Deformation of Composite Micro-Rods

Shape memory alloys (SMAs) have the potential to be used for a wide variety of microelectromechanical systems (MEMS) applications, providing a unique combination of large deflections and high work output. A major drawback for SMAs in many applications has been the low frequency response, which is typically on the order of 100 Hz or lower, even in microscale SMA actuators. In MEMS applications, the higher surface-to-volume ratios have enabled responses to be improved by an order or magnitude or more. By further shrinking the SMA film/device dimensions, the frequency response may be improved even further. In this paper, we present a new, simplified process for fabricating sputtered, thin film SMA MEMS actuators based on nickel-titanium alloy (NiTi or, aka, NITINOL) that consisted of only one photo step to pattern the actuators using SU8. When heated through its solid–solid phase transition from low-temperature martensite to high-temperature austenite, the NiTi alloy undergoes changes in associated physical properties, such as Young’s modulus, resistivity, and surface roughness, that are critical to controlling MEMS performance. For example, these material property changes allow for the design of active or passive microscale sensors and actuators. In the new process, we are able to fabricate ultrathin films of NiTi with nanoscale thickness, which can be thermally cycled through two stable positions very rapidly, making it an intriguing thermal sensor and actuator material for high frequency applications. Additionally, NiTi can be used as an active thermal switch through resistive (i.e. joule) heating. We demonstrated a greatly improved frequency response of up to 3000 Hz with turn on voltages as low as 0.5 V (corresponding to only 1 mW power consumption) for devices exhibiting microns of cantilever tip deflection over millions of cycles, indicating these new SMA MEMS actuators have potential application for low voltage switching, modulation and tuning.

Micro-electro-mechanical system (MEMS) technology has radically changed the scale, performance, and cost of a wide variety of sensors and actuators by taking advantage of batch fabrication. The multidisciplinary nature of MEMS employs knowledge of diverse technical areas to realize improved and novel transducer systems. This also brings various associated challenges that are otherwise being ignored in a simple macro-dimensional system. MEMS devices typically comprise several deposited thick and thin films as well as bonded of dissimilar materials (like silicon, metal, glass, etc.). Residual stress is one of the most common outcomes during this integration/stacking of distinctly different materials for the fabrication of novel MEMS structures. The residual stress may significantly affect the performance and reliability of the fabricated devices. Thus, the evaluation and regulation of residual stress are one of the crucial aspects to assess the functioning of modern-day MEMS devices. This paper reviewed the origins of residual stress in MEMS fabrication processes. Different techniques involved in testing and characterization of the residual stresses are reviewed. Few important case studies are discussed to highlight the effect of residual stress (generated during various fabrication processes) on characteristics of different MEMS structures. The brief overview of the possible route to minimize the residual stresses is also presented.

MEMS (microelectromechanical systems) or nanotechnology is expected as one of the most promising R&D fields for the future business success, as MEMS or nanotechnology has a variety of applications from electronics to bio-technology. However R&D investment to MEMS facility is too heavy even for the large scale companies. Although MEMS foundry services by private companies have been introduced in these five years in Japan, their targets are not small batch production or R&D but mainly large or middle batch production. The number of products of the most MEMS applications is now limited and not enough to be called as "mass production" level except for automobile sensors and ink-jet heads. The above mentioned is the reason why AIST has started R&D activities and services for MEMS commercialization. The activities include foundry service to promote MEMS industry, R&D on Desktop MEMS or Nano Factory. MEMS foundry activities in AIST are described in "MN-One" strategy with special emphasis laid on cost effective micro/nano fabrication and new materials integration to MEMS with rapid realization of new ideas by collaboration. Desktop MEMS and nano factory concept is proposed and the desktop prototypes of EB writing machine and nanoimprint machine are presented. This is mainly targeted for reduction of R&D cost and time, and eventually the speedy realization of ideas to be a winner in high technology based business.

Piezoelectric thin film (PTF) materials present a number of unique properties in different applications, such as high sensitivity for micro electro mechanical systems (MEMS) microphones, and a wide dynamic range, wide displacement and low power consumption for MEMS speakers. Generation and detection of acoustic vibration can be made by piezoelectric devices which use the effects of direct piezoelectricity and inverse piezoelectricity. This paper covers popular PTFs and their applications for acoustic MEMS: lead zirconate titanate (PZT) based thin films and lead free PTFs such as aluminum nitride (AIN), zinc oxide (ZnO) and scandium doped aluminum nitride (ScAIN). The design, vibration mode, and fabrication will determine the frequency range of the acoustic MEMS devices. The performance and properties of PTF are the main parameter for certain MEMS applications are introduced. The main ideas of piezoelectric materials are reviewed and introduced for acoustic MEMS transducers.

Vacuum packaging is very important for some micro-electro-mechanical systems (MEMS) devices to perform their basic functions properly and to enhance their reliability by keeping these devices away from harmful external environment. In order to maintain high vacuum in a cavity of MEMS devices, residual gases and leaking gases must be eliminated by embedded getter materials. Micro/Nano film getters absorbing gases inside the tiny cavity of MEMS packaging were introduced in this paper. The fabrication and characterization of micro/nano getters for MEMS applications were also presented. Various kinds of patterned getter films were prepared for different MEMS applications. The activation temperature and sorption capacity of the nonevaporable getter (NEG[1]) films was investigated. The formation of micro/nano films on the inner surface of MEMS devices is totally compatible with Si-based MEMS process and illustrates the applicability of the technique in vacuum maintenance of MEMS devices.

This paper presents two robust microtransfer printing methods, namely, multiple transfer printing and peeling microprinting methods, to fabricate three-dimensional (3-D) and high-aspect-ratio microelectromechanical systems (MEMS) structures over large areas on flexible polydimethylsiloxane (PDMS) substrates. These techniques enable conformal wrapping of 3-D microstructures, initially fabricated in two-dimensional (2-D) layouts with standard fabrication technology onto a wide range of surfaces with complex and curvilinear shapes. The processes exploit the differential adhesive tendencies of the microstructures formed between a donor and a transfer substrate to accomplish an efficient release and transfer process. Experimental and theoretical studies show that the MEMS structures with a wide variety of pattern densities can be conformally transferred to bendable device substrates while keeping the structural integrity and density intact. Quantitative stress analysis on the micromechanics of such a curvilinear system suggests that the stress induced by wrapping the complete structure onto a cylinder is mostly in the flexible PDMS substrate, while the MEMS structures experience little stress.

MEMS sensors gained over the last two decades an impressive width of applications: (a) ESP: A car is skidding and stabilizes itself without driver intervention (b) Free-fall detection: A laptop falls to the floor and protects the hard drive by parking the read/write drive head automatically before impact. (c) Airbag: An airbag fires before the driver/occupant involved in an impending automotive crash impacts the steering wheel, thereby significantly reducing physical injury risk. MEMS sensors are sensing the environmental conditions and are giving input to electronic control systems. These crucial MEMS sensors are making system reactions to human needs more intelligent, precise, and at much faster reaction rates than humanly possible. Important prerequisites for the success of sensors are their size, functionality, power consumption, and costs. This technical progress in sensor development is realized by micro-machining. The development of these processes was the breakthrough to industrial mass-production for micro-electro-mechanical systems (MEMS). Besides leading-edge micromechanical processes, innovative and robust ASIC designs, thorough simulations of the electrical and mechanical behaviour, a deep understanding of the interactions (mainly over temperature and lifetime) of the package and the mechanical structures are needed. This was achieved over the last 20 years by intense and successful development activities combined with the experience of volume production of billions of sensors. This chapter gives an overview of current MEMS technology, its applications and the market share. The MEMS processes are described, and the challenges of MEMS, compared to standard IC fabrication, are discussed. The evolution of MEMS requirements is presented, and a short survey of MEMS applications is shown. Concepts of newest inertial sensors for ESP-systems are given with an emphasis on the design concepts of the sensing element and the evaluation circuit for achieving excellent noise performance. The chapter concludes with an outlook on arising new MEMS applications such as energy harvester and micro fuel cells.KeywordsPorous SiliconAngular RateInertial SensorAcceleration SensorElectronic Stability ProgramThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Chemical warfare agent sensor using MEMS structure and thick film fabrication method

This review article through light on a highly promising & demanding technology, which is set to revolutionize nearly every product category in present era, while discussing the Concept, Design & Development, Fabrication techniques and applications of micro electro-mechanical systems (MEMS) based Devices or systems. Microelectromechanical system discloses outstanding flexibility and adaptability in miniaturization devices followed by their compact dimension, low power consumption, and fine performance. The MEMS devices have numerous and very high potentials of creating a new field of applications for mobile equipment’s with increased flexibility & more reliability. This work deals with research carried out for the development of MEMS based sensors & Actuators and appropriate uses of MEMS. This work carries information’s regarding subsequent commercial and real life applications of MEMS and discusses various recent technological innovations carried out with their advantages & disadvantages. This work also describes the historical development of micro-electromechanical system (MEMS) sensor technology.

The application of micro electromechanical systems (MEMS) technology in several consumer electronics leads to the development of micro/nano power sources with high power and MEMS integration possibility. This work presents the fabrication of a flexible solid-state Li-ion battery (LIB) (~2.1 μm thick) with a design towards electrodes electrical insulation, using conventional, low cost and compatible MEMS fabrication processes. Kapton® substrate provides flexibility to the battery. E-beam deposited 300 nm thick Ge anode was coupled with LiCoO2/LiPON (cathode/solid-state electrolyte) in a battery system. LiCoO2 and LiPON films were deposited by RF-sputtering with a power source of 120 W and 100 W, respectively. LiCoO2 film was annealed at 400 °C after deposition. The new design includes Si3N4 and LiPO thin-films, providing electrode electrical insulation and a battery chemical stability safeguard, respectively. Microstructure and battery performance were investigated by scanning electron microscopy, electric resistivity and electrochemical measurements (open circuit potential, charge/discharge cycles and electrochemical impedance spectroscopy). A rechargeable thin-film and lightweight flexible LIB using MEMS processing compatible materials and techniques is reported.

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.

In Microelectronic and MEMS (Micro-Electro-Mechanical Systems) applications the volume of solder joints decreases rapidly due to higher packaging density. In recent years, many solder alloys have been developed and used. Many of lead-free-solders show a complex material behaviour due to different mechanical and thermal properties throughout the sandwich which can influence the mechanical and thermal reliability as well as the life time. For this reason, ensuring the solder joint reliability is one of the most critical design aspects of electronic assemblies. To predict the failure of solder joints with the help of the FE-Simulations tools, the description of solder behaviour is needed. The mechanical behaviour of solder is non-linear and temperature dependent. Solder alloy in consideration are above 0.5 of their melting point at − 40°C, so creep processes are expected [1,2]. The failure behaviour of solder is a complex sequence and depends on microstructures, like grain coarsening, micro-voiding, recrystallization, micro-cracking and macro-cracking on alloying content, soldering temperature profile and dissolution of metallizations. Changes of the microstructure can significantly effect the mechanical properties of the solders. Inhomogeneity of solders, espacially of Sn-based lead free solders, can cause local fatigue driven multiple cracking (3,4). Furthermore, plate-like intermetallic compounds (IMC) may cause crack initiation and brittle fracture at interface to metallization, especially if the joint thickness becomes comperable to the IMC-thickness respectively (Figure 1).

Stress distribution is one of the main factors influencing the reliability of MEMS (Micro Electro Mechanical System) structure. In most cases, MEMS devices work in motion state, the dynamic stress often affects the performances of the MEMS devices. For the first time, dynamic streses were measured by means of Raman spectroscopy and high-frequency modulation technology, the measurement result shows that dynamic stress at a certain point in silicon micro-resonator is in agreement with the analysis of theory.

Permanent magnet films for applications in microelectromechanical systems

Polymers such as PC (polycarbonate), PMMA (poly methyl methacryate) and SU-8 epoxy resin are replacing silicon as the major substrate in microfluidic system (or BioMEMS) fabrication. Chemical mechanical polishing (CMP) is an important technology for many advanced microelectromechanical system (MEMS) and micro-optoelectromechanical system applications. In this study, CMP of PC, PMMA and SU-8 polymers was investigated. Four types of slurry were tested for CMP of PC and PMMA. Experiments were then designed and performed to investigate effects of two key process parameters. The experimental results show that an increase in head load or table speed would cause an increase in material removal rates (MRRs). Within the chosen experimental parameter ranges, the variation of table speed introduced a more significant change in MRRs than that of head load. ANOVA was also carried out, and it was found that the interaction of head load and table speed had a significant (95% confidence) effect on surface finish of polished PMMA samples while table speed had a significant effect on surface finish of polished PC samples. CMP is also a process well suited for polishing high-aspect-ratio SU-8 structures. Polished PC, PMMA and SU-8 surfaces had nanometer-order surface roughness, acceptable to most MEMS applications.