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This paper reports on a 1D PZT micromirror integrated with buried piezoresistors for quasi-static feedback position control. The piezoresistors located along or below the PZT actuators could achieve the sensitivity as high as 3.1 mV/°, which was two orders of magnitude higher than the traditional ones located at the torsion springs (8.2 μV/°). This increased the signal-to-noise ratio by 2 orders of magnitude, which could enable the accurate position control. The response of the longitudinal sensors along the beams had a fast settling time less than 1 ms. The average position error was 0.975%, which was much better than that from the conventional shear stress sensor on the torsion bar of 3.1%.

In this study, we proposed an annular-shaped piezoelectric micromachined ultrasonic transducer (pMUT) based on a Pb(Zr,Ti)O3-based monocrystalline thin film. This pMUT is expected to increase the resonance frequency while maintaining displacement sensitivity, making it superior to an island-shaped pMUT, which is a conventional design. To demonstrate the validity of this assumption, annular- and island-shaped pMUTs with a 60 μm-diameter diaphragm were prototyped and characterized. As a result, the annular-shaped pMUT exhibited a resonance frequency of 11.9 MHz, a static displacement sensitivity of 2.35 nm V−1 and a transmitting figure-of-merit (FOM) of 28 nm MHz V−1. On the other hand, the island-shaped pMUT exhibited a resonance frequency of 9.6 MHz and a static displacement of 2.5 nm V−1 and an FOM of 24 nm MHz V−1. Therefore, the annular-shaped pMUT was experimentally demonstrated to provide a higher FOM compared to the island-shaped pMUT. In addition, the annular-shaped pMUT with the optimal dimensions is found to be able to keep a relatively large fabrication margin. This is an advantageous point for the practical device fabrication. We believe this design has a potential to become a standard design for high-performance pMUT devices.

In this paper, we report an actuator with a magnet made of novel rare earth magnetic powder Sm-Fe-N with diameter of 2 µm to 5 µm. Micro magnets were fabricated by mixing the magnetic powder with wax at temperature of 90 °C. Alignment of the easy axis process was employed to enhance the remanence of the micro magnets. A 8 T strong pulse magnetic field was utilized to magnetize the micro magnets. The properties of magnetic powder were revealed with vibrating sample magnetometer by measuring micro magnets with various magnetic powder weight loading percentages. In the best condition, the remanence reaches 0.9 T and the energy product reaches 70 kJ m−3. After that, the electromagnetic actuator was fabricated by embedding the magnetic powder in deep-reactive-ion-etched Si cavity with wax binder and parylene capping. The completed microelectromechanical system structure was mounted on a four-layer printed circuit board with embedded coils. Upon the application of a direct current for actuation, a displacement of 180 μm was obtained from a device volume of only 1.5 mm3 with a low actuation power consumption of 11.5 mW.

This paper describes a new design of piezoelectric micromachined ultrasonic transducer (pMUT) with a monocrystalline Pb(Zr,Ti)O3-based thin film (Mono-PZT) for enhancing the mechanical robustness. In this study, we investigated two design concepts to suppress crack generation in Mono-PZT. First, the area of Mono-PZT is limited by leaving an island Mono-PZT pattern only on the membrane of the pMUT. Second, the edge of Mono-PZT is covered with a polyimide (PI) thin film as a protection layer to prevent the peeling. We prepared three different designs, a new design with both concepts, another design with the first concept, and the conventional one with neither of them for comparison. The robust mechanical analyses of these devices were performed by driving resonantly and increasing the displacement of the membranes. As these results, the proposed structure with both concepts still stands well at the highest displacement, 1600 nm, while the undesired cracks occur on other structures with approximately 800 nm of displacement. The robustness could improve 50% in comparison to the other designs thanks to this unique design. Finite element method simulation results showed that this PI layer contributed to decrease the stress concentrated at the edge both in the static condition and in the dyanamic vibarion of the membrane. This layer also probably played a role in prevention of the peeling of the edge of the island-shaped Mono-PZT. In conclusion, the new design is useful for the Mono-PZT pMUT in terms of excellent mechanical robustness.

We developed a lead zirconate titanate (PZT) thin film actuator integrated with buried piezoresistors for the dynamic and static deformation sensing of a PZT MEMS actuator. We demonstrated the fabrication of sol-gel deposited PZT thin film devices combined with buried piezoresistors and proved, for the first time, the process compatibility of these materials. Dopant concentration measured by secondary ion mass spectrometry (SIMS) analysis confirms that the piezoresistor was successfully buried into the device. Motion detection of the fabricated MEMS cantilever actuated by the PZT thin film was successful and consistent with optical measurement as well as design values. From these results, we can conclude that our PZT actuator and piezoresistive sensors can be monolithically integrated. The fabrication process developed here can be used for high-stability piezoelectric MEMS actuators with feed-back control of position.

In this paper, a novel method to fabricate quartz glass electromagnetically actuated ring resonator for gyroscope application is presented. Sacrificial supporting structures were employed for the fabrication. The fabricated device was electromagnetically driven at resonance, with the resonant frequency of 42 KHz. The Q-factor at the atmospheric pressure was about 142. The frequency difference between primary and secondary mode was 681 Hz.

In this study, the performance of shrouded two-dimensional microimpellers was measured for application to a micro centrifugal pump used in a portable fuel cell system. Two types of microimpellers were designed, and fabricated by a multi-layer photolithography process using an ultrathick photoresist (SU-8 3000). Microimpellers with a diameter of 10 mm were tested using an air spindle up to maximum rotation speeds determined by the destruction of the microimpellers, which are 350 000 rpm for a purely-radial-outlet blade impeller and 450 000 rpm for a backward blade impeller. The purely-radial-outlet blade impeller showed a higher pressure rise—2.8 kPa at 150 000 rpm, 5.1 kPa at 200 000 rpm and 12.5 kPa at 300 000 rpm. The measured performance satisfies the requirement of the micro centrifugal pump. However, the measured pressure rises are roughly half of the simulated values. The influence of the radial clearance and height difference between the impeller and the diffuser was investigated using an electromagnetic motor and impellers with a diameter of 16 mm. Against expectation, a better pumping performance was obtained with a larger tip clearance, and the height difference did not affect the pumping performance. These unexpected results suggest that the tip clearance and the clearance between the impeller shroud and the stationary housing act as a diffuser.

This paper reports a novel method to produce high density feedthrough glass wafers with sufficient thickness for the packaging and interconnection of high density array micro electromechanical systems (MEMS). Pyrex glass wafers with thin film metal lines on the surface are stacked and bonded with each other using phenyl methyl siloxane-based adhesive. The stacked glass wafer block is then sliced using a wire saw as the slicing surfaces cross the adhesive bonding interfaces vertically. Prototyped feedthrough glass wafers were subjected to anodic bonding to a silicon wafer with diaphragms. The anodic bonding was successful, but hermetic sealing was not achieved. The bending of the bonded sample can be reduced by annealing the sample at 400 °C in a vacuum before anodic bonding.

The feasibility of a 100 W class micro-scale gas turbine with a centrifugal impeller of 10 mm diameter has been studied by experimentally verifying the four major component performance requirements found from cycle analysis. The rotor is required to rotate at 870 000 rpm to generate the compressor pressure ratio 3, and it has successfully been achieved by using hydroinertia gas bearings. A compressor efficiency higher than that required by the target cycle has been measured. After correcting the effect of the heat leakage, approximately 65% of the compressor adiabatic efficiency is estimated to be achievable. The combustor has achieved stable self-sustained combustion at a combustion efficiency higher than 99.9%. The heat conduction analysis based on measured data showed that it is possible to keep the compressor below 170 °C when the turbine inlet temperature is 1050 °C. All four requirements are proven to be achievable, and hence, the feasibility of the micro-scale gas turbine at an impeller of 10 mm diameter has successfully been proven at component level.

The microfuel reformer with a suspended membrane structure can realize excellent thermal isolation of the reaction area on the suspended membrane because heat conduction through the thin suspended membrane is quite small. However, it is difficult to form an effective catalyst selectively on the suspended membrane. The solution can be given by an in situ chemical vapor deposition (CVD) method by which alumina is deposited from an alumina precursor selectively on the suspended membrane heated by integrated micro-heaters. The deposits were evaluated by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDX). Self-sustaining hydrogen combustion was demonstrated on the deposited alumina catalyst bed with platinum. The heated area was localized just on the membrane, and temperature difference between the membrane and the bulk substrate reached 570 K, when the temperature of the membrane was 670 ?C. The maximum space velocity (SV) value allowable for the formed catalyst was approximately 680?000 h?1.

This paper describes the development of a micro fuel reformer integrated with a combustor and an evaporator. Fuel reforming tests were performed by using a mixture of methanol and water as reforming fuel and hydrogen as combustion fuel. It was found that the design of the microchannel evaporator is critical to obtain larger hydrogen output. Hydrogen output and CO concentration were investigated by varying the input combustion power at different fuel feeding rates. 32.9 sccm of hydrogen, which is equivalent to 5.9 W in lower heating value, was produced, when input combustion power was 11 W.

Two types of novel micro polymer electrolyte fuel cells (PEFCs) for distributed micro-sensors and wireless microelectromechanical systems (MEMSs) have been manufactured on silicon and glass substrates using MEMS technology. Several tests using single cells were performed to make any problems clear. The maximum power density was less than 100 μW cm−2, and deteriorated gradually during the operation. This was because a polymer electrolyte membrane (PEM) was swelled by water generated at the cathode, and peeled off from the catalytic electrodes. Another micro PEFC which has mechanically clamped electroless-plated membrane electrode assembly (MEA) stably showed much higher power density. From these results, it is concluded that a stable contact between the PEM and the catalytic electrodes is critical for MEMS-based PEFCs. Also, the cyclic voltammetry of a Pt film on porous SiO2, which is used in MEMS-based PEFCs, suggested that it had insufficient catalytic activity.

We microfabricated a MEMS (micro electro mechanical system)-based thin palladium (Pd) membrane microreactor with oxidized porous silicon (PS) support. The membranes were characterized by permeation experiments with hydrogen, nitrogen and helium at temperatures ranging from 200 °C to 250 °C. The hydrogen flux through the Pd membrane with a thickness of 340 nm was 0.112 mol m−2 s−1 at 250 °C and a partial pressure difference of 212 kPa. H2/N2 and H2/He selectivity was about 44 and 10 at 250 °C, respectively. The thermal isolation of the Pd membrane, which was heated by an integrated microheater, was realized by using the oxidized PS ring. We also carried out the hydrogenation of 1-butene at 250 °C using the developed microreactor. The conversion of 1-butene of 100% was obtained at low flow rate of 1-butene. The results show that microreactors have a potential to be used in hydrogen purification and hydrogenation.

Externally pressurized gas bearings with large bearing clearance are successfully used in ultra-high-speed micro spinners. For example, a micro spinner 4 mm in diameter is stably operated at more than 20 krps and its whirl ratio exceeds 20. In such bearings, the inertia effect of the gas flow in bearing clearance becomes predominant and its Mach number exceeds 1. As a result, gas pressure in the bearing clearance becomes negative. These bearings are called hydroinertia gas bearings, in contrast to the conventional hydrostatic gas bearings. Static characteristics of hydroinertia gas bearings are analyzed by considering the viscous effect of gas as wall friction, and the optimum design of hydroinertia gas bearings is shown. Experimental results on micro spinners and trial design of hydroinertia gas bearings for micro gas turbines are also discussed.

A micro-high-speed bearing test rig has been designed and fabricated to develop air bearings for a micro-machine gas turbine. The micro-machine gas turbine requires bearings of diameter 4 mm to operate stably at 870 000 rpm. Based on the preliminary analysis, it has been found that a large bearing gap and very high rotor balance are required to achieve low viscous loss at high speed and to prevent the rotor from hitting the bearing at critical speed. Therefore, a hydro-inertia gas bearing has been selected with half-split bearing sleeves. A hydro-inertia bearing is a type of static air bearing which has large bearing clearance to generate supersonic flow in the bearing gap. Currently, a rotor speed as high as 770 000 rpm has been achieved in the test.

A MEMS-based turbocharger with a novel configuration was developed and demonstrated. The compressor and turbine are installed on the same plane of the rotor. The advantages of this configuration include structural simplicity and good rotor balance. For the fabrication, we developed a special deep RIE condition to realize spike-free, uniform etching. And, we found a low wafer warp condition of five times of the anodic bonding. The device rotated at 50?000 rpm. The tip speed of the compressor approached 25 m s?1 and it is only a twentieth of the aimed tip speed. The device could not pass the natural frequency of the rotor. From the test results, we found some issues to be solved for high speed rotation. Concerning fabrication, the accurate manufacturing of bearing orifices, and a flat, uniform etched surface are required for the thrust bearing. A straight journal bearing wall is required for the hydrostatic journal bearing. Concerning bearing design, the journal bearing does not have sufficient stiffness or load capacity to support the centrifugal force of the rotor because of the remarkably short bearing length.

This paper describes a turbo test rig to test the compressor of a palmtop gas turbine generator at low temperature (

In this paper we describe silicon nitride (Si3N4) ceramic-based microdiffusion combustors with a two-dimensional structure, which is potentially batch-producible by microelectromechanical systems machining technology such as deep reactive ion etching. Si3N4 ceramic structures were fabricated by the nitridation of a spark-plasma-sintered silicon green compact after mechanical micromilling. Five types of combustor with a combustion chamber volume of 181 μl and depths of 1, 2 and 3 mm were tested. The combustors with combustion chamber depths of 2 or 3 mm achieved stable combustion at equivalence ratios from 0.28 to 1.3 and total flow rates from 4.0 to 11.3 SLM. They formed a flame at the center of the combustion chamber as designed, when the equivalence ratio was low. However, the combustor with a combustion chamber depth of 1 mm could not maintain a flame in the combustion chamber. This may be because combustion was not completed due to the shallow combustion chamber with a depth equivalent to the quenching distance of hydrogen.

This paper describes rotational infrared polarization modulators using a micro-electromechanical-system-based (MEMS-based) air turbine with different types of journal bearing. Three types of journal bearing, circular, symmetrical two-lobed and asymmetrical seven-lobed journal bearing, were compared. Using an optical displacement meter and a high speed camera, it was confirmed that all turbines exhibit three modes of rotation: (a) low speed mode, (b) intermediate mode and (c) high speed mode in this order, when decreasing N2 flow rate to an aerostatic thrust bearing. In the low speed mode, the rotor is lifted up by excess flow to the thrust bearing, making a contact with an upper layer. In the high speed mode, the rotor is levitated without any contact to the upper and lower layers by balanced flow to the thrust bearing, and the maximum rotational speed of 74000 rpm was achieved using the asymmetrical seven-lobed bearing. The rotation in this mode is, however, discontinuous due to the collision between the rotor and the journal bearing. It was concluded that a journal bearing with sufficient load capacity is necessary for continuous high speed rotation.

This paper reports an on-chip electrochromic micro display made of polyaniline (PANi) which can be easily made on a CMOS chip. Micro-patterned PANi thin films were selectively deposited on pre-patterned microelectrodes by using electrodeposition. The optimum conditions for deposition and electrochromism were investigated. An 8-pixel on-chip micro display was made on a Si chip. The color of each PANi film could be independently but simultaneously controlled, which means any 1-byte digital data could be displayed on the display. The PANi display had a response time as fast as about 100 ms, which means the transfer data rate was as fast as 80 bits per second.

In this paper, a stylus type MEMS texture sensor covered with a corrugated palylene diaphragm, which prevent debris from jamming into the sensor without significant degradation of sensitivity and bandwidth, was reported. A new fabrication process using a lost-foil method to make the corrugated diaphragm on a 3-axis piezoresistive force sensor at wafer level has been developed. The texture sensor could detect the surface microstructure as small as about 10 in lateral direction and 1.7 in vertical direction. The output signals from the sensor were repeatable, and the Z-axis signal was almost the same regardless of the moving direction, indicating that the hysteresis was small enough. In addiiton, the bandwidth as wide as 1.1 kHz and 500 Hz in lateral and vertical directions, respectively, were confirmed. The surface roughness and friction coefficient of various materials were successfully detected by the fabricated texture sensor.

This paper reports a micro thermal diode based on one-way working fluid circulation driven by surface tension force. In forward mode, working fluid evaporates and condenses at a heated and cooled area, respectively, and the condensed liquid returns to the evaporation area due to the wettability difference. By this vapor-liquid phase change mechanism, the overall heat transfer coefficient becomes high. On the other hand, in reverse mode, no continuous evaporation-condensation cycle exists. The conductive heat loss in reverse mode was minimized by an embedded glass thermal isolation structure, which makes overall heat transfer coefficient low. The test device was made by a standard MEMS process combined with glass reflow and gold bump sealing. The overall heat transfer coefficients of 13 300 for forward mode and 4790 for reverse mode were measured. The performance index of the micro thermal diode was about 2.8.

In this paper, a novel wafer-level hermetic packaging technology for heterogeneous device integration is presented. Hermetic sealing is achieved by low-temperature thermo-compression bonding using electroplated Au micro-sealing frame planarized by single-point diamond fly-cutting. The proposed technology has significant advantages compared to other established processes in terms of integration of micro-structured wafer, vacuum encapsulation and electrical interconnection, which can be achieved at the same time. Furthermore, the technology is also achievable for a bonding frame width as narrow as 30 μm, giving it an advantage from a geometry perspective, and bonding temperatures as low as 300 °C, making it advantageous for temperature-sensitive devices. Outgassing in vacuum sealed cavities is studied and a cavity pressure below 500 Pa is achieved by introducing annealing steps prior to bonding. The pressure of the sealed cavity is measured by zero-balance method utilizing diaphragm-structured bonding test devices. The leak rate into the packages is determined by long-term sealed cavity pressure measurement for 1500 h to be less than Pa m3s−1. In addition, the bonding shear strength is also evaluated to be higher than 100 MPa.

This paper reports an infrared-to-visible transducer array made of temperature sensitive paint (TSP) for a low-cost thermal imaging application. A novel fabrication process using a photo-patternable temperature sensitive paint (PTSP) combined with an SU-8 transfer method was developed. A PTSP microstructure as small as 2 μm was successfully patterned by the normal photolithography process, and sensitivity as high as −0.5%/°C was obtained. The proposed method simplifies the fabrication process, and prevents the TSP from plasma-induced damage. A self-suspended structure as small as 70 μm was successfully fabricated with a large-gap of 40 μm from the substrate. The heated object at 250 °C was detectable with a spatial resolution of about 380 μm.

This paper reports an uncooled infrared (IR) thermal imaging sensor using europium phosphor, Eu(TTA)3, as a temperature-sensitive medium. An Eu(TTA)3 thin film was evaporated and deposited on a thermally isolated microstructure made of SU-8. The temperature dependency of luminescence from Eu(TTA)3 was used to convert the IR radiation power into visible-light intensity, which can be captured and digitized by a charge-coupled device (CCD) camera. The temperature coefficient of luminescence from the evaporated Eu(TTA)3 was −2.1 ± 0.4% K−1. Thermal images of a heater at 75−370 °C were acquired via a Ge lens. The minimum detectable temperature, noise-equivalent temperature difference (NETD), and thermal response time were measured as 75 °C, 2.66 K at 370 °C, and 0.2 s, respectively.

This paper describes laser-assisted film transfer technology for barium strontium titanate (BST) deposited on a sapphire substrate. BST is a promising ferroelectric material for varactors, which are required for frequency-tunable RF applications. However, the deposition temperature of BST (600 ~ 700 °C) is too high for surface acoustic wave (SAW) substrates. In this study, BST grown on a sapphire substrate at 650 °C was transferred at low temperature (140 °C) to a borosilicate glass substrate as well as a LiTaO3 substrate. The transferred BST films were characterized as tunable capacitors. A key process in the BST film transfer technology is the laser pre-irradiation of a buffer Pt layer beneath BST from the backside of the sapphire substrate to weaken the BST-to-Pt adhesion. The mechanism of delamination at the BST/Pt interface is discussed using a simple 1D heat transfer model.

This paper presents the design and fabrication of an infrared (IR) thermal detector array made of Eu(TTA)3-based temperature sensitive paint (TSP). The TSP emits 610 nm visible luminescence depending on temperature, and works as an IR-to-visible converter. An optical readout system was designed to excite and observe the detector array using a 355 nm light-emitting diode (LED) and a charge-coupled-device (CCD) camera, respectively. The temperature coefficient of the TSP was measured to be −1.58% K−1, and thermal images of a 400 °C object were successfully obtained. The noise analysis showed that the noise-equivalent temperature difference (NETD) of the imaging system was about 4.5 K.

This special issue of the Journal of Micromechanics and Microengineering features papers selected from the Fourth International Workshop on Micro and Nanotechnology for Power Generation and Energy Conversion Applications (PowerMEMS 2004). The workshop was held in Kyoto, Japan, on 28–30 November 2004, by The Ritsumeikan Research Institute of Micro System Technology in cooperation with The Global Emerging Technology Institute, The Institute of Electrical Engineers of Japan, The Sensors and Micromachines Society, The Micromachine Center and The Kyoto Nanotech Cluster. Power MEMS is one of the newest categories of MEMS, which encompasses microdevices and microsystems for power generation, energy conversion and propulsion. The first concept of power MEMS was proposed in the late 1990s by Epstein's group at the Massachusetts Institute of Technology, where they continue to study MEMS-based gas turbine generators. Since then, the research and development of power MEMS have been promoted by the need for compact power sources with high energy and power density. Since its inception, power MEMS has expanded to include not only various MEMS-based power generators but also small energy machines and microdevices for macro power generators. At the last workshop, various devices and systems, such as portable fuel cells and their peripherals, micro and small turbo machinery, energy harvesting microdevices, and microthrusters, were presented. Their power levels vary from ten nanowatts to hundreds of watts, spanning ten orders of magnitude. The first PowerMEMS workshop was held in 2000 in Sendai, Japan, and consisted of only seven invited presentations. The workshop has grown since then, and in 2004 there were 5 invited, 20 oral and 29 poster presentations. From the 54 papers in the proceedings, 12 papers have been selected for this special issue. I would like to express my appreciation to the members of the Organizing Committee and Technical Program Committee. This special issue was edited in collaboration with Professor Toshiyuki Toriyama (Ritsumeikan University), Co-chair of the Technical Program Committee, and the Institute of Physics Publishing staff.

This paper reports on the use of hydrogen anneal to enhance the torsional fracture strength of dry-etched single crystal silicon (SCS) microstructures. Moving-magnet-type scanning mirrors with torsion bars were employed as fracture test specimens. Two types of device were fabricated using SCS and silicon-on-insulator (SOI) wafers by deep reactive ion etching (DRIE). For the SCS-wafer-based device, scalloping on DRIE sidewalls were smoothed out and the fracture strength of the torsion bar was improved by a factor of three by 120?min hydrogen anneal. For the SOI-wafer-based device, hydrogen anneal introduced surface irregularity onto the Si sidewalls by hydrogen-induced etching with the existence of SiO2. As a result, the fracture strength of the torsion bar was degraded contrarily. Therefore, hydrogen anneal is effective in improving the mechanical reliability of SCS microstructures without SiO2.

We have developed ultraviolet (UV)-assisted ozone steam etching as a novel SU-8 removal technology. This technology is expected to remove SU-8 at a higher etch rate compared to a conventional wafer cleaning process based on ozone water immersion. An etching apparatus prototyped in this study achieves an etch rate greater than 100 nm min−1 by intermittently rotating an SU-8-coated substrate on a spinner for spinning out the etching products under UV irradiation. Its complete removability is also verified by analyzing the surfaces of etched samples via scanning electron microscopy and x-ray photoelectron spectroscopy. In a micromolding process, the non-swelling removability is successfully demonstrated by removing a SU-8 sacrificial mold and leaving electroplated metal mushroom microstructures without destruction. Such a structure cannot be released by conventional resist strippers, because it is lifted up due to resist swelling. We believe this etching technology becomes a viable option to remove chemically-stable polymers such as SU-8 in microelectromechanical systems.

Resonant 1D microelectromechanical systems (MEMS) optical scanners actuated by piezoelectric unimorph actuators with a Nb-doped lead zirconate titanate (PNZT) thin film were developed for endoscopic optical coherence tomography (OCT) application. The MEMS scanners were designed as the resonance frequency was less than 125 Hz to obtain enough pixels per frame in OCT images. The device size was within 3.4 mm × 2.5 mm, which is compact enough to be installed in a side-imaging probe with 4 mm inner diameter. The fabrication process started with a silicon-on-insulator wafer, followed by PNZT deposition by the Rf sputtering and Si bulk micromachining process. The fabricated MEMS scanners showed maximum optical scan angles of 146° at 90 Hz, 148° at 124 Hz, 162° at 180 Hz, and 152° at 394 Hz at resonance in atmospheric pressure. Such wide scan angles were obtained by a drive voltage below 1.3 Vpp, ensuring intrinsic safety in in vivo uses. The scanner with the unpoled PNZT film showed three times as large a scan angle as that with a poled PZT films. A swept-source OCT system was constructed using the fabricated MEMS scanner, and cross-sectional images of a fingertip with image widths of 4.6 and 2.3 mm were acquired. In addition, a PNZT-based angle sensor was studied for feedback operation.

This paper reports on a novel non-contact thermal imaging method with high spatial, temporal and temperature resolution for microdevice evaluation. This method uses a temperature sensitive paint with europium (III) thenoyltrifluoroacetone (Eu(TTA)3). The luminescence of Eu(TTA)3 was excited by a short pulsed UV light; a temporal resolution as high as 0.2 ms was achieved under normal CCD camera observation. Also, a spatial resolution of about 39 µm and a temperature fluctuation of about ±0.2 °C were demonstrated.

This paper presents a film transfer process to integrate barium strontium titanate (BST) metal–insulator–metal (MIM) structures with surface acoustic wave (SAW) devices on a lithium niobate (LN) substrate. A high-quality BST film grown on a Si substrate above 650 °C was patterned into the MIM structures, and transferred to a LN substrate below 130 °C by Ar-plasma-activated Au–Au bonding and the Si lost wafer process. Simple test SAW devices with the transferred BST variable capacitors (VCs) were fabricated and characterized. The resonance frequency of a one-port SAW resonator with the VC connected in series changed from 999 to 1018 MHz, when a dc bias voltage of 3 V was applied to the VC. Although the observed frequency tuning range was smaller than expected due to the degradation of BST in the process, the experimental result demonstrated that a tunable SAW filter with the transferred BST VCs was feasible.

A solid-state micro magnetic refrigerator (SSMMR) has some advantages to cool microdevices because of its high efficiency and simple structure. In this study, we demonstrated the actual cooling of a thermally-isolated microstructure, which is a main component of the SSMMR, by the magnetocaloric effect. The thermal isolation structure is composed of parylene high-aspect-ratio beams for both high thermal isolation and high stiffness. A magnetic field switch was designed and fabricated to control the magnetic flux density from 0 T to about 1 T. Under this magnetic flux density change, the maximum temperature change of 1.0??C was confirmed.

A solid-contact-type thermal switch requires both high contact force and high thermal isolation, but they are in tradeoff relation. This study demonstrated a novel stiffness-enhanced thermal isolation structure, which can generate high contact force but does not increase heat loss. The stiffness of parylene beams is multiplied by that of silicon stiffening beams, which apply rotational constraint to the parylene beams to reduce the equivalent length of the parylene beams. The stiffening beams are designed as they cause no additional heat loss. The silicon stiffening beams increased the stiffness of the parylene beams by a factor of 1.6, and the unnecessary thermal conductance was still as low as 3.7 × 10−5 W K−1.

This paper describes a wafer bonding process using a 50 µm thick benzocyclobutene (BCB) layer which has vias and metal electrodes. The vias were fabricated by molding BCB using a glass mold. During the molding, worm-like voids grew between BCB and the mold due to the shrinkage of polymerizing BCB. They were completely removed by subsequent reflowing in N2. After patterning Al on the reflowed BCB for the electrodes and via connections, bonding with a glass substrate was performed. Voidless bonding without damage in the vias and electrodes was achieved. Through the process, the control of the polymerization degree of BCB is important, and thus the polymerization degree was evaluated by Fourier transform infrared spectroscopy. The developed process is useful for the wafer-bonding-based integration of different devices, e.g. micro electro mechanical systems and large-scale integrated circuits.

In this paper, we present a polyimide-based Si membrane transfer bonding technology and its application to CMOS-compatible integration of different modes of AlN/Si composite piezoelectric MEMS resonators. The thermosetting polyimide, which has excellent chemical resistance and thermal stability, is used as a bonding adhesion, and is successfully removed as a sacrificial layer by O2 plasma to release free-standing MEMS devices. The whole process temperature is below 350 °C and compatible with CMOS LSI. Using this technology, different modes of AlN/Si resonators, which are film bulk acoustic wave resonators and wine-glass mode disk-type resonators, have been co-fabricated on the same wafer. We also fabricated a ladder-type FBAR filter with a center frequency of 7.71 GHz and a mechanically coupled disk-array filter with a center frequency of 292.8 GHz.

This paper reports novel mercury droplet actuators with a long working range. The actuators were designed so that they can be used as thermal switches. Two types of actuation electrode were investigated: electrowetting type and electrostatic type. It was confirmed that the actuation of a mercury droplet was possible with each electrode. In addition, two types of actuator surface were investigated: flat surface and surface with micropillars. The micropillars showed considerable mobility enhancement of the droplet, but were found to be useful only with an appropriate electrode design. When the mercury droplet was actuated by 100–300 Vp-p, the observed maximum working range was about 200 µm, which is much longer than the values reported previously. Poor repeatability of droplet motion due to the charge-up of the actuator surface was revealed as a problem.

This special issue of the Journal of Micromechanics and Microengineering features papers selected from The 8th International Workshop on Micro and Nanotechnology for Power Generation and Energy Conversion Applications (PowerMEMS 2008) with the 2nd Symposium on Micro Environmental Machine Systems (μMEMS 2008). The workshop was held in Sendai, Japan on 9–12 November 2008 by Tohoku University. This is the second time that the PowerMEMS workshop has been held in Sendai, following the first workshop in 2000. Power MEMS is one of the newest categories of MEMS, which encompasses microdevices and microsystems for power generation, energy conversion and propulsion. The first concept of Power MEMS was born in the late 1990's from a MEMS-based gas turbine project at Massachusetts Institute of Technology. After that, the research and development of Power MEMS have been promoted by the strong need for compact power sources with high energy and/or power density. Since its inception, Power MEMS has expanded to include not only various MEMS-based power generators but also small energy machines and microdevices for macro power generators. Previously, the main topics of the PowerMEMS workshop were miniaturized gas turbines and micro fuel cells, but recently, energy harvesting has been the hottest topic. In 2008, energy harvesting had a 41% share in the 118 accepted regular papers. This special issue includes 19 papers on various topics. Finally, I would like to express my sincere appreciation to the members of the International Steering Committee, the Technical Program Committee, the Local Organizing Committee and financial supporters. This special issue was edited in collaboration with the staff of IOP Publishing.