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 ShA.
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ISSN: 1361-6439
Journal of Micromechanics and Microengineering (JMM) is a leading journal in its field, covering all aspects of nano- and microelectromechanical systems, devices and structures as well as nano/micromechanics, nano/microengineering and nano/microfabrication.
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I D Johnston et al 2014 J. Micromech. Microeng. 24 035017
Megala Ramasamy et al 2023 J. Micromech. Microeng. 33 105016
Polydimethylsiloxane (PDMS) elastomers have been extensively used in the development of microfluidic devices, capable of miniaturizing biomolecular and cellular assays to the microlitre and nanolitre range, thereby increasing the throughput of experimentation. PDMS has been widely used due to its optical clarity and biocompatibility, among other desirable physical and chemical properties. Despite the widespread use of PDMS in microfluidic devices, the fabrication process typically via soft lithography technology requires specialized facilities, instruments, and materials only available in a limited number of laboratories. To expand microfluidic research capabilities to a greater scientific population, we developed and characterized a simple and robust method of fabricating relatively inexpensive PDMS microfluidic devices using readily available reagents and commercially available three-dimensional (3D) printers. The moulds produced from the 3D printers resolve designed microfluidic channel features accurately with high resolution (>100 µm). The critical physical and chemical post-processing modifications we outline here are required to generate functional and optically clear microfluidic devices.
Michelle V Hoang et al 2016 J. Micromech. Microeng. 26 105019
Polyimide is one of the most popular substrate materials for the microfabrication of flexible electronics, while polydimethylsiloxane (PDMS) is the most widely used stretchable substrate/encapsulant material. These two polymers are essential in fabricating devices for microfluidics, bioelectronics, and the internet of things; bonding these materials together is a crucial challenge. In this work, we employ click chemistry at room temperature to irreversibly bond polyimide and PDMS through thiol-epoxy bonds using two different methods. In the first method, we functionalize the surfaces of the PDMS and polyimide substrates with mercaptosilanes and epoxysilanes, respectively, for the formation of a thiol-epoxy bond in the click reaction. In the second method, we functionalize one or both surfaces with mercaptosilane and introduce an epoxy adhesive layer between the two surfaces. When the surfaces are bonded using the epoxy adhesive without any surface functionalization, an extremely small peel strength (<0.01 N mm−1) is measured with a peel test, and adhesive failure occurs at the PDMS surface. With surface functionalization, however, remarkably higher peel strengths of ~0.2 N mm−1 (method 1) and >0.3 N mm−1 (method 2) are observed, and failure occurs by tearing of the PDMS layer. We envision that the novel processing route employing click chemistry can be utilized in various cases of stretchable and flexible device fabrication.
S P Beeby et al 2007 J. Micromech. Microeng. 17 1257
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.
Shadi Shahriari et al 2023 J. Micromech. Microeng. 33 083002
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.
Kevin Ward and Z Hugh Fan 2015 J. Micromech. Microeng. 25 094001
Mixing in microfluidic devices presents a challenge due to laminar flows in microchannels, which result from low Reynolds numbers determined by the channel's hydraulic diameter, flow velocity, and solution's kinetic viscosity. To address this challenge, novel methods of mixing enhancement within microfluidic devices have been explored for a variety of applications. Passive mixing methods have been created, including those using ridges or slanted wells within the microchannels, as well as their variations with improved performance by varying geometry and patterns, by changing the properties of channel surfaces, and by optimization via simulations. In addition, active mixing methods including microstirrers, acoustic mixers, and flow pulsation have been investigated and integrated into microfluidic devices to enhance mixing in a more controllable manner. In general, passive mixers are easy to integrate, but difficult to control externally by users after fabrication. Active mixers usually take efforts to integrate within a device and they require external components (e.g. power sources) to operate. However, they can be controlled by users to a certain degree for tuned mixing. In this article, we provide a general overview of a number of passive and active mixers, discuss their advantages and disadvantages, and make suggestions on choosing a mixing method for a specific need as well as advocate possible integration of key elements of passive and active mixers to harness the advantages of both types.
D J Laser and J G Santiago 2004 J. Micromech. Microeng. 14 R35
We survey progress over the past 25 years in the development of microscale devices for pumping fluids. We attempt to provide both a reference for micropump researchers and a resource for those outside the field who wish to identify the best micropump for a particular application. Reciprocating displacement micropumps have been the subject of extensive research in both academia and the private sector and have been produced with a wide range of actuators, valve configurations and materials. Aperiodic displacement micropumps based on mechanisms such as localized phase change have been shown to be suitable for specialized applications. Electroosmotic micropumps exhibit favorable scaling and are promising for a variety of applications requiring high flow rates and pressures. Dynamic micropumps based on electrohydrodynamic and magnetohydrodynamic effects have also been developed. Much progress has been made, but with micropumps suitable for important applications still not available, this remains a fertile area for future research.
Marcin Michałowski et al 2024 J. Micromech. Microeng. 34 047001
The original design of the smallest two-way rolling thrust micro-bearing with sub-millimeter dimensions is presented. The bearing is self-contained and is capable of transmitting thrust load up to about 8 N in two directions, as well as radial loads up to about 0.4 N. Thanks to special design of the raceways, operation without lubrication is possible. The scope of experimental study is discussed, and preliminary experimental results are reported. Ways of further miniaturization are suggested.
Ali Reda et al 2024 J. Micromech. Microeng. 34 049501
This corrigendum corrects typographic errors in the article. The corrections do not change the conclusions of the article.
Kwang W Oh and Chong H Ahn 2006 J. Micromech. Microeng. 16 R13
This review gives a brief overview of microvalves, and focuses on the actuation mechanisms and their applications. One of the stumbling blocks for successful miniaturization and commercialization of fully integrated microfluidic systems was the development of reliable microvalves. Applications of the microvalves include flow regulation, on/off switching and sealing of liquids, gases or vacuums. Microvalves have been developed in the form of active or passive microvalves employing mechanical, non-mechanical and external systems. Even though great progress has been made during the last 20 years, there is plenty of room for further improving the performance of existing microvalves.
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E Cheng et al 2024 J. Micromech. Microeng. 34 045012
The electrode is an important part of a micro-ultrasonic phased array, commonly fabricated by magnetron sputtering technology. However, with the expansion of the application field, the structures of the phased arrays are becoming more complex, making the traditional magnetron sputtering method no longer applicable, and the realization of micro-scale phased array electrodes by direct printing technology still faces great challenges. Herein, an electric field-driven direct printing method was proposed to fabricate micro-ultrasonic phased array electrodes. The influence of sintering parameters on the resistivity and the effect of printing parameters on the geometric size and surface morphology of the electrode were comprehensively explored, and the mathematical model between the electrode line width and the printing parameters was established. The final printed electrodes exhibit superior properties with a resistivity of 2.4 × 10−7
, a surface roughness range of 460–550 nm, and a line width range of 125–480 µm. Additionally, a micro-scale electrode was printed on the piezoelectric ceramic with PZT-5 as the material, and after polarization treatment, the piezoelectric coefficient can reach 405 pC N−1, which proves that this method can be applied in the field of fabricating phased array electrodes.
Xu Yang et al 2024 J. Micromech. Microeng. 34 055001
A novel monolithic compliant Lorentz-force-driven XY nanopositioning system (MCLNS) is designed, analyzed, and experimentally assessed with the aim of high-resolution positioning across a large workspace. A double-symmetric Lorentz-force actuator (DSLA) with the benefits of zero friction, high thrust, and large stroke is proposed to generate the actuation force. Correspondingly, a monolithic four-prismatic parallel compliant mechanism (4P-PCM) is exploited to transmit the actuation motion to the central platform and minimize the parasitic motion. The unique integration of four DSLAs and one 4P-PCM make the proposed MCLNS possess compact structure and stable performance. The characterization of the MCLNS is formulated by a specially established analytical model and validated by finite-element analysis simulation and experimental tests. Experimental studies show that the workspace of the MCLNS prototype is large than 0.87 × 0.87 mm2 and the positioning resolution of the MCLNS prototype is better than 9 nm. By means of a nonlinear forward proportional integral derivative control strategy, the maximum contouring error of the MCLNS is maintained within 2.7% while tracking a 1257 μm s−1 circular trajectory.
Jian Hu et al 2024 J. Micromech. Microeng. 34 045011
This study used a microfluidic device with a focus-wrapping structure to create double-layer calcium alginate hydrogel drug particles in a one-step process. We validated the double-layer structure of the particles using both a fluorescence and regular light microscope. Curcumin and catalase were distributed independently in each layer, and we expected that such structure could play a role in the slow release of drugs. This scheme greatly reduces the need of hydrophilic and hydrophobic modification treatment, therefore greatly simplifies the experimental process. In the meantime, the requirement for injecting drugs into osteoarthritis and other diseases is expected to be realized, expanding the use of hydrogel in the medical field, because the microsphere is easy to generate, inexpensive, and strong in internal drug substitutability.
Ali Reda et al 2024 J. Micromech. Microeng. 34 049501
This corrigendum corrects typographic errors in the article. The corrections do not change the conclusions of the article.
Xiao Cheng et al 2024 J. Micromech. Microeng. 34 045010
The connection of silicon carbide (SiC) to glass is important for the development of microelectromechanical systems. In the study, glass-SiC-glass with SiC as common anode was effectively bonded by using anodic bonding technology in atmosphere. The interfacial microstructure of bonded joints was analyzed by using scanning electron microscope, energy-dispersive spectrometer and transmission electron microscope. The effect of the bonding voltages and bonding temperatures on the interfacial microstructure and mechanical property of glass/SiC/glass was investigated. The results indicated that a Na+ depletion layer formed in the glass adjacent to the SiC/glass interface due to the decomposition of Na2O compound in the glass and the migration of Na+ towards the upper surface of glass during anodic bonding. With elevating bonding temperatures or bonding voltages, the thickness of Na+ depletion layer was gradually increased and more O2− accumulated at the SiC/depletion layer interface, which was beneficial for the tensile strength of joints. But owing to the increased residual thermal stress, the tensile strength of the joints dropped with enhanced bonding temperature. The maximum tensile strength of the joint was about ∼12.8 MPa when bonding at 450 °C/1000 V/1 min. The joint mainly ruptured in the glass with a brittle fracture mode.
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Meera Garud and Rudra Pratap 2024 J. Micromech. Microeng. 34 013001
Miniaturization of electro-mechanical sensors and actuators has benefited from an advancement in CMOS technology over the years. However, miniaturization of audio speakers has seen considerable development only in the recent times. This paper reviews the developments in micro-electro-mechanical-systems (MEMS) audio speaker research and the initial commercial products available in the market. At first glance, it appears that the relatively slow development of MEMS speakers can be attributed to the fact that the principle of actuation has remained unchanged for several decades. Unfortunately, the physics behind audible sound production holds us back from exclusively adopting miniaturized speakers—sound pressure level is directly proportional to the area of the sound radiating surface. Nevertheless, researchers are continuing to explore new avenues for designing and developing MEMS speakers, without limiting themselves to the existing actuation principles. With newly discovered materials and improving technology, the research in MEMS speakers is gaining attention and new products are emerging. A speaker design based on piezoelectric actuation or electrostatics actuation is favorable at MEMS scale. Indian research community is also contributing to advances in MEMS speakers and near-ultrasonic devices. This paper reviews the development in MEMS audio speakers in India and in the world. The tabulated review findings aim to offer readers an overview of the development of micro-speakers and to provide guidance for designing new micro-speakers.
Xianzheng Lu and Hao Ren 2023 J. Micromech. Microeng. 33 113001
With the development of next-generation wireless communication and sensing technologies, there is an increasing demand for high-performance and miniaturized resonators. Micromachined piezoelectric Lamb wave resonators are becoming promising candidates because of their multiple vibration modes, lithographically defined frequencies, and small footprint. In the past two decades, micromachined piezoelectric Lamb wave resonators based on various piezoelectric materials and structures have achieved considerable progress in performance and applications. This review focuses on the state-of-the-art Lamb wave resonators based on aluminum nitride (AlN), aluminum scandium nitride (AlxSc1−xN), and lithium niobate (LiNbO3), as well as their applications and further developments. The promises and challenges of micromachined piezoelectric Lamb wave resonators are also discussed. It is promising for micromachined piezoelectric Lamb wave resonators to achieve higher resonant frequencies and performance through advanced fabrication technologies and new structures, the integration of multifrequency devices with radio frequency (RF) electronics as well as new applications through utilizing nonlinearity and spurious modes. However, several challenges, including degenerated electrical and thermal properties of nanometer-scale electrodes, accurate control of film thickness, high thin film stress, and a trade-off between electromechanical coupling efficiencies and resonant frequencies, may limit the commercialization of micromachined piezoelectric Lamb wave resonators and thus need further investigation. Potential mitigations to these challenges are also discussed in detail in this review. Through further painstaking research and development, micromachined piezoelectric Lamb wave resonators may become one of the strongest candidates in the commercial market of RF and sensing applications.
Chun-Pu Tsai and Wei-Chang Li 2023 J. Micromech. Microeng. 33 093001
Spurred by the invention of the tapping-mode atomic force microscopy three decades ago, various micromechanical structures and systems that utilize parts with mechanical impact have been proposed and developed since then. While sharing most of the dynamical characteristics with macroscopic vibro-impact systems and benefiting from extensive theories developed, microscale counterparts possess higher percentage of surface force, higher resonance frequency and Q, and more prominent material and structural nonlinearities, all of which lead to unique features and in turn useful applications not seen in macroscopic vibro-impact systems. This paper will first present the basics of vibro-impact systems and techniques used for analyzing their nonlinear behaviors and then review the contact force modeling and numerical analysis tools. Finally, various applications of microscale vibro-impact systems will be reviewed and discussed. This review aims to provide a comprehensive picture of MEMS vibro-impact systems and inspire more innovative applications that take full advantage of the beauty of nonlinear vibro-impact dynamics at the microscale.
Shadi Shahriari et al 2023 J. Micromech. Microeng. 33 083002
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.
Yan Wang et al 2023 J. Micromech. Microeng. 33 083001
Recently, internet of things (IoT) attracts increasing attention and it tends to be applied in every aspect of life, due to the development of computer technology, sensor technology and micro/nano technology. Although IoT plays an important role in modern society to achieve smart life, it has to overcome the restriction of non-durable power source and to construct wireless sensor networks. Micro-energy harvesting technology from the environment is a powerful and promising approach to solve the energy supporting problem for wider applications of IoT. This article gives an overview of the recent developments of self-sustained IoT from the perspectives of energy harvesting technology and related technologies. The various energy harvesting techniques and the applications of IoT in different scenario are collected and presented. The energy schemes to prolong and optimize the energy in the WSN for IoT are discussed. Furthermore, perspectives and outlooks of self-powered IoT based on the micro-energy harvesting technology are presented.
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Ma et al
In recent years, considerable research advancements have emerged in the application of inverse design methods to enhance the performance of electromagnetic metamaterials. Notably, the integration of deep learning (DL) technologies, with their robust capabilities in data analysis, categorization, and interpretation, has demonstrated revolutionary potential in optimization algorithms for improved efficiency. In this review, current inverse design methods for electromagnetic metamaterials are presented, including topology optimization, evolutionary algorithms, and DL-based methods. Their application scopes, advantages and limitations, as well as the latest research developments are respectively discussed. The classical iterative inverse design methods categorized topology optimization and evolutionary algorithms are discussed separately, for their fundamental role in solving inverse design problems. Also, attention is given on categories of DL-based inverse design methods, i.e. classifying into DL-assisted, direct DL, and physics-informed neural network methods. A variety of neural network architectures together accompanied by relevant application examples are highlighted, as well as the practical utility of these overviewed methods. Finally, this review provides perspectives on potential future research directions of electromagnetic metamaterials inverse design and integrated artificial intelligence methodologies.
Zeng et al
Through silicon via (TSV) technology plays a pivotal role in three-dimensional (3D) integrated circuits (ICs). However, excessive surface thickness and uneven wafer plating during TSV copper electroplating pose significant challenges to TSV reliability. This paper proposes a novel rotating cathode electroplating technique that utilizes flow field induction by a rotating cathode to significantly reduce the surface copper thickness by approximately 8 μm, leading to improved uniformity of wafer-scale electroplating and facilitating rapid TSV filling. This study focuses on the impact of cathode rotation speed and chip position on TSV filling quality. The experimental findings demonstrate that increasing the cathode rotation speed reduces the diffusion layer thickness, thereby enhancing filling quality. Additionally, variations in chip position influence surface copper thickness. The introduction of bis(3-sulfopropyl) disulfide (SPS) accelerant expedites the filling process, boosts the filling ratio, and enables defect-free TSV filling. This study offers valuable insights into the wafer-scale TSV electroplating process and facilitates the optimization of parameter settings during electroplating.
CHEN et al
This paper proposes an efficient nonlinear one-dimensional(1D) compact mass-damper-spring model to predict the dynamic response of electrostatic resonant MEMS mirrors with cascaded structure The time-dependent damping moment due to viscous shear and pressure drag is computed using semi-empirical analytical equations for comb-drive structures and device frames. Nonlinear electrostatic force induced by the comb drives is efficiently acquired based on the hybrid method. The optimized device is fabricated using MEMS fabrication processes using a 4-inch SOI wafer. The proposed compact model with the measured key parameters from the fabricated device shows excellent capability to accurately predict nonlinear dynamic responses of the fabricated device, including parametric excitation and hysteretic frequency response, with an average error of less than 5%. In particular, our 1D model is three orders of magnitude faster than the conventional finite element method (FEM) model (0.8s versus 1h), enabling efficient system-level optimization of the critical design parameters. Based on the parametric study, electrode gap distance and torsion spring width are found to be two critical design parameters and dimensional analysis is conducted for design optimization with scan angle enhancing from 16.8° to 24° compared with the first design.
Grover et al
Electrochemical Discharge Machining is an advanced micro-machining process for machining of conductive as well as non-conductive hard and brittle materials i.e., glass, ceramic and silicon wafer etc. The present work explores the machining of glass using in-house developed novel Ultrasonic Assisted Rotary Electrochemical Discharge Machining (UA-RECDM) setup. The setup has specialised features which includes ultrasonic vibrations to tool electrode and rotary motion to workpiece. Experiments were conducted using one factor at a time approach (OFAT) approach by varying tool feed rate, amplitude of vibrations and rotation of workpiece as process parameters. The quality of the machining output was evaluated by observing two key parameters: overcut and circularity of the hole. It was observed that as the workpiece rotation speed increased from 40 RPM to 60 RPM, the overcut in the machined samples decreased from 181.378 µm to 163.564 µm. The rotary motion of workpiece causes seeping action of the electrolyte at hydrodynamic regime and results in thin gas film formation & stabilized discharging phenomenon. The morphology of machined hole exhibits better circularity, low HAZs, minimum micro-cracks and smooth edges at periphery due to stable discharge formation.
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Marcin Michałowski et al 2024 J. Micromech. Microeng. 34 047001
The original design of the smallest two-way rolling thrust micro-bearing with sub-millimeter dimensions is presented. The bearing is self-contained and is capable of transmitting thrust load up to about 8 N in two directions, as well as radial loads up to about 0.4 N. Thanks to special design of the raceways, operation without lubrication is possible. The scope of experimental study is discussed, and preliminary experimental results are reported. Ways of further miniaturization are suggested.
Negin Sherkat et al 2024 J. Micromech. Microeng. 34 045002
In order to optimize their system design and manufacturing processes, it is crucial to undertake a thorough electrical and thermal characterization of micro thermoelectric generators (µTEGs). To address this need, a highly advanced and fully integrated in-situ measurement system has been developed. The main objectives of this system are to (1) enable the measurement of ZT and thereby of all thermoelectric (TE) properties of thermolegs made from powder-based TE materials and (2) at the same time accurately measure the contact resistance between the TE material and the electrical contacts. The µTEG fabrication concept used in this study is based on copper-cladded printed circuit board (PCB) material as a substrate, using the Cu layers for easy contact formation. In a first step, an innovative measurement concept, based on a distinctive vertical rendition of the well-established transfer length method, has been realized, allowing for the in-situ measurement of contact resistance between the TE material and the copper conductors on the PCB substrate. This enables a comprehensive assessment of the impact exerted by the applied force and temperature during e.g. a hot-pressing step for compacting the powder-based thermolegs during the manufacturing process. In a second step, a comprehensive measurement platform, referred to as the ZT-Card, has been devised to facilitate the evaluation of all relevant TE material properties—Seebeck voltage, electrical conductivity and thermal conductivity (all measured in vertical cross-plane orientation)—inherent to a highly miniaturized thermoleg. Additionally, the ZT-Card also allows for the assessment of contact resistance between the copper contacts and the TE material. Successful testing of this measurement system inspires confidence in the capabilities of the platform and will aid in future µTEG development.
Jacob Schopp and Shamus McNamara 2024 J. Micromech. Microeng. 34 035011
Distributed sensing has been of great interest in recent research. Distributed sensors are in part defined by the methods they use to communicate. We demonstrate a new low power method of optical communication. Instead of communicating optically by generating new light to communicate using a light emitting diode or laser, our method uses optical interference to vary the reflectivity of a micro-electromechanical systems (MEMS) optical cavity. A thin air gap between an adjustable MEMS mirror made on a silicon on insulator die and glass encapsulation generates optical interference. By moving the mirror electrostatically, the reflected light intensity is modulated, and signals are transmitted passively. The transmitted signal is measured by observing the reflected light intensity with a photodiode. We demonstrate the use of fiber optic cables to deliver illumination and collect reflected light with modulated intensity. We propose that these devices may also be used in series arrays where reflected light from one optical cavity can be used as illumination for another.
Natalie N Mueller et al 2024 J. Micromech. Microeng. 34 035009
Intracortical microelectrodes (IMEs) can be used to restore motor and sensory function as a part of brain–computer interfaces in individuals with neuromusculoskeletal disorders. However, the neuroinflammatory response to IMEs can result in their premature failure, leading to reduced therapeutic efficacy. Mechanically-adaptive, resveratrol-eluting (MARE) neural probes target two mechanisms believed to contribute to the neuroinflammatory response by reducing the mechanical mismatch between the brain tissue and device, as well as locally delivering an antioxidant therapeutic. To create the mechanically-adaptive substrate, a dispersion, casting, and evaporation method is used, followed by a microfabrication process to integrate functional recording electrodes on the material. Resveratrol release experiments were completed to generate a resveratrol release profile and demonstrated that the MARE probes are capable of long-term controlled release. Additionally, our results showed that resveratrol can be degraded by laser-micromachining, an important consideration for future device fabrication. Finally, the electrodes were shown to have a suitable impedance for single-unit neural recording and could record single units in vivo.
Leonardo Piccolo et al 2024 J. Micromech. Microeng. 34 025009
Microneedles (MNs) are promising alternatives to pills and traditional needles as drug delivery systems due to their fast, localized, and relatively less painful administration. Filling a knowledge gap, this study investigated and optimized the most influential geometrical factors determining the penetration efficiency of MNs. The effects of height, base diameter, and tip diameter were analyzed using the finite element method, with results showing that the most influencing factor was base diameter, followed by height. Moreover, the taper angle, which is dependent on all the geometrical factors, was found to directly affect the penetration efficiency at a fixed height. An additional model was developed to relate the height and taper angle to penetration efficiency, and the results were experimentally validated by compression testing of MN array prototypes printed using two-photon photolithography. The numerical model closely predicted the experimental results, with a root mean square error of 9.35. The results of our study have the potential to aid the design of high-penetration efficiency MNs for better functionality and applicability.
Manu Garg et al 2024 J. Micromech. Microeng. 34 025003
An electrostatically actuated all-metal microelectromechanical systems (MEMS) Pirani gauge with a tunable dynamic range is proposed. Contrary to the conventional fixed gap Pirani gauges, an electrostatic mechanism is employed to tune the gaseous conduction gap. Due to the electrostatic force between the heating element and heat sink, this tuning results in shifting the transition pressure to a higher pressure. As a result, the operating range of the Pirani gauge can be tuned depending on the magnitude of the actuation voltage. Theoretical estimation of the transition pressure corresponding to different gaseous conduction gaps is also presented. Depending on the available margin of gap tuning, the electromechanical and electrothermal analyses are carried out in COMSOL Multiphysics. The analytical approach is validated by experimentally characterizing the fabricated device. The experimentally tested device with the proposed actuation mechanism shows an 11.2 dB increase in dynamic range in comparison to the conventional design. In a complementary metal-oxide-semiconductor (CMOS)-compatible fabrication process flow, the proposed gauge can be used to monitor vacuum from 40 Pa to 5 × 105 Pa with the electrostatic actuation.
Jun Yu et al 2024 J. Micromech. Microeng. 34 015007
This paper investigates the implementation of 1:2 internal resonance (InRes) in a clamped–clamped stepped beam resonator with a strong Duffing effect, focusing on its potential for frequency stabilization in micro-electro-mechanical systems (MEMS) resonators. InRes can arise in a nonlinear system of which mode frequencies are close to an integer ratio, facilitating the internal exchange of energy from an externally driven mode to an undriven mode. The presence of 1:2 InRes and Duffing hardening nonlinearity can result in frequency saturation phenomena, leading to a flat amplitude-frequency response range, which forms the basis for frequency stabilization. The stepped beam resonator design, combined with thermal frequency tuning, enables precise alteration of the frequency ratio between the second and third flexural modes required to achieve the desired 1:2 ratio for InRes. Experimental characterization and theoretical analysis revealed that frequency mismatch plays a significant role, with larger mismatch conditions leading to stronger energy exchange and a wider range of drive force for frequency saturation. The study highlights the frequency saturation mechanism utilizing 1:2 InRes and emphasizes the advantage of Duffing nonlinearity and larger intermodal frequency mismatch for broader frequency stabilization, providing valuable insights for the design and optimization of MEMS resonators.
Jikke de Winter et al 2024 J. Micromech. Microeng. 34 015004
The emerging high-resolution 3D printing technique called two-photon polymerization (2PP) enables to print devices bottom-up rapidly, contrary to the top–down lithography-based fabrication methods. In this work, various polymer microbeams are 3D printed and their resonant characteristics are analyzed to understand the origin of damping. The 2PP printed polymer resonators have shown less damping than other polymer devices reported earlier, with tensile-stressed clamped–clamped beams reaching a record quality factor of 1819. The resonant energy loss was dominant by bulk friction damping. These results pave the path towards using 3D printed microresonators as mass sensors with improved design and fabrication flexibility.
Ioannis Lampouras et al 2024 J. Micromech. Microeng. 34 015005
Dynamic-mode cantilever sensors are based on the principle of a one-side clamped beam being excited to oscillate at or close to its resonance frequency. An external interaction on the cantilever alters its oscillatory state, and this change can be detected and used for quantification of the external influence (e.g. a force or mass load). A very promising approach to significantly improve sensitivity without modifying the established laser-based oscillation transduction is the co-resonant coupling of a micro- and a nanocantilever. Thereby, each resonator is optimized for a specific purpose, i.e. the microcantilever for reliable oscillation detection and the nanocantilever for highest sensitivity through low rigidity and mass. To achieve the co-resonant state, the eigenfrequencies of micro- and nanocantilever need to be adjusted so that they differ by less than approximately 20%. This can either be realized by mass deposition or trimming of the nanocantilever, or by choice of dimensions. While the former is a manual and error-prone process, the latter would enable reproducible batch fabrication of coupled systems with predefined eigenfrequency matching states and therefore sensor properties. However, the approach is very challenging as it requires a precisely controlled fabrication process. Here, for the first time, such a process for batch fabrication of inherently geometrically eigenfrequency matched co-resonant cantilever structures is presented and characterized. It is based on conventional microfabrication techniques and the structures are made from 1 µm thick low-stress silicon nitride. They comprise the microcantilever and high aspect ratio nanocantilever (width 2 µm, thickness about 100 nm, lengths up to 80 µm) which are successfully realized with only minimal bending. An average yield of 
% of intact complete sensor structures per wafer is achieved. Desired geometric dimensions can be realized within ±1% variation for length and width of the microcantilever and nanocantilever length, ±10% and ±20% for the nanocantilever width and thickness, respectively, resulting in an average variation of its eigenfrequency by 11%. Furthermore, the dynamic oscillation properties are verified by vibration experiments in a scanning electron microscope. The developed process allows for the first time the batch fabrication of co-resonantly coupled systems with predefined properties and controlled matching states. This is an important step and crucial foundation for a broader applicability of the co-resonant approach for sensitivity enhancement of dynamic-mode cantilever sensors.
Aleksandra Pokrzywnicka et al 2024 J. Micromech. Microeng. 34 017001
Transillumination microscopes, often with a simple lens-free optical configuration, combined with lab-on-a-chip devices are useful tools for the characterisation of various biological samples. A key issue with these devices is light transparency across a lab-on-a-chip structure. In this work we achieved this by embedding a glass window in a silicon membrane. Despite light transmission, the membrane could be pressure actuated. A second key issue is software analysis of the images due to the holographic nature of the captured images. In this paper, the technology of the silicon/glass membrane and results of porcine oocyte imaging during deformation are presented and compared with our previous micro-electro-mechanical system cytometer working with a reflective microscope. Thus, a unique device that deforms cells and allows deformation measurements with transillumination was developed.