Charge Storage Layer Research Articles

Novel Intercalation Approach in MXene Using Modified Silica Nanospheres to Enhance the Surface Charge Density for Superior Triboelectric Performance

AbstractThis paper proposes a novel intercalation approach to address the challenges of surface triboelectric charge dissipation and self‐restacking of MXene layers in triboelectric nanogenerators (TENGs). The proposed strategy significantly improves the performance of TENGs, as it prevents the loss of surface charges and enhances the structural stability of MXene. First, the modified silica nanospheres (MSNs) of specific dimensions are synthesized, followed by their intercalation between MXene layers. This not only resolves the restacking issue but also dramatically increases the interlayer distance and MXene's surface area. The MSNs, acting as effective charge storage sites, significantly enhance surface charge density, whereas their high dielectric permittivity generates a synergistic effect that modulates the dielectric constant via polarization. Ultimately, the proposed MSN‐intercalated MXene‐based TENG demonstrates outstanding output performance (output voltage of ≈461 V, output current of ≈19 µA, and maximum peak power density of ≈691.2 µW cm−2) at a 2 wt.% MSN‐intercalated MXene concentration. This study paves a new pathway for the structural design of tribonegative and charge storage layers in TENGs for energy harvesting.

Low‐Power Charge Trap Flash Memory with MoS2 Channel for High‐Density In‐Memory Computing

AbstractWith the rise of on‐device artificial intelligence (AI) technology, the demand for in‐memory comptuing has surged for data‐intensive tasks on edge devices. However, on‐device AI requires high‐density, low‐power memory‐based computing to efficiently handle large data volumes. Here, this study proposes a reliable multilevel, high gate‐coupling ratio memory device with MoS2 channel tailored for high‐density 3D NAND Flash‐based in‐memory computing. The MoS2 channel, featured by its small bandgap and high‐mobility, facilitates reliable memory window of approximately 8 V thanks to erase operation through hole injection. This not only suppresses vertical charge loss but also alleviates the burden on voltage generator circuits, indicating the suitability of MoS2 as channel material for 3D NAND Flash architecture. Additionally, a low‐k (≈2.2) tunneling layer deposited via initiated chemical vapor deposition increases the gate‐coupling ratio, thereby reducing the operating voltage. Utilizing Au nanoparticles as the charge storage layer, MoS2 memory devices show synaptic plasticity with 6‐bit, endurance (104 cycles), read disturbance (105 cycles), and retention times (105 s). Furthermore, device‐to‐system simulations for neural networks based on MoS2‐memory devices have successfully achieved a fingerprint recognition of 95.8%. These results provide the foundation to develop multi‐bit MoS2‐memory devices for AI accelerators and 3D NAND Flash memory.

A sustainable biomass-based electret for face mask and non-volatile transistor memory

An electret filter on the middle layer of disposable medical face masks has a similar function to the charge storage layer on the transistor memory devices. Both applications require a polymer electret to trap charges so that it could establish electrostatic attraction to effectively enhance the filtration efficiency of face mask or modulate the electrical behaviours of transistor memory. By virtue of that very same function, we demonstrate the charge storage performance and memory characteristics of transistor memory using the electret filters of face mask material, from the non-renewable polypropylene (PP) to the biomass-based polymers. We demonstrate dextrin, a biomass-derivative, as a sustainable alternative electret. Due to dextrin being produced natural starch products, it is a renewable material that is biocompatible and eco-friendly. Furthermore, by adding sodium methylsiliconate (SMS), the hydrophobic blended dextrin-SMS transistor memory can maintain inherent prolonged electrostatic charges for over 100 days along with relatively wide memory window of 39.5 V. Ultimately, the non-woven nanofiber electret filter using dextrin-SMS can be successfully produced using an industrial compatible electrospinning technique combined with the addition of polyethylene oxide (PEO) to improve the electrospinability of the mat filter and potentially utilized for future biodegradable face masks and green electronics.

Over- and Undercoordinated Atoms as a Source of Electron and Hole Traps in Amorphous Silicon Nitride (a-Si3N4).

Silicon nitride films are widely used as the charge storage layer of charge trap flash (CTF) devices due to their high charge trap densities. The nature of the charge trapping sites in these materials responsible for the memory effect in CTF devices is still unclear. Most prominently, the Si dangling bond or K-center has been identified as an amphoteric trap center. Nevertheless, experiments have shown that these dangling bonds only make up a small portion of the total density of electrical active defects, motivating the search for other charge trapping sites. Here, we use a machine-learned force field to create model structures of amorphous Si3N4 by simulating a melt-and-quench procedure with a molecular dynamics algorithm. Subsequently, we employ density functional theory in conjunction with a hybrid functional to investigate the structural properties and electronic states of our model structures. We show that electrons and holes can localize near over- and under-coordinated atoms, thereby introducing defect states in the band gap after structural relaxation. We analyze these trapping sites within a nonradiative multi-phonon model by calculating relaxation energies and thermodynamic charge transition levels. The resulting defect parameters are used to model the potential energy curves of the defect systems in different charge states and to extract the classical energy barrier for charge transfer. The high energy barriers for charge emission compared to the vanishing barriers for charge capture at the defect sites show that intrinsic electron traps can contribute to the memory effect in charge trap flash devices.

Synergistically enhanced electrochemical performance using N-rich multilayered carbon nanofibers

N-rich multilayered carbon nanofibers with hollow channels (PPMPN) are fabricated to fully utilize the mesopores, micropores, and nitrogen-functional groups of carbon nanofibers (CNFs) for superior electrochemical properties. Among all composites, the PPMPN(10) exhibits high specific surface area (570 m2g−1) with mesopore volume fraction (42%) and rich surface functionalities (∼7.25at% nitrogen and ∼ 16.1at% oxygen), helping to improveelectrochemical performance. The performance of the symmetric supercapacitor of the PPMPN was significantly improved in terms of its specific capacitance of 189 Fg−1 at 1 mAcm−2, good retention of 80% (when the current density is increased from 1 to 20 mAcm−2), energy density of 23.5 Whkg−1 at a power density of 400 Wkg−1, and cycling stability of 94% for 10,000 cycles. The top layer plays a role in charge storage/transport by increasing electrical conductivity due to N-functional groups. The intermediate layer with tubular 1D nanostructures enhances the diffusion of electrolyte ions even at higher current densities. The bottom layer composed of numerous micropores serves as a charge storage layer. Therefore, in the multilayer CNF, the micropores/mesopores and N-functional properties of each layer do not interfere with each other, and the advantages of the factors of each layer are maximized in the electrochemical properties.

Diode-Connected Overpass Channel Synaptic Transistors for Extremely-Low-Power Neuromorphic Systems

A poly-Si overpass channel synaptic (OCS) transistor is proposed for the extremely-low-power operation and low RC delay of neuromorphic systems. The OCS transistor has two major structural advantages. First, the on-current ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</sub> ) can be reduced to sub 100 nA with high on/off ratio (>10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> ) because the channel wraps around the fin-shaped bottom gate. Second, the weights of the OCS transistors are finely divided by increasing the volume of the charge storage layer. The inference and weight update operations of a NOR-type OCS array were experimentally demonstrated. It was confirmed that the fabricated diode-connected (D-C) OCS array is suitable for vector-matrix multiplication (VMM) operation with its weighted-sum error smaller than 0.79% in inference. Each synaptic weight in the D-C OCS array was adjusted into sub-nA resolution by Fowler-Nordheim (FN) tunneling with asymmetric gates. Finally, the classification accuracy of the fashion MNIST dataset is 91.29% even after one year with four-bit quantization of spiking neural network (SNN).

Deep-trap dominated degradation of the endurance characteristics in OFET memory with polymer charge-trapping layer

Organic field-effect transistors (OFETs) with polymer charge-trapping dielectric, which exhibit many advantages over Si-based memory devices such as low cost, light weight, and flexibility, still suffer challenges in practical application due to the unsatisfied endurance characteristics and even the lack of fundamental of behind mechanism. Here, we revealed that the degradation of endurance characteristics of pentacene OFET with poly(2-vinyl naphthalene) (PVN) as charge-storage layer is dominated by the deep hole-traps in PVN by using the photo-stimulated charge de-trapping technique with the fiber-coupled monochromatic-light probes. The depth distribution of hole-traps in PVN film of pentacene OFET is also provided.

A dual doping nonvolatile reconfigurable FET

In this work, we propose a dual doping based nonvolatile reconfigurable field effect transistor with source/drain (S/D) charge storage layers (DDN R-FET). It introduces nonvolatile charge storage layers on both source and drain sides as a floating program gate (FPG) instead of a program gate (PG) that needs independent power supply. The stored charges in the FPG are programmed by the control gate (CG). Therefore, the proposed DDN R-FET essentially requires only one independently powered gate to complete the reconfigurable operation. Moreover, by adjusting the charge stored in the FPGs, the CG can regulate the equivalent voltage in the FPG, which can promote the on-state current and reduce the generation of reversely biased leakage current at the same time. The physical mechanism has also been analyzed in details.

Solid-liquid Triboelectric Nanogenerator based on Interdigitated Laser-induced-graphene and Polyimide Charge-storage Layer

Solid-liquid Triboelectric Nanogenerator based on Interdigitated Laser-induced-graphene and Polyimide Charge-storage Layer

A Novel Single Gate Controlled Nonvolatile Floating Program Gate Reconfigurable FET

AbstractIn this work, a single gate controlled nonvolatile floating program gate (FPG) reconfigurable field effect transistor (RFET) is proposed. Different from the traditional RFET, it introduces a nonvolatile charge storage layer as an FPG instead of a program gate that needs independent power supply. The stored charge in the FPG can be programmed by the control gate (CG). Therefore, the proposed FPG‐RFET essentially requires only one independently powered gate to complete the reconfigurable operation. Moreover, the CG can regulate the equivalent voltage in the FPG, which can effectively reduce the static power consumption and the generation of reverse leakage current. The physical mechanism has also been analyzed in detail.

Concept of Photoactive Invisible Inks toward Ultralow‐Cost Fabrication of Transistor Photomemories (Adv. Electron. Mater. 3/2023)

Transistor Photomemory The fluorescent organic inks of an invisible pen are exploited as a photoactive charge-storage layer in transistor photomemory. This concept is introduced by Suhendro Purbo Prakoso, Yu-Cheng Chiu, and co-workers in article number 2201147. With an estimated usage budget of $0.003 per cm2, the fluorescent organic ink can serve as an ultralow-cost charge-trapping material with exquisite optical properties.

Concept of Photoactive Invisible Inks toward Ultralow‐Cost Fabrication of Transistor Photomemories

AbstractFinding the outperforming photoactive charge trapping materials for a new‐trending transistor photomemory application is labor intensive, costly reagents and solvents, and not to mention, inefficient energy and time consumption. In this work, costless organic‐based inks are introduced as a novel photoactive charge storage material that is inspired by high fluorescent ink of cheap invisible pens when exposed to ultraviolet light. The pure powder inks of invisible pens with bright red and greenish‐yellow emission are selected. The estimated usage costs about $0.003 cm−2, confirming its ultralow‐budget material. The pentacene‐based organic field‐effect transistor memory scheme is employed to evaluate the memory behaviors. These invisible‐ink‐based charge storage layers endow a transistor memory device with photoinduced recovery. Interestingly, by conducting the photoassisted operation on the same device, its threshold voltage shifts toward more positive direction, resulting in broaden memory window and faster device operations. On top of that, invisible‐ink‐based transistor photomemory demonstrates the well‐defined and feasible multibit memory cell for the next‐generation storage media. As a result, the employment of commercial invisible inks as a cheapest photoactive charge trapping material can favor the advancement of transistor photomemory devices and related functional applications.

Metal Oxide/Graphene/Metal Sandwich Structure for Efficient Photoelectrochemical Water Oxidation

AbstractSingle‐layer graphene (SLG) has drawn considerable interest in photoelectrochemical (PEC) cells due to its atomically flat pinhole‐free structure and remarkable in‐plane carrier mobility. It is challenging, however, to obtain efficient SLG‐modified photoelectrodes for PEC water splitting mainly due to the inefficient charge transfer interface. Here, a transition metal oxide/SLG/transition metal sandwich structure modified n‐Si‐based model photoanode is constructed to regulate the interfacial charge transfer behavior for enhanced PEC water oxidation performance. In this sandwich configuration, SLG tailors the morphology, structure, and work function properties of surface metal electrocatalysts to obtain both higher thermodynamic photovoltage and faster kinetical charge transfer at the semiconductor/electrolyte interface. In addition, SLG promotes the surface catalytic reaction as an effective charge trap and storage layer. This study provides a new structural design to engineer the SLG interfacial properties for high‐performance energy conversion devices.

Cerium‐Modified Mesoporous Antimony Doped Tin Oxide as Intercalation‐Free Charge Storage Layers for Electrochromic Devices

AbstractCharge storage layers are an important component of electrochromic devices, which are expected to exhibit high storage capacity and transparency as well as fast electron transfer rates. However, these layers often rely on the (de)intercalation of ions into the crystal lattice of the material and therefore require optimization to be compatible with non‐intercalating electrolytes. In this report, the post‐modification of mesoporous antimony‐doped tin oxide (ATO) nanoparticle layers with a redox‐active cerium compound is described. In particular, the switching of the Ce3+/Ce4+ couple on the conductive nanoparticle scaffold is demonstrated using tetrabutylammonium perchlorate as a non‐intercalating electrolyte. Remarkably, high storage capacities of up to 27 mC cm−2 and transmittance values of ≈90% are achieved. Variation of the antimony doping concentration revealed that nanoparticle layers doped with 15% Sb exhibit the highest capacity, which can be attributed to increased conductivity in the potential range where the Ce3+ ions are oxidized. Finally, the cerium‐modified ATO films show promising performance as charge storage layers in an electrochromic device with a viologen‐anchored ATO layer as the electrochromic working electrode. Switching times of ≈0.4 s highlight the fast electron transfer capability of the cerium‐decorated ATO layer, even when a non‐intercalating electrolyte is used.

Droplet-based Electricity Generator Using Laser-induced Graphene and Polyimide Charge Storage Layer

Droplet-based Electricity Generator Using Laser-induced Graphene and Polyimide Charge Storage Layer

All-aerosol-sprayed high-performance transparent triboelectric nanogenerator with embedded charge-storage layer for self-powered invisible security IoT system and raindrop-solar hybrid energy harvester

Practical utilization of the triboelectric nanogenerators (TENGs), which have unique advantageous aspects of a simple operation mechanism, material selection diversity, and high energy conversion efficiency, requires high functionality as well as a scalable fabrication to broaden the applicable fields. Here, we report the concept of all-aerosol-sprayed transparent TENG (ST-TENG) by sequentially spraying total three layers of a silver nanowire conductive layer, transparent polystyrene charge-storage layer, and fluoropolymer contact layer. All layers were achieved by aerosol spray process, thereby exhibiting high design flexibility enough to fabricate ST-TENGs on various pre-made commercial devices. The presence of the transparent polystyrene layer as a charge storing interlayer significantly enhances the power density of the ST-TENG up to 818 mW/m2. As proof-of-concept applications, a self-powered invisible security internet-of-things system, which could blend with the surroundings, exploited biomechanical energy from foot-step for energy harvesting and invasion sensing. Furthermore, by exploiting the all-aerosol-spray process and high light transmittance of the ST-TENG, a hybrid energy harvester to simultaneously generate electricity from solar and rain energy was directly fabricated on a commercial solar panel. This work provides the brand-new concept of TENG with a scalable in-situ fabrication process, enhanced performance, and outstanding light transmittance.

A novel E-mode GaN p-MOSFET featuring charge storage layer with high current density

In this work, a trench gate enhancement-mode GaN p-type metal oxide semiconductor field effect transistor featuring charge storage (CS) layer is proposed, which exhibits an effectively improved current density. Based on device simulations, the current density can be increased by 154% (@V DS = −5 V, V GS = −7 V) compared with conventional devices without CS layer. Besides, the impact of the critical parameters including AlGaN barrier thickness t, Al mole-fraction x, trench gate depth T recess, and negative charge concentration N CSL on device performance are studied and optimized. In this case, the p-MOSFETs show an on-current |I ON, max| of 14 mA mm−1, V TH of −0.47 V, I ON /I OFF of >108, and on-resistance R ON of 0.27 kΩ mm. The proposed GaN p-MOSFETs exhibit a promising method to improve the current drive capability of GaN p-channel devices.

Ferro‐floating memory: Dual‐mode ferroelectric floating memory and its application to in‐memory computing

AbstractVarious core memory devices have been proposed for utilization in future in‐memory computing technology featuring high energy efficiency. Flash memory is considered as a viable choice owing to its high integration density, stability, and reliability, which has been verified by commercialized products. However, its high operating voltage and slow operation speed issues caused by the tunneling mechanism make its adoption in in‐memory computing applications difficult. In this paper, we introduce a dual‐mode memory device named “ferro‐floating memory”, fabricated using van der Waals (vdW) materials (h‐BN, MoS2, and α‐In2Se3). The vdW material, α‐In2Se3, acts as a polarization control layer for the ferroelectric memory operation and charge storage layer for the conventional flash memory operation. Compared to the tunneling‐based memory operation, the ferro‐floating memory operates 1.9 and 3.3 times faster at 6.7 and 5.8 times lower operating voltages for programming and erasing operations, respectively. The dual‐mode operation improves the linearity of conductance change by 5 times and the dynamic range by 48% through achieving conductance variation regions. Furthermore, we assess the effects of the variation in device operating voltage on neural networks and suggest a memory array operating scheme for maximizing the networks' performance through various training/inference simulations.image

Rechargeable aluminum-ion battery based on interface energy storage in two-dimensional layered graphene/TiO2 electrode

Rechargeable aluminum-ion batteries (AIBs) are expected to be one of the most concerned energy storage devices due to their high theoretical specific capacity, low cost, and high safety. At present, to explore the positive material with a high aluminum ion storage capability is an important factor in the development of high-performance AIBs. This paper proposes an AIB using two-dimensional layered graphene/TiO2 nanosheets composite as the highly reversible positive electrode and chloroaluminate ionic liquid as the electrolyte. AlCl4− and Al2Cl7− are proven to be the main anionic carriers in the charge storage. The AIBs exhibit excellent electrochemical performances in the voltage range of 0.1–0.9 V. A discharge specific capacity of 313.2 mAh/g at 0.1 A/g is achieved. Moreover, a high specific capacity of 40.0 mAh/g is still maintained at 1.0 A/g after 100 cycles. The superior electrochemical properties for the AIBs are attributed to the interfacial energy storage mechanism in the layered graphene/TiO2 nanosheets composite, providing the unique two-dimensional interface charge storage layer for the insertion/de-insertion of the AlxCly−. These meaningful results have important guiding significance for the development of high-performance AIBs.

GaN Non-Volatile Memory Based on Junction Barrier-Controlled Bipolar Charge Trapping

A tunnel-oxide-free GaN-based non-volatile memory (NVM) device is proposed to untangle the trilemma among speed, retention, and endurance in the implementation of conventional NVM. The program and erase (P/E) are based on bipolar charge injection controlled by individual junction barriers, whereas the data retention relies on bipolar charge trapping in an interfacial charge storage layer. The wide bandgap energy of GaN allows the formation of deep-level traps at a dielectric/GaN interface and high junction barriers in GaN, both of which benefit long-term retention. As such, the GaN-based NVM device could get rid of the tunnel oxide, thereby enabling faster P/E processes and facilitating to decouple the enhancement of endurance from that of speed and retention. The proposed device demonstrates a P/E time of 100 ns, endurance over 10⁶ cycles, and long retention time.