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.
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.
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.
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.
Md Ataul Mamun et al 2024 J. Micromech. Microeng. 34 065001
A thorough understanding of arc discharge mechanism as well as determination of arc discharge voltage at the nanometer scale remains challenging due to the complexities associated with electrode preparation and precisely maintaining nanoscale separations in experiments. This work addresses this challenge through a novel approach by accurately measuring electric breakdown/discharge voltages between Pt-coated Si electrodes with separations ranging from ∼5 nm to 370 nm using a combination of fixed and flexible nano-electrodes while inherently creating an ideal environment to mitigate the effect of mechanical vibrations on the measurement results. For separations of 10, 100, and 300 nm, the corresponding discharge voltages are ∼15, 75, and 160 V, respectively, with the apparent electric field for the 10 nm separation exceeding 1.5 GV m−1. The results acquired from the investigated electrode configuration closely resembling the laterally actuated nanoelectromechanical system (NEMS) cantilever relays reveals strong agreement with NEMS relay breakdown characteristics, emphasizing the importance of arc discharge considerations while designing micro/nano electromechanical devices. Furthermore, deliberately applied arc discharge is shown to provide electrode nano-welding for realization of configurable NEMS circuits.
Fahimullah Khan and Mohammad I Younis 2022 J. Micromech. Microeng. 32 013002
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.
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.
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.
Mark A Eddings et al 2008 J. Micromech. Microeng. 18 067001
A number of polydimethysiloxane (PDMS) bonding techniques have been reported in the literature over the last several years as the focus on multilayer PDMS microfluidic devices has increased. Oxygen plasma bonding, despite cost, additional fabrication time and inconsistent bonding results, has remained a widely used method for bonding PDMS layers. A comparative study of four rapid, inexpensive alternative PDMS–PDMS bonding approaches was undertaken to determine relative bond strength. These include corona discharge, partial curing, cross-linker variation and uncured PDMS adhesive. Partial curing and uncured PDMS adhesive demonstrated a considerable improvement in bond strength and consistency by retaining average bond strengths of over 600 kPa, which was more than double the average bond strength of oxygen plasma. A description of each technique and their performance relative to oxygen plasma bonding is included.
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Zhi-Xuan Dai et al 2024 J. Micromech. Microeng. 34 075001
The study explores the fabrication and evaluation of a micro thermoelectric generator (MTG) with long-length thermocouples (TCs) through the utilization of a commercial complementary metal oxide semiconductor process. The MTG consists of 23 TCs, and its performance is intricately linked to the temperature difference (Tdiff) between the cold and hot sides of these TCs. An increase in Tdiff leads to higher output voltage and power for the MTG. To enhance Tdiff, the TCs are designed to be 700 µm in length, and an innovative design has been implemented on the cold side of the TCs, creating a suspended structure to improve heat dissipation A post-process is essential for achieving this suspended TC structure. The results demonstrate that the TC structure is fully suspended and remains undamaged. The measured outcomes reveal an output voltage of 13.8 mV when the Tdiff reaches 3.5 K. Under these conditions, the MTG exhibits a voltage factor of 2.76 mV mm−2K−1. Furthermore, at a Tdiff of 3.5 K, the maximum output power reaches 2.1 nW. The MTG demonstrates a power factor of 0.12 nW mm−2 K−2.
Zhiqiang Ma and Dawei Shen 2024 J. Micromech. Microeng. 34 073001
In our daily life, flexible flow sensors endow us with a 'sixth sense' capability, i.e. 'touch' the fluids, improving living quality. Although there are kinds of flexible flow sensors developed to implement this capability, they still have insufficient sensitivity and limited intelligent applications in daily life. Biomimetic engineering provides us with a powerful and effective approach to develop highly sensitive and intelligent flow sensing systems served in our life, comparable to that in creatures. Here, in this review, we present a comprehensive review of recent studies on the flexible flow sensors for human intelligent life. Firstly, we briefly introduce the excellent flow sensing systems selected by nature, and typical design strategies of artificial flexible flow sensors. Furthermore, we collect and exhibit kinds of flexible flow sensors and their applications in intelligent and digital life. Finally, we discuss the challenges and future perspectives of the flexible flow sensor for the metaverse applications.
Pham Son Minh et al 2024 J. Micromech. Microeng. 34 065004
This study assessed the comprehensive assessment of flexural and fatigue strength of the three-dimensional (3D)-printed polylactic acid (PLA) samples across diverse printing designs and parameters. The experiment framework included a diverse array of printing parameters: layer heights, first layer thicknesses, infill densities, top/bottom infill patterns, extruder temperatures, perimeters, and types of solid layer top and bottom. Our findings suggest that there is an interplay between these parameters and the mechanical properties of PLA specimens. Notably, the fatigue strength of PLA printing specimens is more significantly influenced (0.44%) by an increase in the thickness of the first layer compared to flexural strength (87%). The rate of increase in bending strength is lower in cases of layer height (3.55%) and initial layer height (0.44%) in contrast with other factors. Specimens with an initial layer thickness of 0.4 mm reached the highest number of cycles until failure, recording 21 022 cycles. Furthermore, the study identifies the infill pattern's impact on strength, highlighting that the line infill pattern type case has the highest bending strength of 75.97 MPa and surpasses the honeycomb pattern in bending strength. Compared to the Honeycomb pattern, the rectilinear design has 2.1% higher bending strength. The number of cycles to failure of the rectilinear pattern is greater than those of the honeycomb pattern. In comparison to other patterns, the Rectilinear Top/Bottom infill pattern has a higher interest rate of 27.5% for bending strength and 200.83% for fatigue strength. Additionally, greater bending and flexural strength are obtained by raising the solid layer top, bottom, and perimeter values, respectively. In comparison to the other temperatures, the bending strength and fatigue strength are highest at 200 °C. Therefore, the first layer height of 0.4 mm, the top/bottom rectilinear infill pattern, the extruder temperature of 200 °C, the perimeter value of 3, the solid layer/top value of 3, and the solid layer/bottom value of 3 are the optimal values for the part subjected to at the same time bending strength combined with fatigue strength. This comprehensive study may provide a broader and deeper understanding of individual and combined effects on an overview of the bending and fatigue strength in connection to printing design and printing parameters, as well as the ideal optimal parameters for 3D printing with the PLA material. Manufacturers and designers can use the recommended parameters to optimize the strength of their printed parts, considering both bending and fatigue performance.
Qi Wang et al 2024 J. Micromech. Microeng. 34 065003
In this paper, we propose an unsealed piezoelectric microelectromechanical systems (MEMS) speaker with rigid-flexible composite membrane, which can eliminate the membrane separation and the vibration displacement limitation at high driving voltage compared to that with the sealed rigid-flexible coupling membrane demonstrated in our previous work. Measurements performed on encapsulated prototypes mounted to an artificial ear simulator have revealed that in the human audible range of 20 Hz–20 kHz, higher than 68.5 dB SPLs are obtained at 2 V, and greater than 89.6 dB SPLs are achieved at 10 V. Moreover, the SPL distribution and effective SPLs at each moment when playing the same song exhibit similar characteristics to those of a commercial electromagnetic one. This piezoelectric MEMS speaker achieves high SPLs meeting the basic hearing needs of the human, and will have excellent prospects for future wearable audio electronics.
Ronghua Huan et al 2024 J. Micromech. Microeng. 34 065002
Microelectromechanical systems (MEMS) oscillators with high frequency stability hold significant potential for a myriad of applications across diverse fields. This letter delves into an adaptive frequency stabilization system designed to significantly improve the performance of MEMS oscillators. Our approach leverages the concept of mode coupling to dynamically adjust the oscillator's frequency based on phase control, ensuring optimal stability under varying operating conditions. The MEMS oscillator comprises a nonlinear low-frequency resonator and a linear high-frequency resonator. Through mode coupling and phase control, the nonlinear resonator is harnessed to regulate the oscillation frequency of the linear resonator. Experimental results prove that by applying the proposed approach, the frequency stability of the MEMS oscillator is enhanced by nearly 700 times for long-term stability at 1000 s. Additionally, in the scenario with varying temperature, the system also effectively improves the frequency stability by over 1000 times at 802 s.
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Zhiqiang Ma and Dawei Shen 2024 J. Micromech. Microeng. 34 073001
In our daily life, flexible flow sensors endow us with a 'sixth sense' capability, i.e. 'touch' the fluids, improving living quality. Although there are kinds of flexible flow sensors developed to implement this capability, they still have insufficient sensitivity and limited intelligent applications in daily life. Biomimetic engineering provides us with a powerful and effective approach to develop highly sensitive and intelligent flow sensing systems served in our life, comparable to that in creatures. Here, in this review, we present a comprehensive review of recent studies on the flexible flow sensors for human intelligent life. Firstly, we briefly introduce the excellent flow sensing systems selected by nature, and typical design strategies of artificial flexible flow sensors. Furthermore, we collect and exhibit kinds of flexible flow sensors and their applications in intelligent and digital life. Finally, we discuss the challenges and future perspectives of the flexible flow sensor for the metaverse applications.
Chen Ma et al 2024 J. Micromech. Microeng. 34 053001
In recent years, considerable research advancements have emerged in the application of inverse design methods to enhance the performance of electromagnetic (EM) 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 EM metamaterials are presented, including topology optimization (TO), evolutionary algorithms (EAs), 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 TO and EAs 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 EM metamaterials inverse design and integrated artificial intelligence methodologies.
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.
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Kunte et al
With increasing interest in the use of glassy carbon (GC) for a wide variety of application areas, the need for developing fundamental understanding of its mechanical properties has come to the forefront. Further, recent modeling works that shed some light on the synthesis of GC through the process of pyrolysis of polymer precursors have offered opportunities for a revisit to investigation of its mechanical properties at a fundamental level. This current study fills the gap at the molecular level and investigates the mechanical properties of GC using molecular dynamics (MD) simulations. The molecular model considered for this simulation has a characteristics 3D cagey structure of 5-, 6-, and 7-membered carbon rings and graphitic domain of a flat graphene-like structure. The GC molecular model was subjected to loading under varying strain rates (0.4/ns, 0.6/ns, 1.25/ns, and 2.5/ns) and varying temperatures (300 - 800 K) in each of the three axes. In tension, MD modeling predicted mean elastic modulus of 5.71 GPa for a single GC molecule with some dependency on strain rates and temperature, while in compression, the elastic modulus was also found to depend on the strain rates as well as temperature and was predicted to have a mean value of 35 GPa. For validation of the simulation results and developing insight into the bulk behavior, mechanical tests were carried out on dog-bone shaped testing coupons that were subjected to uniaxial tension. The GC test coupons demonstrated a bulk modulus of 17 ± 2.69 GPa in tension which compare well with those reported in the literature. However, comparing MD simulation outcomes to those of uniaxial mechanical testing, it was clear that the bulk modulus of GC in tension found experimentally is higher than modulus of single GC molecule predicted by MD modeling, which inherently underestimate the bulk modulus.
More et al
Graphene has good mechanical properties including large Young's modulus, making it ideal for many resonant sensing applications. Nonetheless, the development of graphene-based sensors has been limited due to difficulties in fabrication, encapsulation, and packaging. Here, we report a graphene nanoresonator-based resonant pressure sensor. The graphene nano resonator is fabricated on a thin silicon diaphragm that deforms due to pressure differential across it. The deformation-induced strain change results in a resonance frequency shift of the graphene nano resonator. The pressure sensing experiments demonstrate a record high responsivity of 20 kHz/kPa over a range of 270 kPa. The design has the potential to reach responsivities up to 500 kHz/kPa. The reported responsivity is two orders of magnitude higher than the silicon-based resonant pressure sensors. The estimated resolution of pressure sensing is 90 Pa, which is 0.03% of the full-scale range of the pressure sensor. This exceptional performance is attributed to two factors: maintaining a high-quality vacuum environment for the nanoresonator and introducing stimuli through a thin silicon diaphragm. The proposed pressure sensor design provides flexibility to adjust responsivity, range and footprint as needed. The fabrication method is simple and has the potential to be integrated into the modern semiconductor foundries.
Gao et al
Currently, we stand at the forefront of revolutionary advancements in communication technology. The escalating demands of advanced communication necessitate enhanced performance from materials and radio frequency (RF) devices. This paper aims to enhance film performance by depositing scandium-doped aluminum nitride (ScAlN) directly onto a Si substrate. Additionally, ScAlN was deposited on SiO2/AlN/Mo functional layers for comparison purposes. The ScAlN directly deposited on Si demonstrated superior performance in terms of crystalline quality and surface roughness, with a full width at half maximum (FWHM) of 1.7° and a roughness of 1.76 nm. Furthermore, a film bulk acoustic resonator (FBAR) based on the ScAlN film directly deposited on Si was successfully fabricated through thin-film transfer, with critical processes achieved via bonding and wet-etching of the substrate. The ScAlN in the fabricated resonator exhibited a favorable c-axis preferred orientation. The resulting ScAlN-based FBAR displayed a quality factor of 429. This study lays the groundwork for exciting opportunities in the development of higher-performance piezoelectric materials and devices.
Horstmann et al
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, 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.
Zhang et al
This research proposed a vibration monitoring device based on a piezoresistive flexible sensor with microstructured surfaces to achieve a simple acquisition of vibration information in the driver's cabin of automobiles. The shape, size and arrangement mode of microstructures on the piezoresistive flexible sensor performance were investigated by finite element simulation. The polydimethylsiloxane/hydroxylated multi walled carbon nanotubes (PDMS/MWCNTs-COOH) composite membranes were prepared by the combination of high-pressure spraying and spinning coating method. The electromechanical response curves of the piezoresistive flexible sensor composed of a double-layer PDMS/MWCNTs-COOH composite membranes based on a dual-height cylindrical microstructure were tested. A vibration monitoring device was developed to process the signals obtained by the fabricated piezoresistive flexible sensor, and the vibration response of the car cab under different driving conditions was investigated. The results indicated that the cylindrical microstructure with small size can improve the sensitivity of the fabricated piezoresistive flexible sensor. Compared with the single-height and dual-height cylindrical microstructure, the piezoresistive flexible sensor with dual-height cylindrical microstructure can expand the detection range, and improve the linearity and sensitivity. The piezoresistive flexible sensor exhibits excellent performance, with a sensitivity of 1.774 kPa-1 and a detection range is 0-0.5 kPa. The above advances can improve the authenticity of the collected data, and provide a basis for the processing and analysis of the vibration signal before improving the Noise, Vibration and Harshness performance of the vehicle.
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Manali Kunte et al 2024 J. Micromech. Microeng.
With increasing interest in the use of glassy carbon (GC) for a wide variety of application areas, the need for developing fundamental understanding of its mechanical properties has come to the forefront. Further, recent modeling works that shed some light on the synthesis of GC through the process of pyrolysis of polymer precursors have offered opportunities for a revisit to investigation of its mechanical properties at a fundamental level. This current study fills the gap at the molecular level and investigates the mechanical properties of GC using molecular dynamics (MD) simulations. The molecular model considered for this simulation has a characteristics 3D cagey structure of 5-, 6-, and 7-membered carbon rings and graphitic domain of a flat graphene-like structure. The GC molecular model was subjected to loading under varying strain rates (0.4/ns, 0.6/ns, 1.25/ns, and 2.5/ns) and varying temperatures (300 - 800 K) in each of the three axes. In tension, MD modeling predicted mean elastic modulus of 5.71 GPa for a single GC molecule with some dependency on strain rates and temperature, while in compression, the elastic modulus was also found to depend on the strain rates as well as temperature and was predicted to have a mean value of 35 GPa. For validation of the simulation results and developing insight into the bulk behavior, mechanical tests were carried out on dog-bone shaped testing coupons that were subjected to uniaxial tension. The GC test coupons demonstrated a bulk modulus of 17 ± 2.69 GPa in tension which compare well with those reported in the literature. However, comparing MD simulation outcomes to those of uniaxial mechanical testing, it was clear that the bulk modulus of GC in tension found experimentally is higher than modulus of single GC molecule predicted by MD modeling, which inherently underestimate the bulk modulus.
Benjamin Horstmann et al 2024 J. Micromech. Microeng.
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, 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.
Zhiqiang Ma and Dawei Shen 2024 J. Micromech. Microeng. 34 073001
In our daily life, flexible flow sensors endow us with a 'sixth sense' capability, i.e. 'touch' the fluids, improving living quality. Although there are kinds of flexible flow sensors developed to implement this capability, they still have insufficient sensitivity and limited intelligent applications in daily life. Biomimetic engineering provides us with a powerful and effective approach to develop highly sensitive and intelligent flow sensing systems served in our life, comparable to that in creatures. Here, in this review, we present a comprehensive review of recent studies on the flexible flow sensors for human intelligent life. Firstly, we briefly introduce the excellent flow sensing systems selected by nature, and typical design strategies of artificial flexible flow sensors. Furthermore, we collect and exhibit kinds of flexible flow sensors and their applications in intelligent and digital life. Finally, we discuss the challenges and future perspectives of the flexible flow sensor for the metaverse applications.
Md Ataul Mamun et al 2024 J. Micromech. Microeng. 34 065001
A thorough understanding of arc discharge mechanism as well as determination of arc discharge voltage at the nanometer scale remains challenging due to the complexities associated with electrode preparation and precisely maintaining nanoscale separations in experiments. This work addresses this challenge through a novel approach by accurately measuring electric breakdown/discharge voltages between Pt-coated Si electrodes with separations ranging from ∼5 nm to 370 nm using a combination of fixed and flexible nano-electrodes while inherently creating an ideal environment to mitigate the effect of mechanical vibrations on the measurement results. For separations of 10, 100, and 300 nm, the corresponding discharge voltages are ∼15, 75, and 160 V, respectively, with the apparent electric field for the 10 nm separation exceeding 1.5 GV m−1. The results acquired from the investigated electrode configuration closely resembling the laterally actuated nanoelectromechanical system (NEMS) cantilever relays reveals strong agreement with NEMS relay breakdown characteristics, emphasizing the importance of arc discharge considerations while designing micro/nano electromechanical devices. Furthermore, deliberately applied arc discharge is shown to provide electrode nano-welding for realization of configurable NEMS circuits.
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.