Recent advances in flexible and stretchable electronics (FSE), a technology diverging from the conventional rigid silicon technology, have stimulated fundamental scientific and technological research efforts. FSE aims at enabling disruptive applications such as flexible displays, wearable sensors, printed RFID tags on packaging, electronics on skin/organs, and Internet-of-things as well as possibly reducing the cost of electronic device fabrication. Thus, the key materials components of electronics, the semiconductor, the dielectric, and the conductor as well as the passive (substrate, planarization, passivation, and encapsulation layers) must exhibit electrical performance and mechanical properties compatible with FSE components and products. In this review, we summarize and analyze recent advances in materials concepts as well as in thin-film fabrication techniques for high-k (or high-capacitance) gate dielectrics when integrated with FSE-compatible semiconductors such as organics, metal oxides, quantum...

High- k Gate Dielectrics for Emerging Flexible and Stretchable Electronics

https://repository.tudelft.nl/islandora/object/uuid%3Ab12d4d79-67af-4177-b03c-88bfaa8b622d/datastream/OBJ/download

A review on suppression and utilization of the coffee-ring effect.

A Review of Low‐Temperature Solution‐Processed Metal Oxide Thin‐Film Transistors for Flexible Electronics

Direct printing of thin-film transistors has enormous potential for ubiquitous and lightweight wearable electronic applications. However, advances in printed integrated circuits remain very rare. Here we present a three-dimensional (3D) integration approach to achieve technology scaling in printed transistor density, analogous to Moore’s law driven by lithography, as well as enhancing device performance. To provide a proof of principle for the approach, we demonstrate the scalable 3D integration of dual-gate organic transistors on plastic foil by printing with high yield, uniformity, and year-long stability. In addition, the 3D stacking of three complementary transistors enables us to propose a programmable 3D logic array as a new route to design printed flexible digital circuitry essential for the emerging applications. The 3D monolithic integration strategy demonstrated here is applicable to other emerging printable materials, such as carbon nanotubes, oxide semiconductors and 2D semiconducting materials. The scalability of printable integrated circuits is lagging far behind that of conventional silicon-based technologies. Here, Kwon et al. show a three-dimensional integration approach by stacking printeddual-gate organic transistors on plastic foils with a density of 60 transistors per centimeter square.

https://oasis.postech.ac.kr/bitstream/2014.oak/95331/1/s41467-018-07904-5.pdf

Three-dimensional monolithic integration in flexible printed organic transistors.

Drop-on-demand inkjet printing is one of the most attractive techniques from a manufacturing perspective due to the possibility of fabrication from a digital layout at ambient conditions, thus leading to great opportunities for the realization of low-cost and flexible thin-film devices. Over the past decades, a variety of inkjet-printed applications including thin-film transistors (TFTs), radio-frequency identification devices, sensors, and displays have been explored. In particular, many research groups have made great efforts to realize high-performance TFTs, for application as potential driving components of ubiquitous wearable electronics. Although there are still challenges to enable the commercialization of printed TFTs beyond laboratory-scale applications, the field of printed TFTs still attracts significant attention, with remarkable developments in soluble materials and printing methodology. Here, recent progress in printing-based TFTs is presented from materials to applications. Significant efforts to improve the electrical performance and device-yield of printed TFTs to match those of counterparts fabricated using conventional deposition or photolithography methods are highlighted. Moreover, emerging low-dimension printable semiconductors, including carbon nanotubes and transition metal dichalcogenides as well as mature semiconductors, and new-concept printed switching devices, are also discussed.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/advs.201801445

Recent Progress in Inkjet‐Printed Thin‐Film Transistors

An array of inkjet-printed metal-oxide thin-film transistors (TFTs) is demonstrated for the first time with the assistance of surface-energy patterns prepared by printing pure solvent to etch the ultrathin hydrophobic layer. The surface-energy patterns not only restrained the spreading of inks but also provided a facile way to regulate the morphology of metal oxide films without optimizing ink formulation. The fully printed InGaO TFT devices in the array exhibited excellent electron transport characteristics with a maximum mobility of 11.7 cm2 V–1 s–1, negligible hysteresis, good uniformity, and good stability under bias stress. The new route lights a general way toward fully inkjet-printed metal-oxide TFT arrays.

All Inkjet-Printed Metal-Oxide Thin-Film Transistor Array with Good Stability and Uniformity Using Surface-Energy Patterns

Short-channel electronic devices several micrometers in length are difficult to implement by direct inkjet printing due to the limitation of position accuracy of the common inkjet printer system and the spread of functional ink on substrates. In this report, metal oxide thin-film transistors (TFTs) with channel lengths of 3.5 ± 0.7 μm were successfully fabricated with a common inkjet printer without any photolithography steps. Hydrophobic CYTOP coffee stripes, made by inkjet-printing and plasma-treating processes, were utilized to define the channel area of TFTs with channel lengths as short as ∼3.5 μm by dewetting the inks of the source/drain (S/D) precursors. Furthermore, by introduction of an ultrathin layer of PVA to modify the S/D surfaces, the spreading of precursor ink of the InOx semiconductor layer was well-controlled. The inkjet-printed short-channel TFTs exhibited a maximum mobility of 4.9 cm2 V–1 s–1 and an on/off ratio of larger than 109. This approach of fabricating short-channel TFTs by ink...

Coffee-Ring Defined Short Channels for Inkjet-Printed Metal Oxide Thin-Film Transistors.

Ultrasensitive and Highly Stretchable Multifunctional Strain Sensors with Timbre-Recognition Ability Based on Vertical Graphene

Thin-film transistors (TFTs) with neodymium-substituted indium oxide (InNdO) channel layer were demonstrated. The structural properties of the InNdO films as a function of annealing temperature have been analyzed using X-ray diffraction and transmission electron microscopy. The InNdO thin films showed polycrystalline nature when annealed at 450 °C with a lattice parameter (cubic cell) of 10.255 A, which is larger than the cubic In2O3 film (10.117 A). The high-resolution transmission electron microscopy and energy dispersive X-ray spectroscopy showed that no Nd2O3 clusters were found in the InNdO film, implying that Nd was incorporated into the In2O3 lattice. The InNdO TFTs annealed at 450 °C exhibited more excellent electrical properties with a high mobility of 20.4 cm2 V−1 s−1 and better electric bias stability compared to those annealed at 300 °C, which was attributed to the reduction of the scattering centers and/or charge traps due to the decrease of the |Nd3d5/254f4O2p−1⟩ electron configuration.

High-mobility thin film transistors with neodymium-substituted indium oxide active layer

Solution-processed neodymium-substituted indium oxide (InNdO) thin-film transistors (TFTs) based on gel-like aqueous precursors were fabricated with a surface-selective deposition technique associated with ultraviolet irradiation. The Nd concentration can be easily tuned by changing the ratio of Nd2O3 to In2O3 precursors. It was found that Nd played roles of suppressing grain growth, suppressing oxygen vacancy formation, and increasing the electrical stability of TFTs. The InNdO TFT with a Nd:In ratio of 0.02:1 exhibited a mobility of as high as 15.6 cm2 V−1 s−1 with improved stability under gate-bias stress.

Peixiong Gao

Papers

All Inkjet-Printed Metal-Oxide Thin-Film Transistor Array with Good Stability and Uniformity Using Surface-Energy Patterns

Coffee-Ring Defined Short Channels for Inkjet-Printed Metal Oxide Thin-Film Transistors.

Ultrasensitive and Highly Stretchable Multifunctional Strain Sensors with Timbre-Recognition Ability Based on Vertical Graphene

High-mobility thin film transistors with neodymium-substituted indium oxide active layer

Solution-processed high-mobility neodymium-substituted indium oxide thin-film transistors formed by facile patterning based on aqueous precursors