Rotary electrostatic micromirror switches using wafer-scale processing and assembly

The design, micromachining process, wafer-scale assembly, and experimental characterization of our rotary electrostatic micromirrors for optical switching applications are reported in this paper. Some of the proposed microelectromechanical systems (MEMS) optical switches utilize surface-micromachined thin films as the reflection micromirrors which might result in optical degradation due to dynamic warping. Some of these devices fabricated by bulk micromachining highly rely on a delicate post-assembly process to assemble the micromirrors onto the top of MEMS actuators. In this research, we focus on developing rotary electrostatic micromirror switches without the requirement of delicate post-assembly processes. We use the spin-on-glass, which is used as an intermediate layer in a 280°C low-temperature wafer-bonding process, to fabricate our rotary optical switches with a wafer-scale assembly process. The rotary electrostatic actuator and the vertical micromirror are fabricated simultaneously by the same deep RIE process in our design. We have successfully demonstrated the rotary electrostatic micromirror switches via the wafer-scale assembly process with a yield rate of above 70%. Experimental results show that our rotary vertical micromirrors rotate about 1.5° under an applied voltage of 150 V for steady-state measurements. For dynamic measurements, the rotary vertical micromirrors rotate about 3.6° under an applied voltage of 30 V at the resonant frequency. The first vibration mode of our rotary switch is an in-plane rotational mode and appears around 3.4 kHz, which is characterized via a Polytec laser doppler vibrometer.

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Development of Multi Micro Manipulation System Using IPMC Micro Grippers

This paper presents a new design of multi micro manipulation system using ionic polymer metal composite (IPMC) micro grippers for robotic micro assembly where IPMC is used as a light weight actuator for developing the micro grippers. It has the potential of large displacement, low mass force generation and misalignment compensation ability during micro manipulation. These capabilities are utilized for handling of miniature parts like pegs. The analysis of IPMC micro gripper and manipulator are carried out for developing a multi micro manipulation system that can handle pegs in micro assembly operation for shifting one to another hole position in a large work space (100 mm × 100 mm). By developing a prototype, it is demonstrated that IPMC based micro grippers are capable of handling the peg-in-hole assembly tasks in a multi micro manipulation system.     

An Electrothermal Tip–Tilt–Piston Micromirror Based on Folded Dual S-Shaped Bimorphs

This paper presents the design, optimization, fabrication, and test results of an electrothermally actuated tip-tilt-piston micromirror with a large optical aperture of 1 mm. The fabrication of the device is a combination of thin-film surface micromachining and bulk silicon micromachining based on silicon-on-insulator wafers. The device has 3-DOF of actuations, including rotations around two axes in the mirror plane, and out-of-plane piston actuation. The micromirror shows an optical scan range of plusmn30^deg about both x- and y-axes and displaces 480 mum in the z-axis, all at dc voltages that are less than 8 V. Dynamic testing of the micromirror shows that the thermal response time of each actuator is about 10 ms. Resonant frequencies of the piston and rotation motion are 336 and 488 Hz, respectively. The unique structural design of the device ensures that there is no lateral shift for the piston motion and no rotation-axis shift for the rotation scanning. With the large tip-tilt-piston scan ranges and low driving voltage, this type of device is very suitable for biomedical imaging and laser beam steering applications.     

Integrated Design of an Ionic Polymer–Metal Composite Actuator/Sensor

We are studying the robotic application of ionic polymer–metal composite (IPMC). The characteristics of IPMC greatly depend on the type of counterions, and it is considered that the performance of the actuators can be improved by combining the actuators with several types of counterions and applying an integrated control. IPMC also has a sensor function, as the IPMC film generates an electromotive force when it is deformed. It has the possibility to be integrated into an IPMC actuator with soft actuation. In this paper, we consider an integrated design of an IPMC actuator/sensor, and investigate control of the combined IPMC actuators using H _∞ control and the construction of an IPMC sensor system.     

Fabrication and characterization of a piezoelectric micromirror using for optical data tracking of high-density storage

A micromirror actuated by three piezoelectric microcantilevers is presented for optical data tracking of high-density storage application. The microcantilevers are actuated by 2.5-μm-thick lead zirconate titanate (PZT) films which are deposited on the silicon-based substrate by a compatible sol–gel route. The X-ray diffraction result shows that the PZT film is perovskite structure and has a typical good ferroelectric loop. The quasi-static displacement of the mirror plate increases linearly with increasing the driving voltage and the tracking resolution on disk is as high as 8 nm/V. The micromirror also provides a high bandwidth of about 21 kHz, which is high enough to support the optical data tracking of future high-density storage.     

Doping effects on robotic systems with ionic polymer–metal composite actuators

Ionic polymer–metal composite (IPMC) materials are one of the most promising electro-active polymer actuators for applications, and have good properties of response and durability. The characteristics of IPMC materials depend on the type of counter-ion. When applied to mechanical systems such as a robot, there exist possibilities to change the properties of the system dynamics by changing the counter-ions and system parameters according to the environment or purpose. We focus on this 'doping effect' property of the system and will verify the effect on robotic applications. In this paper, we consider dynamic walking of a small-sized biped robot and swimming motion of a snake-like robot, and demonstrate the doping effects by numerical simulations and experiments.     

Analysis of electro-active polymer bending: A component in a low cost ultrathin scanning endoscope

The development of a low-cost active tip bending system for a scanning fiber endoscope or catheterscope has been initiated and proof-of-concept fabrication and testing have been conducted. The actuator material chosen for the design is an ionic conductive polymer metal composites (IPMC) type electro-active polymer (EAP). IPMC materials are inexpensive, especially in small sizes required for ultrathin scopes, allowing the possibility of an active-bending mechanism for the single-use endoscope. The charge and the strain distribution across the 200 μm thick membrane are simulated using finite element analysis (FEA). The deformation results from the numerical analysis agree within 8.5% error of the experimental outcome. An IPMC strip actuator made from a Nafion^® membrane and a platinum-plating recipe is developed. The generative force of the actuator is measured and demonstrated to be sufficient to lift the rigid tip of the scanning fiber endoscope. Therefore, this IPMC material is a candidate to be used as a low-cost active bending mechanism for the ultrathin scanning fiber endoscopes and future catheterscopes.     

Microthermal sensors for determining fluid composition and flow rate in fluidic systems

To analyze fluid mixtures a simple and low cost measurement method is realized using a microthermal sensor that introduces a short heat pulse into the fluid under test whilst the resulting temperature increase reflects thermal parameters of the fluid. For methanol in water this principle showed an almost linear dependence of the temperature increase on the methanol content for the volume concentration range 0–20 %. The sensitivity was determined to S = 0.19 K/(% (V/V)) for a heat pulse of 0.5 s duration and a heater power of 30 mW. The accuracy achieved in stopped-flow single pulse measurements is ~0.5 % (V/V). By integrating additional temperature sensors in front and behind the microheater the flow rate of the liquid can also be determined using thermal anemometry. The low cost sensor construction and simple signal analysis make this principle promising for use in low cost mobile applications like DMFC power supplies for laptops.     

Design, Modeling, and Demonstration of a MEMS Repulsive-Force Out-of-Plane Electrostatic Micro Actuator

An analytical model is developed for a two-layer repulsive-force out-of-plane micro electrostatic actuator by using conformal mapping techniques. The model provides the means to establish the performance characteristics in terms of stroke and generated force of the actuator and is used to develop design and optimization rules for the actuator. Numerical simulations were conducted in order to verify the analytical model. A simple physical model is also presented that explains the mechanism for generating the repulsive force. A Multi-User-MEMS-Processes repulsive-force out-of-plane rotation micromirror is developed to experimentally verify the analytical model and to demonstrate the repulsive-force actuator's capability of driving large-size rotation plates by using surface micromachining technology. Experimental measurements show that the repulsive-force rotation micromirror with a size of 312 mum times 312 mum achieved a mechanical rotation of 0deg-2.1deg at a dc driving voltage of 0-200 V. The micromirror achieved an open-loop settling time of 2.9 ms for a mechanical rotation of 2.3deg and an open-loop bandwidth of 150 Hz (-3 dB).     

Integration of optical waveguide on pneumatic balloon actuator for flexible scanner in endoscopic imaging diagnosis applications

This paper reports a flexible scanner consisting of a scanning actuator and optical waveguides for medical imaging applications such as endoscopic fluorescence imaging diagnosis. The 0.3-mm-thick and 5-mm-wide functional scanner was designed to be smaller enough than the 10 mm-diameter of channel of endoscope. The proposed device can be used to introduce an excitation light into the abdominal cavity or digestive tract. A pneumatic balloon actuator (PBA) consisting of polydimethylsiloxane (PDMS) is used as the scanning actuator for the scanner in consideration of its small, soft, and safe features. The SU-8 optical waveguides with high refractive index (n_SU-8 = 1.575) are integrated onto the PBA structure made of PDMS with a lower refractive index (n_PDMS = 1.405). Excitation light at a wavelength of 405 nm is transmitted through an optical fiber to the SU-8 waveguides. The outgoing light from the waveguide can be scanned by the bending motion of the PBA. The waveguide functions as a detector as well. Our developed device has successfully scanned, excited, and detected light from fluorescence beads at a wavelength of 540 nm distributed in a pseudo-tissue.     

Design and modeling of a novel RF MEMS series switch with low actuation voltage

This paper presents the design, analysis, modeling and simulation of a novel RF MEMS series switches with low actuation voltage. A mechanical modeling is presented to describe the behavior of the series switch. The switch is designed with special mechanical structures. The novel mechanical and mathematical modeling of the switch leads to calculation of the accurate actuation voltage. The spring constant has been calculated in relation to the presence of the residual stress in the beam. The calculated spring constant for this beam is used to determine the accurate actuation voltage. The size of the switch is 60 × 110 µm². The designed RF MEMS series switch was simulated using Intellisuite MEMS tool. He calculated actuation voltage is 4.05 V and simulated one is 4.2 V for 0.6 µm beam thickness. The calculated result is also very close with simulated one. The proposed switch compared with other electrostatic switches has low actuation voltage and small size. The RF characteristics were simulated using HFSS software and the switch has good RF performance. The insertion loss of 0.067 dB, return loss of 26 dB and isolation of 16 dB were achieved at 40 GHz.     

Electro-chemical operation of ionic polymer-metal composites

Currently, there is a major engineering challenge associated with ionic polymer-metal composites (IPMCs) that needs to be resolved before they can be vastly adopted in current and future engineering markets—relaxation of the IPMC actuator under a DC voltage. In this article, we rigorously discuss the potential origin of the relaxation phenomena of IPMCs that can be related to electro-chemically induced surface reactions with electrodes. Our measured voltammograms and deflection data of IPMCs revealed that the relaxation phenomena of the IPMC actuators are primarily caused by the overpotential of the surface electrodes. The overpotential values of ca. +1 V were clearly noted for many IPMC samples. We believe that the relaxation of IPMCs originate from the platinum oxide formation during actuation—a key surface reaction. The IPMC solvated with a typical ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF₆]) as a solvent, showed a larger bending, but there was no relaxation during actuation because there was no platinum oxide formation.     

Electromagnetically actuated biaxial scanning micromirror fabricated with silicon on glass wafer

In this paper, we present an electromagnetically actuated two-axis scanning micromirror with large aperture and tilting angle for laser pointing applications. The two-axis micromirror with the plate size of 3 mm in diameter was realized using gimbaled single crystal silicon with a single-turn electroplated copper coil, and it was assembled with permanent magnets forming radial magnetic field. The micromirror was fabricated on SiOG (Silicon on Glass) wafer using 4 photolithography masks. The permanent magnet assembly composed of a cylindrical and a ring-type magnet was designed to optimize the radial magnetic field, and thus maximize the torque on the coil. Three different magnet assemblies were applied to the fabricated micromirror in order to verify the design. Horizontal resonance frequency of the fabricated micromirror was measured 1.421 kHz and vertical resonant frequency was 396 Hz. The vertical scan angle was 16.87°, 26.32° and 22.61° with the cylindrical magnet diameter of 2.6, 4.0 and 4.8 mm, respectively, at 60 Hz sinusoidal input of 640 mA_pp. For horizontal scan, maximum scan angle of 24.45° was obtained at 48 mA_pp input signal in resonance mode. In addition, the temperature distribution on the micromirror surface was measured with the applied current to the coil.

     

High fill-factor two-axis gimbaled tip-tilt-piston micromirror array actuated by self-Aligned vertical electrostatic combdrives

In this paper, we present a high fill-factor micromirror array actuated by self-aligned vertical electrostatic combdrives. To meet the requirements of applications in free-space communication and imaging, each micromirror has three degrees of freedom of motion: rotation around two axes in the mirror plane and linear translation perpendicular to the mirror plane. Our approach is to integrate the high fill-factor reflectors into the fabrication process of the actuators on the wafer-scale. Multilevel silicon-on-insulator (SOI) bonding is utilized to form the high optical quality reflectors and high aspect-ratio vertical combdrive actuators. The wiring for electrical access to the multielectrode per pixel array is fabricated on separate wafers by thin film processing, and flip-chip bonded to the reflector/actuator chip. This architecture overcomes the fill-factor limitation of top-side accessed electrical addressing of mirrors made on SOI. Our 360/spl mu/m pixel size mirror array achieves a 99% fill-factor with optically flat reflectors.     

Development and evaluation of a Venus flytrap-inspired microrobot

Nature has provided the inspiration for many robots, leading to the development of biomimetic machines based on stick insects, jellyfish, butterflies, lobsters, and inchworms. Some carnivorous plants are capable of rapid motion, including mimosa, Venus flytraps, telegraph plants, sundews, and bladderworts, all of which are of interest in the design of biomimetic robots that can be activated in a controlled manner to capture prey using trigger hairs. Here, we describe a biomimetic robotic inspired by a Venus flytrap and fabricated using two ionic polymer metal composite (IPMC) actuators. First, we describe the structure of the robotic flytrap, which consists of two IPMC lobes and a proximity sensor, and discuss the design of the control circuitry. We then evaluate the deformation and bending force of the IPMC actuator with various applied signal voltages. We describe a prototype robotic flytrap utilising a proximity sensor to imitate the trigger hairs of the Venus flytrap. We conducted an experiment to assess the feasibility of the biomimetic flytrap. To evaluate grasping ability, we measured the maximum grasping payload with different applied voltages. To enlarge the working area, we integrated biomimetic walking and rotating motion into the robotic Venus flytrap. This paper describes a prototype movable robotic Venus flytrap and evaluates its walking and rotating speeds.     

Fabrication of micro-gelatin fiber utilizing coacervation method

Biotechnology has drastically been advanced by the development of iPS and ES cells, which are representative forms induced pluripotent stem cells. In the micro/nano bio field, the development of cells and Taylor-made medicine for a potential treatment of incurable diseases has been a center of attention. The melting point of gelatin is between 25 and 33 °C, and the sol–gel transition occurs in low temperature. This makes the deformation of this useful biomaterial easy. The examples of gelatin fiber applications are suture threads, blood vessel prosthesis, cell-growth-based materials, filter materials, and many others. Because the cell size differs depending on the species and applications, it is essential to fabricate gelatin fibers of different diameters. In this paper, we have developed a fabrication method for gelatin fibers the coacervation method. We fabricated narrow gelatin fibers having a diameter over 10 μm.     

Design,fabrication and characterization of a low-noise Z-axis micromachined gyroscope

This paper presents the design, fabrication and characterization of a low-noise Z-axis micromachined gyroscope. A triple-mass scheme is adopted to obtain a decoupled mode and matched vibration structure. The gyroscope was fabricated based on a 30-μm silicon on insulator wafer. A DRIE, lag-effect-based, dicing-free process was used to easily and rapidly create the gyroscope devices without requiring normal dicing. The fabricated gyroscopes were vacuum packaged (pressure of approximately 2,000 Pa) and tested. The measured power spectral density of the noises is as low as 17.5 μV/√Hz, and the resolution of the fabricated gyroscope is 7.1 × 10–4°/s/√Hz (2.52°/h/√Hz).     

Development of copper based miniature electrostatic actuator using WEDM with low actuation voltage

Fabricating electrostatic micro actuator, such as comb-drive actuator, is one of the demanding areas of the MEMS technology because of the promising applications in modern engineering, such as, micro-switches, attenuators, filters, micro-lenses, optical waveguide couplers, modulation, interferometer, dynamic focus mirror, and chopper. For the fabrication, most of the cases silicon monocrystalline wafers are used through complex process. To etch the silicon substrates, researchers often use deep reactive-ion etching or anisotropic wet etching procedure which are time consuming and unsuitable for batch fabrication process. Again, resent research shows that comb-drive actuators need comparatively high voltage for actuation. In solving these problems, the study presents a copper based electrostatic micro actuator with low actuation voltage. Using wire electrical discharge machine (WEDM), the actuator is fabricated where a light weight flexible spring model is introduced. Capacitor design model is applied to present a voltage controlling electronic circuit using Arduino micro controller unit. The experimental result shows that the actuator is able to produce 1.38 mN force for 15 V DC. The experiment also proves that coper based actuator design using WEDM technology is much easier for batch processing and could provide the advantages in rapid prototyping.     

Design of swing arm type actuators considering thermal and dynamic characteristics

The present state of the design of swing arm actuators for optical disc drives is to obtain the highly efficient dynamic characteristics within a very compact volume. As a necessary consequence, the need of the small form factor (SFF) storage device has arisen as a major interest in the information storage technology. Due to the size constraint, the thermal stability of the optical pick-up head is important: therefore, the actuator is designed to emit the heat, which is generated by the optical pick-up, along the structural body easily. In this paper, we suggest the miniaturized swing arm type actuator that has effective heat emission quality as well as satisfies the dynamic requirements for the SFF optical disk drive (ODD). The actuator is targeted to be installed in CF-II card size drive to be competitive with flash memory or mini hard disk drive used in mobile electric devices; therefore the dimension of the actuator is required as 11.0 mm × 2.5 mm × 25.0 mm (width × height × length). Because of its small size, the dynamic requirements are severe to ensure the enough gain-margin for the system control together with satisfying the DC/AC sensitivity conditions. Moreover, due to the small size, the maximum pick-up temperature is critical in design because the system has high possibility to reach the shut-down temperature. For the operating mechanism, it uses a tracking electromagnetic (EM) circuit for the focusing motion together and the initial model is designed and promoted by the design of experiments (DOE) only considering the dynamic characteristics. New concept design is suggested based on the topology optimization method considering the thermal conductivity. Furthermore, the new design is modified by DOE to maintain the high sensitivity and to have wide control bandwidth and decreasing mass and inertia. The final design of a swing arm type actuator for SFF ODD is suggested and its dynamic characteristics are verified.     

Design, Fabrication, and Characterization of a High Fill-Factor, Large Scan-Angle, Two-Axis Scanner Array Driven by a Leverage Mechanism

We report on the design, fabrication, and characterization of a high fill-factor, large scan-angle, two-axis scanner array. The two-axis microelectromechanical-systems (MEMS) mirror is driven by electrostatic vertical comb-drive actuators through four motion amplifying levers. The maximum mechanical rotation angles are$pm 6.7^circ$at 75 V for both axes, leading to total optical scan angle of 26.8$^circ$. The resonant frequency is 5.9 kHz before metallization. A linear fill factor of 98% is achieved for the one-dimensional (1-D) micromirror array. This 1D array of two-axis micromirrors was designed for$1times N ^2$wavelength-selective switches (WSSs). In addition to two-axis rotation, piston motion with a stroke of 11.7$mu m$is also attained.1731