Sensors and Actuators最新文献

After discussing the features of a differential ISFET/REFET measuring concept, the published attempts to construct a proper REFET are summarized. It is concluded that the present REFETs are based upon the addition of a blocking polymeric layer to the gate surface of an ISFET, but that this approach fails with respect to the required insensitivity to ionic strength variations as well as with respect to the electrical stability.

As a solution to these problems, this paper describes the development of a REFET concept that is based on the chemical attachment of a non-blocking polymeric layer. Characterization methods of these layers with respect to the electrical as well as the chemical behaviour are given and discussed.

Finally, the experimental results of an acrylate/polyHEMA-REFET are shown in a differential ISFET/REFET system.

It is difficult to realize an odour or gas sensor with a high selectivity. From a biomimetic viewpoint, it is promising to make a sensor array and analyse the output pattern to recognize the various sorts of gases. We use six quartz resonators, with different coating materials, whose oscillation frequencies decrease when gas molecules are adsorbed on the sensing membranes over them. The pattern analysis method used in the present study is neural network pattern recognition. This network has been trained to identify the types of odours using the back-propagation algorithm. The system is trained to identify 11 kinds of liquors on the market and its recognition probability is 73% when the liquor signals used in the training are input. In order to enhance the odour recognition ability, the data vectors for the liquors are input to the network after subtracting those for aqueous ethanol solutions that have the same ethanol concentrations as the liquors. The recognition probability is then improved to 88%.

Five pressure sensors with a four-terminal gauge using shear stress have been developed. In order to obtain high fracture strength of the sensors, a quasi-circular diaphragm, in place of a square one, has been made by an aqueous solution of potassium hydroxide and isopropyl alcohol. Since a four-terminal gauge is small, four four-terminal gauges with different distances from the centre are made on a diaphragm so that an optimum gauge for various pressure ranges, i.e., various thickness of the diaphragm, can be chosen. This sensor makes a custom pressure sensor possible. For measuring very low pressures, a square pressure sensor consisting of a cross rib with the four-terminal gauge, thin membranes and a centre boss (EI-type cross-section) has been developed. This sensor can be used as an acceleration sensor by etching off the membranes.

Using TiO₂, ZrO₂ and SnO₂ as additives, the intrinsic electrical resistivity-humidity characteristics of MgCr₂O₄ material used for humidity sensors is varied. By choosing a particle size fraction of the starting powders with a radius less than or equal to 1 μm and varying the sintering temperature from 1200 °C to 1500 °C, the sintered porosity and pore-size distribution of the sensor ceramic elements are controlled. By macerating the ceramic elements with solutions of various salts containing CO₃²⁻ ions, the sensitivity of the impedance of the sensor elements to CO₂ in air is diminished.

After a brief introduction to the mechanisms involved in semiconductor gas sensors, questions of linearity and superposition are considered for mixtures of gases. It is established that Taguchi gas sensors (TGS) can provide a good approximation to a linear model and that superposition principles apply under certain conditions. This greatly facilitates the analysis of data and the identification of constituent components in a mixture of gases. Innovative techniques have been applied to alcohols and tobaccos with conspicuous success. These relate to pattern recognition and cluster separation, using simple mathematical procedures to enhance the identification of closely similar batches of test samples. It is confidently expected that many other applications for these methods will arise.

Long-life, integrated multiple-ISFETs with CMOS interface circuits have been developed. The interface circuits are designed for impedance conversion and rapid multiplexing of the signal from each ISFET. Three kinds of ion-selective membranes for sodium, potassium and chloride are formed on the gates and separated by a patterned thick polyimide layer. The poor adhesion of the polymeric membrane to the ISFET gate is improved by selecting the proper plasticizer for use in the membrane. As a result, a chemical response for sodium, potassium and chloride can be obtained for more than two months.

A durable sodium ion-selective field-effect transistor (ISFET) is proposed with Urushi as the membrane matrix. The sodium ion-sensing membrane is composed of sodium ionophore (ETH 227), di-2-ethylhexylphthalate, potassium tetrakis(p-chlorophenyl)borate and Urushi. The prepared Urushi matrix ISFET showed a linear response in the sodium ion activity range from 100 M to 10^−3.5 M and about 53 mV per decade change of sodium ion activity. The selectivity of the Urushi matrix ISFET was almost the same as that of the corresponding PVC matrix ion-selective electrode. The Urushi ISFET showed excellent stability with drift below 0.15 mV per hour and durability for over a month, because of strong adhesion of the membrane to the Si₃N₄ gate.

A new concept for the calibration and temperature compensation of a piezoresistive silicon pressure sensor is proposed, in which the piezoresistive Wheatstone bridge is combined on chip with a trimmable polysilicon resistor network. The design, fabrication and measured characteristic of a sensor based on this concept are presented.

An amperometric micro enzyme electrode for the analysis of glucose is described. Micro gold electrodes fabricated by the sputtering method are used as transducers of micro glucose sensors. Glucose oxidase (GOD) is strongly adsorbed onto a polypyrrole film electropolymerized in aqueous solution. 1,1′-Dimethylferrocene is used as a mediator of electron transfer between adsorbed GOD adn the polypyrrole-modified electrode. Glucose determination within a wide range (2.5 – 30 mM) is possible. The stability of the enzyme electrode has been improved with a lower electrochemical potential (0.1 V versus SCE) over 10 days. By comparison, micro electrodes with a polypyrrole film, which are prepared from an acetonitrile solution of pyrrole, show no response to glucose. Scanning electron microscopy reveals that the surface area of the polypyrrole film prepared in KCl aqueous solution is much larger than that in acetonitrile solution.