Cost-effective Fabrication Process Research Articles

Extremely durable electrical impedance tomography–based soft and ultrathin wearable e-skin for three-dimensional tactile interfaces

In the rapidly evolving field of human-machine interfaces (HMIs), high-resolution wearable electronic skin (e-skin) is essential for user interaction. However, traditional array-structured tactile interfaces require increased number of interconnects, while soft material–based computational methods have limited functionalities. Here, we introduce a thin and soft e-skin for tactile interfaces, offering high mapping capabilities through electrical impedance tomography (EIT). We employed an organic/inorganic hybrid structure with simple, cost-effective fabrication processes, ensuring flexibility and stability. The conductive and stretchable sensing domain includes a micropatterned multiwall carbon nanotube and elastomer composite. The skin-like tactile interface effectively detects pressure-induced conductivity changes, offering superior spatiotemporal resolution with fewer interconnects (pixel/interconnects >57). This EIT-based tactile interface discerns external pressures to a submillimeter degree and vertical deformations of a few hundred micrometers. It sustains stable functions under external damage or environmental changes, confirming its suitability for persistent wearable use. We demonstrate practical applications in real-time HMIs: handwriting recognition and drone control.

Curved HSIW: an affordable performance for non-planar millimeter-wave applications

This paper introduces a Curved Hollow Substrate Integrated Waveguide (CHSIW) to address the growing demand for millimeter-wave applications, including communication, sensing, imaging, radar, and wireless power transfer systems. Leveraging advancements in integrated circuits and system-in-package (SiP) technology, the CHSIW tackles the challenges associated with hardware integration into curved structures. The design utilizes MultiJet Printing (MJP) for the M3 crystal dielectric substrate and a water laser cutter system for copper sheets, streamlining the fabrication process by eliminating complex via manufacturing steps through prefabricated through-hole vias. Operating in the frequency range of 21.7 GHz to 32 GHz, the CHSIW exhibits outstanding performance on curved surfaces, with measured average attenuation constants of 1.89 Np m−1 (16.42 dB m−1) and 1.95 Np m−1 (16.94 dB/m) for samples with radii of curvature of 166.8 mm and 125.1 mm, respectively. Beyond addressing technical challenges, the CHSIW presents a cost-effective and simplified fabrication process, positioning it as a breakthrough solution for diverse millimeter-wave applications, including future robotic and UAV communications. Furthermore, the proposed design and fabrication technique hold promise for the realization of conformal and free-form Hollow Substrate Integrated Waveguide (HSIW) devices in the future.

Polymer enhanced sensitivity and figure of merit SPR optical fiber sensor for high refractive index and wide detection range

A highly sensitive sensor based on surface plasmon resonance (SPR) for high refractive index (RI) sensing is proposed, whose most unique feature lies in a high RI of polyvinylpyrrolidone (PVP) layer embedded between the optical fiber and Au film. The use of the high RI PVP layer amplifies the evanescent wave, thereby increasing sensitivity and improving figure of merit (FOM) of the SPR sensor. In addition, SPR sensor coated with a high RI PVP film breaks through the limitation that the inherent RI of optical fiber can only detect low RI, and can measure higher RI values and expand the measurement range. Experimental results demonstrate that, with a PVP layer thickness of 60 nm, showcasing superior performance compared to sensors lacking a PVP layer. Notably, this SPR sensor offers a cost-effective and straightforward fabrication process, promising broad application in environmental monitoring and biosensing.

Upcycling Compact Disks to Flexible Nanoporous Gold Electrodes for Nitrite Biosensing

Electrochemical biosensors are crucial in disease detection due to their simplicity, rapidity, and sensitivity. As a wearable or e-skin platform, electrochemical sensors are frequently restricted by gradual degradation, complexity, limited active surface area, arduous fabrication process, and high cost. Therefore, soft electrochemical biosensors that are mechanically biocompatible, easy to prototype, and robust for sensitive biosensing are highly sought. To mitigate such an issue, recordable compact disks (CDs) have been upcycled to advanced biosensors exhibiting flexible and disposable and being applicable to various biomedical applications, making them an economical and practical option. However, the limited surface area of the gold CDs electrode prevents optimal electrochemical catalytic performance. Nanostructure has been widely embedded in electrochemical biosensor construction to optimize electrode surface area and the number of active sites, which can contribute to improved detection sensitivity, selectivity, and electron transfer.Here, we aim to develop an advanced nanoporous gold film electrode (NPGFE) from CD for a simple, flexible, sensitive, and larger surface area electrode with reproducible areas. The fabrication and modification of gold CDs film were accomplished through two steps: 1) A mechanical cutter tailored the gold film after being transferred from CDs into a flexible substrate (Polyimide tape). Before placing the CDs film between the two laminating sheets, an aperture (1 mm diameter) was made in one of the laminating sheets to expose the tailored gold film electrode (GFE) and insulate the undesired area using a thermal laminator to ensure an adequate seal as a simple and low-cost approach; 2) The nanoporous gold (NPG) was electrochemically deposited onto the gold CDs film surface in gold (III) chloride trihydrate (HAuCl4·3H2O) and ammonium chloride (NH4Cl) solution at a potential of -4V for 100 s. Surface morphology characteristics and elemental analyses were investigated using scanning electron microscopy, while electrochemical studies were carried out in the CH Instruments potentiostat.The SEM images confirm a homogeneous distribution of NPG across the electrode’s surface. The energy-dispersive X-ray analyses exhibited the purity of the deposited NPG. The effective surface area was investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in 1 M KCl and 1 mM K3[Fe(CN)6] solution. From the slope of the Ip vs. v1/2 plot and the Randles-Sevcik equation, the active surface area of the NPGFE was significantly increased compared to the unmodified GFE. EIS was conducted to evaluate electron transfer resistance and obtain the semicircular diameter in Nyquist plots. In comparison to the unmodified GFE, the NPGFE showed a semicircle with a smaller diameter, indicating that the electron transfer resistance is minimized. The electrochemical characterization of the NPGFE was investigated by CV and amperometric techniques in 0.1 M PBS solution at ambient temperature (25°C) and pH 7.4. The NPGFE performance was studied at a fixed potential (0.77 V vs. Ag/AgCl) by analyzing the current response upon adding nitrite and anodic peak current at a potential range from 0.3 to 0.9 V (vs. Ag/AgCl). The calibration curve plot was linear over 0.5 μM to 9 mM with 20 nA·μM−1·cm−2 sensitivity and a low detection limit of 0.5 μM with a correlation coefficient (R2) of 0.99. The NPGFE's reproducibility reusability studies were conducted to evaluate electrode stability when prepared independently and utilized repeatedly under the same condition. Results demonstrate remarkable reproducibility and highly satisfactory reusability, making it suitable for practical application. The effect of pH on nitrite detection was investigated at different pH values. The anodic peak currents decreased and shifted to the low potential when the pH was increased from 5.0 to 10.0, indicating that protons were directly involved in the nitrite redox reaction. Also, the selectivity studies showed a significant increase in the current response when nitrite, ascorbic acid, and sodium sulfite were introduced to the solution, and there were no remarkable changes when other interferents were added. The long-term stability results showed that the NPGFE retains 99% of its initial current response to NO2 - after six months of storage, indicating satisfactory stability and long service life of NPGFE. Importantly, the sensing performance while stretching the NPGFE will be investigated to produce biocompatible relevant results.The flexible, nanoporous upcycled CDs electrode utilizing craft machines provide fast prototyping electrochemical biosensors for skin-interfaced bioelectronics. The nanoporous CD-based biosensor significantly improves electrocatalytic performance toward nitrite detection along with exceptional improvements in the cost-effective and sustainable fabrication process for flexible electronics. Future work relies on developing system-integrated biosensors based on systematic reliability and feasibility tests. Soft upcycled bioelectronics holds significant potential in advancing biomedical in situ real-time analysis in various platforms of flexible and nanostructured biosensors. Figure 1

Iron-nickel-cobalt selenide nanoparticles as an efficient and transparent counter electrode for dye-sensitized solar cells

In this study, we developed a quaternary metal selenide (Fe0.35Ni0.11Co0.19Se) counter electrode (CE) material, grown onto fluorine-doped tin oxide, for dye-sensitized solar cells (DSSCs) using the potential-reversal electrochemical deposition technique at ambient conditions. Under optimized conditions, the Fe0.35Ni0.11Co0.19Se CE exhibited excellent electrocatalytic activity in the I-/I3- redox reaction with the average transmittance of 78.85 %. The additional valence states of Fe in the Ni0.3Co0.3Se electrode material further enhanced the catalytic activity during the electrochemical redox process. The DSSC employing this electrocatalytically active CE realized a power conversion efficiency of 7.73 %, surpassing the efficiency of both Pt and Ni0.3Co0.3Se CEs-based DSSCs (7.23 % and 7.23 %, respectively). This electro-preparation method offers a simpler and more cost-effective fabrication process for CE design, demonstrating a good potential for replacing expensive platinum CEs in DSSCs.

Cost-Effective Fabrication of Polydimethylsiloxane (PDMS) Microfluidics for Point-of-Care Application

Microfluidics fabrication pertains to the construction of small-scale devices and systems that manipulate and control small volumes of fluids. This process involves precise engineering and manufacturing procedures aimed at designing and producing these devices, which find applications in healthcare, environmental monitoring, and chemical analysis. The present study showcases an inexpensive approach to fabricate microfluidics channels using PDMS biopolymer and soft lithography technique to achieve laminar fluid flow. Initially, a robust and adhesive mold was created by fabricating a master template using several layers of SU-8 5 and SU-8 2015 negative photoresists. Subsequently, PDMS microfluidics channels were replicated and sealed onto a glass substrate through plasma bonding treatment. High-power microscopy images and profilometer analyses demonstrated successful fabrication with minimal deviation from the initial designs and the fabricated devices (less than 0.07 mm, less than 0.6°). Both the SU-8 master template and PDMS replicate displayed average microchannel height values and surface roughness of 100 μm and 0.26 μm or lower, respectively. Additionally, the fluid test confirmed laminar flow without any leakage post plasma oxidation, indicating the completion of an efficient and cost-effective fabrication process.

Development of flexible high-performance PDMS-based triboelectric nanogenerator using nanogratings

This article investigates the performance of a contact-mode Triboelectric Nanogenerator (TENG) utilizing polydimethylsiloxane (PDMS) with nano gratings as a dielectric in a metal-dielectric configuration. The evaluation encompasses the impact of gratings, tapping frequency, various load conditions, and contact area on the TENG performance. The fabrication involves spin-coating PDMS onto a master mold to create the device. Experimental measurements reveal a significant enhancement of 97% in open-circuit voltage by introducing gratings on PDMS. Furthermore, as the tapping frequency increases from 1 Hz to 3 Hz, there is a corresponding rise of 108% in output voltage. The influence of load resistance on TENG output performance demonstrates its ability to drive different loads efficiently. Moreover, enlarging the contact area of the device substantially increases the open-circuit voltage. A device with a 400 mm2 contact area can generate a voltage of 80 V at a low frequency of 3 Hz, indicating the importance of considering device size and contact area for specific applications. A practical circuit integrating a TENG with a full-wave bridge rectifier demonstrates energy harvesting capabilities by successfully illuminating a light-emitting diode (LED) and charging various capacitors. The fabricated devices exhibit better performance along with a cost-effective and easy fabrication process.

Communication—Fabrication of Micro-Holes in PMMA Using Micro-ECDM Process: Geometric Characteristics and EC Discharge Behaviour

High-quality micro-features with low production cost are in high demand for the development of cost-effective microfluidic devices. In this work, we present a scalable and cost-effective fabrication process for fabricating blind micro-holes in PMMA substrates via micro-electrochemical discharge machining (Micro-ECDM) for the first time. By providing the suitable applied voltage (Va), uniformity of the electrochemical (EC) discharges and subsequent geometric characteristics of the micro-holes can be controlled. The stable and unstable EC discharge zones and micro-hole machining quality for different Va and tool conditions have been identified. For unstable and non-uniform EC discharge zone at Va of 26 V, the variation in the micro-hole output parameters is higher compared to stable and uniform EC discharge zones at Va of 28 V and 30 V. Based on the results, micro-holes with appropriate quality have been fabricated and characterized.

Designing sensing material with fractal geometry: A gateway for enhanced ethanol sensing under ambient conditions

In this work, a comparative study of ethanol vapor sensing is reported for tin oxide based vertical fractal structures (VFSs) against non-fractal structures (NFSs). The materials were synthesized by cost-effective microwave synthesis route followed by controlled drying of tin oxide colloidal solution. A thin layer of fractal material was coated on an ordinary glass capillary that served as the tubular sensor. While the VFS sensor responded well to ethanol vapors under ambient conditions with faster response (τres) of ∼ 8.2 ±0.5 s and recovery time (τrec) of ∼ 10.3 ± 0.5 s, respectively, the NFS sensor exhibited τres ∼15.2±1.0 s and τrec∼ 38.4±1.8 s. The performance of the VFSs was found to be satisfactory when tested under varying humid conditions (∼ 45 RH% to 90 RH%). The sensor exhibited a low detection limit of 1 ppm ethanol vapor. The better sensing properties are attributed to the characteristic patterned growth of fractals with interconnections ranging from nano to macro-scale, inter-crossing of fractal branches, surface as well as 3D roughness which are hallmarks of fractal geometry. In addition to this remarkable ethanol vapor sensing characteristics, easy and cost-effective fabrication process encourages to develop "single use" sensors as breath analyzer devices that can curb the risk of infection from person to person. This study projects the use of VFS samples and sensors fabricated thereof as reliable and economical disposable sensors.

Low-Temperature Solution-Based Molybdenum Oxide Memristors.

Solution-based memristors have gained significant attention in recent years due to their potential for the low-cost, scalable, and environmentally friendly fabrication of resistive switching devices. This study is focused on the fabrication and characterization of solution-based molybdenum trioxide (MoO3) memristors under different annealing temperatures (200 to 400 °C). A MoO3 ink recipe is developed using water as the main solvent, enabling a simplified and cost-effective fabrication process. Material analysis reveals the presence of a Mo6+ oxidation state and an amorphous structure in the films annealed up to 250 °C. Electrical tests confirm a bipolar resistive switching behavior in the memristors according to the valence change mechanism (VCM). Endurance tests demonstrate stable memristors, indicating their robust nature after multiple cycles. Memristors annealed at 250 °C exhibit a nonvolatile behavior with a retention time up to 105 s under ambient air conditions. The high reproducibility observed in these memristors highlights their potential for practical applications and scalability.

Uniformly scalable and stackable porous transport layer manufactured by tape casting and calendering for efficient water electrolysis

Proton exchange membrane water electrolysis (PEMWE) stands out as the most promising and eco-friendly technology for directly converting renewable energy into hydrogen. A critical element within a PEMWE cell is the porous transport layer (PTL), typically constructed from Ti to withstand the rigorous conditions of water electrolysis. Herein, we present a cost-effective and viable fabrication process for Ti-PTLs, utilizing tape-casting method in combination with a lamination-roll calendering procedure, facilitating precise thickness control. By systematical fine-tuning the debinding conditions, we obtained a phase-pure Ti-PTL endowed with a highly-interconnected pore structure. A comprehensive analysis of digitally twinned Ti-PTL, constructed through a state-of-the-art three-dimensional (3D) reconstruction process, reveals a remarkable uniformity in the open pore structures across Ti-PTLs of varying thicknesses, highlighting their considerable practical potential. Furthermore, the electrochemical performance of PEMWE cells using our Ti-PTLs surpassed that of the benchmark commercial Ti-PTL, demonstrating the significant promise of our tape-casting process followed by lamination-roll calendering procedure in practical Ti-PTL fabrication.

Fabrication and characterization of the novel tubular ceramic membrane using walnut shells and its application in TiO2 nanoparticles separation from suspension

Low-cost ceramic membranes have become highly popular in water treatment and gas separation industries. This study focuses on creating an affordable yet efficient ceramic membrane for effective separation processes. The cost-effective fabrication process combines locally sourced raw materials with optimal manufacturing techniques, resulting in minimal production expenses. To create this unique, low-cost ceramic membrane, a mixture of kaolin, quartz, and additives like zirconia and dolomite is used in shaping and sintering procedures. Walnut shell powder serves as a pore-forming agent, while carmellose sodium acts as a membrane-binding agent. The membrane is prepared through extrusion with dimensions of 110 mm in length and 12 mm in diameter, and it is sintered at temperatures of 850 °C, 900 °C, and 950 °C. Various analytical methods, including FESEM, XRD, and TGA, are employed for comprehensive characterization. The water flux increased with increasing pressure (54–215 kPa), and the pore diameter obtained from the test was consistent with the pore size obtained from FESEM. The membranes' pore size increases with higher sintering temperatures while porosity decreases. The membrane demonstrates mechanical strength, chemical stability, and high rejection efficiency in TiO2 separation. The total cost of one tubular membrane comes out to be $112 per square meter.

Facile and Cost-Effective Fabrication of Highly Sensitive, Fast-Response Flexible Humidity Sensors Enabled by Laser-Induced Graphene.

The need to simplify fabrication processes and reduce costs for high-performance humidity sensors is increasingly vital, especially in fields such as healthcare and agriculture. This study introduces a simple and cost-effective approach using laser-induced graphene (LIG) on a polyimide film to create highly sensitive and fast-response flexible humidity sensors. The LIG acts as the electrode, while the porous polyimide between the interdigital LIG electrodes serves as the humidity sensing material, showing changes in electrical conductivity based on the humidity levels. The LIG humidity sensor, an ionic-conduction type, exhibits remarkable sensitivity, with a 28,231-fold increase in current as relative humidity changes from 26.1 to 90.2%. It also boasts of ultrashort response/recovery times (less than 0.5/7 s), providing significant advantages in detecting rapid and subtle humidity variations compared to a commercially available MEMS humidity sensor. We successfully demonstrated the LIG humidity sensor's capabilities in ultrafast breathing monitoring (≈174 times per minute), moisture detection of grains, and detection of sudden water pipe leakage. Due to its straightforward and cost-effective fabrication process, the LIG humidity sensor holds immense practical value for affordable, widespread use across various applications.

A sustainable approach towards printed graphene ink for wireless RFID sensing applications

Graphene-based printable inks are advanced and promising candidates for flexible printed electronic devices. To develop large-scale graphene-based highly conductive electronics based on existing printing approaches of the material, it is imperative to scale up its ink production methods and optimize the electrical properties of the printed films. Here, a sustainable approach is reported for preparing high-conductive screen-printing graphene ink by recycling cellulose solvents. The ink uses Cyrene solvent in circulation and produces highly concentrated and conductive graphene ink to conquer the limitation of graphene inks in massive industrial production brought by the high cost of the cellulose solvents. A systematic study of the sheet resistance variation with the number of cycles has been carried out. The average conductivity of the ink can exceed 3 × 104 S m−1, with only a 2-h shear exfoliation process, which exhibits about the same conductivity of recent works (using toxic NMP solvent, complex centrifugation, ultrasonication, etc.) but with much more straightforward and cost-effective fabrication process. The formulation of graphene inks allows flexible metal-free far-field tag antenna to be screen-printed and integrated with an off-the-shelf sensory chip to achieve battery-free wireless UHF RFID far-field temperature sensing. The high responsiveness, accuracy, and sensitivity of the RFID sensing tag were observed with instantaneous detection of accurate and reliable wireless data transmission.

A controllable humidity sensitivity measurement solution based on a pure FPI fiber tip and the harmonic Vernier effect

Hygroscopic films used to enhance the humidity sensitivity of fiber-optic sensors often experience material aging and nonlinear response issues. To address this issue, this study proposes a controllable humidity sensitivity measurement solution that offers a simple and cost-effective fabrication process without requiring humidity-sensitive material sensitization. The solution is based on a Fabry-Perot interferometer (FPI) fiber tip and the harmonic Vernier effect. By employing a cascade structure of single-mode fiber (SMF)-hollow core fiber (HCF)-no core fiber (NCF) with fiber grinding techniques, the FPI-based fiber sensing probe constructed a resonance cavity to detect small variations in air refractive index (RI) induced by humidity. A reference spectrum, which can flexibly control parameters, such as free spectral range (FSR), contrast, phase, and intensity, is superimposed onto the sensing spectrum acquired by the FPI fiber sensing tip. By extracting features from the internal envelope generated by the harmonic Vernier effect, the mapping relationship between the center wavelength of the inner envelope and the humidity is determined. The harmonic Vernier effect amplifies the humidity sensitivity of the fiber-optic FPI sensing tip, with the magnification factor determined by the optical path length (OPL) detuning of the created reference and sensing spectra. For the harmonic order j = 4, a humidity sensitivity of approximately 76.01 pm/% RH@ 24 ℃ was achieved without using hygroscopic material sensitization. The proposed solution offers numerous advantages and enables high-precision and high environmental reliability humidity monitoring.

A Review of Paper-Based Sensors for Gas, Ion, and Biological Detection

Gas, ion, and biological sensors have been widely utilized to detect analytes of great significance to the environment, food, and health. Paper-based sensors, which can be constructed on a low-cost paper substrate through a simple and cost-effective fabrication process, have attracted much interests for development. Moreover, many materials can be employed in designing sensors, such as metal oxides and/or inorganic materials, carbon-based nanomaterials, conductive polymers, and composite materials. Most of these provide a large surface area and pitted structure, along with extraordinary electrical and thermal conductivities, which are capable of improving sensor performance regarding sensitivity and limit of detection. In this review, we surveyed recent advances in different types of paper-based gas, ion, and biological sensors, focusing on how these materials’ physical and chemical properties influence the sensor’s response. Challenges and future perspectives for paper-based sensors are also discussed below.

Simple fabrication of amorphous nanocomposite NiCoP@NiMoSe@NF nanospheres as a binder-free and high-performance electrocatalyst for alkaline hydrogen evolution reaction

Hydrogen generation through electrochemical water electrolysis using high-performance, low-cost, and non-precious metal electrocatalysts is crucial for the conversion of renewable energy toward hydrogen energy. This paper reports the synthesis of NiCoP nanoparticles on NiMoSe/NF nanospheres structure composite by a facile two-step hydrothermal strategy as a 3D amorphous binder-free electrocatalyst for efficient hydrogen evolution reaction (HER). The interface NiMoSe layer can accelerate the dissociation of H2O, promote electron conductivity, and strongly boost the electrocatalytic HER activity/stability of NiCoP/NiMoSe/NF alloy. Simple fabrication of NiCoP on NiMoSe@NF leads to an increase in ample active sites, optimizes hydrogen adsorption sites, and facilitates bubble release enabling the NiCoP@NiMoSe@NF electrode to manifest outstanding HER performance in alkaline electrolyte, with overpotentials of 40 and 167 mV to achieve the current density of 10 and 100 mA.cm−2. The easiness and cost-effective fabrication process in this work can open a new route for preparing state-of-the-art Ni-based catalysts for a wide range of industrial applications in water splitting.

Comparison of Anodic and Au-Au Thermocompression Si-Wafer Bonding Methods for High-Pressure Microcooling Devices.

Silicon-based microchannel technology offers unmatched performance in the cooling of silicon pixel detectors in high-energy physics. Although Si-Si direct bonding, used for the fabrication of cooling plates, also meets the stringent requirements of this application (its high-pressure resistance of ~200 bar, in particular), its use is reported to be a challenging and expensive process. In this study, we evaluated two alternative bonding methods, aiming toward a more cost-effective fabrication process: Si-Glass-Si anodic bonding (AB) with a thin-film glass, and Au-Au thermocompression (TC). The bonding strengths of the two methods were evaluated with destructive pressure burst tests (0-690 bar) on test structures, each made of a 1 × 2 cm2 silicon die etched with a tank and an inlet channel and sealed with a plain silicon die using either the AB or TC bonding. The pressure resistance of the structures was measured to be higher for the TC-sealed samples (max. 690 bar) than for the AB samples (max. 530 bar), but less homogeneous. The failure analysis indicated that the AB structure resistance was limited by the adhesion force of the deposited layers. Nevertheless, both the TC and AB methods provided sufficient bond quality to hold the high pressure required for application in high-energy physics pixel detector cooling.

Biocomposite Cryogels for Photothermal Decontamination of Water.

An effective and sustainable approach to deal with the scarcity of freshwater is interfacial solar-driven evaporation. Nonetheless, some serious challenges for photothermal materials still need to be considered, such as long-term stability in harsh environments, eco-friendly materials, and cost-effective and simple fabrication processes. Keeping these points in mind, we present a multifunctional silver-coated vegetable waste biocomposite cryogel that not only exhibits high porosity and enhanced wettability and stability but also possesses high light absorption and low thermal conductivity favorable for heat localization, solar steam generation, and efficient photothermal conversion efficiency. The achieved solar evaporation rate is 1.17 kg m-2 h-1 with a solar-to-vapor conversion efficiency of 81.11% under 1 Sun irradiation. The developed material is able to effectively desalinate artificial seawater and decontaminate synthetic wastewater (e.g., water containing dye molecules and mercury ions) with an efficiency of >99%. Most importantly, the composite cryogel presents antifouling properties, and in particular, salt antifouling ability and anti-biofouling properties. Thus, the numerous functionalities of the biocomposite cryogel make it a cost-effective promising device for prolonged water decontamination processes.

Cost-Effective Strategy for Developing Small Sized High Frequency PMUTs Toward Phased Array Imaging Applications

This article presents the development of small sized piezoelectric micromachined ultrasound transducer (PMUT) with cost effective fabrication process. Improved ultrasound imaging quality requires small sized, high frequency and high performance PMUT cell and further high density arrays. Fabrication with currently well developed and cost effective sacrificial process benefits their mass production and application. To determine small sized AlN PMUT cell, commonly reported elastic layer materials including Si, Si3N4, SiO2 are compared by mathematic derivation under the same stack thickness and device frequency. SiO2 has the smallest Young modulus and it serving as elastic layer can yield the expected one. Arranging SiO2 layer at the top of the device is compatible with phosphor silicate glass (PSG) sacrificial manufacturing process for cost effective fabrication. This fabrication strategy further downsizes cell size since extra device protection layer is omissible. We make 12MHz PMUT linear arrays with cell diameter, thickness and element pitch to be <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$40~\mu \text{m}$ </tex-math></inline-formula> , <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.9~\mu \text{m}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$120~\mu \text{m}$ </tex-math></inline-formula> . Their electrical and ultrasound results are quite uniform at both device and wafer levels. One PMUT line with 20 parallelly connected units can produce pulse-echo signal with over 25dB SNR at 10mm distance. Lateral and axial ultrasound imaging resolutions of ~1 mm and ~0.3 mm are obtained in practical verification. These indicate the good ultrasound performance of our developed PMUT array. Plus the advantages of small size and cost effective fabrication, using SiO2 elastic layer and arranging it at the top of the device is a competitive strategy to develop phased array PMUTs. [2022-0184]