Optical Coherence Tomography (OCT) is an imaging technology that has stimulated considerable interest in the medical application, because it can noninvasively observe cross section of an object such as retina and skin tissues. Fast Swept Source OCT (SS-OCT) is one of the promising methods thanks to the high-speed frame rate and large S/N ratio comparing with those of the conventional time-domain OCT. Key specifications of OCT are frame rate, resolution and penetration depth of the light. In particular, fast frame rate over 100 kHz is required for the next generation OCT. We have developed a fast swept-source laser using a micro electro mechanical systems (MEMS) optical scanner of 2-degrees of freedom (2-DOF) vibration mechanism and demonstrated the OCT at 140 kHz utilizing bi-directional wavelength sweep.

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This paper describes a stochastic MEMS sensor, which will be used in low S/N environments like in high temperature plants. A mass which vibrates between two counter electrodes by white voltage noise is “pulled in” to either of the electrodes by the application of pulse voltage to the mass. The direction of the pull-in is determined stochastically, and the probability that the mass is “pulled in” to a particular side depends on mechanical strain applied to the sensor structure. The behavior of the stochastic MEMS sensor was simulated using a developed simulator based on a physical model. The stochastic MEMS sensor was prototyped on an SOI wafer and the probability was measured as a function of the bias voltage. This experimental result was compared with the simulated result. Both results agree well, confirming the validity of the developed simulator and the physical model.

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A new type preconcentrator was realized by using a SAW (Surface Acoustic Wave) device and a peltier device to raise concentration of a low-volatile compound efficiently and rapidly. It can rapidly desorb odor with the low-volatile compound in comparison with a preconcentrator tube using adsorbent material. In the proposed device, the odor is atomized using acoustic streaming caused by the SAW device after it accumulates the odor on a surface of that device cooled by the peltier device. A new measurement cell including both the preconcentrator and a QCM (Quartz Crystal Microbalance) sensor was fabricated to increase sensitivity. As a result, we obtained much higher response of the QCM sensor to 1-nonanol, one of low-volatile compounds, due to the preconcentrator effect in comparison with a previous structure of the preconcentrator cell separated from the sensor.

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For the first time a peripheral electrode is employed to a high-frequency quartz plate resonator that has a rectangular excitation electrode. The two-dimensional finite element method is used to optimize the electrode and verify resonator performance. The results show that optimized electrodes provide effective energy trapping and less vibration coupling. The optimized peripheral electrode efficiently suppresses inharmonic overtone mode. High Q-factor is also achieved.

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A thin film piezoelectric actuator stacking five PZT (Pb(Zr_0.52,Ti_0.48)O₃) layers has been developed to achieve large displacement and large force at low driving voltage. In this paper, the fabrication process and the operation characteristics of the developed PZT actuator are reported. Each PZT layer of 200nm thickness was deposited by sol-gel method and sandwiched with thin Pt electrodes, which were electrically connected to plus and minus terminals alternately. The displacement-force characteristic of the fabricated actuator shows the maximum displacement of 43µm without load and the estimated maximum contact force of 16µN at a driving voltage of 5V. The developed PZT actuator is applicable to RF-MEMS switches, which need both high contact force and large isolation gap within a limited footprint.

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We have developed a tactile sensor network system, which consists of integrated MEMS-LSI tactile sensors (sensor nodes), relay nodes, a host and flexible bus power/interconnection lines for mounting a large amount of tactile sensor elements on the whole body of robots. Each sensor node, which is connected on the common bus lines, transmits sensing data independently to the relay node on the bus when exceeding a predefined sensing threshold value. There are system-level issues such as a threshold value choice for sensing data transmission and a throughput control considering data collision on the bus line. Before fabricating the integrated MEMS-LSI sensor devices, performance of the whole system should be estimated, because to fabricate the integrate devices is expensive. In this paper, we report a less costly simulated network system for resolving the issues without the integrated devices. The simulated system uses easily-available components such as discreet sensors, FPGAs (Field Programmable Gate Array) and a PC. In the system, we implemented sensor node monitoring circuits to analyze network characteristics precisely. The circuits cannot be implemented in the real integrated devices and systems. By using this simulated system, we analyzed data collisions and average transmission delay time. The experimental results show that in the case of 20 sensors pressed with strong forces simultaneously the data collision rate is about 44% when the transmission rate is 1Mbps and about 0.7% when the transmission rate is 10Mbps, respectively. We found that when more sensor nodes transmit their data on the bus simultaneously and/or the transmission rate is lower than several Mbps, each sensor node should control the network traffic for avoiding the collisions with a more smart control mechanism than a simple mechanism we applied.

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A new z-axis capacitive accelerometer for the airbag system has been developed. This accelerometer has a unique sensing mechanism by which the displacement of an inertial mass caused by acceleration in the z-axis direction is converted to the rotational displacement of a pair of detection plates. Significant immunity of the sensor output to extremely high-magnitude acceleration with high frequency has been attained by the squeeze damping effect and its variable resonant frequency structure. Accurate collision velocity detection without mechanical contact between movable electrodes and fixed electrodes is demonstrated by the high frequency impact tests.

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In this work, we have developed an alternative and improved “optical softlithographic” microfabrication method for patterning on a concave substrate as well as the fabrication of micro patterned PDMS cylindrical stamps for the potential application to nano imprinting. Firstly, we fabricated SU-8 micro patterns with high aspect ratio (over 4) on a concave glass substrate using optical softlithography, where UV light was exposed through a very flexible mask attached on the concave surface. We investigated the optimal experimental conditions depending on shapes and scales, and examined the resolutions of patterns. Next, we replicated a PDMS cylindrical stamp using SU-8 micro patterns as a mold. Intermediate female molds were made from the original cylindrical mold. Then, the stamp was made by filling the intermediate mold with PDMS monomer and solidifying it. Thus, this technique provides us with novel fabrication technique of 3D micro patterns on curved substrate as well as a cylindrical polymer stamp for roll micro contact printing.

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We developed a silicon electret condenser microphone (ECM) fabricated with the micro-electro-mechanical systems (MEMS) process using single-crystalline silicon. A silicon ECM has a SiO₂/Si₃N₄ inorganic electret film (permanently charged dielectric) within microphone element, and it can remove 48-V bias voltage. We confirmed that a prototype microphone operated with 3-V or 1.5-V power supply had excellent acoustic characteristics. Experimental results also show that developed silicon-based electret had high heat and humidity resistance. We conclude that it is feasible to use such low-voltage high-performance MEMS microphones for a wide range of applications such as broadcasting, hearing-aids, and mobile communications.

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In this study, the prototype of CMOS Inverter-Based Differential Amplifier has been developed with ROHM 0.18 mm standard CMOS process. In order to get high DC gain, Nauta’s operational transconductance amplifier (OTA) is adopted as the amplifier stage and nested miller compensation is selected as the phase compensation. The measurement results indicate that power consumption is 18µW, DC Gain is 71dB, input offset voltage is 1.2mV, CMRR is 57dB and PSRR is 83dB at the supply voltage V_DD=1V.

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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.

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We conducted uni-axial tensile test using electrostatic-force grip on thin film single crystal silicon of <110> direction. The specimens were fabricated on (110) SOI wafer (length: 120µm, width: 5µm, thickness: 5µm) and went through 3 different conditions of patterning process composed of Bosch process and wet etching process for surface residue removal. As a result, improvement of surface morphology brought increase of average tensile strength from 1.9GPa to 3.6GPa. SEM observation of fractured specimens suggests that, regardless of processing conditions, relationship between tensile strength and the top-view length of (110) crystal plane of specimens can be expressed with a common equation.

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