Non‐Volatile Ferroelectric Memory with Position‐Addressable Polymer Semiconducting Nanowire

One‐dimensional nanowires (NWs) have been extensively examined for numerous potential nano‐electronic device applications such as transistors, sensors, memories, and photodetectors. The ferroelectric‐gate field effect transistors (Fe‐FETs) with semiconducting NWs in particular in combination with ferroelectric polymers as gate insulating layers have attracted great attention because of their potential in high density memory integration. However, most of the devices still suffer from low yield of devices mainly due to the ill‐control of the location of NWs on a substrate. NWs randomly deposited on a substrate from solution‐dispersed droplet made it extremely difficult to fabricate arrays of NW Fe‐FETs. Moreover, rigid inorganic NWs were rarely applicable for flexible non‐volatile memories. Here, we present the NW Fe‐FETs with position‐addressable polymer semiconducting NWs. Polymer NWs precisely controlled in both location and number between source and drain electrode were achieved by direct electrohydrodynamic NW printing. The polymer NW Fe‐FETs with a ferroelectric poly(vinylidene fluoride‐co‐trifluoroethylene) exhibited non‐volatile ON/OFF current margin at zero gate voltage of approximately 10² with time‐dependent data retention and read/write endurance of more than 10⁴ seconds and 10² cycles, respectively. Furthermore, our device showed characteristic bistable current hysteresis curves when being deformed with various bending radii and multiple bending cycles over 1000 times.     

Triboiontronic Transistor of MoS2

Electric double layers (EDLs) formed in electrolyte‐gated field‐effect transistors (FETs) induce an extremely large local electric field that gives a highly efficient charge carrier control in the semiconductor channel. To achieve highly efficient triboelectric potential gating on the FET and explore diversified applications of electric double layer FETs (EDL‐FETs), a triboiontronic transistor is proposed to bridge triboelectric potential modulation and ion‐controlled semiconductor devices. Utilizing the triboelectric potential instead of applying an external gate voltage, the triboiontronic MoS₂ transistor is efficiently operated owing to the formation of EDLs in the ion‐gel dielectric layer. The operation mechanism of the triboiontronic transistor is proposed, and high current on/off ratio over 10⁷, low threshold value (75 μm), and steep switching properties (20 µm dec^?1) are achieved. A triboiontronic logic inverter with desirable gain (8.3 V mm^?1), low power consumption, and high stability is also demonstrated. This work presents a low‐power‐consuming, active, and a general approach to efficiently modulate semiconductor devices through mechanical instructions, which has great potential in human–machine interaction, electronic skin, and intelligent wearable devices. The proposed triboiontronics utilize ion migration and arrangement triggered by mechanical stimuli to control electronic properties, which are ready to deliver new interdisciplinary research directions.     

Printing Semiconductor–Insulator Polymer Bilayers for High‐Performance Coplanar Field‐Effect Transistors

Source–semiconductor–drain coplanar transistors with an organic semiconductor layer located within the same plane of source/drain electrodes are attractive for next‐generation electronics, because they could be used to reduce material consumption, minimize parasitic leakage current, avoid cross‐talk among different devices, and simplify the fabrication process of circuits. Here, a one‐step, drop‐casting‐like printing method to realize a coplanar transistor using a model semiconductor/insulator [poly(3‐hexylthiophene) (P3HT)/polystyrene (PS)] blend is developed. By manipulating the solution dewetting dynamics on the metal electrode and SiO₂ dielectric, the solution within the channel region is selectively confined, and thus make the top surface of source/drain electrodes completely free of polymers. Subsequently, during solvent evaporation, vertical phase separation between P3HT and PS leads to a semiconductor–insulator bilayer structure, contributing to an improved transistor performance. Moreover, this coplanar transistor with semiconductor–insulator bilayer structure is an ideal system for injecting charges into the insulator via gate‐stress, and the thus‐formed PS electret layer acts as a “nonuniform floating gate” to tune the threshold voltage and effective mobility of the transistors. Effective field‐effect mobility higher than 1 cm² V^?1 s^?1 with an on/off ratio > 10⁷ is realized, and the performances are comparable to those of commercial amorphous silicon transistors. This coplanar transistor simplifies the fabrication process of corresponding circuits.     

Investigation of Electrode Electrochemical Reactions in CH3NH3PbBr3 Perovskite Single‐Crystal Field‐Effect Transistors

Optoelectronic devices based on metal halide perovskites, including solar cells and light‐emitting diodes, have attracted tremendous research attention globally in the last decade. Due to their potential to achieve high carrier mobilities, organic–inorganic hybrid perovskite materials can enable high‐performance, solution‐processed field‐effect transistors (FETs) for next‐generation, low‐cost, flexible electronic circuits and displays. However, the performance of perovskite FETs is hampered predominantly by device instabilities, whose origin remains poorly understood. Here, perovskite single‐crystal FETs based on methylammonium lead bromide are studied and device instabilities due to electrochemical reactions at the interface between the perovskite and gold source–drain top contacts are investigated. Despite forming the contacts by a gentle, soft lamination method, evidence is found that even at such “ideal” interfaces, a defective, intermixed layer is formed at the interface upon biasing of the device. Using a bottom‐contact, bottom‐gate architecture, it is shown that it is possible to minimize such a reaction through a chemical modification of the electrodes, and this enables fabrication of perovskite single‐crystal FETs with high mobility of up to ≈15 cm² V^?1 s^?1 at 80 K. This work addresses one of the key challenges toward the realization of high‐performance solution‐processed perovskite FETs.     

Organic Ferroelectric‐Based 1T1T Random Access Memory Cell Employing a Common Dielectric Layer Overcoming the Half‐Selection Problem

Organic electronics based on poly(vinylidenefluoride/trifluoroethylene) (P(VDF‐TrFE)) dielectric is facing great challenges in flexible circuits. As one indispensable part of integrated circuits, there is an urgent demand for low‐cost and easy‐fabrication nonvolatile memory devices. A breakthrough is made on a novel ferroelectric random access memory cell (1T1T FeRAM cell) consisting of one selection transistor and one ferroelectric memory transistor in order to overcome the half‐selection problem. Unlike complicated manufacturing using multiple dielectrics, this system simplifies 1T1T FeRAM cell fabrication using one common dielectric. To achieve this goal, a strategy for semiconductor/insulator (S/I) interface modulation is put forward and applied to nonhysteretic selection transistors with high performances for driving or addressing purposes. As a result, high hole mobility of 3.81 cm² V^?1 s^?1 (average) for 2,6‐diphenylanthracene (DPA) and electron mobility of 0.124 cm² V^?1 s^?1 (average) for N ,N ′‐1H,1H‐perfluorobutyl dicyanoperylenecarboxydiimide (PDI‐FCN₂) are obtained in selection transistors. In this work, we demonstrate this technology's potential for organic ferroelectric‐based pixelated memory module fabrication.     

Metal‐Ion‐Modified Black Phosphorus with Enhanced Stability and Transistor Performance

Black phosphorus (BP), a burgeoning elemental 2D semiconductor, has aroused increasing scientific and technological interest, especially as a channel material in field‐effect transistors (FETs). However, the intrinsic instability of BP causes practical concern and the transistor performance must also be improved. Here, the use of metal‐ion modification to enhance both the stability and transistor performance of BP sheets is described. Ag⁺ spontaneously adsorbed on the BP surface via cation–π interactions passivates the lone‐pair electrons of P thereby rendering BP more stable in air. Consequently, the Ag⁺‐modified BP FET shows greatly enhanced hole mobility from 796 to 1666 cm² V^?1 s^?1 and ON/OFF ratio from 5.9 × 10⁴ to 2.6 × 10⁶. The mechanisms pertaining to the enhanced stability and transistor performance are discussed and the strategy can be extended to other metal ions such as Fe³⁺, Mg²⁺, and Hg²⁺. Such stable and high‐performance BP transistors are crucial to electronic and optoelectronic devices. The stability and semiconducting properties of BP sheets can be enhanced tremendously by this novel strategy.     

An All‐Solution‐Based Hybrid CMOS‐Like Quantum Dot/Carbon Nanotube Inverter

The development of low‐cost, flexible electronic devices is subordinated to the advancement in solution‐based and low‐temperature‐processable semiconducting materials, such as colloidal quantum dots (QDs) and single‐walled carbon nanotubes (SWCNTs). Here, excellent compatibility of QDs and SWCNTs as a complementary pair of semiconducting materials for fabrication of high‐performance complementary metal‐oxide‐semiconductor (CMOS)‐like inverters is demonstrated. The n‐type field effect transistors (FETs) based on I^? capped PbS QDs (V _th = 0.2 V, on/off = 10⁵, S _S‐th = 114 mV dec^?1, µ _e = 0.22 cm² V^?1 s^?1) and the p‐type FETs with tailored parameters based on low‐density random network of SWCNTs (V _th = ?0.2 V, on/off > 10⁵, S _S‐th = 63 mV dec^?1, µ _h = 0.04 cm² V^?1 s^?1) are integrated on the same substrate in order to obtain high‐performance hybrid inverters. The inverters operate in the sub‐1 V range (0.9 V) and have high gain (76 V/V), large maximum‐equal‐criteria noise margins (80%), and peak power consumption of 3 nW, in combination with low hysteresis (10 mV).     

Ultrahigh Responsivity in Graphene–ZnO Nanorod Hybrid UV Photodetector

Ultraviolet (UV) photodetectors based on ZnO nanostructure/graphene (Gr) hybrid‐channel field‐effect transistors (FETs) are investigated under illumination at various incident photon intensities and wavelengths. The time‐dependent behaviors of hybrid‐channel FETs reveal a high sensitivity and selectivity toward the near‐UV region at the wavelength of 365 nm. The devices can operate at low voltage and show excellent selectivity, high responsivity (R_I ), and high photoconductive gain (G). The change in the transfer characteristics of hybrid‐channel FETs under UV light illumination allows to detect both photovoltage and photocurrent. The shift of the Dirac point (V _Dirac) observed during UV exposure leads to a clearer explanation of the response mechanism and carrier transport properties of Gr, and this phenomenon permits the calculation of electron concentration per UV power density transferred from ZnO nanorods and ZnO nanoparticles to Gr, which is 9 × 10¹⁰ and 4 × 10¹⁰ per mW, respectively. The maximum values of R_I and G infer from the fitted curves of R_I and G versus UV intensity are 3 × 10⁵ A W^?1 and 10⁶, respectively. Therefore, the hybrid‐channel FETs studied herein can be used as UV sensing devices with high performance and low power consumption, opening up new opportunities for future optoelectronic devices.     

Direct Growth of Perovskite Crystals on Metallic Electrodes for High‐Performance Electronic and Optoelectronic Devices

Metal halide perovskite has attracted enhanced interest for its diverse electronic and optoelectronic applications. However, the fabrication of micro‐ or nanoscale crystalline perovskite functional devices remains a great challenge due to the fragility, solvent, and heat sensitivity of perovskite crystals. Here, a strategy is proposed to fabricate electronic and optoelectronic devices by directly growing perovskite crystals on microscale metallic structures in liquid phase. The well‐contacted perovskite/metal interfaces ensure these heterostructures serve as high‐performance field effect transistors (FETs) and excellent photodetector devices. When serving as an FET, the on/off ratio is as large as 10⁶ and the mobility reaches up to ≈2.3 cm² V^?1 s^?1. A photodetector is displayed with high photoconductive switching ratio of ≈10⁶ and short response time of ≈4 ms. Furthermore, the photoconductive response is proved to be band‐bending‐assisted separation of photoexcited carriers at the Schottky barrier of the silver and p‐type perovskites.     

Highly Flexible and Transparent Multilayer MoS2 Transistors with Graphene Electrodes

A highly flexible and transparent transistor is developed based on an exfoliated MoS₂ channel and CVD‐grown graphene source/drain electrodes. Introducing the 2D nanomaterials provides a high mechanical flexibility, optical transmittance (～74%), and current on/off ratio (>10⁴) with an average field effect mobility of ～4.7 cm² V^?1 s^?1, all of which cannot be achieved by other transistors consisting of a MoS₂ active channel/metal electrodes or graphene channel/graphene electrodes. In particular, a low Schottky barrier (～22 meV) forms at the MoS₂/graphene interface, which is comparable to the MoS₂/metal interface. The high stability in electronic performance of the devices upon bending up to ±2.2 mm in compressive and tensile modes, and the ability to recover electrical properties after degradation upon annealing, reveal the efficacy of using 2D materials for creating highly flexible and transparent devices.     

Organic High Electron Mobility Transistors Realized by 2D Electron Gas

A key breakthrough in inorganic modern electronics is the energy‐band engineering that plays important role to improve device performance or develop novel functional devices. A typical application is high electron mobility transistors (HEMTs), which utilizes 2D electron gas (2DEG) as transport channel and exhibits very high electron mobility over traditional field‐effect transistors (FETs). Recently, organic electronics have made very rapid progress and the band transport model is demonstrated to be more suitable for explaining carrier behavior in high‐mobility crystalline organic materials. Therefore, there emerges a chance for applying energy‐band engineering in organic semiconductors to tailor their optoelectronic properties. Here, the idea of energy‐band engineering is introduced and a novel device configuration is constructed, i.e., using quantum well structures as active layers in organic FETs, to realize organic 2DEG. Under the control of gate voltage, electron carriers are accumulated and confined at quantized energy levels, and show efficient 2D transport. The electron mobility is up to 10 cm² V^?1 s^?1, and the operation mechanisms of organic HEMTs are also argued. Our results demonstrate the validity of tailoring optoelectronic properties of organic semiconductors by energy‐band engineering, offering a promising way for the step forward of organic electronics.     

Novel Tunnel‐Contact‐Controlled IGZO Thin‐Film Transistors with High Tolerance to Geometrical Variability

Thin insulating layers are used to modulate a depletion region at the source of a thin‐film transistor. Bottom contact, staggered‐electrode indium gallium zinc oxide transistors with a 3 nm Al₂O₃ layer between the semiconductor and Ni source/drain contacts, show behaviors typical of source‐gated transistors (SGTs): low saturation voltage (V_{D_SAT} ≈ 3 V), change in V_{D_SAT} with a gate voltage of only 0.12 V V^?1, and flat saturated output characteristics (small dependence of drain current on drain voltage). The transistors show high tolerance to geometry: the saturated current changes only 0.15× for 2–50 µm channels and 2× for 9‐45 µm source‐gate overlaps. A higher than expected (5×) increase in drain current for a 30 K change in temperature, similar to Schottky‐contact SGTs, underlines a more complex device operation than previously theorized. Optimization for increasing intrinsic gain and reducing temperature effects is discussed. These devices complete the portfolio of contact‐controlled transistors, comprising devices with Schottky contacts, bulk barrier, or heterojunctions, and now, tunneling insulating layers. The findings should also apply to nanowire transistors, leading to new low‐power, robust design approaches as large‐scale fabrication techniques with sub‐nanometer control mature.     

Aluminum‐Ion‐Intercalation Supercapacitors with Ultrahigh Areal Capacitance and Highly Enhanced Cycling Stability: Power Supply for Flexible Electrochromic Devices

Electrochemical capacitor systems based on Al ions can offer the possibilities of low cost and high safety, together with a three‐electron redox‐mechanism‐based high capacity, and thus are expected to provide a feasible solution to meet ever‐increasing energy demands. Here, highly efficient Al‐ion intercalation into W₁₈O₄₉ nanowires (W₁₈O₄₉NWs) with wide lattice spacing and layered single‐crystal structure for electrochemical storage is demonstrated. Moreover, a freestanding composite film with a hierarchical porous structure is prepared through vacuum‐assisted filtration of a mixed dispersion containing W₁₈O₄₉NWs and single‐walled carbon nanotubes. The as‐prepared composite electrode exhibits extremely high areal capacitances of 1.11–2.92 F cm^?2 and 459 F cm^?3 at 2 mA cm^?2, enhanced electrochemical stability in the Al³⁺ electrolyte, as well as excellent mechanical properties. An Al‐ion‐based, flexible, asymmetric electrochemical capacitor is assembled that displays a high volumetric energy density of 19.0 mWh cm^?3 at a high power density of 295 mW cm^?3. Finally, the Al‐ion‐based asymmetric supercapacitor is used as the power source for poly(3‐hexylthiophene)‐based electrochromic devices, demonstrating their promising capability in flexible electronic devices.     

A Fermi‐Level‐Pinning‐Free 1D Electrical Contact at the Intrinsic 2D MoS2–Metal Junction

Currently 2D crystals are being studied intensively for use in future nanoelectronics, as conventional semiconductor devices face challenges in high power consumption and short channel effects when scaled to the quantum limit. Toward this end, achieving barrier‐free contact to 2D semiconductors has emerged as a major roadblock. In conventional contacts to bulk metals, the 2D semiconductor Fermi levels become pinned inside the bandgap, deviating from the ideal Schottky–Mott rule and resulting in significant suppression of carrier transport in the device. Here, MoS₂ polarity control is realized without extrinsic doping by employing a 1D elemental metal contact scheme. The use of high‐work‐function palladium (Pd) or gold (Au) enables a high‐quality p‐type dominant contact to intrinsic MoS₂, realizing Fermi level depinning. Field‐effect transistors (FETs) with Pd edge contact and Au edge contact show high performance with the highest hole mobility reaching 330 and 432 cm² V^?1 s^?1 at 300 K, respectively. The ideal Fermi level alignment allows creation of p‐ and n‐type FETs on the same intrinsic MoS₂ flake using Pd and low‐work‐function molybdenum (Mo) contacts, respectively. This device acts as an efficient inverter, a basic building block for semiconductor integrated circuits, with gain reaching 15 at V_D = 5 V.     

Diameter‐ and Metallicity‐Selective Enrichment of Single‐Walled Carbon Nanotubes Using Polymethacrylates with Pendant Aromatic Functional Groups

Current methods for the synthesis of single‐walled nanotubes (SWNTs) produce mixtures of semiconducting (sem‐) and metallic (met‐) nanotubes. Most approaches to the chemical separation of sem‐/met‐SWNTs are based on small neutral molecules or conjugated aromatic polymers, which characteristically have low separation/dispersion efficiencies or present difficulties in the postseparation removal of the polymer so that the resulting field‐effect transistors (FETs) have poor performance. In this Full Paper, the use of three polymethacrylates with different pendant aromatic functional groups to separate cobalt–molybdenum catalyst (CoMoCAT) SWNTs according to their metallicity and diameters is reported. UV/Vis/NIR spectroscopy indicates that poly(methyl‐methacrylate‐co‐fluorescein‐o‐acrylate) (PMMAFA) and poly(9‐anthracenylmethyl‐methacrylate) (PAMMA) preferentially disperse semiconducting SWNTs while poly(2‐naphthylmethacrylate) (PNMA) preferentially disperses metallic SWNTs, all in dimethylforamide (DMF). Photoluminescence excitation (PLE) spectroscopy indicates that all three polymers preferentially disperse smaller‐diameter SWNTs, particularly those of (6,5) chirality, in DMF. When chloroform is used instead of DMF, the larger‐diameter SWNTs (8,4) and (7,6) are instead selected by PNMA. The solvent effects suggest that diameter selectivity and change of polymer conformation is probably responsible. Change of the polymer fluorescence upon interaction with SWNTs indicates that metallicity selectivity presumably results from the photon‐induced dipole–dipole interaction between polymeric chromophore and SWNTs. Thin‐film FET devices using semiconductor‐enriched solution with PMMAFA have been successfully fabricated and the device performance confirms the sem‐SWNTs enrichment with a highly reproducible on/off ratio of about 10³.     

A Facile and Effective Method for Patching Sulfur Vacancies of WS2 via Nitrogen Plasma Treatment

Although transition metal dichalcogenides (TMDs) are attractive for the next‐generation nanoelectronic era due to their unique optoelectronic and electronic properties, carrier scattering during the transmission of electronic devices, and the distinct contact barrier between the metal and the semiconductors, which is caused by inevitable defects in TMDs, remain formidable challenges. To address these issues, a facile, effective, and universal patching defect approach that uses a nitrogen plasma doping protocol is developed, via which the intrinsic vacancies are repaired effectively. To reveal sulfur vacancies and the nature of the nitrogen doping effects, a high‐resolution spherical aberration corrected scanning transmission electron microscopy is used, which confirms the N atoms doping in sulfur vacancies. In this study, a typical TMD material, namely tungsten disulfide, is employed to fabricate field‐effect transistors (FETs) as a preliminary paradigm to demonstrate the patching defects method. This doping method endows FETs with high electrical performance and excellent contact interface properties. As a result, an electron mobility of up to 184.2 cm² V^?1 s^?1 and a threshold voltage of as low as 3.8 V are realized. This study provides a valuable approach to improve the performance of electronic devices that are based on TMDs in practical electronic applications.     

InAs Nanowire Devices with Strong Gate Tunability:Fundamental Electron Transport Properties and Application Prospects:A Review

The high electron mobility has granted indium arsenide(InAs) nanowires(NWs) as an important class of nanomaterials for high performance electronics such as field-effect transistors(FETs).We reviewed recent progresses on the studies of quantum coherence,gate tunable one-dimensional(1D) confinement and spin orbit interaction(SOI) in InAs NW based electronic and thermoelectric transport devices.We also demonstrated gas sensing response of InAs NW FETs and elucidated the mechanism via a gating experiment.By using InAs NWs as an example,these fundamental transport studies have shed important lights on the potential thermoelectric,spintronic and gas sensing applications of semiconductor NWs where the 1D confinement,SOI or surface states effects are exploited.     

25th Anniversary Article: Isoindigo‐Based Polymers and Small Molecules for Bulk Heterojunction Solar Cells and Field Effect Transistors

Driven by the potential advantages and promising applications of organic solar cells, donor‐acceptor (D‐A) polymers have been intensively investigated in the past years. One of the strong electron‐withdrawing groups that were widely used as acceptors for the construction of D‐A polymers for applications in polymer solar cells and FETs is isoindigo. The isoindigo‐based polymer solar cells have reached efficiencies up to ～7% and hole mobilities as high as 3.62 cm² V^?1 s^?1 have been realized by FETs based on isoindigo polymers. Over one hundred isoindigo‐based small molecules and polymers have been developed in only three years. This review is an attempt to summarize the structures and properties of the isoindigo‐based polymers and small molecules that have been reported in the literature since their inception in 2010. Focus has been given only to the syntheses and device performances of those polymers and small molecules that were designed for use in solar cells and FETs. Attempt has been made to deduce structure‐property relationships that would guide the design of isoindigo‐based materials. It is expected that this review will present useful guidelines for the design of efficient isoindigo‐based materials for applications in solar cells and FETs.     

Uniaxial Alignment of Conjugated Polymer Films for High‐Performance Organic Field‐Effect Transistors

Polymer semiconductors have been experiencing a remarkable improvement in electronic and optoelectronic properties, which are largely related to the recent development of a vast library of high‐performance, donor–acceptor copolymers showing alternation of chemical moieties with different electronic affinities along their backbones. Such steady improvement is making conjugated polymers even more appealing for large‐area and flexible electronic applications, from distributed and portable electronics to healthcare devices, where cost‐effective manufacturing, light weight, and ease of integration represent key benefits. Recently, a strong boost to charge carrier mobility in polymer‐based field‐effect transistors, consistently achieving the range from 1.0 to 10 cm² V^?1 s^?1 for both holes and electrons, has been given by uniaxial backbone alignment of polymers in thin films, inducing strong transport anisotropy and favoring enhanced transport properties along the alignment direction. Herein, an overview on this topic is provided with a focus on the processing–structure–property relationships that enable the controlled and uniform alignment of polymer films over large areas with scalable processes. The key aspects are specific molecular structures, such as planarized backbones with a reduced degree of conformational disorder, solution formulation with controlled aggregation, and deposition techniques inducing suitable directional flow.     

Development of ultra-high density silicon nanowire arrays for electronics applications

This article reviews our recent progress on ultra-high density nanowires (NWs) array-based electronics. The superlattice nanowire pattern transfer (SNAP) method is utilized to produce aligned, ultra-high density Si NW arrays. We fi rst cover processing and materials issues related to achieving bulk-like conductivity characteristics from 10 20 nm wide Si NWs. We then discuss Si NW-based fi eld-effect transistors (FETs). These NWs & NW FETs provide terrifi c building blocks for various electronic circuits with applications to memory, energy conversion, fundamental physics, logic, and others. We focus our discussion on complementary symmetry NW logic circuitry, since that provides the most demanding metrics for guiding nanofabrication. Issues such as controlling the density and spatial distribution of both p-and n-type dopants within NW arrays are discussed, as are general methods for achieving Ohmic contacts to both p-and n-type NWs. These various materials and nanofabrication advances are brought together to demonstrate energy effi cient, complementary symmetry NW logic circuits.