Impedance changes in phospholipid LB (Langmuir-Blodgett) and protein-mixed phospholipid LB films by several taste substances were measured. The resistance of the phospholipid LB film increased by bitter and sweet substances, whereas the resistance decreased for salty, sour and umami substances. For sweetness the larger change was observed in the protein-mixed phospholipid LB film, and hence discrimination between sweetness and bitterness was possible.

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A planar humidity sensor using anodic oxidized aluminium film (Porous alumina) has been developed. The basic structure of sensor is similar to n-MOSFET except that the gate region is formed by porous alumina as a humidity sensing element. Anodic oxidation is carried out in dilute H₃PO₄ solution at constant voltage of 10V. The sensors show a large current response for exposure to a high humidity (>50% RH) at room temperature. The time response of sensor during transient exposure to humidity is a few minutes. The mechanism of the current response to humidity is qualitatively discussed.

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A new method for detecting dissolved oxygen in water is proposed here. The sensor is based on the enhancement of fluorescence yield by an interaction between tetoraphenylporphine (TPP) dye and oxygen molecules. In the presence of oxygen, when pumped by a He-Cd laser line of λ=441nm, it produced a strong fluorescence at around λ=656nm. The fiber-type sensor head was fabricated by cladding the fiber core (ARTON; n_d=1.51) with the poly-4-methyl-l-pentene polymer (PMP; n_d=1.47) doped with TPP. The experimental results indicated a good enhancement in the fluorescence for both oxygen gas and water dissolved oxygen (DO). The response was found to be linear and stable in the range of 100ppm- 1% for oxygen gas and lmg/l- 8mg/l for DO. The theoretical analysis and the sensor response for change in termperature are also discussed.

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Output patterns of four types of tin oxide gas sensors for compound gaseous indoor air-pollutants are investigated. The sensor patterns prefer higher gas-sensitivity characteristics when there is a compound gaseous pollutant including two kinds of gases. After the experimental system detects a lower gas-sensitivity pattern in a residence, it can detect a higher one. The reverse is impossible. Three NDVs (NDVA, NDVC, NDVN) characteristics are also adopted to increase the reliability of the system. NDVA characterisitic decreases for a few minutes and gets back to an original state or under the state when an alcoholic gas generates. The system can identify whether the alcoholic gas is generating or not in an indoor environment by using NDV characteristics with high reliability.

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A search for semiconducting oxides was carried out to design a sensor selective to NO over NO₂. Bi₂0₃ was very selective to NO though not very sensitive among the various oxides examined, and NiO was proved to be the most effective promoter to Bi₂0₃ for enhancing NO sensitivity. The sensor element using 5wt%NiO-Bi₂O₃ showed fairly good sensing properties to NO in the range of 0-400ppm in sensitivity, selectivity over NO₂ and response rate, at 300°C. The cross-sensitivities to C₃H₆, C₃H₈, H₂ and O₂ were modest or insignificant, compared to the sensitivity to NO. Catalytic activity tests and TPD measurements indicated that the response to NO (increase in resistance) was associated with its reaction with the surface oxygen of the element, while that to NO₂ (decrease in resistance) resulted from its anionic adsorption.

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The authors have developed a novel chemical imaging sensor, which enables us to observe two-dimensional pH-distribution in an electrolyte solution. A sample solution is in contact with the insulator (Si₃N₄/SiO₂) on the Si substrate, which forms the electrolyteinsulator-semiconductor (EIS) structure. When modulated laser beam illuminates the backside of the Si substrate, ac photocurrent flows through the EIS structure. Since the photocurrent depends on pH value on the illuminated region, the two-dimensional pH distribution can be microscopically obtained by scanning the focused laser beam. The thickness of the Si substrate as well as the spot diameter of the laser beam restricts the spatial resolution of this sensor, This can be theoretically explained by the carrier diffusion model. The bonded Si on insulator (bonded SOI) wafer is employed for the thinner Si substrate. The chemical anisotropic etching is used in order to remove the Si bulk of SOI wafer. Using the sensor with the active Si thickness of 20μm, the spatial resolution as good as 5μm was attained. It is also estimated that the pH resolution is good as 0.01 in pH.

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A sensitive chloroorganics sensor using lipid coated quartz crystal microbalance (QCM) was developed. The mass change caused by a selective adsorption of chloroorganics on the surface of thin lipid film was detected as a frequency change of the QCM. Among the several lipids tested, the DC-7-12 gave the highs sensitivity for Trichroloethylene (TCE). A QCM coated with 5000ng of DC-7-12 gave the frequency change of 53Hz per 1000ppm of TCE, the calibration curve was linear up to 1000ppm. The response time was less than 2min. The sensitivity gradually decreased but it still showed more than 90% sensitivity after a months. By increase the amount of the coated lipid and by increase the basic frequency of the QCM, the sensitivity was improved up to 179Hz per 1000ppm. A possibility of selective determination of three different chlorrorganies was also shown by using the thin QCM coated with different kind of lipids

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We have developed a multifunctional humidity-gas sensor on a silicon substrate by using thin-film technology and IC fabrication process. The size of the sensing film is 400μm×400μm, which is defined by photolithography. The sensing film is composed of Fe₂O₃(91mol%), TiO₂(5mol%) and MgO(4mol%). It is deposited by rf sputtering on a porous Al₂0₃ film, which is made from Al by anodic oxidation. A Ta film is used as the bottom electrode while a Pt film is used as the top electrode. A part of the Ta film is oxidized into Ta₂O₅ just below the porous Al₂O₃ film. The impedance between the two electrodes is measured as a function of relative humidity or gas concentration.
This sensor is sensitive to humidity when it is kept at room temperature. It is also sensitive to hydrogen gas when it is heated to 400°C. The porous structure increases the adsorption of water and gas molecules. The sensor is entirely made of stable materials with high melting points. So its sensitivity is recovered to its initial value by heat cleaning. The response times of the sensor to humidity change and concentration change of hydrogen gas are short.

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We have developed an integrated thin-film gas sensor using semiconducting thin-films on an SiO₂ diaphragm, which is formed on an Si substrate. A micro heater is fabricated on the same diaphragm. The fabrication procedure is based on thin-film and micromachining technologies and IC fabrication process. The two sensing films are composed of multi-layered metal oxides; an SnO₂-based film on an Fe₂0₃-based film and a WO₃-based film on an Fe₂0₃-based film.
Both of the films are sensitive to reducing gases such as hydrogen (H₂), isobutane (i-C₄H₁₀), and carbon monoxide(CO) as well as NO_x gases when they are heated to 400°C by feeding an electric power of 540mW to the heater.
The advantageous features of the sensor are as follows. It is a small and light-weighted device. It does not consume much materials and energy in the fabrication process. It does not contain any hazardous or poisonous materials that contaminate the environment. It can be mass-produced. It would be promising as a smart sensor in conjunction with electronic circuits on the same substrate.

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Improvement of the stabilization and repeatability of the sensor response was investigated for the development of a tea taste sensor. For a semiconductor taste sensor (SPV sensor) with lipid membrane as the sensitive film, various washing methods were studied for the electrode cleaning after the tea taste measurement since hydrophobic molecules remain on the surface even after water rince. As the results, it was shown that effective refreshing method is possibly found by the selection of washing chemicals although the cleaning effect is different for the different lipid membranes. It was next shown that the commercial ion sensor was successfully applied as a tea taste sensor. The response was highly stable for the repeated measurements of the tea taste.

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We investigated thin catalytic metal gate Schottky diodes and pn heterojunctions for NO_x detection. Thin Pt-Pd/Si/Al Schottky diodes were employed successfully to detect NO₂ concentrations from 6ppm to 30ppm and NO concentrations from 50 to 250ppm, with a response roughly proportional to the logarithm of gas concentration. We investigated the fabrication of the diodes on a porous Si surface and the formation of a Si/WO₃ heterojunction as possible ways to improve sensitivity. Diodes fabricated on porous Si showed slightly higher sensitivity to NO₂. The sensitivity of a Pt-Pd/WO₃/Si/Al heterojunction was comparable to the sensitivity of the Schottky diodes. The differences between the sensing mechanisms of these structures were also investigated and the results suggest that they provide different possibilities to enhance the sensitivity. An advantage of these sensors is to operate at room temperature. Moreover, the semiconductor junction structure is convenient to make smaller and intelligent sensors. Therefore, these structures may be considered for future development of NO_x gas sensors at room temperature with miniaturization, integration and power saving features.

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If blood glucose levels measuring procedure is developed that can monitor blood glucose levels noninvasively, it will ease medical check drastically detection and cure of the disease at an early stage. This study aim to develop a noninvasively measuring of blood glucose using saliva. We manufactured a saliva analyzing system using glucose sensor and performed in vivo evaluations of it. As the results, it was cleared that determination of saliva glucose levels were in the range of 0.1 to 10.0mg/dl. This system allows us to monitor the time-course changes of saliva glucose levels. Thus, this measurement system of saliva glucose levels can be used as an indicator of blood glucose levels.

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The novel semiconductor NO_x gas sensor based on a heterojunction structure workable at room temperature has been investigated. The sensor consists of Pt/Tin-dioxide (SnO₂)/n-Si/p⁺Si/Al in which vertical direction current between Pt and Al electrode was measured with applying reverse direction bias voltage on Pt electrode. All the films including SnO₂ with the thickness of 50_??_200nm were deposited on an epitaxial layer of n-Si over p⁺-Si substrate by RF sputtering method. As a result, the current in the sensor decreased when the gas flow was switched from dry air to mixed gas of air and NO_x. Clear response was obtained at the NO_x gas concentration as low as 1ppm at room temperature, while the almost no response was observed for the n-Si and p-Si substrate. The generation of large change in current for the sensor with heterojunction structure was considered that barrier height change or conductivity change of SnO₂ gas sensitive layer may cause the modulation of the depletion layer at the n/p⁺-junction of Si substrate.

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Detection of some toxic substances in water is a time consuming process because large number of substances need to be analyzed. When some toxic substances in the drains flow into the river, they cause environmental destruction. Accurate detection of substances which have serious effects on living organism is required as well as short measurement time. Although a sensing system employing living fish is devised, there are some problems in reliability, maintenance and evaluation because they are living thing. It is possible to measure the influence of pollutant for living organism directly by a sensor which is similar to biological systems. So we investigate a method of detection of toxic substances by multichannel lipid membrane sensors which are modeled on living organism.
SA401 has multichannel sensor with lipid membranes which are modeled on living organism. It is able to detect some toxic substances in the water. For the reason, this system has been applied to measure water quality, such as, mineral water, tap water, contaminated river water and factory drains. We have found this method is effective and many pollutants (e. g. CN^-, Fe³⁺, Cu²⁺, etc.), in factory drains, have been measured in a few minutes, the detection limits are lower than regulations of drain. It is possible to detect cyanide of factory drains selectively in short time by applying lipid membrane sensor. In conclusion, it is an effective mean to use multichannel lipid membrane sensors for observation of water quality especially for factory drains.

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A bulk-micromachined silicon angular rate sensor has been developed. Electromagnetic excitation is adopted for driving its resonator with a large amplitude vibration (70μm). The induced vibration by the Coriolis' force is detected by electromotive voltage. The sensor is composed of a silicon-glass-magnet structure and only three masks are needed for this process. The sensitivity of this sensor was 233μV/(deg./sec) and highly sensitive and low cost silicon angular rate is achieved.

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A capacitive AFM probe having capacitive structure was fabricated by micromachining techniques. For obtaining a high sensitivity and a low voltage-actuation, the thin micro sensor consists of a single crystalline-silicon with a narrow gap between micro-cantilever and opposite electrode was fabricated. The gap is lμm, the thickness of the cantilever is 0.5μm, and the size is 80×100μm. As a result of evaluation of the performance, the micro-probe showed a sufficient performance for nanometric sensing. The capacitive AFM probe has a both functions for sensing and actuation, because the deflection of the micro-cantilever can be measured from the capacitance, and the micro-cantilever can be electrostatically actuated. By reducing the cantilever size, the operation with a high speed imaging is expected.

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