Long-term durability is essential for those fiber-optic sensors that detect changes of the optical properties due to the mechanical deformation of the sensing fiber. The lifetime of a sensing fiber determines the durability of the sensor, and the debonding of the polyimide coat to the fiber affects the fiber lifetime. We report in this paper the debonding property of a water-resistant polyimide coat under high temperature and humidity. We found that the adhesion property of the polyimide film improved when an adhesion promoter was added. We also found the optical fiber showed an excellent adhesion property after being exposed to 85°C and 85% relative humidity for 1000 h . This protective coating of a water-resistant polyimide makes it possible to fabricate more reliable optical fiber sensors.

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We investigated a new measurement method of mechanical characteristics of thin films which are used as structural materials in MEMS devices. This on-chip tensile testing method is characterized by that the tensile specimen and loading mechanisms are integrated on a same silicon chip. We proved the accuracy of the stress and strain measurement by measuring Young's moduli of single-crystal silicon films having different crystallographic orientations. The measured Young's moduli showed good agreement with results from separately performed bending test and values in literature. Thus we concluded that the stress and strain measurement was correctly performed with our new method.
We developed a fabrication process of testing chip that allows tensile testing of single-crystal silicon film having arbitrary crystallographic orientations. The process starts with an SOI wafer whose top layer having a certain orientation was carefully aligned against the lower wafer. With three steps of etching, we fabricated test chips of 12×12×0.4mm, containing a specimen of 14_??_21μm thick, 80μm wide, and 400μm long.

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Mechanical properties of titanium thin films of 0.40μm thickness, microfabricated by magnetron sputtering, were measured by using a novel tensile machine. The test section of these specimens was 0.3mm in width and 1.4mm in length. The stress concentration factor at the fillets of the specimens was about 1.02, therefore, the designed shape of the specimens was suitable for uniaxial tensile tests. Tensile tests were conducted on specimens of 1.0 to 1.4mm gauge length in order to examine the effect of gauge length on the measurements of mechanical properties. Stress-strain diagrams of thin films were measured continuously in the atmosphere at room temperature. Specimens didn't neck down with almost no plastic deformation. Fractured specimens and measured stress-strain diagrams showed that the material had a low ductility. The experimental results indicated that measurements of Young's modulus and breaking elongation were independent of gauge length for our range of measurements.

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The TTP (Temperature-sensitive Magnetic Thin Film Photosensor) is a device, which converts the magnetic change due to received radiation-light power. Up to now photoelectrical sensors using photoconductive, photovoltaic, photoemissive and pyroelectric effects have been put to practical use. The authors have already proposed the sensor system using a TMC (Temperature-sensitive Magnetic Thick Film) of 55μm-thickness and a Hall element, however it shows a slow response because of its large size. Then, the miniature-sized sensor TTP system combined with a TMN (Temperature-sensitive Magnetic Thin Film) of 1μm-thickness prepared by RF sputtering and a magnetoresistance element has been investigated. When the TTP is irradiated by light, itt receives its energy and the device temperature rises, which causes magnetic change. After this minute change is read out by a magnetoresistance element, it is converted into voltage. The TTP to the step input of light has the pulse response of which the peak value is proportional to lightt intensity. The TTP gives a quick light. response of about 0.2 second, which is below 1/20 as compared with the sensor system using the TMC.

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In this paper, a novel optical encoder having pitch-modulated photodiode array as an index scale has been proposed for integrating the gratings with the detectors. The pitch-modulated photodiode array, which obtains four phase-shifted signals simultaneously, is specially designed to reduce higher harmonics distortions of displacement signal and then fabricated by using integrated circuit process technology. In a preliminary study, the effect of the sensitivity distribution of the photodiode on the measurement has been evaluated. In the encoder experiment, it is shown that the 3rd and 5th order distortions for the pitch-modulated pho-todiode array are reduced by approximately a factor of more than 10, and are almost independent of the air gap between the main scale and the index scale. The proposed encoder is effective for obtaining precise positioning.

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We have fabricated an electrostatic servo capacitive pressure sensor by using bulk silicon micromachining and SODIC(SOot-Deposited Integrated Circuit) wafer. The sensor consists of fixed electrodes and two diaphragms which are connected with pillars to move together for electrostatic servo force balancing. It detects pressure by the servo-voltage which is supplied between the lower diaphragm and the fixed electrodes to keep the diaphragm at the initial position. The diaphragm position is detected by the capacitance change between the upper diaphragm and the fixed electrodes. The capacitances versus pressure and the servo-voltage are measured. The results of these mea-surements show that this sensor can detect the pressure by the servo-voltage and have high sensitivity and wide dynamic range in comparison with the open-loop sensors. The sensor has an advantage that it is not affected by dusts or particles because the capacitor gap is isolated from the external environments.

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A micro infrared filter capably of transforming a transmitted wavelength is the most important component of a micro infrared spectroscope. This report describes the spectrum characteristics resulting from a Micro Variable Infrared Filter being experimentally produced. The design theory of the filter is based on the phenomenon that as the spacer layers thickness varies along the length of the filter, so dose the transmitted wavelength. The correlation between coating thickness and spatial position is very repeatable. We adopted a structure that transforms the center wavelength by changing the thickness of the only type spacer layer in the five layers SHW filter. The thickness of the spacer ranges of 400nm to 550nm. By using a sputtering system that includes a slit shutter with a film thickness error within 1% of the 1inch diameter, we can make the Micro Variable Infrared Filter with a continuous wavelength of 1.8 to 2.1μm. The results of the experiment are in good agreement with the thinfilm optical simulation for the spectrum transmission characteristics, with the linearity of the transmitted band being within 1% for different wavelengths.

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Current (I)-voltage (V) characteristics of porous ZnO varistors with and without Bi₂O₃-based, Cr₂O₃ and Y₂O₃ additives have been investigated in air as well as in NO₂ and NO at elevated temperatures. All the varistors exhibited nonlinear IV characteristics under every atmosphere, whereas the nonlinearity tended to deteriorate with a rise in temperature. The breakdown voltage of all the varistors shifted to a high electric field upon exposure to NO₂, and the magnitude of the shift, i.e. the sensitivity to NO₂, was increased by the simultaneous addition of Bi₂O₃-based additive and Cr₂O₃ (or Cr₂O₃+Y₂O₃) at 300°C. However, the sensing behavior of NO depended markedly on both the compositions of the varistors and the operating temperature. The breakdown voltage of pure ZnO and ZnO added only with the Bi₂O₃-based additive shifted to a low electric field upon exposure to NO at 300°C, but it shifted to a high electric at higher temperatures. This suggested different chemisorption states of NO on the surface of ZnO, i.e., NO⁺ (nitrosyl-type) at 300°C and ONO_??_ (nitrito-type) at higher temperatures. Further addition of Cr₂O₃ or Cr₂O₃ plus Y₂O₃ resulted in a shift to a lower breakdown voltage upon exposure to NO at every temperature, suggesting the stabilization of NO⁺ adsorbates even at higher temperatures. Especially at 300°C, the further addition led to enhancement in NO sensitivity. A. c. impedance measurements have revealed that the variation in the potential height induced by the chemisorption of NO₂ and NO determines the resistance of the grain boundary and hence controls the breakdown voltage of the varistors.

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We report a new self-alignment technique of surface-micromachined polysilicon structures to bulkmicromachined silicon V-grooves which are used to accommodate optical fibers. Most of the conventional surface micromachined optical structures have used thin guiding rails or marks on a silicon substrate to align optical fibers to microstructures, and thus they require careful manual positioning. We have newly developed a technique to hold fibers in V-grooves, which have been defined at the same time as optical microstructures, to eliminate fiber manipulation for alignment. The process is simple with only two additional masks to the existing surface micromachining process and can be generally applied to MEMS fabrication.

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This study proposes an optical fiber coupler sensitive to strain for matrix-style sensor array. It consists of a crossed fiber pair which has optical coupling through the radiated light from the grooves made on the fibers. The stress/strain is detected as a modulation of the magnitude of optical coupling. In this letter, this optical coupler has been applied to a 4 × 4 sensor array for trial, and some measurements of stress distribution are demonstrated.

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