Miniaturization Of Devices Research Articles

Progress of Photocapacitors.

In response to the current trend of miniaturization of electronic devices and sensors, the complementary coupling of high-efficiency energy conversion and low-loss energy storage technologies has given rise to the development of photocapacitors (PCs), which combine energy conversion and storage in a single device. Photovoltaic systems integrated with supercapacitors offer unique light conversion and storage capabilities, resulting in improved overall efficiency over the past decade. Consequently, researchers have explored a wide range of device combinations, materials, and characterization techniques. This review provides a comprehensive overview of photocapacitors, including their configurations, operating mechanisms, manufacturing techniques, and materials, with a focus on emerging applications in small wireless devices, Internet of Things (IoT), and Internet of Everything (IoE). Furthermore, we highlight the importance of cutting-edge materials such as metal-organic frameworks (MOFs) and organic materials for supercapacitors, as well as novel materials in photovoltaics, in advancing PCs for a carbon-free, sustainable society. We also evaluate the potential development, prospects, and application scenarios of this emerging area of research.

Miniaturized Flexible Non-Contact Interface Based on Heat Shrinkage Technology.

High-performance miniaturized flexible sensors are becoming increasingly important in wearable electronics. However, miniaturization of devices often requires high-precision manufacturing processes and equipment, which limits the commercialization of flexible sensors. Therefore, revolutionary technologies for manufacturing miniaturized flexible sensors are highly desired. In this work, a new method for manufacturing miniaturized flexible humidity sensor by utilizing heat shrinkage technology is presented. This method successfully achieves much smaller sensor and denser interdigital electrode. Utilizing this method, a miniaturized flexible humidity sensor and array are presented, fabricated by anchoring nano-Al2 O3 into carbon nano-tube as the humidity sensitive film. This heat shrinkage technology, forming wrinkle structure on the humidity sensitive film, endows the sensor with a high sensitivity over 200% (ΔR/R0 ) at humidity levels ranging from 0 to 90%RH and a fast recovery time (0.5s). The sensor allows non-contact monitoring human respiration and alerting in case of an asthma attack and the sensor array can be adaptively attached to the wrist as a non-contact human-machine interface to control the mechanical hand or computer. This work provides a general and effective heat shrinkage technology for the development of smaller and more efficient flexible circuits and sensor devices.

Fabrication of Ultrasmall Si Encapsulated in Silicon Dioxide and Silicon Nitride as Alternative to Impurity Doping

Further miniaturization of complementary metal oxide semiconductor devices based on impurity‐doped semiconductors is limited due to statistical fluctuation of the impurity concentration in very small volumes and dopant deactivation, increasing the resistance and power consumption. Based on density functional theory calculations and backed by experimental data, the nanoscale electronic structure shift induced by anions at surfaces (NESSIAS) has been described recently. It explains the structure shift of low‐doped single‐crystalline Si nanowells (Si‐NWs) with thicknesses ≤3 nm embedded in SiO2 (Si3N4) toward n‐type (p‐type) behavior. The influence of the anions is on the scale of a few nanometers, allowing for very steep p–n junctions without the drawbacks of impurity doping. The process to fabricate crystalline silicon (c‐Si) NWs embedded in SiO2 and Si3N4, starting with silicon on insulator (SOI) across 15 × 15 mm2 samples, is described. Four possible methods to fabricate Si‐NWs by thinning down single‐crystalline top‐Si of an SOI substrate are evaluated in terms of reproducibility and surface roughness.

Hardmask engineering by mask encapsulation for enabling next generation reactive ion etch scaling

Miniaturization and scaling of semiconductor devices require development of innovative techniques to sustain advancements. A promising trend is the migration from 2D to 3D device architectures that necessitate fabrication of high-aspect-ratio narrow features through layers of different materials. Reactive ion etching can achieve this but poses unique challenges due to the requirement of etch chemistries capable of etching dissimilar materials with varying etch rates while maintaining high productivity. The choice of hardmask is also crucial, as it plays a critical role in determining efficacy of the etch process and the final shape of the feature being etched. To address these challenges, we introduce a new concept of hardmask engineering that involves a bilayer hardmask scheme consisting of a patterned conventional hardmask encapsulated with a thin layer of etch-resistant ruthenium (Ru) layer. Experimental results for etching multilayer stacks consisting of alternating pairs of SiO2 and Mo show that this engineered hardmask results in improved hardmask remaining and etch profile with smaller critical dimensions (CDs). Technology computer-aided design simulations with the Ru encapsulation layer on conventional carbon hardmask demonstrate increased poly-Si etch depth with reduced bow CD. This concept can be extended to any semiconductor nanofabrication step involving high-aspect-ratio etching where precise control of CDs is essential in the vertical direction.

Insight into heat transfer process of graphene aerogel composite phase change material

With electronic device miniaturization and integration, its thermal management is encountering challenges of high heat flux and eliminating thermal stress. Phase change thermal control is paid more attention to due to its high energy density and temperature uniformity. Therefore, a visual experimental platform was established to investigate the heat transfer and phase change characteristics of graphene aerogel composite phase change materials in this study. The results indicate that the heat dissipation enhancement of those composite materials can reach 220.8%, while graphene aerogel has the opposite effects of heat conduction enhancement and convection suppression. Furthermore, two new cascade arrangements are proposed and the effects of cascade arrangements on heat transfer performance are discussed. The improvement effect is best when the thermal conductivity increases longitude from top to bottom, whose heat dissipation efficiency is 207.5%, which is 11% higher than that of the group without cascade configurations. The horizontal cascade arrangement proposed in this study achieves an effective combination of heat conduction enhancement and convection heat transfer. Its heat dissipation is 12% more effective than the cavity filled with pure CPMCs using the same amount of porous materials, and the phase change speed is increased by 149 s.

Real time full-color imaging in a Meta-optical fiber endoscope

Endoscopes are an important component for the development of minimally invasive surgeries. Their size is one of the most critical aspects, because smaller and less rigid endoscopes enable higher agility, facilitate larger accessibility, and induce less stress on the surrounding tissue. In all existing endoscopes, the size of the optics poses a major limitation in miniaturization of the imaging system. Not only is making small optics difficult, but their performance also degrades with downscaling. Meta-optics have recently emerged as a promising candidate to drastically miniaturize optics while achieving similar functionalities with significantly reduced size. Herein, we report an inverse-designed meta-optic, which combined with a coherent fiber bundle enables a 33% reduction in the rigid tip length over traditional gradient-index (GRIN) lenses. We use the meta-optic fiber endoscope (MOFIE) to demonstrate real-time video capture in full visible color, the spatial resolution of which is primarily limited by the fiber itself. Our work shows the potential of meta-optics for integration and miniaturization of biomedical devices towards minimally invasive surgery.

Wafer-scale heterogeneous integration of self-powered lead-free metal halide UV photodetectors with ultrahigh stability and homogeneity

Large-scale growth and heterogeneous integration with existing semiconductors are the main obstacles to the application of metal halide perovskites in optoelectronics. Herein, a universal vacuum evaporation strategy is presented to prepare copper halide films with wafer-scale spatial homogeneity. Benefiting from the electric field manipulation method, the built-in electric fields are optimized and further boost the self-powered UV photodetecting performances of common wide-bandgap semiconductors by more than three orders of magnitude. Furthermore, with effective modulation of the interfacial charge dynamics, the as-fabricated GaN-substrate heterojunction photodetector demonstrates an ultrahigh on/off ratio exceeding 107, an impressive responsivity of up to 256 mA W–1, and a remarkable detectivity of 2.16 × 1013 Jones at 350 nm, 0 V bias. Additionally, the device exhibits an ultrafast response speed (tr/td = 716 ns/1.30 ms), an ultra-narrow photoresponse spectrum with an FWHM of 18 nm and outstanding continuous operational stability as well as long-term stability. Subsequently, a 372-pixel light-powered imaging sensor array with the coefficient of variation of photocurrents reducing to 5.20% is constructed, which demonstrates exceptional electrical homogeneity, operational reliability, and UV imaging capability. This strategy provides an efficient way for large-scale integration of metal halide perovskites with commercial semiconductors for miniature optoelectronic devices.

Parametric optimization of vortex generator configuration for flow control in an intake duct for waterjet propulsion

Vortex generators (VG) are simple miniature devices that suppress flow separation in aeronautical elements. In this study, VG device operation in a submerged flush waterjet inlet was numerically investigated to improve the flow quality entering the jet pump at low Inlet Velocity Ratio (IVR). Steady Reynolds-averaged Navier-Stokes equations are solved using the SST k-ω turbulence model and used to simulate the flow field, with the effects of the orientation, angle of attack, height and installation position of VGs thoroughly analyzed. The hydrodynamic performance of the intake duct was assessed over the operational range. The results show that VGs arranged in a divergent configuration better suppress flow separation. The zonal magnitude of the high turbulent kinetic energy on the ramp side was reduced, with the non-uniformity in the pump face plane reduced from 0.41 to 0.26. Excessive angles of attack and VG heights have negative effects. Through parametric studies, VGs were found to have best performance in the target duct with an angle of attack of 40⁰ and a height measuring 20% of the bottom boundary layer thickness. In addition, VGs installed along the keel of a ship can effectively suppress the flow distortion and improve the overall efficiency of the intake duct.

Mapping fluid structuration to flow enhancement in nanofluidic channels.

Fluid flow in miniature devices is often characterized by a boundary "slip" at the wall, as opposed to the classical paradigm of a "no-slip" boundary condition. While the traditional mathematical description of fluid flow as expressed by the differential forms of mass and momentum conservation equations may still suffice in explaining the resulting flow physics, one inevitable challenge against a correct quantitative depiction of the flow velocities from such considerations remains in ascertaining the correct slip velocity at the wall in accordance with the complex and convoluted interplay of exclusive interfacial phenomena over molecular scales. Here, we report an analytic engine that applies combined physics-based and data-driven modeling to arrive at a quantitative depiction of the interfacial slip via a molecular-dynamics-trained machine learning algorithm premised on fluid structuration at the wall. The resulting mapping of the system parameters to a single signature data that bridges the molecular and continuum descriptions is envisaged to be a preferred computationally inexpensive route as opposed to expensive multi-scale or molecular simulations that may otherwise be inadequate to resolve the flow features over experimentally tractable physical scales.

Electrochemical Protein-based Bioanalytical Devices for Drug Analysis.

Proteins are vital components of living cells and the loss of their native functions has been associated with a wide variety of medical conditions. From this point of view, investigation of the protein microenvironment is crucial to support the development of therapeutic approaches capable of ensuring cellular functions. Therefore, analytical assays for the detection, quantification, and characterization of proteins, drugs, and protein-drug complexes play an essential role in fundamental research and clinical applications. Electrochemistry arises as an alternative methodology for fast assessment of proteins and drugs and is attractive due to the adaptability to miniaturization and scalability of electroanalytical devices, which then can be further employed as strategies towards personalized medical care. Thus, this review summarizes electrochemical investigations in the past 10 years on protein-based analytical devices and biosensors. A general overview of electrochemical assays that integrate proteins with nanostructured materials and conductive polymers is presented. Applications of electrochemical assays and biosensors were divided into four categories. First, those designed for drug screening strategies that focus on targeting specific intracellular, extracellular, or membrane protein subdomains to modulate their functions, aggregation/misfolding of proteins, and protein degradation pathways. Then, drug metabolism assays that involve mimicking natural metabolic pathways to identify potential safety and efficacy issues related to a drug or its metabolites. The third was dedicated to electrochemical drug delivery systems with anchored drugs in the form of bioconjugates, while the fourth was dedicated to electroanalytical methodologies for quantitative drug assays, where the electroactivity of the target species is often used to correlate the electrochemical signal to their concentration.

Li2WO4 Composite Ba3Ti4Nb4O21 Microwave Dielectric Ceramics with Near-Zero Temperature Coefficient and Low-Temperature Sintering for 5G Communication Devices

In order to solve the problem of device miniaturization, it is urgent to develop high performance medium K materials. A series of (1-x) Ba3Ti4Nb4O21-x Li2WO4 ceramics (1-xBTN-xLW, x=12, 15, 17 and 20 mol%) were fabricated by soild-state reaction method. Li2WO4 as the effective sintering aids (~640°C) not only promoted ceramic densification and also decreased the temperature to 925°C. Among them, the 0.83BTN-0.17LW ceramic achieved best microwave performance with ε r~21.85, Q×f~10534 GHz, τ f ∼-7.78 ppm/°C. Especially, the second phase BaWO4 played major factor on microwave performance, making high K materials transfer into medium K materials and decrease the loss. More encouragingly, the temperature coefficient τ f was near zero. The above outstanding results signified that the 0.83BTN-0.17LW ceramic was expected to be a candidate material for LTCC miniaturized devices.

Special Issue on Nano-Electronic Devices and Functional Applications

Nano-electronic devices and materials hold considerable promise due to their inherent structural and material benefits, such as device miniaturization, increased integration density, and reduced power consumption [...]

Metasurface Patch for Wireless Power Transfer in Implantable Devices

AbstractWireless power transfer (WPT) systems enable the long‐term operation and miniaturization of implantable devices by eliminating the need for battery replacement and wired power supplies. Although wireless power transfer systems for implantable devices are extensively studied, their practical application is still challenging owing to the constraints and requirements of the human body, such as reflection loss owing to differences in the tissue dielectric properties, mm‐sized devices, and electromagnetic (EM) wave attenuation of the tissue. Here, a phase‐gradient metasurface patch is presented to achieve 5.8 GHz EM power focusing at a focal point of depth 10 mm in the tissue via EM wavefront modulation at the skin–air interface. The proposed metasurface patch is fabricated by arranging subwavelength‐thickness (<λ/10) unit cell structures composed of four metallic layers separated by dielectric substrates that exhibit high‐Q resonance properties and a sufficient phase modulation range with enhanced transmission. By applying the fabricated metasurface patch to a wireless power transfer system for implantable devices, it is experimentally confirmed that the transmission coefficient (S21) is improved by 6.37 dB compared with that of a wireless power transfer system without the metasurface patch. Furthermore, it is confirmed that the transmission coefficient can be maintained for an incident angle variation up to 30° from the transmitter to the metasurface patch, resulting in a stable power delivery of the proposed wireless power transfer system.

N-Doped Graphene-like Film/Silicon Structures as Micro-Capacitor Electrodes.

Currently, the miniaturization of portable and autonomous devices is challenging for modern electronics. Graphene-based materials have recently emerged as one of the ideal candidates for supercapacitor electrodes, while Si is a common platform for direct component-on-chip integration. We have proposed the direct liquid-based CVD of N-doped graphene-like films (N-GLFs) on Si as a promising way to achieve solid-state on-chip micro-capacitor performance. Synthesis temperatures in the range from 800 °C to 1000 °C are investigated. Capacitances and electrochemical stability of the films are evaluated using cyclic voltammetry, as well as galvanostatic measurements and electrochemical impedance spectroscopy in 0.5 M Na2SO4. We have shown that N-doping is an efficient way to improve the N-GLF capacitance. 900 °C is the optimal temperature for the N-GLF synthesis with the best electrochemical properties. The capacitance rises with increasing film thickness which also has an optimum (about 50 nm). The transfer-free acetonitrile-based CVD on Si yields a perfect material for microcapacitor electrodes. Our best value of the area-normalized capacitance (960 mF/cm2) exceeds the world's achievements among thin graphene-based films. The main advantages of the proposed approach are the direct on-chip performance of the energy storage component and high cyclic stability.

Oxygen Vacancy-Induced Ferromagnetism and Resistive-Magnetization Switching Characteristics in In2O3 Films

Ordered porous indium oxide thin films (In2O3) with higher ferromagnetism were prepared by the direct current magnetron sputtering method using porous anodic aluminum oxide thin films as the template. The experiment results show that the saturation magnetization reaches a maximum of about 42.03 emu/cm3 at a sputtering pressure of 3.2 Pa. The room-temperature ferromagnetism of In2O3 films mainly originates from the oxygen vacancies in the films. In addition, the spin can generally only be regulated by a magnetic field, which makes it challenging to realize miniaturization and integration of spin devices, while the regulation by an electric field can solve this contradiction. Based on this, the In2O3 composite thin-film resistive-magnetization switching device (Ag/In2O3/PAA/Al) was successfully prepared, showing bipolar resistive-magnetization switching characteristics and stable electrical and magnetic control characteristics. This research provides a way to develop a new multifunctional memory combining magnetic and resistive-magnetization storage and lays the foundation for the application of In2O3 in spintronic devices.

Loss Determination Techniques for Piezoelectrics: A Review

Nowadays, heat dissipation in electronic devices is one of the serious issues to be resolved in energy and environmental terms. Piezoelectric materials are being utilized in many electronic devices, yet the roadblock toward further miniaturization of piezoelectric devices was identified as heat dissipation. Three types of losses (dielectric, elastic, and piezoelectric) are known to be related to the heat dissipation mechanism of piezoelectric materials, therefore obtaining accurate values of the loss factors is essential for minimizing the heat dissipation of piezoelectric devices. The purpose of this review is to introduce several loss determination techniques for piezoelectric materials. The review starts with brief discussions of the loss factors and of the importance of piezoelectric loss that is related to the antiresonance frequency. Then, the review covers the methods developed by our research group, including High Power Piezoelectric Characterization Systems (HiPoCSTM), the crystallographic orientation method and the partial electrode method, as well as other methods such as the pulse-echo method and computer-based approaches. The review continues with a discussion of piezoelectric device modeling (analytical solution and equivalent circuits) that considers loss factors. Finally, the review provides concluding remarks for addressing current issues and suggesting possible solutions.

Improvement in the Thermal Conductivity of Silver Epoxy Adhesive by Treating with Water Vapor.

With the miniaturization of electronic devices, electronic packaging has become increasingly precise and complex, which presents a significant challenge in terms of heat dissipation. Electrically conductive adhesives (ECAs), particularly silver epoxy adhesives, have emerged as a new type of electronic packaging material, thanks to their high conductivity and stable contact resistance. However, while there has been extensive research on silver epoxy adhesives, little attention has been paid to improving their thermal conductivity, which is a critical requirement in the ECA industry. In this paper, we propose a straightforward method for treating silver epoxy adhesive with water vapor, resulting in a remarkable improvement in thermal conductivity to 9.1 W/(m·K), three times higher than the sample cured using traditional methods (2.7 W/(m·K)). Through research and analysis, the study demonstrates that the introduction of H2O into the gaps and holes of the silver epoxy adhesive increases the path of electron conduction, thereby improving thermal conductivity. Furthermore, this method has the potential to significantly improve the performance of packaging materials and meet the needs of high-performance ECAs.

Enhanced Thermal Conductivity of Nanodiamond Nanosheets/Polymer Nanofiber Composite Films by Uniaxial and Coaxial Electrospinning: Implications for Thermal Management of Nanodevices

Nanotechnology is gradually applied to the preparation of heat dissipation materials with the miniaturization of electronic devices. Electrospinning technology has received extensive attention due to its unique advantages in constructing continuous nanofibers. In this work, uniaxial-polyvinyl alcohol/nanodiamond (U-PVA/ND) and coaxial-polyvinyl alcohol/nanodiamond (C-PVA/ND) composite fiber films with different microscopic morphologies were constructed by uniaxial and coaxial electrospinning. The results show that the thermal conductivities of U-PVA/ND and C-PVA/ND composite fibers with 60 wt % ND content are 71.3 and 85.3 W m–1 K–1, respectively, which are 171.2 and 205.1 times greater than that of the pure PVA fiber film. In addition, the maximum thermal decomposition temperature (Tmax) and volume resistivity of the C-PVA/ND composite fiber film were 364.3 °C and 2.29 × 1015 Ω·cm, respectively, demonstrating the excellent thermal stability and electrical insulation of the composite fiber film. This experiment results provide strong evidences of electrospinning technology for the preparation of highly thermally conductive composites. So, thermally conductive films can be used as the outer layer of electronic components to accelerate their heat dissipation and extend their service life.

Broadband polarization-insensitive metalens with excellent achromaticity and high efficiency for the entire visible spectrum

Metasurface-based flat optics is continuously attracting interest owing to its ability for miniaturization of optical devices and systems. Over the last few years, broadband achromatic metalenses have been extensively studied for focusing and imaging in the visible band. However, it is still a substantial challenge to design an achromatic metalens that can produce high-focusing efficiency and high-consistency focal length over the entire visible spectrum. In this Letter, we propose a polarization-independent achromatic metalens operating at wavelengths from 400 to 760 nm, which comprises only a single layer of cross-shaped and square-ring silicon nitride-based nanopillars on a glass substrate in the transmission mode. Numerical results demonstrate that the achromatic metalens has an average efficiency of 75.9% and a maximum focal shift of less than 0.3λ (λ being the operating wavelength) over the entire visible band, which indicate significant improvement over the previously reported achromatic metalenses for focusing visible light in terms of focal-shift suppression and wideband operation with high efficiency. This study recommends a means to develop a high-quality achromatic metalens for the whole visible spectrum. The proposed approach is also suitable for achromatic metalens designs of other wavebands.

Heterogeneous Ultradense Networks With Traffic Hotspots: A Unified Handover Analysis

With the ever-growing communication demands and the unceasing miniaturization of mobile devices, the Internet of Things is expanding the amount of mobile terminals to an enormous level. To deal with such numbers of communication data, plenty of base stations (BSs) need to be deployed. However, denser deployments of heterogeneous networks (HetNets) lead to more frequent handovers, which could increase network burden and degrade the users experience, especially in traffic hotspot areas. In this paper, we develop a unified framework to investigate the handover performance of wireless networks with traffic hotspots. Using the stochastic geometry, we derive the theoretical expressions of average distances and handover metrics in HetNets, where the correlations between users and BSs in hotspots are captured. Specifically, the distributions of macro cells are modeled as independent Poisson point processes (PPPs), and the two tiers of small cells outside and inside the hotspots are modeled as PPP and Poisson cluster process (PCP) separately. A modified random waypoint (MRWP) model is also proposed to eliminate the density wave phenomenon in traditional models and to increase the accuracy of handover decision. By combining the PCP and MRWP model, the distributions of distances from a typical terminal to the BSs in different tiers are derived. Afterwards, we derive the expressions of average distances from a typical terminal to different BSs, and reveal that the handover rate, handover failure rate, and ping-pong rate are deduced as the functions of BS density, scattering variance of clustered small cell, user velocity, and threshold of triggered time. Simulation results verify the accuracy of the proposed analytical model and closed-form theoretical expressions.