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Abstract An infrared (IR) absorber is a crucial component for thermal detectors, requiring high absorptance over a broad wavelength range while maintaining low heat capacity for optimal performance. Most thermal detectors use a thin film IR absorber that is suspended in air, supported by a layer beneath it for mechanical stability. However, this support layer increases heat capacity without contributing to IR absorptance, thereby reducing the performance of thermal detectors. In this paper, we introduce a polarization-independent nanowire array absorber using flanged nanowires with a C-shaped cross-section. This C-shaped design provides mechanical stability, eliminating the need for a support layer. Although nanowire array is generally known to exhibit polarization characteristics, the unique structure of the proposed flanged nanowires enables them to achieve polarization-independent properties, resulting in high absorptance similar to that of film absorbers. We theoretically analyzed the polarization-independent characteristics of the flanged nanowires using an optical circuit model and optimized the flanged nanowire structure using finite-difference time-domain (FDTD) simulations. Finally, we experimentally demonstrated the polarization-independent characteristics of the flanged nanowires and confirmed their high absorptance comparable to that of film absorbers.

Abstract The increasing significance of hydrogen (H2) gas as a clean energy source has prompted the development of high-performance H2 gas sensors. Palladium (Pd)-based sensors, with their advantages of selectivity, scalability, and cost-effectiveness, have shown promise in this regard. However, the long-term stability and reliability of Pd-based sensors remain a challenge. This study not only identifies the exact cause for performance degradation in palladium (Pd) nanowire H2 sensors, but also implements and optimizes a cost-effective recovery method. The results from density functional theory (DFT) calculations and material analysis confirm the presence of C = O bonds, indicating performance degradation due to carbon dioxide (CO2) accumulation on the Pd surface. Based on the molecular behavior calculation in high temperatures, we optimized the thermal treatment method of 200 °C for 10 minutes to remove the C = O contaminants, resulting in nearly 100% recovery of the sensor’s initial performance even after 2 months of contamination.

Abstract Antireflection, vital in optoelectronics devices such as solar cells and photodetectors, reduces light reflection and increases absorption. Antireflective structures (ARS), a primary method by which to realize this effect, control the refractive index (RI) profile based on their shape. The antireflection efficiency depends on the refractive index profile, with the quintic RI profile being recognized as ideal for superior antireflection. However, fabricating nano-sized structures with a desired shape, particularly in silicon with a quintic RI profile, has been a challenge. In this study, we introduce a funnel-shaped silicon (Si) ARS with a quintic RI profile. Its antireflective properties are demonstrated through reflectance measurements and by an application to a photodetector surface. Compared to the film Si and cone-shaped ARS types, which are common structures to achieve antireflection, the funnel-shaped ARS showed reflectance of 4.24% at 760 nm, whereas those of the film Si and cone-shaped ARS were 32.8% and 10.6%, respectively. Photodetectors with the funnel-shaped ARS showed responsivity of 0.077 A/W at 950 nm, which is 19.54 times higher than that with the film Si and 2.45 times higher than that with the cone-shaped ARS.

Abstract The rapid growth of data‐intensive applications has significantly heightened the concerns about power consumption in current computing systems. From this perspective, there have been substantial efforts to implement ultra‐low power systems by integrating nanoelectromechanical non‐volatile switches (NEM‐NVS) with near‐zero leakage current into standard complementary metal‐oxide‐semiconductor (CMOS) circuits. To practically harness the potential of the NEM‐NVS, it is imperative to achieve high performance, such as low voltage, high on/off ratio, and high reliability, while simultaneously ensuring wafer‐scale CMOS compatibility. However, achieving these requirements is still challenging, primarily due to their electrostatic operation, in‐plane electrode configuration, and conventional fabrication methods. Here, an electro‐thermally actuated nanomechanical non‐volatile switch (ETAN‐NVS) with an out‐of‐plane electrode configuration along with an 8‐inch wafer‐scale CMOS‐compatible fabrication method is reported. By introducing the electrothermal mechanism into a vertically actuated buckling nanostructure, the fabricated ETAN‐NVS attains CMOS‐level voltage (108), and exceptional reliability (>1300 cycles). Moreover, a successful wafer‐scale demonstration of the ETAN‐NVS using only a CMOS‐compatible process paves the way for 3D integration with CMOS logic.

Abstract Miniaturized fluorescence imaging systems are promising platforms that overcome the limited use of conventional microscopes in the biomedical field. However, there are physical limitations for multicolor fluorescence imaging in existing miniaturized imaging systems because multiple filters have to be integrated into a small structure. Here, we present a miniaturized multicolor fluorescence imaging system integrated with single polydimethylsiloxane (PDMS) light-guide plate (LGP) for multicolor fluorescence imaging. The PDMS LGP allows guiding the transmitted light from the light source only to the fluorescent samples regardless of the wavelength of the light source. Thus, our system is capable of multicolor fluorescence imaging without multiple filters that block the excitation light. We demonstrated the usability of our system in the biomedical field by observing green- and red-labeled cells in the incubator. Our proposed system can be used in a wide range of applications for studies that require multicolor fluorescence imaging in the biomedical field.

Achieving both low energy consumption and radiation-hardness is highly challenging in memory devices. Here, the authors demonstrate a sub-10 fJ/bit, radiation-hard nanoelectromechanical non-volatile memory through structural and material approaches.

Abstract Recently, copper oxide (CuO) has drawn much attention as a promising material in visible light photodetection with its advantages in ease of nanofabrication. CuO allows a variety of nanostructures to be explored to enhance the optoelectrical performance such as photogenerated carriers scattering and bandgap engineering. However, previous researches neglect in-depth analysis of CuO’s light interaction effects, restrictively using random orientation such as randomly arranged nanowires, single nanowires, and dispersed nanoparticles. Here, we demonstrate an ultra-high performance CuO visible light photodetector utilizing perfectly-aligned nanowire array structures. CuO nanowires with 300 nm-width critical dimension suppressed carrier transport in the dark state and enhanced the conversion of photons to carriers; additionally, the aligned arrangement of the nanowires with designed geometry improved the light absorption by means of the constructive interference effect. The proposed nanostructures provide advantages in terms of dark current, photocurrent, and response time, showing unprecedentedly high (state-of-the-art) optoelectronic performance, including high values of sensitivity (S = 172.21%), photo-responsivity (R = 16.03 A/W, λ = 535 nm), photo-detectivity (D * = 7.78 × 1011 Jones), rise/decay time (τ r /τ d = 0.31 s/1.21 s).

Abstract 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%.

The development of a mechanically operated random access memory using an electrostatically actuated metallic microswitch for nonvolatile memory application is described. Good endurance and retention properties were observed due to the Au-to-Au contact microswitch with an on/off current ratio over [10.super.7], an abrupt switching with less than 1mV/dec and a zero off current.

We describe a very simple breathing rate-sensing method that detects a significant electric current change between two metal electrodes on an oxidized surface. The current change is caused by the formation of a water layer from exhaled breath. We discovered that breathing onto the oxidized surface causes instant water condensation, and it generates 20 times increased current than that measured in the inhalation period. The condensed water quickly evaporates, enabling us to detect dynamic human breathing in real time. We also investigated the breathing rate sensor by varying the relative humidity, temperature, and breathing frequency and confirmed its potential for practical applications. [ABSTRACT FROM AUTHOR]

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 Ω (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 × 106 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. [ABSTRACT FROM AUTHOR]

In this paper, an ultra-low voltage microelectromechanical system (MEMS) switch is proposed, modeled and demonstrated. Through the introduction of torsional hinges, stiction-recovery actuation was possible, and thus irreversible stiction could be overcome. Owing to this see-saw-like actuation, the switch could be freely designed to have low stiffness resulting in an ultra-low actuation voltage. The proposed switch shows an actuation voltage of around 3 V, which is especially low compared with typical values of several tens of volts in conventional microelectromechanical switches. Variation of the actuation voltage stayed under 12% during 106 cycles. Switching performance was degraded by an increase of contact resistance rather than in-use stiction. Using the proposed switches, low-voltage mechanical logic gates were also proposed and successfully demonstrated, operating at VDD of 3 V. [ABSTRACT FROM AUTHOR]