Electricity: measuring and testing – Determining nonelectric properties by measuring electric... – Semiconductors for nonelectrical property
Patent
1991-09-25
1993-08-10
Wieder, Kenneth A.
Electricity: measuring and testing
Determining nonelectric properties by measuring electric...
Semiconductors for nonelectrical property
324678, 422 8202, G01N 2700
Patent
active
052352676
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a circuit for measuring a quantity influencing the capacitance-voltage characteristic of a capacitive element, as well as to a method of measuring a quantity influencing the capacitance-voltage characteristic of a capacitive element.
Capacitive MOS structures have a voltage-dependent capacitance value. The behavior of the capacitance-voltage curve is, e.g. in the case of capacitive MOS structures, influenced by additional quantities if the metallic layer consists of catalytic metals or contains at least a certain percentage of catalytic metals. This influence of specific quantities on the voltage-dependent capacitance behavior of such capacitive structures is utilized for constructing sensors adapted to be used for detecting the respective quantity which influences the voltage-dependent capacitance behavior.
Known fields of use of such capacitive elements are, for example, gas sensors responding to specific gases, e.g. hydrogen sensors. One embodiment of the last-mentioned hydrogen sensor whose voltage-dependent capacitance curve varies depending on the ambient humidity is disclosed in the scientific publication by G. J. Maclay, "MOS hydrogen sensors with ultrathin layers of palladium", IEEE Trans. Electron Devices, vol. ED-32, pages 1158 to 1164, 1985.
At present, two different techniques are used for detecting the change in the capacitance-voltage characteristic and, consequently, for determining the quantity influencing the capacitance-voltage characteristic:
In the first technique, which is known from "Sensors and Actuators, 1, 1981, pages 403 to 426", a constant bias voltage is applied to the capacitive MOS element, the constant bias voltage having superimposed on it a high-frequency voltage signal of predetermined amplitude. In the case of a displacement of the capacitance-voltage characteristic caused by the quantity to be measured, the capacitance will change at the working point determined by the bias voltage. This change in capacitance can be detected in a measuring bridge.
In the second technique, the capacitive MOS element in a feedback control circuit is subjected to a bias voltage of such nature that the capacitive MOS element has a constant capacitance value. The controlled bias voltage and/or the displacement of the voltage working point can be used for determining the quantity which influences the capacitance-voltage characteristic.
Both techniques described necessitate the use of a comparatively complicated circuit for detecting the quantity which influences the capacitance-voltage characteristic. In both techniques, migrations of ions can occur within the capacitive MOS structure in the interior of the structure and at the surface thereof, and this will impair the long-term stability as far as the detection of the quantity influencing the capacitance-voltage characteristic is concerned. Both techniques are based on the detection of a comparatively small signal variation in the working point. It follows that both techniques fail to have a sufficient signal-to-noise ratio with regard to the quantity determined, i.e. the humidity or the gas concentration.
Further distortions of the measuring results obtained using these known techniques come from the fact that the capacitance-voltage characteristic of the capacitive MOS element will normally not only depend on one quantity to be measured, but, to a certain extent, it will also be influenced by additional interference quantities.
In comparison with this prior art, the object of the present invention is further development of a circuit and a method of the type mentioned at the beginning, which are used for measuring a quantity influencing the capacitance-voltage characteristic of a capacitive element, in such a way that the accuracy in determining the influencing quantity can be improved still further.
In a circuit arrangement for measuring the concentration of a gas in a mixture of gases or the ion concentration in a liquid by means of a capacitive semiconductor element having a concentration-dependent capaci
REFERENCES:
patent: 4112356 (1978-09-01), Toy
patent: 4149231 (1979-04-01), Bukosky et al.
patent: 4166974 (1979-09-01), Vermeers
patent: 4636714 (1987-01-01), Allen
patent: 4641084 (1987-02-01), Komatsu
patent: 4831325 (1989-05-01), Watson, Jr.
patent: 5103183 (1992-04-01), Klein et al.
"Transition Metal-Gate MOS Gaseous Detectors", T. L. Poteat et al, IEEE Tsactions on Electron Devices, vol. ED-29, No. 1, pp. 123-129, Jan. 1982.
"An Interface Circuit for Capacitive Sensors", T. Nagasawa et al, Transactions of the Institute of Electronics, vol. E70, No. 11, pp. 1049-1050, Nov. 1987.
"Sliding Capacitive Displacement Transducer", B. D. Bryner et al., NTIS Tech Notes, pp. 729-730, Aug. 1987.
Article entitled Hydrogen Sensitive MOS-Structures, Part 1, Principles and Applications by Ingemar Lundstrom, Sensors and Actuators, 1/ (1981) pp. 403-426.
MOS Hydrogen Sensors with Ultrathin Layers of Palladium, by G. Jordan Maclay, IEEE Transactions, vol. ED32, No. 7, Jul. 1985.
Bedrich Hosticka
Maclay Jordan
Schoneberg Uwe
Zimmer Gunther
Brown Glenn
Dougherty Ralph H.
Fraunhofer-Gesellschaft zur Forderung der Angewandten Forschung
Wieder Kenneth A.
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