Journal of Micromechanics and Microengineering

Polydimethylsiloxane (PDMS) elastomers are extensively used for soft lithographic replication of microstructures in microfluidic and micro-engineering applications. Elastomeric microstructures are commonly required to fulfil an explicit mechanical role and accordingly their mechanical properties can critically affect device performance. The mechanical properties of elastomers are known to vary with both curing and operational temperatures. However, even for the elastomer most commonly employed in microfluidic applications, Sylgard 184, only a very limited range of data exists regarding the variation in mechanical properties of bulk PDMS with curing temperature. We report an investigation of the variation in the mechanical properties of bulk Sylgard 184 with curing temperature, over the range 25 °C to 200 °C. PDMS samples for tensile and compressive testing were fabricated according to ASTM standards. Data obtained indicates variation in mechanical properties due to curing temperature for Young's modulus of 1.32–2.97 MPa, ultimate tensile strength of 3.51–7.65 MPa, compressive modulus of 117.8–186.9 MPa and ultimate compressive strength of 28.4–51.7 GPa in a range up to 40% strain and hardness of 44–54 Sh_A.

Electrode-integrated microfluidic chips play a pivotal role in applying electrochemical impedance spectroscopy (EIS) across various domains. This technology has significantly transformed biomedical research, facilitating progress in drug discovery, diagnostics, and cell analysis. The architecture of these chips integrated with electrodes critically influences the precision and dependability of EIS outcomes. This study developed diverse microfluidic chip designs, including circular, deltoid, and deltoid-like shapes, to explore microenvironmental dynamics on EIS assessments. Moreover, computational fluid dynamics was utilized to examine the flow properties within the proposed chip designs by investigating the relationship between pressure and velocities in the microenvironment. The study also assessed the effects of varying flow rates (1, 10, 100 µl) on EIS analysis and the simulation studies. Findings indicated that there were empty spaces in the circular design, which is commonly used, and it was not suitable for EIS experiments. Furthermore, it was noted that even with reduced altitude in the EIS measurement area, the environment remained conducive to more accurate measurements. A flow rate of 10 µl min⁻¹ was identified as optimal in this research, as it offered the best balance among charge transfer resistance (R_ct), capacitance (Q), and open circuit potential values, while also minimizing the sample volume which is very important for microfluidic chip design and applications. This study demonstrated a strong interaction between microfluidic chip designs for electrode integration and EIS outcomes. On the other hand, it has yielded a reliable, cost-effective, rapid, practical, reusable, and portable platform after choosing an appropriate architecture for the electrode housing.

In the dynamic landscape of semiconductor manufacturing, the demand for innovative and efficient techniques is ever-growing. Dicing is a singulation process where a machine known as a dicing saw or dicer uses a diamond blade or laser to separate dies from a wafer through a manual, semi-automated, or fully automated process. In diamond blade or mechanical dicing, the dicing saw utilizes a thin blade to cut through a wafer. This paper presents the design and implementation of an alignment teaching-assisted fully automated dicing process for the singulation of microelectromechanical systems (MEMS) devices. A pseudo-MEMS device with potential alignment targets was designed and manufactured by conventional microfabrication techniques. Alignment teaching operation was optimized for the dicing saw by finding the most appropriate alignment targets, as alignment teaching is as a pre-requisite for realizing both auto-alignment and automated dicing processes. A systematic trial-and-error approach was employed to discover the most suitable alignment targets from a pool of twenty-three potential target patterns. A circle was identified as an excellent macro target, while the addition symbol, hash symbol, and rectangle-pair were determined to be the most appropriate micro targets. The developed versatile singulation process is capable of executing an alignment teaching assisted fully automated (i.e. a total of one-click to initiate and finalize) dicing for singulating MEMS device chips, irrespective of alignment target color, die size, or wafer material. Furthermore, we developed, and experimentally validated, a mathematical model to estimate the total process time for the automated dicing.

The demand for rapid, high-quality, and controlled mixing at the microscale has led to the development of various types of micromixers. Micromixers are commonly categorised as active, or passive based on whether they utilise external energy to enhance mixing. Passive micromixers utilise a complex geometry to enhance the diffusion coefficient at lower Reynolds numbers and induce chaotic advection at higher Reynolds numbers for effectively mixing fluids without external energy. Active micromixers, on the other hand, achieve precise, fast, and controllable mixing by employing external energy sources such as pressure, electric, magnetic, or acoustic fields. Some active methods such as magnetic field-driven micromixers need fluids with specific properties. Others, such as acoustic field-driven micromixers apply to various types of fluids. Bubbles can be used as membranes or stirrers in microfluidic devices for both passive and active micromixers. They are easy to use, compatible with microfluidic systems, low cost, and effective. Improvements in manufacturing methods, notably, 3D printing have emerged as promising methods for the development of new micromixer designs. In this paper, a wide range of micromixer types is reviewed and the main mechanism for enhanced mixing is investigated. This study aims to guide researchers proposing innovative designs. Furthermore, it is shown that combining different methods can lead to the development of more effective micromixers, promising further advancements in microscale mixing technology.

Cryogenic deep reactive ion etching (Cryo DRIE) of silicon has become an enticing but challenging process utilized in front-end fabrication for the semiconductor industry. This method, compared to the Bosch process, yields vertical etch profiles with smoother sidewalls not subjected to scalloping, which are desired for many microelectromechanical systems (MEMS) applications. Smoother sidewalls enhance electrical contact by ensuring more conformal and uniform sidewall coverage, thereby increasing the effective contact area without altering contact dimensions. The versatility of the Cryo DRIE process allows for customization of the etch profiles by adjusting key process parameters such as table temperature, O₂ percentage of the total gas flow rate (O₂ + SF₆), RF bias power and process pressure. In this work, we undertake a comprehensive study of the effects of Cryo DRIE process parameters on the trench profiles in the structures used to define cantilevers in MEMS devices. Experiments were performed with an Oxford PlasmaPro 100 Estrelas ICP-RIE system using positive photoresist SPR-955 as a mask material. Our findings demonstrate significant influences on the sidewall angle, etch rate and trench shape due to these parameter modifications. Varying the table temperature between −80 °C and −120 °C under a constant process pressure of 10 mTorr changes the etch rate from 3 to 4 μm min⁻¹, while sidewall angle changes by ∼2°, from positive (<90° relative to the Si surface) to negative (>90° relative to the Si surface) tapering. Altering the O₂ flow rate with constant SF₆ flow results in a notable 10° shift in sidewall tapering. Furthermore, SPR-955 photoresist masks provide selectivity of 46:1 with respect to Si and facilitates the fabrication of MEMS devices with precise dimension control ranging from 1 to 100 μm for etching depths up to 42 μm using Cryo DRIE. Understanding the influence of each parameter is crucial for optimizing MEMS device fabrication.

Lift-off process is an alternative to deposition, lithography, and etching of materials. Lift-off is a simple and economical process because it does not require subsequent wet or dry etching. Lifting-off nanometer thick films is a well-developed and repeatable process. However, lifting-off a few micrometer thick films may be challenging. Previously, different techniques were proposed to lift-off micrometer thick films. Herein, a novel method for lifting-off high thickness materials is proposed using a multi-layer AZ 5214E photoresist. The novel method was successful in lifting-off 4 µm thick copper while the copper could even be deposited up to 6 µm with tri-layer AZ 5214E. With four layers of AZ 5214E, the photoresist thickness can be even thicker than 9 µm. As detailed in the study, the photoresist layer thickness can be adjusted by varying the number of layers. This enables the selection of the appropriate number of layers to achieve the desired material thickness. To show the merits of the proposed method, the method is compared to the bi-layer method with AZ 4562 photoresist which is used for lifting-off high thickness materials. In addition to lifting-off thick materials, the proposed method is faster compared to lifting-off using bi-layer AZ 4562. Despite the ability to lift-off thick films, both methods could suffer from lift-off flags if the deposition process is not anisotropic. Solutions to remove the lift-off flags, and reduce the undercut width are demonstrated.

Microfluidic devices have been conventionally fabricated using traditional photolithography or through the use of soft lithography both of which require multiple complicated steps and a clean room setup. Xurography is an alternative rapid prototyping method which has been used to fabricate microfluidic devices in less than 20–30 minutes. The method is used to pattern two-dimensional pressure-sensitive adhesives, polymer sheets, and metal films using a cutting plotter and these layers are bonded together using methods including adhesive, thermal, and solvent bonding. This review discusses the working principle of xurography along with a critical analysis of parameters affecting the patterning process, various materials patterned using xurography, and their applications. Xurography can be used in the fabrication of microfluidic devices using four main approaches: making multiple layered devices, fabrication of micromolds, making masks, and integration of electrodes into microfluidic devices. We have also briefly discussed the bonding methods for assembling the two-dimensional patterned layers. Due to its simplicity and the ability to easily integrate multiple materials, xurography is likely to grow in prominence as a method for fabrication of microfluidic devices.

This paper reviews the recent developments of micro-electromechanical system (MEMS) based electrostatically actuated tunable capacitors. MEMS based tunable capacitors (MBTCs) are important building blocks in advanced radio frequency communication systems and portable electronics. This is due to their excellent performance compared to solid state counterpart. Different designs, tuning mechanisms, and performance parameters of MBTCs are discussed, compared, and summarized. Several quantitative comparisons in terms of tuning range, quality factor (Q factor), and electrodes configurations are presented, which provide deep insight into different design studies, assists in selecting designs, and layouts that best suit various applications. We also highlight recent modern applications of tunable capacitors, such as mobile handsets, internet of things, communication sensors, and 5G antennas. Finally, the paper discusses different design approaches and proposes guidelines for performance improvement.

In the domain of micro-nano electronic printing technology, the integration of the operational characteristics with piezoelectric inkjet printing (PIJP) and electrohydrodynamic printing overcomes the limitations of single-mode printing. This integration facilitates the advancement and enhancement of hybrid printing technology, encompassing piezoelectric and electric forces. A study is conducted on jet printing utilizing a hybrid force as the driving power. The hybrid printing system is initially developed and assembled. The study focuses on the printing mechanism of piezoelectric deforming units and electrohydrodynamic generating units, leading to the development and integration of hybrid printing equipment. Secondly, three types of printing models are established using simulation software, including piezoelectric, electrohydrodynamic, and hybrid models. The jetting mechanism of the single force and hybrid force is described, and the feasibility of the process is assessed. The experiment is designed to assess the performance of hybrid printing in comparison to other single-force printing methods. The experimental results indicate that hybrid printing demonstrates superior precision and consistency compared to single-force printing. The average diameters of the printed droplet dots for piezoelectric-driven and composite-driven methods are 225.9 μm and 181.4 μm, respectively. Compared to PIJP, hybrid printing ensures uniform droplet formation and reduces satellite formation through electrohydrodynamic stabilization. Compared to electrohydrodynamic methods, hybrid printing improves deposition accuracy, refines jetting control, minimizes unintended spreading, and achieves higher resolution.

Vibration energy harvesting is receiving a considerable amount of interest as a means for powering wireless sensor nodes. This paper presents a small (component volume 0.1 cm³, practical volume 0.15 cm³) electromagnetic generator utilizing discrete components and optimized for a low ambient vibration level based upon real application data. The generator uses four magnets arranged on an etched cantilever with a wound coil located within the moving magnetic field. Magnet size and coil properties were optimized, with the final device producing 46 µW in a resistive load of 4 kΩ from just 0.59 m s⁻² acceleration levels at its resonant frequency of 52 Hz. A voltage of 428 mVrms was obtained from the generator with a 2300 turn coil which has proved sufficient for subsequent rectification and voltage step-up circuitry. The generator delivers 30% of the power supplied from the environment to useful electrical power in the load. This generator compares very favourably with other demonstrated examples in the literature, both in terms of normalized power density and efficiency.

Laser transmission welding (LTW) is a technique for joining a transparent polymer to an opaque polymer. This paper presents the results of nanosecond pulsed laser (1064 nm) transmission welding of cyclic olefin copolymer (COC). COC has a wide range of applications in biological, biomedical, membrane, and semiconductor fields. LTW has advantages over conventional adhesive and thermal-based methods of bonding. These include precision sealing and minimised heat affected zone, which makes this process favourable for bio-applications. The effect of laser processing parameters, such as the laser pulse energy and the laser scan speed, on the weld morphology as well as on the bonding strength was studied via cross-sectional optical microscopy and lap shear tests. The lap-shear strength of laser bonded COC substrates achieved lap-shear strength of 0.15 N mm⁻² to 0.5 N mm⁻² which is comparable to the strength found in adhesive bonded substrates. These studies provide novel insights into the welded region at the interface of the two materials and demonstrate the impact of laser parameters on the weld seam width and bond strength. Leak tests were performed on laser welded fluidic channels and no leakages were detected. Further, the analysis of lap-shear tests demonstrates that laser welding produces joining strengths similar to those of adhesive-bonded COC. The joining interface area for laser welding is in general smaller than that of adhesive bonding, which potentially can enable more design freedom and capacity for accommodating complex functionalities on a singular COC-based device.

Viscosity is a critical fluid property that significantly influences fluid behavior and performance across various systems. Most commercial viscometers require relatively large sample volumes (on the order of milliliters), which restricts their utility in scenarios where only limited sample volumes are available. For instance, human tear fluid—essential for developing effective treatment strategies—is scarce (typically on microliters), especially in individuals with dry eye disease. To address this limitation, we present a novel microfluidic viscometer platform capable of measuring the viscosity of ultra-small volumes (i.e. ∼10 μl) of Newtonian and non-Newtonian fluids. The working principle is based on the Hagen–Poiseuille equation, incorporating the Weissenberg–Rabinowitsch–Mooney correction for slit-flow, and employs an optically transparent microfluidic chip integrated with supporting devices including a syringe pump, manifold, camera, and differential pressure transducer. Preliminary validation was conducted using glycerol solutions, artificial tears, and tear samples from dry and healthy eyes. This microfluidic viscometer holds promise for measuring the shear viscosity of small volumes of biofluid samples (e.g. synovial fluid, cerebrospinal fluid, tear films) or pharmaceuticals (e.g. monoclonal antibodies, ophthalmic drug delivery products) by developing surface coating materials appropriate for specific samples.

In this paper, ball-burning and bonding tests were conducted using Ag–Au–Pd alloy wires with a diameter of ϕ 0.025 mm, and the performance of free air ball (FAB) morphology and bonding strength under various bonding parameters was investigated. The results showed that when the electronic flame off (EFO) current is 20 mA, the FAB of Ag–Au–Pd bonding alloy wire appears small ellipsoid, whereas increasing the EFO current to 40 mA resulted in a golf club-shaped FAB. Similarly, when the EFO time was 0.4 ms, the FAB appears as a small spherical, but extending the EFO time to 1.2 ms caused the FAB to enlarge and exhibit a golf club phenomenon. The addition of Pd element reduced the FAB heat affected zone length of Ag–Au–Pd alloy wire by 19.4% compared to Ag–Au wire. Insufficient ultrasonic power and bonding pressure lead to weak bonding at the bonded interface, thereby reducing the bonding strength, while excessive ultrasonic power and bonding pressure can cause short circuits and pad damage. The optimized bonding parameters for the Ag–Au–Pd alloy wire determined to be: an ultrasonic power of 65 mW and a bonding pressure of 45 g for the ball bond, and an ultrasonic power of 95 mW and a bonding pressure is 75 g for the wedge bond.

In the domain of micro-nano electronic printing technology, the integration of the operational characteristics with piezoelectric inkjet printing (PIJP) and electrohydrodynamic printing overcomes the limitations of single-mode printing. This integration facilitates the advancement and enhancement of hybrid printing technology, encompassing piezoelectric and electric forces. A study is conducted on jet printing utilizing a hybrid force as the driving power. The hybrid printing system is initially developed and assembled. The study focuses on the printing mechanism of piezoelectric deforming units and electrohydrodynamic generating units, leading to the development and integration of hybrid printing equipment. Secondly, three types of printing models are established using simulation software, including piezoelectric, electrohydrodynamic, and hybrid models. The jetting mechanism of the single force and hybrid force is described, and the feasibility of the process is assessed. The experiment is designed to assess the performance of hybrid printing in comparison to other single-force printing methods. The experimental results indicate that hybrid printing demonstrates superior precision and consistency compared to single-force printing. The average diameters of the printed droplet dots for piezoelectric-driven and composite-driven methods are 225.9 μm and 181.4 μm, respectively. Compared to PIJP, hybrid printing ensures uniform droplet formation and reduces satellite formation through electrohydrodynamic stabilization. Compared to electrohydrodynamic methods, hybrid printing improves deposition accuracy, refines jetting control, minimizes unintended spreading, and achieves higher resolution.

In the dynamic landscape of semiconductor manufacturing, the demand for innovative and efficient techniques is ever-growing. Dicing is a singulation process where a machine known as a dicing saw or dicer uses a diamond blade or laser to separate dies from a wafer through a manual, semi-automated, or fully automated process. In diamond blade or mechanical dicing, the dicing saw utilizes a thin blade to cut through a wafer. This paper presents the design and implementation of an alignment teaching-assisted fully automated dicing process for the singulation of microelectromechanical systems (MEMS) devices. A pseudo-MEMS device with potential alignment targets was designed and manufactured by conventional microfabrication techniques. Alignment teaching operation was optimized for the dicing saw by finding the most appropriate alignment targets, as alignment teaching is as a pre-requisite for realizing both auto-alignment and automated dicing processes. A systematic trial-and-error approach was employed to discover the most suitable alignment targets from a pool of twenty-three potential target patterns. A circle was identified as an excellent macro target, while the addition symbol, hash symbol, and rectangle-pair were determined to be the most appropriate micro targets. The developed versatile singulation process is capable of executing an alignment teaching assisted fully automated (i.e. a total of one-click to initiate and finalize) dicing for singulating MEMS device chips, irrespective of alignment target color, die size, or wafer material. Furthermore, we developed, and experimentally validated, a mathematical model to estimate the total process time for the automated dicing.

Currently, micromachined ultrasonic transducers are classified as capacitive micromachined ultrasonic transducer (CMUT) and piezoelectric micromachined ultrasonic transducers (PMUTs). CMUT present higher electromechanical coupling coefficients, high receiving sensitivity, and higher bandwidth, exhibiting superior performance compared to PMUT and their traditional counterparts. Micro-nano materials, with advantages such as high surface area, improved electronic performance, biocompatibility, and easy integration with miniaturization, are widely applied in various fields including electronics, energy, environment protection, and medicine. The combination of CMUT and micro-nano materials has become a hot research topic in the fields of medicine and biochemistry in recent years. Integrating CMUT with micro-nano materials plays an important role in biochemical testing, drug monitoring, and medical diagnosis, promoting the prediction of disease progression and timely implementation of effective measures. This work primarily discusses the integration of CMUT with micro-nano materials, emphasizing that the innovative application of these materials significantly enhances the performance, thereby advancing the development of related technologies.

Beam-type piezoelectric energy harvesters (PEHs), particularly those utilizing piezoelectric materials, have garnered considerable attention as efficient devices for converting ambient mechanical vibrations into electrical energy. This comprehensive review article thoroughly examines the mathematical models employed in beam-type PEHs, emphasizing their evolution and limitations. The study also delves into both theoretical and experimental analyses of design configurations, placing a special focus on the impact of geometries on energy harvesting efficiency. In conclusion, the paper explores recent advancements and improvements, along with potential avenues for future research, providing a concise overview tailored for professionals and scholars engaged in this specialized field.

Inspired by the advances in microfabrication of microelectromechanical systems (MEMSs), microphysiological systems (MPSs) capitalized on the fabrication techniques of MEMS technology and pivoted to biomedical applications with select biomaterials and design principles. With the new initiative to refute animal testing and develop valid and reliable alternatives, MPS platforms are in greater demand than ever. This paper will first present the major types of MPSs in the cardiovascular research space, and then review the core design principles of such systems to closely replicate the in vivo physiology. Fabrication methodologies of the platform, as well as technologies that enable patterning and functionalizing scaffolds, and the various sensing modalities that can interface with such MPS platforms, are reviewed and discussed. This review aims to provide a comprehensive picture of cardiac MPSs in which microfluidics play an important role in the design, fabrication, and sensing modalities, and prospects of how this platform can continue to drive further improvements in cardiovascular research and medicine.

The demand for rapid, high-quality, and controlled mixing at the microscale has led to the development of various types of micromixers. Micromixers are commonly categorised as active, or passive based on whether they utilise external energy to enhance mixing. Passive micromixers utilise a complex geometry to enhance the diffusion coefficient at lower Reynolds numbers and induce chaotic advection at higher Reynolds numbers for effectively mixing fluids without external energy. Active micromixers, on the other hand, achieve precise, fast, and controllable mixing by employing external energy sources such as pressure, electric, magnetic, or acoustic fields. Some active methods such as magnetic field-driven micromixers need fluids with specific properties. Others, such as acoustic field-driven micromixers apply to various types of fluids. Bubbles can be used as membranes or stirrers in microfluidic devices for both passive and active micromixers. They are easy to use, compatible with microfluidic systems, low cost, and effective. Improvements in manufacturing methods, notably, 3D printing have emerged as promising methods for the development of new micromixer designs. In this paper, a wide range of micromixer types is reviewed and the main mechanism for enhanced mixing is investigated. This study aims to guide researchers proposing innovative designs. Furthermore, it is shown that combining different methods can lead to the development of more effective micromixers, promising further advancements in microscale mixing technology.

The burgeoning internet of things and artificial intelligence technologies have prospered a variety of emerging applications. Human–machine interfaces (HMIs), for instance, enables users with intuitive, efficient, and friendly way to interact with machines, capable of instant information acquisition, processing, communication, and feedback, etc. These features require ultra-compact and high-performance transducers, and therefore self-powered sensors have become the key underlying technology for HMI applications. This review focuses on the piezoelectric, triboelectric, and hybrid self-powered sensors with particular attention to their microstructures and fabrication methods, showing that both traditional microfabrication and emerging fabrication methods like three-dimensional (3D) printing, electrospinning, and braiding have contributed to the planar, array, porous, fabric, and composite type self-powered sensors. Moreover, the integration method of piezoelectric and triboelectric sensor arrays is investigated. The crosstalk issue is highlighted, i.e. the signal interference between adjacent sensing units, and current solutions such as array design optimization, signal processing improvement, and material innovation to reduce crosstalk sensitivity have been reviewed through specific examples. Three categories of HMI applications have been outlined, including intelligent interaction, robotics, and human monitoring, with detailed explanations of how the self-powered sensors support these HMI applications. Through discussion of challenges and prospects, it is proposed that further coordinating the design and fabrication of micro devices with HMIs will potentially boost the intelligent application with even higher level of diversification, convenience, and interconnectivity.

A significant challenge for power sources of small-scale quadrotors is the simultaneous need for high gravimetric energy density and high power density. While aluminum-air batteries can provide the high energy density, achieving high power density typically necessitates expensive catalysts such as platinum, which can be a significant cost driver. In this context, we present microfabricated silver-based air-cathodes for high-power aluminum-air batteries that are suitable for small-scale quadrotor applications. Experimental results, supported by a diffusion-reaction model, indicate that the power performance of the Ag-based cathode is largely determined by the electrochemically active catalyst surface area. To maximize the surface area, we exploit a microfabrication technique involving co-sputtering of a silver-copper alloy on a carbon paper substrate, followed by selective etching of the copper. This process results in the Ag-based paper cathode that delivers a power density of 202 mW/cm2 with 0.3 mg-silver/cm2 catalyst loading. Under battery discharge conditions relevant to small-scale quadrotor operations, the discharge performance of the silver-based aluminum-air battery is examined. The silver-based cathode achieves a discharge peak power density of 1000 W/kgbattery, which is 70% of the platinum-based cathode. Notably, when discharging above the 800 W/kgbattery threshold required for the small-scale quadrotor, the silver-based cathode achieves a comparable discharge duration compared with the platinum-based cathode. The cost analysis reveals a significant economic advantage, with this high-power silver-based cathode being 460 times less expensive than the commercial platinum-based cathode. This significant cost reduction, combined with the comparative discharge performance, highlights the promise of silver-based cathodes to achieve extended operational times at a fraction of the cost of platinum-based cathodes.&#xD;

This study was conducted to investigate the mechanical properties of polymer optical fiber microconnectors fabricated via two-photon polymerization. This experimentally demonstrates the vital role of substrate surface treatment in enhancing the adhesion characteristics of polymer microconnectors to the surface. Comprehensive bend and peel tests were performed, and stress limits in various directional orientations were defined. These findings indicate that the microconnectors exhibited substantial adhesion to the substrate when an additional Ti buffer layer was applied. The mechanisms of fracture and stress distribution under applied loads were also examined. The results underscore the critical importance of optimal geometric design and precise installation of microconnectors to ensure their reliability. This study opens avenues for further optimization of the geometry and mechanical properties of microconnectors.

A moving edge of a small mechanical structure, closely placed in front of a photodetector, can offer an easy means of monitoring its motion via the optical knife-edge effect. Here, we present a detailed analysis of this nanomechanical motion detection scheme, in which the miniaturized mechanical device to be probed also serves as an effective knife edge. Especially the optical modulation generated from the expected motion of the mechanical structure as well as the corresponding detection sensitivity is considered by analytical and numerical modeling along with the experimental observation in light of the relevant key factors such as the optical spot size and the device dimension. The results discussed would benefit further implementation of the compact optical detection scheme demonstrated.

A significant challenge for power sources of small-scale quadrotors is the simultaneous need for high gravimetric energy density and high power density. While aluminum-air batteries can provide the high energy density, achieving high power density typically necessitates expensive catalysts such as platinum, which can be a significant cost driver. In this context, we present microfabricated silver-based air-cathodes for high-power aluminum-air batteries that are suitable for small-scale quadrotor applications. Experimental results, supported by a diffusion-reaction model, indicate that the power performance of the Ag-based cathode is largely determined by the electrochemically active catalyst surface area. To maximize the surface area, we exploit a microfabrication technique involving co-sputtering of a silver-copper alloy on a carbon paper substrate, followed by selective etching of the copper. This process results in the Ag-based paper cathode that delivers a power density of 202 mW/cm2 with 0.3 mg-silver/cm2 catalyst loading. Under battery discharge conditions relevant to small-scale quadrotor operations, the discharge performance of the silver-based aluminum-air battery is examined. The silver-based cathode achieves a discharge peak power density of 1000 W/kgbattery, which is 70% of the platinum-based cathode. Notably, when discharging above the 800 W/kgbattery threshold required for the small-scale quadrotor, the silver-based cathode achieves a comparable discharge duration compared with the platinum-based cathode. The cost analysis reveals a significant economic advantage, with this high-power silver-based cathode being 460 times less expensive than the commercial platinum-based cathode. This significant cost reduction, combined with the comparative discharge performance, highlights the promise of silver-based cathodes to achieve extended operational times at a fraction of the cost of platinum-based cathodes.&#xD;

Laser transmission welding (LTW) is a technique for joining a transparent polymer to an opaque polymer. This paper presents the results of nanosecond pulsed laser (1064 nm) transmission welding of cyclic olefin copolymer (COC). COC has a wide range of applications in biological, biomedical, membrane, and semiconductor fields. LTW has advantages over conventional adhesive and thermal-based methods of bonding. These include precision sealing and minimised heat affected zone, which makes this process favourable for bio-applications. The effect of laser processing parameters, such as the laser pulse energy and the laser scan speed, on the weld morphology as well as on the bonding strength was studied via cross-sectional optical microscopy and lap shear tests. The lap-shear strength of laser bonded COC substrates achieved lap-shear strength of 0.15 N mm⁻² to 0.5 N mm⁻² which is comparable to the strength found in adhesive bonded substrates. These studies provide novel insights into the welded region at the interface of the two materials and demonstrate the impact of laser parameters on the weld seam width and bond strength. Leak tests were performed on laser welded fluidic channels and no leakages were detected. Further, the analysis of lap-shear tests demonstrates that laser welding produces joining strengths similar to those of adhesive-bonded COC. The joining interface area for laser welding is in general smaller than that of adhesive bonding, which potentially can enable more design freedom and capacity for accommodating complex functionalities on a singular COC-based device.

Viscosity is a critical fluid property that significantly influences fluid behavior and performance across various systems. Most commercial viscometers require relatively large sample volumes (on the order of milliliters), which restricts their utility in scenarios where only limited sample volumes are available. For instance, human tear fluid—essential for developing effective treatment strategies—is scarce (typically on microliters), especially in individuals with dry eye disease. To address this limitation, we present a novel microfluidic viscometer platform capable of measuring the viscosity of ultra-small volumes (i.e. ∼10 μl) of Newtonian and non-Newtonian fluids. The working principle is based on the Hagen–Poiseuille equation, incorporating the Weissenberg–Rabinowitsch–Mooney correction for slit-flow, and employs an optically transparent microfluidic chip integrated with supporting devices including a syringe pump, manifold, camera, and differential pressure transducer. Preliminary validation was conducted using glycerol solutions, artificial tears, and tear samples from dry and healthy eyes. This microfluidic viscometer holds promise for measuring the shear viscosity of small volumes of biofluid samples (e.g. synovial fluid, cerebrospinal fluid, tear films) or pharmaceuticals (e.g. monoclonal antibodies, ophthalmic drug delivery products) by developing surface coating materials appropriate for specific samples.

In this paper, ball-burning and bonding tests were conducted using Ag–Au–Pd alloy wires with a diameter of ϕ 0.025 mm, and the performance of free air ball (FAB) morphology and bonding strength under various bonding parameters was investigated. The results showed that when the electronic flame off (EFO) current is 20 mA, the FAB of Ag–Au–Pd bonding alloy wire appears small ellipsoid, whereas increasing the EFO current to 40 mA resulted in a golf club-shaped FAB. Similarly, when the EFO time was 0.4 ms, the FAB appears as a small spherical, but extending the EFO time to 1.2 ms caused the FAB to enlarge and exhibit a golf club phenomenon. The addition of Pd element reduced the FAB heat affected zone length of Ag–Au–Pd alloy wire by 19.4% compared to Ag–Au wire. Insufficient ultrasonic power and bonding pressure lead to weak bonding at the bonded interface, thereby reducing the bonding strength, while excessive ultrasonic power and bonding pressure can cause short circuits and pad damage. The optimized bonding parameters for the Ag–Au–Pd alloy wire determined to be: an ultrasonic power of 65 mW and a bonding pressure of 45 g for the ball bond, and an ultrasonic power of 95 mW and a bonding pressure is 75 g for the wedge bond.

In the domain of micro-nano electronic printing technology, the integration of the operational characteristics with piezoelectric inkjet printing (PIJP) and electrohydrodynamic printing overcomes the limitations of single-mode printing. This integration facilitates the advancement and enhancement of hybrid printing technology, encompassing piezoelectric and electric forces. A study is conducted on jet printing utilizing a hybrid force as the driving power. The hybrid printing system is initially developed and assembled. The study focuses on the printing mechanism of piezoelectric deforming units and electrohydrodynamic generating units, leading to the development and integration of hybrid printing equipment. Secondly, three types of printing models are established using simulation software, including piezoelectric, electrohydrodynamic, and hybrid models. The jetting mechanism of the single force and hybrid force is described, and the feasibility of the process is assessed. The experiment is designed to assess the performance of hybrid printing in comparison to other single-force printing methods. The experimental results indicate that hybrid printing demonstrates superior precision and consistency compared to single-force printing. The average diameters of the printed droplet dots for piezoelectric-driven and composite-driven methods are 225.9 μm and 181.4 μm, respectively. Compared to PIJP, hybrid printing ensures uniform droplet formation and reduces satellite formation through electrohydrodynamic stabilization. Compared to electrohydrodynamic methods, hybrid printing improves deposition accuracy, refines jetting control, minimizes unintended spreading, and achieves higher resolution.

In the dynamic landscape of semiconductor manufacturing, the demand for innovative and efficient techniques is ever-growing. Dicing is a singulation process where a machine known as a dicing saw or dicer uses a diamond blade or laser to separate dies from a wafer through a manual, semi-automated, or fully automated process. In diamond blade or mechanical dicing, the dicing saw utilizes a thin blade to cut through a wafer. This paper presents the design and implementation of an alignment teaching-assisted fully automated dicing process for the singulation of microelectromechanical systems (MEMS) devices. A pseudo-MEMS device with potential alignment targets was designed and manufactured by conventional microfabrication techniques. Alignment teaching operation was optimized for the dicing saw by finding the most appropriate alignment targets, as alignment teaching is as a pre-requisite for realizing both auto-alignment and automated dicing processes. A systematic trial-and-error approach was employed to discover the most suitable alignment targets from a pool of twenty-three potential target patterns. A circle was identified as an excellent macro target, while the addition symbol, hash symbol, and rectangle-pair were determined to be the most appropriate micro targets. The developed versatile singulation process is capable of executing an alignment teaching assisted fully automated (i.e. a total of one-click to initiate and finalize) dicing for singulating MEMS device chips, irrespective of alignment target color, die size, or wafer material. Furthermore, we developed, and experimentally validated, a mathematical model to estimate the total process time for the automated dicing.

Electrode-integrated microfluidic chips play a pivotal role in applying electrochemical impedance spectroscopy (EIS) across various domains. This technology has significantly transformed biomedical research, facilitating progress in drug discovery, diagnostics, and cell analysis. The architecture of these chips integrated with electrodes critically influences the precision and dependability of EIS outcomes. This study developed diverse microfluidic chip designs, including circular, deltoid, and deltoid-like shapes, to explore microenvironmental dynamics on EIS assessments. Moreover, computational fluid dynamics was utilized to examine the flow properties within the proposed chip designs by investigating the relationship between pressure and velocities in the microenvironment. The study also assessed the effects of varying flow rates (1, 10, 100 µl) on EIS analysis and the simulation studies. Findings indicated that there were empty spaces in the circular design, which is commonly used, and it was not suitable for EIS experiments. Furthermore, it was noted that even with reduced altitude in the EIS measurement area, the environment remained conducive to more accurate measurements. A flow rate of 10 µl min⁻¹ was identified as optimal in this research, as it offered the best balance among charge transfer resistance (R_ct), capacitance (Q), and open circuit potential values, while also minimizing the sample volume which is very important for microfluidic chip design and applications. This study demonstrated a strong interaction between microfluidic chip designs for electrode integration and EIS outcomes. On the other hand, it has yielded a reliable, cost-effective, rapid, practical, reusable, and portable platform after choosing an appropriate architecture for the electrode housing.

The need for materials with low density and high strength has drawn a lot of interest from researchers and industry in the last few years. Aluminum 6061 (Al6061) is one of these materials that has the required qualities. Powder-mixed electric discharge machining has become a practical choice for cutting such materials because of its versatile machining capabilities. However, this technique's excessive energy usage and poor cutting efficiency have drawn criticism. Furthermore, there are serious health and environmental risks associated with the typical dielectric (kerosene) used in EDM. Deionized water, a replacement to kerosene, has been used in this work to address the aforementioned problems, improving resource reusability and lowering the dielectric cost. Here, deionized water further makes the operation sustainable and protects the environment from harmful emissions produced during the machining process. Additionally, alumina (Al₂O₃) nano-powder has been mixed in dielectric and used to improve the machining responsiveness. Response surface methodology was used to carry out the investigation. The purpose of this study was to use microscopic analysis to examine the effects on the electrode wear rate (EWR) and accuracy index (AI). Analysis of variance (ANOVA) analyses for both responses revealed that all four parameters are highly significant, with p-values nearly zero (<0.05). Additionally, the coefficient of determination (R²) values for EWR (0.9611) and AI (0.9285) indicate that the proposed models are reliable. The parametric optimization by grey relational analysis (GRA) approach highlighted that the magnitude for EWR and AI is improved by 50.85% and 2.67%, respectively, when optimal condition (I_P: 5 A, S_V: 2 V, S_T: 3 µs, and C_P:1.5 g/100 ml) is set during EDM of Al6061. The proposed EDM model yielded 48.29% and 5.11% better outcomes than the conventional EDM model in terms of EWR and AI, respectively.

Beam-type piezoelectric energy harvesters (PEHs), particularly those utilizing piezoelectric materials, have garnered considerable attention as efficient devices for converting ambient mechanical vibrations into electrical energy. This comprehensive review article thoroughly examines the mathematical models employed in beam-type PEHs, emphasizing their evolution and limitations. The study also delves into both theoretical and experimental analyses of design configurations, placing a special focus on the impact of geometries on energy harvesting efficiency. In conclusion, the paper explores recent advancements and improvements, along with potential avenues for future research, providing a concise overview tailored for professionals and scholars engaged in this specialized field.

Strain sensors have been developed in various fields by converting mechanical deformation into electrical signals. Surface acoustic wave (SAW) devices are beneficial for strain sensing due to their simplicity of fabrication and wireless operation capabilities. In this study, we investigate SAW strain sensors operating at 1.25 $\mathrm{GHz}$. The fabricated SAW resonators using standard photolithography technology are characterized with a custom-made cantilever setup capable of applying defined strain values up to approximately −4000 µε to 4000 µε. From these measurements, a high responsivity even up to this high strain values is demonstrated. We also explore the impact of geometric design parameters on strain-sensing performance. We vary the length of the SAW resonator and observe that the longer the SAW resonator, the more responsive the device gets to strain changes. When the distance between the two reflectors confining the SAW is 2207 $\mu\mathrm{m}$, the responsivity to strain is 114.99 $\mathrm{Hz}\,\mu\epsilon^{-1}$. In summary, this study investigates the feasibility of GHz SAW resonators as high-strain sensors on non-flexible substrates with a custom-built experimental setup, to evaluate their potential for future applications in extreme mechanical environments.