Microfabrication Techniques Research Articles

Sputter-deposited Ni-rich NiTi thin films: Mechanical behavior and composition sensitivity

In this study, we investigated the mechanical behavior of sputter-deposited Ni-rich NiTi thin films with various chemical compositions. Freestanding thin films were successfully produced by employing magnetron sputtering and microfabrication techniques. Notably, films containing Ni within the range of 52.6–57.6 at. % exhibited distinct stress-induced martensitic transformations. Among these, 53.3 at. % and 54.2 at. % Ni–Ti films demonstrated a remarkable combination of strength exceeding 1.5 GPa and elastic strain approaching 5%. Conversely, films with the highest Ni content displayed nearly linear elastic behavior, showcasing an exceptional tensile strength of 2.2 GPa. As the element composition deviated from the equiatomic ratio, the grain size of the deposited films underwent a transition from several micrometers to nano-scale. In addition, the critical stresses showed lower sensitivity to chemical composition compared to bulk alloys, indicating that superelastic behavior persists over a wider composition range in Ni-rich NiTi thin films. By comparing the NiTi matrix and precipitate morphology between bulk alloys and thin films, we discussed the variations in the mechanical behavior of thin films.

Preparation of brittle ITO microstructures using Laser-Induced forward transfer technology

The performance of transparent conductive microstructures plays a significant role in determining the device efficiency. The fabrication of ITO microstructures on the flexible optoelectronic devices remains challenging because of the high-temperature processing requirements and brittleness of the ceramic material. This paper highlights a three-dimensional microfabrication technique that combines sacrificial layer etching and laser-induced transfer. By studying the donor material thickness and the laser energy density, control of the sacrificial layer transfer thrust was achieved to yield an optimal microstructure performance. Different shapes of ITO transparent conductive microstructures were fabricated on polydimethylsiloxane (PDMS) surfaces, demonstrating structural integrity, visible light transmittances > 90 %, and resistivities of ≤ 8 × 10−4 Ω·cm. Finite element analysis was employed to simulate the impact transfer of the donor material onto the receiving substrate, thereby elucidating the energy-absorbing protective role of the flexible PDMS layer. Effective control of the transfer force was identified as a crucial factor in achieving the successful transfer of brittle films. This high-precision and rapid array processing approach meets the demands of automated batch manufacturing, indicating its potential for use in patterned processing on flexible substrates, as an alternative to lithographic techniques. This technique could be applied in the preparation of electronic skins and flexible devices. Additionally, for the first time, a 3 × 3 pixel resistive array sensor was integrated on a Ag nanowires/PDMS surface, demonstrating array pressure-sensing capabilities at pressures of 0–80 kPa. This study represents a significant step towards the development of multifunctional flexible optoelectronic devices.

Minimal actuation and control of a soft hydrogel swimmer from flutter instability

Micro-organisms propel themselves in viscous environments by the periodic, nonreciprocal beating of slender appendages known as flagella. Active materials have been widely exploited to mimic this form of locomotion. However, the realization of such coordinated beating in biomimetic flagella requires complex actuation modulated in space and time. We prove through experiments on polyelectrolyte hydrogel samples that directed undulatory locomotion of a soft robotic swimmer can be achieved by untethered actuation from a uniform and static electric field. A minimal mathematical model is sufficient to reproduce, and thus explain, the observed behavior. The periodic beating of the swimming hydrogel robot emerges from flutter instability thanks to the interplay between its active and passive reconfigurations in the viscous environment. Interestingly, the flutter-driven soft robot exhibits a form of electrotaxis whereby its swimming trajectory can be controlled by simply reorienting the electric field. Our findings trace the route for the embodiment of mechanical intelligence in soft robotic systems by the exploitation of flutter instability to achieve complex functional responses to simple stimuli. While the experimental study is conducted on millimeter-scale hydrogel swimmers, the design principle we introduce requires simple geometry and is hence amenable for miniaturization via micro-fabrication techniques. We believe it may also be transferred to a wider class of soft active materials.

Feasibility Study for a High-Frequency Flexible Ultrasonic Cuff for High-Precision Vagus Nerve Ultrasound Neuromodulation.

In the emerging research field of bioelectronic medicine, it has been indicated that neuromodulation of the vagus nerve (VN) has the potential to treat various conditions such as epilepsy, depression, and autoimmune diseases. In order to reduce side effects, as well as to increase the effectiveness of the delivered therapy, sub-fascicle stimulation specificity is required. In the electrical domain, increasing spatial selectivity can only be achieved using invasive and potentially damaging approaches like compressive forces or nerve penetration. To avoid these invasive methods while obtaining a high spatial selectivity, a 2-mm diameter extraneural cuff-shaped proof-of-concept design with integrated lead zirconate titanate (PZT) based ultrasound (US) transducers is proposed in this article. For the development of the proposed concept, wafer-level microfabrication techniques are employed. Moreover, acoustic measurements are performed on the device, in order to characterize the ultrasonic beam profiles of the integrated PZT-based US transducers. A focal spot size of around [Formula: see text] is measured for the proposed cuff. Moreover, the curvature of the device leads to constructive interference of the US waves originating from multiple PZT-based US transducers, which in turn leads to an increase of 45% in focal pressure compared to the focal pressure of a single PZT-based US transducer. Integrating PZT-based US transducers in an extraneural cuff-shaped design has the potential to achieve high-precision US neuromodulation of the VN without requiring intraneural implantation.

A simple, practical experiment to investigate atomic wavefunction reduction within a Stern–Gerlach magnet

For nearly one hundred years most quantum-mechanics texts have depicted a continuous, spin-direction superposition of the wavefunction of the silver atom traversing a Stern–Gerlach (S–G) magnet. But there are sound scientific arguments which deny that understanding. Schrodinger’s equation for that continuous wavefunction development cannot describe the transfer of energy from the magnetic field to that atom. Modern micro-fabrication techniques now make it possible to implement a simple, accessible experiment testing whether a spin superposition does continue in the magnet. Because the S–G experiment is the prototype for quantum measurement, that observation is crucial to implementing a realistic quantum theory of measurement.

Fractures of low-k materials in a RF package with integrated passive device based on TGV

The radio frequency (RF) chips and passive devices integrated on the through-glass-via (TGV) substrate meets the demands of miniaturization, high performance and low losses in the application. The RF chip and integrated passive devices (IPDs) are interconnected electrically by a redistribution layer (RDL) on the TGV substrate with the isolation low-k materials. The low-k materials, however, are susceptible to fracture during the thermal process in packaging due to their weak mechanical properties. In this study, the fractures of the low-k material were studied by experiments and the finite element analysis (FEA) for a RF package with integrated passive device based on TGV. The mechanical properties of the low-k material used in the FEA were tested by fabricating freestanding low-k films using microfabrication techniques. Then the fracture behaviors of the low-k material in the package and its impact factors under thermal loadings were examined. The impact factors, such as the initial defect location, direction and length, were investigated by evaluating the stress intensity factors (SIFs) at the defect tips. The results revealed that the most hazardous location in the low-k material is the region below the micro-joint of RF chip. The vertical defects along thickness in low-k film are more likely to propagate than horizontal ones. The SIF value increases linearly with the defect length both in heating and cooling conditions.

A Staggered Vane-Shaped Slot-Line Slow-Wave Structure for W-Band Dual-Sheet Electron-Beam-Traveling Wave Tubes.

A staggered vane-shaped slot-line slow-wave structure (SV-SL SWS) for application in W-band traveling wave tubes (TWTs) is proposed in this article. In contrast to the conventional slot-line SWSs with dielectric substrates, the proposed SWS consists only of a thin metal sheet inscribed with periodic grooves and two half-metal enclosures, which means it can be easily manufactured and assembled and has the potential for mass production. This SWS not only solves the problem of the dielectric loading effect but also improves the heat dissipation capability of such structures. Meanwhile, the SWS design presented here covers a -15 dB S11 frequency range from 87.5 to 95 GHz. The 3-D simulation for a TWT based on the suggested SWS is also investigated. Under dual-electron injection conditions with a total voltage of 17.2 kV and a total current of 0.3 A, the maximum output power at 90 GHz is 200 W, with a 3 dB bandwidth up to 4 GHz. With a good potential for fabrication using microfabrication techniques, this structure can be a good candidate for millimeter-wave TWT applications.

Ethanol Solvation of Polymer Residues in Graphene Solution-Gated Field Effect Transistors.

The persistence of photoresist residues from microfabrication procedures causes significant obstacles in the technological advancement of graphene-based electronic devices. These residues induce undesired chemical doping effects, diminish carrier mobility, and deteriorate the signal-to-noise ratio, making them critical in certain contexts, including sensing and electrical recording applications. In graphene solution-gated field-effect transistors (gSGFETs), the presence of polymer contaminants makes it difficult to perform precise electrical measurements, introducing response variability and calibration challenges. Given the absence of viable short to midterm alternatives to polymer-intensive microfabrication techniques, a postpatterning treatment involving THF and ethanol solvents was evaluated, with ethanol being the most effective, environmentally sustainable, and safe method for residue removal. Employing a comprehensive analysis with XPS, AFM, and Raman spectroscopy, together with electrical characterization, we investigated the influence of residual polymers on graphene surface properties and transistor functionality. Ethanol treatment exhibited a pronounced enhancement in gSGFET performance, as evidenced by a shift in the charge neutrality point and reduced dispersion. This systematic cleaning methodology holds the potential to improve the reproducibility and precision in the manufacturing of graphene devices. Particularly, by using ethanol for residue removal, we align our methodology with the principles of green chemistry, minimizing environmental impact while advancing diverse graphene technology applications.

Gas phase growth of metal-organic frameworks on microcantilevers for highly sensitive detection of volatile organic compounds

A gas-phase technique, known as chemical vapor deposition of metal-organic frameworks (MOF-CVD), is used for sensitizing silicon cantilevers. These cantilevers are coated with a uniform and compact Zn(EtIm)2 (MAF-6) film, enabling the detection of volatile organic compounds (VOCs) through a change in the resonance frequency of the cantilever. The MOF-coated sensor exhibits remarkable sensitivity to VOCs within the 0.33–0.71 Hz/ppm range and a limit of detection (LOD) spanning from 4 to 9 ppb. Notably, these sensitivities surpass those achieved by ZnO-coated cantilevers by two orders of magnitude. This high sensitivity is attributed to the high porosity and large surface area of MAF-6. The approach employed in this work is compatible with conventional microfabrication techniques and offers an advantageous avenue for the development of highly sensitive gas sensors.

Multimodal Biosensing of Foodborne Pathogens.

Microbial foodborne pathogens present significant challenges to public health and the food industry, requiring rapid and accurate detection methods to prevent infections and ensure food safety. Conventional single biosensing techniques often exhibit limitations in terms of sensitivity, specificity, and rapidity. In response, there has been a growing interest in multimodal biosensing approaches that combine multiple sensing techniques to enhance the efficacy, accuracy, and precision in detecting these pathogens. This review investigates the current state of multimodal biosensing technologies and their potential applications within the food industry. Various multimodal biosensing platforms, such as opto-electrochemical, optical nanomaterial, multiple nanomaterial-based systems, hybrid biosensing microfluidics, and microfabrication techniques are discussed. The review provides an in-depth analysis of the advantages, challenges, and future prospects of multimodal biosensing for foodborne pathogens, emphasizing its transformative potential for food safety and public health. This comprehensive analysis aims to contribute to the development of innovative strategies for combating foodborne infections and ensuring the reliability of the global food supply chain.

Flexible zinc-ion hybrid micro-supercapacitors with polymeric current collector for integrated energy storage in wearable devices

The ubiquity of conventional micro-fabrication techniques has encountered impediments in constructing cost-effective micro-devices, thereby constraining their broad deployment. Concurrently, the suboptimal energy density inherent to supercapacitors exacerbates this challenge. This study presents a straightforward assembly methodology for the fabrication of a mechano-electrochemically efficient micro-zinc ion hybrid supercapacitor (M−ZSC), alongside the introduction of an innovative polymeric current collector. The M−ZSC is fabricated through a process involving masked spray deposition of a novel adhesive current collector and the electrode materials, and electroplating of zinc nanosheets onto the anode finger, creating an electrochemically performant and mechanically robust device. The resulting M−ZSC exhibits a notable areal capacitance of 52.2 mF/cm2 and an energy density of 18.5 µWh/cm2 for the normal mass-loading of 3.6 mg/cm2, which is amongst the highest reported values for energy storage. The masked spray deposition/hot pressing technique enabled us to fabricate free-standing thick electrodes with a loading density of up to 56.1 mg/cm2, facilitating the achievement of an ultrahigh areal capacitance of 227 mF/cm2 and an energy density of 80.5 µWh/cm2. Furthermore, the M−ZSC exhibits a robust retention of 95 % capacitance at 1 mA/cm2. Critical to its flexibility, the device is constructed using purely additive deposition methods on flexible substrates and is therefore well-tailored for deployment in flexible electronics and on-chip applications. These micro-devices are well-poised for seamless integration within a singular electronics package or chip architecture.

Understanding the Effect of Dispersant Rheology and Binder Decomposition on 3D Printing of a Solid Oxide Fuel Cell.

Solid oxide fuel cells (SOFCs) are a green energy technology that offers a cleaner and more efficient alternative to fossil fuels. The efficiency and utility of SOFCs can be enhanced by fabricating miniaturized component structures within the fuel cell footprint. In this research work, the parallel-connected inter-digitized design of micro-single-chamber SOFCs (µ-SC-SOFCs) was fabricated by a direct-write microfabrication technique. To understand and optimize the direct-write process, the cathode electrode slurry was investigated. Initially, the effects of dispersant Triton X-100 on LSCF (La0.6Sr0.2Fe0.8Co0.2O3-δ) slurry rheology was investigated. The effect of binder decomposition on the cathode electrode lines was evaluated, and further, the optimum sintering profile was determined. Results illustrate that the optimum concentration of Triton X-100 for different slurries was around 0.2-0.4% of the LSCF solid loading. A total of 60% of solid loading slurries had high viscosities and attained stability after 300 s. In addition, 40-50% solid loading slurries had relatively lower viscosity and attainted stability after 200 s. Solid loading and binder affected not only the slurry's viscosity but also its rheology behavior. Based on the findings of this research, a slurry with 50% solid loading, 12% binder, and 0.2% dispersant was determined to be the optimal value for the fabricating of SOFCs using the direct-write method. This research work establishes guidelines for fabricating the micro-single-chamber solid oxide fuel cells by optimizing the direct-write slurry deposition process with high accuracy.

Plasma jet printing of copper and silver antennas operating at 2.4 GHz

Printing has emerged as a technically feasible and economically viable approach to fabricate antennas on a wide range of rigid and flexible substrates. Printing offers several advantages such as rapid prototyping, minimal number of processing steps and minimal equipment needs relative to conventional microfabrication and other antenna manufacturing techniques, versatility in the choice of substrates and low cost. Here we use a plasma-based printing approach to print self-sintered copper and silver antennas. The morphology of the printed films is continuous with nanoparticles agglomerated and fused together under the influence of the plasma. The printed antennas exhibit a reflection coefficient of about −20 dB or lower and bandwidth over 10% at a resonant frequency around 2.4 GHz. The results show the feasibility of printing high performance antennas on flexible substrates such as polyimide using plasma printing technology.

Responsive materials nanoarchitectonics at interfaces

AbstractAdvanced materials could perform functions in response to external stimuli. These are responsive materials. In order for us to develop advanced functional systems with a good responsive nature, we need to create a methodology that goes one step further. It is the artificial architecture of functional material systems based on the knowledge of nanotechnology. The task will be fulfilled by the new concept of nanoarchitectonics. Nanoarchitectonics integrates nanotechnology with various material sciences, basic chemistry, microfabrication techniques, and biological processes to architect functional material systems from atomic, molecular, and nanomaterial units. This review will deal with the nanoarchitectonics of responsive materials related with phenomena at interfaces. In order to demonstrate the effectiveness of responsive materials nanoarchitectonics at interfaces for functional systems of various sizes, this review article is organized by size for various functional systems. Specifically, this review has grouped them into (i) molecular level response, (ii) nanodevice level response, (iii) material level response, and (iv) living cell level response. If the social demand for these materials is fully recognized, such development is expected to efficiently progress. This review article would play a role in stimulating such development.

Dynamics of microdroplet generation via drop impact on a superhydrophobic micropore

This study delves into the dynamics of generating microdroplets by impacting a droplet onto a micropore on superhydrophobic copper substrates. It identifies the necessary impact velocities for single microdroplet formation for each micropore and characterizes microdroplet size in relation to micropore diameter. The results underscore the significant role of viscosity, especially as the diameter of the micropore decreases. For micropores measuring 400 μm, an increase in viscosity up to 8 cP does not alter the critical impact velocities, while smaller diameters of 50 and 100 μm see a notable change in critical velocities with even minor increases in viscosity. Remarkably, the diameter of the microdroplet remains consistent regardless of changes in the liquid viscosity or impact velocity. This research showcases two practical uses of single microdroplets: printing on paper and fabricating microbeads. The insights gained from these findings pave the way for advancements in printing technology and microfabrication techniques.

Hepatic spheroid-on-a-chip: Fabrication and characterization of a spheroid-based in vitro model of the human liver for drug screening applications.

The integration of microfabrication and microfluidics techniques into cell culture technology has significantly transformed cell culture conditions, scaffold architecture, and tissue biofabrication. These tools offer precise control over cell positioning and enable high-resolution analysis and testing. Culturing cells in 3D systems, such as spheroids and organoids, enables recapitulating the interaction between cells and the extracellular matrix, thereby allowing the creation of human-based biomimetic tissue models that are well-suited for pre-clinical drug screening. Here, we demonstrate an innovative microfluidic device for the formation, culture, and testing of hepatocyte spheroids, which comprises a large array of patterned microwells for hosting hepatic spheroid culture in a reproducible and organized format in a dynamic fluidic environment. The device allows maintaining and characterizing different spheroid sizes as well as exposing to various drugs in parallel enabling high-throughput experimentation. These liver spheroids exhibit physiologically relevant hepatic functionality, as evidenced by their ability to produce albumin and urea at levels comparable to in vivo conditions and the capability to distinguish the toxic effects of selected drugs. This highlights the effectiveness of the microenvironment provided by the chip in maintaining the functionality of hepatocyte spheroids. These data support the notion that the liver-spheroid chip provides a favorable microenvironment for the maintenance of hepatocyte spheroid functionality.

Ultrathin and Deformable Graphene Etch Mask for Fabrication of 3D Microstructures.

Three-dimensional (3D) microfabrication techniques play a crucial role across various research fields. These techniques enable the creation of functional 3D structures on the microscale, unlocking possibilities for diverse applications. However, conventional fabrication methods have limits in producing complex 3D structures, which require numerous fabrication steps that increase the costs. Graphene is an atomically thin material known for its deformability and impermeability to small gases and molecules, including reactive gases like XeF2. These features make graphene a potential candidate as an etch mask for 3D microfabrication. Here, we report the fabrication of various 3D microstructures using graphene etch masks directly grown and patterned on a Si substrate. The patterned graphene deforms and wraps the etched structures, allowing for the fabrication of complicated 3D microstructures, such as mushroom-like and step-like microstructures. As a practical demonstration of the graphene etch mask, we fabricate an omniphobic surface of reentrant 3D structures on a Si substrate. Our work provides a method for fabricating complex 3D microstructures using a graphene etch mask, contributing to advancements in etching and fabrication processes.

Bio-Electronics Interface between Electronics and Biological Systems for Healthcare Applications.

The intersection of electronics and biology has led to the emergence of bio-electronics interfaces, which hold tremendous potential for revolutionizing healthcare applications. These interfaces facilitate seamless communication between electronic devices and biological systems, enabling a range of diagnostic, therapeutic, and monitoring capabilities with unprecedented precision and efficiency.This paper provides a comprehensive overview of the recent advancements in bio-electronics interfaces and their diverse applications in healthcare. The fundamental principles underlying the integration of electronics with biological systems, including the design and fabrication of bio-compatible materials, signal transduction mechanisms, and biointegration strategies are discussed. [1] The paper discusses specific healthcare applications enabled by bio-electronics interfaces, such as bio-sensing for disease diagnosis, neural interfaces for brain-machine communication and prosthetics, bio-electronic implants for targeted drug delivery and neuromodulation, and wearable devices for continuous health monitoring. We also examine the challenges and opportunities associated with the development and implementation of bio-electronics interfaces in healthcare settings. These challenges include biocompatibility issues, signal interference, power management, data security, and regulatory considerations. However, rapid advancements in materials science, microfabrication techniques, wireless communication, and machine learning are driving innovation and overcoming these hurdles. We highlight the potential of bio-electronics interfaces to transform personalized medicine by enabling real-time monitoring of physiological parameters, early detection of diseases, and personalized therapeutic interventions tailored to individual patients' needs. By integrating electronic devices with biological systems at the molecular, cellular, and organismal levels, bio-electronics interfaces have the potential to revolutionize healthcare delivery, improve patient outcomes, and enhance quality of life.

Design and validation of a piezoelectric diaphragm micropump for drug delivery

There is a common eye ailment called Dry Eye Disease (DED) that causes symptoms of discomfort, visual disturbance, and tear film instability, which cause damage to the ocular surface. For treatment of this illness, the application of artificial tear fluid is usually prescribed. This work presents the design process of a piezoelectric micropump to become part of an automatic pumping system for delivering artificial tear fluid to people suffering from DED. Low polarizing voltage, portability, and achieving a variable output flow rate in the range of 1 µl/min, which is the necessary range needed by a person suffering from DED, are the focus of this design. Standard microfabrication techniques widely used in the CMOS industry and for MEMS development will be used for manufacturing the proposed micropump. For this reason, the materials and manufacturing processes involved must be CMOS-compliant. For the piezoelectric actuator, zinc oxide (ZnO) was selected due to its compatibility with CMOS technology and because it is readily available in thin film form through a sputtering process. Other materials involved in the device are silicon and aluminum. The design was validated through finite element analysis software, COMSOL Multiphysics®. The maximum flow rate obtained by a single micropump device was 2.51µl/min operating at 20V peak with a frequency of 900Hz. Also, the flow rate is controllable through variations in frequency, thus making it suitable for the application previously described.

Development of eutectic gallium-indium-based transparent conductive electrodes on flexible substrates for touch sensor integration

In this study, the adaptability of liquid metal (LM)-based transparent conductive electrodes (TCEs) to flexible substrates and their potential applications in various electronics fields were investigated. To achieve this, conventional microfabrication techniques were employed to pattern polydimethylsiloxane (PDMS) channels and introduce an Eutectic Gallium-Indium (EGaIn) LM with the aim of enhancing transmittance and reducing sheet resistance. Microfluidic channel structures with varying pitch lengths and widths were fabricated in the types of grid patterns, labeled Pattern A (2000 μm pitch, 40 μm width), Pattern B (2000 μm pitch, 80 μm width), Pattern C (200 μm pitch, 40 μm width), and Pattern D (200 μm pitch, 80 μm width. The corresponding average transmittance values for the EGaIn LM-based TCE were 90 %, 71.8 %, 61.8 %, and 43.2 % for Patterns A, B, C, and D, respectively. To illustrate the potential in touch sensor applications, resistance changes in Patterns A, B, C, and D were assessed under applied forces ranging from 0 N to 150 N, revealing resistance changes of 0.0265 Ω, 0.03617 Ω, 0.03977 Ω, and 0.11629 Ω, respectively.