Device Layer Research Articles

Low-Temperature Nanosecond Laser Process of HZO-IGZO FeFETs toward Monolithic 3D System on Chip Integration.

Ferroelectric field-effect transistors (FeFETs) are increasingly important for in-memory computing and monolithic 3D (M3D) integration in system-on-chip (SoC) applications. However, the high-temperature processing required by most ferroelectric memories can lead to thermal damage to the underlying device layers, which poses significant physical limitations for 3D integration processes. To solve this problem, the study proposes using a nanosecond pulsed laser for selective annealing of hafnia-based FeFETs, enabling precise control of heat penetration depth within thin films. Sufficient thermal energy is delivered to the IGZO oxide channel and HZO ferroelectric gate oxide without causing thermal damage to the bottom layer, which has a low transition temperature (<250 °C). Using optimized laser conditions, a fast response time (<1 µs) and excellent stability (cycle >106, retention >106 s) are achieved in the ferroelectric HZO film. The resulting FeFET exhibited a wide memory window (>1.7V) with a high on/off ratio (>105). In addition, moderate ferroelectric properties (2·Pr of 14.7 µCcm-2) and pattern recognition rate-based linearity (potentiation: 1.13, depression: 1.6) are obtained. These results demonstrate compatibility in HZO FeFETs by specific laser annealing control and thin-film layer design for various structures (3D integrated, flexible) with neuromorphic applications.

Constructal design of comb-shaped high thermal conductivity channel in a stacked chip

A model of stacked chip with comb-shaped high thermal conductivity channel (HTCC) is established. With fixed number of through‑silicon vias (TSVs), constructal designs of comb-shaped HTCC are performed with single-degree-of-freedom (DOF), two-DOF and three-DOF optimizations, and effects of heat generation rate per volume (HGRPV) of device layer, HGRPV of TSV and filling materials of HTCC on its optimal construct and maximum temperature difference (MTD) in stacked chip are analyzed. Furtherly, constructal design of two-stage branched comb-shaped HTCC is studied. The optimal constructs of comb-shaped HTCC are obtained under single-DOF, two-DOF and three-DOF optimizations, which make the MTD of stacked chip reach the minimum. The minimum MTD obtained by three-DOF optimization is 43.74 K, which is 1.21 K and 0.45 K lower than that obtained by single-DOF and two-DOF optimizations, respectively. Compared with the initial design, the MTD under optimizations of single-, two- and three-DOFs decreased by 2.8%, 4.5% and 5.5%, respectively. Filling materials of HTCC have effect on optimal constructs of comb-shaped HTCC, however, the HGRPVs of device layer and TSV have not. The first-stage branches of two-stage branch comb-shaped HTCC are close together by constructal design, so embedding single-stage branch comb-shaped HTCC is more beneficial to heat dissipation of stacked chip.

One‐Step Synthesis and Deposition of Metal Oxides: NiO Quantum Dots as a Transport Layer for Perovskite Photovoltaics

One‐step synthesis and deposition of nickel oxide quantum dots using a gas‐phase microplasma process is demonstrated and their applicability as a transport layer for solar cell devices is shown. The process uses a solid nickel metal wire as sacrificial electrode, and the concentration of oxygen gas required in the synthesis is investigated. The quantum dots are characterized for physical, chemical, and optical properties and critical process parameters such as the process throughput are also estimated. Direct one‐step deposition directly on perovskite solar cells is carried out using a computer‐controlled x–y stage and the performance of the solar cell device is assessed.

Compact light couplers for lateral III-V membrane devices grown on SOI platforms.

Compact light couplers between III-V devices and Si waveguides are crucial for advancing the scalability of Si photonics. Here, we present a compact light coupling strategy for lateral III-V membrane lasers and PDs directly grown on SOI platforms. Benefiting from the coplanar configuration of epitaxial III-V membranes and Si device layer, we designed novel, to our knowledge, butt couplers to achieve both small footprint and high efficiency coupling. We employed sub-wavelength grating structures to gradually bridge the effective refractive index between the III-V membranes and Si waveguide and obtained a coupling loss of less than 0.5 dB across the entire telecom band in a length of less than 10 μm. Our work here offers a fresh perspective for future densely integrated Si photonics.

Electrodeposition of Phase–Pure n–Type Cu2O: Role of Electrode Reactions and Local pH

Cuprous oxide (Cu2O) thin films, antithetically exhibiting n-type conductivity, were electro–deposited on Fluorine-doped Tin Oxide (FTO) coated glass substrates. Linear sweep voltammetry, chronoamperometry, and chronopotentiometry studies coupled with structural characterization of the deposit identify the occurrence of multiple reduction reactions, including “corrosion” of Cu2O to Cu. Interestingly, an underpotential conversion (negative of +0.039 V vs Ag/AgCl) of the Cu2O film to Cu islands is observed during potentiostatic deposition. The same process is also shown as a potential spike in chronopotentiometry curves, during galvanostatic deposition, at current densities that are cathodic of −0.2 mAcm−1. The reason for the formation of Cu is attributed to the decrease in local pH in the vicinity of the working electrode, whence thermodynamic conditions favor the formation of Cu. The proroguation of Cu formation is achieved by continuously stirring the solution, thereby stabilizing the pH at the electrode. Deferment of film corrosion to increasingly longer times is observed with increasing stirring rates. Mott-Schottky analysis of phase-pure films reveals the formation of degenerately doped n-type Cu2O films (n ∼1020 cm−3). The phase pure Cu2O films could be used as an electron transport layer in several photo-conversion devices and ultimately pave the way for an oxide homojunction device.

Thermally Induced Phase Separation of the PEDOT:PSS Layer for Highly Efficient Laminated Polymer Light-Emitting Diodes.

Among various conductive polymers, the poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) film has been studied as a promising material for use as a transparent electrode and a hole-injecting layer in organic optoelectronic devices. Due to the increasing demand for the low-cost fabrication of organic light-emitting diodes (OLEDs), PEDOT:PSS has been employed as the top electrode by using the coating or lamination method. Herein, a facile method is reported for the fabrication of highly efficient polymer light-emitting diodes (PLEDs) based on a laminated transparent electrode (LTE) consisting of successive PEDOT:PSS and silver-nanowire (AgNW) layers. In particular, thermally induced phase separation (TIPS) of the PEDOT:PSS film is found to depend on the annealing temperature (Tanneal) during preparation of the LTE. At Tanneal close to the glass transition temperature of the PSS chains, a PSS-rich phase with a large number of PSS- molecules enhances the work function of the PEDOT:PSS on the glass-side surface relative to the air side. By using the optimized LTEs, bidirectional laminated PLEDs are obtained with a total external quantum efficiency of 2.9% and a turn-on voltage of 2.6 V, giving a comparable performance to that of the reference bottom-emitting PLED based on a costly evaporated metal electrode. In addition, an analysis of the angular characteristics, including the variation in the electroluminescence spectra and the change in luminance according to the emission angle, indicates that the laminated PLED with the LTE provides a more uniform angular distribution regardless of the direction of emission. Detailed optical and electrical analyses are also performed to evaluate the suitability of LTEs for the low-cost fabrication of efficient PLEDs.

Analytical Model for Describing Transient Photocurrents in Bias‐Assisted Charge Extraction for Low‐Mobility Organic Solar Cells

Bias‐assisted charge extraction (BACE) is a powerful technique for measuring the carrier density in organic solar cells under operational conditions and to deduce information on the charge recombination properties. Hereby, the carrier density in the active layer device is determined by integrating the transient extraction current, while non‐geminate recombination during the charge extraction processes is neglected. This assumption becomes questionable for low‐mobilities, e.g. at low temperatures and in case of high energetic disorder. In this study, we theoretically investigate the extraction process in BACE measurement by incorporating both drift and bimolecular recombination of charges during charge extraction into a unified framework. We propose an explicit analytical model to describe the time dependence of the transient photocurrent in BACE measurement and found excellent agreement with drift‐diffusion simulations. We show that global fitting of transient photocurrents measured at various collection biases with this analytical model allows to determine the carrier density in the device with high accuracy. Furthermore, the analytical model is demonstrated to provide accurate mobilities for both the fast and slow carriers within the device, rendering it a valuable supplement to other mobility measurement techniques such as resistance‐dependent photovoltage and space‐charge‐limited current.This article is protected by copyright. All rights reserved.

Fine-Tuning Crystal Structures of Lead Bromide Perovskite Nanocrystals by Trace Cadmium(II) Doping Enables Efficient Color-Saturate Green LEDs.

Decreasing perovskite nanocrystal size increases radiative recombinationdue to the quantum confinement effect, but also increases the Auger recombination rate which leads to carrier imbalance in the emitting layers of electroluminescent devices. Here, we overcome this trade-off by increasing the exciton effective mass without affecting the size, which is realized through the trace Cd2+doping of formamidinium lead bromide perovskite nanocrystals. We observe an ~2.7 times increase in the exciton binding energy benefiting from a slight distortion of the [BX6]4-octahedra caused by doping in the case of that the Auger recombination rate is almost unchanged. As a result, bright color-saturated green emitting perovskite nanocrystals with a photoluminescence quantum yield of 96% are obtained. Thelight-emitting devices based on those nanocrystals reached a high external quantum efficiency (EQE) of 29.4% corresponding to a current efficiency of 123 cd A-1, and showed dramatically improved device lifetime, with a narrow bandwidth of 22 nm and Commission Internationale de I'Eclairage coordinates of(0.20, 0.76) for color-saturated green emission for the electroluminescence peak centered at 534 nm, thus being fully compliant with the latest standard for wide color gamut displays.

Fine‐Tuning Crystal Structures of Lead Bromide Perovskite Nanocrystals by Trace Cadmium(II) Doping Enables Efficient Color‐Saturate Green LEDs

Decreasing perovskite nanocrystal size increases radiative recombination due to the quantum confinement effect, but also increases the Auger recombination rate which leads to carrier imbalance in the emitting layers of electroluminescent devices. Here, we overcome this trade‐off by increasing the exciton effective mass without affecting the size, which is realized through the trace Cd2+ doping of formamidinium lead bromide perovskite nanocrystals. We observe an ~2.7 times increase in the exciton binding energy benefiting from a slight distortion of the [BX6]4− octahedra caused by doping in the case of that the Auger recombination rate is almost unchanged. As a result, bright color‐saturated green emitting perovskite nanocrystals with a photoluminescence quantum yield of 96% are obtained. The light‐emitting devices based on those nanocrystals reached a high external quantum efficiency (EQE) of 29.4% corresponding to a current efficiency of 123 cd A‐1, and showed dramatically improved device lifetime, with a narrow bandwidth of 22 nm and Commission Internationale de I’Eclairage coordinates of (0.20, 0.76) for color‐saturated green emission for the electroluminescence peak centered at 534 nm, thus being fully compliant with the latest standard for wide color gamut displays.

Enhanced Nanotwinned Copper Bonding through Epoxy-Induced Copper Surface Modification.

For decades, Moore's Law has neared its limits, posing significant challenges to further scaling it down. A promising avenue for extending Moore's Law lies in three-dimensional integrated circuits (3D ICs), wherein multiple interconnected device layers are vertically bonded using Cu-Cu bonding. The primary bonding mechanism involves Cu solid diffusion bonding. However, the atomic diffusion rate is notably low at temperatures below 300 °C, maintaining a clear and distinct weak bonding interface, which, in turn, gives rise to reliability issues. In this study, a new method of surface modification using epoxy resin to form fine grains on a nanotwinned Cu film was proposed. When bonded at 250 °C, the interfacial grains grew significantly into both sides of the Cu film. When bonded at 300 °C, the interfacial grains extended extensively, eventually eliminating the original bonding interface.

Recent Advances in Carbon Nanotube Utilization in Perovskite Solar Cells: A Review.

Due to their exceptional optoelectronic properties, halide perovskites have emerged as prominent materials for the light-absorbing layer in various optoelectronic devices. However, to increase device performance for wider adoption, it is essential to find innovative solutions. One promising solution is incorporating carbon nanotubes (CNTs), which have shown remarkable versatility and efficacy. In these devices, CNTs serve multiple functions, including providing conducting substrates and electrodes and improving charge extraction and transport. The next iteration of photovoltaic devices, metal halide perovskite solar cells (PSCs), holds immense promise. Despite significant progress, achieving optimal efficiency, stability, and affordability simultaneously remains a challenge, and overcoming these obstacles requires the development of novel materials known as CNTs, which, owing to their remarkable electrical, optical, and mechanical properties, have garnered considerable attention as potential materials for highly efficient PSCs. Incorporating CNTs into perovskite solar cells offers versatility, enabling improvements in device performance and longevity while catering to diverse applications. This article provides an in-depth exploration of recent advancements in carbon nanotube technology and its integration into perovskite solar cells, serving as transparent conductive electrodes, charge transporters, interlayers, hole-transporting materials, and back electrodes. Additionally, we highlighted key challenges and offered insights for future enhancements in perovskite solar cells leveraging CNTs.

Plasmon-exciton interactions in ZnO/AuNPs heterostructure film for high photoconductivity

This study investigatesplasmon-exciton interactions within ZnO/AuNPs heterostructure films. Elemental, structural, and morphological analyses validate the successful formation of these films. The observed shift in the plasmonic resonance band and absorption edge otowards the red region the red region is attributed to strong surface plasmon damping influenced by exciton interactions within ZnO. Irradiation with blue light induces plasmonic electrons, generation in the ZnO/AuNPs film, enhancing electrical conductivity through interaction with ZnO excitonic states. UV light irradiating generates the electron-hole pair in the ZnO film and interacts with the free electrons in AuNPs. The ZnO/AuNPs heterostructure films hold promise for applications such as high-performance UV-photodetectors, photoactive layers in solar cells, light-emitting diodes, and energy storage devices.

Self‐Assembled Monolayer Hole‐Selective Contact for Up‐Scalable and Cost‐Effective Inverted Perovskite Solar Cells

AbstractInverted positive‐intrinsic‐negative (p‐i‐n) perovskite solar cells (IPSCs) have attracted widespread attention due to their low fabrication temperature, good stability in ambient air, and the potential for use in flexible and tandem devices. In recent years, self‐assembled monolayers (SAMs) have been investigated as a promising hole‐selective contact for IPSCs, leading to an impressive record efficiency of about 26%, which is comparable to that of the regular n‐i‐p counterparts. This review focuses on the progress of SAM‐based IPSCs from the perspective of energy level matching, defect passivation, interface carrier extraction, and SAMs’ stability improvement, as well as the advances in up‐scalable fabrication of SAMs and perovskite layers for efficient solar modules and tandem devices. A cost analysis of the SAMs and other commonly used hole‐selective materials is conducted to evaluate their cost‐effectiveness for photovoltaic applications. Finally, the future challenges are pointed out and the perspectives on how to up‐scale SAM‐based IPSCs and improve their long‐term operational stability are provided.

Enhanced field emission characteristics of WS2 nano-films by diamond film and Mo film

WS2 is a type of transition metal chalcogenide materials (TMDCs) that exhibits exceptional photoelectric properties. Due to its atomically sharp edges, WS2 has the capability to enhance the electric field around its edges, thus presenting significant potential in field emission applications. In this study, the electron beam vapor deposition (EBVD) system and microwave plasma chemical vapor deposition (MPCVD) system were used to prepare a series of single-layer WS2 films，single-layer diamond films and diamond/WS2 nano-composite films on N-type highly doped Si substrate, and Mo/WS2 nano-composite films were prepared on Al2O3 ceramic substrate. Based on the characterization and analysis of the microstructure and chemical composition of each thin film layer in the above film devices, the field emission (FE) characteristics of each thin film device are compared and studied. The results demonstrate that the maximum FE current density of diamond/WS2 nano-composite film device is 912 μA/cm2, which is 2.7 times of the maximum FE current density of Mo/WS2 nano-composite film device 330 μA/cm2, and 3.4 times of the maximum FE current density of the single-layer diamond thin film device 267 μA/cm2. The single layer WS2 film did not exhibit measurable FE performance. The working principles of thin film field emission devices with various structures are introduced. It is considered that the diamond layer plays the role of electron accelerating layer, which not only effectively improves the FE characteristics of diamond/WS2 nanocomposite film, but also improves the repeatability and long-term stability of diamond/WS2 nanocomposite film FE devices.

Improved contact performance and thermal stability of Co–Ni alloy barrier layer for bismuth telluride-based thermoelectric devices

Improved contact performance and thermal stability of Co–Ni alloy barrier layer for bismuth telluride-based thermoelectric devices

Local manipulation of skyrmion lattice in Fe3GaTe2 at room temperature

Motivated by advances in spintronic devices, extensive explorations are underway to uncover materials that host topologically protected spin textures, exemplified by skyrmions. One critical challenge involved in the potential application of skyrmions in van der Waals (vdW) materials is the attainment and manipulation of skyrmions at room temperature. In this study, we report the creation of an intrinsic skyrmion state in the van der Waals ferromagnet Fe3GaTe2. By employing variable temperature magnetic force microscopy, the skyrmion lattice can be locally manipulated on Fe3GaTe2 flakes. The ordering of skyrmion state is further analyzed. Our results suggest Fe3GaTe2 emerges as a highly promising contender for the realization of skyrmion-based layered spintronic memory devices.

Recent Achievements for Flexible Encapsulation Films Based on Atomic/Molecular Layer Deposition.

The purpose of this paper is to review the research progress in the realization of the organic-inorganic hybrid thin-film packaging of flexible organic electroluminescent devices using the PEALD (plasma-enhanced atomic layer deposition) and MLD (molecular layer deposition) techniques. Firstly, the importance and application prospect of organic electroluminescent devices in the field of flexible electronics are introduced. Subsequently, the principles, characteristics and applications of PEALD and MLD technologies in device packaging are described in detail. Then, the methods and process optimization strategies for the preparation of organic-inorganic hybrid thin-film encapsulation layers using PEALD and MLD technologies are reviewed. Further, the research results on the encapsulation effect, stability and reliability of organic-inorganic hybrid thin-film encapsulation layers in flexible organic electroluminescent devices are discussed. Finally, the current research progress is summarized, and the future research directions and development trends are prospected.

Analysis of CdS/CdTe Thin Film Solar Cells as a Function of CdS Doping Concentration: A Numerical Simulation Perspective

Cadmium Telluride (CdTe) photovoltaics, incorporating a thin film of Cadmium Sulfide (CdS), present a costeffective yet less efficient solar cell technology. Improving CdS/CdTe solar cell efficiency involves optimizing parameters like doping concentration and CdS layer thickness. However, limited research on cell defects necessitates a comprehensive analysis, including the often-overlooked impact of temperature. This study aims to analyze defect-free and defective CdS/CdTe solar cells, exploring the effects of doping concentration and other parameters. Using the SCAPS-1D simulator, design parameter variations will be investigated, and key metrics— open-circuit voltage (Voc), short-circuit current density (Jsc), fill factor (FF), and efficiency (η)—will be extracted. Simulation results indicate minimal efficiency impact from increased doping concentration in the ntype CdS layer for defect-free devices. The optimal doping concentration for CdS is 5 × 10&lt;sup&gt;18&lt;/sup&gt; cm&lt;sup&gt;-3&lt;/sup&gt;, with an optimum electron affinity of 4.0 eV. CdS thickness shows no significant efficiency impact, with the chosen optimum at 10 nm. In the defect-free CdS/CdTe solar cell, key metrics were Voc: 1.06 V, Jsc: 24.60 mA cm&lt;sup&gt;-2&lt;sup&gt;, FF: 87.89%, and η: 23.01%. Analysis of defects revealed single acceptor defects significantly impacting solar cell performance in both interfacial and bulk defects. Defect structure simulations demonstrated that increasing doping concentration, decreasing electron affinity, and thickness enhance efficiency. New optimum values for these parameters—1 × 10&lt;sup&gt;18&lt;/sup&gt; cm&lt;sup&gt;-3&lt;/sup&gt;, 4.0 eV, and 10 nm—yielded Voc: 1.03 V, Jsc: 23.88 mA cm&lt;sup&gt;-2&lt;/sup&gt;, FF: 87.15%, and η: 21.40%. Additionally, a temperature decrease was associated with increased efficiency.

Analysis of comprehensive magnetic shielding and optimization design of high-conductive layers in magnetic shielding devices for atomic magnetometer

Since the frequency of the biological magnetic field is DC to 500 Hz, it is important to improve the ability of the magnetic shielding device within this range for the measurement of the biological magnetic field and the reduction of the magnetic noise of the SERF magnetometer. At present, the optimization of AC magnetic field shielding in the frequency range of 0.01 to 500 Hz is rarely considered. To optimize the AC shielding factor, this paper analyzed the influence of the position and structure of the high-conductive layer in the magnetic shielding device and proposed an optimized structure of the high conductive layer. What’s more, the theoretical formula was improved by introducing frequency coefficients, solving the problem of significant differences between theoretical calculation results, FEM results and measurement results. Finally, it was verified by experiments that the optimized high-conductivity layer structure can improve the AC shielding factor of magnetic shielding device.

GeSe ovonic threshold switch: the impact of functional layer thickness and device size

Three-dimensional phase change memory (3D PCM), possessing fast-speed, high-density and nonvolatility, has been successfully commercialized as storage class memory. A complete PCM device is composed of a memory cell and an associated ovonic threshold switch (OTS) device, which effectively resolves the leakage current issue in the crossbar array. The OTS materials are chalcogenide glasses consisting of chalcogens such as Te, Se and S as central elements, represented by GeTe6, GeSe and GeS. Among them, GeSe-based OTS materials are widely utilized in commercial 3D PCM, their scalability, however, has not been thoroughly investigated. Here, we explore the miniaturization of GeSe OTS selector, including functional layer thickness scalability and device size scalability. The threshold switching voltage of the GeSe OTS device almost lineally decreases with the thinning of the thickness, whereas it hardly changes with the device size. This indicates that the threshold switching behavior is triggered by the electric field, and the threshold switching field of the GeSe OTS selector is approximately 105 V/μm, regardless of the change in film thickness or device size. Systematically analyzing the threshold switching field of Ge–S and Ge–Te OTSs, we find that the threshold switching field of the OTS device is larger than 75 V/μm, significantly higher than PCM devices (8.1–56 V/μm), such as traditional Ge2Sb2Te5, Ag–In–Sb–Te, etc. Moreover, the required electric field is highly correlated with the optical bandgap. Our findings not only serve to optimize GeSe-based OTS device, but also may pave the approach for exploring OTS materials in chalcogenide alloys.