The sequence of optical MEMS development is described, wherein research reached its climax in 2000, during the tumultuous crescendo of the telecommunication industry boom in USA and slowed down thereafter. However, recently in Japan, there are indications that efforts to fabricate stable high-performed devices are on-going, although not on a large-scale. The problems to be solved to facilitate the research of optical MEMS are also mentioned.

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Recent developments in CMOS image sensors are reviewed. High-speed, wide-dynamic-range, and range or 3D cameras are typical examples of recent success of CMOS image sensors. The fastest CMOS image with 100 M pixels reaches 2000 frames/s. Many techniques for achieving wide dynamic range have been proposed. CMOS image sensors employing wide dynamic range pixels with logarithmic response are applied for imaging of arc-welding process. CMOS sensors for real-time range imaging based on light stripe scanning, TOF (time of flight), and stereoscopic measurement methods are developed. The image quality of CMOS image sensor is being improved by the process technology and signal processing techniques.

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An electrostatically driven tunable Fabry-Perot filter with wide wavelength range from 2.5 µm to 4.5 µm has been developed by silicon-CMOS-compatible and MEMS fabrication process. For the movable mirror, we adopted a three-layer membrane which consists of polycrystalline silicon, silicon nitride and polycrystalline silicon. To optimize the mechanical characteristics of the membrane, such that the membrane stress and the driving voltage, as well as to optimize the optical characteristics, the thickness of the membrane and annealing temperatures are designed such that the top and bottom layers have opposite stress to the middle layer. This paper describes the optical and mechanical designs, fabrication process and results of evaluating the fabricated devices.

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We present a new architecture of a 2-axis comb-driven micromirror array that combines a large deflection angle in a stationary operation, a low drive voltage, and easy scalability for a 3D MEMS optical switch. By using an SOI wafer with 100-mm thick top and bottom Si layers and a 1-mm buried oxide layer and, bulk micromachining with DRIE, we fabricated a 2-axis comb-driven micromirror array with a V-shaped torsion bar and comb teeth. To implement a 2-axis tilt motion, we fabricated a gold bump for creating a gap under the comb teeth on the electrode substrate and mounted the mirror array substrate onto the electrode substrate by using the flip-chip-transfer technique. We fabricated an 80 x 80 switch chip and achieved a +/-5 degree rotation of the 2-axis stationary operation with a 60-V drive voltage.

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We have designed, fabricated, and evaluated a micromachined optical scanner intended for optical measurement systems. It consists of a micromachined Si resonator, a Si spacer and a permalloy piece for electromagnetic actuation. An FEM-based simulator was used to design both a scanner structure and a magnetic circuit. We replaced a tuning fork scanner with the micromachined scanner in a commercial equipment for measureing the diameter of strings. The measurement accuracy was as good as the commercial system, but the energy consumption was 10 times lower than it. Consequently, the micormachined optical scanner offers advantages for various optical measurement systems.

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Gray scale lithography has been recently researched to make 3D structures such as a microlens, prism etc. In this research, a novel gray scale mask was fabricated by chrome mask and EB lithography system that can apply bitmap data (tiff form file) to drawing data. The gray scale was realized using half-tone pattern which consists of array of micro spots (diameters are 0.2µm - 1.6µm). Thick positive UV resist (AZ-p4620) on Si was exposed, defocusing the half-tone pattern by holding the gap of 80µm. Relation between gray scale value and depth was examined, and Fresnel lens pattern was formed on the resist.

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Plant air-purification effect to reduce formaldehyde in a real office environment was examined. A potted Areca palm (height: about 2m) was adopted as a subjective plant. Plant purification effect was evaluated using a tin oxide gas sensor and a commercial tool for formaldehyde measurement was also used. The effect became higher as the atmospheric formaldehyde concentration was higher. The concentration became lower as the plants were installed. The effect did not greatly increase when the number of the installed pots was increased to seven from four. Concentration of carbon dioxide increased up to 450ppm by placing the pots at night. It is, however, below the regulated value (1000ppm) of Japan building managing law. Light intensity in the room fluctuated periodically and the carbon dioxide concentration changed periodically according to the fluctuation of light intensity from outside. There was a negative correlation between their characteristics. When the characteristic of carbon dioxide concentration was shifted forward by 1 hour with respect to the light intensity characteristic, the maximum value of correlation coefficient was obtained to be about -0.9. An integration value of a sensor output curve with time after the setting of potted plants could be regarded as a measure of an exposure volume of the plants to formaldehyde. The exposure value was found to become smaller as the number of the plants increased. In the experiment, formaldehyde was emitted continuously and the atmospheric concentration was kept at about 0.3ppm and the value was decreased to about 0.1ppm by the potted plants. This is close to the regulated value of 0.08ppm by WHO.

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In this paper, fabrication technology and device characteristics of junction field effect transistor (JFET) which can be integrated in CMOS sensor interface circuits are presented. The JFET is applicable to CMOS (operational) amplifiers to realize a very low-noise front-end amplifier in sensor interface circuits. It is formed with isolated p-well area in CMOS device. Extra processes to a standard CMOS technology are one photolithography process and two ion-implantation processes. N-type channel in JFET is formed by deep ion-implantation of phosphorous with energy of 150 keV to connect n⁺ source and drain regions. After that, p-type top gate region is formed by shallow ion-implantation of borron with energy of 30 keV. Fabricated JFET devices showed enough transconductance and low drain conductance, which are suitable to use them in analog amplifiers. Noise power-spectrum of the fabricated JFET was evaluated, and compared with n-MOSFET and p-MOSFET. As a result, noise-spectrum of JFET below 1 kHz was much lower than that of CMOS devices. Since many physical sensors have their signal bandwidth in low frequency band, this JFET device can be utilized in CMOS-based front-end amplifiers as the key device of low-noise sensor interface circuits.

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A new laser micromachining technique to realize high aspect ratio microstructure with free shaped wall using newly developed resist was proposed. The resist is made of ethylcellulose in which nano-particles with average diameter of 3.4 nm was dispersed. Since this resist has a strong absorption at wavelength of about 530 nm, it can be processed using focused low power output Nd: YVO₄-SHG laser (CW, wavelength of 532 nm, power output of 23 mW). From the experiments, it was confirmed that the cross-sectional shape can be controlled by the Au concentration (1-50 wt%) and the laser beam power. The processed depth showed a strong dependency on Au concentration and showed maximum at 17 wt% Au concentration. From the theoretical calculation of the resist temperature rise and analysis of the processed resist surface, it was revealed that the Au aggregation at the bottom of the processed channel played an important role for the processed depth.

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This paper treats a liquid propellant microthruster because its thrust flexibility and small tank are advantageous to pico-satellites for many types of missions. Two major fluidic concerns are investigated using test devices fabricated by MEMS technique. One is the catalytic decomposition of hydrogen peroxide in a microchannel. The other is the effect of wettability on two-phase flow. A platinum-coated channel with a height of 5 µm was found to work well because of its large surface-volume ratio. However, the heat dissipation into the structure components is critical especially for the starting period. An additional electric heater was tested and discussed for quick and effective operation. The dependence of boiling flow on surface wettability should be concerned for the fluidic design of microchannel-based liquid microthrusters. The test results showed that the electric heater is effective to obtain practical thrust from liquid propellant.

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Analysis of an electrostatic wobble motor is first strictly done by conformal mapping, especially by image method. Capacitances and torques calculated theoretically are in very good agreement with those calculated by FEM simulation, ANSYS, whose relative errors are within 1 %. Then, the effectiveness of detection of commutation timing is suggested by some numerical experiment based on this proposed analysis.

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The recent advanced in Fluxgate’s applications has spurred renewed interest in designing more accurate and omnipresent magnetometer. This paper presents on-chip embedded software design for a new generation of a portable digital fluxgate magnetometer using PIC (Peripheral Interface Controller). The system’s hardware has been modified to harmonize the new software design and its performance can be enhanced by modifying the embedded software.

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A new ocean pathways current detecting system has been designed and implemented using a Fluxgate Magnetometer technology with GPS data. The performance of the proposed detector is analyzed and compared to that of the conventional ADCP detector. Our design’s approach shows that the proposed system can achieve a significant performance and a low-cost detecting device compared with recent ADCP detector.

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