Limits Of Miniaturization Research Articles

Miniaturized spectroscopy system based on a semiconductor nanofilm

Abstract Spectroscopy plays a pivotal role in various applications for industrial and commercial analysis. Conventional spectroscopy instruments include various discrete optical components like light sources, monochromators and detectors. These components are mechanically intricate and require space for the mechanisms that adjust and calibrate them, which increases the instrument’s footprint and make them less adjustable for portable applications. This drawback initiated the increase in the demand for miniatured spectral detection systems. Here, we present a low-cost ultra-compact miniaturized spectral detection system, which integrates both linear variable light sources, sample chambers and detectors within a centimetre-scale chip. The linear variable light generation across wavelengths ranging from 480 nm to 600 nm is achieved by stimulating different regions of the ZnCdSeS bandgap-graded semiconductor nanofilm with ultraviolet light. We demonstrate the capability of the system with precise identification of liquids. Our device overcomes the typical miniaturization limits imposed by discrete optical components, and long light paths in conventional spectroscopy instruments and opens up numerous potential applications across various fields due to its portability, ease of use, and lower cost.

Revealing hidden spin polarization in centrosymmetric van der Waals materials on ultrafast timescales

One of the key challenges for spintronic and quantum technologies is to achieve active control of the spin angular momentum of electrons in nanoscale materials on ultrafast, femtosecond timescales. While conventional ferromagnetic materials and materials supporting spin texture suffer both from conceptional limitations in miniaturization and inefficiency of optical and electronic manipulation, non-magnetic centrosymmetric layered materials with hidden spin polarization may offer an alternative pathway to manipulate the spin degree of freedom by external stimuli. Here we demonstrate an approach for generating transient spin polarization on a femtosecond timescale in the otherwise spin-unpolarized band structure of the centrosymmetric 2H-stacked group VI transition metal dichalcogenide WSe2. Using ultrafast optical excitation of a fullerene layer grown on top of WSe2, we trigger an ultrafast interlayer electron transfer from the fullerene layer into the WSe2 crystal. The resulting transient charging of the C60/WSe2 interface leads to a substantial interfacial electric field that by means of spin-layer-valley locking ultimately creates ultrafast spin polarization without the need of an external magnetic field. Our findings open a novel pathway for true optical engineering of spin functionalities such as the sub-picosecond generation and manipulation of ultrafast spin currents in 2D heterostructures.

Highly stretchable nanocomposite piezofibers: a step forward into practical applications in biomedical devices.

High-performance biocompatible composite materials are gaining attention for their potential in various fields such as neural tissue scaffolds, bio-implantable devices, energy harvesting, and biomechanical sensors. However, these devices currently face limitations in miniaturization, finite battery lifetimes, fabrication complexity, and rigidity. Hence, there is an urgent need for smart and self-powering soft devices that are easily deployable under physiological conditions. Herein, we present a straightforward and efficient fabrication technique for creating flexible/stretchable fiber-based piezoelectric structures using a hybrid nanocomposite of polyvinylidene fluoride (PVDF), reduced graphene oxide (rGO), and barium-titanium oxide (BT). These nanocomposite fibers are capable of converting biomechanical stimuli into electrical signals across various structural designs (knit, braid, woven, and coil). It was found that a stretchable configuration with higher output voltage (4 V) and a power density (87 μW cm-3) was obtained using nanocomposite coiled fibers or knitted fibers, which are ideal candidates for real-time monitoring of physiological signals. These structures are being proposed for practical transition to the development of the next generation of fiber-based biomedical devices. The cytotoxicity and cytocompatibility of nanocomposite fibers were tested on human mesenchymal stromal cells. The obtained results suggest that the developed fibers can be utilized for smart scaffolds and bio-implantable devices.

First‐Principles Design of Ohmic FET Devices from 2D Transition Metal Dichalcogenides

AbstractA chlorine‐doped ultrathin phase of hafnium disulfide (HfS2) is proposed as an ideal candidate material for 2D field‐effect transistor (FET) device applications, down to the extreme sub‐5 nm miniaturization limit. This transition metal dichalcogenide 2D material is designed to combine features of both a metal and a semiconductor, exhibiting a high electric conductivity comparable with ordinary metals, that can be abruptly cut down via gating due to an energy gap immediately below the Fermi level and its anomalous metallic properties. These unique features enable realizing an alternative design of a FET device in which electrode and channel are made of the same Cl‐doped ML HfS2 phase, a potential breakthrough bypassing all issues associated with electronic (Schottky) and structural dis‐homogeneities or low conductivity that have hindered progress in this field. This material/design combination shall lead to a FET device with purely ohmic behavior, high metallic conductance, no interfacial contact resistance, and facile gating with extremely high on/off ratio.

Hybrid fiber–solid-state laser with 3D-printed intracavity lenses

Microscale 3D-printing has revolutionized micro-optical applications ranging from endoscopy, imaging, to quantum technologies. In all these applications, miniaturization is key, and in combination with the nearly unlimited design space, it is opening novel, to the best of our knowledge, avenues. Here, we push the limits of miniaturization and durability by realizing the first fiber laser system with intra-cavity on-fiber 3D-printed optics. We demonstrate stable laser operation at over 20 mW output power at 1063.4 nm with a full width half maximum (FWHM) bandwidth of 0.11 nm and a maximum output power of 37 mW. Furthermore, we investigate the power stability and degradation of 3D-printed optics at Watt power levels. The intriguing possibilities afforded by free-form microscale 3D-printed optics allow us to combine the gain in a solid-state crystal with fiber guidance in a hybrid laser concept. Therefore, our novel ansatz enables the compact integration of a bulk active media in fiber platforms at substantial power levels.

Functionality and Mechanical Performance of Miniaturized Non-Assembly Pin-Joints Fabricated in Ti6Al4V by Laser Powder Bed Fusion.

In this work, additively manufactured pin-joint specimens are analyzed for their mechanical performance and functionality. The functionality of a pin-joint is its ability to freely rotate. The specimens were produced using laser powder bed fusion technology with the titanium alloy Ti6Al4V. The pin-joints were manufactured using previously optimized process parameters to successfully print miniaturized joints with an angle to the build plate. The focus of this work lies in the influence of joint clearance, and therefore all specimens were manufactured with a variety of clearance values, from 0 µm up to 150 µm, in 10 µm steps. The functionality and performance were analyzed using torsion testing and tensile testing. Furthermore, a metallographic section was conducted to visually inspect the clearances of the additively manufactured pin-joints with different joint clearance values. The results of the torsion and tensile tests complement each other and emphasize a correlation between the joint clearance and the maximal particle size of the powder utilized for manufacturing and the mechanical behavior and functionality of the pin-joints. Non-assembly multibody pin-joints with good functionality were obtained reliably using a joint clearance of 90 µm or higher. Our findings show how and with which properties miniaturized pin-joints that can be integrated into lattice structures can be successfully manufactured on standard laser powder bed fusion machines. The results also indicate the potential and limitations of further miniaturization.

Predicting the miniaturization limit of vertical organic field effect transistor (VOFET) with perforated graphene as a source electrode

Vertical organic field effect transistors (VOFETs) are of paramount importance due to their fast switching speed, low power consumption, and higher density on a chip compared to lateral OFETs. The low charge carrier mobility in organic semiconductors and longer channel lengths in lateral OFETs lead to higher operating voltages. The channel length in VOFETs can be less than 100 nm which reduces the size of the channel and hence the operating voltages. Another important factor in the operation of VOFETs is the thickness and width of the source electrode. The channel length, source electrode thickness and width sets the miniaturization limit of the VOFETs. The graphene monolayer can be exploited as a source electrode due to its thinness, high carrier mobility, and metallic behaviors. However, for better gate modulation, perforations in the source material are desired. Here, we simulate the VOFET having perforated graphene monolayer as a source electrode and n-type organic semiconductor N, N′-dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C8) as an active channel material, while aluminum as a drain electrode to predict the best-miniaturized device. The miniaturization limit of such a VOFET has a limit to the gate opening/perforation in which the minimum source width is 10 nm, as in the sub 10 nm range graphene starts behaving like a semiconductor. The subthreshold swing, deduced from the drain current (J D) versus gate voltage (V G) graph, advocates the limit of the organic semiconductor height/channel length to 50 nm, while 50 nm for the gate.

Strain engineering of magnetic exchange and topological magnons in chromium trihalides from first-principles

Recent experiments evidence the direct observation of spin waves in chromium trihalides and the presence of a gap at the Dirac points of the magnon dispersion in bulk CrI3. However, the topological origin of this feature remains unclear and its emergence at the 2D limit has not yet been proven experimentally. Herein, we perform a fully self-consistent ab initio analysis to deeply understand magnetic exchange of chromium trihalides in the 2D limit. We compute the orbital dependent magnetic interactions and Curie temperatures under applied biaxial strain. Our results confirm the existence of a gap around the K high-symmetry point in the linear magnon dispersion of CrI3, which originates as a direct consequence of intralayer Dzyaloshinskii–Moriya (DM) interaction. In addition, our orbital resolved analysis reveals the microscopic mechanisms that can be exploited using strain engineering to increase the strength of the DM interaction and thus control the topological gap width in CrI3. This paves the way to the further development of this family of materials as building-blocks for topological magnonics at the limit of miniaturization.

Dual-Pass Hollow-Core Fiber Gas Spectroscopy Using a Reflective Configuration With Heterodyne-Based Signal Detection

Hollow-core optical fibers have been used for laser gas sensing for almost two decades. However, to date, the vast majority of sensing systems have used hollow-core fiber only as a replacement for bulky gas cells (single- or multi-pass). Here, we investigate a reflective, dual-pass configuration in which light enters and exits hollow-core fiber from the same side. The advantage of this approach is the fact that the hollow-core fiber can be used not only as a cell but also as an endoscope-like probe, which does not need any additional tubing for sample delivery. <p xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">In this paper, we identify unwanted reflections from various fiber-to-fiber connections in the setup as the main challenge limiting the performance of the sensor in reflective configuration. We propose and experimentally demonstrate that the problem of reflections can be addressed using heterodyne-based detection, which allows for identifying and extracting useful signals in the radio frequency domain. Absorption and dispersion spectroscopy of methane are performed as a proof-of-concept with a detection limit of methane concentration below 10 ppm. Discussion insights into further development are provided, including strategies for miniaturization and detection limit improvement.

Metasurface reflector enables room-temperature circularly polarized emission from VCSEL

While most lasers are linearly polarized, circularly polarized laser sources are crucial components for many optical applications such as biosensing, quantum technologies, and AR/VR. However, conventional methods for generating chiral light have limitations in device miniaturization. Vertical-cavity surface-emitting lasers (VCSELs), with their small footprint and surface emission feature, can be integrated with ultrathin metasurfaces for light manipulation, offering an opportunity to realize ultracompact chiral lasers. Here we report, to our knowledge, the first demonstration of chiral lasing from electrically pumped VCSELs at room temperature, without spin injection. This is enabled by incorporating a high-contrast chiral metasurface reflector as the VCSEL top mirror, favoring one specific circular polarization for lasing. Our demonstrated 940 nm VCSELs show stable single-mode chiral lasing and achieve a circular-polarization degree of up to 59%. This study provides a scalable approach for circular-polarization control of VCSELs and holds great promise for applications that desire ultracompact chiral emitters.

Research Progress of Vertical Channel Thin Film Transistor Device.

Thin film transistors (TFTs) as the core devices for displays, are widely used in various fields including ultra-high-resolution displays, flexible displays, wearable electronic skins and memory devices, especially in terms of sensors. TFTs have now started to move towards miniaturization. Similarly to MOSFETs problem, traditional planar structure TFTs have difficulty in reducing the channel's length sub-1μm under the existing photolithography technology. Vertical channel thin film transistors (V-TFTs) are proposed. It is an effective solution to overcome the miniaturization limit of traditional planar TFTs. So, we summarize the different aspects of VTFTs. Firstly, this paper introduces the structure types, key parameters, and the impact of different preparation methods in devices of V-TFTs. Secondly, an overview of the research progress of V-TFTs' active layer materials in recent years, the characteristics of V-TFTs and their application in examples has proved the enormous application potential of V-TFT in sensing. Finally, in addition to the advantages of V-TFTs, the current technical challenge and their potential solutions are put forward, and the future development trend of this new structure of V-TFTs is proposed.

Self-Adaptation of Oxygen Adsorption and Sub-Surface Junction Formation in Thin Nanometric Sheets of Metal Oxides

Oxygen adsorption at metal oxide (MOX) surfaces and the formation of sub-surface depletion zones in thin nanometric sheets of MOX materials are theoretically investigated. It is shown that—under conditions of sufficient oxygen mobility—the bulk thermal generation of oxygen vacancy donors and the adsorption of surface oxygen ions cooperate in a self-organizing manner to form narrow sub-surface depletion zones which optimally fit into the limited spaces of MOX layers with nanometric cross sections. With this self-organization process in place, both the oxygen adsorption at free surfaces and the bulk generation of oxygen vacancy donors continuously increases as the MOX sheet thickness L is reduced, maintaining at the same time overall electro-neutrality and a state of perfect volume depletion of free carriers in bulk. This process comes to an end when MOX sheet thicknesses of L ≈ 1 nm are approached and when 3d-volumes of about 1 nm3 contain only one single double-donor and two surface oxygen ions on average. It is argued that at this limit of miniaturization, different interpretations of MOX gas sensing phenomena might be required than on larger length scales.

Development of low-temperature bonding platform using ultra-thin area selective deposition for heterogeneous integration

The Cu-Cu bonding technology is an indispensable vehicle for achieving heterogeneous integration, providing architects and designers with a new solution to address the limitations of transistor miniaturization. In this study, a next-generation efficient-process passivation bonding technology has been developed and investigated. The area-selective passivation bonding platform enables chips to be bonded at ambient temperatures below 200 ℃, while mitigating potential patterning issues and simplifying the complex conventional passivation process. The surface exploration of the area-selective films and their bonding mechanism have been thoroughly investigated through the use of transmission electron microscope (TEM) analyses. The results demonstrate exceptional film quality and the bonded reliability of the area-selective films. Furthermore, devices bonded using an optimized process exhibit more reliable mechanical strength than those bonded using conventional passivation methods.

Miniaturization of 2 × 4 90-Degree Hybrid Optical Couplers

In this work we study the limits of miniaturization of a 90-degree hybrid coupler working in the L, C and S bands, with respect to a number of performance parameters aimed at its application for balanced detection. We investigate the main effects responsible for the degradation of the performance of the devices during miniaturization, and establish the minimal dimension that such devices can have without significant degradation for photonic applications such as balanced detection. The miniaturized device in InP generic technology has a footprint of only 2200μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , more than 5 times smaller than the conventional device used as reference. The scaling approach is based on the use of the number of propagating modes which are sustained in both the miniaturized MMI and port waveguides as scaling parameters. This approach allows us to generalize the miniaturization problem from a specific platform and offers a methodology which is flexible and transferable to multiple platforms. We tested the scaling methodology based on the number of modes in other platforms commonly used in integrated photonics, such as Si/SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (SOI), TriPleX or polymer platforms, obtaining comparable results and proving the universality of our approach, finally we performed a fabrication tolerance analysis of the miniaturized devices.

Characterization of Orbital Angular Momentum Quantum States Empowered by Metasurfaces

Twisted photons can in principle carry a discrete unbounded amount of orbital angular momentum (OAM), which are of great significance for quantum communication and fundamental tests of quantum theory. However, the methods for characterization of the OAM quantum states present a fundamental limit for miniaturization. Metasurfaces can exploit new degrees of freedom to manipulate optical fields beyond the capabilities of bulk optics, opening a broad range of novel and superior applications in quantum photonics. Here we present a scheme to reconstruct the density matrix of the OAM quantum states of single photons with all-dielectric metasurfaces composed of birefringent meta-atoms. We have also measured the Schmidt number of the OAM entanglement by the multiplexing of multiple degrees of freedom. Our work represents a step toward the practical application of quantum metadevices for the measurement of OAM quantum states in free-space quantum imaging and communications.

Actively Tunable Spectral Filter for Compact Hyperspectral Camera Using Angle‐Sensitive Plasmonic Structures

AbstractHyperspectral imaging provides enhanced classification and identification of veiled features for diverse biomedical applications such as label‐free cancer detection or non‐invasive vascular disease diagnostics. However, hyperspectral cameras still have technical limitations in miniaturization due to the inherently complex and bulky configurations of conventional tunable filters. Herein, a compact hyperspectral camera using an active plasmonic tunable filter (APTF) with electrothermally driven spectral modulation for feature‐augmented imaging is reported. APTF consists of angle‐sensitive plasmonic structures (APS) over an electrothermal MEMS (Microelectromechanical systems) actuator, fabricated by combining nanoimprint lithography, and MEMS fabrication ona 6‐inch wafer. APS have a complementary configuration of Au nanohole and nanodisk arrays supported on asilicon nitride membrane. APTF shows a large angular motion at operational voltages of 5–9 VDC for continuous spectral modulation between 820 and 1000 nm (45 nm/V). The compact hyperspectral camera was fully packaged with a linear polarizer, APTF and amonochromatic camera, exhibiting asize of 16 mm (ϕ) × 9.5 mm (h). Feature‐augmented images of subcutaneous vein and a fresh fruit have been successfully demonstrated after the hyperspectral reconstruction and spectral feature extraction. This functional camera provides a new compact platform for point‐of‐care or in vivo hyperspectral imaging in biomedical applications.

Diode effect in Josephson junctions with a single magnetic atom

Current flow in electronic devices can be asymmetric with bias direction, a phenomenon underlying the utility of diodes1 and known as non-reciprocal charge transport2. The promise of dissipationless electronics has recently stimulated the quest for superconducting diodes, and non-reciprocal superconducting devices have been realized in various non-centrosymmetric systems3–10. Here we investigate the ultimate limits of miniaturization by creating atomic-scale Pb–Pb Josephson junctions in a scanning tunnelling microscope. Pristine junctions stabilized by a single Pb atom exhibit hysteretic behaviour, confirming the high quality of the junctions, but no asymmetry between the bias directions. Non-reciprocal supercurrents emerge when inserting a single magnetic atom into the junction, with the preferred direction depending on the atomic species. Aided by theoretical modelling, we trace the non-reciprocity to quasiparticle currents flowing by means of electron–hole asymmetric Yu–Shiba–Rusinov states inside the superconducting energy gap and identify a new mechanism for diode behaviour in Josephson junctions. Our results open new avenues for creating atomic-scale Josephson diodes and tuning their properties through single-atom manipulation.

마이크로웨이브 캐비티 모드 전환에 의한 웨이퍼 가열 특성

As a solution to the limitations of semiconductor miniaturization and multilayer technology, Atomic Layer Deposition(ALD) and Atomic Layer Etching(ALE) technologies are attracting attentions. For ALD and ALE process technologies, temperature uniformity is an important factor in determining the film quality of thin films and aspect ratio. Conventionally, an indirect heating method by a buried heater that heats the substrate is used, but the method has a decrease in productivity due to the preheating process. This study introduce a direct wafer heating method using GHz band microwaves to suggest the direction for new heater equipment to solve the problems of the existing method. At atmospheric pressure, the 2.45 GHz microwave is radiated through a double-slot antenna to heat a 12inch silicon wafer. The microwave propagates through the waveguide in TE10 mode and heats the wafer by cavity heating. It was confirmed through simulations and experiments that the wafer can be heated quickly using microwaves and the temperature distribution can be made uniform by the cavity conversion.

Towards single atom computing via high harmonic generation

The development of alternative platforms for computing has been a longstanding goal for physics, and represents a particularly pressing concern as conventional transistors approach the limit of miniaturization. A potential alternative paradigm is that of reservoir computing, which leverages unknown, but highly nonlinear transformations of input-data to perform computations. This has the advantage that many physical systems exhibit precisely the type of nonlinear input-output relationships necessary for them to function as reservoirs. Consequently, the quantum effects which obstruct the further development of silicon electronics become an advantage for a reservoir computer. Here we demonstrate that even the most basic constituents of matter–atoms–can act as a reservoir for computing where all input-output processing is optical, thanks to the phenomenon of High Harmonic Generation. A prototype single-atom computer for classification problems is proposed, where a classification model is mapped to an all-optical setup, with linear filters chosen to correspond to the trained model’s parameters. We numerically demonstrate that this ‘all-optical’ computer can successfully perform classification tasks, and does so with an accuracy that is strongly dependent on dynamical nonlinearities. This may pave the way for the development of petahertz information processing platforms.

Sensor selection and miniaturization limits for detection of interictal epileptiform discharges with wearable EEG

Objective. The goal of this paper is to investigate the limits of electroencephalography (EEG) sensor miniaturization in a set-up consisting of multiple galvanically isolated EEG units to record interictal epileptiform discharges (IEDs), referred to as ‘spikes’, in people with epilepsy. Approach. A dataset of high-density EEG recordings (257 channels) was used to emulate local EEG sensor units with short inter-electrode distances. A computationally efficient sensor selection and interictal spike detection algorithm was developed and used to assess the influence of the inter-electrode distance and the number of such EEG units on spike detection performance. Signal-to-noise ratio, correlation with a clinical-grade IEDs detector and Cohen’s kappa coefficient of agreement were used to quantify performance. Bayesian statistics were used to confirm the statistical significance of the observed results. Main results. We found that EEG recording equipment should be specifically designed to measure the small signal power at short inter-electrode distance by providing an input referred noise 300 nV. We also found that an inter-electrode distance of minimum 5 cm between electrodes in a setup with a minimum of two EEG units is required to obtain near equivalent performance in interictal spike detection to standard EEG. Significance. These findings provide design guidelines for miniaturizing EEG systems for long term ambulatory monitoring of interictal spikes in epilepsy patients.