Hiroki Kuwano

Electromagnetic microrelays : concepts and fundamental characteristics

Abstract An electromagnetic microrelay is proposed as a practical application of microelectrochemical system (MEMS) technology and the basic performance of its key components is evaluated. The contact resistance and breakdown voltage of contact electrodes are measured for very small loads and gaps. The static and dynamic deflection of the contact springs is measured for very small movements. Based on these experimental results, design guidelines for key components are proposed. Two prototypes that partly use MEMS technology are produced and their switching performance is demonstrated. One prototype uses a flat microspring with a length and width of 0.3 mm; its switching speed is more than ten times that of a conventional relay. The other is a 2×2 matrix relay, with four self-latching switches; each switch has two stable positions, open and closed, and is driven by a current pulse. This component study and prototype development verify the suitability of MEMS technology for mechanical relays.

Experimental Duffing oscillator for broadband piezoelectric energy harvesting

This paper presents an experimental piezoelectric energy harvester exhibiting strong mechanical nonlinear behavior. Vibration energy harvesters are usually resonant mechanical systems working at resonance. The resulting mechanical amplification gives an output power multiplied by the mechanical quality factor Q when compared to non-resonant systems, provided that the electromechanical coupling k2 is high as well as the mechanical quality factor Q. However, increasing the Q value results in a narrowband energy harvester, and the main drawback is the difficulty of matching a given vibration frequency range to the energy harvesters resonance frequency. Mechanical nonlinear stiffness results in a distortion of the resonance peak that may lead to a broadband energy harvesting capability while keeping a large output power as for high Q systems. This paper is devoted to an experimental study of a Duffing oscillator exhibiting piezoelectric electromechanical coupling. A nonlinear electromechanical model is first presented including piezoelectric coupling, a nonlinear stiffness as for a Duffing oscillator, and an additional nonlinear loss term. Under harmonic excitation, it is shown that for a particular excitation range, the power frequency bandwidth is multiplied by a factor of 5.45 whereas the output power is decreased by a factor of 2.4. In addition, when compared to a linear system exhibiting the same power bandwidth as for the nonlinear one (which is here 7.75%), the output power is increased by a factor of 16.5. Harmonic study is, however, partially irrelevant, because Duffing oscillators exhibit a frequency range where two stable harmonic solutions are possible. When excited with sine bursts or colored noise, the oscillator remains most of the time at the lowest solution. In this paper, we present a technique—called fast burst perturbation—which consists of a fast voltage burst applied to the piezoelectric element. It is then shown that the resonator may jump from the low solution to the high solution at a very small energy cost. Time-domain solution of the model is presented to support experimental data.

Simulation of a Duffing oscillator for broadband piezoelectric energy harvesting

Vibration energy harvesters are usually resonant mechanical systems working at resonance. The subsequent mechanical amplification results in output powers multiplied by the mechanical quality factor when compared to non-resonant systems. The main drawback is the difficulty of matching a given vibration frequency range to the energy harvesters resonance frequency. Among several techniques, the use of nonlinear mechanical resonators was proposed in several studies for enlarging energy harvester power bandwidth. In addition, microelectromechanical systems become nonlinear when driven even at moderate levels due to their small size. This paper is devoted to a theoretical study of a Duffing oscillator exhibiting piezoelectric electromechanical coupling. After presenting the dimensionless model, it is solved both in the frequency domain and in the time domain. The frequency-domain simulations show that a huge gain in bandwidth is possible when the resonator is highly nonlinear. Special attention has been paid to the influence of electromechanical coupling. However, this encouraging result is counterbalanced by the difficulty to make the resonator reach high level vibration. Indeed, the Duffing oscillator exhibits a frequency range where two harmonic solutions are possible. When excited with sine bursts or colored noise, the oscillator remains most of the time on the lowest solution. From simulations in the time domain, it is shown that fast burst perturbation (FBP) applied to the piezoelectric voltage may induce the jump from lowest solution to highest solution. Consequently a huge gain may be expected in output power. Finally, the resonator is excited with colored noise and the previously developed strategy is applied. Once again, the mean output power may be greatly enhanced.

Scanning near‐field optical microscope using an atomic force microscope cantilever with integrated photodiode

A combined atomic force and scanning near‐field optical microscope is presented. The critical component of the instrument is a single crystal silicon, microfabricated force‐sensing cantilever with an integrated photodiode. Near‐field optical images are obtained by monitoring variations in the optical power detected by the photodiode while the cantilever tip is scanned in an evanescent optical field created by illuminating the sample by total internal reflection. Near‐field optical power was detected at tip‐sample spacings of one‐quarter wavelength. Atomic force and scanning near‐field optical microscope images of the same samples show corresponding features as small as 25 nm.

Electromagnetic microrelays: concepts and fundamental characteristics

An electromagnetic microrelay is proposed as a practical application of microelectromechanical systems (MEMS) technology, and the basic performance of key components is evaluated experimentally and analytically. A 1-mm/sup 3/ relay target is the most practical and economical choice for electromagnetic actuation. As a first step in development, electrical characteristics of the electrodes, i.e., contact resistance and breakdown voltage, are measured at very small spacing and low contact forces. Next, mechanical characteristics of the moving parts, i.e., static and dynamic deflections of flat springs, are measured for very small loads and displacements. A miniature prototype having a spiral flat spring with a diagonal length of 0.5 mm was manufactured, and its basic switching performance was found to be more than ten times faster than conventional relays.<<ETX>>

Friction‐reducing coatings by dual fast atom beam technique

Friction‐reducing coatings were formed by the dual fast atom beam technique. The coatings were double‐layer films consisting of hard underlayers (B, TiB2, B4C, and BN) with an added upperlayer of MoS2 solid lubricant. The double‐layer solid lubricants had 50% lower friction coefficients than lubricant films alone, less than 0.01 and had high durability. The hard films obtained by the accelerated fast atom bombardment of their growth surface had either a single or polycrystalline structure, while those without bombardment had an amorphous structure. Feasibility of the double‐layer solid lubricants was demonstrated by fabrication (<40 g cm) double‐layer solid lubricant ball bearings which were tested up to 106 cycles and demonstrated a low (<40 g cm) motive torque under a 3‐kg load.

Electromagetically driven microvalve

We discuss photolithographic fabrication techniques and experimental results for a prototype electromagnetically driven microvalve. The valve is constructed on a silicon substrate, using a magnetic suspension spring with a valve cap, a valve plate with a 30 μm diameter bore, and an external coil for driving the valve cap. The external electromagnetic drive approach was chosen for its ease of use and practicality in controlling the valve actuator. The valve cap, made of soft magnetic material (NiFe) and supported by the spring, moves vertically as a result of the magnetic field applied by the external coil. To precisely adjust both the valve cap and the valve plate bore and to minimize fluid leakage, a new self-alignment process was developed. The valve is controlled by a 0.1–100 Hz rectangular magnetic field applied by the external coil. The resulting minimum gas flow rate can be controlled to within the neighborhood of 3 × 10−5 torr·l/s.

Magnetic micro-actuator

The characteristics of three types of magnetic microactuators made by silicon-based microfabrication are described. The microfabrication, actuator configuration, and dynamic characteristics of a fabricated microactuator with a planar coil are examined. This microactuator is shown to operate in the nanometer range. It has a conical soft-magnetic tip 10 microns high with a one-turn copper coil. This actuator will be applied to microvalves, micropumps, and microsyringes.<<ETX>>

Resistivity and morphology of TiSi2 formed on Xe+-implanted polycrystalline silicon

Xe ion irradiation of polycrystalline silicon before Ti deposition is found to affect subsequent silicide formation. Silicide films were prepared by implanting 60, 100, or 240 keV Xe+ ions into 500‐nm‐thick undoped polycrystalline silicon before depositing Ti and annealing in vacuum. Preimplantation altered the subsequent silicide resistivity, x‐ray diffraction patterns, and morphology as compared to films prepared on unimplanted polycrystalline Si substrates. We found that minimal TiSi2 resistivities were achieved at lower temperatures with preimplantation, indicating that the Xe‐implanted substrate promotes a lower temperature transition from the metastable C49 phase to the low‐resistivity equilibrium C54 phase of TiSi2. X‐ray diffraction results confirmed the lower temperature formation of the C54 phase with preimplantation. Low‐temperature annealing (650 °C, 30 min) of 6×1016 cm−2, 240 keV Xe+‐implanted samples yielded low‐resistivity (∼22 μΩ cm) silicide films, while simultaneously annealed samples w...

Dry Development of Resists Exposed to Focused Gallium Ion Beam

This report proposes a new lithography method employing focused ion beam exposure and subsequent dry development. It is shown that the plasma etching rate of resists exposed to gallium ions is much lower than that of resists not exposed. As this characteristic is applied to resist lithography, fine patterns can be obtained successfully. This dry development is applicable to many kinds of resist, such as PMMA, CMS, PGMA, FBM etc.