Asymmetric Electrode Structure Research Articles

Highly sensitive diamond X-ray detector array for high-temperature applications

Diamond is a highly suitable material for X-ray detectors that can function effectively in harsh environments due to its unique properties, such as an ultrawide bandgap, high resistance to radiation, excellent carrier mobility, and remarkable chemical and thermal stability. However, the sensitivity of diamond X-ray detectors needs further improvement due to the relatively low X-ray absorption efficiency of diamond, and the exploration of single-crystal diamond array imaging remains unexplored. Herein, a 10×10 X-ray photodetector array was constructed from single-crystal diamond. To improve the sensitivity of the diamond X-ray detector, an asymmetric sandwich electrode structure was utilized. Additionally, trenches are created through laser cutting to prevent crosstalk between adjacent pixels. The diamond X-ray detector array shows exceptional performance, including a low detection limit of 4.9 nGy s-1, a sensitivity of 14.3 mC Gy-1 cm-2, and a light-dark current ratio of 18312, which are among the most favorable values ever reported for diamond X-ray detectors. Furthermore, these diamond X-ray detectors can operate at high temperatures up to 450 °C, making them suitable for development in harsh environments.

Mixed etching-oxidation process to enhance the performance of spin-transfer torque MRAM for high-performance computing

Spin-transfer torque magnetic random access memory (MRAM) devices have considerable potential for high-performance computing applications; however, progress in this field has been hindered by difficulties in etching the magnetic tunnel junction (MTJ). One notable issue is electrical shorting caused by the accumulation of etching by-products on MTJ surfaces. Attempts to resolve these issues led to the development of step-MTJs, in which etching does not proceed beyond the MgO barrier; however, the resulting devices suffer from poor scalability and unpredictable shunting paths due to asymmetric electrode structures. This paper outlines the fabrication of pillar-shaped MTJs via a four-step etching process involving reactive-ion etching, ion-beam etching, oxygen exposure, and ion-trimming. The respective steps can be cross-tuned to optimize the shape of the pillars, prevent sidewall redeposition, and remove undesired shunting paths in order to enhance MTJ performance. In experiments, the proposed pillar-MTJs outperformed step-MTJs in key metrics, including tunneling magnetoresistance, coercivity, and switching efficiency. The proposed pillar-MTJs also enable the fabrication of MRAM cells with smaller cell sizes than spin–orbit torque devices and require no external field differing from voltage-controlled magnetic anisotropy devices.

High figure-of-merit A1-mode lamb wave resonators operating around 6 GHz based on the LiNbO3 thin film

The first asymmetric mode (A1 mode) lamb wave resonator (LWR) with a resonant frequency of 6 GHz based on Z-cut lithium niobate (LN) films is presented. An asymmetric electrode structure with different-sized electrode pads in the center and edged regions has been proposed, which can be used to optimize the distribution of the electric field and decrease acoustic impedance mismatch to improve the target mode. Experiment results reveal that LWRs with an asymmetric electrode structure can successfully enhance the A1 mode, achieving a high effective electromechanical coefficient ( keff2 ) of 26%, a quality factor (Q) of 1123, and an excellent figure-of-merit (FOM = keff2 ∙Q) of 262. It demonstrates that asymmetric electrode structure provides a new way to suppress the spurious modes for LWRs and shows a great application prospect in wide-bandwidth and low-loss filters used in the sub-6 G frequency range.

Kilogram-scale high-yield production of PbI2 microcrystals for optimized photodetectors

In this work, PbI2-based photodetectors with symmetric Au–Au and asymmetric Au-graphene electrode structures are made. The asymmetric PbI2 device shows 3–4.8 times higher photocurrent compared to the symmetric device under the same light intensities.

Ultra-stability and high output performance of a sliding mode triboelectric nanogenerator achieved by an asymmetric electrode structure design

A new type of sliding-TENG with asymmetric electrode design achieves high output performance and ultra-stability by the balance of electrostatic shielding and charge accumulation for providing power supply to some electrical devices.

Triboelectric nanogenerator with asymmetric multilayer arc electrodes to improve performance

The role of wind energy in the emerging energy market is crucial and it holds the potential to emerge as a promising clean energy source. The triboelectric nanogenerator represents a revolutionary paradigm in wind energy harvesting devices, having engendered considerable scholarly interest due to its innovative approach and potential implications. Among its various working modes, freestanding mode is considered the most effective for harvesting rotating energy. In this paper, a freestanding mode multilayer triboelectric nanogenerator is proposed, which is characterized by asymmetric arc electrode structure, and the usual freestanding mode electrodes are positioned at a certain angle to improve the output of the generator. Operating at a frequency of 1 Hz, it is exclusively the single-layer arc electrode that can yield an instantaneous power output of 1.625 mW, while concurrently facilitating the transfer of a charge quantified at 197 nC. Compared to an untreated electrode, exhibiting an enhancement of 11-fold in terms of power output and 3.5-fold with respect to charge transfer. Additionally, the generator’s electrodes are cleverly designed with an asymmetric multilayer structure, resulting in higher space utilization within the generator. The asymmetric arc triboelectric nanogenerator (AA-TENG) presents a viable solution for effectively harvesting wind energy in nature.

Electrochemical bulk and film-type oxygen sensors: Strategies for detecting extremely low concentration in hydrogen environments

Potentiometric oxygen sensors with excellent sensitivity in a low oxygen concentration range are designed based on intrinsic logarithmic response characteristics, and an asymmetric electrode structure, differentiated from conventional oxygen sensors with reference oxygen gases or parts exposed to air, is implemented. Electrolytes and electrode materials that formulate oxygen sensor devices are evaluated by comprehensively considering their reactivity to trace oxygen, oxygen ion formation, and ease of movement. The sensor using an yttria-stabilized zirconia bulk ceramic electrolyte measures the oxygen concentration in an oxygen-hydrogen mixture down to 0.5%, with a response time of 7.8 s. The sensor with a Nafion proton conductor film and a polyimide gas separation membrane allows room-temperature sensing and measures the oxygen concentration to a minimum of 2%.

All-Solution-Processed Reduced Graphene Oxide Flexible Photodetectors for Use in Low-Light Environments

All-solution-processed reduced graphene oxide (rGO)-based flexible photodetectors (PDs) with asymmetric electrode structures of Ag nanowires (NWs) — Cu NWs are demonstrated for stable photodetection in weak-light environments. At first, we aimed to optimize the fabrication parameters of rGO layers for minimum roughness and high uniformity according to the field emission scanning electron microscope (FESEM) images; the average absorbance of optimal rGO layers is ~17.4% from 400 to 1600 nm. Additionally, compared to Ag NWs — Ag NWs and Cu NWs — Cu NWs electrodes, rGO PDs with Ag NWs—Cu NWs asymmetric electrodes showed a higher photocurrent-to-dark-current ratio (PDCR) (~6), which was due to the improved carrier transport with using Ag and Cu as cathodes and anodes. Furthermore, the highest photoresponsivity (5.5 mA/W) and detectivity ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</i> *) (~1×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9</sup> cm Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> /W) of rGO PDs with Ag NWs — Cu NWs electrodes have been measured and evaluated at 8 V bias. This work demonstrates the significant potential of all-solution processed rGO-based flexible PDs for high-performance and low-cost photo sensing applications.

Phenomenon of photo-regulation on gold/diamond Schottky barriers and its detector applications

A thickness asymmetric electrode structure on an oxygen-terminated type IIa diamond was designed and prepared (one electrode was semitransparent to ultraviolet light and the other blocked the transmission of ultraviolet light). This structure exhibited an apparent photo-induced rectification property under irradiation by a deuterium lamp. This is attributed to the mechanism by which the light penetrating the electrode reduces the metal–diamond contact barrier. Furthermore, we developed a light-modulated Schottky barrier diamond photodetector based on this mechanism. Solar-blind light can lower the Schottky barrier height in situ in the presence of light, which significantly enhances the photocurrent. However, the Schottky barrier is not reduced by light regulation when there is no light; therefore, the low dark current of the detector is still guaranteed. Compared with the non-photo-regulated Schottky barrier detector, the photo-regulated Schottky barrier detector exhibits a 128% increase in responsivity at 220 nm under a 1.6 V/μm bias. For such an obvious difference in detection performance, this mechanism has rarely been a focus of studies on diamond detectors. In addition to diamond detectors, light-modulated barrier technology can also be applied to other fields related to the diamond surface potential, such as color center control and Schottky diodes; it can also be used to control or evaluate device performance.

High-performance asymmetric electrode structured light-stimulated synaptic transistor for artificial neural networks.

Photonics neuromorphic computing shows great prospects due to the advantages of low latency, low power consumption and high bandwidth. Transistors with asymmetric electrode structures are receiving increasing attention due to their low power consumption, high optical response, and simple preparation technology. However, intelligent optical synapses constructed by asymmetric electrodes are still lacking systematic research and mechanism analysis. Herein, we present an asymmetric electrode structure of the light-stimulated synaptic transistor (As-LSST) with a bulk heterojunction as the semiconductor layer. The As-LSST exhibits superior electrical properties, photosensitivity and multiple biological synaptic functions, including excitatory postsynaptic currents, paired-pulse facilitation, and long-term memory. Benefitting from the asymmetric electrode configuration, the devices can operate under a very low drain voltage of 1 × 10-7 V, and achieve an ultra-low energy consumption of 2.14 × 10-18 J per light stimulus event. Subsequently, As-LSST implemented the optical logic function and associative learning. Utilizing As-LSST, an artificial neural network (ANN) with ultra-high recognition rate (over 97.5%) of handwritten numbers was constructed. This work presents an easily-accessible concept for future neuromorphic computing and intelligent electronic devices.

Impedance Analysis of Chitin Nanofibers Integrated Bulk Acoustic Wave Humidity Sensor with Asymmetric Electrode Configuration.

This paper fabricated a high-performance chitin nanofibers (ChNFs)-integrated bulk acoustic wave (BAW) humidity sensor with an asymmetric electrode configuration. The ChNFs were successfully prepared from crab shells and used as moisture-sensitive materials to compare the performance of quartz crystal microbalance (QCM) humidity sensors with symmetric and asymmetric electrode structures. The QCM humidity sensor with a smaller electrode area exhibited high sensitivity of 58.84 Hz/%RH, competitive response/recovery time of 30/3.5 s, and low humidity hysteresis of 2.5% RH. However, it is necessary to choose a suitable electrode diameter to balance the stability and sensitivity because the impedance analysis result showed that the reduction of the electrode diameter leads to a sharp decrease in the Q value (stability). Next, the possible humidity-sensitive mechanism of the ChNFs-integrated asymmetric n-m electrode QCM humidity sensor was discussed in detail. Finally, the reasons for the highest sensitivity of the asymmetric n-m electrode QCM humidity sensors having a smaller electrode diameter were analyzed in detail in terms of both mass sensitivity and fringing field effect. This work not only demonstrates that the chitin nanofiber is an excellent potential material for moisture detection, but also provides a new perspective for designing high-performance QCM humidity sensors.

Two-dimensional SiC Schottky junctions with symmetrical and asymmetrical metal electrode contacts

Four symmetrical and six asymmetrical Schottky contacts in the metal–semiconductor-metal structures were constructed by using two-dimensional (2D) SiC material as channel and four metal materials (Ag, Al, Au, Pd) as electrodes. On the basis of density functional theory and ab initio calculation method, devices’ transmission spectra, current–voltage characteristics, local density of states, rectification ratio, current–temperature characteristics and negative differential thermoelectric resistance were studied. The results show that Schottky contact is formed between the four metal materials and the 2D SiC. Partially asymmetrical metal electrode structure devices have excellent rectification characteristics. The device has the optimal rectification characteristics with a rectification ratio of 747 when Pd and Au are used as asymmetrical electrodes. Moreover, the temperature dependence of thermionic excitation transport has a key influence on the rectification properties of the device. The rectification ratio reaches to 2100 around 200 K in the junction of Pd–SiC–Au. A key finding is that the negative differential thermoelectric resistance can be generated in Pd–SiC–Au device when a temperature difference applied between two electrodes without external bias voltage. The results of this study can provide theoretical reference for the subsequent design of transistors and other device based on 2D SiC material.

Schottky-type GaN-based UV photodetector with atomic-layer-deposited TiN thin film as electrodes.

In this work, a GaN-based UV photodetector with an asymmetric electrode structure was fabricated by atomic layer deposition (ALD) of TiN layers. The thickness of the TiN can be monitored in situ by a quartz crystal microbalance (QCM) and precisely controlled through the modulation of deposition cycles. During the ALD process, periodic variation in the QCM frequency was observed and correlated to the physical adsorption, chemical bonding, and the excessive precursor exhaust, which included tetrakis(dimethylamino)titanium (TDMAT) and N sources. The asymmetric TiN/GaN/TiN photodetector showed excellent photosensing performance, with a UV-visible rejection ratio of 173, a responsivity of 4.25 A/W, a detectivity of 1.1×1013 Jones, and fast response speeds (a rise time of 69 μs and a decay time of 560 μs). Moreover, the device exhibits high stability, with an attenuation of only approximately 0.5% after 360 nm light irradiation for 157 min. This result indicates the potential of TiN as a transparent contact electrode for GaN-based optoelectronic devices.

On-Chip High-Power Supply Unit: Micro Supercapacitor With Superb Capacitance Density and Fast Charge/Discharge Ability

Stable working voltage is critical for integrated systems to keep functioning, yet it suffered from instantaneous high-power demands and the resulting voltage disturbance. An on-chip micro supercapacitor (MSC) with superb capacitance density can act as a promising high-power supply unit to satisfy power demands and stabilize the system. However, severe capacitance decay of MSC under fast charge/discharge rate greatly weakens the device power output thus making it incompetent. This work demonstrates an on-chip high-power MSC featured by the improved capacitance density, fast charge/discharge ability and scaling-down capability. The improvement is brought by the applied mesoporous gold as electrode framework, which offers fast electronic/ionic pathway and reduces porous effect under high charge/discharge rate; as well as the uniform MnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> active layer, which is decorated by an electrochemical potential-modulated deposition method, providing large pseudocapacitance. Moreover, the asymmetric electrode structure is constructed to expand the single device operation voltage. As a result, a large steady capacitance density of 9 mF/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and small capacity loss of 28% at high scan rate of 1 V/s have been achieved, leading to an unprecedented power density of 138 mW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

Measurement of the mass sensitivity of QCM with ring electrodes using electrodeposition

A practical method for calculating the mass sensitivity of quartz crystal microbalance (QCM) resonators with ring-shaped Au electrodes on one side based on electrodeposition is presented in this communication. While for standard QCMs, an average mass sensitivity can be calculated despite its approximately Gaussian distribution, the mass sensitivity of QCMs with an asymmetrical electrode structure is difficult to calculate. However, non-standard electrode geometries might be beneficial for sensor applications especially in the area of electrochemistry. By measuring the resonance frequency change of a quartz crystal during deposition and applying Faraday’s law, we determined the mass sensitivity of QCM resonators with a ring electrode. We also studied the influence of the gold electrode thicknesses on the mass sensitivity of the ring-shaped and disc shaped electrodes. The experimental results showed that the mass sensitivity of the ring-shaped electrodes was 5%∼20% higher than those of the disc shaped electrodes. This method is practical and convenient for determining the mass sensitivity of the QCM with ring electrode, and it can be extended to measure QCMs with symmetrical and asymmetrical electrode structures. Such resonators with modified electrode structures may be of interest for studying electrochemical processes where a higher mass sensitivity is desirable.

Facile fabrication of high sensitivity cellulose nanocrystals based QCM humidity sensors with asymmetric electrode structure

In this paper, a new approach to enhance the humidity sensitivity of quartz crystal microbalance (QCM) humidity sensor was proposed. By the asymmetric treatment of QCM electrode, the as-fabricated QCM humidity sensor produces an additional frequency shifts associated with the change of dielectric constant of sensitive material besides mass sensitivity. Renewable cellulose nanocrystals (CNCs) as humidity sensing material was deposited on the sensing electrode of QCM. The material characteristics of the synthesized CNCs were examined by TEM, AFM, FTIR and XRD, respectively. The humidity sensing performances of CNCs based QCM humidity sensor, including humidity sensitivity, stability, humidity hysteresis and dynamic response and recovery, were comprehensively studied by using an oscillating circuit method. The results proved that the humidity sensitivity of CNCs based QCM humidity sensor can be effectively enhanced by the asymmetric treatment of QCM electrode structure. Further, the underlying sensitivity enhancement mechanism was analyzed and discussed using an equivalent circuit analysis method. This work highlights that QCM transducer with an asymmetric sensitive electrode structure is a promising approach to improve the humidity sensitivity, and CNCs is also a promising material for humidity sensing.

Novel P‐Type Wide Bandgap Manganese Oxide Quantum Dots Operating at Deep UV Range for Optoelectronic Devices

AbstractWide bandgap semiconductor (WBGS)‐based deep UV (DUV) devices lag behind those operating in the visible and IR range, as no stable p‐type WBGS that operates in the DUV region (&lt;300 nm) presently exists. Here, solution‐processed p‐type manganese oxide WBGS quantum dots (MnO QDs) are explored. Highly crystalline MnO QDs are synthesized via femtosecond‐laser ablation in liquid. The p‐type nature of these QDs is demonstrated by Kelvin probe and field effect transistor measurements, along with density functional theory calculations. As proof of concept, a high‐performance, self‐powered, and solar‐blind Schottky DUV photodetector based on such QDs is fabricated, which is capable of detecting under ambient conditions. The carrier collection efficiency is enhanced by asymmetric electrode structure, leading to high responsivity. This novel p‐type MnO QD material can lead to cost‐effective industrial production of high‐performance solution‐processed DUV optoelectronics for large‐scale applications.

Performance improvement of a vanadium redox flow battery with asymmetric electrode designs

A two-dimensional transient model with considering vanadium ions crossover and incorporating the impact of electrode compression was presented for a vanadium redox flow battery (VRFB). Emphasis is located on examining the effects of the proposed asymmetric electrode structure designs on capacity degradation, vanadium ions crossover, the charge-discharge voltages and efficiency of the VRFB during long-time cycling. It was indicated that for asymmetric electrode compression with same original thickness, the capacity decay can be effectively alleviated with increasing the positive compression ratio, due to the fact that the electrolyte crossover is balanced by adjusting the convection flux during a charge-discharge cycle. The charge-discharge performance and energy efficiency of the VRFB can also be simultaneously boosted resulting from the reduced contact resistance and increased electrolyte flow velocity in the compressed positive electrode. Also, it was found that with appropriate design of asymmetric original thickness of uncompressed electrode, the capacity decay can be avoided and battery charge-discharge performance can be improved. This study will provide fundamental information for optimizing the asymmetric electrode structures such that the overall battery performance during long-time cycling can be enhanced.

Low-gamma shift asymmetrical double-side blue-phase liquid crystal display

ABSTRACT A single-domain blue-phase liquid crystal display (BPLCD), which has asymmetrical double-side electrode structure, is proposed to reduce gamma shift. Firstly, the electro-optical curve and gamma shift of the proposed BPLCD are discussed under the comparison with conventional in-plane switching (IPS) BPLCD. And then, its gamma shift is investigated under various conditions. Compared with the conventional IPS-BPLCD, the operating voltage can be reduced by ~31%, and the transmittance is increased by ~6%. The indistinguishable gamma shift can be obtained under various electrodes’ sizes, when the cell gap is appropriate. The results also indicate that if the electrodes’ height and Kerr constant of BPLC increase, the operating voltage can be further reduced (only 9.6 V in this work), and the gamma shift almost do not change. Moreover, a certain misalignment between the top and bottom glasses are permitted, which is good for reducing the fabrication difficulty. In terms of viewing angle, the proposed BPLCD has an average contrast ratio of ~5000:1, and the gamma shifts at full viewing angles are all indistinguishable.

Effects of Pb content and electrode materials on the ferroelectric properties of Pb(Zr0.52Ti0.48)O3 thin films

We investigated the effects of Pb content and electrode materials on the ferroelectric properties of metal/Pb(Zr0.52Ti0.48)O3/metal thin film capacitors for non-volatile memory device applications. The increase of Pb content resulted in a change from the non-ferroelectric pyrochlore phase to the ferroelectric perovskite phase, and consequently, the enhancement of polarization-voltage hysteresis loops. Non-noble metal/PZT/noble metal asymmetric electrode structures were fabricated by using non-noble metals and a noble metal with different work functions. The asymmetric electrode and the resultant internal field, not only made a shift in the initial hysteresis loops, but also caused continuous degradation of the reliability characteristics of ferroelectric capacitors.