Vacuum Tunneling Transistor with Nano Vacuum Chamber for Harsh Environments

A nano vacuum tube which consists of a vacuum transistor and a nano vacuum chamber was demonstrated. For the device, a vacuum region is an electron transport channel, and a vacuum is a tunneling barrier. Tilted angle evaporation was studied for the formation of the nano level vacuum chamber structure. This vacuum tube was ultraminiaturized with several tens of 10–18 L scale volume and 10–6 Torr of pressure. The device structure made it possible to achieve a high integration density and to sustain the vacuum state in various real operations. In particular, the vacuum transistor performed stably in extreme external environments because the tunneling mechanism showed a wide range of working stability. The vacuum was sustained well by the sealing layer and provided a defect-free tunneling junction. In tests, the high vacuum level was maintained for more than 15 months with high reliability. The Al sealing layer and tube structure can effectively block exposed light such as visible light and UV, enabling the stable operation of the tunneling transistor. In addition, it is estimated that the structure blocks approximately 5 keV of X-ray. The device showed stable operating characteristics in a wide temperature range of 100–390 K. Therefore, the vacuum tube can be used in a wide range of applications involving integrated circuits while resolving the disadvantages of a large volume in old vacuum tubes. Additionally, it can be an important solution for next-generation devices in various fields such as aerospace, artificial intelligence, and THz applications

High-Quality Microprintable and Stretchable Conductors for High-Performance 5G Wireless Communication

With the advent of 5G wireless and Internet of Things technologies, flexible and stretchable printed circuit boards (PCBs) should be designed to address all the specifications necessary to receive signal transmissions, maintaining the signal integrity, and providing electrical connections. Here, we propose a silver nanoparticle (AgNP)/silver nanowire (AgNW) hybrid conductor and high-quality microprinting technology for fabricating flexible and stretchable PCBs in high-performance 5G wireless communication. A simple and low-cost reverse offset printing technique using a commercial adhesive hand-roller was adapted to ensure high-resolution and excellent pattern quality. The AgNP/AgNW micropatterns were fabricated in various line widths, from 5 μm to 5 mm. They exhibited excellent pattern qualities, such as fine line spacing, clear edge definition and outstanding pattern uniformity. After annealing via intense pulsed light irradiation, they showed outstanding electrical resistivity (15.7 μΩ cm). Moreover, they could withstand stretching up to a strain of 90% with a small change in resistance. As a demonstration of their practical application, the AgNP/AgNW micropatterns were used to fabricate 5G communication antennas that exhibited excellent wireless signal processing at operating frequencies in the C-band (4–8 GHz). Finally, a wearable sensor fabricated with these AgNP/AgNW micropatterns could successfully detected fine finger movements in real time with excellent sensitivity

Stretchable Substrate Surface-Embedded Inkjet-Printed Strain Sensors for Design Customizable On-Skin Healthcare Electronics

Stretchable strain sensors have been proposed for personalized healthcare monitoring or human motion detection in a skin-mountable form factor. For customization and stretchable substrate-compatible low-temperature processing, various printing technologies have been utilized to fabricate strain sensors. Hydrophobic stretchable polymers and low viscosity conductive inks are typically used in printed high resolution strain sensor fabrications. However, directly printed strain sensors on hydrophobic stretchable substrates have shown limited printability in pattern continuity, spatial resolution, stretchability, and linearity. Therefore, there is still a need to develop a simple printing process that can fabricate high-resolution stretchable strain sensors for skin-mountable healthcare electronics. In this work, we developed a simple inkjet printing and substrate transfer process for stretchable strain sensors by optimizing a polymer coating layer for enhancing the printed pattern formation, spatial resolution, and substrate transfer efficiency simultaneously while maintaining the benefits of inkjet printing, such as customizability and large-area applicability. The printed stretchable strain sensors are embedded into a stretchable substrate, improving stretchability up to 45% of strain, which successfully detects various parts of our body, such as wrists, fingers, and arms. Further, the printing process scales down the sensors to 150 μm × 6 mm, and the miniaturization enables distinguishing subtle movements of different fingers

Inkjet-Printed Polyelectrolyte Seed Layer-Based, Customizable, Transparent, Ultrathin Gold Electrodes and Facile Implementation of Photothermal Effect

Recently, interest in transparent electrodes has been increasing in biomedical engineering applications for such as electro-optical hybrid neuro-technologies. However, conventional photolithography-based electrode fabrication methods have limited design customization and large-area applicability. For biomedical engineering applications, it is crucial that we can easily customize the electrode design for different patients over a large body area. In this paper, we propose a novel method to fabricate customization-friendly, transparent, ultrathin, gold microelectrodes using inkjet printing technology. Unlike with typical direct printing of conductive inks, we inkjet-printed a polymer nucleation-inducing seed layer, followed by mask-less vacuum deposition of ultrathin gold (<6 nm) to produce selectively, high-transparency electrodes in the predefined shapes of the inkjet-printed polymer. Owing to the design flexibility of inkjet printing, the transparent ultrathin gold electrodes can be highly efficient in design customization over a large area. Simultaneously, a layer of nonconductive gold islands is formed in the nonprinted region, and this nanostructured layer can implement a photothermal effect that offers versatility for novel biomedical applications. As a demonstration of the effectiveness of these transparent electrodes, and the facile implementation of the photothermal effect for biomedical applications, we successfully fabricated transparent resistive temperature detectors. We used these to directly sense the photothermal effect and to demonstrate their bioimaging capabilities

High-Quality Microprintable and Stretchable Conductors for High-Performance 5G Wireless Communication

With the advent of 5G wireless and Internet of Things technologies, flexible and stretchable printed circuit boards (PCBs) should be designed to address all the specifications necessary to receive signal transmissions, maintaining the signal integrity, and providing electrical connections. Here, we propose a silver nanoparticle (AgNP)/silver nanowire (AgNW) hybrid conductor and high-quality microprinting technology for fabricating flexible and stretchable PCBs in high-performance 5G wireless communication. A simple and low-cost reverse offset printing technique using a commercial adhesive hand-roller was adapted to ensure high-resolution and excellent pattern quality. The AgNP/AgNW micropatterns were fabricated in various line widths, from 5 μm to 5 mm. They exhibited excellent pattern qualities, such as fine line spacing, clear edge definition and outstanding pattern uniformity. After annealing via intense pulsed light irradiation, they showed outstanding electrical resistivity (15.7 μΩ cm). Moreover, they could withstand stretching up to a strain of 90% with a small change in resistance. As a demonstration of their practical application, the AgNP/AgNW micropatterns were used to fabricate 5G communication antennas that exhibited excellent wireless signal processing at operating frequencies in the C-band (4–8 GHz). Finally, a wearable sensor fabricated with these AgNP/AgNW micropatterns could successfully detected fine finger movements in real time with excellent sensitivity

Stretchable Substrate Surface-Embedded Inkjet-Printed Strain Sensors for Design Customizable On-Skin Healthcare Electronics

Stretchable strain sensors have been proposed for personalized healthcare monitoring or human motion detection in a skin-mountable form factor. For customization and stretchable substrate-compatible low-temperature processing, various printing technologies have been utilized to fabricate strain sensors. Hydrophobic stretchable polymers and low viscosity conductive inks are typically used in printed high resolution strain sensor fabrications. However, directly printed strain sensors on hydrophobic stretchable substrates have shown limited printability in pattern continuity, spatial resolution, stretchability, and linearity. Therefore, there is still a need to develop a simple printing process that can fabricate high-resolution stretchable strain sensors for skin-mountable healthcare electronics. In this work, we developed a simple inkjet printing and substrate transfer process for stretchable strain sensors by optimizing a polymer coating layer for enhancing the printed pattern formation, spatial resolution, and substrate transfer efficiency simultaneously while maintaining the benefits of inkjet printing, such as customizability and large-area applicability. The printed stretchable strain sensors are embedded into a stretchable substrate, improving stretchability up to 45% of strain, which successfully detects various parts of our body, such as wrists, fingers, and arms. Further, the printing process scales down the sensors to 150 μm × 6 mm, and the miniaturization enables distinguishing subtle movements of different fingers

Stretchable Substrate Surface-Embedded Inkjet-Printed Strain Sensors for Design Customizable On-Skin Healthcare Electronics

Stretchable strain sensors have been proposed for personalized healthcare monitoring or human motion detection in a skin-mountable form factor. For customization and stretchable substrate-compatible low-temperature processing, various printing technologies have been utilized to fabricate strain sensors. Hydrophobic stretchable polymers and low viscosity conductive inks are typically used in printed high resolution strain sensor fabrications. However, directly printed strain sensors on hydrophobic stretchable substrates have shown limited printability in pattern continuity, spatial resolution, stretchability, and linearity. Therefore, there is still a need to develop a simple printing process that can fabricate high-resolution stretchable strain sensors for skin-mountable healthcare electronics. In this work, we developed a simple inkjet printing and substrate transfer process for stretchable strain sensors by optimizing a polymer coating layer for enhancing the printed pattern formation, spatial resolution, and substrate transfer efficiency simultaneously while maintaining the benefits of inkjet printing, such as customizability and large-area applicability. The printed stretchable strain sensors are embedded into a stretchable substrate, improving stretchability up to 45% of strain, which successfully detects various parts of our body, such as wrists, fingers, and arms. Further, the printing process scales down the sensors to 150 μm × 6 mm, and the miniaturization enables distinguishing subtle movements of different fingers

Enhancement of Interface Characteristics of Neural Probe Based on Graphene, ZnO Nanowires, and Conducting Polymer PEDOT

In the growing field of brain–machine interface (BMI), the interface between electrodes and neural tissues plays an important role in the recording and stimulation of neural signals. To minimize tissue damage while retaining high sensitivity, a flexible and a smaller electrode with low impedance is required. However, it is a major challenge to reduce electrode size while retaining the conductive characteristics of the electrode. In addition, the mechanical mismatch between stiff electrodes and soft tissues creates damaging reactive tissue responses. Here, we demonstrate a neural probe structure based on graphene, ZnO nanowires, and conducting polymer that provides flexibility and low impedance performance. A hybrid Au and graphene structure was utilized to achieve both flexibility and good conductivity. Using ZnO nanowires to increase the effective surface area drastically decreased the impedance value and enhanced the signal-to-noise ratio (SNR). A poly­[3,4-ethylenedioxythiophene] (PEDOT) coating on the neural probe improved the electrical characteristics of the electrode while providing better biocompatibility. In vivo neural signal recordings showed that our neural probe can detect clearer signals

Balancing Charge Carrier Transport in a Quantum Dot P–N Junction toward Hysteresis-Free High-Performance Solar Cells

In a quantum dot solar cell (QDSC) that has an inverted structure, the QD layers form two different junctions between the electron transport layer (ETL) and the other semiconducting QD layer. Recent work on an inverted-structure QDSC has revealed that the junction between the QD layers is the dominant junction, rather than the junction between the ETL and the QD layers, which is in contrast to the conventional wisdom. However, to date, there have been a lack of systematic studies on the role and importance of the QD heterojunction structure on the behavior of the solar cell and the resulting device performance. In this study, we have systematically controlled the structure of the QD junction to balance charge transport, which demonstrates that the position of the junction has a significant effect on the hysteresis effect, fill factor, and solar cell performance and is attributed to balanced charge transport