Device Fabrication Process Research Articles

Solid additive enables efficient and stable organic solar cells by stabilizing morphology of active layer

Additive strategy is an effective method for optimizing the morphology of active layer in organic solar cells (OSCs). However, common high boiling points solvent additives may compromise device stability. In this work, 1‑bromo-8-chloronaphthalene (BCN) was used as a solid additive to improve device performance. The introduction of BCN promotes the crystallinity, H-aggregation and fibrillation of L8-BO. The active layer film with additive BCN exhibits optimized phase separation and refined fiber network, thus enhancing the exciton dissociation and charge transport in the corresponding devices. Compared with control devices (without additives), the power conversion efficiency (PCE) of optimized devices (with 20 wt % BCN) based on D18:L8-BO was increased from 17.49 % to 18.20 %. The detailed process of device fabrication is in experimental section. Furthermore, devices processed by BCN preserved 96.6 % and 96.3 % of the initial PCE after aging for 60 min with maximum power point (MPP) tracking and aging of storage for 960 h, respectively. The universality of BCN was verified in different systems, which offers promising opportunities to regulate BHJ morphology toward highly efficient OSCs.

Patterning functional oxides: Some failures and solutions in fabricating a Hall bar

Functional oxides exhibit diverse useful properties, opening attractive prospects for electronic, magnetic, and optoelectronic devices. However, the chemical instability of these oxides with some microfabrication processes, especially when dealing with thin films (<40 nm) or micrometer-scale lateral dimensions, can pose a considerable challenge. Here, we describe the fabrication process of a Hall bar device used as a test structure for thin functional oxide films. This process employs photolithography and dry etching, utilizing standard clean-room materials and methods. The device layout and fabrication process are described in detail, including conclusions and lessons gained from several failed attempts during process development. A key lesson is the advantage of employing an ultrathin protective layer to protect the oxide film surface. In addition, we encountered two additional fabrication challenges: photoresist hardening during dry etching and edge accumulation of photoresist during spin-coating. Effective solutions to these issues are described. We hope that our lessons and conclusions, not limited to functional oxides, will help to shorten the process development for other materials and devices.

High‐sensitive and fast MXene/silicon photodetector for single‐pixel X‐ray imaging

AbstractThe demand for high‐performance X‐ray detectors leads to material innovation for efficient photoelectric conversion and carrier transfer. However, current X‐ray detectors are often susceptible to chemical and irradiation instability, complex fabrication processes, hazardous components, and difficult compatibility. Here, we investigate a two‐dimensional (2D) material with a relatively low atomic number, Ti3C2Tx MXenes, and single crystal silicon for X‐ray detection and single‐pixel imaging (SPI). We fabricate a Ti3C2Tx MXene/Si X‐ray detector demonstrating remarkable optoelectronic performance. This detector exhibits a sensitivity of 1.2 × 107 μC Gyair−1 cm−2, a fast response speed with a rise time of 31 μs, and an incredibly low detection limit of 2.85 nGyair s−1. These superior performances are attributed to the unique charge coupling behavior under X‐ray irradiation via intrinsic polaron formation. The device remains stable even after 50 continuous hours of high‐dose X‐ray irradiation. Our device fabrication process is compatible with silicon‐based semiconductor technology. Our work suggests new directions for eco‐friendly X‐ray detectors and low‐radiation imaging system.image

Enhance Carrier Diffusion of Monolayer MoSe2 by Interface Engineering.

Two-dimensional materials hold great potentials for beyond-CMOS (complementary metal-oxide-semiconductor) electronical and optoelectrical applications, and the development of field effect transistors (FET) with excellent performance using such materials is of particular interest. How to improve the performance of devices thus becomes an urgent issue. The performance of FETs depends greatly on the intrinsic electrical properties of the channel materials, meanwhile the device interface quality, such as extrinsic scattering of charged impurities, charge traps, and substrate surface roughness have a great influence on the performance. In this paper, the impact of the interface quality on the carrier diffusion behaviors of monolayer (ML) MoSe2 has been investigated by using an in situ ultrafast laser technique to avoid the surface contamination during device fabrication process. Two types of self-assembled monolayers (SAMs) are introduced to modify the gate dielectric surface through an interface engineering approach to obtain chemical-stable interfaces. The results showed that the transport properties of ML MoSe2 were enhanced after interface engineering, for example, the carrier mobility of ML MoSe2 was improved from ∼59.4 to ∼166.5 cm2 V-1 s-1 after the SAM modification. Meanwhile, the photocarrier dynamics of ML MoSe2 before and after interfacial engineering were also carefully studied. Our studies provide a feasible method for improving the carrier diffusion behaviors of such materials, and making them suited for application in future integrated circuit.

Enhancing performance of Au-hyperdoped Si photodetectors for infrared detection

Hyperdoping Si with transition metals to form intermediate bands for infrared absorption has attracted attention recently for producing sub-bandgap photoconductivity. In particular, Si hyperdoped with Au has been demonstrated to exhibit optoelectronic response at 1550 nm. However, the reported external quantum efficiencies (EQEs) are low, and the device fabrication processes had not been optimized. In this paper, we demonstrate a significant improvement in sub-bandgap EQE through modification of the material and device fabrication processes. By increasing the Si:Au layer thickness, modification of device design, and formation of Ohmic contacts, the EQE was measured to be as high as 0.44% at 1550 nm, nearly two orders of magnitude higher than previous reports from similar devices. Additionally, the EQE was measured to be in the 10-3 range for wavelengths as long as 2.4 μm. The EQE spectrum showed features that were attributed to defect levels from a substitutional Au acceptor defect. The above bandgap EQE showed gain in one device. Thermal annealing at 300 °C does not improve the efficiency of Si:Au photodiodes. These results demonstrate the viability of Au-hyperdoped Si for infrared detection below the bandgap of Si.

Activation of TADF in Photon Upconverting Crystals of Dinuclear Cu(I)-Iodide Complexes by Ligand Engineering.

This work reports that ligand engineering can modulate the triplet harvesting mechanism in iodide-bridged rhombic Cu2I2 complexes. Complex-1, with a smaller Cu-Cu distance, exhibits phosphorescence from 3(M+X)LCT and 3CC states with 66% quantum yield, whereas an increased Cu-Cu distance in complex-2 results in a switch of the emission from phosphorescence to TADF, which occurs via 1/3(M+X)LCT states with 83% quantum yield. The TADF property of complex-2 has been utilized for the fabrication of a pc-LED emitting efficient warm white light. Moreover, the high charge-transfer nature of these complexes leads to the emergence of third-harmonic generation (THG). Interestingly, complex-1 exhibits efficient third-harmonic generation with a χ(3) value of 1.15 × 10-18 m2 V-2 and LIDT value of 14.73 GW/cm2. This work aims to provide a structure-property relationship to achieve effective harvestation of triplet excitons in iodide-bridged rhombic Cu2I2 complexes and their effective utilization in OLED device fabrication and nonlinear photon upconversion processes.

From GaN crystallinity to device performance: Nucleation mode vs Surface energy of single-crystalline AlN template

In this paper, the surface state of the single-crystalline AlN template's impact on the epitaxial growth of gallium nitride (GaN) was studied. Subsequently, Schottky barrier devices were fabricated and analyzed. The results indicate that surface states subjected to different treatments exhibit varying epitaxial growth modes at the initial nucleation stage, which have a correlated effect on surface topography, crystalline quality, strain and other material characteristics of the epitaxial GaN. Higher surface energy leads to a reduction in screw dislocation of GaN material, but has less influence on edge dislocation. Single-crystalline AlN templates with higher surface energy are more likely to exhibit Stranski-Krastanow and Frank-van der Merwe growth model and achieve high-quality epitaxial materials. Schottky devices prepared using GaN material with lower screw dislocation density exhibit lower reverse leakage current. First-principles simulation analysis revealed that the migration barrier of gallium and nitrogen atoms on the surface can be overcome with the larger surface energy of single-crystalline AlN template. This facilitates their migration on the surface, resulting in higher quality material epitaxy. The conclusions of this work provide insights for quality control of epitaxial GaN materials on single-crystalline AlN templates, as well as for studying device leakage in the backend of the device fabrication process, or similar homogeneous compound semiconductor heteroepitaxy studies.

Improving the Stability of Ink-Jet Printed Red QLEDs By Optimizing The Device Fabrication Process

Improving the Stability of Ink-Jet Printed Red QLEDs By Optimizing The Device Fabrication Process

Ambipolar Charge Injection and Bright Light Emission in Hybrid Oxide/Polymer Transistors Doped with Poly(9‐Vinylcarbazole) Based Polyelectrolytes

AbstractLight‐emitting transistors (LETs) are a remarkable, emerging class of electronic devices that combine the switching function of field‐effect transistors (FETs) and the light‐emitting function of light‐emitting diodes (LEDs). In order to achieve efficient light emission, effective electron and hole injection from source and drain electrodes is necessary. Various strategies have been introduced to accomplish this, such as incorporating asymmetric electrodes or charge injection layers during device fabrication. These approaches have inevitably introduced complexity in the device fabrication process. Herein, light‐emitting electrochemical transistors (LECTs) are demonstrated that combine principles of electrochemistry and optoelectronics to achieve multi‐functionality in a simple device architecture. Hybrid polyelectrolytes, poly(9‐vinylcarbazolesulfonate)‐ lithium and copper (II) salts (PVK‐Li and PVK‐Cu) incorporating Li+ ion and Cu2+ ions are added at variable concentrations to the organic emitting layer of LECTs to effect electrochemical p‐type doping. This electrochemical doping approach yielded improvements in electrical and optical performances including mobilities, brightnesses, and external quantum efficiency of the LECTs. The dynamics of how charges including ions, electrons, and holes move and interact are discussed in the device to facilitate emissive charge carrier recombination and light emission. This investigation provides valuable insights into the realms of both electrochemistry and optoelectronics.

Simultaneous multiple target detection platform based on vertical flow immunoassay

In general, vertical flow assay (VFA) has a disadvantage of requiring a complex analysis process that involves manually injecting various reagents (target analyte, washing buffer, detection conjugate, etc.) sequentially. However, in this study, we have developed an innovative paper-based VFA device that replaces the complex analysis process with one-step and enables the detection of multiple targets. The fabrication process of the multi-target detection VFA device is as follows: preparation and pre-treatment of the strip materials, design of strip cartridge, design of the multiple detection VFA device, optimization experiments for strip sample flow rates, determination of device analysis time, determination of device limit of detection (LOD), multiple target signal uniformity experiment, immunoglobulin G (IgG) and C-reactive protein (CRP) antigen-antibody multiple detection experiment, and data extraction and analysis method. The use of paper-based materials enables the device to be produced at cost-effective, and cartridge production allowed for uniform array formation. IgG and CRP are used to evaluate the performance of the device as common biomarkers. The device proposed in this study is currently under research. To validate multiple target detection capability of the VFA device proposed in this study, two types of antigens-antibodies (Human IgG and Human CRP) were employed. The detection limit is 0.15 μg/mL for IgG and 0.19 μg/mL for CRP in naked eye. Furthermore, it was confirmed that there is no cross-reactivity caused by the device structure through IgG and CRP antigens. In conclusion, the VFA device proposed in this study consists of a one-step analysis process, and it has been confirmed that it can detect multiple targets simultaneously.

Facile synthesis of Zn2V2O7/RGO nanocomposite for enhancing the electrochemical performance and evaluating the supercapacitor device

Pyrochlore-structured zinc vanadium oxide with RGO (Zn2V2O7/RGO) composite was synthesized using the simple hydrothermal process for energy storage device fabrication. The structural, vibration spectrum, surface morphology, and elemental of the Zn2V2O7/RGO composite were analyzed using different analytical methods. Then, the electrochemical performance was examined using Zn2V2O7/RGO composite modified electrode with 3-electrode and 2-electrode setup by cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectrum (EIS) techniques. Consequently, the Zn2V2O7/RGO composite revealed notable pseudo-capacitive behavior which has been confirmed through CV analysis. The nano size-based Zn2V2O7/RGO composite electrode material obtained notable specific capacitance (Csp) of 1400.51F/g owing to the synergistic promotion of Zinc and vanadium oxides. Furthermore, the ASC device of Zn2V2O7/RGO ||RGO displayed the efficient power density of 1371 kW/kg at the energy density of 8Wh/kg and the device has enhanced cycling performance with 72.8 % capacitance.

Photochemical and Patternable Synthesis of 2D Covalent Organic Framework Thin Film Using Dynamic Liquid/Solid Interface.

2D covalent organic frameworks (COFs) are highly porous crystalline materials with promising applications in organic electronics. Current methods involve either on-surface synthesis (solid surface) or interfacial synthesis (liquid/liquid, liquid/gas interface) to create thin films for these applications, each with its drawbacks. On-surface synthesis can lead to contamination from COF powder or unreacted chemicals, while interfacial synthesis risks damaging the film during post-transfer processes. These challenges necessitate the development of alternative synthesis methods for high-quality 2D COF films. This study presents a novel approach for synthesizing homogeneous 2D COF thin films by combining photochemistry and a liquid-flowing system. Leveraging previous work on liquid flow systems to prevent contamination during solvothermal synthesis, this approach to the photochemical method, resulting in the synthesis of high-crystalline 2D COF films with tunable thickness is adopted. The photochemical approach offers spatially controllable energy sources, enabling patternable COF synthesis. Notably, it is successfully fabricated ultrasmooth patterned 2D COF films on hexagonal boron nitride, offering a streamlined process for optoelectronic device fabrication without additional pre, post-processing steps.

A Twisting Fabrication Process for Wearable Electronic Devices

A Twisting Fabrication Process for Wearable Electronic Devices

Tunable In Situ Synthesis of Ultrathin Extracellular Matrix-Derived Membranes in Organ-on-a-Chip Devices.

Thin cell culture membranes in organ-on-a-chip (OOC) devices are used to model a wide range of thin tissues. While early and most current platforms use microporous or fibrous elastomeric or thermoplastic membranes, there is an emerging class of devices using extra-cellular matrix (ECM) protein-based membranes to improve their biological relevance. These ECM-based membranes present physiologically relevant properties, but they are difficult to integrate into OOC devices due to their relative fragility. Additionally, the specialized fabrication methods developed to date make comparison between methods difficult. This work presents the development and characterization of a method to produce ultrathin matrix-derived membranes (UMM) in OOC devices that requires only a preassembled thermoplastic device and a micropipette, decoupling the device and UMM fabrication processes. Control over the thickness and permeability of the UMM is demonstrated, along with integration of the UMM in a device enabling high-resolution on-chip microscopy. The reliability of the UMM fabrication method is leveraged to develop a medium-throughput well-plate format device with 32 independent UMM-integrated samples. Finally, proof-of-concept cell culture experiments are demonstrated. Due to its simplicity and controllability, the presented method has the potential to overcome technical barriers preventing wider adoption of physiologically relevant ECM-based membranes in OOC devices.

Trap-assisted tunneling in type II Ag2O/β-Ga2O3 self-powered solar blind photodetector

This study investigates a high-performance Ag2O/β-Ga2O3 self-powered photodiode through experimental and modeling approaches. Initially, a p-type Ag2O film, with a bandgap close to 4 eV and a hole density of approximately 6.35×1018 cm−3, was fabricated using faced two-target sputtering. The conduction and valence band offsets between Ag2O and β-Ga2O3 were determined via X-ray photoelectron spectroscopy, confirming a type II heterojunction. The device had a low on-voltage of 1.50 V and a low on-resistance of 5.40 mΩ.cm² in the dark. Subsequent illumination at 254 nm resulted in a notably high photocurrent, responsivity, and detectivity. To confirm the role of trap-assisted tunneling in the type II Ag2O/β-Ga2O3 heterojunction, Silvaco simulations were employed to model both the dark current and photocurrent. These simulations confirmed the prevalence of the trap-assisted tunneling mechanism, particularly through energy levels situated above the equilibrium Fermi level at the Ag2O/β-Ga2O3 interface, as described by the Danielsson model. Understanding the transport mechanism is paramount for the development of high-performance photodetectors. By comprehending how charge carriers navigate through the device and the influence of traps on their behavior, researchers can optimize device design and fabrication processes to enhance performance.

PEAKFORCE QUANTITATIVE NANOMECHANICAL MAPPING FOR SURFACE ENERGY CHARACTERIZATION ON THE NANOSCALE: A MINI-REVIEW

Surface energy characterization is important to design the fabrication process of reliable electronic devices. Surface energy is influenced by various factors such as surface functionality and morphology. Owing to the high surface-to-volume ratio, surface energy at the nanoscale can be different from that of the bulk. However, the conventional methods for characterization of surface energy such as a sessile drop or Washburn methods cannot be used for nanoscale samples, owing to the limited volume for characterization. Recently, surface energy characterization on the nanoscale using atomic force microscopy (AFM) with Peak Force-Quantitative Nanomechanical Mapping (PF-QNM) imaging mode has been proposed. The nanoscale AFM tips measure the adhesion forces at the nanoscale, which are converted into surface energy through pre-calibrated curves. Successful surface energy characterization of nanoscale metal samples using AFM with the PF-QNM method has been reported previously. This mini-review discusses the recent progress on surface energy characterization at the nanoscale using AFM with the PF-QNM method. The fundamentals of the PF-QNM mode are introduced, and the results of surface energy characterization are summarized. Consequently, the future research direction for surface energy characterization at the nanoscale is discussed.

Ultra-broadband MMI power splitter from 1.26 to 1.67 μm with photonic bound states in the continuum

Photonic bound states in the continuum (BIC) have excellent effects in localizing light fields. Low propagation loss of TM mode has been achieved in different orders of BICs on an etchless lithium niobate (LiNbO3) platform. Herein, we simulatively demonstrate a 1 × 2 MMI (Multimode interference) power splitter based on waveguides constructed by low-refractive-index structure (ZEP-520A) on a high-refractive-index thin membrane (LiNbO3), which can optimize the bandwidth, insertion loss and other performance indicators of optical devices. Simulation results show that the working wavelength cover the entire communication band ranging from 1260 nm to 1675 nm, and the transmission efficiency is more than 48.7%, while the insertion loss is less than 0.01 dB covering a 415 nm bandwidth. The field distribution results verify that the designed MMI demonstrated high mode purity at the output, and the mode field is well localized in the LiNbO3 film, leading to a reduce of the dependence of the transmission efficiency originated from the quality of the sidewall of the device, and the device can evenly distribute the TM0 mode of the ultra-broadband incident light to the two output ports. Furthermore, the fabrication process of the MMI device can be immensely simplified by a one-step exposure method, which reduces the scattering loss and asymmetry caused by the fabrication.

The Failure Mechanism of Micro Thermoelectric Devices under the Action of the Temperature Field.

The micro thermoelectric device (m-TED) boasts features such as adjustable volume, straightforward structure, and precise, rapid temperature control, positioning it as the only current solution for managing the temperature of microelectronic systems. It is extensively utilized in 5G optical modules, laser lidars, and infrared detection. Nevertheless, as the size of the m-TED diminishes, the growing proportion of interface damages the device's operational reliability, constraining the advancement of the m-TED. In this study, we used commercially available bismuth telluride materials to construct the m-TED. The device's reliability was tested under various temperatures: -40, 85, 125, and 150 °C. By deconstructing and analyzing the devices that failed during the tests, we discovered that the primary cause of device failure was the degradation of the solder layer. Moreover, we demonstrated that encapsulating the device with polydimethylsiloxane (PDMS) could effectively delay the deterioration of its performance. This study sparks new insights into the service reliability of m-TEDs and paves the way for further optimizing device interface design and enhancing the device manufacturing process.

Diagnostics of Tuberculosis with Single-Walled Carbon Nanotube-Based Field-Effect Transistors.

Tuberculosis (TB) is still threatening millions of people's lives, especially in developing countries. One of the major factors contributing to the ongoing epidemic of TB is the lack of a fast, efficient, and inexpensive diagnostic strategy. In this work, we developed a semiconducting single-walled carbon nanotube (SWCNT)-based field-effect transistor (FET) device functionalized with anti-Mycobacterium tuberculosis antigen 85B antibody (Ab85B) to detect the major M. tuberculosis-secreted antigen 85B (Ag85B). Through optimizing the device fabrication process by evaluating the mass of the antibody and the concentration of the gating electrolyte, our Ab85B-SWCNT FET devices achieved the detection of the Ag85B spiked in phosphate-buffered saline (calibration samples) with a limit of detection (LOD) of 0.05 fg/mL. This SWCNT FET biosensor also showed good sensing performance in biological matrices including artificial sputum and can identify Ag85B in serum after introducing bovine serum albumin (BSA) into the blocking layer. Furthermore, our BSA-blocked Ab85B-SWCNT FET devices can distinguish between TB-positive and -negative clinical samples, promising the application of SWCNT FET devices in point-of-care TB diagnostics. Moreover, the robustness of this SWCNT-based biosensor to the TB diagnosis in blood serum was enhanced by blocking SWCNT devices directly with a glutaraldehyde cross-linked BSA layer, enabling future applications of these SWCNT-based biosensors in clinical testing.

Low-loss chalcogenide photonic devices with a secondary coating method.

In the traditional dry etching process for photonic device fabrication, the etching effect is influenced in many ways, usually resulting in relatively large sidewall roughness and high transmission loss. In this study, an effective method, namely the secondary coating method, is proposed to reduce the transmission loss of a Ge-Sb-Se chalcogenide waveguide and increase the quality factor (Q-factor) of a Ge-Sb-Se chalcogenide micro-ring resonator. The Ge-Sb-Se waveguide and micro-ring resonator are fabricated by ultraviolet exposure/electron beam lithography and inductively coupled plasma etching technology. Afterward, a 10 nm-thick Ge-Sb-Se thin film is deposited by thermal evaporation. The measurements show that after secondary coating, the sidewall roughness of the waveguide is reduced from 11.96 nm to 6.52 nm, with the transmission loss reduced from 2.63± 0.19 dB/cm to 1.86± 0.11 dB/cm at 1.55 µm wavelength. Keeping an equal coupling condition with equal radius and coupling distance, the Q-factor of the micro-ring resonator is improved by 47.5% after secondary coating. All results indicate that the secondary coating method is a feasible way to generate low-loss and high Q-factor integrated chalcogenide photonic devices.