神田 健介

Vibration energy harvesters that use resonance phenomena exhibit a high output power density for constant frequency vibrations, but they suffer from a significant drop in performance for non-steady-state vibrations, which are important for practical applications. In this work, we demonstrate that the output power under an impulsive force can be increased significantly by placing a U-shaped metal component, called a dynamic magnifier (DM), under an MEMS piezoelectric vibration energy harvester (MEMS-pVEH) with a 6 mm long cantilever using a 3  μm thick Pb(Zr,Ti)O₃ film. Based on the results of numerical calculations using a model of pVEH with a two-degree-of-freedom (2DOF) system, the DM was designed to have the same resonant frequency as the MEMS-pVEH and a high mechanical quality factor ([Formula: see text]). The waveforms of the output voltage of the fabricated 2DOF-pVEHs were measured for impulsive forces with various duration times, and the output power was calculated by integrating the waveforms over time. The output power of the MEMS-pVEH placed on the DM with a [Formula: see text] of 56 showed a gradual change according to the duration of applying an impulsive force and a maximum of 19 nJ/G² (G: gravitational acceleration) when the duration of the impulsive force was 3.8 ms. This result was about 90 times greater than the output power of the MEMS-pVEH without a DM. While it is not easy to fabricate pVEHs with a complex 2DOF structure using only the MEMS process, we have demonstrated that the output power can be significantly improved by adding a spring structure to a simple MEMS-pVEH.

To evaluate the characteristics of Pb(Zr,Ti)O3 (PZT) thin films (about 10~mu text{m} thick) with three different sputtering configurations - single-layer (SL) deposition, multilayer (ML) deposition with internal electrodes, and multistep (MS) deposition - were prepared. The SL films exhibited poorer dielectric characteristics than the ML and MS films. The reliability and piezoelectric characteristics were especially high in the MS film, with an {e}_{ { 31},text {f } } constant of -9.5 C · m-2. To investigate the porosity of the films, reconstructed 3-D SEM technique is employed. Reconstructed 3-D SEM images revealed decreased void densities in the ML and MS films, which improved their performance. The MS configuration provided the best dielectric and piezoelectric performance of PZT films.

© 2020 The Japan Society of Applied Physics. Microrod-type CoFe2O4(CFO)/Bi3.25Nd0.65Eu0.10Ti3O12(00ℓ) (BNEuT) composite thin films were fabricated by a combination of high-temperature sputtering, reactive ion etching, and metal organic chemical vapor deposition (MOCVD) on Pt(100)/MgO(100) substrates. The substrate temperature for MOCVD was varied from 450 °C to 600 °C to examine its effect on the structural, magnetic, and ferroelectric properties. The substrate temperature affects the compressive stress at the interface between the CFO and BNEuT. The surface morphology changed drastically above 550 °C. The room temperature magnetization-magnetic field hysteresis loops for the films showed clear ferromagnetic hysteresis loop and magnetic shape anisotropy. The room temperature polarization-electric field (P-E) hysteresis loops for the films showed a clear ferroelectric hysteresis loop, and slightly leaky P-E hysteresis loop. The coercive field increased slightly with increasing substrate temperature. Judging from the structural, ferromagnetic, and ferroelectric properties, the film deposited at 550 °C has potential as an excellent multiferroic material.

© 2020 The Japan Society of Applied Physics. This study investigated the electromechanical properties of MEMS piezoelectric vibration energy harvesters (MEMs-pVEHs) under various impulsive forces to discuss effective harvesting energy from random vibrations. MEMS-pVEHs with different resonance frequencies with an energy conversion efficiency close to the theoretical maximum were used. The output waveforms for various impulsive force could be fitted well with the dynamic model of pVEHs. The output energy density reached 34 nJ g-1 for an impulsive force with an acceleration of 8 m s-2. To obtain high energy conversion efficiency, pVEHs should have a response time longer than the duration of the impulsive force; efficiency higher than 50% was obtained by an impulsive force with a short duration. Furthermore, the study investigated the pVEH requirements for impulsive force based on the results of numerical simulation.

© 2019 The Institute of Electrical Engineers of Japan. Tactile devices that provide touch sensation to humans by direct contact have been realized. A tactile device based on a piezoelectric MEMS is improved in this study. The driving voltage is lowered by using multilayer lead zirconate titanate (PZT) thin film. The lower voltage is experimentally validated by measuring the cantilever displacement in the device. The displacement per voltage becomes four times larger by using four layers of PZT thin film. In addition, the polymer supporting material is also investigated to reduce the temperature dependence of the device. By using polyimide as an alternative to conventional SU-8, not only the initial warpage but also the temperature dependence is dramatically improved. The driving test of the polyimide device reveals cantilever displacement comparable to that in conventional devices. In conclusion, structural improvements resulted in low-voltage actuation and reduced warpage of the piezoelectric MEMS tactile device.

© 2019 The Japan Society of Applied Physics. The influence of design parameters of piezoelectric thin films on the performance of vibration-type piezoelectric energy harvesting devices is investigated experimentally. The devices have four layers of Pb(Zr,Ti)O3 thin films on a silicon-based microfabricated structure to obtain high output power. The initial deformation and output power are measured. The results indicate that the initial shape due to residual stress can influence the mechanical quality factor and output power, particularly for the low-acceleration regime. In addition, the influence of the weight of the mass is investigated by changing the weight of the harvester. It is experimentally demonstrated that the power density and the generative power's ratio to the theoretical limit can be improved by increasing the weight. A very large value of the normalized power density, 55.45 mW cm-3 G-2 (1 G = 9.8 m s-2), is obtained when a tungsten mass is attached to the microfabricated harvesting device.

© 2018 The Japan Society of Applied Physics. For the application of bidirectional communication between a human activity monitoring system and a human using tactile sensation, a tactile MEMS device is developed. To obtain the displacement and provide energy to the human skin, a driving actuator and a displacement sensor are integrated. The tactile device is based on a cantilever with a lamination structure of polymer and Pb(Zr,Ti)O3 thin films. The characterization of the device showed that the sensor output agreed well with the tip displacement. For the touch experiment of the device, the frequency response demonstrates hardening-spring-like behavior. By using a piecewise linear system model, the behavior is analyzed. The experimental results and analytical model showed similar tendencies. These results indicate a potential application of the stiffness sensor of an object.

This study aims to report the design of high-performance piezoelectric MEMS energy harvesters using a full batch MEMS-fabrication process with a Si proof mass and multilayered Pb(Zr,Ti)O-3 (PZT) thin films without bonding of a proof mass and/or bulk piezoelectric ceramics. These devices contain sputtered multilayered PZT thin films with internal metal electrodes as a thick energy-conversion layer. The thickening of the piezoelectric layer by multilayer sputter deposition technique enabled the batch fabrication of high-performance piezoelectric MEMS harvesters. These fabricated device with the footprint of 10 x 10 mm(2) was found to provide a high output power of 53.7 mu W per gravitational acceleration. These results are expected to be useful for the future development of alternatives to batteries for autonomous sensor systems. (C) 2018 Elsevier B.V. All rights reserved.

© Published under licence by IOP Publishing Ltd. Piezoelectric MEMS energy harvesters based on multilayer (ML) Pb(Zr,Ti)O3(PZT) thin films with interdigitated electrodes (IDE) as their internal and top electrodes are proposed and designed. Thick PZT thin films with good piezoelectric characteristics can be deposited by using multilayer deposition technique. Furthermore, IDE is adopted to the harvester design in order to take advantage of the longitudinal piezoelectric effect, which typically has twice piezoelectric constant as large as transverse effect. The energy harvesters with two electrode configurations, parallel plate electrodes (PPE) and IDE, are designed and estimate these output power. According to the result of finite element analysis, the output power per gravitational acceleration is about 124 μW for the PPE configuration. On the other hand, the output power per gravitational acceleration for the IDE configuration is about three times as large as that for PPE. Moreover, the influence of IDE patterns and the number of PZT layers were investigated. The larger number of layers results in the larger output power.

© 2018 Wiley Periodicals, Inc. In this study, we have fabricated membranes which are composed of two- and four-layer Pb(Zr,Ti)O3 thin films with internal electrodes by using sputtering depositions. Electrical and driving characteristics as ultrasonic transducers of these membranes are evaluated. By increasing number of layers, the static displacement is reduced. However, for the multilayered membrane, the dynamic displacement became large because of the large mechanical Q factor in resonant vibration. The emitted sound pressure level and characteristics of the ultrasonic transducer are estimated.

© 2018 The Institute of Electrical Engineers of Japan. Blood pressure changes every second and cannot be continuously monitored by conventional cuff method. In order to solve this problem, we proposed a blood pressure estimation system by pulse transit time (PTT) method. The system includes two devices; a master device which monitors ECG for starting time of the pulse wave, and a slave device for monitoring the propagated pulse wave at the wrist. Both devices have some sensors, such as an accelerometer and barometer, for monitoring the condition of the body and wrist. The detected condition will be used for compensation of the PTT data. As a result, estimation of the blood pressure by PTT is accurate enough comparing to sphygmomanometer for home use. In addition, the relation between barometric pressure and PTT by hand position was measured and used for establishing the correction equations.

Regardless of the deposition time (30-90 min), almost single-phase magnetite (Fe3O4) films with a cubic inverse-spinel structure were produced at a substrate temperature of 500 degrees C by metalorganic chemical vapor deposition (MOCVD). The Fe3O4/(Bi(3.25)Nd(0.65)Eu(0.1)0) Ti3O12 (BNEuT) composite film deposited at 500 degrees C for 90 min by MOCVD exhibited excellent room-temperature magnetic properties, such as a saturation magnetization of 480 emu/cm(3), a residual magnetization of 160 emu/cm(3), and a coercivity of 297 Oe. Ferromagnetic Fe3O4 electrodes micropatterned using a combination of photolithography and reactive ion etching were fabricated after MOCVD, and their structural, leakage current, and ferroelectric characteristics were investigated. The room-temperature leakage current density-applied electric field and polarization-electric field (P-E) characteristics of the composite films were successfully measured using Fe3O4 electrodes. The room-temperature P-E hysteresis loop for a sample with the structure Fe3O4/BNEuT/Nb: TiO2/Ti had a relatively good shape, with a remanent polarization of 8 mu C/cm(2) and a coercive field of 193 kV/cm. (C) 2017 The Japan Society of Applied Physics

© 2017 IOP Publishing Ltd. For the realization of piezoelectric microelectromechanical systems (MEMS) with multiple degrees-of-freedom, lead zirconate titanate thin films were deposited and micropatterned on the sidewalls of a pre-etched substrate with a feature depth of several hundred micrometers. The piezoelectric test structures, consisting of concave geometries and cantilevers with vertical and sloped sidewalls were successfully fabricated onto a 4 inch full sized wafer. Characterization of the fundamental properties of the lead zirconate titanate thin films indicated values comparable to those deposited on flat substrates. Actuation tests demonstrated that the triangular column cantilevers can be driven both in-plane and out-of-plane. The deposition of lead zironate titanate thin films onto a vertical sidewall created bimorph cantilevers composed of piezo/non-piezo/piezo structures in the horizontal direction. The use of microfabrication techniques to deposit lead zironate titanate thin films on pre-etched substrates gives MEMS actuators with multiple degrees-of-freedom and batch process compatibility.

© 2017 The Institute of Electrical Engineers of Japan. Novel miniaturized tactile devices, which provide a person with vibration stimulation, are proposed. The strategy is to hit the skin with a resonantly oscillating proof mass. The tactile devices consist of a Si proof mass and a beam formed by laminated thin-film PZT and polymer. The fabricated devices generated large displacement with high durability. Tactile experiments suggest that all examinees experienced vibration at displacement of 1.3 mm for a 4 mm × 4 mm device. For wearable monitoring systems of human activities, the energy consumption was estimated at 12 μW and the major energy loss was attributed to dielectric loss.

We designed and evaluated ASICs (application-specific integrated circuits) for a human activity monitoring system in order to reduce total power consumption. The ASIC extracts the HR from the measured electrocardiogram (ECG) raw signal. To create an ASIC with ultra-low power consumption, we used a novel algorithm based on fuzzy logic that is very simple and requires minimal processing power. The fabricated ASIC shows sufficient functionality and a power level as low as 2 mu W. A total of 85% of the power consumption in microprocessing unit (MPU) processing was cut by using the heart rate extraction ASIC.

© 2016 The Institute of Electrical Engineers of Japan. This paper demonstrates an improvement in the generated power of a NdFeB electromagnetic vibration energy harvester by optimizing the device dimensions considering a mass-damper-spring system and the Lorentz force. The electromagnetic harvester follows a velocity-damped-resonant-generator (VDRG) model. When the electrical and mechanical attenuation coefficients are equivalent and the device is operated at a resonant state, the maximum power will be obtained. In this paper, we simulated and optimized the power generation considering a mass-damper-spring structure and the Lorentz force. From our simulation results, we determined an optimal design for 100 Hz and 3 μmp-p of sinusoidal external vibration to generate 0.42 μW of power from the device with a 10 × 10 × 0.5 mm3 active harvesting area and 50 of Q-factor. This exhibits power that is 43 times larger than the previous design.

Multimorph structures composed of multiple thin-film piezoelectric layers and electrode layers were realized by sputtering deposition. Cantilevers with four layers of Pb(Zr,Ti)O-3 (PZT) thin film are fabricated and evaluated. The electrical and piezoelectric characteristics of each PZT layer are very similar and are comparable to those of conventional single-layer PZT thin film. The piezoelectric constant d(31) is estimated to be -38.3pm/V from the relationship between tip displacement and applied voltage under the condition of driving four all piezoelectric layers. The generative force is also estimated from the tip displacement. It is confirmed that multimorph cantilevers have larger generative force than those of conventional unimorph and bimorph cantilevers for identical driving voltage. (C) 2015 The Japan Society of Applied Physics

We studied the effects of increasing the thickness of bimorph structures containing double layers of Pb(Zr,Ti)O-3 (PZT) thin films. Thick PZT films allow high-voltage application (e.g. in terms of coercive electric field and breakdown voltage) and large generative force, which are effective in microelectromechanical systems (MEMS) applications. Improvement of the deposition conditions and electrode structures facilitates the fabrication of the thin-film PZT/PZT bimorph structure. The PZT/PZT bimorph with a total thickness of 5.8 mu m, deposited using a radio-frequency (RF) magnetron sputtering system is much thicker than conventional bimorph structures. The characteristics of the two piezoelectric layers were similar to each other and revealed good electric and ferroelectric characteristics with a remanent polarization of 20 mu C cm(-2) and a coercive electric field of 50 kV cm(-1). PZT/PZT bimorph cantilevers were fabricated in order to evaluate their characteristics for actuator applications. The residual stress of the bimorph cantilever was reduced by an annealing process. The vibration test on the fabricated bimorph cantilevers during electrical voltage application revealed a twice as large displacement as compared with a single layer actuation, and the piezoelectric coefficient value d(31) was estimated to be -61 pm V-1, which is better than the value of conventional PZT/PZT bimorph cantilevers (-13 pm V-1). It was also shown that the influence of the temperature change is much less than that in unimorph structures with similar dimensions. The evaluated results demonstrate that the PZT/PZT bimorph structures are effective as MEMS devices.

We designed and evaluated low power ASIC (Application Specific Integrated Circuits) for the human activity and health monitoring systems to reduce the total power consumption. The ASIC extracts walking and running steps and holds the maximum and minimum values from raw data of acceleration sensor. To realize ultra-low power consumption, the algorithm is designed to reduce the amount of the data calculation for pedometer. Power consumption was reduced to 15% from previous prototype system by using the designed ASIC.

© 2015 The Institute of Electrical Engineers of Japan. This paper presents an electrostatic vibration energy harvester with a bipolar-charged electret for high output power and for low electrostatic force. In conventional electrostatic energy harvesters, electrets are charged by monopolar charge (mainly by negative) with a high potential for large power harvesting. We propose a bipolar charging method in order to form an electret, which not only has negative charge but also positive charge. The electrostatic energy harvester, with a size of 13×12×1.2 mm3, was fabricated and charged by a -250-V monopolar potential and by a ±250-V bipolar potential. The maximum output power of the monopolar- and bipolar-charged harvester is 3.1 μW and 9.8 μW, respectively with an applied acceleration of 7 g at 352 Hz with a 0.9-MΩ load resistance. The output power is 9 μW at 1.4 g and the maximum effectiveness against the velocity-damped resonant-generator (VDRG) limit is 2.5%. By using the bipolar-charged electret, the high output power obtained from the high charging potential was compared to a conventional harvester charged by the monopolar method. Further, using the finite element method (FEM) analysis, we determined that the electrostatic force that prevents harvesting mass movement is significantly reduced on the bipolar-charged electret. The electrostatic forces under static conditions along the vertical and horizontal directions obtained through the FEM analysis were reduced to 15% and 20%, respectively, from those of the monopolar-charged electret.

© 2015 The Institute of Electrical Engineers of Japan. This paper presents an equivalent circuit model of an electrostatic energy harvester for a SPICE circuit simulator. The output power and impedance of the proposed model are approximated by using a simplified model of a voltage-controlled capacitor. The relationship between the capacitance and the electrode position is calculated by FEM analysis by taking the fringing effect into account; this relationship is applied to a sub-circuit model for the SPICE simulator. Further, the results of this study show that the output waveform and the optimal resistance obtained using the SPICE simulator correspond with the measurement results. In addition, the operation of a harvesting system connected with a commercially available power management IC is demonstrated.

This paper presents an electrostatic vibration energy harvester with a conventional monopolar-charged and a novel bipolar-charged electret. The maximum output power of the -200 V monopolar-charged and ±100 V bipolar-charged harvester were 1.1 µW and 0.9 µW, respectively with a vibration amplitude of 350 µmpp at 323 Hz with a 0.8 MΩ load resistance. The bipolar-charged harvester generates higher output power than the monopolar-charged harvester with an applied acceleration from 0 g to 0.7 g, because electrostatic force of the monopolar-chaged electret along the vibration direction prevents harvesting mass movement compared to the bipolar-charged electret. Further, we analyzed a SPICE model with electrostatic force and confirmed that the characteristics were according to the experiment results.

This paper demonstrates successful deposition and etching of Pb[Zr,Ti]O3 (PZT) thin films on pre-etched Si substrate with pits having depths of several hundred micrometers. Conventionally, for fabrication of microelectromechanical systems, PZT films are deposited onto a flat substrate because of inherent difficulties associated with stable deposition and processing. We successfully established the fabrication of PZT thin films and electrodes on non-flat and pre-etched substrate by using sputtering deposition and projection exposure techniques. The evaluation results reveal that the PZT thin film deposited onto the pre-etched substrate has good ferroelectric characteristics, including piezoelectric d33 constant of 80 pm/V. © 2014 The Institute of Electrical Engineers of Japan.

Previously, we have developed a human monitoring system, which used 8051 microcontroller. The system has a 3-axis acceleration sensor, a pressure sensor, a humidity sensor, and an electrocardiogram (ECG) circuit. This paper reports the newly developed system by using PSoC (Programmable System-on-Chip), which is a microcontroller with some analog blocks in a single chip. The ECG and the acceleration are sampled at 125 Hz, the others are at 1 Hz by the PSoC. The sampled data are stored on the micro SD card or Static RAM (SRAM), transmitted by a Bluetooth module or USB interface to a PC. The multipurpose I/O pins for addition of some sensors are designed in the system. The multipurpose I/O pins are utilized to control and communicate with an infrared temperature sensor. The system was designed and fabricated by 4-layer printed circuit board (PCB). In comparison with the previous work, the system size was reduced from 85×48×15 mm3 to 50×50×15 mm3, the power consumption without Bluetooth communication was reduced from 45.0 mA to 24.6 mA when the power supply voltage is 3.3 V and the master clock is 48 MHz.

We designed and evaluated ASICs (Application Specific Integrated Circuits) for the human activity monitoring systems to reduce the total power consumption. The ASIC extracts the heart rate from measured ECG (Electrocardiogram) raw signal. To realize the ASIC with ultra-low power consumption, we used novel algorithm based on fuzzy logic which is very simple and light processing. The fabricated ASIC shows sufficient function and low power as low as 2 µW.85% of the power consumption for MPU (Micro-Processing Unit) processing was cut by using the heart rate extraction ASIC.

X線自由電子レーザSACLA 井上 純一，田中 祐至，松本 裕貴，神田 健介

Continuous human monitoring will be substantially useful to realize a high quality of life society. In the previous work, we fabricated a prototype system for monitoring an electrocardiograph, heart rate (HR), 3 axes human body acceleration and temperature for human body and human circumstances, simultaneously. These data are transmitted to the host PC and analyzed for the human activities or conditions recognitions. Above all a heart rate variability (HRV) that calculated from HR is extremely valuable for recognizing a mental or physical stress of human subjects. In this study, we demonstrate a fuzzy logic HR extraction algorithm on the daisy chain shaped wearable prototype device to realize an autonomous HRV monitoring system. On-board fuzzy logic algorithm not only reduces the communication traffic but also improves an accuracy of the HR extraction comparing to the simple threshold methods. © 2013, TSI® Press.