Microelectromechanical Systems Components Research Articles

Achieving high fatigue endurance of nanocrystalline Ni/Ni-W layered composites through thermally and mechanically-induced relaxations

Stabilizing non-equilibrium nanograin boundaries has been shown to enhance the strength of nanocrystalline metals. Nevertheless, a thorough comprehension of how these stable grain boundaries impact the fatigue behavior in nanocrystalline metallic layered composites with heterogeneous interfaces is currently lacking. Here, aiming to develop high-performance small components in microelectromechanical systems, we prepared nanocrystalline Ni/Ni-W layered composites that underwent various degrees of annealing treatment. Our results reveal that the Ni/Ni-W layered composites annealed at 200 °C exhibit significantly higher fatigue strength, surpassing that of the as-prepared composites by 40 % and the Pt-10 at.% Au alloy by 17 % which is one of the best candidates for the microelectromechanical systems switches at present. The enhanced fatigue strength is primarily attributed to the annealing-induced grain boundary relaxation and mechanically-induced structural relaxation. Grain boundary relaxation enhances the strength by improving GB stability, while the mechanically-induced structural relaxation results in the coarsening and expansion of triangular columnar grains towards the Ni-W layer during fatigue loading. As a result, the dispersive strain localized regions triggered by the triangular columnar grains undertook cyclic strain accumulation and weakened localized damage accumulation in Ni layers, and thus further improved the fatigue resistance. The finding of the underlying mechanisms may offer a promising approach for designing high-performance materials for microelectromechanical systems switches operating at elevated temperatures.

MEMS sensitive structure sand and dust friction contamination test and electrical variation characteristics

The impact of dust pollution on the sensitive components of Micro-Electro-Mechanical Systems (MEMS) has been a hot topic in current reliability research. However, previous studies have rarely focused on the fundamental analysis of the influence of dust pollutants on the sensitive components of MEMS, and these research results lack universality. This paper aims to present experimental results on the electrical characteristic changes of MEMS thermal sensitive resistors based on dust friction, providing a more detailed description and explanation. Through dust friction experiments, we investigated the effects of dust particle size and relative humidity on the electrical characteristics of MEMS devices. We chose the resistance value output as the electrical characteristic parameter, based on the performance exhibited during the dust friction experiments. We conducted a detailed analysis of the reasons for the changes in the electrical characteristic parameters. The research results showed that when dust particles settle on the device, the failure mode of the device manifests as resistance drift. The inducing factor is the electrostatic current generated by the friction between dust particles, which enters the sensitive components through the principle of electrostatic dissipation. The measurement principle leads to changes in the resistance value measurement, although the actual resistance value does not change. The magnitude of this electrostatic current is directly proportional to the size of the particles and inversely proportional to the relative humidity. This finding provides theoretical guidance for identifying failure-inducing factors in MEMS failure modes.

Low-Temperature Wafer-Level Bonding with Cu-Sn-In Solid Liquid Interdiffusion for Microsystem Packaging

This work demonstrates the potential use of Cu-Sn-In metallurgy for wafer-level low-temperature solid-liquid interdiffusion (LT-SLID) bonding process for microelectromechanical system (MEMS) packaging. Test structures containing seal-ring shaped SLID bonds were employed to bond silicon and glass wafers at temperatures as low as 170 °C. Scanning acoustic microscopy (SAM) was utilized to inspect the quality of as-bonded wafers. The package hermeticity was characterized by cap-deflection measurements and evaluated through finite element modelling. The results indicate the bonds are hermetic, but residual stresses limit the quantitative analysis of the hermeticity. The microstructural studies confirm the bonds contain a single-phase intermetallic Cu6(Sn,In)5 that remains thermally stable up to 500 °C. This work shows Cu-Sn-In based low-temperature bonding method as a viable packaging option for optical MEMS or other temperature-sensitive components.

Assessment of machine learning methods predicting the axial vibration frequencies of microbars

AbstractMicrobars are one of the important components of microelectromechanical systems. With the recent increase in their applications, the importance of understanding their mechanical response has become an important topic. In this study, for the first time, the mechanical behavior of microbars based on the strain gradient theory is investigated using a machine learning (ML) approach. Four distinct ML models, namely artificial neural network (ANN), support vector regression (SVR), decision tree regression (DTR), and random forest regression (RFR), are developed for microbars with clamped boundary conditions. The performance of these models is individually assessed using five different metrics: coefficient of determination (R2), Mean Absolute Error (MAE), root mean square error (RMSE), mean absolute percentage error (MAPE) and Nash‐Sutcliffe efficiency coefficient (NSE). The best‐performing model is selected based on these comparisons. Additionally, a semi‐analytical approach is employed to determine the natural frequencies of microbars under general elastic boundary conditions using the Fourier sine series and Stokes' transform. While the R2 value for all four models indicated a good fit of 0.999, the percentage difference in MAE and RMSE values between the training and testing data for DTR and RFR models was relatively higher as compared to ANN and SVR. The results showed that ANN and SVR models exhibit the best performance in predicting the natural frequencies on both training and testing data across all three metrics. Finally, a study on the free axial vibration frequencies of microbar under various effects was conducted.

(Invited) Wafer Bonding for MEMS Integration and Packaging

Wafer bonding is a critical manufacturing process for a vast number of experimental and commercial microelectromechanical system (MEMS) devices [1-5]. Wafer bonding is used for both the hermetic sealing of MEMS [3-5], and for integrating MEMS with electronic integrated circuits (IC) [1-2]. In this invited talk we present recent examples of wafer bonding approaches targeted at hermetic sealing of emerging MEMS devices such as silicon photonic MEMS [3, 4]. In these processes, the MEMS are sealed by wafer bonding and transferring individual lids, while at the same time keeping the final total die thickness as thin as possible. Furthermore, we also present examples of wafer bonding techniques targeted at integrating MEMS or nanoelectromechanical systems (NEMS) directly on top of electronic integrated circuits (IC), thereby closely packaging the MEMS devices with the electronic circuits that provide an interface to the outside world [1-2]. Ultimately the presented wafer bonding approaches can contribute to further miniaturization and thickness reduction of the final packaged MEMS components. REFERENCES [1] Fischer, A.C., Forsberg, F., Lapisa, M., Bleiker, S.J., Stemme, G., Roxhed, N. and Niklaus, F., 2015. Integrating mems and ics. Microsystems & Nanoengineering, 1(1), pp.1-16.[2] Lapisa, M., Stemme, G. and Niklaus, F., 2011. Wafer-level heterogeneous integration for MOEMS, MEMS, and NEMS. IEEE Journal of Selected Topics in Quantum Electronics, 17(3), pp.629-644.[3] Jo, G., Edinger, P., Bleiker, S.J., Wang, X., Takabayashi, A.Y., Sattari, H., Quack, N., Jezzini, M., Lee, J.S., Verheyen, P. and Zand, I., 2022. Wafer-level hermetically sealed silicon photonic MEMS. Photonics Research, 10(2), pp.A14-A21.[4] Edinger, P., Jo, G., Van Nguyen, C.P., Takabayashi, A.Y., Errando-Herranz, C., Antony, C., Talli, G., Verheyen, P., Khan, U., Bleiker, S.J. and Bogaerts, W., 2023. Vacuum-sealed silicon photonic MEMS tunable ring resonator with an independent control over coupling and phase. Optics Express, 31(4), pp.6540-6551.[5] Wang, X., Bleiker, S.J., Edinger, P., Errando-Herranz, C., Roxhed, N., Stemme, G., Gylfason, K.B. and Niklaus, F., 2019. Wafer-level vacuum sealing by transfer bonding of silicon caps for small footprint and ultra-thin MEMS packages. Journal of microelectromechanical systems, 28(3), pp.460-471. Figure 1

Molecular Dynamics Study on the Effects of Substrate Grain Boundaries on the Adsorption State of Graphene: Implications for Nanoscale Lubrication

Graphene on polycrystalline surfaces, such as stainless steel, exhibits frictional strengthening properties during nanofriction. The adsorption state of graphene is directly related to the nanofriction behavior, and graphene’s adsorption state is affected by substrate grain boundaries. However, the mechanism of the influence of the substrate grain boundaries on the adsorption state of graphene is not clear. Herein, the adsorption states of graphene on different stainless-steel grain boundary surfaces are analyzed, and the mechanism of the substrate grain boundaries regulating the surface graphene bulge is revealed. The notion that graphene bulges are related to the type of substrate grain boundaries has been confirmed. Moreover, we demonstrate that the difference in the crystal surfaces on both sides of the grain boundaries and the gradient of adsorption energy are the key factors regulating the graphene bulge. Graphene bulging can only be caused by the existence of crystal surface differences in the grain boundary structure; therefore, the tilt grain boundaries are unable to cause graphene bulging. In addition, the adsorption energy distribution within the grain boundary will also influence graphene bulging if there is a grain surface difference in the grain boundary structure. When the direction of the adsorption energy gradient is perpendicular to the grain boundary, such a grain boundary structure favors the appearance of graphene bulges. In contrast, graphene bulging is suppressed when the direction of the adsorption energy gradient is parallel to the grain boundary. It provides a theoretical basis for explaining graphene’s nanofriction on polycrystalline substrates such as stainless steel. It is important for the use of graphene for the nano-lubrication of stainless-steel components in microelectromechanical systems.

Toward Tungsten Electrodeposition at Moderate Temperatures Below 100 °C Using Chloroaluminate Ionic Liquids

The electrodeposition of tungsten at moderate temperatures (<100 °C) has been of significant interest for the fabrication of thin films and microelectromechanical system components to decrease energy consumption and increase process safety. In this study, we investigated the electrochemical reduction of WCl4 and WCl5 in 1-ethyl-3-methylimidazolium chloride (EMIC) and EMIC–AlCl3 ionic liquids at 80 °C–120 °C. W-rich films with a thickness of approximately 1 μm were obtained from the Lewis acidic EMIC–AlCl3–WCl5 bath, whereas the other baths did not yield any deposits. The films obtained from the EMIC–AlCl3–WCl5 bath at 80 °C had higher W contents of 54 at.% than those obtained at 120 °C. X-ray absorption near-edge structure spectra of the W-rich films indicated that W existed in an oxidized state. The findings of this study can be used as a guide to explore optimal electrolytes and electrolytic conditions for the electrodeposition of metallic W at moderate temperatures.

Enhancing high-temperature tensile properties of Ni/Ni-W laminated composites for MEMS devices

There is an increasing demand for materials with excellent mechanical performance for Micro-Electro-Mechanical System (MEMS) devices serving at elevated temperatures. However, how to enhance the high-temperature strength of the materials without losing their plasticity is a pending problem. Here, the Ni/Ni-W laminated composites with different monolayer thicknesses and the same ratio of the constituent layer thicknesses were fabricated successfully by using the dual-bath electrodeposition technique. The microstructure stability and tensile properties of annealed Ni/Ni-W laminated composites with different monolayer thicknesses were investigated at 400 °C. The results show that the annealed Ni0.5/Ni-W0.05 laminated composites have both high yield strength (450 MPa) and excellent elongation to failure (25.1%) at 400 °C, being superior to that of the monotonic Ni (179 MPa and 17.7%). Such a high strength of the laminated composite at 400 °C results from the contribution of the intrinsically high strength of the Ni-W layers with excellent thermal stability, the thickness-constrained effect on grain growth of Ni layers and the interface coupling effect of heterogeneous structures. The good plasticity may be derived from the heterogeneous laminated structure and the decrease in the constituent layer thickness, providing a good co-deformation ability. Basic mechanisms for the high tensile strength and good plasticity of the Ni/Ni-W laminated composites at 400 °C were analyzed theoretically. The findings reveal a potential strategy to fabricate MEMS components with excellent high-temperature tensile properties through tailoring the microstructure thermal stability and the constituent layer scale.

Production of a superhydrophobic frame-cone structure by laser etching and Ni electrodeposition

ABSTRACT Metal components in microelectromechanical systems are prone to failure and corrosion due to droplet adhesion in wet environments. Several multi-level structures on the micro-nano scale may induce effective superhydrophobicity to prevent such adhesion. This study proposes a hybrid manufacturing process to generate ‘frame-cone’ textures on the surfaces of metals by combining ultra-fast laser etching and electrodeposition. Periodically distributed frame recesses and pits were coated with nano-submicron Ni coatings with conical shapes, and the pit depth and cone height were controlled by tuning the laser scanning time and current density, respectively. The surface adhesion force was reduced to 22.8 μN, and the static contact angle was maintained at 156.7° using the hybrid process, while the adhesion forces of laser etched samples with the same depth were 164.7 μN. The multi-level ‘frame-cone’ structure stored more air and reduced the contact areas between the bottoms of the pits and droplets. The hybrid process of ultra-fast laser etching and electrodeposition aided in improving the superhydrophobicity, with less damage to the substrate.

A new linear stability analysis approach for microchannel flow based on the Boltzmann Bhatnagar–Gross–Krook equation

Microchannels are important components of microelectromechanical systems (MEMSs) that encounter rarefaction effects due to their small-scale characteristics. The influence of rarefaction effects on the flow stability of microchannels should be investigated to improve MEMS performance. Based on kinetic theory, a linear stability analysis approach for low-speed rarefied flows was developed by using the Bhatnagar–Gross–Krook (BGK) model of the Boltzmann equation with an external force term. This approach was applied to study the linear temporal stability of microchannel flows. A slip flow model was introduced for comparison. The corresponding eigenvalue problem was solved with a Chebyshev collocation method. This novel approach yielded a critical Reynolds number of 5778. Analysis of the validity and accuracy of the slip flow model shows that although this model cannot capture the Knudsen layer structure, this approach effectively improves the prediction accuracy of the growth rate of the least stable mode. However, the prediction accuracy gradually decreases with increasing Knudsen number. Compared with the stability results obtained from the BGK equation, the Navier–Stokes equations-based stability analysis method always underestimates the disturbance growth rate, regardless of whether a slip flow model is used. The stability analysis results show that rarefaction effects stabilize the flow. The degree of rarefaction does not affect the trends of growth rate and phase velocity with wavenumber, nor does it affect the shape of the velocity eigenfunctions. For a rarefied case, increasing the Mach number has a destabilizing effect on low-speed microchannel flows.

Experimental investigation of electrochemical micromilling on titanium alloy (Ti6Al4V)

The demand for microscale components in Micro-Electromechanical Systems, the automobile industry, aerospace industry, and the medical field is rapidly increasing in the past few years. Titanium and titanium composite materials are the most appropriate material for all of these applications because of their high strength-to-weight ratio and high corrosion resistance. The machining of titanium at the microscale level has many challenges because of the mechanical and chemical qualities of titanium, it can be machined using both traditional and non-conventional methods. Electrochemical micromachining (EMM) is a noncontact, anodic dissolution of materials that are tough to fabricate, like in titanium alloy 'Ti6Al4V' can be achieved using a stress-free machining method. This research presents a thorough experimental analysis of electrochemical micro-milling on the titanium alloy Ti6Al4V. The impact of various treatment input variables like duty ratio, tool feed rate, machining voltage, and pulse frequency on geometrical accuracy of micro-features was investigated. The optimum parameters for microfeatures were identified as machining voltage of 12 V along with pulse frequency and micro tool feed rate of 180 KHz and 5 µ/sec respectively. The micro-features were generated by a layer-by-layer micro-milling technique with the help of a micro tool of 255-µm diameter.

RSM Modeling and Validation of Glass Assisted Laser Micro Drilling of Silicon Wafer

Rapid growths in the electronic industries provide opportunities for the industries to expand the using of silicon wafer in modern and advanced technologies especially Micro Electromechanical Systems (MEMS). Laser cutting is one of the most significant and important application for fabrication MEMS components. The objective of this study is to investigate the cutting capability of industrial laser, CO2 laser, in silicon wafer processing. Experiment was conducted in two conditions which is with assisted of pyrex glass and without assist of pyrex glass. In this work, silicon wafer with thickness 525 μm were cut into several rectangular sample shapes. The surface roughness produce at the cutting edge on each sample were investigated and analyzed. Analysis of Variance (ANOVA) was used to analyze the result and generated an appropriate model for the laser cutting processing. The laser parameters involved were laser power, cutting speed, and pulse frequency. Experimental results evident that, the laser cutting process with assist of glass give a better surface roughness on silicon cutting edge compared to without assist of glass.

Design and simulation of an out-of-plane electrothermal microactuator

Microactuators are one of the most important components in microelectromechanical systems (MEMS). Therefore, designing effective out-of-plane actuators has been in progress for the last decade. This paper presents a novel design of the microactuator with a double stepped beam structure for large out-of-plane deflection output applied to microvalves. The design and analysis of the out-of-plane microactuator are implemented by the finite element method. Silicon is selected as the material of the actuator and the beam motion is generated by the Joule heating effect. Compared to a single stepped beam design reported in the literature, the simulation results show that the proposed double-stepped beam structure can deliver a much larger out-of-plane deflection. Under an applied current of 15 mA, the maximum deflection of the double stepped beam is nearly seven times higher than that of the single stepped beam structure. In addition, the stress analysis indicates that the largest stress (1.46 GPa) induced in the beam is much smaller than the yield strength (7 GPa) of the selected silicon material.

Effects of Sample Geometry and Grain Size on Mechanical Property of Electrodeposited Gold Evaluated By Micro-Bending Test

In recent years, MEMS (microelectromechanical systems) devices are required to have high functionality and small size, especially for MEMS acceleration sensors, and sensitivity of a MEMS acceleration sensor is highly dependent on the Brownian noise [1,2]. The Brown noise is known to be inversely proportional to mass of movable parts in the sensor, and the noise is lowered by increasing the mass [1,2], which implies a number of volume is needed to ensure high sensitivity. However, increasing size of the component is not preferable. Because of this, a design of gold-based MEMS acceleration sensor is proposed. The density of gold is 19.3 g/cm3, and gold has high corrosion resistance and chemical stability. Most importantly, gold electrodeposition process can be easily integrated with current MEMS fabrication process.Mechanical properties of the material are essential informtion for design of MEMS components. For instance, the yield stress is needed to guarantee elastic deformation of the material during operation of the MEMS device. Mechanical properties of metallic materials are known to change with size of the sample used in a mechanical property characterization becomes smaller than micrometer scale, which is known as the sample size effect [3]. Therefore, mechanical property characterization of materials toward MEMS should be conducted using samples having the same dimensions as those used in MEMS. Various micro-mechanical testing methods have been developed to characterize micro-specimens, such as micro-compression test, micro-tensile test, and micro-bending test. Among them, micro-bending test is suggested to be the most suitable method to evaluate materials for applications in MEMS when compared with micro-compression and micro-tensile tests since cantilever-like structure is commonly utilized in movable components, such as the micro-spring in MEMS accelerometers. On the other hand, micro-cantilevers are reported to have the sample geometry effect [4], which the sample size effect is only observed when varying thickness of the micro-cantilever. Also, it has been reported that the sample size effect is dependent on ratio of the sample diameter to the average grain size, and materials prepared by electrodeposition are usually polycrystal. Thus, relationship between the sample geometry effect and the average grain size is investigated in this study.Two gold films were electrodeposited at different current density to change the average grain size. The average grain size was determined by electron backscatter diffraction, and the average grain size of film A and B were 1.2~1.3 and 0.6 μm, respectively. Samples used in the micro-bending test were micro-cantilevers fabricated from the gold films by focus ion beam. Thicknesses of the micro-cantilever were ranged from 6.0 to 13 μm. The micro-bending tests are conducted using a test machine specially designed for micro-specimens developed in our group as shown in Fig. 1.The yield stresses were in a range of 428 to 553MPa, which were all higher than that of the bulk gold (55 to 220 MPa). Table 1 shows the detailed dimensions and yield stress of all samples. Yield stresses were plotted against the log scale of thickness shown in Fig. 2. At first, the sample geometry effect was confirmed in samples fabricated from both film A and B. Then, the yield stresses of samples fabricated from film B were all higher than those of film A, which was a result of the Hall-Petch relationship. In Fig. 2, the slop was steeper for film A indicating the sample geometry effect was more obvious in samples composed of larger grains. [1] D. Yamane, T. Konishi, T. Matsushima, K. Machida, H. Toshiyoshi, and K. Masu, Appl Phys Lett 104 (2014) 074102[2] K. Machida, T. Konishi, D. Yamane, H. Toshiyoshi, K. Masu, ECS Trans. 61 (2014) 21-39.[3] J.R. Greer and J.Th.M. De Hosson: Plasticity in small-sized metallic systems: Intrinsic versus extrinsic size effect. Prog. Mater. Sci. 56, 654 (2011).[4] K. Suzuki, “Sample Geometry Effect on Mechanical Property of Electrodeposited Gold Evaluated by Micro-Bending Test", 45th International Conference on Micro & Nano Engineering (MNE2019), Rhodes Greece, Sep. 2019 Figure 1

Shoulder fillet effects in strength distributions of microelectromechanical system components

The failure forces and fracture strengths of polysilicon microelectromechanical system (MEMS) components in the form of stepped tensile bars with shoulder fillets were measured using a sequential failure chain methodology. Approximately 150 specimens for each of four fillet geometries with different stress concentration factors were tested. The resulting failure force and strength distributions of the four geometries were related by a common sidewall flaw population existing within different effective stressed lengths. The failure forces, strengths, and flaw population were well described by a weakest-link based analytical framework. Finite element analysis was used to verify body-force based expressions for the stress concentration factors and to provide insight into the variation of specimen effective length with fillet geometry. Monte Carlo simulations of flaw size and location, based on the strength measurements, were also used to provide insight into fillet shape and size effects. The successful description of the shoulder fillet specimen strengths provides further empirical support for application of the strength and flaw framework in MEMS fabrication and design optimization.

Electrophoretic Deposition of Binder-Free MOF-Derived Carbon Films for High-Performance Microsupercapacitors.

Recently, miniaturized power supplies have become essential components of micro-electromechanical systems (MEMS) and portable microdevices due to their high-power density, moderate specific energy, and superior long-term cyclability. In this study, microsupercapacitors with ZIF-8-derived carbons as active materials were successfully fabricate by electrophoretic deposition method. The carbon materials on microsupercapacitors, which are directly deposited or obtained by pyrolyzing predeposited ZIF-8 particles, play a crucial role in achieving outstanding electrochemical performances. The microsupercapacitor of 16 interdigital finger electrodes, prepared by electrophoretic deposition of ZIF-8 particles and subsequent pyrolysis, shows maximum specific power 687.6 mW cm-3 , specific energy 2.87 mWh cm-3 , and 97.8 % capacitance retention rate after 10 000 cycles. The simple and facile process of electrophoretic deposition and subsequent pyrolysis of ZIF-8 particles generates a film of densely populated microporous carbon particles on microsupercapacitor, leading to superior capacitive performances.

Electrodeposition of Au-Cu Alloys and the Micro-Mechanical Properties

Electrodeposited gold is used in movable micro-components of micro-electro-mechanical systems (MEMS) devices to allow further enhancement in the sensitivity and miniaturization of the device [1]. Mechanical strengths of gold are low among materials commonly used as structure materials in electronic devices. Electrodeposition method is advantageous in strengthening metallic materials because of the ability to refine the average grain size to nano-scale, which the mechanical strength increases along with a reduction in the grain size based on the grain boundary strengthening mechanism or the Hall-Petch relationship. Alloying of metallic materials is also an effective strategy to achieve the strengthening according to the solid solution strengthening mechanism.On the other hand, mechanical properties of metallic materials exhibit the sample size effect when dimensions of the specimen are reduced to micro or sub-micro scale. Therefore, mechanical property characterization of materials for MEMS applications should be conducted using specimens having dimensions in micro-scale. Various micro-mechanical testing methods have been developed in our group to characterize micro-specimens, such as micro-compression test [2,3], micro-tensile test [4], and micro-bending test [5]. Among them, micro-bending test is suggested to be the most suitable method to evaluate materials for applications in MEMS when compared with micro-compression and micro-tensile tests since cantilever-like structures are often applied in MEMS components, such as the micro-spring in a MEMS accelerometer.In this study, Au-Cu alloys are prepared by electrodeposition, and micro-mechanical properties of the electrodeposited Au-Cu alloys are characterized by a micro-bending test. Young’s modulus is an important information in design of movable micro-components. A non-destructive Young’s modulus evaluation method, resonance frequency measurement, is conducted using the Au-Cu alloy micro-cantilevers. Also, long-term vibration tests are conducted to reveal structure stability of the Au-Cu alloy micro-cantilevers.The Au-Cu electrolyte used in this work was a commercially available electrolyte provided by MATEX Co. Japan, which contained 17.3 g/L of X3Au(SO3)2 (X = Na, K), 1.26 g/L of CuSO4, and ethylenediaminetetraacetic acid as the additive with pH at 7.5. The electrodeposition was carried out at 50 °C, and the current density was varied from 0.1 to 8 mA/cm2. Specimens used in the micro-bending test were micro-cantilevers fabricated from the Au-Cu alloy films by focused ion beam. Dimensions of the micro-cantilevers fabricated were 10 µm × 10 µm × 50 µm. The micro-bending tests were conducted using a test machine equipped with a spherical diamond indenter at a constant displacement rate of 0.05 µm/s.For the Young’s modulus and long-term structure stability evaluations, the micro-cantilevers were prepared by electrodeposition combined with lithography process. The long-term vibration test was carried out under conditions of the cycle number in a range from 103 to 106, the frequency of 10.0 Hz, and the acceleration of 1.0 G (1 G = 9.8 m/s2). The structure stability was determined by evaluating height profiles of top surface of the micro-cantilevers before and after the vibration test by a 3D optical microscope.The Au-Cu alloy film electrodeposited at 5 mA/cm2 had the finest average grain size among films prepared in this work, which the grain size was 4.76 nm. Bending test of a micro-cantilever prepared from this film shows a high yield stress at 1826 MPa. Gold, copper, and Au-Cu alloys are known to be ductile materials, but brittle fracture was observed during the bending test when the current density used in prepared the film was higher than 5 mA/cm2.From the resonance frequency method, Young’s moduli of the Au-Cu alloy micro-cantilevers were ranged from 68.0 to 79.5 GPa, which were similar to the value of bulk-size specimens and indicated no sample size effect on the Young’s modulus. Regarding the long-term structure stability, after 106 cycles of the vibration test, all the micro-cantilever were still intact, and the height profiles did not change much after the vibration. Results obtained in this study confirmed high mechanical strength and structure stability in the electroplated Au-Cu alloys and demonstrated the advantage in applications as movable components in MEMS devices.[1] D. Yamane et. al. Appl. Phys. Lett. 104 (2014) 074102.[2] C.Y. Chen et. al. Electrochem. Commun. 51 (2016) 51-54.[3] H. Tang et. al. J. Electrochem. Soc. 164 (2017) 244-247[4] Y. Kihara et. al. Mater. Lett. 153 (2015) 36-39[5] K. Asano et. al. ECS J. Solid State Sci. Technol. 8 (2019) P412-P415.

Fully-Differential TPoS Resonators Based on Dual Interdigital Electrodes for Feedthrough Suppression

As one of the core components of MEMS (i.e., micro-electro-mechanical systems), thin-film piezoelectric-on-silicon (TPoS) resonators experienced a blooming development in the past decades due to unique features such as a remarkable capability of integration for attractive applications of system-on-chip integrated timing references. However, the parasitic capacitive feedthrough poses a great challenge to electrical detection of resonance in a microscale silicon-based mechanical resonator. Herein, a fully-differential configuration of a TPoS MEMS resonator based on a novel structural design of dual interdigital electrodes is proposed to eliminate the negative effect of feedthrough. The fundamental principle of feedthrough suppression was comprehensively investigated by using FEA (i.e., finite-element analysis) modeling and electrical measurements of fabricated devices. It was shown that with the help of fully-differential configuration, the key parameter of SBR (i.e., signal-to-background ratio) was significantly enhanced by greatly suppressing the in-phase signal. The S-parameter measurement results further verified the effectiveness of this novel feedthrough suppression strategy, and the insertion loss and SBR of proposed TPoS resonators were improved to 4.27 dB and 42.47 dB, respectively.

Development Trends and Perspectives of Future Sensors and MEMS/NEMS.

With the fast development of the fifth-generation cellular network technology (5G), the future sensors and microelectromechanical systems (MEMS)/nanoelectromechanical systems (NEMS) are presenting a more and more critical role to provide information in our daily life. This review paper introduces the development trends and perspectives of the future sensors and MEMS/NEMS. Starting from the issues of the MEMS fabrication, we introduced typical MEMS sensors for their applications in the Internet of Things (IoTs), such as MEMS physical sensor, MEMS acoustic sensor, and MEMS gas sensor. Toward the trends in intelligence and less power consumption, MEMS components including MEMS/NEMS switch, piezoelectric micromachined ultrasonic transducer (PMUT), and MEMS energy harvesting were investigated to assist the future sensors, such as event-based or almost zero-power. Furthermore, MEMS rigid substrate toward NEMS flexible-based for flexibility and interface was discussed as another important development trend for next-generation wearable or multi-functional sensors. Around the issues about the big data and human-machine realization for human beings’ manipulation, artificial intelligence (AI) and virtual reality (VR) technologies were finally realized using sensor nodes and its wave identification as future trends for various scenarios.

Studies on ferroelectric and nanomechanical response of single-layered PZT thick film for energy harvester applications

We have made an attempt to fabricate free standing warpage free PZT thick films of 100 µm thickness by tape casting method. The poly crystalline nature and nanoscale polarization switching of free standing thick film were confirmed using X-ray diffraction technique and piezo force microscopy, respectively. The piezoelectric coefficient (d33) of 100 µm free-standing Pb(Zr0.56Ti0.44)O3 [PZT] thick film was calculated using double beam laser interferometer and found to be 400 pm/V. From the results, it indicates that free-standing PZT thick films are suitable candidate for miniaturization of harvesting device by directly bonding them on microsystem components for microelectromechanical systems (MEMS) applications.