Permanent magnet films for applications in microelectromechanical systems

For the MR strips stabilized by the permanent magnet films, we numerically analyze the effects of the leakage field of the permanent magnet films on the bias angle in the MR films. Using the magnet films as the domain control films, magnetization rotation in the MR films at the track edges is suppressed by their leakage fields and will in turn decrease the effective track width. The decrease effective track width is thought to be due to the large leakage field especially at the track edges, so we examined some cases of decreasing the leakage field at track edges. Among the cases, the effective track width was most effectively enlarged when the distance between the magnet films was widened compared with the spacing of the leads. >

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.

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).

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.

We are interested in the deformation of a thin magnetoelastic film. This has many possible applications, such as in microfluidic actuators and sensors. In previous articles a finite element method has been used for transient simulation of the deformation of a film, for the special case of soft magnetic material only. Here the approach is extended to the case of permanent magnetoelastic materials. The key enhancements required for simulation of magnetoelastic materials are a nonlinear hyperelastic Mooney-Rivlin material model, addition of an implicit system of equations for the scalar magnetic potential, and a more complex asymmetric Maxwell stress tensor. A simple test problem was constructed, and simulations for a soft magnetic film and a permanent magnetic film are compared.

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.

Microelectromechanical systems (MEMS) have found several applications in various fields from homeland security to personalized health care. However, rendering MEMS into autonomous wireless systems operating in any given environment requires the integration of energy harvesters into the MEMS structures, ensuring thus the self-powering of the devices. In this work, we investigated the mechanical and magnetic properties of Samarium Cobalt (SmCo) thin films, with the goal to implement them into electromagnetic energy harvesters. The films were deposited by sputtering on suspended silicon cantilevers fabricated with a front-side micromachining process. The magnetic films, grown under various pressures and thermally annealed at several temperatures and ambient conditions, were studied in terms of their mechanical and magnetic properties. Depending on the fabrication parameters, the stresses that developed in the magnetic material, deposited on top of the cantilevers, are altered from compressive (downward deflection of the cantilevers) to tensile (upward deflection), indicating that it is possible to control not only the magnetic properties of the films, but also the mechanical properties of the complete structure. Our results suggest that SmCo magnetic films are suitable candidates for integration in suspended structures for the development of electromagnetic micro-generators.

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.

Electroplating of nanocrystalline NiFe and NiFeW thin films were successfully carried out on the copper substrate from ammonium citrate bath at a current density of 1 mA/dm2 and controlled pH of 7 with constant bath temperature. The magnetic and corrosion properties were studied using VSM and electrochemical techniques. The results of vibrating sample magnetometer for NiFeW nanocrystalline thin films reveal its soft magnetic properties such as coercivity and saturation magnetization. From the electrochemical studies, corrosion resistance and corrosion inhibition efficiency were calculated. The electrochemical studies of all the coated films reveal that the NiFeW thin film exhibits the enhanced corrosion resistance as compared with NiFe thin film which in turn enhances the soft magnetic nature of NiFeW thin films. Thus, the electroplated NiFeW thin films can be used for Microelectromechanical System (MEMS) and Nanoelectromechanical System (NEMS) applications due to their excellent magnetic- and corrosion-resistant behaviour.

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.

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.

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.

Micromachine technologies based on IC-compatible micromachining have advantages denoted by three M's'.Miniaturization is the most popular but Multiplicity, which means the batch fabrication capability of many complicatedelements, and Microelectronics to control motions or to add different functions such as the optical function are equallyimportant. This paper deals with the application of micromachine technologies to micro optical devices. A basic conceptmaking the best use of the advantages is proposed. Recent examples of optical microelectromechanical systems(MEMS) are reviewed. Keywords: MEMS, micromachine, optics, microactuator, LIGA process, silicon 1. INTRODUCTIONStudies on micromechanical systems(MEMS) have reached such stage that we can built three dimensional microstructures on a silicon substrate and operate micromotors/actuators without particular difficulty[1,2]. Now we mustidentify practical applications of MEMS in order to accelerate the development. Figure 1 shows application opportunities ofmicroactuators and MEMS[3J. Promising applications of MEMS for the near future will be in optics[4-40J, magnetic andoptical heads[1 1, 12], fluidics[13, 14], OA apparatus[15], the handling of cells and macro molecules[16,17}, and microscopywith microprobes{1&.'22] such as STMs (scanning tunneling microscopes) and AFMs (atomic force microscopes). Theseapplications have a common feature in that only very light objects such as mirrors, heads, valves, cells and microprobes aremanipulated and that little physical interaction with the external environment is necessary. One reason is that presentmicroactuators are still primitive and large forces cannot be transmitted to the external world. The other reason is difficulty inpackaging.All the mechanical work can be completed within a microsystem for optical applications. Non contact interfacingbetween the microsystem and the external world is possible. In addition, most of the optical components such as lasers,