Showing papers in "Advanced electronic materials in 2019"

Recommended Methods to Study Resistive Switching Devices

Abstract: Resistive switching (RS) is an interesting property shown by some materials systems that, especially during the last decade, has gained a lot of interest for the fabrication of electronic devices, with electronic nonvolatile memories being those that have received the most attention. The presence and quality of the RS phenomenon in a materials system can be studied using different prototype cells, performing different experiments, displaying different figures of merit, and developing different computational analyses. Therefore, the real usefulness and impact of the findings presented in each study for the RS technology will be also different. This manuscript describes the most recommendable methodologies for the fabrication, characterization, and simulation of RS devices, as well as the proper methods to display the data obtained. The idea is to help the scientific community to evaluate the real usefulness and impact of an RS study for the development of RS technology. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

The Thermoelectric Properties of Bismuth Telluride

Abstract: DOI: 10.1002/aelm.201800904 made for efficient thermoelectric cooling or temperature management uses Bi2Te3 alloys. Such solid-state devices dominate the market for temperature control in optoelectronics. As the need to eliminate greenhouse-gas refrigerants increases, Peltier cooling is becoming more attractive particularly in small systems where efficiencies are comparable to traditional refrigerant based cooling. Such small devices may enable distributive heating/ cooling (only where and when it is needed) with higher system level energy efficiency, for example in electric vehicles where energy for heating/cooling competes with vehicle range. Even for thermoelectric power generation, e.g., recovery of waste heat, Bi2Te3 alloys are most used because of superior efficiency up to 200 °C and the technology to make devices with Bi2Te3 is most advanced.[1–3] While the material and production technology for making Bi2Te3-based devices has remained essentially unchanged since the 1960s, our understanding of these materials has advanced considerably. Most recently, the interest in topological insulators (TI) has led to new insights into the complex electronic structure[4,5] revealing that with the accuracy in assessing the band structures available today, improvements in the electronic structure by band engineering should not only be possible but predictable.[6–9] Indeed, the p-type alloys chosen for use in commercial Peltier coolers appear to have unintentionally arrived at a composition close to a band convergence. The understanding of defects and doping is also advancing rapidly that will lead to new strategies for additional improvements in the electronic properties. The thermal conductivity of Bi2Te3-based alloys can also be engineered, where in particular there is much recent interest in microstructure engineering or nanostructuring.[10–22] Reduced thermal conductivity has led to numerous reports of exceptionally high efficiency (zT) that would be sufficient to revolutionize the industry. However, between measurement and material uncertainties, a revolutionary new Bi2Te3-based material has not made it to the market. Because even small but reliable improvements could make significant impact, it is worthwhile to better understand all the complex, interdependent effects of band engineering and microstructure engineering. To demonstrate and quantify improvements in thermoelectric properties, it is necessary to have well characterized properties or reliable benchmarks for comparison. Bismuth telluride is the working material for most Peltier cooling devices and thermoelectric generators. This is because Bi2Te3 (or more precisely its alloys with Sb2Te3 for p-type and Bi2Se3 for n-type material) has the highest thermoelectric figure of merit, zT, of any material around room temperature. Since thermoelectric technology will be greatly enhanced by improving Bi2Te3 or finding a superior material, this review aims to identify and quantify the key material properties that make Bi2Te3 such a good thermoelectric. The large zT can be traced to the high band degeneracy, low effective mass, high carrier mobility, and relatively low lattice thermal conductivity, which all contribute to its remarkably high thermoelectric quality factor. Using literature data augmented with newer results, these material parameters are quantified, giving clear insight into the tailoring of the electronic band structure of Bi2Te3 by alloying, or reducing thermal conductivity by nanostructuring. For example, this analysis clearly shows that the minority carrier excitation across the small bandgap significantly limits the thermoelectric performance of Bi2Te3, even at room temperature, showing that larger bandgap alloys are needed for higher temperature operation. Such effective material parameters can also be used for benchmarking future improvements in Bi2Te3 or new replacement materials.

Dual-Functional Graphene Composites for Electromagnetic Shielding and Thermal Management

Abstract: Author(s): Kargar, Fariborz; Barani, Zahra; Balinskiy, Michael; Magana, Andres Sanchez; Lewis, Jacob S.; Balandin, Alexander A.

A Fully Printed Flexible MoS 2 Memristive Artificial Synapse with Femtojoule Switching Energy

Abstract: EPSRC (EP/L016087/1), A*STAR Science and Engineering Research Council (Grant No. 152-70-00013, and 152-70-00017), Singapore National Research Foundation’s Returning Singapore Scientist Scheme (Grant No. NRF-RSS2015-003), The National Research Foundation, Prime Minister's Office, Singapore.

The Recent Advance in Fiber-Shaped Energy Storage Devices

Abstract: Over the past decades, the rapid development of mobile electronics has brought enormous convenience to our daily life. With these miniature electronic devices, the communication and social networking become more prompt and frequent among people. In the course of its evolvement, wearable electronic devices that can be directly worn onto human body or combined with daily textiles, experience a booming development.[1–3] These wearable electronic devices strongly demand indispensable, high performance power systems with small size, high flexibility and adaptability to comfort frequent deformations during usage.[4,5] However, conventional energy storage systems such as supercapacitors and lithium batteries are typically rigid and limited by their lifespan, which cannot effectively satisfy the above requirements. Fabricating high-performance energy storage systems in a 1D shape like fiber is recognized as a promising strategy to Wearable electronic devices that can be directly worn on the human body or combined with daily textiles have experienced a booming development with the rapid development of mobile electronics. These wearable electronic devices strongly demand indispensable, high performance power systems with small size, high flexibility, and adaptability to comfort frequent deformations during usage. Fabricating high-performance energy storage systems in a 1D shape like fiber is recognized as a promising strategy to address the above issues. These fiber-shaped power systems with diameters from tens to hundreds of micrometers can adapt to various deformations for stable operation in close contact with the human body. It is also possible to further weave such 1D energy storage devices into breathable textiles with matching electrochemical performances for the wearable electronics. Here, the key advancements related to fiber-shaped energy storage devices are reviewed, including the synthesis of materials, the design of structures, and the optimization of properties for the most explored energy storage devices, i.e., supercapacitors, aprotic lithium-based batteries, as well as novel aqueous battery systems. The remaining challenges are finally discussed to highlight the future direction of the development of fiber-shaped energy storage devices.

Dimensionality Dependent Plasticity in Halide Perovskite Artificial Synapses for Neuromorphic Computing

Abstract: DOI: 10.1002/aelm.201900008 properties of biological synapses and perform parallel operations, they require larger energy than a biological synapse. Therefore, development of an artificial synapse with energy consumption on the level of a biological synapse remains an open problem. Organic–inorganic halide perovskite (OHPs) may provide a material to solve this problem, because of their low activation energy of ion migration. Moreover, various structural modulation of polycrystalline films is possible with facile solution processing so that organic parts in the OHPs can control the ion migration and electrical conduction. OHPs have an ABX3 crystal structure; the A-site cation is located at the center of a BX6 octahedral cage, and the B-site metal cation is surrounded by the six nearest-neighbor X-site halide anions.[7] OHPs have a significant hysteresis property that is caused by ion migration or space charges, or both, which may enable gradual modulation of conductance in OHP.[8] Two-terminal artificial synapses based on 3D methylammonium (MA) lead halide perovskite (MAPbX3, X = Br, I) films showed synaptic responses that are caused by ion migration in the OHP layer.[9,10] Ion migration in 3D OHP film is induced by relatively low activation energy and a low energy consumption of ≈20 fJ per synaptic event was achieved in the synaptic devices. However, the energy consumption could be further reduced to the energy level of biological synapses when the ion migration was controlled by engineering the structure of OHP films could be optimally done. In this work, we introduce 2D and quasi-2D OHP films into artificial synapses to enable control of ion migration and resultant synaptic responses. For this purpose, we replaced the small MA ion with a bulky phenethylammonium (PEA) ion in their crystalline structures. To prepare 2D, quasi-2D, and 3D OHP films, we controlled the stoichiometric ratio of PEA and MA cations to induce self-assembly of a layered structure. This replacement of an MA cation with PEA cation suppresses ion migration in the out-of-plane direction of the OHP films.[11–13] Thereby, the activation energy EA of ion migration is increased, so ion migration and excitatory postsynaptic current (EPSC) can be reduced. Also, energy consumption of the device is reduced to ≈0.7 fJ per synaptic event, which is comparable to that of biological synapses. Memory retention of artificial The hysteretic behavior of organic–inorganic halide perovskites (OHPs) are exploited for application in neuromorphic electronics. Artificial synapses with 2D and quasi-2D perovskite are demonstrated that have a bulky organic cation (phenethylammonium (PEA)) to form structures of (PEA)2MAn-1PbnBr3n+1. The OHP films have morphological properties that depend on their structure dimensionality (i.e., n value), and artificial synapses fabricated from them show synaptic responses such as short-term plasticity, paired-pulse facilitation, and long-term plasticity. The operation mechanism of OHP artificial synapses are also analyzed depending on the dimensionality and it is found that quasi-2D (n = 3–5) OHP artificial synapses show much longer retention than 2D and 3D OHP counterparts. The calculated energy consumption of a 2D OHP artificial synapse (≈0.7 fJ per synaptic event) is comparable to that of biological synapses (1–10 fJ per synaptic event). These OHP artificial synapses may enable development of neuromorphic electronics that use very little energy.

Poly(3,4-ethylenedioxythiophene): Chemical Synthesis, Transport Properties, and Thermoelectric Devices

Abstract: Since their discovery in the seventies, conducting polymers have been chemically designed to acquire specific optical and electrical properties for various applications. Poly(3,4-ethylenedioxythiop ...

The Critical Role of Electron-Donating Thiophene Groups on the Mechanical and Thermal Properties of Donor–Acceptor Semiconducting Polymers

Abstract: Author(s): Zhang, S; Ocheje, MU; Huang, L; Galuska, L; Cao, Z; Luo, S; Cheng, YH; Ehlenberg, D; Goodman, RB; Zhou, D; Liu, Y; Chiu, YC; Azoulay, JD; Rondeau-Gagne, S; Gu, X | Abstract: Organic semiconducting donor–acceptor polymers are promising candidates for stretchable electronics owing to their mechanical compliance. However, the effect of the electron-donating thiophene group on the thermomechanical properties of conjugated polymers has not been carefully studied. Here, thin-film mechanical properties are investigated for diketopyrrolopyrrole (DPP)-based conjugated polymers with varying numbers of isolated thiophene moieties and sizes of fused thiophene rings in the polymer backbone. Interestingly, it is found that these thiophene units act as an antiplasticizer, where more isolated thiophene rings or bigger fused rings result in an increased glass transition temperature (T g ) of the polymer backbone, and consequently elastic modulus of the respective DPP polymers. Detailed morphological studies suggests that all samples show similar semicrystalline morphology. This antiplasticization effect also exists in para-azaquinodimethane-based conjugated polymers, indicating that this can be a general trend for various conjugated polymer systems. Using the knowledge gained above, a new DPP-based polymer with increased alkyl side chain density through attaching alky chains to the thiophene unit is engineered. The new DPP polymer demonstrates a record low T g , and 50% lower elastic modulus than a reference polymer without side-chain decorated on the thiophene unit. This work provides a general design rule for making low-T g conjugated polymers for stretchable electronics.

Carbon-Nanotube-Based Electrical Conductors: Fabrication, Optimization, and Applications

Abstract: DOI: 10.1002/aelm.201800811 and environmentally friendly conductive cables or wires as a replacement for copper. From this view, carbon-based nanomaterial is a potential candidate. Carbon related nanomaterials including fullerenes, carbon nanotubes (CNTs), and graphene are promising due to their exceptional conductive and electronic transport properties, which may accelerate the practical and potential applications for various kinds of novel engineering areas spanning from electronics, energy storage, and advanced materials to nanotechnology and biotechnology. Among the family of carbon nanomaterials, CNTs have been a particularly attractive material since its discovery in 1991 by Iijima,[1] due to their nanoscale 1D shape, excellent mechanical properties, tunable electrical properties either metallic or semiconducting, high current carrying capacity, and many other exciting properties. These properties have highlighted the potential of CNTs use in a plethora of applications, including electrically conductive fillers in polymer composites, flexible and transparent conductive films, microelectronics (transistors, interconnectors, heat dissipaters), and lightweight conducting wires and cables.[2] Figure 1 points out the forecast presented by Endo et al.[3] on the present, near future, and long term applications of CNTs in various fields. An interesting potential application of CNTs is the long-term electrical conductors, which are able to transmit power from plants to plants or households, as well as be used in electronic devices. Compared to conventional copper cables or wires, CNT based cables have several advantages including 1) a lower density of 1.3 g cm−3 for single-walled carbon nanotubes (SWCNTs)[4] and 2.1 g cm−3 for multiwalled carbon nanotubes (MWCNTs),[5] both of which are much lower than that of copper, 8.96 g cm−3;[6] 2) environmental stability, which can stand with severe conditions including high pressure, large temperature changes, etc.; 3) excellent mechanical performance with a Young’s modulus and strength in the ranges of 1.0 TPa and 50 GPa, respectively;[7] 4) ultrahigh electrical conductivity as high as 108 S m−1 for SWCNTs, which is higher than that of copper (≈107 S m−1)).[8] Furthermore, the limited amount of conventional conductive metal resources in nature and their soaring market price greatly increased the need for a desirable alternative solution that are abundant in nature, low-cost, and The lack of progress to obtain commercially available large-scale production of continuous carbon nanotube (CNT) fibers has provided the motivation for researchers to develop high-performance bulk CNT assemblies that could more effectively transfer the superb mechanical, electrical, and other excellent properties of individual CNTs. These wire-like bulk assemblies of CNTs have demonstrated the potential for being used as electrical conductors to replace conventional conductive materials, such as copper and aluminum. CNT conductors are extremely lightweight, corrosive-resistive, and mechanically strong while being potentially cost-effective when compared to other conventional conductive materials. However, great technical challenges still exist in transferring the superior properties of individual CNTs to highly conductive bulk CNT assemblies, such as continuous wires, cables, and sheets. This paper gives an overview of the state-of-the-art advances in CNT-based conductors in terms of fabrication methods, characterization, conduction mechanisms, and applications. In addition, future research directions and possible attempts to improve performance are analyzed. The opportunities and challenges for related nonmetal competitive conductors are also discussed.