₃/Fe₃GeTe₂/CrCl₃ heterostructure demonstrates the presence of an exchange bias effect. As the temperature increases, the values of the exchange bias field decrease and ultimately vanish at 11 K, near the Néel temperature of CrCl₃. Concurrently, the width of the hysteresis loop diminishes and disappears above 150 K. These findings suggest that the pinning effect and exchange bias effect are not present simultaneously, and the pinning effect has a temperature range wider than that of the exchange bias effect. Our findings underscore the potential of antiferromagnet–ferromagnet coupling interfaces as a powerful means for manipulating magnetic properties, with implications for both advanced spintronic device design and fundamental understanding of magnetic interactions.

The doping of two-dimensional (2D) transition metal dichalcogenides (TMDCs) by an approach compatible with circuit integration is crucial. However, ion implantation, the most commonly used method for doping semiconductors, poses significant challenges for 2D-TMDCs because of the requirement for ultralow ion energy and the difficulty of restoring damaged 2D materials. Here, we achieve bipolar transport in intrinsic n-type WS₂ monolayers through phosphorus (P) ion implantation using commercial ion implanters. Millisecond flash lamp annealing is employed to remove ion-induced defects and activate P. Experimental results show a clear change in carrier type with increasing ion fluence. Samples implanted with a fluence of 7.5 × 10¹² cm^–2 display ambipolar transport behavior with an on/off ratio of 4.4 × 10⁵ and 1.6 × 10⁶ for p- and n-branch, respectively. At the same time, the optical and structural properties of WS₂ are well preserved. All of these findings not only complement the fundamental understanding of 2D-TMDCs but also provide a possible route for heterointegration of TMDCs into current Si-based semiconductor technologies.

In the burgeoning field of electronic skin (e-skin) and wearable technology, the development of flexible and sensitive tactile sensors is of paramount importance. This paper presents the fabrication and characterization of a capacitive flexible tactile sensor with an inverted frustum structure, designed to address the limitations of existing sensors in terms of sensitivity, response speed, and durability. The sensor was developed using a combination of 3D-printing and layer-by-layer (LBL) techniques, leveraging the benefits of conductive silver adhesive and silicone rubber for enhanced performance. The fabrication process involved the use of COMSOL Multiphysics for simulation, followed by 3D printing of molds and curing of silicone rubber at specific temperatures to form the sensor components. Electrical conductivity was ensured through the application of conductive silver adhesive, and the assembly was finalized through vacuum drying. Key findings from the study include the sensor’s high sensitivity to both normal and tangential forces, with a sensitivity of 0.2 N^–1 in the 0–4 N range and 0.11 N^–1 from 4 to 15 N under normal force, and a rapid response time of 25 ms. The sensor also demonstrated excellent mechanical durability with a hysteresis error of 4.8% and maintained a stable performance across a wide temperature range, indicating its robustness and reliability. Furthermore, the sensor showed potential in applications such as human–computer interaction and binary encoding, highlighting its versatility. This study significantly contributes to the field by presenting a sensor with good sensitivity and rapid response, along with excellent mechanical durability and temperature stability. The findings pave the way for the development of advanced e-skin and wearable devices that can provide real-time monitoring and feedback in various applications.

Semiconductors based on metal halide perovskites have been extensively studied recently due to their potential as materials for optoelectronic applications. In the realm of cesium-based inorganic perovskite light-emitting diodes (PeLEDs), several aspects are of paramount importance to achieve high photoluminescence (PL) and electroluminescence (EL) of the PeLEDs. The fabrication of CsPbBr₃ via thermal evaporation, employing different ratios and stoichiometries, has demonstrated an efficient PL performance in films at high CsBr concentrations. Interface engineering approaches and defect-passivating additives can promote the growth of uniform and high-quality perovskite films. However, such strategies may lead to device degradation, resulting in low stability. Currently, obtaining defect-free thin films is a crucial prerequisite. From a materials perspective, this critical review article covers the composition of the active layer and its effect on the PL and, from the device, the role of additives in obtaining uniform films, assuring optimal charge transport, and electrical injection to achieve high EL.

Memristor-based optoelectronic artificial synapses have a great potential to enhance the efficiency of future neuromorphic computing. Like neurons of the retina, they have the potential to enable real-time visual preprocessing. This highlights the growing importance of improving optoelectronic artificial synapses for next-generation neuromorphic computing and neuromorphic visual systems. These artificial synapses can enhance neuromorphic visual systems, extending their capabilities beyond visible light. This study introduces a P-type copper oxide-based optical memristor device that exhibits fundamental biosynaptic characteristics like long-term potentiation (LTP) and long-term depression (LTD), which can be tuned using optical stimuli. These LTP/LTD characteristics were used as weights in a single-layer perceptron neural network to classify the MNIST data set using an off-chip training algorithm. We also demonstrated light-induced short-term plasticity and optical paired-pulse facilitation, which are the two important characteristics of neurons of the human retina that help in image preprocessing. We also implemented Pavlovian conditioning on the device using a combination of electrical and optical stimuli. These results indicate the possibility of using this device as an optically controlled artificial synaptic device for neuromorphic vision sensor applications.

Scaling down the charge-trap memory cell for high storage density causes severe reliability issues such as the decreased trapped charge density, migration of stored charges to adjacent cells, electrostatic interference between neighboring cells, and gate dielectric breakdown. Therefore, it is highly required to explore the advanced charge-trap layer (CTL) having a high trap density with a deep level for improved performance and reliability. In this study, nonvolatile charge-trap memory characteristics are demonstrated using a low-temperature atomic layer deposition (ALD) of hafnium oxide (HfO₂) CTL and Al₂O₃ tunneling and blocking oxides. The use of a high-k dielectric stack enhances the electric field for efficient and reliable device operations in scaled-down devices. In particular, the low-temperature ALD HfO₂ CTL deposited at 50 °C has a high charge-trap areal density of 9.65 × 10¹² cm^–2, exhibiting a large threshold voltage shift of ∼5 V. The proposed device presents a nonvolatile retention of 81.7% for 10 h thanks to the amorphous phase of the low-temperature HfO₂ CTL, in contrast to a poor retention of 44.8% in the device with the crystalline high-temperature HfO₂ CTL deposited at 200 °C. Furthermore, rapid thermal annealing at 600 °C on the dielectric stack significantly enhances hole trapping in the HfO₂ CTL via creation of acceptor-level traps by interdiffusion between HfO₂ and Al₂O₃, securing the large threshold voltage shift of ∼7.8 V. It paves the way for providing the optimized gate dielectric stack of CTF consisting of Al₂O₃ and defective HfO₂ for improved CTF characteristics.

In recent years, there has been a surge in interest surrounding the advancement of gel-free, ultrathin, skin-conformable tattoo electrodes for continuous and extended monitoring of ECG signals. This development aims to mitigate the limitations associated with traditional electrodes. However, all of these results are limited to data from individual subjects. Hence, replicability is reduced by individual variability due to a small sample size, which may lead to inconclusive results. Consequently, the suitability of these outcomes for clinical validation has been inadequately investigated. In this study, an ultrathin, gel-free, skin-conformable PEDOT:PSS-based tattoo electrode was fabricated and characterized. A preclinical skin irritation test of the PEDOT:PSS-based tattoo electrode was performed before clinical assessment. Next, we accessed the performance of these tattoo electrodes involving 34 healthy volunteers and compared the ECG signals acquired from these ultrathin electrodes with those recorded by traditional Ag/AgCl electrodes. The fabricated tattoo electrode is approximately 10 μm thick and has a skin–electrode impedance of 72 KΩ at 50 Hz. The preclinical skin irritation study confirmed that the film of PEDOT:PSS is nontoxic, noncorrosive, and biocompatible with rabbit skin. In healthy volunteers, the data points from the sample population all cluster closely around the bias line, and we observed no significant systematic error associated with the ECG measurement. This PEDOT:PSS-based skin-conformal tattoo electrode retained its characteristics even after continuous wear for up to 24 h during routine activities, and the electrodes remained stable even after 60 days of storage. Altogether, our findings confirmed the suitability of these skin-conformal PEDOT:PSS-based tattoo electrodes for ECG monitoring.

The rapid advancement of multifunctional wearable strain sensors has substantially increased their potential applications in human–computer interfaces and health monitoring. Strain sensors generally suffer from reliable response and hysteresis, adversely impacting the sensing device’s application. This study demonstrates a “one-pot” synthesis method to converge silver nanowires (AgNWs) and reduced graphene oxide (rGO) sheets into a dual interconnected framework using the sandwiched assembly technique. AgNWs and rGO have been explored extensively due to their high electrical and thermal conductivity, optical transparency, ease of synthesis, etc. The transversely oriented AgNWs bridge the underlying longitudinal rGO sheets to effectively prevent microcrack propagation, resulting in a gauge factor of ∼11.78 at a 11.33% operating range. The microscopic structure allows the sensor to disperse heat during specific operations, exhibiting thermal conductivity of ∼1 W m^–1 K^–1. Furthermore, the sensor exhibits a highly reproducible response for >4000 cycles with minimal hysteresis (∼5.33%). This might be attributed to the dual-linked conductive network of AgNWs and rGO, which mitigates the microcrack propagation during long cycling. This study is expected to provide research insights into the multifunctional integration of human garments and wearable electronics.