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This paper reports on the unprecedented 4 W power microelectromechanical systems (MEMS) relay with a contact- force-maximizing structure in a dual-contact material system. A MEMS relay with dual (hard and soft) contact materials is known to have high durability in hot-switching conditions, and the contact force is also considered to be the most important factor that contributes to an efficient reduction of the contact resistance. We devised a contact-force-maximizing structure with a plate-type suspended structure and in-plate springs and applied it to a dual-contact material system to achieve extremely low contact resistance. The fabricated MEMS relay successfully operated sequential switching between the dual contact materials in the contact-force-maximizing structure and thereby showed an extremely low contact resistance of 1.65 $\text{m}\Omega $ with a switching time of $7 {\mu \text {s}}$ at an operating voltage of 80 V. Thanks to the contact-force-maximizing structure with the dual-contact material system, the fabricated MEMS relay achieved a lifetime of up to $1.3\times 10^{\mathbf {3}}$ cycles in the hot-switching conditions of 4 W (10 V/400 mA) in an air atmosphere with a negligible variation of the contact resistance. This power level is the highest reported to date. [2020-0223]

Gas sensors that can operate with sub-10 mW power consumption are in great demand in application where mobile devices are used to detect harmful gases in real time. Such low power gas sensors can be realized by employing miniaturized and air-suspended microheater platforms; however, a productive and reliable fabrication method should be developed for their practical use. Here, we present a batch-fabrication method based on a surface micro-machining process to uniformly and reliably produce the sub-10 mW power oerating gas sensors on an 8-inch wafer area. The fabricated gas sensors showed a reproducible and sensitive response to various concentrations of carbon monoxide gas (as low as 1 ppm) with 5.0 mW power operation, which is among the lowest power achieved for semiconducting metal-oxide gas sensors. In addition, the devices showed low sample-to-sample variation and high reliability in a long-term stability test, verifying their potential for practical use in mobile gas sensing applications.

Recently, copper oxide (CuO)-based visible-light photodetectors have attracted great interest due to their narrow bandgap (1.2 eV), low cost, and ease of fabrication. However, there has been insufficient theoretical analysis and study of CuO-based photodetectors, resulting in inferior performance in terms of responsivity, detectivity, and response speed. This work develops a method to enhance the performance of CuO photodetectors by engineering a grain structure based on a newly-developed theoretical model. In the developed theoretical grain-structure model, the grain size and the connections between grains are considered because they can strongly affect the optoelectronic characteristics of CuO photodetectors. Based upon the proposed model, the engineered CuO device achieves enhanced optoelectronic performance. The engineered device shows high responsivity of 15.3 A/W and detectivity of 1.08 × 1011 Jones, which are 18 and 50 times better than those of the unoptimized device, and also shows fast rising and decaying response speeds of 0.682 s and 1.77 s, respectively. In addition, the proposed method is suitable for the mass-production of performance-enhanced, reliable photodetectors. By using a conventional semiconductor fabrication process, a photodetector-array is demonstrated on a 4-inch wafer. The fabricated devices show uniform, high, and stable optoelectronic performance for a month.

Pd nanowire-based H2 sensors have attracted significant attention because of their superior sensing performance. However, when exposed to H2 concentrations of more than 2%, Pd experiences volume expansion over 10%, resulting in a significant amount of mechanical stress. Thus, exposure to such high H2 concentrations causes physical destruction of Pd nanowires, such as breaks and peel-offs, leading to severe difficulty in the reliable detection of H2 over a wide concentration range. Here, we proposed a structural approach to resolve this issue by introducing a partially anchored Pd nanowire (PA-PdNW) structure. In this configuration, most of the structure was air-suspended, leaving a small portion anchored to the substrate. Air-suspension enabled PA-PdNW to expand freely, thus relieving the mechanical stress; therefore, the Pd nanowires could withstand numerous exposures to high H2 concentrations. To demonstrate the PA-PdNW structure, we developed a nano-fabrication method based on conventional semiconductor processes and successfully manufactured H2 sensor devices with uniform, perfectly aligned PA-PdNW arrays stably air-suspended with designed gaps from the substrate. The fabricated sensors achieved reliable detection of H2 in the 0.1%–3.9% concentration range with a significant resistance change. In addition, compared with fully anchored Pd nanowire (FA-PdNW) sensors, the PA-PdNW sensors showed superior durability, and the nanowires retained their initial structures even after 300 exposures to high H2 concentrations. Furthermore, it was confirmed that the PA-PdNW sensor can stably operate even in extremely humid environments at 85% relative humidity.

In this work, we present a compact self-powered wireless gas sensor node based on photovoltaic (PV) energy harvesting (EH). Instead of a bulky and power-hungry gas sensor with separate gas signal processing (GSP) circuits, a mm3-sized colorimetric sensor film is integrated with a PV cell, and the GSP function is seamlessly embedded within EH circuits. Also, a dual-input shared-inductor boost converter is used to improve the EH efficiency under gas exposure. Offset cancellation is performed in GSP circuits to provide accurate gas-sensing readout without any external trimming.

Electrical circuits require ideal switches with low power consumption for future electronic applications. However, transistors, the most developed electrical switches available currently, have certain fundamental limitations such as increased leakage current and limited subthreshold swing. To overcome these limitations, micromechanical switches have been extensively studied; however, it is challenging to develop micromechanical switches with high endurance and low contact resistance. This study demonstrates highly reliable microelectromechanical switches using nanocomposites. Nanocomposites consisting of gold nanoparticles (Au NPs) and carbon nanotubes (CNTs) are coated on contact electrodes as contact surfaces through a scalable and solution-based fabrication process. While deformable CNTs in the nanocomposite increase the effective contact area under mechanical loads, highly conductive Au NPs provide current paths with low contact resistance between CNTs. Given these advantages, the switches exhibit robust switching operations over 5 × 106 cycles under hot-switching conditions in air. The switches also show low contact resistance without subthreshold region, an extremely small leakage current, and a high on/off ratio.

This paper reports an unprecedented 4 W MEMS relay that utilizes a dual contact-material system and a contact force maximizing structure. The contact force-maximizing structure is designed to achieve extremely low contact resistance. So far, commercialized MEMS relays have achieved a power level of 0.03 W in hot-switching conditions. In this work, we achieved a MEMS relay with operation reliability up to $5.7\times 10^{4}$ cycles and $1.3\times 10^{3}$ cycles at 10 V/300 mA (3 W) and 10 V/400 mA (4 W) signals, respectively, in hot-switching conditions. This achievement was due to an extremely-low contact resistance of $1.65\ \mathrm{m}\Omega$ achieved by utilizing the proposed contact force maximizing structure coupled with dual contact materials.

Probing micro-bumps for pre-bond testing is an essential process to check for a known good die. In recent technologies, micro-bumps such those used in 3-D-IC are too small and dense, which gives the probing a new challenge. Moreover, developers are concerned that the tip ends of the micro-bumps are mechanically damaged during the pre-bond testing, which is detrimental for the post-process IC assembly. Thus, many low damage probing solutions have been developed, but they still inevitably damage the tip end of the micro-bumps when the conventional probing method, vertical contact, is used. In this paper, for the first time, we demonstrate lateral contact probing on 55- $\mu \text{m}$ pitch micro-bumps without any damage to the tip ends. We successfully realized the testing with monolithically fabricated probes by nickel electroplating with a high aspect ratio photoresist mold. The measured fatigue life of the fabricated probes was at least100 000 cycles. Furthermore, the measured current carrying capacity was more than 180 mA. Proving our concept, the contact test results on the micro-bumps showed no damage to the tip end, and the contact resistance was below 1.13 $ {\Omega }$ . Finally, the10 000 probes achieved a uniform 55- $\mu \text{m}$ pitch, which ensured the possibility in real testing. [2018-0041]

A 4-terminal microelectromechanical systems (MEMS) relay has long been sought for signal switching applications because it allows de-coupling of the actuation (body and gate) and signal (source and drain) components unlike a 3-terminal MEMS relay. However, the contact resistance still remains a serious problem in current 4-terminal MEMS relays compared with the 3-terminal MEMS relays. In this paper, using theoretical analysis, we first determined that the two-contact design, which was the most common design in the 4-terminal MEMS relay, was the origin of the high contact resistance. We subsequently developed a 4-terminal MEMS relay with a novel single-contact design. The fabricated 4-terminal MEMS relay with the single-contact design exhibited a contact resistance of 18 $\text{m}\Omega $ . To the best of our knowledge, this result is the lowest value among 4-terminal MEMS relays. In addition, we demonstrated that the two-contacts are the origin of the high contact resistance using measurement. The relay operated up to $1.1\times 10^{6}$ cycles at 1 V / 50 mA in air and hot switching conditions. Finally, the proposed 4-terminal MEMS relay was hermetically packaged for use in commercial applications. [2017-0183]

High contact force in a microelectromechanical systems (MEMS) relay is known to be the most important factor in achieving low contact resistance. Achieving a high contact force in an electrostatically-actuated MEMS relay usually requires high actuation voltage to exert a high electrostatic force. In this paper, for the first time, we demonstrate the successful use of a mechanical adhesion force as a high contact force for realizing an extremely low contact resistance, even at a low actuation voltage of 3.8 V. To maximize the mechanical adhesion, we designed a suitably-large contact area (100 μm × 100 μm) in the MEMS relay and a detachment spring structure to separate the two electrodes that were in contact with one another by only the mechanical adhesion force, thereby enabling the MEMS switch to perform multiple switching operations. The proposed MEMS relay exhibited an extremely low contact resistance of 4.9 mΩ with only the mechanical adhesion force after we applied an actuation voltage of 3.8 V, and it achieved a retention time of 105 s because of stable mechanical contact. Through this experiment, we verified that the mechanical adhesion force can provide an efficient source for generating high contact force in the MEMS relay.

We present a fast, energy-efficient nano-thermomechanical encoding scheme for digital information storage and retrieval. Digital encoding processes are conducted by the bistable electrothermal actuation of a scalable nanobridge device. The electrothermal energy is highly concentrated by enhanced electron/phonon scattering and heat insulation in a sub-100 nm metallic layer. The efficient conversion of electrothermal energy into mechanical strain allows digital switching and programming processes within 60 ns at 0.75 V with a programming energy of only 54 pJ. Furthermore, this encoding scheme together with the thermally robust design enables data retention at temperatures up to 400 °C. These results suggest that the proposed nano-thermomechanical encoding method could contribute to low-power electronics and robust information storage/retrieval systems.

Nanowire (NW) transfer technology has provided promising strategies to realize future flexible materials and electronics. Using this technology, geometrically controlled, high-quality NW arrays can now be obtained easily on various flexible substrates with high throughput. However, it is still challenging to extend this technology to a wide range of high-performance device applications because its limited temperature tolerance precludes the use of high-temperature annealing, which is essential for NW crystallization and functionalization. A pulsed laser technique has been developed to anneal NWs in the presence of a flexible substrate; however, the induced temperature is not high enough to improve the properties of materials such as ceramics and semiconductors. Here, we present a versatile nanotransfer method that is applicable to NWs that require high-temperature annealing. To successfully anneal NWs during their transfer, the developed fabrication method involves sequential removal of a nanoscale sacrificial layer. Using this method, we first produce an ultralong, perfectly aligned polycrystalline barium titanate (BaTiO

This paper first reports a highly reliable self-powered hydrogen (H 2 ) sensor employing a palladium (Pd)-based nano-transducer. The developed sensor is based on the principle of a novel chemomechanical mechanism of the Pd nano-transducer exploiting a solar cell. We theoretically and experimentally demonstrated that the proposed device can achieve highly durable operation for a wide range of H 2 concentrations with remarkable sensitivity (3.1% at 2%-H 2 ) and response time (111 s at 2%-H 2 ) without external power. Significantly, the proposed sensor, which has a novel sensing mechanism, maintains high sensing performance for more than 150 cycles under various H 2 conditions (0.5 to 2%).

A major obstacle to the industrial application of nanowires is difficulty in fabricating nanowire devices with uniform performance. In this study, we newly developed a wafer-level uniformly size-controlled nanowire fabrication method for reliable demonstration of a high-yield, uniform nano-sensor device. We show that the developed fabrication method can be used to simply fabricate remarkably small nanowires (sub-50 nm) with a wide material selection. Importantly, the fabricated nanowires have ultra-high size uniformity on the 4-inch wafer. Finally, we demonstrate nanowire-based hydrogen (H 2 ) sensors using the developed method. Owing to the geometric uniformity of the fabricated nanowires, the sensor devices achieved highly uniform sensitivity of 10.9±0.5 % at a 2% H 2 concentration.

This work demonstrates a highly reliable microelectromechanical (MEM) switch with high switching performance by integrating gold (Au)-decorated carbon nanotube (CNT) network in the contact area. By decorating the CNTs with Au nanoparticles (Au-NPs), we obtained several times extension in the lifetime of the MEM switch with low contact resistance. We verified that the extended lifetime and the low contact resistance originate from the deformable CNTs under mechanical load and the Au NPs with high conductivity at the contact-interface. Our switch also revealed low adhesion force at the contact-interface, which results in highly repeatable and stable actuation voltages at both turn-on and off, whereas typical MEM switches with high adhesion force show irreversible stiction or unstable turn-off voltage. The proposed switch exhibited 1.9 times longer lifetime under hot-switching conditions, compared to previously studied MEM switches based on Au-Au contact.

This paper reports a high-sensitivity wearable transparent pressure sensor by maximizing the percolation effect using a sub-100 nm nano-valley. The secret to achieving high sensitivity is to make the nano-valley as narrow as possible to maximize the percolation effect (stress concentration effect). The narrow nano-valley pressure sensor showed a remarkable 400% enhancement in sensitivity compared to a sensor with no nano-valley while maintaining a high transmittance of 83%. This sensitivity value is higher than those of the previous wearable transparent pressure sensors. The fabricated sensor also showed high durability with low variation of 1.2% in repeated pressing of up to 100,000 times under 100 kPa pressure.

This paper reports a Pd hydrogen gas sensor that uses perfectly aligned uniform nanogap arrays. Depending on the nanogap size, the sensor can differentiate hydrogen concentration thanks to the volume expansion of Pd. The fabrication method of the sensor is based on conventional semiconductor processes; thus, perfectly aligned uniform nanogap arrays can be easily obtained. The standard deviation of the measured nanogap widths was less than 5 nm, and this level of uniformity has not been previously demonstrated in Pd-switching-type sensors. The fabricated sensors with the uniform nanogap array showed abrupt switching characteristics when they were exposed to H2 concentrations over a certain threshold level. Furthermore, based on the unprecedented high uniformity of the nanogap widths, a fine modulation of the threshold level of the H2 concentrations was firstly demonstrated.

The electrostatic actuation method has not been used widely in bimorph cantilevers despite its advantage of large displacement and low power consumption, mostly owing to the fact that it is limited to just two stable positions: 1) initial curled; and 2) final flat positions. In this paper, we first demonstrate a bimorph cantilever actuator having multiple steady-state positions in between those two boundary positions, accomplished by simply dividing the bottom electrode. We found that the number of steady-state positions and the steady-state tip heights can be controlled by the design of the bottom electrode. In our test experiment, the steady-state bimorph cantilever tip heights were 48 $\mu \text{m}$ at 0 V, 28 $\mu \text{m}$ at 21 V, 7 $\mu \text{m}$ at 25 V, and 0 $\mu \text{m}$ (flat) at 29 V, respectively. In order to relieve low reliability of the electrostatic bimorph cantilever, we devised non-contact actuation method and demonstrated that the lifetime of the electrostatic bimorph actuator greatly increased. This paper will pave the way to utilize bimorph cantilever actuators with greater versatility. [2016-0081]

This paper reports a highly reliable electrostatic microelectromechanical systems (MEMS) relay for high-power switching applications. The main proposal to elevate reliability is to reduce thermal damage in the contact area. Since a contact resistance is the key parameter determining the amount of Joule-heating and the corresponding thermal damage, we devised a unique spring structure to maximize the contact force (resulting in a low contact resistance) using a reasonable actuation voltage named a two-step spring system. Another important feature was applied to alleviate Joule-heating, which is to use an insulator having high thermal conductivity to dissipate the generated heat efficiently, named a heat sink insulator. The fabricated MEMS relay exhibited 2 $\text{m}\Omega $ in contact resistance, which is the lowest level reported so far with an actuation voltage of 45 V. Reliability was remarkably enhanced over ten times by the heat sink insulator. Consequently, by applying these two approaches simultaneously, the fabricated MEMS relay was successfully operated up to the $5.3 \times 10^{6}$ cycles at 1 V/200 mA in ambient air and hot switching condition, which is the highest reliability reported at that power level. [2015-0237]

In article number 2004448, Jun‐Bo Yoon and co‐workers propose the concept of two distinctive nanowire arrays with an ‘air‐bridge’ structure, with the first of the two nanowire arrays acting as a heater and the second nanowire array as the sensing material. The developed configuration greatly suppresses beam conduction loss to the substrate, overcoming the fundamental power consumption limits of conventional microheaters.

Air suspension and alignment are fundamental requirements to make the best use of nanowires' unique properties; however, satisfying both requirements is very challenging due to the mechanical instability of air-suspended nanowires. Here, a perfectly aligned air-suspended nanowire array called "nanolene" is demonstrated, which has a high mechanical stability owing to a C-channel-shaped cross-section of the nanowires. The excellent mechanical stability is provided through geometrical modeling and finite element method simulations. The C-channel cross-section can be realized by top-down fabrication procedures, resulting in reliable demonstrations of the nanolenes with various materials and geometric parameters. The fabrication process provides large-area uniformity; therefore, nanolene can be considered as a 2D planar platform for 1D nanowire arrays. Thanks to the high mechanical stability of the proposed nanolene, perfectly aligned air-suspended nanowire arrays with an unprecedented length of 1 mm (aspect ratio ≈5100) are demonstrated. Since the nanolene can be used in an energy-efficient nanoheater, two energy-stringent sensors, namely, an air-flow sensor and a carbon monoxide gas sensor, are demonstrated. In particular, the gas sensor achieves sub-10 mW operations, which is a requirement for application in mobile phones. The proposed nanolene will pave the way to accelerate nanowire research and industrialization by providing reliable, high-performance nanowire devices.

Micro-/nano-electromechanical (M/NEM) switches have received significant attention as promising switching devices for a wide range of applications such as computing, radio frequency communication, and power gating devices. However, M/NEM switches still suffer from unacceptably low reliability because of irreversible degradation at the contacting interfaces, hindering adoption in practical applications and further development. Here, we evaluate and verify graphene as a contact material for reliability-enhanced M/NEM switching devices. Atomic force microscopy experiments and quantum mechanics calculations reveal that energy-efficient mechanical contact–separation characteristics are achieved when a few layers of graphene are used as a contact material on a nickel surface, reducing the energy dissipation by 96.6% relative to that of a bare nickel surface. Importantly, graphene displays almost elastic contact–separation, indicating that little atomic-scale wear, including plastic deformation, fracture, and atomic attrition, is generated. We also develop a feasible fabrication method to demonstrate a MEM switch, which has high-quality graphene as the contact material, and verify that the devices with graphene show mechanically stable and elastic-like contact properties, consistent with our nanoscale contact experiment. The graphene coating extends the switch lifetime >103 times under hot switching conditions.

This paper reports a novel transfer method to fabricate ultralong, fully aligned nanowires, made of diverse materials on a flexible substrate. For the uniform transfer of nanowires made from a wide range of materials, a facile and robust mechanics-based nano-transfer method has been developed. A selectively dry-removable amorphous carbon nano-sacrificial layer between a vacuum-deposited nanowire and the underlying master mold is newly introduced, and it facilitates the robust and reliable mechanical transfer of dense and aligned nanowires onto a flexible substrate. Using the developed method, we first fabricated ultralong and fully aligned metal/metal-oxide (gold, platinum, and copper-oxide) nanowires on a large-area flexible substrate (2.5 × 2 cm2). We also fabricated a unique nanowire-heater-embedded gas-sensor using the transferred gold and copper-oxide nanowires, respectively. The developed heater-embedded device exhibited a 33-fold enhancement in sensitivity, responding to 10 ppm NO 2 using a 0.6 V heater bias.

This paper reports on a high-resolution lensless fluorescence imaging system using membrane deflection for reducing the gap between fluorescent samples and a CMOS image sensor array. The presented system applied the principle of the total internal reflection of excitation light inside a PDMS chip to minimize the exposure of excitation light to the image sensor. We integrated a very thin (5.5 μm) PDMS membrane as a flexible deflector, which allowed for significant reduction of the gap (∼20 μm) inevitably created during the conventional packaging (i.e., wire bonding) of image sensors. In the fabricated system, we achieved minimum distance of 7.5 μm between fluorescent samples and an image sensor array. This reduced gap almost directly corresponds to a resolution as high as ∼7.5 μm, based on the point spread function (PSF).

The phenomenon that a common positive photoresist (PR) releases nitrogen (N2) gas when exposed to UV light has never been used or received any particular attention. Fabrication process to intentionally trap the generated N2 gas during UV exposure, thereby, to form the microcavity structure is proposed. Various dome-shaped structures are demonstrated with the proposed process. This process is best suited to make various cavity packages in microelectromechanical systems. Also, microlens arrays are fabricated using plastic replication of the dome-shaped microcavities. All these results lead to a different view of the conventional positive photoresist and inspire various new applications.

This paper presents an extremely power-insensitive microelectromechanical systems (MEMS) tunable capacitor equipped with immobilization capability in the moving plates when an radio frequency signal is flowing. The proposed tunable capacitor is similar to the conventional metal–insulator–metal capacitor, but the top metal plate is capable of moving laterally as well as vertically; it moves to the left and right to set the capacitance value by modulating the overlap area between the top and bottom plates (analog tuning and high capacitance tuning ratio are the merits), and then the top plate is pulled down to be immobilized resulting in remarkable robustness to the signal power, as well as high capacitance value. The proposed tunable capacitor, which was fabricated by metal surface micromachining, showed the tuning ratio of 181% at 2 MHz (470–852 fF) and 194% at 1 GHz with lateral and vertical actuation voltages under 50 V. It also exhibited small capacitance change against the radio frequency (RF) signal power; the maximum capacitance variation by the signal power of up to 9 W was

This paper reports on a two-axis actuated microelectromechanical systems (MEMS) relay to realize a unique contact-refresh concept. In comparison with all other conventional MEMS relays utilizing only several designated contact spots during their whole lifetime, the proposed concept can change the real contact spots (asperities) by altering the lateral position of contact asperities, thus providing highly reliable contact endurance. In addition, it can enhance lifetime of the switches that fail by contact resistance increase, and potentially even for switches that fail by contact stiction if the contact position is changed before a critical number of switching cycles is reached; however, the device inevitably has a relatively large device area and additional control circuitry in this stage of development. The fabricated relays showed vertical actuation voltages under 40 V, a switching delay of 190 $\mu \text{s}$ , and a maximum lateral displacement of 10 $\mu \text{m}$ . Owing to the suggested contact-refresh scheme, the total contact endurance in one switching device was dramatically increased, and the sum of dozens of lifetimes measured at the selected lateral positions reached $6 \times 10^{7}$ cycles at 100 mA in hot switching conditions (Au-to-Au contact), which is nearly 50 times higher than the average value of the measured lifetimes in a designated contact spot. [2014-0225]

In order to increase two important factors of capacitance and self-resonant frequency (SRF) of the microelectromechanical systems (MEMS)-switched capacitor, we developed a room-temperature-grown high- $\kappa $ TiO2 dielectric layer in the metal–insulator–metal (MIM) capacitor and an SU-8 bridged beam structure in the MEMS switch. The high- $\kappa $ TiO2 dielectric layer, which has a relative dielectric constant of up to 32, was utilized to minimize the MIM capacitors’ sizes while maintaining their high capacitance values. In addition, the SU-8 bridged beam structure of the MEMS switch, whose radio frequency (RF) signal interconnecting part is electrically isolated from the switching mechanism, was introduced to shorten the RF signal path. Because of the high- $\kappa $ dielectric and the bridged beam structure, we have achieved a very high capacitance of up to 14.3 pF with an SRF of 1.8 GHz (the MIM capacitor size was $50~\mu $ m $\times 1200~\mu $ m). The same-sized MIM capacitor with a conventional Si3N4 dielectric layer and a conventional cantilever beam-switched capacitor showed only 4.9 pF with an SRF of 2.8 GHz. In a similar capacitance value, the proposed switched capacitor showed 22% increase in SRF (7.1 GHz at 0.92 pF) compared with the conventional cantilever beam switched capacitor with a Si3N4 dielectric layer (5.8 GHz at 1.01 pF). The high SRF was attributed to the short RF signal path and the minimized capacitor size, thereby reducing parasitic inductance. [2014-0130]

Energy harvesting techniques have attracted great deal of attention for sustainable energy security. Among those techniques, solar cell is most widely used energy harvesting device. However, power conversion efficiency of solar cell is seriously affected by weather conditions and contamination from airborne dust. In this paper, hybrid cell, which has high immunity against weather condition and contamination by simultaneously harvesting raindrop and solar energy, is proposed. The hybrid cell consists of transparent triboelectric nanogenerator (TENG) and conventional solar cell. The transparent TENG is fabricated with superhydrophobic PDMS and ITO/PEN substrate. Output voltage are current were 7 V and 128 nA, respectively. Maximum output power is 0.27 μW. Also, output characteristics of water TENG is investigated with various solutions including actual rainwater and flowing water to explore realistic potential of water TENG in harvesting actual raindrop energy. Moreover, enhanced cleaning effect of hybrid cell is experimentally demonstrated with the carbon powder for the first time and hybrid cell successfully harvested both energy without any cross-effect. These results suggest great potential of water TENG in actual environment and insight into utilizing superhydrophobic surface of water TENG.

A novel edge type local dimming backlight unit (BLU) for LCD based mobile applications is proposed. The BLU has ultra-thin (1 mm) and two dimensional local dimming feature. For this, a tile-like lightguide plate (LGP) is newly designed and demonstrated with an LCD system.

This paper proposes a device level solution to achieve linear frequency tuning with respect to a tuning voltage (V tune ) sweep in an inductor (L)–capacitor (C) resonant system. Since the linearity of the resonant frequency vs. tuning voltage (f–V) relationship in an LC-resonant system is closely related to the C–V response characteristic of the varactor, we propose a C–V response tunable varactor to realize the linear frequency tuning. The proposed varactor was fabricated using microelectromechanical system (MEMS) surface micromachining. The fabricated MEMS varactor has the ability to dynamically change the C–V response characteristic according to a curve control voltage (V curve-control ). When V curve-control was increased from zero to 9 V, the C–V response curve was changed from a linear to a concave form (i.e., the capacitance decreased quickly in the low tuning voltage region and slowly in the high tuning voltage region). This change in the C–V response characteristic resulted in a change in the f–V relationship, and we successfully demonstrated almost perfectly linear frequency tuning in the LC-resonant system, with a linearity factor of 99.95%.

This paper reports a unique 4-terminal MEMS relay (actuation is electrically isolated with signal passage) employing a novel one-contact design to overcome high contact resistance problem of the conventional 4-terminal MEMS relay which utilizes a typical two-contact design. The fabricated 4-terminal MEMS relay with the one-contact design demonstrated a contact resistance of 18 mΩ, which is two order-of-magnitude lower value than that of the conventional two-contact design. To the best of our knowledge, this result is the lowest value in the 4-terminal MEMS relay and comparable value with the state-of-the-art in 3-terminal MEMS relay [14]. In addition, the relay was operated up to 1.1 × 106 cycles at 1 V / 50 mA in an air and hot switching condition with negligible contact resistance variation. The lifetime is 10 times longer than that of the conventional 4-terminal MEMS relay.

This paper firstly reports a high-performance flexible tactile-sensor array using a large-area plastic nanograting substrate. Using a large area 200 nm-pitch plastic nanograting substrate, we fabricated high-performance flexible tactile sensor array, which shows 220 % enhancement in sensitivity with 104) with ROC = 4 mm. Finally, the large area fabricated prototype sensor-array showed the real-time capacitance change by various finger touches, including time and strength different impacts.

Since a microelectromechanical (MEM) switch with an electrostatically actuated cantilever was first demonstrated by Petersen in 1978 [1], MEM switches have actively been researched by many research groups. However, comparing with the conventional metal-oxide-semiconductor field-effect transistor (MOSFET), MEM switches are still suffering from their high actuation voltage and insufficient operational reliability, which still remain as a difficult challenge to many MEMS researchers and hinder commercialization of the MEM switches. In this work, we look at what lies behind these difficulties in MEM switches and illustrate bright ideas that have been sought to enhance the actuation voltage and switch endurance (lifetime) problems.

This paper reports a novel method of integrating magnetic nanoparticles (MNPs) with a MEMS inductor. The proposed method is based on the self-alignment of MNPs in response to a magnetic field generated by the integrated MEMS inductor itself. Because it is the natural tendency of MNPs to gravitate towards spots of maximum magnetic flux density, the alignment process results in an MNP distribution that is optimal for maximizing inductance. This new method of increasing the inductance of a MEMS inductor has been first suggested and demonstrated here. With only a 1wt% MNP mixture and a simple planar spiral inductor structure, the proposed method yielded a significant inductance gain of over 50%, which is comparable to the state of the art inductance gain achieved with MNPs by any method. In previous reports, this much gain was obtained with a 50wt% MNP mixture.

This paper firstly reports a highly reliable MEMS-switch employing a CNTs-network lubricant in the contact-area. By covering the contact-area with the CNTs-network, we achieved more than an order of magnitude extension in the lifetime of the MEMS-switch. We determined that this drastic improvement in the reliability arises from the compressibility of the CNTs-network, generating remarkable contact-area widening with suppressed adhesive interaction at the contact interface. We also observed that the highly flexible CNTs-network does not deteriorate high-speed operation of the device. The proposed switch exhibited a lifetime more than 10 times longer under hot-switching condition than a device without CNTs.

A hybrid complementary logic inverter consisting of a microelectromechanical system switch as a promising alternative for the p-type oxide thin film transistor (TFT) and an n-type oxide TFT is presented for ultralow power integrated circuits. These heterogeneous microdevices are monolithically integrated. The resulting logic device shows a distinctive voltage transfer characteristic curve, very low static leakage, zero-short circuit current, and exceedingly high voltage gain.

This paper presents a microelectromechanical systems contact switch having both hard and soft contact materials in a single cantilever-type switching device. It operates with a zipping mechanism within which both contact materials (Pt-to-Pt and Au-to-Au) make individual contact sequentially and then detach in a reverse sequence to take advantage of both contact materials: low contact resistance and high reliability in a hot switching condition. In addition, an extended gate electrode and double T-shape cantilever beam structures effectively facilitate the sequential actuation. The fabricated switch successfully demonstrated a “dual-contact concept”—it made two sequential contacts at 31 (Pt-to-Pt) and 56 V (Au-to-Au) and it was then detached at 49 (Au-to-Au) and 23 V (Pt-to-Pt) in a single switching operation. Also, it achieved a low contact resistance of 0.3–0.5 $\Omega$ (including beam and some portion of the signal line resistances) at gate voltage from 60 to 70 V owing to the Au-to-Au contact in the device. Simultaneously, negligible contact resistance variation was observed during 2 $\times 10^{{6}}$ cycles at a voltage/current level of 10 V/10 mA under hot switching and unpackaged environments, representing ${>}{100}$ -fold longer lifetime than that of a conventional Au-to-Au cantilever switch fabricated on the same wafer. $\hfill[2013\hbox{--}0085]$

In a conventional parallel plate MEMS variable capacitor, the capacitance versus voltage response (C-V response) has been deterministic. In this work, the C-V response is tuned versatilely through the application of a control voltage to an additional electrode in order that the initial gap between the parallel capacitor plates is set by the control voltage. Then, the capacitor plates are lifted (capacitance decreases) as the actuation voltage applied to the levering actuator increases. In this manner, the shape of the C-V response can be controlled even after the device is fabricated. At a zero control voltage, the fabricated MEMS variable capacitor exhibited a convex shape in the C-V response (i.e., the capacitance decreases slowly in the low actuation voltage region and rapidly in the high actuation voltage region). When 3 V was applied to the control voltage, the capacitor exhibited an almost linear C-V response with a linearity factor of 0.999. At 5 V of control voltage, the C-V response changed to a relatively concave shape (i.e., the capacitance decreases rapidly in the low actuation voltage region and slowly in the high actuation voltage region). The capacitance tuning ratio of the fabricated device exceeded 120% at all control voltages. The proposed C-V response tuning capability is vital and amenable to various circuit demands.

Nanowires are being actively explored as promising nanostructured materials for high performance flexible electronics, biochemical sensors, photonic applications, solar cells, and secondary batteries. In particular, ultralong (centimeter-long) nanowires are highly attractive from the perspective of electronic performance, device throughput (or productivity), and the possibility of novel applications. However, most previous works on ultralong nanowires have issues related to limited length, productivity, difficult alignment, and deploying onto the planar substrate complying with well-matured device fabrication technologies. Here, we demonstrate a highly ordered ultralong (up to 20 cm) nanowire array, with a diameter of 50 nm (aspect ratio of up to 4,000,000:1), in an unprecedented large (8 in.) scale (2,000,000 strands on a wafer). We first devised a perfectly connected ultralong nanograting master template on the whole area of an 8 in. substrate using a top-down approach, with a density equivalent to that achieved with e-beam lithography (100 nm). Using this large-area, ultralong, high-density nanograting template, we developed a fast and effective method for fabricating up to 20 cm long nanowire arrays on a plastic substrate, composed of metal, dielectric, oxide, and ferroelectric materials. As a suggestion of practical application, a prototype of a large-area aluminum wire grid polarizer was demonstrated.

This paper reports a dual-contact microelectromechanical switch, which consists of two contacts in a single switch: one with a soft contact material and the other with a hard contact material to achieve low contact resistance and high reliability at the same time under hot switching conditions. In a single switching operation, the proposed dual-contact switch makes contact twice in sequence, where the first contact is made with a hard contact material (Pt-to-Pt) that can withstand an abrupt hot switching condition (high electric field or micro-arcing). The second contact is then accomplished with the soft contact material (Au-to-Au) that has low-contact resistance, through which most of the current flows. In contrast, when the switch releases contact, the Au-to-Au contact is initially detached, and this is followed by the release of the Pt-to-Pt contact. In this way, the dual-contact switch showed longer lifetime than that of a single Au-to-Au contact-only switch by up to fortyfold, and even better lifetime than that of a single Pt-to-Pt contact-only switch by more than two times in open laboratory environments (unpackaged). At the same time, contact resistance of the dual-contact switch was under 0.3 Ω at 50 V of the gate voltage, which is more than seven times smaller than that of the single Pt-to-Pt contact-only switch (2.2 Ω), due to the Au-to-Au contact sub-switch (the contact resistance of the single Au-to-Au contact-only switch was 2.2 Ω).

Nanoelectromechanical (NEM) switches have received widespread attention as promising candidates in the drive to surmount the physical limitations currently faced by complementary metal oxide semiconductor technology. The NEM switch has demonstrated superior characteristics including quasi-zero leakage behaviour, excellent density capability and operation in harsh environments. However, an unacceptably high operating voltage (4-20 V) has posed a major obstacle in the practical use of the NEM switch in low-power integrated circuits. To utilize the NEM switch widely as a core device component in ultralow power applications, the operation voltage needs to be reduced to 1 V or below. However, sub-1 V actuation has not yet been demonstrated because of fabrication difficulties and irreversible switching failure caused by surface adhesion. Here, we report the sub-1 V operation of a NEM switch through the introduction of a novel pipe clip device structure and an effective air gap fabrication technique. This achievement is primarily attributed to the incorporation of a 4-nm-thick air gap, which is the smallest reported so far for a NEM switch generated using a 'top-down' approach. Our structure and process can potentially be utilized in various nanogap-related applications, including NEM switch-based ultralow-power integrated circuits, NEM resonators, nanogap electrodes for scientific research and sensors.

This paper reports on a novel electrostatically actuated microelectromechanical systems (MEMS) relay for use in power-switching applications. It features a levering and torsional spring to enhance the stand-off voltage and contact endurance by means of an active-opening scheme. The proposed relay is based on a unique stacked-electrode structure and a soft insulating layer under the contact material that make it possible to obtain extremely low contact resistance, resulting in high current driving capability and reliable contact endurance. The fabricated relay demonstrated actuation voltages under 40 V, a switching time of 230 μs, and a maximum stand-off voltage of 360 V, which is the highest level among electrostatically actuated MEMS relays reported to date. The contact resistance was under 5 mΩ at 40 V of applied voltage, and more than 1 A could be carried. The contact reliability in a hot-switching condition was investigated for various dc current levels. At a current of 10 mA, the relay operated for more than 107 cycles before the test was stopped. In addition, the permanent contact stiction during switching operation at a 200-mA current level was overcome with a pull-off (active-opening) voltage of 90 V by the levering and torsional spring. Using this healing process, a device that failed at about 104 switching cycles in the 200-mA hot-switching mode was revived and reoperated with negligible contact resistance variation, lasting up to 4.9 ×105 cycles, constituting an order-of-magnitude enhancement in the lifetime even after failure.

In addition to contact angle changes, adhesion force changes by electrowetting on a polymer microlens are reported in this paper. A flexible poly(dimethylsiloxane) (PDMS) microlens array was fabricated with an embedded Cr/Au double-layered electrode and a dielectric layer of parylene and Teflon. On microlens structures with a Teflon layer, a deionized water droplet on the microlens array surface shows a high contact angle of 137° before electrowetting. The contact angle is decreased to 63° by electrowetting with an external bias of 250 V. The electrowetting process carried out on the microlens array also enhances the adhesion force between the water droplet and the microlens array. This change in the adhesion force after electrowetting is demonstrated by a water droplet that hangs upside down on the fabricated microlens array. From the computed work of adhesion, it is shown that a larger difference in the adhesion force by electrowetting can be achieved on the fabricated microlens array than on a...

This paper reports a label-free biosensor for the detection of DNA hybridization. The proposed biosensor measures the surface potential on oligonucleotide modified electrodes using a direct charge accumulation method. The sensor directly and repeatedly measures the charges induced in the working electrode, which correspond to intrinsic negative charges in immobilized molecules. The sensor achieves an improved signal-to-noise ratio (SNR), through the oversampling effect of accumulation for charges and the differential architecture. The sensor also shows stable, robust, and reproducible measurement independent of slight changes in the reference voltage, unlike previous ion-sensitive field effect transistors (ISFETs), providing the benefits of choosing a wide variety of reference electrode materials. The proposed device is integrated with working electrodes, a reference electrode and readout circuits into one package via a 0.35 μm complementary metal-oxide-semiconductor (CMOS) process. The sensor achieves a detectable range of 88.3 dB and a detection limit of 36 μV for surface potential. It is demonstrated that the sensor successfully achieves specific detection of oligonucleotide sequences derived from the H5N1 avian influenza virus. The experiments show a limit of detection of 100 pM and include a single-base mismatch test in 18-mer oligonucleotides.