Showing papers in "Advanced electronic materials in 2021"

Organic Memory and Memristors: From Mechanisms, Materials to Devices

Abstract: Facing the exponential growth of data digital communications and the advent of artificial intelligence, there is an urgent need for information technologies with huge storage capacity and efficient computing processing. However, the traditional von Neumann architecture and silicon-based storage and computing technology will reach their limits and cannot meet the storage requirements of ultrasmall size, ultrahigh density, and memory computing. Considering these issues, organic material resistance switching memory and memristor devices have become promising candidates for high-density storage, logic computing, and neuromorphic computing because of their advantages of fast speed, high energy efficiency, nonvolatile storage, and low cost. In this article, the working mechanism, material design strategy, and device performance of organic memory and memristors are reviewed.

2D WS2: From Vapor Phase Synthesis to Device Applications

Abstract: The rising of 2D materials research is ignited by the discovery of graphene, a one-atom-thick carbon sheet, in 2004.[1] Due to the excellent physical and chemical properties of 2D materials, they become a hot topic in many disciplines, such as physical science, chemical science, materials science, and engineering.[2–4] Until now, there are already a large number of 2D materials developed, including graphene,[1] transition metal dichalcogenides (TMDs),[5] black phosphorene,[6] Germanane,[7,8] GeTe,[9] 2D covalent organic frameworks,[10] etc. In theory, it is predicted to have more than 5000 different kinds of 2D materials,[11] which cover a wide range of material categories in insulators, semiconductors, semimetals, metals, superconductors, etc., making them possible to construct various 2D materials devices with novel functions. Particularly, graphene is the most intensively studied material. Although it possesses superior properties with the large carrier mobility,[12,13] flat light absorption in a wide spectrum,[14,15] and strong mechanical strength,[16,17] the lack of a band gap would greatly limited its applications in electronics and optoelectronics. For example, transistors made from graphene cannot be effectively turned off,[1] while graphene-based photodetectors always have a substantially large dark current.[18] In this case, semiconducting 2D materials with suitable band gaps, rather than graphene, are highly desired for high-performance electronic and optoelectronic devices. Among many semiconducting 2D materials, TMDs are the most promising alternatives because of their appropriate band gaps, good stability in ambient, excellent electrical, and optoelectronic characteristics.[19–21] WS2 is one of the TMD materials that has superior properties as compared with other TMDs. It has the relatively high carrier mobility,[22] large exciton binding energy,[23] large spin–orbit splitting,[24] and strong photoluminescence (PL).[25] These properties make it idle for a wide range of applications, such as transistors,[26] photodetectors,[27] lightemitting devices (LEDs),[28] etc. Despite the fact that there are numerous reports focused on the synthesis, properties, and applications of 2D WS2, there is still a lack of the comprehensive review on 2D WS2. In this review article, we would focus on the vapor phase synthesis, property assessment, and electronic and optoelectronic applications of 2D WS2. At first, the fundamental properties of 2D WS2 are introduced in details. Then, The discovery of graphene has triggered the research on 2D layer structured materials. Among many 2D materials, semiconducting transition metal dichalcogenides (TMDs) are widely considered to be the most promising ones due to their excellent electrical and optoelectronic characteristics. Tungsten disulfide (WS2) is a kind of such TMDs with fascinating properties, such as the high carrier mobility, appropriate band gap, strong light–matter interaction with the large light absorption coefficient, very large exciton binding energy, large spin splitting, and polarized light emission. All these interesting properties can make the 2D WS2 being highly favorable for applications in memristors, light-emitting devices, optical modulators, and many others. Here, the comprehensive review on the properties, vapor phase synthesis, electronic and optoelectronic applications of 2D WS2 is presented. This review does not only serve as a design guideline to elevate the material quality of 2D WS2 films via enhanced synthesis approaches, but also provides valuable insights to various strategies to improve their device performances. With the fast development of wafer-scale synthesis methods and novel device structures, 2D WS2 can undoubtedly be a rising star for the next-generation devices in the near future.

Ferroelectric Synaptic Transistor Network for Associative Memory

Abstract: Brain‐inspired associative memory is meaningful for pattern recognitions and image/speech processing. Here, a ferroelectric synaptic transistor network is proposed that is capable of associative learning and one‐step recalling of a whole set of data from only partial information. The competition between an external field and the internal depolarization field governs the ferroelectric creep of domain walls and offers each single ferroelectric synapse a full and subfemtojoule‐energy‐cost Hebbian synaptic plasticity, including short‐term memory (STM) to long‐term memory (LTM) transition, and remarkably both spike‐timing‐dependent plasticity (STDP) and spike‐rate‐dependent plasticity (SRDP). Assisted by the third terminal to control the ferroelectric domain dynamics, self‐adaptive coupling between neurons is realized by updating synaptic weight concurrently. Pavlov's dog experiment and multiassociative memories are demonstrated in this ferroelectric synaptic transistor network. Such ferroelectric synaptic transistor network is available for building multilayer neural networks and provides new avenues for associative‐memory information processing.

A Current–Voltage Model for Double Schottky Barrier Devices

Abstract: Schottky barriers are often formed at the semiconductor/metal contacts and affect the electrical behaviour of semiconductor devices. In particular, Schottky barriers have been playing a major role in the investigation of the electrical properties of mono and two-dimensional nanostructured materials, although their impact on the current-voltage characteristics has been frequently neglected or misunderstood. In this work, we propose a single equation to describe the current-voltage characteristics of two-terminal semiconductor devices with Schottky contacts. We apply the equation to numerically simulate the electrical behaviour for both ideal and non-ideal Schottky barriers. The proposed model can be used to directly estimate the Schottky barrier height and the ideality factor. We apply it to perfectly reproduce the experimental current-voltage characteristics of ultrathin molybdenum disulphide or tungsten diselenide nanosheets and tungsten disulphide nanotubes. The model constitutes a useful tool for the analysis and the extraction of relevant transport parameters in any two-terminal device with Schottky contacts.

Core–Sheath Fiber-Based Wearable Strain Sensor with High Stretchability and Sensitivity for Detecting Human Motion

Abstract: Fiber-based strain sensors are considered to be an important part of smart wearables due to their flexible performance, lightness, and easily processing into various structures. However, the low sensitivity of fiber-based strain sensors has limited their real-life applications for detecting human movements. In this work, a poly(styrene-butadiene-styrene) (SBS)/multi-walled carbon nanotube (MWCNTs) core–sheath fiber (SSCCSF) strain sensor is fabricated via a simple and facile coaxial wet-spinning method. The cross-sectional morphology, the mechanical properties, and the electromechanical performance of the SSCCSFs are investigated. Scanning electron microcopy results show that SSCCSFs have a bean-like cross-section with SBS as the core and SBS/MWCNTs as the sheath. Electromechanical performance evaluation confirms that the SSCCSF show a high sensitivity in a broad working range (gauge factor = 25832.77 at 41.5% strain) and excellent durability (5000 cycles at 10% strain). Furthermore, the SSCCSF displays outstanding sensing performance for detecting large motions in human movements including hand joint bending (such as knuckles and wrists) and subtle motions in physiological activities, involved in swallowing behavior, breathing, and pulse beat. This study demonstrates the potential application of SSCCSFs for wearable electronics with activity monitoring sensors.

Enhancing the Electrochemical Doping Efficiency in Diketopyrrolopyrrole-Based Polymer for Organic Electrochemical Transistors

Abstract: The increasing interest in organic electrochemical transistors (OECTs) for next-generation bioelectronic applications motivates the design of novel conjugated polymers with good electronic and ionic transport. Many conjugated polymers developed for organic field-effect transistors (OFETs) exhibit high charge carrier mobilities but they are not suitable for OECTs due to poor ion-uptake arising from the non polar alkyl chain substituted on the conjugated backbone. They are also sensitive to moisture, resulting in poor performance in aqueous electrolytes. Herein, the widely used conjugated building block diketopyrrolopyrrole (DPP) is used and functionalized it with polar triethylene glycol side chains (PTDPP-DT) to promote ion penetration. The electrical performance of PTDPP-DT based OECT in two types of aqueous electrolytes is studied and the electrochemical doping response is investivated. It is found that the tetrafluoroborate (BF4−) anion with large crystallographic radius allows high-efficiency electrochemical doping of the PTDPP-DT polymer, and thus gives rise to the high transconductance of 21.4 ± 4.8 mS with good device stability, where it maintained over 91 % of its doped-state drain current after over 500 cycles of pulse measurement.

Solid-state thermal control devices

Abstract: Over the past decade, solid-state thermal control devices have emerged as potential candidates for enhanced thermal management and storage. They distinguish themselves from traditional passive thermal management devices in that their thermal properties have sharp, nonlinear dependencies on direction and operating temperature, and can lead to more efficient circuits and energy conversion systems than what is possible today. They also distinguish themselves from traditional active thermal management devices (e.g., fans) in that they have no moving parts and are compact and reliable. In this article, the recent progress in the four broad categories of solid-state thermal control devices that are under active research is reviewed: diodes, switches, regulators, and transistors. For each class of device, the operation principle, material choices, as well as metrics to compare and contrast performance are discussed. New architectures that are explored theoretically, but not experimentally demonstrated, are also discussed.

One Nanometer HfO2-Based Ferroelectric Tunnel Junctions on Silicon

Abstract: Author(s): Cheema, SS; Shanker, N; Hsu, CH; Datar, A; Bae, J; Kwon, D; Salahuddin, S | Abstract: In ferroelectric materials, spontaneous symmetry breaking leads to a switchable electric polarization, which offers significant promise for nonvolatile memories. In particular, ferroelectric tunnel junctions (FTJs) have emerged as a new resistive switching memory which exploits polarization-dependent tunnel current across a thin ferroelectric barrier. This work integrates FTJs with complementary metal-oxide-semiconductor-compatible Zr-doped HfO2 (Zr:HfO2) ferroelectric barriers of just 1 nm thickness, grown by atomic layer deposition on silicon. These 1 nm Zr:HfO2 tunnel junctions exhibit large polarization-driven electroresistance (g20 000%), the largest value reported for HfO2-based FTJs. In addition, due to just a 1 nm ferroelectric barrier, these junctions provide large tunneling current (g1 A cm−2) at low read voltage, orders of magnitude larger than reported thicker HfO2-based FTJs. Therefore, this proof-of-principle demonstration provides an approach to simultaneously overcome three major drawbacks of prototypical FTJs: a Si-compatible ultrathin ferroelectric, large electroresistance, and large read current for high-speednoperation.