Wearable, Ultrawide-Range, and Bending-Insensitive Pressure Sensor Based on Carbon Nanotube Network-Coated Porous Elastomer Sponges for Human Interface and Healthcare Devices

Flexible and wearable pressure sensors have attracted a tremendous amount of attention due to their wider applications in human interfaces and healthcare monitoring. However, achieving accurate pressure detection and stability against external stimuli (in particular, bending deformation) over a wide range of pressures from tactile to body weight levels is a great challenge. Here, we introduce an ultrawide-range, bending-insensitive, and flexible pressure sensor based on a carbon nanotube (CNT) network-coated thin porous elastomer sponge for use in human interface devices. The integration of the CNT networks into three-dimensional microporous elastomers provides high deformability and a large change in contact between the conductive CNT networks due to the presence of micropores, thereby improving the sensitivity compared with that obtained using CNT-embedded solid elastomers. As electrical pathways are continuously generated up to high compressive strain (∼80%), the pressure sensor shows an ultrawide pressure sensing range (10 Pa to 1.2 MPa) while maintaining favorable sensitivity (0.01–0.02 kPa–1) and linearity (R2 ∼ 0.98). Also, the pressure sensor exhibits excellent electromechanical stability and insensitivity to bending-induced deformations. Finally, we demonstrate that the pressure sensor can be applied in a flexible piano pad as an entertainment human interface device and a flexible foot insole as a wearable healthcare and gait monitoring device

Oxide thin-film transistor-based vertically stacked complementary inverter for logic and photo-sensor operations

Numerous studies have addressed the utilization of oxide thin-film transistor (TFT)-based complementary logic circuits that are based on two-dimensional (2D) planar structures. However, there are fundamental limits to the 2D planar structured complementary logic circuits, such as a large dimension and a large parasitic resistance. This work demonstrated a vertically stacked three-dimensional complementary inverter composed of a p-channel tin monoxide (SnO) TFT and an n-channel indium-gallium-zinc oxide (IGZO) TFT. A bottom-gate p-channel SnO TFT was formed on the top-gate n-channel IGZO TFT with a shared common gate electrode. The fabricated vertically stacked complementary inverter exhibited full swing characteristics with a voltage gain of ~33.6, a high noise margin of 3.13 V, and a low noise margin of 3.16 V at a supplied voltage of 10 V. The achieved voltage gain of the fabricated complementary inverter was higher than that of the vertically stacked complementary inverters composed of other oxide TFTs in previous works. In addition, we showed that the vertically stacked complementary inverter exhibited excellent visible-light photoresponse. This indicates that the oxide TFT-based vertically stacked complementary inverter can be used as a sensitive photo-sensor operating in the visible spectral range with the voltage read-out scheme

High-Sensitivity and Low-Power Flexible Schottky Hydrogen Sensor Based on Silicon Nanomembrane

High-performance and low-power flexible Schottky diode-based hydrogen sensor was developed. The sensor was fabricated by releasing Si nanomembrane (SiNM) and transferring onto a plastic substrate. After the transfer, palladium (Pd) and aluminum (Al) were selectively deposited as a sensing material and an electrode, respectively. The top-down fabrication process of flexible Pd/SiNM diode H₂ sensor is facile compared to other existing bottom-up fabricated flexible gas sensors while showing excellent H₂ sensitivity (Δ<i>I</i>/<i>I</i>₀ > 700–0.5% H₂ concentrations) and fast response time (τ_10–90 = 22 s) at room temperature. In addition, selectivity, humidity, and mechanical tests verify that the sensor has excellent reliability and robustness under various environments. The operating power consumption of the sensor is only in the nanowatt range, which indicates its potential applications in low-power portable and wearable electronics

High-Sensitivity and Low-Power Flexible Schottky Hydrogen Sensor Based on Silicon Nanomembrane

High-performance and low-power flexible Schottky diode-based hydrogen sensor was developed. The sensor was fabricated by releasing Si nanomembrane (SiNM) and transferring onto a plastic substrate. After the transfer, palladium (Pd) and aluminum (Al) were selectively deposited as a sensing material and an electrode, respectively. The top-down fabrication process of flexible Pd/SiNM diode H₂ sensor is facile compared to other existing bottom-up fabricated flexible gas sensors while showing excellent H₂ sensitivity (Δ<i>I</i>/<i>I</i>₀ > 700–0.5% H₂ concentrations) and fast response time (τ_10–90 = 22 s) at room temperature. In addition, selectivity, humidity, and mechanical tests verify that the sensor has excellent reliability and robustness under various environments. The operating power consumption of the sensor is only in the nanowatt range, which indicates its potential applications in low-power portable and wearable electronics

Wide Range-Sensitive, Bending-Insensitive Pressure Detection and Application to Wearable Healthcare Device

This paper reports a wide range-sensitive, bending-insensitive pressure sensor based on a carbon nanotube (CNT)-coated porous elastomer for a wearable healthcare application. (1) Sensing performance was evaluated over ~1MPa, which includes whole human tactile and body weight levels. The sensor exhibits a very wide sensing range from ultralow to high pressure (50Pa-1MPa) with maintenance of favorable sensitivity and reliable dynamic responses. (2) To our knowledge this is the first to investigate bending-insensitivity of the CNTs-coated porous PDMS, which facilitates accurate detection of normal pressures even on curved surfaces like human skins. (3) Finally, we demonstrated a foot insole for real-time monitoring of foot plantar pressure distribution

Extremely Robust and Patternable Electrodes for Copy-Paper-Based Electronics

We propose a fabrication process for extremely robust and easily patternable silver nanowire (AgNW) electrodes on paper. Using an auxiliary donor layer and a simple laminating process, AgNWs can be easily transferred to copy paper as well as various other substrates using a dry process. Intercalating a polymeric binder between the AgNWs and the substrate through a simple printing technique enhances adhesion, not only guaranteeing high foldability of the electrodes, but also facilitating selective patterning of the AgNWs. Using the proposed process, extremely crease-tolerant electronics based on copy paper can be fabricated, such as a printed circuit board for a 7-segment display, portable heater, and capacitive touch sensor, demonstrating the applicability of the AgNWs-based electrodes to paper electronics

Extremely Robust and Patternable Electrodes for Copy-Paper-Based Electronics

We propose a fabrication process for extremely robust and easily patternable silver nanowire (AgNW) electrodes on paper. Using an auxiliary donor layer and a simple laminating process, AgNWs can be easily transferred to copy paper as well as various other substrates using a dry process. Intercalating a polymeric binder between the AgNWs and the substrate through a simple printing technique enhances adhesion, not only guaranteeing high foldability of the electrodes, but also facilitating selective patterning of the AgNWs. Using the proposed process, extremely crease-tolerant electronics based on copy paper can be fabricated, such as a printed circuit board for a 7-segment display, portable heater, and capacitive touch sensor, demonstrating the applicability of the AgNWs-based electrodes to paper electronics