Device Instability Research Articles

Effect of Microwave Annealing on Transparent In–Ga–ZnO Thin-Film Transistors With Graphene Source and Drain Electrodes

In this letter, we investigated the effects of microwave heat treatment on amorphous In–Ga–ZnO (a-IGZO) thin-film transistors (TFTs) with transparent graphene source and drain (S/D) electrodes. Microwave annealing (MWA) was simultaneously applied to post-deposition annealing of the a-IGZO channel layer and post-metallization annealing of the graphene S/D electrode, and then, the influence of MWA on the a-IGZO channel and graphene S/D electrode was evaluated and compared with conventional thermal annealing. We measured the ${I}$ – ${V}$ characteristics of the a-IGZO TFTs, analyzed the trap density of the channel layer, the interface trap density between the gate oxide and the channel, and the instability of device was evaluated. In addition, the effect of MWA on the contact resistance and process stability of transparent graphene electrodes was analyzed. As a result, we improved the electrical properties of the a-IGZO TFTs, simplified the annealing step, and reduced the thermal budget without damaging the graphene S/D electrode for transparent and flexible displays.

Retrospective analysis of complications after surgical treatment of congenital kyphosis in children

Congenital kyphosis occurs as a result of a disruption in the formation or vertebral segmentation in the presence of active semi-vertebra, characterized by rapid progression and, as a rule, development of significant neurological complications. The main surgeries at congenital kyphosis are: ventral and/or posterior fusion in situ, with or without metal devices, vertebroectomy and osteotomy in different modifications. Among postoperative complications in patients with congenital kyphosis, the most common are neurological and fractures of metal devices.Objective: to conduct a retrospective analysis of surgical outcomes of the treatment of congenital kyphosis in children. Methods: case histories were analyzed, patients with congenital kyphosis, whose age did not exceed 18 years, and the follow-up period was at least 2 years after the operation. We assessed the value of the total and local kyphosis, lumbar lordosis. Infectious complications, deformity progression, as well as the complications associated with the instability of metal devices were analyzed.Results: of the 25 patients, 5 had complications: metal device instability with the loss of correction in 3 cases, the infectious — 1, the increase in total kyphosis — 1. In 4 patients revision surgeries were made.Conclusions: use of existing technologies for surgical treatment of congenital kyphosis leads to development of complications after operations. Their main reasons were tactical errors associated with inadequate evaluation of growth potential of the spine, as well as instability of metal devices due to lack of mature bone block. It is necessary to create a technology that can model the growth of the spine and contribute the bone block in the place of osteotomy.

Polymer assist crystallization and passivation for enhancements of open-circuit voltage and stability in tin-halide perovskite solar cells

It has been a widely-known and intractable issue due to very rapid degradation of tin (Sn) based organic-inorganic hybrid perovskites (OIHPs). To incorporate organic chain polymers into the OIHPs based photo-active polycrystalline films seems to be a unique strategy to passivate naturally formed defects at grain boundaries and surfaces, to prevent surface oxidation, and consequently, to optimize photovoltaic performance, as well as to tackle with device instability. In this work, a Lewis-type organic insulating polymer, polymethylmethacrylate (PMMA), was utilized as an effective additive in formamidinium tin tri-iodide (FASnI3) precursor solutions, and the corresponding solid films were made by a one-step processing method. By tuning different concentrations of PMMA, the solar cells have exhibited remarkable improvements of and FF by comparing with a control device without PMMA. The role of PMMA is functional for surface morphology optimization, trap density reduction and current density–voltage (J–V) hysteresis elimination. As a result, it is helpful to effectively impede degradation speeds of FASnI3 based solar cells.

Dipolar Switching of Charge‐Injection Barriers at Electrode/Semiconductor Interfaces as a Mechanism for Water‐Induced Instabilities of Organic Devices

AbstractAn electrode contact–related mechanism for the operational instability of organic electronic devices is proposed and confirmed via observation of a water‐induced change in charge‐injection barrier heights at the electrode/organic‐semiconductor interfaces. Water molecules in air penetrate into the organic crystal via diffusion, and an external electric field orients the electric dipole of the water molecules at the electrode surfaces, leading to dipolar switching of the charge‐injection barrier height. As a result of the switching, current–voltage curves of two‐terminal Au–rubrene–Au devices change from symmetric to asymmetric, showing diode‐like rectification and reversible switching of the diode polarity. The device shows the highest current switching ratio of 267 for the switching voltage of 3 V, corresponding to an electrode work function change of >144 meV. The mechanism proposed herein will be important especially for short‐channel organic devices, which are indispensable for applications such as organic integrated circuits.

Band-Aligned Polymeric Hole Transport Materials for Extremely Low Energy Loss α-CsPbI3 Perovskite Nanocrystal Solar Cells

Summary Emerging all-inorganic perovskite nanocrystals can retain a desired crystal structure under ambient conditions and offer easy solution processability. In this work, we have demonstrated CsPbI3 perovskite quantum dot (QD) solar cells with a remarkable efficiency approaching 13% and an extremely low energy loss of 0.45 eV by employing a series of dopant-free polymeric hole-transporting materials (HTMs). The CsPbI3 QD solar cells use polymer HTMs to achieve efficient charge extraction at QD/polymer interfaces and avoid device instability caused by complex doping and oxidation processes required by conventional Spiro-OMeTAD. Meanwhile, the CsPbI3 QD photovoltaic devices can be fabricated at room temperature and exhibit more reproducible film quality, showing potential advantages over current all-inorganic thin-film perovskite solar cells. We believe that our findings will catalyze the development of new device structures, specifically for perovskite QDs, and help realize the promising potential of all-inorganic perovskite solar cells.

Effects of the compositional ratios of sputtering target on the device performance and instability in amorphous InGaZnO thin film transistors

The effects of the compositional ratios of sputtering target on the device performance and instability in amorphous InGaZnO thin film transistors (a-IGZO TFTs) have been investigated. Four kinds of a-IGZO TFTs according to the contents of In, Ga, and Zn were fabricated by RF magnetron sputtering system. The electrical performances were enhanced with increasing In ratio in a-IGZO TFTs. The resistances of the source/drain electrodes and the effective channel length were decreased with increasing In ratio. Since the effective barrier energy is increased with increasing the sum of In and Zn ratios, the threshold voltage shifts under positive bias stress were decreased with increasing the sum of In and Zn ratios in a-IGZO TFTs. A-IGZO TFTs with increasing In ratio in a-IGZO TFTs exhibit a conductor behavior under negative bias illumination stress.

Measure of high frequency input impedance to study the instability of power devices in short circuit

In this paper, we use a pulsed technique for measuring the input impedance of power devices when they are operated in real operating conditions like short circuit for identifying the situations for which these devices can become instable. The measurement results are used to study the stability in SC of several devices like IGBTs, Power MOSFETs in Si and in SiC, GaN power HEMTs. It is demonstrated that the proposed approach can be a very useful tool for designing the external circuit, and in particular the driver, in such a way to prevent the SC instabilities of power devices.

Analysis of asymmetrical hysteresis phenomena observed in TMD-based field effect transistors

To realize field effect transistors with multi-layered MoS2 and WSe2 (hereafter denoted as MoS2 FET and WSe2 FET), many device instability problems should be surmounted, such as the hysteresis generation of the devices. In order to clarify the mechanism of the asymmetrical hysteresis phenomena observed in the transfer characteristics of the MoS2 and WSe2 FET, the temperature dependencies of their characteristics are analyzed. Based on these analyses, it can be concluded that donor-like traps present in both the SiO2/MoS2 interface and the MoS2 bulk in multi-layered MoS2 FETs, and that acceptor-like traps present in both the SiO2/WSe2 interface, and the WSe2 bulk in multi-layered WSe2 FETs. Furthermore, based on the chemical analyses and the arguments presented in previous studies, we propose that the sulfur vacancy (SV) is the origin of donor-like traps present in MoS2, and the tungsten vacancy (TV) is the origin of acceptor-like traps present in WSe2. This work may provide a potential clue to overcome many practical problems for realization of the transition metal dichalcogenides (TMDs) based FETs.

Improving the stability of metal halide perovskite solar cells from material to structure

Abstract Metal halide perovskites (MHPs) are promising photovoltaic (PV) materials owing to their advantages such as high carrier mobility, excellent absorption coefficient, bandgap tenability, long diffusion length, and low material cost. These qualities have increased the efficiency of MHP solar cells to 23.3%. However, MHPs are hindered by a lack of stability. In addition, the applications of MHP solar cells are restricted by the instability of perovskite materials and devices. In this article, the most urgent stability problems faced by perovskite solar cells are identified, and recent progresses in MHPs are enumerated. The factors affecting the stability of perovskite materials and devices are also discussed. We analyzed the thermal and humid stability of perovskite materials in terms of transporting materials and their interface. In view of these recent advances, future works should focus on the large-scale application of MHP solar cells.

Review on instability of dielectric elastomer structures and devices subjected to electromechanical loading

Dielectric elastomer (DE), as one typical soft electroactive material which processes the advantages including light weight, high energy density, high efficiency, low cost, quiet operation and so on. DE is widely used in the design and development of various transducers, such as smart actuators, sensors, generators, soft displays, soft robots and so on. In practical application, stability is a very important issue for the lifetime and performance of the DE structures and devices. In this paper, we summarize the modes of instabilities, the methods, and applications of the stability analysis of the DE structures and devices when subjected to electromechanical loading. The instabilities of DE structures and devices include pull-in/snap-through instability, buckle, and electro-cavitation. Moreover, the buckling behavior is introduced with film/substrate, membrane, and inflated diaphragm structures. We also discuss the challenges and further development of stability analysis. This paper may provide help in the design and development of novel DE structures and devices in the future.

A Cooperative Quality-Aware Service Access System for Social Internet of Vehicles

Because of the enormous potential to guarantee road safety and improve driving experience, social Internet of Vehicle (SIoV) is becoming a hot research topic in both academic and industrial circles. As the ever-increasing variety, quantity, and intelligence of on-board equipment, along with the ever-growing demand for service quality of automobiles, the way to provide users with a range of security-related and user-oriented vehicular applications has become significant. This paper concentrates on the design of a service access system in SIoVs, which focuses on a reliability assurance strategy and quality optimization method. First, in lieu of the instability of vehicular devices, a dynamic access service evaluation scheme is investigated, which explores the potential relevance of vehicles by constructing their social relationships. Next, this work studies a trajectory-based interaction time prediction algorithm to cope with an unstable network topology and high rate of disconnection in SIoVs. At last, a cooperative quality-aware system model is proposed for service access in SIoVs. Simulation results demonstrate the effectiveness of the proposed scheme.

Electrical and Reliability Properties of Tungsten Doped Indium Based Oxide Thin Film Transistor Fabricated on Polyimide Substrate

In the recent research, a novel type of dopant element in the indium based oxide thin film transistor: tungsten was proposed to replace the expensive and rare gallium element for its low price and even higher oxygen bond dissociation energy, which may further improve the device instability and keep the carrier mobility with a low temperature process at the same time. Therefore, the tungsten doped channel material is more suitable for the flexible device than other transparent amorphous oxide semiconductors. In this work, the devices with tungsten doped channel material were manufactured on a polyimide substrate, which exhibit an acceptable electrical performance and reliability characteristic without a high temperature treatment. In addition, a bending test was also carried out to check the stability for the flexible device.

BODIPY-Based Conjugated Polymers for Use as Dopant-Free Hole Transporting Materials for Durable Perovskite Solar Cells: Selective Tuning of HOMO/LUMO Levels.

Recently, perovskite solar cells (PSCs) have emerged as an excellent photovoltaic device owing to the outstanding power conversion efficiency (PCE). Nevertheless, device instability remains a critical issue in this field. To overcome device instability without deteriorating PCE, dopant-free hole transporting materials (HTMs) are needed to separate the air-sensitive perovskite layer from extrinsic factors, which induce its degradation. Herein, we developed novel conjugate polymers of benzo[1,2- b:4,5- b']dithiophene (BDT) and 4,4-difluoro-4-bora-3 a,4 a-diaza- s-indacene (BODIPY) for use as HTMs without dopants. The pBDT-BODIPY polymer allows individual "dialing" of the highest occupied molecular orbital (HOMO) or lowest unoccupied molecular orbital (LUMO) levels with small modifications to the molecular structure, enabling study of the impact of the frontier molecular orbital on PSC performance. Different alkyl chains on BDT can minutely adjust the HOMO level, and meso-substituents on BODIPYs can selectively set the LUMO level of the resulting polymers. Application of BODIPY-containing polymer into the perovskite solar cell as an HTM leads to a high PCE value (16.02%) and exceptional solar cell stability shown by the fact that over 80% of its original PCE value was maintained after 10 days under ambient air conditions.

3D-printed heart model to guide LAA closure: useful in clinical practice?

Correct device sizing for left atrial appendage (LAA) closure remains challenging due to complex LAA shapes. The aim of our study was to investigative the utility of personalized 3D-printed models (P3DPM) of the LAA to guide device size selection. Fifteen patients (75.4 ±8.5years) scheduled for LAA closure using an Amulet device underwent cardiac computed tomography (CT). The LAA was segmented by semiautomatic algorithms using Vitrea® software. A 1.5-mm LAA thick shell was exported in stereolithography format and printed using TangoPlus flexible material. Different Amulet device sizes on the P3DPM were tested. New P3DPM-CT with the device was acquired in order to appreciate the proximal disc sealing the LAA ostium and the compression of the distal lobe within the LAA. We predicted the device size with P3DPM and compared this with the device sizes predicted by transesophageal echocardiography (TEE) and CT as well as the device size implanted in patients. The device size predicted by 3D-TEE and CT corresponded to the implanted device size in 8/15 (53%) and 10/15 (67%), respectively. The predicted device size from the P3DPM was accurate in all patients, obtaining perfect contact with the LAA wall, without device instability or excessive compression. P3DPM-CT with the deployed device showed device deformation and positioning of the disk in relation to the pulmonary veins, allowing us to determine the best device size in all 15 cases. P3DPM allowed us to simulate the LAA closure procedure and thus helped to identify the best Amulet size and position within the LAA. • A 3D-printed heart model allows to simulate the LAA closure procedure. • A 3D-printed heart model allowed to identify the optimal Amulet size and position. • 3D-printed heart models may contribute to reduce the Amulet implantation learning curve.

Solvent Additives: Key Morphology-Directing Agents for Solution-Processed Organic Solar Cells.

Organic photovoltaics (OPV) have the advantage of possible fabrication by energy-efficient and cost-effective deposition methods, such as solution processing. Solvent additives can provide fine control of the active layer morphology of OPVs by influencing film formation during solution processing. As such, solvent additives form a versatile method of experimental control for improving organic solar cell device performance. This review provides a brief history of solution-processed bulk heterojunction OPVs and the advent of solvent additives, putting them into context with other methods available for morphology control. It presents the current understanding of how solvent additives impact various mechanisms of phase separation, enabled by recent advances in in situ morphology characterization. Indeed, understanding solvent additives' effects on film formation has allowed them to be applied and combined effectively and synergistically to boost OPV performance. Their success as a morphology control strategy has also prompted the use of solvent additives in related organic semiconductor technologies. Finally, the role of solvent additives in the development of next-generation OPV active layers is discussed. Despite concerns over their environmental toxicity and role in device instability, solvent additives remain relevant morphological directing agents as research interests evolve toward nonfullerene acceptors, ternary blends, and environmentally sustainable solvents.

Perovskites-Based Solar Cells: A Review of Recent Progress, Materials and Processing Methods.

With the rapid increase of efficiency up to 22.1% during the past few years, hybrid organic-inorganic metal halide perovskite solar cells (PSCs) have become a research “hot spot” for many solar cell researchers. The perovskite materials show various advantages such as long carrier diffusion lengths, widely-tunable band gap with great light absorption potential. The low-cost fabrication techniques together with the high efficiency makes PSCs comparable with Si-based solar cells. But the drawbacks such as device instability, J-V hysteresis and lead toxicity reduce the further improvement and the future commercialization of PSCs. This review begins with the discussion of crystal and electronic structures of perovskite based on recent research findings. An evolution of PSCs is also analyzed with a greater detail of each component, device structures, major device fabrication methods and the performance of PSCs acquired by each method. The following part of this review is the discussion of major barriers on the pathway for the commercialization of PSCs. The effects of crystal structure, fabrication temperature, moisture, oxygen and UV towards the stability of PSCs are discussed. The stability of other components in the PSCs are also discussed. The lead toxicity and updated research progress on lead replacement are reviewed to understand the sustainability issues of PSCs. The origin of J-V hysteresis is also briefly discussed. Finally, this review provides a roadmap on the current needs and future research directions to address the main issues of PSCs.

P‐4: Reliability Analysis and Improvement of Self‐aligned Coplanar a‐IGZO TFTs for OLED Display

A TG‐SA a‐IGZO TFT technology is demonstrated with a good VTH uniformity in the whole 14” OLED panel and a high reliability of +0.03V and −0.52V under PBTS and NBTIS, respectively. Mechanisms for device instability and the relative relationship between PBTS and NBTIS have been systematically analyzed. Finally, the prototype 14″ FHD OLED display with an excellent brightness uniformity using TG‐SA a‐IGZO TFTs backplane have been made successfully. Besides, the high reliability of devices have been confirmed through a longtime RA test without no obvious defects generated, which indicates excellent mass‐production prospect.

Quantitative Analysis of Depletion Regime Charges in a Pristine a-Igzo TFT

Amorphous Indium Gallium Zinc Oxide (a-IGZO) based thin film transistors (TFTs) are the most suitable switching devices for flexible electronics due to their compatibility with room temperature processing with high yield, high field-effect mobility (μfe), low threshold voltage (VTH) and subthreshold swing (SS).1 Many prospective applications have been reported using metal-oxide thin-film transistors such as RFID2 and high-resolution displays3. The biggest challenges of a-IGZO TFTs are the process repeatability due to the ambient sensitivity of IGZO, for example to contamination by hydrogen, oxygen, or nitrogen, which affect device performance and reliability. It has been reported that the addition of hydrogen atoms, which act as donors, shifts the transfer characteristics negatively due to enhancing the n-type free carriers.4 On the contrary the addition of oxygen, which acts as an acceptor, shifts the transfer positively by suppressing the free carriers. In PVD deposited a-IGZO TFTs, oxygen partial pressure is a key parameter to control the turn-on voltage and field-effect mobility. Annealing either post-fabrication or mid-process can also provide controllability. Interface formation around very thin IGZO films plays a big role on performance and reliability. It is now important to investigate the quantitative measurement of charge distribution/density-of-states (DoS) in IGZO material/interfaces, especially within the depletion regime in thin-film transistors to understand any correlation between device reliability and charges in the depletion regime. Commonly positive bias stress (PBS) shifts the transfer characteristic positively. The origin is explained as the negative charge (electron) traps or migration around the interfaces. The migration process has been attributed to the transformation of the ionized positive charge state (VO 2+ + 2e-) to neutral oxygen vacancy state (VO) by capturing two free electrons. 5,6 Negative bias illumination stress (NBIS) conversely shifts the transfer characteristics negatively due to the creation/formation of positive charges (VO to VO 2+ + 2e-) in the channel region.1 In our investigation, the depletion regime interface charge, bulk charge, and DoS distribution in pristine a-IGZO devices has been quantified using electrical measurements. To do this, we added an extra contact in the IGZO TFTs at the same time as patterning the source/drain metal in a coplanar top gate device architecture. During gate voltage dependent drain current measurement, we measured the potential changes in the extra contact point (between source & drain) using a high input impedance measurement channel which directly provides information on the depletion regime charges around the interface, since the potential proportionally represents the charge. With a gate voltage of -6V and source/drain voltage of 0V the measured potential at the extra probe is -0.47V (representing a charge density in depletion regime of ~ 8.5 x 10-7 C/cm2), which gradually increased to ~0V as the gate voltage increased to -0.2V. The decrement/increment of depletion regime charges under PBS/NBIS, will provide the correct interpretation about the origin of device instabilities. For -0.2V to +6V gate voltage the extra probe channel potential depends on drain voltage and the position between the source and drain. This appears to be a very simple measurement to understand the depletion regime charges in wide bandgap amorphous metal oxide thin film transistor, which is not possible using conventional capacitance-voltage and Kelvin probe potential measurement.7

24.4: High Performance Top‐gate Self‐aligned Coplanar a‐IGZO TFTs with Light Shielding Metal Design

The TG‐SA a‐IGZO TFTs with different light shielding metal (SM) layers design were demonstrated and compared in this paper. Their electrical characteristics have been measured in order to systematically analyze the effect that the SMs ever made on. The relationship between device instability and different SMs design have been systematically analyzed. Then the prototype 14″ OLED display with an excellent performance using TG‐SA a‐IGZO TFTs backplane have been made successfully, which indicates an excellent mass‐production prospect.

Influence of Environmentally Affected Hole-Transport Layers on Spatial Homogeneity and Charge-Transport Dynamics of Organic Solar Cells.

After organic photovoltaic (OPV) cells achieved efficiency of more than 10%, the control of stability and degradation mechanisms of solar cells became a prominent task. The increase of device efficiency due to incorporation of a hole-transport layer (HTL) in bulk-heterojunction solar cells has been extensively reported. However, the most widely used HTL material, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), is frequently suspected to be the dominating source for device instability under environmental conditions. Thereby, effects like photooxidation and electrode corrosion are often reported to shorten device lifetime. However, often in environmental device studies, the source of degradation, whether being from the HTL, the active layer, or the metal cathode is rather difficult to distinguish because the external diffusion of oxygen and water affects all components. In this study, different HTLs, namely, those prepared from traditional PEDOT:PSS and also two types of molybdenum trioxide (MoO3) are exposed to different environments, such as oxygen, light, or humidity, prior to device finalization under inert conditions. This allows investigating any effects within the HTL and from reactions at its interface to the indium tin oxide electrode or the active layer. The surface and bulk chemistry of the exposed HTL has been monitored and discussed in context to the observed device physics, dynamic charge transport, and spatial performance homogeneity of the corresponding OPV device. The results show that merely humidity exposure of the HTL leads to decreased device performance for PEDOT:PSS, but also for one type of the tested MoO3. The losses are related to the amount of absorbed water in the HTL, inducing loss of active area in terms of interfacial contact. The device with PEDOT:PSS HTL after humid air exposure showed seriously decreased photocurrent by microdelamination of swelling/shrinkage of the hygroscopic layer. The colloidal MoO3 with water-based precursor solution presents slight decay of solar cell performance, also here caused by swelling/shrinking reaction, but by a combination of in-plane particle contact and resistance scaling with particle expansion. However, the device with quasi-continuous and alcohol-based MoO3 showed unharmed stable electrical performance.