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Series-connected thin film piezoelectric elements can generate large output voltages. The output voltage ideally is proportional to the number of connections. However, parasitic capacitances formed by the insulation layers and derived from peripheral circuitry degrade the output voltage. Conventional circuit models are not suitable for predicting the influence of the parasitic capacitance. Therefore we proposed the simplest model of piezoelectric elements to perform simulation program with integrated circuit emphasis (SPICE) circuit simulations). The effects of the parasitic capacitances on the thin-film Pb(Zr, Ti)O-3, (PZT) elements connected in series on a SiO2 insulator are demonstrated. The results reveal the negative effect on the output voltage caused by the parasitic capacitances of the insulation layers. The design guidelines for the devices using series-connected piezoelectric elements are explained.

In this paper, we describe about small sized and extremely low power consumption transceiver module for wireless sensor network, especially suitable for bio-signal transmission. Currently, many types of transceiver modules, such as Bluetooth, ZigBee, low power radio modules for 315MHz and so on, are available in the market. However, when we consider extremely small and light system including a battery and transceiver module for wireless sensor network installed on a human body, almost all the transceiver modules in the market consume too large power and too large area for assembling. In this study, we concentrated on realizing an extremely low power consumption and small/lightweight transceiver module for 315MHz radio band. As a result, we successfully designed and fabricated the transceiver module with size of 11×11×1.5 mm³ including a bipolar ASIC for radio circuit and 8bit micro controller. The operation currents of the receiver and transmitter are 2 and 1 mA, respectively for supply voltage of 2.5V. These results are generally sufficient for many cases of wireless sensor network systems not only for bio-signal applications.

In this paper, we address the fabrication and characterization of bimorph structures with relatively thick double-layered Pb(Zr,Ti)O 3 (PZT) thin films. The PZT/PZT layers are deposited by RF magnetron sputtering. Hysteresis loops of polarization and electrical field for the top and bottom PZT thin films revealed good ferroelectric characteristics with remanent polarization at approximately 20 μC/cm 2 and a coersive electric field of about 100 kV/cm. The vibration tests of fabricated bimorph cantilevers during electrical voltage application revealed a twofold displacement compared with single layer driving, and the piezoelectric coefficient value d31 is estimated to be 13 pm/V. The residual stress difference between the top and bottom layers after the annealing process is calculated to be -0:32 MPa. For a further thickening of the bimorph structure, 6-μm-thick PZT/PZT is also sputtered. The thicker bimorph has a smaller residual stress difference, -30 MPa, between the two layers prepared without the annealing process. The evaluated results demonstrate that the PZT/PZT bimorph structures are applicable to micro-electromechanical systems (MEMS) devices. © 2012 The Japan Society of Applied Physics.

Previously, we developed a flexible and biocompatible wiring that has excellent performance to tension and good inflectional characteristics. Using this technique, we prepared the flexible strain sensor and we successfully achieved to measure the strain level.

In this paper, we address the fabrication and characterization of bimorph structures with relatively thick double-layered Pb(Zr,Ti)O3 (PZT) thin films. The PZT/PZT layers are deposited by RF magnetron sputtering. Hysteresis loops of polarization and electrical field for the top and bottom PZT thin films revealed good ferroelectric characteristics with remanent polarization at approximately 20 μC/cm2 and a coersive electric field of about 100 kV/cm. The vibration tests of fabricated bimorph cantilevers during electrical voltage application revealed a twofold displacement compared with single layer driving, and the piezoelectric coefficient value d_{31} is estimated to be 13 pm/V. The residual stress difference between the top and bottom layers after the annealing process is calculated to be -0.32 MPa. For a further thickening of the bimorph structure, 6-μm-thick PZT/PZT is also sputtered. The thicker bimorph has a smaller residual stress difference, -30 MPa, between the two layers prepared without the annealing process. The evaluated results demonstrate that the PZT/PZT bimorph structures are applicable to micro-electromechanical systems (MEMS) devices.

In our development of a new monitoring system for human utterance, we investigated temporal variation when a participant verbalized five Japanese vowels by using an acceleration sensor attached to the lower teeth. We then analyzed the variation by wavelet transform and obtained the temporal spectral density. We were able to observe the frequencies corresponding to voice sound and the lower jaw movements. The results indicated that the possibility of speech recognition with not only voice sounds but also lower jaw movements by our system.

A novel gas-sealed capacitive pressure sensor with a temperature compensation structure is reported. The pressure sensor is sealed by Au-Au diffusion bonding under a nitrogen ambient with a pressure of 100 kPa and integrated with a platinum resistor-based temperature sensor for human activity monitoring applications. The capacitance-pressure and capacitance-temperature characteristics of the gas-sealed capacitive pressure sensor without temperature compensation structure are calculated. It is found by simulation that a ring-shaped structure on the diaphragm of the pressure sensor can mechanically suppress the thermal expansion effect of the sealed gas in the cavity. Pressure sensors without/with temperature compensation structures are fabricated and measured. Through measured results, it is verified that the calculation model is accurate. Using the compensation structures with a 900 mu m inner radius, the measured temperature coefficient is much reduced as compared to that of the pressure sensor without compensation. The sensitivities of the pressure sensor before and after compensation are almost the same in the pressure range from 80 kPa to 100 kPa.

    In this article, the fabrication of single crystal silicon (SCS) nanowire (NW) structures and their novel characteristics are described. We have produced in-plane and out-of-plane SCS NWs by means of two different types of fabrication processes including wet and dry etching. In-plane SCS NWs were fabricated using nano-lithography based on a local anodization technique with an atomic force microscope (AFM). 200-nm-wide SCS NW bridges were realized on an active layer in a silicon-on-insulator (SOI) wafer. The strength that was measured by AFM bending testing was larger by 40 times than that of bulk SCS. Even at temperatures ranging from 373 to 573 K, the NWs showed plastic deformation with dislocation slips. Out-of-plane SCS NWs were fabricated using the combination of deep reactive ion etching (DRIE) and thermal oxidation. By DRIE, SCS nano-pillars with scalloping sidewalls were produced on a SCS wafer. Thermal oxidation and wet etching were carried out as the post-process; consequently 100-nm-diameter out-of-plane SCS NWs array without scallops was realized. The NWs with the tremendous aspect ratio of 160 showed very large elastic deformation originating from their own weight and sticking. Novel size effect phenomena occurred in the SCS NWs produced were discussed.

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Electret materials are useful for electrostatic type energy harvesters. Since the power generated from the electret energy harvester is proportional to the surface charge concentration, i.e. charged voltage on the electret, frequency and dynamic range of the capacitance change. To fabricate the electret, the corona discharge is a very popular charging method, which consists of a high voltage needle for corona ions generation and a grid electrode applying a bias voltage that implants the electrons from corona ions to the electret material. We have established the charging method with finely patterned charging area by using the buried grid electrodes (BGE) applied with a bias voltage for organic material CYTOP. However, CYTOP has slightly poor characteristics in terms of the thermal robustness. In this study we report a fabrication technique of the selectively charged SiN/SiO2 as electret material alternative to the CYTOP. By using the BGE method to SiN/SiO2 film, a fine patterned electret with highly thermal robustness was obtained.

Previously, we developed a flexible and biocompatible wiring that has excellent performance to tension and good inflectional characteristics. Using this technique, we prepared the flexible strain sensor and we successfully achieved to measure the strain level. © 2012 The Institute of Electrical Engineers of Japan.

This study presents a wafer-level batch fabrication technique of NdFeB film for MEMS (Micro Electromechanical Systems) based electromagnetic type energy harvester. By using 20 mu m thickness NdFeB sputtered magnetic film on a trench-etched Si microstructure, fine patterned magnet structures for energy harvester had been realized. However the size of the sputtered sample was limited to the slightly small size. In this study, we improve the sputtering equipment to apply the NdFeB film process on a four-inch Si wafer. The film characteristics, estimation of the compatibility with the MEMS process and also energy harvesting result are presented. (C) 2012 Elsevier Ltd....Selection and/or peer-review under responsibility of the Symposium Cracoviense Sp. z.o.o.

A 1.1 mu W power dissipation, voltage-output humidity sensor with 10% relative humidity accuracy was developed in the LFoundry 0.15 mu m CMOS technology without post-processing. The sensor consists of a woven lateral array of electrodes implemented in CMOS top metal, a humidity-sensitive layer of Intervia Photodielectric 8023D-10, a CMOS capacitance to voltage converter, and the self-calibration circuitry.

In our development of a new monitoring system for human utterance, we investigated temporal variation when a participant verbalized five Japanese vowels by using an acceleration sensor attached to the lower teeth. We then analyzed the variation by wavelet transform and obtained the temporal spectral density. We were able to observe the frequencies corresponding to voice sound and the lower jaw movements. The results indicated that the possibility of speech recognition with not only voice sounds but also lower jaw movements by our system. © 2012 The Institute of Electrical Engineers of Japan.

In this paper, we describe about small sized and extremely low power consumption transceiver module for wireless sensor network, especially suitable for bio-signal transmission. Currently, many types of transceiver modules, such as Bluetooth, ZigBee, low power radio modules for 315 MHz and so on, are available in the market. However, when we consider extremely small and light system including a battery and transceiver module for wireless sensor network installed on a human body, almost all the transceiver modules in the market consume too large power and too large area for assembling. In this study, we concentrated on realizing an extremely low power consumption and small / lightweight transceiver module for 315 MHz radio band. As a result, we successfully designed and fabricated the transceiver module with size of 11×11×1.5 mm3 including a bipolar ASIC for radio circuit and 8bit micro controller. The operation currents of the receiver and transmitter are 2 and 1 mA, respectively for supply voltage of 2.5 V. These results are generally sufficient for many cases of wireless sensor network systems not only for bio-signal applications. © 2012 The Institute of Electrical Engineers of Japan.

Electro-magnetically actuated Vibratory Beam Actuator (VBA) with high resolution and stability has been reported. The VBA senses acceleration from the frequency changes of the beams supporting a proof-mass. In this paper, piezoelectric PZT (Pb[Zr, Ti]O-3) thin films are employed to actuate the beam and to sense the vibration frequency for miniaturizing the VBA. Well-established fabrication processes including dry-etching PZT are applied to the VBA fabrications. For the acceleration sensing by using VBA, a self-oscillation system, which includes phase-lock-loop (PLL) to maintain resonant oscillations of the beams is constructed. Gravity sensing test, i.e. inclining the sensor, demonstrates a good linearity between applied acceleration and sensing signal. The VBA, promising as a next generation accelerometer, is miniaturized to the area of 4 mm(2). (C) 2012 Elsevier Ltd .... Selection and/or peer-review under responsibility of the Symposium Cracoviense Sp. z.o.o.

This study describes the fabrication and measurement of an electromagnetic-type energy harvester by using buried NdFeB/Ta multilayer films. The energy harvester is fabricated by bonding a vibratory mass with buried micro-magnets and a stator with integrated micro-coils together. The performance of the micro-magnets was enhanced by new methods of a mechanical polishing process of buried NdFeB. The output power of the energy harvester was improved to 760 pW with an applied vibration amplitude of 48 μm p-p at 94.9 Hz. © 2012 IEEE.

This paper reports a fabrication process of pulse wave sensor and detection result of pulse wave using the ring-shaped sensor, which has ring-shaped photodiode. An LED is located at the center of a photodiode. This structure achieved noninvasive detection of the pulse wave and does not have the directivity. Therefore, the ring-shaped sensor is expected to reduce noises of body motion (motion artifacts). We evaluated the characteristics of the photodiode and detected the pulse wave using the fabricated sensor. As a result, the ring-shaped sensor can detect the pulse wave. Furthermore, detection of the pulse wave can be applied to measure the pulse wave velocity (PWV).

A novel capacitive absolute pressure sensor is fabricated and evaluated in this paper. The pressure sensitive membrane is formed by SON (Silicon on Nothing) technology [1], and a glass chip with Au/Ti electrodes is bonded on the membrane opposite by anodic bonding technique at 400°C to detect the pressure change. Compared to the existing capacitive absolute pressure sensors, the hermetical sealing process is not required, high vacuum cavity can be easily formed, an excellent long-term stability can be achieved, and detection circuitry can be easily integrated with the sensor. © 2012 IEEE.

In this paper, fabrication method of acceleration sensor with low parasitic capacitance is descried. By using Silicon on Honeycomb Insulator (SOHI) wafer as a base material instead of Silicon on insulator (SOI) wafer, parasitic capacitance has reduced to 20%. The sensitivity of the acceleration sensor measured from differential capacitance change revealed 1.5 fF/G. The linear relationship between gravity acceleration and detection capacitance is measured by using commercial C/V converting circuit. By combining the SOHI acceleration sensor and specially designed C/V converting circuit with ultra-low power consumption, the sensitivity of the acceleration sensor can be expected to increase in 22 times than that for SOI wafer. The C/V converter circuit with ultra low power consumption of 1.13-mu W will realize long term and continuous monitoring of human activities by assembled with capacitive-type sensors based on SOHI wafer.

Continuous monitoring of human physical and mental conditions are heavily required solving issues to realize a high quality of life society. The human condition data especially; heartbeat, ECG (electrocardiogram), respiration and blood pressure are very important vital signs to prevent a human sudden disease, such as a heart attack. In this study, we fabricated a novel sensor to monitor the heartbeat and respiration, which is made on a flexible thin film of P(VDF/TrFE) as a sensing material and PDMS (poly dimethyl siloxane) as a substrate material. The PDVF (poly vinylidene fluoride) that is thin, flexible and piezoelectric material can be used for the flexible force sensor. The fabrication steps and some experimental results for human monitoring system are described.

The efficiency of transportation system depends on many factors, such as traffic congestion, vehicle accidents and road conditions. To improve the reliability, productivity and safety of the system, many researchers propose to use a wireless sensor network (WSN) as a solution. A WSN usually consists of many tiny sensor nodes for sensing, data processing and communication. In this study, we present the development of a small-sized, low-power and lightweight wireless sensor node. It is equipped with a 3-axes accelerometer, an altimeter sensor, humidity sensor, temperature sensor, 315 MHz RF transceiver module and a typical coin-sized lithium battery (3.0 V, 220 mAh). The entire sensor node fits within a 28 x 20 x 8 mm(3) volume and is only 7 grams (not including the antenna). An 8-bit MCU is included in the RF transceiver module to control sensor node operation. It collects and transmits sensors data in real time to the RF repeater with bit rate 24 kbps. During continuous operation, the sensor node consumes less than 3 mA current. Thus for a 220 mAh battery, the wireless sensor node can continue operating for more than 75 hours.

An inductor in standard CMOS process having an inductance of 52 nH and a quality factor of 1.5 at frequency equal to 80 Mhz was fabricated. The polymer passivation layer of the standard CMOS inductor was etched out. The silicon substrate under the inductor, having a thickness of 280 μm was also etched out by deep reactive ion etching (DRIE). Ferrite material ZnFe2O 4 and amorphous material Fe4.7Co70.3Si 15B10 was then sputtered on top of the inductor sequentially. The same sputtering procedure was also performed into the bottom of the inductor. The result is an inductor that is sandwiched by multiple ferromagnetic layers. The inductance of the new ferromagnetic inductor has increased by 15% from 52 nH to 60 nH. The quality factor has also increased by 20% from 1.5 to 1.8. © 2012 Materials Research Society.

The size of conventional Geiger counters is large because the detector (GM tubes: Geiger muller tubes) is fabricated by mechanical processing. In this paper, an MEMS (micro electro mechanical systems) GM tube using a wafer level packaging is proposed. The MEMS-GM tube with glass/Si/glass stacked structure was fabricated by using anodic bonding and polymer bonding. With the supplied voltage of 2.6 kV to the MEMS-GM tube, pulse waves were observed when a radioactive material approached to the fabricated device.

To realize extremely low-power consuming sensor systems, a SOHI (Silicon on Honeycomb Insulator) wafer, which has ultra-small parasitic capacitance, is proposed and an accelerometer is fabricated to demonstrate use of the technique. In case of using a low-power-consumption switched capacitor measurement circuit, parasitic capacitance decreases sensor sensitivity dramatically. The concept of the SOHI wafer is a special SOI (Silicon on Insulator) wafer with the buried SiO2 layer replaced with a honeycomb-shaped SiO2 thick layer (20 mu m thick) to reduce the parasitic capacitance. In this paper, two types of SOHI wafer, which could reduce the parasitic capacitance to about 21% and 2% of typical SOI wafers, respectively are proposed. On a trial production, the structure of a prototype three-dimensional accelerometer is fabricated. By demonstrating the application of sensor fabrication, the SOHI wafer is shown as a useable material as the base substrate. Also, the ability to realize the accelerometer with low parasitic capacitance by using the SOHI wafer is demonstrated.

For maintaining our health, we need to know our physical condition. The daily monitoring which is one of methods for taking our physical condition is very important. Because we have to attach such a monitoring device on some part of our body for taking our condition, noninvasive monitoring devices are needed. For realizing such a noninvasive monitoring device, several micro electro mechanical system (MEMS) based monitoring system has been developed. From a viewpoint of attaching monitoring devices on our body, the smaller size of such monitoring system is better. An ultra-small monitoring device should have ultra-small size power source. Therefore, we need to design and develop a very small size of monitoring software with lower power consumption.

Surface MEMS (microelectromechanical systems), which is fabricated by the micro processing techniques based on thin film deposition and processing, are incorporated into consumer electronics and automobiles. The structures of the surface MEMS having thin shape with small aspect ratio are difficult to drive to the lateral direction. The conventional electrostatic actuators have comb electrodes, resulting in a complex structure. This research addresses on the actuators available to move in a lateral direction by using thin-film Pb(Zr, Ti)O3. Test cantilevers with two segmented top electrodes on the piezoelectric film are fabricated and the driving characteristics are evaluated. Applications of electrical voltages with reversed phases to the segmented top electrodes at the resonant frequency with lateral oscillation mode moved the cantilever with large displacement of 7 mm. A non-linear effect in the frequency response was also observed for the large applied voltages. © 2012 IEEE.

This paper presents a wearable PPG (photoplethysmographic) sensor system with a PSoC microcontroller unit (Cypress Semiconductor Corp., USA). We have developed a pulse wave monitoring system on earlobe, which has a PIC microcontroller and analog circuits. However, analog sensors need some discrete parts, resulting in difficulty in reducing the system size. The PSoC microcontroller includes a CPU, analog and digital blocks to configure mixed-signal circuits, and an internal oscillator in a single IC package. Therefore, PSoC allows designers to reduce the number of external discrete devices and the system size. The novel system consists of a photo interrupter, the PSoC, and the Bluetooth module, which are on PCBs (Printed Circuit Board) of 18, 13, and 10 mm in diameter, respectively. The photo interrupter detects the pulse wave due to the change in volume of blood vessels. The PSoC includes an analog filter, amplifiers, and digital circuits to calculate HR (heart rate) from the pulse wave of human body. The system was able to detect the pulse wave and transmit the HR data to a PC wirelessly. The power supply voltage is 3.3 V, and the total current consumption is about 51 mA. In comparison with the previous work, the area of discrete RCL (resistor, capacitor, and inductor) devices is reduced from 1230 mm(2) to 466 mm(2), and the number of such devices is reduced from 26 to 6.

This paper describes a development of MEMS (Micro Electromechanical Systems) -based electrostatic energy harvester for scavenging energy from ambient vibration. Generally, power output of electret harvester is increased with the narrower air-gap between an electret and an opposite electrode. However, electrostatic attraction force between the electret and the opposite electrode is also increased. Hence the gap control is crucial to avoid the pull-in. We measured the displacement of the vibrating mass moved by electrostatic force. As a result, the electric discharge between the Si grid and the base electrode (BE) is occurred when the BE was supplied over 110 V. The vibrating mass is pulled-in at 150 V if the discharge does not occur at the potential. Therefore we proposed and design the electrostatic energy harvester using the micro spacer to prevent the pull-in situation. The size of the spacer is 86 x 86 x 27 mu m(3) to prevent the mass fixed by the friction.

The authors have been developing a human monitoring system for preventing various kinds of human errors and for realising safe, reliable and comfort public transportation. Electrocardiogram (ECG) is one of the most important physiological indices of human response to a variety of stress environment. Recently, MEMS (Micro Electro Mechanical Systems) became the centre of attention for its features of small size and low-invasive measurement. In this research, a Mini-Electro-Mechanical-Systems apparatus was introduced for measurement of ECG. R-R intervals of heart beat during operation were extracted by using a filtering technique, and this helps to reach the stage of practical application of in-situ analysis and evaluation of heart rate variability.

Electret materials are useful for electrostatic type energy harvesters. Since the power generated from the electret energy harvester is proportional to the surface charge concentration, i.e. charged voltage on the electret, frequency and dynamic range of the capacitance change. To fabricate the electret, the corona discharge is a very popular charging method, which consists of a high voltage needle for corona ions generation and a grid electrode applying a bias voltage that implants the electrons from corona ions to the electret material. We have established the charging method with finely patterned charging area by using the buried grid electrodes (BGE) applied with a bias voltage for organic material CYTOP. However, CYTOP has slightly poor characteristics in terms of the thermal robustness. In this study we report a fabrication technique of the selectively charged SiN/SiO2 as electret material alternative to the CYTOP. By using the BGE method to SiN/SiO 2 film, a fine patterned electret with highly thermal robustness was obtained. © 2012 TSI Press.

In order to maintain our health care, daily monitoring our physical condition is very important. A multiple microelectromechanical system (MEMS) based monitoring system has been developed. The MEMS based monitoring system is developed for aiming noninvasive and unconstrained monitoring to our physical condition. From a viewpoint of the hardware, the smaller size of such monitoring system is better for us. Additionally, the smaller size is better for power consumption. Therefore, we need to design and develop a very small size of monitoring software. Two-step abstraction method for estimating human behavior had been proposed. In this paper, we propose an extended method of the two-step abstraction for ultra-small hardwares.

This paper reports an evaluation of a human vibration for autonomous power source that generate an electrical power from human vibration. The actual energy harvesting results from the MEMS (micro electromechanical systems) electret based energy harvester on the human body is also described. The harvester consists of the silicon grid structure, stripe-pattern charged electret material and support spring structures. Using a multipurpose data-logging device that can gather the 3-axis acceleration, pressure, humidity temperature and also harvesting voltage simultaneously investigate an actual harvested power from the human movement.

Continuous human monitoring is substantially useful to realize a high QoL (quality of life) society. In the previous work, we fabricated a prototype system for monitoring an electrocardiograph (ECG), heart rate (HR), 3 axes human body acceleration, temperature for human body and human circumstances, simultaneously. These data are transmitted to the host PC and used for analyzing the human activities and conditions such as a heart rate variability (HRV). The HRV that calculated from HR is valuable for recognizing a mental or physical stress of human subjects. In this study, we demonstrate a fuzzy logic HR extraction algorithm on the prototype system to realize an autonomous HRV monitoring system. On-board fuzzy algorithm will reduce the communication traffic and improve an accuracy of the HR extraction. From the implementation result, the error ratio of the HR extraction is improved from 0.9 % to 0.4 %.

In this study, an electret charging method for fabricating energy harvester with SiN/SiO_2 film that is selectively charged by using biased electrodes is demonstrated. Inorganic material of SiN and SiO_2 have high thermal robustness to endure the soldering temperature and the electret charging method by using the biased electrode doesn't require physical patterning of the electret film. Our charging method to SiN/SiO_2 film, a fine patterned electret with highly thermal robustness is obtained.

In this paper, we presented a measurement of power output versus acceleration with a data logger. The vibration energy harvester consists of a Si grid, a vibration mass, which has a charged electret film, and a cover glass. The data logger can measure voltage outputs, acceleration, temperature, humidity, and electrocardiogram (ECG). Accelerations and output voltages from the harvester were measured by 10 bit ADC (analog-to-digital converter) and the sampling frequency was 125 Hz. The power output at different accelerations on modal thruster is calculated by the output voltage from the harvester and the 20 MΩ load resistance. The power output was proportional to acceleration and the maximum generated power was 17.3 nW. The generated power worn on ankle while walking was 2.1 nW.