Device Area Research Articles

Fluorine-Containing Passivation Layer via Surface Chelation for Inorganic Perovskite Solar Cells.

Minimizing surface defect is vital to further improve power conversion efficiency (PCE) and stability of inorganic perovskite solar cells (PSCs). Herein, we designed a passivator trifluoroacetamidine (TFA) to suppress CsPbI3-xBrx film defects. The amidine group of TFA can strongly chelate onto the perovskite surface to suppress the iodide vacancy, strengthened by additional hydrogen bonds. Moreover, three fluorine atoms allow strong intermolecular connection via intermolecular hydrogen bonds, thus constructing a robust shield against moisture. The TFA-treated PSCs exhibit remarkably suppressed recombination, yielding the record PCEs of 21.35% and 17.21% for 0.09 cm2 and 1.0 cm2 device areas, both of which are the highest for all-inorganic PSCs so far. The device also achieves a PCE of 39.78% under indoor illumination, the highest for all-inorganic indoor photovoltaic devices. Furthermore, TFA greatly improves device ambient stability by preserving 93% of the initial PCE after 960 h.

Large-Area Blade-Coated Deep-Blue Polymer Light-Emitting Diodes with a Narrowband and Uniform Emission.

Large-area polymer light-emitting diodes (PLEDs) manufactured by printing are required for flat-panel lighting and displays. Nevertheless, it remains challenging to fabricate large-area and stable deep-blue PLEDs with narrowband emission due to the difficulties in precisely tuning film uniformity and obtaining single-exciton emission. Herein, efficient and stable large-area deep-blue PLEDs with narrowband emission are prepared from encapsulated polydiarylfluorene. Encapsulated polydiarylfluorenes presented an efficient and stable deep-blue emission (peak: 439nm; full width at half maximum (FWHM): 39nm) in the solid state due to their single-chain emission behavior without inter-backbone chain aggregation. Large-area uniform blade-coated films (16 cm2 ) are also fabricated with excellent smoothness and morphology. Benefitting from efficient emission and excellent printed capacity, the blade-coated PLEDs with a device area of 9 mm2 realized uniform deep-blue emission (FWHM: 38nm; CIE: 0.153, 0.067), with a corresponding maximum external quantum efficiency and the brightness comparable to those of devices based on spin-coated films. Finally, considering the essential role of deep-blue LEDs, a preliminary patterned PLED array with a pixel size of 800 × 1000 µm2 and a monochrome display is fabricated, highlighting potential full-color display applications.

Switch mode capacitive pressure sensors

Switch mode capacitive pressure sensors are proposed as a new class of microfabricated devices that transform pressure into a mechanically switching capacitance to form an analog-to-digital signal with zero power, high sensitivity, and a high signal-to-noise ratio. A pressure-sensitive gold membrane suspended over a capacitive cavity makes ohmic contact with patterned gold leads on the substrate, closing circuits to fixed on-chip capacitors outside the cavity and leading to significant step responses. This function is achieved by allocating the switch leads on the part of the counter electrode area, while the remaining area is used for touch mode analog capacitive sensing. The sensor microchip is prototyped through a novel design approach to surface micromachining that integrates micro-Tesla valves for vacuum sealing the sensor cavity, showing an unprecedented response to applied pressure. For a gauge pressure range of 0–120 mmHg, the sensor exhibits an increase of 13.21 pF with resultant switch events, each of which ranges from 2.53–3.96 pF every 12–38 mmHg, in addition to the touch mode linear capacitive increase between switches. The equivalent sensitivity is 80–240 fF/mmHg, which is 11–600× more than commercial and reported touch mode sensors operating in similar pressure ranges. The sensor is further demonstrated for wireless pressure tracking by creating a resonant tank with the sensor, showing a 32.5–101.6 kHz/mmHg sensitivity with frequency jumps led by the switch events. The developed sensor, with its promising performance, offers new application opportunities in a variety of device areas, including health care, robotics, industrial control, and environmental monitoring.

Hierarchical Nanoscale Structuring of Solution-Processed 2D van der Waals Networks for Wafer-Scale, Stretchable Electronics

Two-dimensional (2D) semiconductors are promising for next-generation electronics that are lightweight, flexible, and stretchable. Achieving stretchability with suppressed crack formation, however, is still difficult without introducing lithographically etched micropatterns, which significantly reduces active device areas. Herein, we report a solution-based hierarchical structuring to create stretchable semiconducting films that are continuous over wafer-scale areas via self-assembly of two-dimensional nanosheets. Electrochemically exfoliated MoS2 nanosheets with large lateral sizes (∼1 μm) are first assembled into a uniform film on a prestrained thermoplastic substrate, followed by strain relief of the substrate to create nanoscale wrinkles. Subsequent strain-relief cycles with the presence of soluble polymer films produce hierarchical wrinkles with multigenerational structures. Stretchable MoS2 films are then realized by curing an elastomer directly on the wrinkled surface and dissolving the thermoplastic. Three-generation hierarchical MoS2 wrinkles are resistant to cracking up to nearly 100% substrate stretching and achieve drastically enhanced photoresponsivity compared to the flat counterpart over the visible and NIR regimes, while the flat MoS2 film is beneficial in creating strain sensors because of its strain-dependent electrical response.

An Innovative method for adjustable broadband THz to Mid-IR optical modulator using Graphene Gratings surface plasmon Fabry–Perot resonances with low insertion loss, high speed and modulation depth

Through numerical modeling, we present an ultrasensitive tunable Terahertz (THz) to Mid-IR modulator composed of single-layer graphene-based gratings combined with a Fabry–Perot (FP) cavity. The perpendicular-polarized incident light on gratings causes the grating edges to act as an electrical dipole, resulting in an FP interferometer of induced plasmonic waves on the graphene surface. The electric field in the cavity is substantially limited by the activation of standing-waves (SWs) graphene surface plasmon polaritons. The multi-mode SWs formation inside the gratings provides an excellent platform for THz to Mid-IR light modulation with promising features. We have demonstrated a modulation depth of 100% in desired frequencies with near zero insertion loss via full-wave electromagnetic simulations at the normal incident in the THz to Mid-IR range. The light reflection and absorption of the proposed structure have a multi-band profile due to the FP behavior. Therefore, it can be easily tuned by electrically directing the chemical potential of graphene. Due to multi-resonance-based reflected light, each resonance represents different behavior with different modulation parameters. In other words, not only any desired frequency can be chosen, but also at the constant frequency of interest; by choosing the appropriate mode, the desired linewidth, FWHM, and modulation depth can be easily obtained. Finally, we investigated the device bandwidth. The THz modulator requires a large device area for an average number of gratings, and the device area at the 3 dB frequency reaches as high as 1.5 THz, which depicts the high modulation speed in the proposed modulator. The proposed graphene plasmonic grating scheme is a promising candidate for developing the on-chip integrated THz to Mid-IR optical telecommunications. Moreover, the perfect absorption of graphene opens an opportunity to design photodetectors with high responsivity and quantum efficiency, which gives the proposed structure a multi-function capability.

A Small Capacity Methane-Hydrogen Blend Fueled Gas Turbine

Nowadays the environmental problem is of issue for many scientists around the world. This is stemming from climate changes caused by greenhouse gas emissions (the industrial sector accounts for 50% of them). Therefore, urgent measures have to be taken to reduce the emissions of these gases significantly. In this connection, we are witnessing a worldwide trend toward predominant use of renewable energy sources, with the hydrogen energy being the most significant one of them. The aim of the work was to study the effect an addition of hydrogen to methane as fuel has on the thermal characteristics of a 100 kWe micro gas turbine unit and on the geometrical dimensions of the fuel admission device at constant values of the volumetric flow rates of air supplied and flue combustion gases generated in the same installation. The study, which was carried out using the EPSILON computer program, has shown that the addition of hydrogen to methane leads to an increase in the volumetric fuel flowrate and, hence, generates the need to increase the fuel admission device cross-section area. An increase in the percentage content of hydrogen leads to a decrease of temperatures upstream of the turbine by no more than 12°C. If methane is completely replaced by hydrogen, the power unit efficiency decreases by only 1%. Thus, the thermal characteristics of the micro gas turbine unit under study do not change significantly; however, the design of the fuel injection device has to be modified.

Lag Time in Diffusion-Controlled Release Formulations Containing a Drug-Free Outer Layer

Theoretical considerations along with extensive Monte Carlo simulations are used to calculate the lag time before the initiation of diffusion-controlled drug release in multilayer planar devices with an outer layer containing no drug. The presented results are also relevant in formulations coated by a drug-free membrane as well as in other reservoir systems. The diffusion of drug molecules through the outer layer towards the release medium is considered, giving rise to the observed lag time. We have determined the dependence of lag time on the thickness and the diffusion coefficient of the drug-free outer layer, as well as on the initial drug concentration and the surface area of the planar device. A simple expression, obtained through an analytical solution of diffusion equation, provides an approximate estimate for the lag time that describes the numerical results reasonably well; according to this relation, the lag time is proportional to the squared thickness of the outer layer over the corresponding diffusion coefficient and inversely proportional to the logarithm of the linear number density of the drug that is initially loaded in the inner layer.

Current spray-coating approaches to manufacture perovskite solar cells

The research interest in perovskite solar cells (PSCs) is increasing because of the rapid developments in the recent times. PSCs exhibit exceptional photovoltaic performance, which is presently more than 25% for single-junction solar cells; thus, they have a high potential of achieving industrial commercialization and production. Nevertheless, the greatest issue faced by commercial applications is the device area of a PSC. Several fabrication techniques have been presented to create large-area PSCs such as slot-die coating, spray coating, blade coating and vacuum deposition. This paper reviews the spray coating method for the development of PSC. Developments in spray-cast PSCs that have occurred in the last few years are summarized in the study, with the focus on the deposition method, performance, morphology, stability, and large-area fabrication. It concludes that spray coating is the most suitable method for achieving the scalable manufacturing of large-area PSCs with moderate to high efficiencies.

Experimental study on the aerodynamic performance of variable geometry low-pressure turbine adjustable guide vanes

An annular cascade testing rig of a variable-geometry low-pressure turbine with a large expansion angle was designed and built, combining a five-hole probe, a surface static pressure test system, and a PIV(Particle Image Velocimetry) measurement system. The effects of exit Mach numbers (0.2, 0.3, 0.4), turning angles (−1.5°, 0°, 3°), and adjustable device diameters (30 mm, 40 mm) on turbine cascade aerodynamic performance were experimentally investigated. Numerical simulations were also carried out to gain more insight into the flow fundamentals. Results show that the endwall clearance and the adjustable device significantly influence the flow field, with leakage flows before, after, and around the disc. The leakage vortex and passage vortex formation resulted in two high-loss regions in the shroud and hub endwall regions. The aerodynamic loss structures at the exit section were similar at different Mach numbers and varied considerably at different turning angles. Besides, a larger area of the adjustable device (d = 40 mm) was found to reduce the leakage loss caused by upper and lower clearance leakage flows and inhibit the development of secondary flows, resulting in a more straightforward secondary flow structure and a smaller influence range. Quantitatively, the adjustable device with a diameter of 40 mm could decrease the average total pressure loss coefficients by 11.5%, 16.6%, and 6.3% at three turning angles (−1.5°, 0°, 3°), respectively, compare to the adjustable device with a diameter of 30 mm.

Suppress Short Channel Effects on Split Channel-Cylindrical GAA TFET Using Buried Oxide Layer

The idea of a buried oxide layer (BOx) in a split channel Gate All Around-Tunnel Field Effect Transistor (GAA-TFET) was investigated in this paper. This work examined the impact of buried oxide layer on the device's performance. With the BOx layer present and channel length of 20nm, the channel area of the TFET device investigated in this study is divided equally on the same side. The doping concentration has been transferred to the split channel on the drain side. The device’s performance was examined using numerical simulation utilizing simulation software of CAD devices. The final results which incorporate the buried oxide layer were being compared to the uniform split channel GAA-TFET. The parameters like ON current (Ion),OFF current (Ioff), subthreshold swing (SS) and electric-field (E) intensity are observed and compared with silicon (Si) based GAA-TFET and Indium phosphide (InP) based GAA-TFET. It is found that InP based GAA-TFET with buried oxide layer is more advanced device design than the others with Ion and Ioff of 3.02 x 10-05 A/um and 2.09 x 10-22 A/um, respectively.

Enhancement of liquid-solid mixing and particle hydrophobization by an impeller-less flotation pulp conditioning device

An impeller-less device was proposed to employ opposite rotational jet flows conditioning pulp before flotation. The flow field characteristics and relevant effects on the liquid-solid mixing performance were investigated by the numerical simulation of computational fluid dynamics that was proved effective by the particle image velocimetry technique. The outcome of particle surface modification was clarified by variations in the contact angle and surface species of quartz particles. Results showed that the increase of turbulent kinetic energy induced by the opposite rotational flows remarkably improved the dispersion of mineral particles. Smaller particle size and larger circulation rate were conductive to a more uniform distribution of particles. In the case of a volume flow of 3.6 m3/h and a feed volume fraction of 7 % with an average particle size of −45 μm, nearly 4/5th of the whole device area exhibits a particle volume fraction within the range of 6 % and 7 %, and the coefficient of variation was as low as 0.151. Meanwhile, strong turbulence and high shear induced by opposite rotational flows provided favorable conditions for the collector adsorption and particle hydrophobization, which was responsible for the increase in contact angle under relatively higher volumetric flow rates. However, when the volume flow exceeded 3.0 m3/h, over-increasing shear stresses and excessive turbulence caused the desorption of adsorbed collectors, reflected as the decreased nitrogen content on quartz surfaces from 0.85 % to 0.51 %, thereby accounting for the declined contact angle of conditioned quartz particles. This study highlighted the dominant effect of turbulence and shear strain on particle surface modification, and the significance of proper parameter control.

Threshold switching stabilization of NbO2 films via nanoscale devices

The stabilization of the threshold switching characteristics of memristive NbOx is examined as a function of sample growth and device characteristics. Sub-stoichiometric Nb2O5 was deposited via magnetron sputtering and patterned in nanoscale (50×50–170×170nm2) W/Ir/NbOx/TiN devices and microscale (2×2–15×15μm2) crossbar Au/Ru/NbOx/Pt devices. Annealing the nanoscale devices at 700 °C removed the need for electroforming the devices. The smallest nanoscale devices showed a large asymmetry in the IV curves for positive and negative bias that switched to symmetric behavior for the larger and microscale devices. Electroforming the microscale crossbar devices created conducting NbO2 filaments with symmetric IV curves whose behavior did not change as the device area increased. The smallest devices showed the largest threshold voltages and most stable threshold switching. As the nanoscale device area increased, the resistance of the devices scaled with the area as R∝A−1, indicating a crystallized bulk NbO2 device. When the nanoscale device size was comparable to the size of the filaments, the annealed nanoscale devices showed similar electrical responses as the electroformed microscale crossbar devices, indicating filament-like behavior in even annealed devices without electroforming. Finally, the addition of up to 1.8% Ti dopant into the films did not improve or stabilize the threshold switching in the microscale crossbar devices.

Chemotaxis along local chemical gradients enhanced bacteria dispersion and PAH bioavailability in a heterogenous porous medium

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous, EPA-designated priority pollutants for soil and groundwater, remaining recalcitrant to bioremediation because of limited bioavailability. In this work, we used naphthalene as a model PAH and soil bacteria Pseudomonas putida G7 to investigate the potential role of chemotaxis to enhance access to PAHs in heterogenous porous media. To this aim, we conducted transport experiments and numerical simulations with chemotactic bacteria and naphthalene trapped within a non-aqueous phase liquid (NAPL) mainly in low permeable areas of a dual-permeability microfluidic device. Microscopic imaging showed higher accumulations of chemotactic bacteria, about eight times that of nonchemotactic bacteria, at the junctures between high and low permeability regions. Pore-scale simulations for fluid flow and naphthalene revealed that the junctures are stagnant areas of fluid flow, which generated strong and temporally persistent naphthalene gradients. The landscape and densities of bacterial accumulation at the junctures were strongly regulated by flow profiles and naphthalene gradients especially those transverse to flow. We conducted macroscale simulations using convective dispersion equations with an added chemotactic velocity to account for directed migration toward naphthalene. Simulated results showed good consistency with experiments and pore-scale simulation as normalized bacterial accumulation per mm of NAPL was 7.80, 7.84 and 7.71 mm−1 for experiments, pore-scale and macroscale simulations, respectively. Macroscale simulations indicated that in the absence of grain-boundary restrictions associated with the pore structure bacterial dispersion needed to be increased by 50 % to account for the interplay between chemotactic response and naphthalene gradients at the pore-scale level. Our work details the mechanism of pore-scale chemotaxis in enhancing bioavailability of PAHs and its impact on biomass retention at the system level, which provides a potential solution toward more efficient bioremediation for contaminants such as PAHs with limited bioavailability.

Strategies for Giant Mass Sensitivity Using Super-High-Frequency Acoustic Waves

Surface acoustic wave (SAW) devices are powerful platforms for mass sensing, chemical vapor or gas detection, and biomolecular identification. Great efforts have been made to achieve high sensitivities by using super-high-frequency SAW devices. Conventional SAW sensing is based on mass-loading effects at the acoustic wave propagation (or delay line) region between two interdigitated transducers (IDTs). However, for many super-high-frequency SAW devices with their small sizes, there is a huge challenge that the sensitivity is difficult to be further increased, simply because there are very limited areas between the IDTs to deposit a sensing layer. Herein, we proposed a novel strategy based on giant mass-sensitivity effects generated on the global area of acoustic wave device (defined as areas of both delay line region and IDTs), which significantly enhances sensitivity and reduces the detection limit of the SAW device. Both theoretical analysis and experimental results proved this new strategy and mechanism, which are mainly attributed to the efficient energy confinement at the IDTs’ region for the super-high-frequency SAW devices. The achieved mass sensitivity using this new strategy is as high as 2590 MHz <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\cdot $ </tex-math></inline-formula> mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{{2}} \cdot \mu \text{g}^{-{1}}$ </tex-math></inline-formula> , which is about 500 times higher than that obtained from only using the acoustic wave propagation region with a SAW frequency of 4.43 GHz. Hypersensitive humidity detection has been demonstrated using this newly proposed sensing platform, achieving an extremely high sensitivity of 278 kHz/%RH and the fast response and recovery times of ~37 and ~35 s, respectively.

Thermal performance of a directional heat radiation device utilizing the Monte Carlo ray tracing method

Conventional air conditioning systems heat and cool an entire space for the total volume but are deficient in terms of energy efficiency. Partial and personalized devices rarely take into account moving occupants and are deficient in terms of flexibility. To address these problems, a directional heat radiation (DHR) device was introduced. The effectiveness of the DHR device under heating conditions was verified by experiments and the thermal performance of the DHR device under three different arrangements was analyzed. Based on energy balance, the radiation distribution factor calculation model and the heat transfer model of the DHR device were established by combining the Monte Carlo ray tracing method and the thermal network method. The results showed that the thermal performance of the DHR device arranged level downward was best and twice that of the level upward arrangement. The mathematical model of the heat transfer process was verified by experimental data, and the relative error was within 2 %. The simulation results showed that the radiation temperature at different positions θdprt in the center of the room increased with increasing tube diameter and reflecting cover opening width and decreased with increasing tube spacing. Under simulated heating conditions, the optimal structure of the DHR device has a tube diameter of 16 mm, reflecting cover opening width of 60 mm, and tube spacing of 80 mm. The heat flux per unit floor area of the DHR device was approximately 56 W/m2, which reduced the heating capacity by 20 % compared to that without the reflector cover, while improving the local thermal environment of the space and increasing energy efficiency.

Racetrack microring resonator with improved quality factor based on asymmetric waveguide bend

Racetrack microring resonators with improved quality factors based on asymmetric Bezier waveguide bend for silicon nitride photonics integration platform have been proposed and demonstrated experimentally in this paper. The asymmetric Bezier waveguide bend can reduce bend loss which is one of the major limitations of the Q factor of racetrack microring resonators. The proposed racetrack microring resonator structure based on an asymmetric Bezier bend waveguide can significantly improve the Q factor while maintaining the same device area. Such racetrack microring resonators with superior performance can help improve the performance of on-chip devices and further promote the development of a photonic integration platform.

Special Issue on High-Speed Vision and its Applications

In recent years, advances in CMOS imagers and AI have rapidly expanded the application fields of image processing. Spatial resolution, sensitivity, dynamic range, etc. for devices have dramatically improved, while various recognition functions have been implemented with the introduction of learning-based information processing, making progress day by day. However, the temporal resolution or temporal dynamics of an image has been limited to the video rate level of processing, because image processing has been required to realize the functions of the human eye. In the case of processing for high-speed moving objects or controlling machine dynamics as machine eyes, rather than processing in the range visible to the human eye, high-speed vision, i.e., high-speed image processing in a bandwidth that covers the dynamics of the object, and a system that utilizes such processing, are required. This special issue summarizes such advanced research on high-speed vision, highlighting its current status and future development in the areas of devices, systems, and application developments. High-speed vision has entered a new era, as the basic technology and various applications have been developed and new functions are being added one after another. We hope that this timely special issue will help its readers grasp this major technological trend and create new system values.

Quick and surfactant-free dispersion of various carbon nanoparticles in aqueous solution as casting technique for devices

Tremendous applications of carbon-based nanomaterials need the individualization of particles in the liquid phase, preferably in an aqueous solution. Currently, one of the main challenges is how to obtain highly monodispersed and high-quality colloidal solutions and make it usable in electronic devices without performing badly. In this study, carbon nanoparticles (i.e., fullerenes, carbon nanotubes, graphene) were individualized and stabilized well in an aqueous solution by using a novel cutting-edge dispersion technique using sodium hypochlorite (NaClO) and sodium bromide (NaBr) assisted by brief low-power sonication treatment. This new method improves colloidal properties, provides a means by which carboxylate groups are introduced to the surface of the carbon nanoparticles that facilitates the formation of Na-carbon salts when the particles are exposed to the NaClO and NaBr mixed-salt solution. As a metal-salt complex, the Na-carbon is then readily susceptible to dispersion within a polar medium. Vacuum-filtration prepared salted carbon nanotube film, graphene and C60 have high electrical conductivity, and the representative carbon nanotube has a value up to 1.72 × 104 S/m, comparable to that dispersed by other traditional dispersants. Because of its nontoxicity and facile water-based solution features, we expect this dispersion and casting technique would pave its way into more device areas, etc.

Epidermal Inspired Flexible Sensor with Buckypaper/PDMS Interfaces for Multimodal and Human Motion Monitoring Applications.

The advancements in the areas of wearable devices and flexible electronic skin have led to the synthesis of scalable, ultrasensitive sensors to detect and differentiate multimodal stimuli and dynamic human movements. Herein, we reveal a novel architecture of an epidermal sensor fabricated by sandwiching the buckypaper between the layers of poly(dimethylsiloxane) (PDMS). This mechanically robust sensor can be conformally adhered on skin and has the perception capability to detect real-time transient human motions and the multimodal mechanical stimuli of stretching, bending, tapping, and twisting. The sensor has feasibility for real-time health monitoring as it can distinguish a wide range of human physiological activities like breathing, gulping, phonation, pulse monitoring, and finger and wrist bending. This multimodal wearable epidermal sensor possesses an ultrahigh gauge factor (GF) of 9178 with a large stretchability of 56%, significant durability for 5000 stretching–releasing cycles, and a fast response/recovery time of 59/88 ms. We anticipate that this novel, simple, and scalable design of a sensor with outstanding features will pave a new way to consummate the requirements of wearable electronics, flexible touch sensors, and electronic skin.

Reverse voltage protection circuits for power MOSFETs in low dropout power applications

This paper proposed three reverse voltage protection circuits for the power MOSFETs in low dropout power applications. Power devices are vulnerable to instantaneous current overshoot when the input voltage is lower than the output voltage. Compared with conventional solutions using diode for reverse current block, the proposed three structures consume fewer voltage drop during normal operation. The first design is suitable for applications with wide output ranges but requires the largest die area. The other two solutions are for applications with low output voltages, and are characterized with effective area arrangement and dead-zone free control, respectively. The proposed three protection structures require 126.2%, 12.25% and 43.05% extra die area of the power devices, respectively.