High-performance inkjet-printed four-terminal microelectromechanical relays and inverters

Lorentz Force-Actuated Bidirectional Nanoelectromechanical Switch with an Ultralow Operation Voltage

The high operating voltage of conventional nanoelectromechanical switches, typically tens of volts, is much higher than the driving voltage of the complementary metal oxide semiconductor integrated circuit (∼1 V). Though the operating voltage can be reduced by adopting a narrow air gap, down to several nanometers, this leads to formidable manufacturing challenges and occasionally irreversible switch failures due to the surface adhesive force. Here, we demonstrate a new nanowire-morphed nanoelectromechanical (NW-NEM) switch structure with ultralow operation voltages. In contrast to conventional nanoelectromechanical switches actuated by unidirectional electrostatic attraction, the NW-NEM switch is bidirectionally driven by Lorentz force to allow the use of a large air gap for excellent electrical isolation, while achieving a record-low driving voltage of <0.2 V. Furthermore, the introduction of the Lorentz force allows the NW-NEM switch to effectively overcome the adhesion force to recover to the turn-off state.

High-Temperature-Operable Electromechanical Computing Units Enabled by Aligned Carbon Nanotube Arrays

Nano/micro-electromechanical (NEM/MEM) contact switches have great potential as energy-efficient and high-temperature-operable computing units to surmount those limitations of transistors. However, despite recent advances, the high-temperature operation of the mechanical switch is not fully stable nor repetitive due to the melting and softening of the contact material in the mechanical switch. Herein, MEM switches with carbon nanotube (CNT) arrays capable of operating at high temperatures are presented. In addition to the excellent thermal stability of CNT arrays, the absence of a melting point of CNTs allows the proposed switches to operate successfully at up to 550 °C, surpassing the maximum operating temperatures of state-of-the-art mechanical switches. The switches with CNTs also show a highly reliable contact lifetime of over 1 million cycles, even at a high temperature of 550 °C. Moreover, symmetrical pairs of normally open and normally closed MEM switches, whose interfaces are initially in contact and separated, respectively, are introduced. Consequently, the complementary inverters and logic gates operating at high temperatures can be easily configured such as NOT, NOR, and NAND gates. These switches and logic gates reveal the possibility for developing low-power, high-performance integrated circuits for high-temperature operations.

Unclonable Perovskite Fluorescent Dots with Fingerprint Pattern for Multilevel Anticounterfeiting

Anticounterfeiting techniques based on physical unclonable functions exhibit great potential in security protection of extensive commodities from daily necessities to high-end products. Herein, we propose a facile strategy to fabricate an unclonable super micro fingerprint (SMFP) array by introducing in situ grown perovskite crystals for multilevel anticounterfeiting labels. The unclonable features are formed on the basis of the differential transportation of a microscale perovskite precursor droplet during the inkjet printing process, coupled with random crystallization and Ostwald ripening of perovskite crystals originating from their ion crystal property. Furthermore, the unclonable patterns can be readily tailored by tuning in situ crystallization conditions of the perovskite. Three-dimensional height information on the perovskite patterns are introduced into a security label and further transformed into structural color, significantly enhancing the capacity of anticounterfeiting labels. The SMFPs are characterized with tunable multilevel anticounterfeiting properties, including macroscale patterns, microscale unclonable pattern, fluorescent two-dimensional pattens, and colorful three-dimensional information.

Integration of a Carbon Nanotube Network on a Microelectromechanical Switch for Ultralong Contact Lifetime

Micro-/nanoelectromechanical (MEM/NEM) switches have been extensively studied to address the limitations of transistors, such as the increased standby power consumption and performance dependence on temperature and radiation. However, their lifetimes are limited owing to the degradation of the contact surfaces. Even though several materials and structural designs have been recently developed to improve the lifetime, the production of a microswitch that is compatible with a complementary metal-oxide semiconductor (CMOS) with a long lifetime remains a significant challenge. We demonstrate a vertically actuated MEM switch with extremely high reliability by integrating a carbon nanotube (CNT) network on a gold electrode as the contact material using a low-temperature, CMOS-compatible solution process. In addition to their outstanding mechanical and electrical properties of CNTs, their deformability dramatically increases the effective contact area of the switch, thus resulting in the extension of the lifetime. The CNT-coated MEM switch exhibits a lifetime that is more than 7 × 10⁸ cycles when operated in hot-switching conditions, which is 1.9 × 10⁴ times longer than that of a control device without CNTs. The switch also shows an excellent switching performance, including a low electrical resistance, high on/off ratio, and an extremely small off-state current.

Recent Progress in Inkjet-Printed Thin-Film 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.

Printing Reinforcing Structures onto Microsieves That Are Floating on a Water Surface

This article describes the preparation of hierarchically structured microsieves via a suitable combination of float-casting and inkjet-printing: A mixture of hydrophobized silica particles of 600 nm ± 20 nm diameter, a suitable non-water-soluble nonvolatile acrylic monomer, a nonvolatile photoinitiator, and volatile organic solvents is applied to a water surface. This mixture spontaneously spreads on the water surface; the volatile solvents evaporate and leave behind a layer of the monomer/initiator mixture comprising a monolayer of particles, each particle protruding out of the monomer layer at the top and bottom surface. Photopolymerization of the monomer converts this mixed layer into a solid composite membrane floating on the water surface. Onto this membrane, while still floating on the water surface, a hierarchical reinforcing structure based on a photocurable ink is inkjet-printed and solidified. In contrast to the nonreinforced membrane, the reinforced membrane can easily be lifted off the water surface without suffering damage. Subsequently, the silica particles are removed, and thus, the reinforced composite membrane is converted into a reinforced microsieve of 350 nm ± 50 nm thickness bearing uniform through pores of 465 nm ± 50 nm diameter. This reinforced microsieve is mounted into a filtration unit and used to filter model dispersions: its permeance for water at low Reynolds numbers is in accordance with established theories on the permeance of microsieves and significantly above the permeance of conventional filtration media; it retains particles exceeding the pore size, while letting particles smaller than the pore size pass.

All Inkjet-Printed Amperometric Multiplexed Biosensors Based on Nanostructured Conductive Hydrogel Electrodes

Multiplexing, one of the main trends in biosensors, aims to detect several analytes simultaneously by integrating miniature sensors on a chip. However, precisely depositing electrode materials and selective enzymes on distinct microelectrode arrays remains an obstacle to massively produced multiplexed sensors. Here, we report on a "drop-on-demand" inkjet printing process to fabricate multiplexed biosensors based on nanostructured conductive hydrogels in which the electrode material and several kinds of enzymes were printed on the electrode arrays one by one by employing a multinozzle inkjet system. The whole inkjet printing process can be finished within three rounds of printing and only one round of alignment. For a page of sensor arrays containing 96 working electrodes, the printing process took merely ∼5 min. The multiplexed assays can detect glucose, lactate, and triglycerides in real time with good selectivity and high sensitivity, and the results in phosphate buffer solutions and calibration serum samples are comparable. The inkjet printing process exhibited advantages of high efficiency and accuracy, which opens substantial possibilities for massive fabrication of integrated multiplexed biosensors for human health monitoring.

Three-Dimensionally Printed Micro-electromechanical Switches

Three-dimensional (3D) printers have attracted considerable attention from both industry and academia and especially in recent years because of their ability to overcome the limitations of two-dimensional (2D) processes and to enable large-scale facile integration techniques. With 3D printing technologies, complex structures can be created using only a computer-aided design file as a reference; consequently, complex shapes can be manufactured in a single step with little dependence on manufacturer technologies. In this work, we provide a first demonstration of the facile and time-saving 3D printing of two-terminal micro-electromechanical (MEM) switches. Two widely used thermoplastic materials were used to form 3D-printed MEM switches; freely suspended and fixed electrodes were printed from conductive polylactic acid, and a water-soluble sacrificial layer for air-gap formation was printed from poly(vinyl alcohol). Our 3D-printed MEM switches exhibit excellent electromechanical properties, with abrupt switching characteristics and an excellent on/off current ratio value exceeding 10⁶. Therefore, we believe that our study makes an innovative contribution with implications for the development of a broader range of 3D printer applications (e.g., the manufacturing of various MEM devices and sensors), and the work highlights a uniquely attractive path toward the realization of 3D-printed electronics.

Fabricating Metallic Circuit Patterns on Polymer Substrates through Laser and Selective Metallization

Nowadays, with the rapid development of portable electronics, wearable electronics, LEDs, microelectronics, and bioelectronics, the fabrication of metallic circuits onto polymer substrates with strong adhesion property is an ever-increasing challenge. In this study, the high-resolution and well-defined metallic circuits were successfully prepared on the polymer surface via laser direct structuring (LDS) based on copper hydroxyl phosphate [Cu₂(OH)PO₄], and the key mechanism of the selective metallization was systematically investigated. XPS confirmed that Cu⁰ (elemental copper) was formed through photochemical reduction reaction of Cu₂(OH)PO₄, after 1064 nm NIR pulsed laser irradiation. During the electroless plating, because it is the important active catalytic center, this newly formed Cu⁰ was the key factor to achieve the successful selective metallization. SEM revealed that after the electroless plating, the copper layer actually physically anchored into the polymer substrate, giving an excellent mechanical adhesion property of the obtained metallic patterns. In addition, the micro-Raman surface imaging approved the generation of the amorphous carbon on the polymer composites' surface after NIR laser irradiation, and the chemical reaction region caused by the pulsed laser spot was found at approximately 40 μm. This environmentally friendly and effective strategy for fabricating circuit patterns on the polymer surface has a possible application in the printed circuit plate (PCB) industry.

Rapid Laser Printing of Paper-Based Multilayer Circuits

Laser printing has been widely used in daily life, and the fabricating process is highly efficient and mask-free. Here we propose a laser printing process for the rapid fabrication of paper-based multilayer circuits. It does not require wetting of the paper, which is more competitive in manufacturing paper-based circuits compared to conventional liquid printing process. In the laser printed circuits, silver nanowires (Ag-NWs) are used as conducting material for their excellent electrical and mechanical properties. By repeating the printing process, multilayer three-dimensional (3D) structured circuits can be obtained, which is quite significant for complex circuit applications. In particular, the performance of the printed circuits can be exactly controlled by varying the process parameters including Ag-NW content and laminating temperature, which offers a great opportunity for rapid prototyping of customized products with designed properties. A paper-based high-frequency radio frequency identification (RFID) label with optimized performance is successfully demonstrated. By adjusting the laminating temperature to 180 °C and the top-layer Ag-NW areal density to 0.3 mg cm(-2), the printed RFID antenna can be conjugately matched with the chip, and a big reading range of ∼12.3 cm with about 2.0 cm over that of the commercial etched Al antenna is achieved. This work provides a promising approach for fast and quality-controlled fabrication of multilayer circuits on common paper and may be enlightening for development of paper-based devices.

Printed unmanned aerial vehicles using paper-based electroactive polymer actuators and organic ion gel transistors

We combined lightweight and mechanically flexible printed transistors and actuators with a paper unmanned aerial vehicle (UAV) glider prototype to demonstrate electrically controlled glide path modification in a lightweight, disposable UAV system. The integration of lightweight and mechanically flexible electronics that is offered by printed electronics is uniquely attractive in this regard because it enables flight control in an inexpensive, disposable, and easily integrated system. Here, we demonstrate electroactive polymer (EAP) actuators that are directly printed into paper that act as steering elements for low cost, lightweight paper UAVs. We drive these actuators by using ion gel-gated organic thin film transistors (OTFTs) that are ideally suited as drive transistors for these actuators in terms of drive current and frequency requirements. By using a printing-based fabrication process on a paper glider, we are able to deliver an attractive path to the realization of inexpensive UAVs for ubiquitous sensing and monitoring flight applications.