Organic Transistor Arrays Research Articles

Self‐Encapsulated N‐Type Semiconducting Photoresist Toward Complementary Organic Electronics

AbstractSemiconducting photoresists hold great promise for scale‐up manufacturing of organic field‐effect transistors (OFETs) for integrated organic electronics. While photolithographic p‐type OFETs have achieved a considerable balance among patterning precision, electrical properties and process stability, it remains challenging for n‐type OFETs due to the inherent limited mobility and ambient instability. Herein, a n‐type semiconducting photoresist (SPr) is developed that is compatible with photolithography procedures. By utilizing the solvent‐driven force, a self‐encapsulated blend film with gradient semiconductor phase is prepared, where the underneath transistor active layer is protected by the upper cross‐linked network, avoiding solvent erosion and air doping. As such, a mobility up to 1.1 cm2 V−1 s−1 that is comparable with amorphous Si is achieved, with remained mobility by ≈90% after long‐term exposure to developer and stripper or atmospheric conditions. The sub‐micrometer patterning accuracy of SPr enables the fabrication of organic transistor arrays with a density of 9 × 105 units cm−1, which is comparable to other state‐of‐the‐art devices fabricated by the printing or photolithography, demonstrating immense potential in integrated organic electronics.

A detachable interface for stable low-voltage stretchable transistor arrays and high-resolution X-ray imaging

Challenges associated with stretchable optoelectronic devices, such as pixel size, power consumption and stability, severely brock their realization in high-resolution digital imaging. Herein, we develop a universal detachable interface technique that allows uniform, damage-free and reproducible integration of micropatterned stretchable electrodes for pixel-dense intrinsically stretchable organic transistor arrays. Benefiting from the ideal heterocontact and short channel length (2 μm) in our transistors, switching current ratio exceeding 106, device density of 41,000 transistors/cm2, operational voltage down to 5 V and excellent stability are simultaneously achieved. The resultant stretchable transistor-based image sensors exhibit ultrasensitive X-ray detection and high-resolution imaging capability. A megapixel image is demonstrated, which is unprecedented for stretchable direct-conversion X-ray detectors. These results forge a bright future for the stretchable photonic integration toward next-generation visualization equipment.

All-Photolithography Fabrication of Ion-Gated Flexible Organic Transistor Array for Multimode Neuromorphic Computing.

Organic ion-gated transistors (OIGTs) demonstrate commendable performance for versatile neuromorphic systems. However, due to the fragility of organic materials to organic solvents, efficient and reliable all-photolithography methods for scalable manufacturing of high-density OIGT arrays with multimode neuromorphic functions are still missing, especially when all active layers are patterned in high-density. Here, a flexible high-density (9662 devices per cm2) OIGT array with high yield and minimal device-to-device variation is fabricated by a modified all-photolithography method. The unencapsulated flexible array can withstand 1000 times' bending at a radius of 1mm, and 3 months' storage test in air, without obvious performance degradation. More interesting, the OIGTs can be configured between volatile and nonvolatile modes, suitable for constructing reservoir computing systems to achieve high accuracy in classifying handwritten digits with low training costs. This work proposes a promising design of organic and flexible electronics for affordable neuromorphic systems, encompassing both array and algorithm aspects.

Triboelectric Potential Powered High-Performance Organic Transistor Array.

Triboelectric potential gated transistors have inspired various applications toward mechanical behavior controlled logic circuits, multifunctional sensors, artificial sensory neurons, etc. Their rapid development urgently calls for high-performance devices and corresponding figure of merits to standardize the tribotronic gating properties. Organic semiconductors paired with solution processability promise low-cost manufacture of high-performance tribotronic transistor devices/arrays. Here, we demonstrate a record high-performance tribotronic transistor array composed of an integrated triboelectric nanogenerator (TENG) and a large-area device array of C8-BTBT-PS transistors. The working mechanism of effective triboelectric potential gating is elaborately explained from the aspect of conjugated energy bands of the contact-electrification mediums and organic semiconductors. Driven by the triboelectric potential, the tribotronic transistor shows superior properties of record high current on/off ratios (>108), a steep subthreshold swing (29.89 μm/dec), high stability, and excellent reproducibility. Moreover, tribotronic logic devices modulated by mechanical displacement have also been demonstrated with good stability and a high gain of 1260 V/mm. The demonstrated large-area tribotronic transistor array of organic semiconductor exhibits record high performance and offers an effective R&D platform for mechano-driven electronic terminals, interactive intelligent system, artificial robotic skin, etc.

Flexible organic transistors for neural activity recording

Flexible electronics capable of interacting with biological tissues, and acquiring and processing biological information, are increasingly demanded to capture the dynamic physiological processes, understand the living organisms, and treat human diseases. Neural interfaces with a high spatiotemporal resolution, extreme mechanical compliance, and biocompatibility are essential for precisely recording brain activity and localizing neuronal patterns that generate pathological brain signals. Organic transistors possess unique advantages in detecting low-amplitude signals at the physiologically relevant time scales in biotic environments, given their inherent amplification capabilities for in situ signal processing, designable flexibility, and biocompatibility features. This review summarizes recent progress in neural activity recording and stimulation enabled by flexible and stretchable organic transistors. We introduce underlying mechanisms for multiple transistor building blocks, followed by an explicit discussion on effective design strategies toward flexible and stretchable organic transistor arrays with improved signal transduction capabilities at the transistor/neural interfaces.

Photolithographic High‐Conductivity Transparent Conformal rGO/PEDOT:PSS Electrodes for Flexible Skin‐Like All Solution‐Processed Organic Transistors

AbstractReduced graphene oxide (rGO) electrodes are known to exhibit high transparency, excellent chemical stability, low‐cost solution processability, and good compatibility for use in solution‐processed organic transistors, but they face fundamental challenges in conductivity and conformability for skin‐like electronics. Here, by inserting a poly(3,4‐ethylenedioxythiophene):poly‐(styrenesulfonate) (PEDOT:PSS) layer, the photolithographic conformal rGO/PEDOT:PSS electrodes with conductivity as high as 2000 S cm−1 can be achieved. Simultaneously, the rGO/PEDOT:PSS hybrid electrodes exhibit high precision down to 1 µm, high transparency of >90% over the visible spectra (400–700 nm), and imperceptible adherence onto damselfly wing without affecting flying. The resulting all‐solution processed organic transistor array presents the enhanced modulation effect of the gate voltage on current, 5.5‐fold increased mobility, and the on‐state current increased by one order of magnitude compared with the neat rGO electrode device, and shows the good adherence to deforming human skins and stable operation on the 10 mm spherical surface with mobility as high as 2.33 cm2 V−1 s−1. The strategy provides a high‐precision, high‐integration, flexible pattern‐designable, and scalable route to produce the high‐conductive transparent conformal rGO/PEDOT:PSS hybrid electrodes for flexible skin‐like all solution‐processed organic transistor array, showing the outstanding potential for future low‐cost soft electronics.

Real‐Time Multi‐Ion Detection in the Sweat Concentration Range Enabled by Flexible, Printed, and Microfluidics‐Integrated Organic Transistor Arrays

AbstractOrganic electrochemical transistors (OECTs) show remarkable promise as biosensors, thanks to their high signal amplification, simple architecture, and the intrinsic flexibility of the organic material. Despite these properties, their use for real‐time sensing in complex biological fluids, such as human sweat, is strongly limited due to the lack of cross‐sensitivity and selectivity studies and the use of rigid and bulky device configurations. Here, the development of a novel flexible microfluidics‐integrated platform with an array of printed ion‐selective OECTs enables multi‐ion detection in a wearable fashion. This is achieved by coating the poly(3,4‐ethylene dioxythiophene):polystyrene sulfonate (PEDOT:PSS) channels of the transistors with three different ion‐selective membranes (ISMs). Systematic electrical and sensing analysis of the OECTs with ISMs show a minimal impact of the membranes on the electrical and time responses of the transistors while providing high ion selectivity. This work combines for the first time real‐time and selective multi‐ion detection with an array of inkjet‐printed and flexible organic transistors coated with different ISMs, demonstrating state‐of‐the‐art sensing capabilities of≈10µA dec−1for potassium, sodium, and pH. This flexible OECTs sensing platform paves the way to the next generation devices for continuous electrolytes monitoring in body fluids.

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.

A photolithographic stretchable transparent electrode for an all-solution-processed fully transparent conformal organic transistor array

A photolithographic stretchable transparent electrode comprising PEDOT:PSS and SWCNT was developed for an all-solution-processed transparent conformal organic transistor array.

Organic Transistors: Chemically Robust Ambipolar Organic Transistor Array Directly Patterned by Photolithography (Adv. Mater. 11/2017)

Organic Transistors: Chemically Robust Ambipolar Organic Transistor Array Directly Patterned by Photolithography (Adv. Mater. 11/2017)

Chemically Robust Ambipolar Organic Transistor Array Directly Patterned by Photolithography.

Organic ambipolar transistor arrays for chemical sensors are prepared on a flexible plastic substrate with a bottom-gate bottom-contact configuration to minimize the damage to the organic semiconductors, for the first time, using a photolithographically patternable polymer semiconductor. Well-balanced ambipolar charge transport is achieved by introducing graphene electrodes because of the reduced contact resistance and energetic barrier for electron transport.

Organic Transistor Arrays Integrated with Finger-Powered Microfluidics for Multianalyte Saliva Testing.

A compact multianalyte biosensing platform is reported, composed of an organic electrochemical transistor (OECT) microarray integrated with a pumpless "finger-powered" microfluidic, for quantitative screening of glucose, lactate, and cholesterol levels. A biofunctionalization method is designed, which provides selectivity towards specific metabolites as well as minimization of any background interference. In addition, a simple method is developed to facilitate multi-analyte sensing and avoid electrical crosstalk between the different transistors by electrically isolating the individual devices. The resulting biosensing platform, verified using human samples, offers the possibility to be used in easy-to-obtain biofluids with low abundance metabolites, such as saliva. Based on our proposed method, other types of enzymatic biosensors can be integrated into the array to achieve multiplexed, noninvasive, personalized point-of-care diagnostics.

Flexible All-organic, All-solution Processed Thin Film Transistor Array with Ultrashort Channel.

Shrinking the device dimension has long been the pursuit of the semiconductor industry to increase the device density and operation speed. In the application of thin film transistors (TFTs), all-organic TFT arrays made by all-solution process are desired for low cost and flexible electronics. One of the greatest challenges is how to achieve ultrashort channel through a cost-effective method. In our study, ultrashort-channel devices are demonstrated by direct inkjet printing conducting polymer as source/drain and gate electrodes without any complicated substrate’s pre-patterning process. By modifying the substrate’s wettability, the conducting polymer’s contact line is pinned during drying process which makes the channel length well-controlled. An organic TFT array of 200 devices with 2 μm channel length is fabricated on flexible substrate through all-solution process. The simple and scalable process to fabricate high resolution organic transistor array offers a low cost approach in the development of flexible and wearable electronics.

Large scale, flexible organic transistor arrays and circuits based on polyimide materials

Polyimide (PI) materials are lightweight, flexible, resistant strongly to heat and chemicals, and have been widely used in electronics industry such as working as electronic packaging materials in large-scale integrated circuits. In this letter, PI materials, for the first time, are introduced into organic field-effect transistors (OFETs) and circuits as insulator layers in order to be compatible with the photolithography process. Moreover, a novel method is developed to make the PI films strong enough to endure the critical processes of photolithography (e.g., the influence of developer on polyimide layer). Based on the intact PI insulator and the modified photolithographic technique, large scale, flexible transistor arrays and circuits were fabricated with high resolution and high performance (mobility up to 0.55cm2V−1s−1 for bottom-contact bottom-gate OFETs). It provides a new way for the fabrication of large-area organic devices and circuits beyond solution printed techniques, especially for the application of organic semiconductors with poor solubility, e.g., pentacene.

Lithography-free high-resolution organic transistor arrays on polymer substrate by low energy selective laser ablation of inkjet-printed nanoparticle film

Inkjet direct writing of functional materials provides a promising pathway towards realization of ultra-low-cost, large-area printed electronics, albeit at the expense of lowered resolution (∼20–50 μm). We demonstrate that selective laser sintering and ablation of inkjet-printed metal nanoparticles enables low-temperature metal deposition as well as high-resolution patterning. Combined with an air-stable carboxylate-functionalized polythiophene, all-inkjet-printed and laser-processed organic field effect transistors with micron to submicron critical feature resolution were fabricated in a fully maskless sequence, eliminating the need for any lithographic processes. All processing and characterization steps were carried out at plastic-compatible low temperatures and in air under ambient pressure.

Pentacene thin-film transistors with sol–gel derived amorphous Ba 0.6Sr 0.4TiO 3 gate dielectric

An amorphous Ba 0.6Sr 0.4TiO 3 (BST) film with the thickness of 200 nm was deposited on indium-tin-oxide (ITO)-coated glass substrate through sol–gel route and post-annealing at 500 °C. The dielectric constant of the BST film was determined to be 20.6 at 100 kHz by measuring the Ag/BST/ITO parallel plate capacitor, and no dielectric tunability was observed with the bias voltage varying from −5 to 5 V. The BST film shows a dense and uniform microstructure as well as a smooth surface with the root-mean-square (RMS) roughness of about 1.4 nm. The leakage current density was found to be 3.5 × 10 −8 A/cm 2 at an applied voltage of −5 V. The transmittance of the BST/ITO/glass structure is more than 70% in the visible region. Pentacene based transistor using the as-prepared BST film as gate insulator exhibits a low threshold voltage of −1.3 V, the saturation field-effect mobility of 0.68 cm 2/Vs, and the current on/off ratio of 3.6 × 10 5. The results indicate that the sol–gel derived BST film is a promising high- k gate dielectric for large-area transparent organic transistor arrays on glass substrate.