Stretchable Thin-film Transistors Research Articles

Biomimetic wafer-scale alignment of tellurium nanowires for high-mobility flexible and stretchable electronics.

Flexible and stretchable thin-film transistors (TFTs) are crucial in skin-like electronics for wearable and implantable applications. Such electronics are usually constrained in performance owing to a lack of high-mobility and stretchable semiconducting channels. Tellurium, a rising semiconductor with superior charge carrier mobilities, has been limited by its intrinsic brittleness and anisotropy. Here, we achieve highly oriented arrays of tellurium nanowires (TeNWs) on various substrates with wafer-scale scalability by a facile lock-and-shear strategy. Such an assembly approach mimics the alignment process of the trailing tentacles of a swimming jellyfish. We further apply these TeNW arrays in high-mobility TFTs and logic gates with improved flexibility and stretchability. More specifically, mobilities over 100 square centimeters per volt per second and on/off ratios of ~104 are achieved in TeNW-TFTs. The TeNW-TFTs on polyethylene terephthalate can sustain an omnidirectional bending strain of 1.3% for more than 1000 cycles. Furthermore, TeNW-TFTs on an elastomeric substrate can withstand a unidirectional strain of 40% with no performance degradation.

Stretchable Thin-Film Transistors Based on Wrinkled Graphene and MoS2 Heterostructures.

Two-dimensional (2D) materials are outstanding candidates for stretchable electronics, but a significant challenge is their heterogeneous integration into stretchable geometries on soft substrates. Here, we demonstrate a strategy for stretchable thin film transistors (2D S-TFT) based on wrinkled heterostructures on elastomer substrates where 2D materials formed the gate, source, drain, and channel and characterized them with Raman spectroscopy and transport measurements. The 2D S-TFTs had initial mobility of 4.9 ± 0.7 cm2/(V s). The wrinkling reduced the strain transferred into the 2D materials by a factor of 50, allowing a substrate stretch of up to 23% that could be cycled thousands of times without electrical degradation. The stretch did not alter the mobility but did lead to strain-induced threshold voltage shifts by ΔVT = -1.9 V. These 2D S-TFTs form the foundation for stretchable integrated circuits and enable investigations of the impact of heterogeneous strain on electron transport.

Low-Voltage Intrinsically Stretchable Organic Transistor Amplifiers for Ultrasensitive Electrophysiological Signal Detection.

Stretchability is a prerequisite for electronic skin devices. However, state-of-the-art stretchable thin-film transistors do not possess sufficiently low operating voltages and good stability, significantly limiting their use in real-world biomedical applications. Herein, a van der Waals-controlling elastomer/carbon quantum dot interfacial polarization methodology is proposed to form a hybrid polymer dielectric with 620% tensile strain and large-area film uniformity (>A4 paper size). Using the hybrid polymer dielectrics, the prepared intrinsically stretchable organic thin-film transistors demonstrate a low operating voltage below 5V, 100% strain tolerance, and excellent operational stability, as well as a high on-current/off-current ratio of 105 and a steep subthreshold slope of 500mV dec-1 . Based on this device technology, an amplifier with a high gain of 90V V-1 among the highest values of reported stretchable transistors is realized. This amplifier is at the first time applied to detect human electrophysical signals with an output signal amplitude of over 0.2V, which even outperforms other types of the state-of-the-art organic amplifiers for human electrophysiology monitoring. This stretchable device technology sufficiently meets the safety and portability requirements of wearable biomedical applications, opening a new opportunity to e-skin with signal control and amplification capabilities.

The effect of substrate curvature on capacitance and transfer characteristics for thin film transistors on the surface of spheres

Conformable, flexible, and stretchable thin film transistors hold promise for ubiquitous and low-cost electronics. As part of the research endeavor toward this goal, the challenges associated with compatible materials and growth processes have been intensely studied. What is seldom considered, however, is how device electrostatics change as the physical form of devices change. In this report, we study how one would expect the current–voltage characteristics of thin film transistors to change as they are deformed on the surface of a sphere. We derive analogous equations to those derived in the gradual channel approximation to relate current to applied voltage for various spherical geometries. Combined with a finite-difference strategy to evaluate geometric capacitance, example current–voltage characteristics are calculated. The results demonstrate for certain deformations in this geometry, the behavior deviates from what one would expect using just the gradual channel approximation. For flexible electronics to be commercially viable, it must be predictable in any physical form. These results represent some of the first steps in a broader effort to quantify the relationship between device geometry and electrical behavior.

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 (

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.

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.

Printable carbon nanotube-based elastic conductors for fully-printed sub-1 V stretchable electrolyte-gated transistors and inverters

Single-walled carbon nanotube (SWCNT)-based hybrid electrodes are promising for fully-printed stretchable thin-film transistors and inverters.

(Invited) Superacid-Surfactant Exchange

Attaining aqueous solutions of individual single-walled carbon nanotubes is the critical first step for harnessing the extraordinary properties of these materials. However, current approaches cause structural damage and cuts the nanotubes into short pieces. In this talk, we will introduce an unexpectedly simple solution to this decade-old challenge by directly neutralizing a nanotube-superacid solution in the presence of a surfactant. This straightforward superacid-surfactant exchange (S2E) involves two simple solution-mixing steps that completely eliminate the need for both ultrasonication and ultracentrifugation. The result allows us to advance multiple fronts, including aqueous sorting of ultralong nanotubes and stretchable thin film transistors with high carrier mobility.

(Invited) Inkjet-Printed Stretchable Electronic Devices, Circuits, Sensors, and Displays

Stretchable electronic systems built on soft substrates offer more conformal surface coverage and better durability than flexible electronics, and have generated significant research interests recently for potential applications in wearable/implantable health monitoring and diagnostic devices, electronic skin for prosthesis or soft robotics, stretchable displays and many more. Nevertheless, the large-area and low-cost fabrication of high-performance intrinsically stretchable electronic devices has remained to be extremely challenging. In this talk, I will present our recent work on addressing the two major challenges faced by stretchable electronics - the development of intrinsically-stretchable electronic materials and the need for scalable fabrication processes. We have developed nanomaterials-based metal, semiconductor, and dielectric materials with superior electronic property, stretchability, and inter-layer adhesion. Such materials are formulated as electronic inks to allow highly uniform and scalable material patterning using a inkjet-printed process, allowing us to achieve intrinsically stretchable thin-film transistors (TFTs) and integrated logic circuits made entirely by printing on ultrathin elastic polydimethylsiloxane (PDMS) substrates. Electrical and mechanical characterizations reveal that the TFTs and logic circuits can withstand up to 100% tensile strain along either channel length or channel width directions for thousands of cycles while showing no noticeable degradation in electrical performance. In addition to the above, I will also present our work on printed stretchable sensors and displays for wearable electronics and soft robotics applications. Our platform may offer a new entry into more sophisticated stretchable electronic systems with monolithically integrated sensors, actuators, and displays, fabricated by scalable and low-cost methods for real-life applications.

Stretchable thin-film transistors with molybdenum disulfide channels and graphene electrodes.

Two-dimensional (2D) materials including graphene and transition metal dichalcogenides (TMDCs) have attracted great interest as new electronic materials, given their superior properties such as optical transparency, mechanical flexibility, and stretchability, especially for application in next-generation displays. In particular, the integration of graphene and TMDCs enables the implementation of 2D materials-based thin-film transistors (TFTs) in stretchable displays, given that TFTs are the fundamental element of various modern devices. In the present study, we demonstrate chemical-vapor-deposited molybdenum disulfide and graphene-based TFTs on a polymer substrate and investigate the electrical characteristics of TFTs under mechanical deformation to determine the stretchability of our devices. Furthermore, the mechanisms leading to TFT performance degradation are investigated, as they relate to the change in the contact resistance that is closely associated with the relative deformation of 2D materials under mechanical stress. Therefore, the synergetic integration of 2D materials with versatile electrical properties provides an important strategy for creating 2D materials-based stretchable TFTs, thus extending the excellent potential of 2D materials as innovative materials for stretchable active-matrix displays.

Fully Printed Stretchable Thin-Film Transistors and Integrated Logic Circuits

This paper reports intrinsically stretchable thin-film transistors (TFTs) and integrated logic circuits directly printed on elastomeric polydimethylsiloxane (PDMS) substrates. The printed devices utilize carbon nanotubes and a type of hybrid gate dielectric comprising PDMS and barium titanate (BaTiO3) nanoparticles. The BaTiO3/PDMS composite simultaneously provides high dielectric constant, superior stretchability, low leakage, as well as good printability and compatibility with the elastomeric substrate. Both TFTs and logic circuits can be stretched beyond 50% strain along either channel length or channel width directions for thousands of cycles while showing no significant degradation in electrical performance. This work may offer an entry into more sophisticated stretchable electronic systems with monolithically integrated sensors, actuators, and displays, fabricated by scalable and low-cost methods for real life applications.

Intrinsically stretchable and transparent thin-film transistors based on printable silver nanowires, carbon nanotubes and an elastomeric dielectric.

Thin-film field-effect transistor is a fundamental component behind various mordern electronics. The development of stretchable electronics poses fundamental challenges in developing new electronic materials for stretchable thin-film transistors that are mechanically compliant and solution processable. Here we report the fabrication of transparent thin-film transistors that behave like an elastomer film. The entire fabrication is carried out by solution-based techniques, and the resulting devices exhibit a mobility of ∼30 cm2 V−1 s−1, on/off ratio of 103–104, switching current >100 μA, transconductance >50 μS and relative low operating voltages. The devices can be stretched by up to 50% strain and subjected to 500 cycles of repeated stretching to 20% strain without significant loss in electrical property. The thin-film transistors are also used to drive organic light-emitting diodes. The approach and results represent an important progress toward the development of stretchable active-matrix displays.

Graphene-based conformal devices.

Despite recent progress in bendable and stretchable thin-film transistors using novel designs and materials, the development of conformal devices remains limited by the insufficient flexibility of devices. Here, we demonstrate the fabrication of graphene-based conformal and stretchable devices such as transistor and tactile sensor on a substrate with a convoluted surface by scaling down the device thickness. The 70 nm thick graphene-based conformal devices displayed a much lower bending stiffness than reported previously. The demonstrated devices provided excellent conformal coverage over an uneven animal hide surface without the need for an adhesive. In addition, the ultrathin graphene devices formed on the three-dimensionally curved animal hide exhibited stable electrical characteristics, even under repetitive bending and twisting. The advanced performance and flexibility demonstrated here show promise for the development and adoption of wearable electronics in a wide range of future applications.

Flexible and stretchable thin-film transistors based on molybdenum disulphide.

The outstanding physical and chemical properties of two-dimensional materials, which include graphene and transition metal dichalcogenides, have allowed significant applications in next generation electronics. In particular, atomically thin molybdenum disulphide (MoS2) is attracting widespread attention because of its large bandgap, effective carrier mobility, and mechanical strength. In addition, recent developments in large-area high-quality sample preparation methods via chemical vapour deposition have enabled the use of MoS2 in novel functional applications, such as flexible and stretchable electronic devices. In this perspective, we focus on the current progress in generating MoS2-based flexible and stretchable thin-film transistors. The reported virtues and novelties of MoS2 provide significant advantages for future flexible and stretchable electronics.

Graphene-based flexible and stretchable thin film transistors

Graphene has been attracting wide attention owing to its superb electronic, thermal and mechanical properties. These properties allow great applications in the next generation of optoelectronics, where flexibility and stretchability are essential. In this context, the recent development of graphene growth/transfer and its applications in field-effect transistors are involved. In particular, we provide a detailed review on the state-of-the-art of graphene-based flexible and stretchable thin film transistors. We address the principles of fabricating high-speed graphene analog transistors and the key issues of producing an array of graphene-based transistors on flexible and stretchable substrates. It provides a platform for future work to focus on understanding and realizing high-performance graphene-based transistors.

Silicone substrate with in situ strain relief for stretchable thin-film transistors

We have manufactured stretchable thin-film transistors and interconnects directly onto an engineered silicone matrix with localized and graded mechanical compliance. The fabrication only involves planar and standard processing. Brittle active device materials are patterned on non deformable elastomer regions (strain <1% at all times) while interconnects run smoothly from “stiff” to “soft” elastomer. Pentacene thin-film transistors sustain applied strain up to 13% without electrical degradation and mechanical fracture. This integrated approach opens promising options for the manufacture of physically adaptable and transformable circuitry.