Stretchable Transistors Research Articles

Carbon nanotube-based van der Waals heterojunction electrodes for high-performance intrinsically stretchable organic photoelectric transistors

Intrinsically stretchable organic field-effect transistors (STOFETs) that behave much like skin, have garnered widespread attention and demonstrated potential to more comfortable wearing electronics. Despite considerable efforts being exerted in stretchable hybrid polymeric semiconductors to achieve high-mobility and high-stretchability STOFETs, carbon nanotubes (CNTs) as ideal electrode materials, its interfacial quality seldom attracts research interests. Herein, we demonstrate a novel and general strategy on flexible CNT-based heterojunction electrodes by pentacene modification layer to enable high-performance and functional STOFETs. Pentacene transition layer can reduce the surface roughness and tune the heterogeneity of functional groups on the CNT thin film, as well as enhance the compatibility and van der Waals contact between CNT electrodes and organic semiconductors. The experimental results reveal that the carrier mobility of the resulting STOFETs increases by 2-3 times and the subthreshold slope decreases by 5 times compared with unmodified devices. The on-current/off-current ratio reaches nearly 107, which is approximately 1000 times as high as unmodified devices, and the highest value for stretchable organic transistors reported so far. Furthermore, STOFETs with heterojunction electrodes demonstrate better performance homogeneity and higher strain-independent capability. Noteworthy, these are the first intrinsically stretchable organic phototransistors (STOPTs) with superior photoswitching performances and high strain tolerance developed.

Selection of Insulating Elastomers for High-Performance Intrinsically Stretchable Transistors

An insulating elastomer, as one of the indispensable components of skin-like electronic devices, significantly affects the mechanical and electrical properties of devices. However, the detailed inf...

Strain-insensitive intrinsically stretchable transistors and circuits

Intrinsically stretchable electronics can form intimate interfaces with the human body, creating devices that could be used to monitor physiological signals without constraining movement. However, mechanical strain invariably leads to the degradation of the electronic properties of the devices. Here we show that strain-insensitive intrinsically stretchable transistor arrays can be created using an all-elastomer strain engineering approach, in which the patterned elastomer layers with tunable stiffnesses are incorporated into the transistor structure. By varying the cross-linking density of the elastomers, areas of increased local stiffness are introduced, reducing strain on the active regions of the devices. This approach can be readily incorporated into existing fabrication processes, and we use it to create arrays with a device density of 340 transistors cm–2 and a strain insensitivity of less than 5% performance variation when stretched to 100% strain. We also show that it can be used to fabricate strain-insensitive circuit elements, including NOR gates, ring oscillators and high-gain amplifiers for the stable monitoring of electrophysiological signals.

Recent advances in stretchable field-effect transistors

Recent advances in stretchable field-effect transistors have been reviewed, including stretchable material designs, structural designs, processing designs and their applications. Moreover, the challenges and outlook on stretchable field-effect transistors are discussed from different standpoints.

Stretchable transistors and functional circuits for human-integrated electronics

Stretchable transistors and functional circuits for human-integrated electronics

Regioregular, yet ductile and amorphous indacenodithiophene-based polymers with high-mobility for stretchable plastic transistors

Regioregular yet near-amorphous indacenodithiophene-based polymers exhibit superior deformability as well as high mobility values up to 1.67 cm2 V−1 s−1.

Facile Approach to Fabricating Stretchable Organic Transistors with Laser-Patterned Ag Nanowire Electrodes.

Stretchable electronics are poised to revolutionize personal healthcare and robotics, where they enable distributed and conformal sensors. Transistors are fundamental building blocks of electronics, and there is a need to produce stretchable transistors using low-cost and scalable fabrication techniques. Here, we introduce a facile fabrication approach using laser patterning and transfer printing to achieve high-performance, solution-processed intrinsically stretchable organic thin-film transistors (OTFTs). The device consists of Ag nanowire (NW) electrodes, where the source and drain electrodes are patterned using laser ablation. The Ag NWs are then partially embedded in a poly(dimethylsiloxane) (PDMS) matrix. The electrodes are combined with a PDMS dielectric and polymer semiconductor, where the layers are individually transfer printed to complete the OTFT. Two polymer semiconductors, DPP-DTT and DPP-4T, are considered and show stable operation under the cyclic strain of 20 and 40%, respectively. The OTFTs maintain electrical performance by adopting a buckled structure after the first stretch-release cycle. The conformability and stretchability of the OTFT is also demonstrated by operating the transistor while adhered to a finger being flexed. The ability to pattern highly conductive Ag NW networks using laser ablation to pattern electrodes as well as interconnects provides a simple strategy to produce complex stretchable OTFT-based circuits.

Substrate-free, stretchable electrolyte gated transistors

Abstract Improving device deformability under mechanical stress is an essential requirement for the realization of next-generation wearable electronic applications. Herein, we report a new concept of stretchable thin-film transistors (TFTs) that can be fabricated without substrate components. Instead of using plastic substrates, we employ an elastic (and also free-standing) solid-state electrolyte as a gate insulator. The strategy not only realizes stretchable TFTs, but also enhances the device performance (e.g. mobility, operation voltage) by the formation of high-capacitance electric double layers. As source-drain electrodes, semi-circular shaped gold (Au) thin-film was employed to enhance the device stretchability. By the combination of a solid electrolyte (gate insulator), metal film (electrodes), and polymer semiconductor (channel layer), the device is stretchable up to around 10%, and shows typical p-channel switching performance with low operation voltage of 1 V and TFT mobility of about 0.81 cm2/V s. The devices were processed by a simple solution process and thermal evaporation under low temperature (

Improvement in Mechanical Durability of Stretchable Charge-Trap Memory Transistors with Engineered Wavy-Dimensional Structures

Charge-trap memory thin-film transistors (CTM-TFTs) were fabricated with wavy-dimensional structures, and their device performances were demonstrated under mechanically stretching conditions. The f...

Fully stretchable active-matrix organic light-emitting electrochemical cell array

Intrinsically and fully stretchable active-matrix-driven displays are an important element to skin electronics that can be applied to many emerging fields, such as wearable electronics, consumer electronics and biomedical devices. Here, we show for the first time a fully stretchable active-matrix-driven organic light-emitting electrochemical cell array. Briefly, it is comprised of a stretchable light-emitting electrochemical cell array driven by a solution-processed, vertically integrated stretchable organic thin-film transistor active-matrix, which is enabled by the development of chemically-orthogonal and intrinsically stretchable dielectric materials. Our resulting active-matrix-driven organic light-emitting electrochemical cell array can be readily bent, twisted and stretched without affecting its device performance. When mounted on skin, the array can tolerate to repeated cycles at 30% strain. This work demonstrates the feasibility of skin-applicable displays and lays the foundation for further materials development.

Omnidirectionally Stretchable Organic Transistors for Use in Wearable Electronics: Ensuring Overall Stretchability by Applying Nonstretchable Wrinkled Components.

With the emergence of wearable human interface technologies, new applications based on stretchable electronics, such as skin-attached sensors or wearable displays, must be developed. Difficulties associated with developing electronic components with the high stretchabilities required for such applications have restricted the range of appearance and utilization of cost- or process-efficient stretchable electronics. Herein, we present omnidirectionally stretchable wrinkled transistors having a shape that replicates human skin, which operates stably on deformable objects or complex surfaces. Our device offers excellent mechanical and electrical stabilities for preserving relative field-effect mobilities within a standard deviation of nearly 5.6%, under a strain level of up to 62%. Even after 10 000 cycles of stretching to 60% strain, the devices exhibited stable operation with little performance changes. These results indicate that the devices display stretchability properties superior to those of organic transistor arrays by utilizing existing nonstretchable device components.

Tuning the Mechanical Properties of a Polymer Semiconductor by Modulating Hydrogen Bonding Interactions

Conjugation breakers (CBs) with different H-bonding chemistries and linker flexibilities are designed and incorporated into a diketopyrrolopyrrole (DPP)-based conjugated polymer backbone. The effects of H-bonding interactions on polymer semiconductor morphology, mechanical properties, and electrical performance are systematically investigated. We observe that CBs with an H-bonding self-association constant >0.7 or a denser packing tendency are able to induce higher polymer chain aggregation and crystallinity in as-casted thin films, resulting in a higher modulus and crack on-set strain. Additionally, the rDoC (relative degree of crystallinity) of the stretched thin film with the highest crack on-set strain only suffers a small decrease, suggesting the main energy dissipation mechanism is the breakage of H-bonding interactions. By contrast, other less stretchable polymer films dissipate strain energy through the breakage of crystalline domains, indicated by a drastic decrease in rDoC. Furthermore, we evaluate their electrical performances under mechanical strain in fully stretchable field-effect transistors. The polymer with the highest crack on-set strain has the least degradation in mobility as a function of strain. Overall, these observations suggest that we can aptly tune the mechanical properties of a polymer semiconductor by modulating intermolecular interactions, such as H-bonding chemistry and linker flexibility. Such understanding provides molecular design guidelines for future stretchable semiconductors.

F4‐TCNQ as an Additive to Impart Stretchable Semiconductors with High Mobility and Stability

AbstractNumerous strategies are developed to impart stretchability to polymer semiconductors. Although these methods improve the ductility, mobility, and stability of such stretchable semiconductors, they nonetheless still need further improvement. Here, it is shown that 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F4‐TCNQ) is an effective molecular additive to tune the properties of a diketopyrrolopyrrole‐based (DPP‐based) semiconductor. Specifically, the addition of F4‐TCNQ is observed to improve the ductility of the semiconductor by altering the polymer’s microstructures and dynamic motions. As a p‐type dopant additive, F4‐TCNQ can also effectively enhance the mobility and stability of the semiconductor through changing the host polymer’s packing structures and charge trap passivation. Upon fabricating fully stretchable transistors with F4‐TCNQ‐DPP blended semiconductor films, it is observed that the resulting stretchable transistors possess one of the highest initial mobility of 1.03 cm2 V−1 s−1. The fabricated transistors also exhibit higher stability (both bias and environmental) and mobility retention under repeated strain, compared to those without F4‐TCNQ additive. These findings offer a new direction of research on stretchable semiconductors to facilitate future practical applications.

Stretchable synaptic transistors with tunable synaptic behavior

Stretchable synaptic transistors (SSTs) are of paramount importance for the development of soft machines and neuromorphic systems. Unfortunately, the reports about SSTs are very limited and more importantly, the impact of the mechanical deformations that occur in stretchable electronics during practical applications, on the behavior of SSTs has never been reported. In this work, a simple and universal method was introduced to fabricate a stretchable organic synaptic transistor using wavy networks P3HT nanofibers as a semiconductor and the effect of mechanical deformation on its behavior at different deformation states is investigated for the first time. Our SSTs exhibited excellent mechanical stability even after experiencing large stretching deformation. More importantly, our results demonstrated that the learning and memory behavior, and the decay constants of synaptic transistors, which are among the most important parameters for biologic sensory neurons, can be tuned by mechanical deformation, which is associated with mechanical deformation dependant ion transport in ion-gel. These results offer a promising direction for utilizing mechanical deformation to develop different functional devices. Our SSTs with tunable synaptic behavior can facilitate the development of wearable and implantable artificial neuromorphic systems and soft machines. A stretchable organic synaptic transistor is demonstrated using wavy P3HT-NF as semiconductor. Stretchable synaptic transistor exhibits excellent mechanical stability and its behavior can be tuned by mechanical deformation via controlling the movement of ion in ion-gel. Our work shows the possibility of utilizing mechanical deformation to regulate electrical performance for stretchable devices and develop synapses with different decay constants and functionality. • A stretchable organic synaptic transistor with excellent mechanical stability using wavy poly(3-hexylthiophene) nanofibrils (P3HT-NF) as a semiconductor is demonstrated. • The stretchable synapse transistor exhibits a series of synaptic behavior and electrical performance at released states even after large stretching deformation. • Our works firstly demonstrated that the learning and memory behavior and the decay constants of synaptic transistors can be significantly impacted by mechanical deformation, offering another degree of freedom to manipulate the electronic properties of synaptic transistors.

Preparation and Application of Organic-Inorganic Nanocomposite Materials in Stretched Organic Thin Film Transistors.

High-transparency soluble polyimide with COOH and fluorine functional groups and TiO2-SiO2 composite inorganic nanoparticles with high dielectric constants were synthesized in this study. The polyimide and inorganic composite nanoparticles were further applied in the preparation of organic-inorganic hybrid high dielectric materials as the gate dielectric for a stretchable transistor. The optimal ratio of organic and inorganic components in the hybrid films was investigated. In addition, Jeffamine D2000 and polyurethane were added to the gate dielectric to improve the tensile properties of the organic thin film transistor (OTFT) device. PffBT4T-2OD was used as the semiconductor layer material and indium gallium liquid alloy as the upper electrode. Electrical property analysis demonstrated that the mobility could reach 0.242 cm2·V−1·s−1 at an inorganic content of 30 wt.%, and the switching current ratio was 9.04 × 103. After Jeffamine D2000 and polyurethane additives were added, the mobility and switching current could be increased to 0.817 cm2·V−1·s−1 and 4.27 × 105 for Jeffamine D2000 and 0.562 cm2·V−1·s−1 and 2.04 × 105 for polyurethane, respectively. Additives also improved the respective mechanical properties. The stretching test indicated that the addition of polyurethane allowed the OTFT device to be stretched to 50%, and the electrical properties could be maintained after stretching 150 cycles.

Thin‐Film Transistors: Polyvinyl Alcohol/SiO2 Hybrid Dielectric for Transparent Flexible/Stretchable All‐Carbon‐Nanotube Thin‐Film‐Transistor Integration (Adv. Electron. Mater. 5/2020)

By adopting polyvinyl alcohol/SiO2 hybrid layer as dielectric and carbon nanotubes as channel and source/drain/gate, high-performance flexible and stretchable thin-film transistors are realized by Min Zhang and co-workers in article number 1901133 using only traditional photolithography-etching and low-temperature solution processing. The fabricated devices could push many soft application scenarios a step forward.

Stretchable and Healable Bioelectronics

Organic electronics, based on semiconducting and conducting polymers, have been extensively investigated in the past decades and have found commercial applications in lighting panels, smartphone and TV screens using OLEDs (organic light emitting diodes) technology. Many other applications are foreseen to reach the commercial maturity in future in areas such as transistors, sensors and photovoltaics.Organic electronic devices, apart from consumer applications, are paving the path for key applications at the interface between electronics and biology, such as in polymer electrodes for recording and stimulating neural activity in neurological diseases. In such applications, organic polymers are very attractive candidates due to their distinct property of mixed conduction: the ability to transport both electron/holes and ionic species. Additionally, conducting polymers offer the possibility to tune their surface properties (e.g., wettability or chemical reactivity) by changing their oxidation state, thus promoting or hindering the adhesion of biomolecules. This feature can be particularly useful for enhancing the biocompatibility of implantable electrodes.My talk will deal with processing and characterization of conducting polymer films and devices for flexible, stretchable and healable electronics as well as for implantable electrodes.Our group fabricated water-stable and flexible organic electrochemical transistors based on poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate) (PEDOT:PSS) on a plastic substrate using a new process based on a fluorinated photoresist. The PEDOT:PSS films, mixed solely with a biocompatible conductivity enhancer, show robust adhesion on plastic substrates, and exhibit unchanged electrical properties under extreme bending. This simplifies the fabrication of high-performance OECTs and places them in a highly competitive position for flexible electronics and healthcare applications.The fabrication of stretchable electronic devices is presently rather challenging due to both the limited number of materials showing the desired combination of mechanical and electrical properties and the lack of techniques to process and pattern them. My group reported on transfer patterning process to fabricate high-resolution metal microelectrodes on polydimethylsiloxane (PDMS) by using ultrathin Parylene films (2 μm thick). By combining transfer patterning of metal electrodes with orthogonal patterning of PEDOT:PSS on a pre-stretched PDMS substrate and a biocompatible “cut and paste” hydrogel, we demonstrated fully stretchable organic electrochemical transistors, relevant for wearable electronics, biosensors and surface electrodes to monitor body conditions.Self-healing electronic materials are highly relevant for application in biology and sustainable electronics. We observed mechanical and electrical healability of PEDOT:PSS thin films. Upon reaching a certain thickness (about 1 µm), PEDOT:PSS thin films damaged with a sharp blade can be healed by simply wetting the damaged area with water. The process is rapid, with a response time on the order of 150 ms. Significantly, after being wetted, the films are transformed into autonomic self-healing materials without the need of external stimulation. This reveals a new property of PEDOT:PSS and enables its immediate use in flexible and biocompatible electronics, such as electronic skin and bio-implanted electronics, placing conducting polymers on the front line for healing applications in bioelectronics.We have recently electropolymerized PEDOT coatings on sharp platinum-iridium recording and stimulating neural electrodes and demonstrated its mechanical and electrochemical stability Electropolymerization of PEDOT:tetrafluoroborate was carried out in three different solvents: propylene carbonate, acetonitrile and water. The stability of the coatings was assessed via ultrasonication, phosphate buffer solution soaking test, autoclave sterilization and electrical pulsing. Coatings prepared with propylene carbonate or acetonitrile possessed excellent electrochemical stability and survived autoclave sterilization, prolonged soaking and electrical stimulation without major changes in electrochemical properties. Stimulating microelectrodes were implanted in for 60 days. The electrochemical properties monitored in vivo demonstrated that coated electrodes show lower impedance and higher stability over time.

Polyvinyl Alcohol/SiO2 Hybrid Dielectric for Transparent Flexible/Stretchable All‐Carbon‐Nanotube Thin‐Film‐Transistor Integration

AbstractFlexible and stretchable electronic (FSE) transistors create various novel applications. Carbon nanotubes possess high intrinsic mobility and exceptional mechanical and optical characteristics, which lead to a great potential as channel and electrodes in FSE transistors. At the same time, gate dielectric is also required to be intrinsically flexible/stretchable and integratable. However, few high‐performance solutions have been reported. By adopting polyvinyl alcohol (PVA)/SiO2 hybrid layer as dielectric, the integration of high‐performance intrinsically flexible/stretchable carbon‐nanotube‐based thin film transistors is proposed and realized simply by traditional photolithography‐etching and low‐temperature solution processes. The PVA/SiO2 dielectric simultaneously provides a relatively high‐k value, improves the carrier conduction interface, increases the carbon nanotube (CNT) density, and protects the PVA from plasma damage. Soft transistors with carbon nanotube channel and electrodes exhibit carrier mobility of 14 cm2 V−1 s−1 within an operation voltage of 0.3 V. These transistors show a small bending radius of 3 mm, and the stretchable transistors can withstand 50% strain with no significant electrical degradation observed, when measured in situ and along different directions for more than 1000 cycles. This work provides a solution for soft transparent transistor integration, indicating promising applicability to soft circuits, displays, and wearable electronics.

Communication—High Fidelity All-Carbon Based Carbon Nanotube Thin Film Transistors

This work reports transfer curve characterization, capacitance-voltage measurement, bias stress test, bending and stretching tests of the high fidelity flexible and stretchable thin-film transistors constructed on unsorted single-walled carbon nanotubes drain-source-gate electrodes, sorted semiconducting single-walled carbon nanotubes thin film active layer, and nonpolar styrene−ethylene−butadiene−styrene (SEBS) hydrogenated elastomer dielectric and substrate. The air-stable, hysteresis-less, negligible threshold shift under bias stress test, stable performance during bending, and slightly current density changes under stretching strains of these all-carbon based thin-film transistors qualify for basic elements applicable in industrial flexible and stretchable electronics.

Intrinsically stretchable all-carbon-nanotube transistors with styrene-ethylene-butylene-styrene as gate dielectrics integrated by photolithography-based process.

In recent years, stretchable electronics have attracted great attention because of their broad application prospects such as in the field of wearable electronics, skin-like electronics, medical transplantation and human–machine interaction. Intrinsically stretchable transistors have advantages in many aspects. However, integration of intrinsically stretchable layers to achieve stretchable transistors is still challenging. In this work, we combine the excellent electrical and mechanical properties of carbon nanotubes with excellent dielectric and mechanical properties of styrene–ethylene–butylene–styrene (SEBS) to realize intrinsically stretchable thin film transistors (TFTs). This is the first time that all the intrinsically stretchable components have been combined to realize multiple stretchable TFTs in a batch by photolithography-based process. In this process, a plasma resistant layer has been introduced to protect the SEBS dielectric from being damaged during the etching process so that the integration can be achieved. The highly stretchable transistors show a high carrier mobility of up to 10.45 cm2 V−1 s−1. The mobility maintains 2.01 cm2 V−1 s−1 even after the transistors are stretched by over 50% for more than 500 times. Moreover, the transistors have been scaled to channel length and width of 56 μm and 20 μm, respectively, which have a higher integration level. The stretchable transistors have light transmittance of up to 60% in the visible range. The proposed method provides an optional solution to large-scale integration for stretchable electronics.