The development of highly sensitive pressure sensors with a low-cost and facile fabrication technique is desirable for electronic skins and wearable sensing devices. Here a low-cost and facile fabrication strategy to obtain multiscale-structured elastomeric electrodes and a highly sensitive and robust flexible pressure sensor is presented. The principles of spontaneous buckle formation of the PDMS surface and the embedding of silver nanowires are used to fabricate the multiscale-structured elastomeric electrode. By laminating the multiscale-structured elastomeric electrode onto the dielectric layer/bottom electrode template, the pressure sensor can be obtained. The pressure sensor is based on the capacitive sensing mechanism and shows high sensitivity (>3.8 kPa(-1)), fast response and relaxation time (<150 ms), high bending stability and high cycle stability. The fabrication process can be easily scaled up to produce pressure sensor arrays and they can detect the spatial distribution of the applied pressure. It is also demonstrated that the fingertip pressure sensing device can sense the pressure distribution of each finger, when grabbing an object.

Two-dimensional (2D) transition-metal dichalcogenides (TMDCs) have gained considerable attention as an emerging semiconductor due to their promising atomically thin film characteristics with good field-effect mobility and a tunable band gap energy. However, their electronic applications have been generally realized with conventional inorganic electrodes and dielectrics implemented using conventional photolithography or transferring processes that are not compatible with large-area and flexible device applications. To facilitate the advantages of 2D TMDCs in practical applications, strategies for realizing flexible and transparent 2D electronics using low-temperature, large-area, and low-cost processes should be developed. Motivated by this challenge, we report fully printed transparent chemical vapor deposition (CVD)-synthesized monolayer molybdenum disulfide (MoS) phototransistor arrays on flexible polymer substrates. All the electronic components, including dielectric and electrodes, were directly deposited with mechanically tolerable organic materials by inkjet-printing technology onto transferred monolayer MoS, and their annealing temperature of <180 °C allows the direct fabrication on commercial flexible substrates without additional assisted-structures. By integrating the soft organic components with ultrathin MoS, the fully printed MoS phototransistors exhibit excellent transparency and mechanically stable operation.

Development of highly sensitive pressure sensors that function well even in bending environments and operate at ultralow voltage is desirable for wearable applications. Here, a highly sensitive and bendable capacitive pressure sensor with the ability to distinguish pressure and bending stimuli and a pressure-sensitive transistor (PST) that can be easily integrated into wearable sensor system due to ultralow voltage (as low as 1 V for stable signal detection) operation is demonstrated. By introducing surface treatment and bonding technique, all components of the pressure sensor are tightly bonded to each other, enabling high bending stability. The sensor shows high pressure sensitivity (9.9 kPa −1 ) and can detect pressure even in the bending state. Additional bending sensors enables to separately detect signals from the actual pressure and bending deformation. In order to implement low-power sensor circuitry, the PST is fabricated by integrating the pressure sensor and inkjet-printing single-walled carbon nanotube thin film transistor. Such low-voltage operation of the PST enables to demonstrate the stand-alone wearable user-interactive pulse monitoring system by using commercially available electronic devices. The strategy for bendable low-power sensor may enable realization of wearable sensing system and electronic skins with low power consumption in near future.

High-performance all-inkjet-printed organic inverters are fabricated on flexible substrates. By introducing end-functionalized polystyrene on both surfaces of inkjet-printed source/drain Ag electrodes and poly(4-vinylphenol) dielectrics, organic-compatible and hydroxyl-free interfaces between those layers and 6,13-bis(triisopropylsilylethynyl)pentacene drastically reduce the interfacial trap and contact resistance. The resulting organic inverters show a full up-down switching performance and a high voltage gain of 19.8.

The electronic properties of solution-processable small-molecule organic semiconductors (OSCs) have rapidly improved in recent years, rendering them highly promising for various low-cost largearea electronic applications. However, practical applications of organic electronics require patterned and precisely registered OSC films within the transistor channel region with uniform electrical properties over a large area, a task that remains a significant challenge. Here, we present a technique termed "controlled OSC nucleation and extension for circuits" (CONNECT), which uses differential surface energy and solution shearing to simultaneously generate patterned and precisely registered OSC thin films within the channel region and with aligned crystalline domains, resulting in low device-to-device variability. We have fabricated transistor density as high as 840 dpi, with a yield of 99%. We have successfully built various logic gates and a 2-bit halfadder circuit, demonstrating the practical applicability of our technique for large-scale circuit fabrication.organic semiconductors | patterning | small molecules | transistors | circuits