Thin-film Array Research Articles

Programmable multi-wavelength distributed feedback laser array integrated in a liquid crystal polymer waveguide.

Liquid crystal (LC) distributed feedback (DFB) lasers hold significant potential for integrated photonics applications. However, limitations in wavelength spacing for wavelength switching, device size, and compatibility with other technologies have impeded advancements of the LC DFB laser in integration and responsiveness. Herein, we propose a thin-film multi-wavelength DFB laser array utilizing high-resolution patterned programmable nematic LC polymers, enabling rapid switching with high-resolution wavelength spacing between wavelength division multiplexing channels while maintaining a stable single longitudinal mode (SLM) for each laser. The underlying physical mechanism involves modulating the effective refractive index of the DFB laser by varying the LC molecules' orientation angles between adjacent regions of the LC grating to achieve wavelength modulation. Additionally, a specialized LC waveguide design connects the DFB lasers, facilitating wavelength modulation as well as straight-line and bending propagation of the laser. Furthermore, the laser array demonstrates a relatively low energy threshold, facilitating its applications in high-integration scenarios.

The Sustainable Development Trend, Progress and Challenge of Solar Cells

The current development of solar cells indicates that this field is experiencing rapid technological progress and market expansion. Various types of solar cells, from traditional silicon-based ones to emerging thin-film, dye-sensitized, perovskite, and organic solar cells, are constantly being developed to improve efficiency, reduce costs, and meet different application needs. While silicon-based solar cells remain one of the most mainstream types on the market, researchers are exploring third-generation photovoltaic devices such as multi-junction series cells, intermediate band gap cells, multiple exciton-generating cells hot carrier cells thermal-light photovoltaic solar cells to further bolster efficiency and reduce costs. These new solar cell technologies theoretically offer higher conversion efficiency and are anticipated to replace traditional silicon-based ones in the future. Advancements in the technology of solar cells mainly involve continuous progress and innovation in materials' development structural design manufacturing processes-from early silicon-based designs to today's thin-film arrays. Each generation is developed with the goal improving efficiency lowering costs; subsequently leading to recent developments in organic and perovskite arrays currently under exploration creating a final product at a lower price. At present, current attention within development primarily lies towards material components advancement efficiency maximization. Cost reduction strategies large scale production Although faced with certain obstacles; through consistent research proving their overwhelming effectiveness; implications for widespread use suggest performance. Overall prospects within Solar energy appear limitless.

Magnetic field-augmented photoelectrochemical water splitting in Co3O4 and NiO nanorod arrays

Effective charge separation is crucial for improving the sensitivity of photoelectrochemical studies. Here, we provide an immense magnetic field-based electron spin polarization approach for an efficient charge carrier separation. We have fabricated NiO and Co3O4 thin film and nanorod arrays by electron beam evaporation glancing angle method followed by annealing in a two-zone furnace. The photoelectrochemical performance was investigated for NiO and Co3O4 samples in the presence and absence of a magnetic field. The NiO and Co3O4 nanorods array samples exhibit better absorption compared with the thin film samples. The Co3O4 and NiO nanorod arrays showed the highest photocurrent density of 0.12 and 0.55 mA/cm2 in a magnetic field. The superior photoelectrochemical response of NiO and Co3O4 nanorods in a magnetic field could be ascribed to the limitation of non-radiative recombination of carriers manipulated by Lorentz force and spin polarization. Furthermore, the electrochemical impedance spectra of NiO and Co3O4 nanorod arrays in a magnetic field show the least charge transfer resistance. This study sheds light on the interaction process between external fields and radiative/non-radiative recombination of manipulating carriers. Thus, the application of a magnetic field presents an efficient and versatile approach to enhance the performance of photoelectrodes in solar water splitting.

Real-Time Radiation Beam Monitoring by Flexible Perovskite Thin Film Arrays.

Real-time and in-line transversal monitoring of ionizing radiation beams is a crucial task for several applications which span from medical treatments to particle accelerators in high energy physics. Here a flexible and large area device based on 2D hybrid perovskite thin films (phenylethylammonium lead bromide), fabricated onto a thin flexible polyimide substrate, able to map the transversal beam profile of high energy radiation beams is reported. The performance of this novel tool is here compared with the one offered by standard commercial large-area technology, namely radiochromic sheets. The great potential of this class of devices is demonstrated by successfully mapping in real-time a 5 MeV proton beam at fluxes between 108 and 1010 H+ s-1 cm-2, confirming the capability to operate in a radiation-harsh environment without output signal saturation issues. The versatility and scalability of here proposed detecting system are demonstrated by the development of a multipixel array able to map in real-time a 40 kVp X-ray beam spot (dose rate 8 mGy s-1). Perovskite thin film-based detectors are thus assessed as a very promising class of thin, flexible devices for real-time, in-line, large-area, conformable, reusable, transparent, and low-cost transversal beam monitoring of different ionizing radiation.

Origami-inspired soft fluidic actuation for minimally invasive large-area electrocorticography

Electrocorticography is an established neural interfacing technique wherein an array of electrodes enables large-area recording from the cortical surface. Electrocorticography is commonly used for seizure mapping however the implantation of large-area electrocorticography arrays is a highly invasive procedure, requiring a craniotomy larger than the implant area to place the device. In this work, flexible thin-film electrode arrays are combined with concepts from soft robotics, to realize a large-area electrocorticography device that can change shape via integrated fluidic actuators. We show that the 32-electrode device can be packaged using origami-inspired folding into a compressed state and implanted through a small burr-hole craniotomy, then expanded on the surface of the brain for large-area cortical coverage. The implantation, expansion, and recording functionality of the device is confirmed in-vitro and in porcine in-vivo models. The integration of shape actuation into neural implants provides a clinically viable pathway to realize large-area neural interfaces via minimally invasive surgical techniques.

Self-holding magneto-optical switch integrated on silicon photonic platforms

We demonstrated what we believe to be a novel self-holding waveguide switch integrated on silicon photonic platforms utilizing the magneto-optical (MO) effect with electrical switching operation. In this study, we designed thin-film magnet arrays and electrodes positioned beside the waveguide. The switching states were changed by flipping the magnetization of thin-film magnets with an applied current of 700 mA, and the switching states were successfully maintained with zero current. The fabricated MO switch has an extinction ratio (ER) of 16.5 dB and an insertion loss (IL) of 7.3 dB at a wavelength of 1546.2 nm, with a phase shift of π/2. This study shows the potential of self-holding silicon photonic switches, enabling large-scale photonic integrated circuits with extremely low energy consumption.

On the Design, Fabrication, and Characterization of a Novel Thin-Film Electrode Array for Use in Cochlear Implants.

Thin-film electrode arrays (TFEAs) have been developed as an alternative to conventional electrode arrays (CEAs) used in cochlear implants. However, TFEAs produced by microfabrication techniques have not yet been used clinically because their structural and mechanical properties are far from those of CEAs. The aim of this study is to design, fabricate, and investigate the mechanical and tribological behavior and evaluate the performance of different TFEA designs. Finite Element Analysis (FEA) is performed to determine the elastic properties of several designs. A custom-build experimental setup is designed to observe the tribological behavior in different speeds and environments where frictional (lateral) and vertical force (normal force) are measured on a flat surface and within artificial cochlea. According to the FEA results, the maximum stiffness of the CEA is 37.93 mN/mm and 0.363 mN/mm and TFEA-4 has a maximum stiffness of 39.08 mN/mm and 0.306 mN/mm in the longitudinal and transverse axes, respectively. It is shown experimentally that adding a dummy wire to the carrier of the EA enhances both its longitudinal and transverse stiffness, thereby postponing the initiation of dynamic sliding due to the elevated buckling limit. It is also revealed that the type of TFEA support structure affects both normal and frictional forces, as well as the coefficient of friction.

Boom-Membrane Space Structure’s Incomplete Deployment After Storage in OrigamiSat-1 Ground Demonstrator

This study investigates the deployment reliability of multifunctional membrane deployable space structures that can be compactly stored and deployed in a two-dimensional direction using carbon composite booms to realize the construction of thin-film solar arrays and membrane antennas. Herein, two aspects are experimentally clarified using the structural models of a nano-satellite OrigamiSat-1, which is a 1 m-by-1 m square multifunctional deployable membrane structure demonstrator. First, a measurement system is developed to quasi-statically quantify the deployment torque of the structural models that failed to complete deployment after long-term storage and fell into an undesirable equilibrium shape. The measurement results confirm that the deployment torque decreases with long-term storage of the structure, and the torque in the deployment direction becomes negative at the deployment angle of the undesirable equilibrium shape. Therefore, as the second contribution, design modifications are made to the boom and membrane, and quasi-static and dynamic deployment tests are employed to evaluate their effects. The deployment reliability evaluation method and two design updates proposed herein will contribute to future space demonstrations and the utilization of lightweight membrane deployment structures with high packaging efficiency.

Enhanced UV photodetection in SnO2 microwire arrays (MWAs) thin films by γ-ray irradiation

In this study, the gamma ray irradiation-induced photoelectric responses of SnO2 microwire arrays (MWAs) UV photodetectors were investigated and compared with the unirradiated state. The corresponding surface morphology, crystal structure, and XPS spectrum were analyzed. Results indicated that low doses (≤500krad) of gamma ray irradiation led to enhanced photocurrent and responsivity, whereas high doses resulted in significant degradation of the photoelectric response. At a radiation dose of 300krad, a photocurrent of 264 μA and a responsivity of 1.83 A/W were realized under 365 nm UV light illumination at a bias voltage of 5 V. These values represent an increase of 34.6 % and 44.1 %, respectively, compared with the unirradiated sample. Surprisingly, the fabricated SnO2 MWAs UV photodetectors demonstrated resilience to gamma ray irradiation doses up to 500krad, which is equivalent to the radiation dose accumulated by satellites in low-Earth orbit over 20 years. Our findings suggested that the fabricated SnO2 microwire arrays (MWAs) UV detector has the potential to be used for long-term space missions.

NeuroBus - Architecture for an Ultra-Flexible Neural Interface.

This article presents the system architecture for an implant concept called NeuroBus. Tiny distributed direct digitizing neural recorder ASICs on an ultra-flexible polyimide substrate are connected in a bus-like structure, allowing short connections between electrode and recording front-end with low wiring effort and high customizability. The small size (344 μm × 294 μm) of the ASICs and the ultraflexible substrate allow a low bending stiffness, enabling the implant to adapt to the curvature of the brain and achieving high structural biocompatibility. We introduce the architecture, the integrated building blocks, and the post-CMOS processes required to realize a NeuroBus, and we characterize the prototyped direct digitizing neural recorder front-end as well as polyimide-based ECoG brain interface. A rodent animal model is further used to validate the joint capability of the recording front-end and thin-film electrode array.

Recording Quality Is Systematically Related to Electrode Impedance.

Extracellular recordings with planar microelectrodes are the gold standard technique for recording the fast action potentials of neurons in the intact brain. The introduction of microfabrication techniques has revolutionized the in vivo recording of neuronal activity and introduced high-density, multi-electrode arrays that increase the spatial resolution of recordings and the number of neurons that can be simultaneously recorded. Despite these innovations, there is still debate about the ideal electrical transfer characteristics of extracellular electrodes. This uncertainty is partly due to the lack of systematic studies comparing electrodes with different characteristics, particularly for chronically implanted arrays over extended time periods. Here a high-density, flexible, and thin-film array is fabricated and tested, containing four distinct electrode types differing in surface material and surface topology and, thus, impedance. It is found that recording quality is strongly related to electrode impedance with signal amplitude and unit yield negatively correlated to impedance. Electrode impedances are stable for the duration of the experiment (up to 12 weeks) and recording quality does not deteriorate. The findings support the expectation from the theory that recording quality will increase as impedance decreases.

Large-scale smart bioreactor with fully integrated wireless multivariate sensors and electronics for long-term in situ monitoring of stem cell culture.

Achieving large-scale, cost-effective, and reproducible manufacturing of stem cells with the existing devices is challenging. Traditional single-use cell-bag bioreactors, limited by their rigid and single-point sensors, struggle with accuracy and scalability for high-quality cell manufacturing. Here, we introduce a smart bioreactor system that enables multi-spatial sensing for real-time, wireless culture monitoring. This scalable system includes a low-profile, label-free thin-film sensor array and electronics integrated with a flexible cell bag, allowing for simultaneous assessment of culture properties such as pH, dissolved oxygen, glucose, and temperature, to receive real-time feedback for up to 30 days. The experimental results show the accurate monitoring of time-dynamic and spatial variations of stem cells and myoblast cells with adjustable carriers from a plastic dish to a 2-liter cell bag. These advances open up the broad applicability of the smart sensing system for large-scale, lower-cost, reproducible, and high-quality engineered cell manufacturing for broad clinical use.

Intrinsically Antifouling, soft and conformal bioelectronic from scalable fabrication of Thin-Film OECT arrays by zwitterionic polymers

Thin-film bioelectronic arrays, emerging as a new medical tool, offers significant opportunities for health monitoring, medical diagnosis, medical treatment, life science studies, etc. Thin film devices face several challenges, including biofouling which hinders targeted electrocoupling in complex biological environments, high surface Young's modulus that causes mechanical mismatches with biological matter, and poor surface adhesion that makes it difficult to conform to undeveloped biosurfaces. Here, we developed a universal lithography fabrication platform with high yield, uniformity, and precision to prepare a biomimetic thin-film organic electrochemical transistor (OECT) array featuring intrinsic biofouling resistance, tissue-like surface softness, and strong adhesion to undeveloped surfaces. This fabrication platform is based on the photolithography fabrication of zwitterionic-polymer-based conducting channels and hermetic encapsulation systems without compromising their electrical properties and low permeability. The all-zwitterionic feature softens the surface and helps prevent proteins and cells from approaching the encapsulation and channel surface, thus protecting the OECT array from interference from nonspecific protein and cell interactions. The strong capillary force from the hydrated zwitterions drives the thin-film device to conform well on nonplanar surfaces. Utilizing this biomimetic device, we successfully demonstrated cell-selective electrocoupling in the presence of white blood cells (WBCs) and simultaneously realized close and stable on-skin electrocardiogram (ECG) monitoring via good skin contact and robust epidermal surface lipid resistance. We envision that our process would provide a versatile platform for producing antifouling and flexible bioelectronic devices that seamlessly integrate with biological systems, and promote the practical application of thin-film bioelectronic arrays in real-life scenarios.

Enhancing β-Ga2O3-film ultraviolet detectors via RF magnetron sputtering with seed layer insertion on c-plane sapphire substrate

Gallium oxide (Ga2O3) possesses a band gap of approximately 4.9 eV, aligning its detection wavelength within the solar-blind region, making it an ideal semiconductor material for solar-blind photodetectors. This study aims to enhance the performance of Ga2O3 ultraviolet (UV) detectors by pre-depositing a Ga2O3 seed layer on a c-plane sapphire substrate. The x-ray diffraction and x-ray photoelectron spectroscopy analyses validated that the deposited films, following high-temperature annealing, comprised β-Ga2O3. Comparing samples with and without a 20 nm seed layer, it was found that the former exhibited fewer oxygen defects and substantially improved crystal quality. The incorporation of the seed layer led to the realization of detectors with remarkably low dark current (≤15.3 fA). Moreover, the photo-to-dark current ratio was enhanced by 30% (surpassing 1.3 × 104) and the response/recovery time reduced to 0.9 s/0.01 s, indicating faster performance. Furthermore, these detectors demonstrated higher responsivity (4.8 mA W−1), improved detectivity (2.49 × 1016 Jones), and excellent solar-blind characteristics. This study serves as a foundational stepping toward achieving high-quality β-Ga2O3 thin film and UV detector arrays.

Thin colorimetric film array for rapid and selective detection of v-type nerve agent mimic in potentially contaminated areas

The expeditious detection and quantification of V-series nerve agents (VX) on potentially contaminated surfaces are crucial for the prevention of regional conflict incidents, acts of terrorism, or illicit activities. However, the low volatility and high toxicity of VX make these tasks challenging. Herein, we designed two novel colorimetric thin polymeric films to rapidly and sensitively detect demeton-S, a VX mimic, in contaminated areas. The polymeric films were specifically engineered to include a coordination site for Au (III) ions. Initially, these films were coordinated with Au (III), causing a discernible alteration in color due to enhancement in intramolecular charge transfer process. In the presence of demeton-S, the Au (III) ligands in the films are displaced with demeton-S, resulting in the restoration of the original color of the film, as the enhanced intramolecular charge transfer process is inhibited and thereby serving as an indicator of the presence of demeton-S. The polymeric films exhibit remarkable selectivity toward demeton-S compared to G-type nerve agents and other interference. The reusability of the polymeric films for demeton-S detection was achieved owing to the reversibility of the films during the alternative exposure of Au (III) and demeton-S. The polymeric films demonstrated their applicability for demeton-S detection and quantification in several contaminated areas, including different water, soil, and skin, rendering them highly suitable for on-site measurements.

Laser Microengineering in SnO2 microwire array films for high performance ultraviolet photodetectors

Tin oxide (SnO2) has emerged as promising applications in ultraviolet photodetectors (UV PDs) due to its prominent photoelectronic properties. However, the slow photoresponse of UV PDs based on SnO2 films limits the application. In this work, the absorbing intermediate layer-assisted femtosecond (fs) laser microprocessing technology is employed to engineer the SnO2 microwire arrays (MWAs) thin film. The obtained UV PDs based on SnO2 MWA films exhibit enhanced responsivity and ultrafast response in the UV region. Under light irradiation with a wavelength of 365 nm, the optimized responsivity and rising/decaying time reach 1.62 A/W and 0.89/2.3 ms with the bias voltage of 5 V. The results demonstrate that the SnO2 MWA film can serve as a high-performance photodetector in the UV region.

High-speed 2D beam steering based on a thin-film lithium niobate optical phased array with a large field of view

An on-chip optical phased array (OPA) is considered as a promising solution for next generation solid-state beam steering. However, most of the reported OPAs suffer from low operating bandwidths, making them limited in many applications. We propose and demonstrate a high-speed 2D scanning OPA based on thin-film lithium niobate phase modulators with traveling-wave electrodes. The measured modulation bandwidth is up to 2.5 GHz. Moreover, an aperiodic array combined with a slab grating antenna is also used to suppress the grating lobes of far-field beams, which enables a large field of view (FOV) as well as small beam width. A 16-channel OPA demonstrates an FOV of 50°×8.6° and a beam width of 0.73°×2.8° in the phase tuning direction and the wavelength scanning direction, respectively.

The Effects of Temperature Variation with Surface Triangle Grating on Silicon Thin-Film Solar Cell Array Efficiency

AbstractThis paper examines the effect of temperature variation on the surface triangular grating of the surface plasmon polariton (SPP) on the effectiveness of the entire array of silicon thin-film solar cells. Thin-film solar cells’ optical and electrical characteristics are examined using the electromagnetic and semiconductor models. The 3D Multiphysics simulator is used to present this study. The MATLAB/SIMULINK model based on mathematical formulas is developed to simulate the entire array of solar cells with thin films. This approach is suggested for quickly simulating the thin-film array. The presented model was applied on thin-film solar cells with and without SPP depending on the complete cell parameters from the COMSOL Multiphysics model. The triangle’s SPPs accomplish a 14.76% efficiency increase of 1.07% over a solar cell without SPPs.

Receiving energy analysis and optimal design of crystalline silicon solar cell array on solar airship

The energy of solar airships comes from solar array, and the amount of solar radiation received by solar array determines airship endurance. Many studies optimize the solar array layout to receive more solar radiation. However, most of them are for flexible thin-film array. The influence of the size of the currently commonly used crystalline silicon panels on received energy is not considered. This paper establishes a solar irradiation model and a receiving energy model suitable for crystalline silicon arrays. The effects of array shape, array location, and module size on the energy received by crystalline silicon solar arrays are analyzed at different flight latitudes. Then, an improved genetic algorithm is designed to optimize the array geometric parameters. The results show that altering the size and layout of solar modules significantly influences energy capture, with opposing trends between regions of mid-low latitudes and high latitudes. Airships flying at mid-low latitudes should adopt larger solar modules, while airships flying at high latitudes should adopt smaller ones. After the optimization using the proposed algorithm, the received energy of solar array is further enhanced. The optimization resulted in a 2% improvement at mid-low latitudes and an 18% improvement at high latitudes over conventional optimization.

Non-monolithic fabrication of thin-film microelectrode arrays on PMUT transducers as a bimodal neuroscientific investigation tool.

Ultrasound (US)-based neuromodulation has recently emerged as a spatially selective yet non-invasive alternative to conventional electrically-based neural interfaces. However, the fundamental mechanisms of US neuromodulation are not yet clarified. Thus, there is a need for in-vitro bimodal investigation tools that allow us to compare the effect of US versus electrically-induced neural activity in the vicinity of the transducing element. To this end, we propose a MicroElectrode-MicroTransducer Array (MEMTA), where a dense array of electrodes is co-fabricated on top of a similarly dense array of US transducers.In this paper, we test the proof of concept for such co-fabrication using a non-monolithic approach, where, at its most challenging scenario, desired topologies require electrodes to be formed directly on top of fragile piezoelectric micromachined ultrasound transducer (PMUTs) membranes. On top of the PMUTs, a thin-film microelectrode array was developed utilizing microfabrication processes, including metal sputtering, lithography, etching and soft encapsulation. The samples were analysed through focused ion beam-scanning electron microscopy (FIB-SEM), and the results have shown that damage to the membranes does not occur during any of the process steps. This paper proves that the non-monolithic development of a miniaturised bimodal neuroscientific investigation tool can be achieved, thus, opening up a series of possibilities for further understanding and investigation of the nervous system.