Electrical resistors – Resistance value responsive to a condition – Fluid- or gas pressure-actuated
Reexamination Certificate
1997-09-05
2001-04-03
Easthom, Karl D. (Department: 2832)
Electrical resistors
Resistance value responsive to a condition
Fluid- or gas pressure-actuated
C338S004000, C338S036000, C257S419000, C073S721000, C073S727000
Reexamination Certificate
active
06211772
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to sensors for detecting the flow rate or pressure in chemical plants, iron mills and power plants, and in particular to highly reliable semiconductor composite sensors which continue to have high accuracy even if they are used for a long period of time.
As pressure sensors using the piezoresistance effect of silicon, various techniques have been proposed heretofore.
For example, two piezoresistive elements formed in the same n-type semiconductor region subjected to p-n separation are known as described in “Miniature Piezoresistive Strain and Pressure Sensors with On-Chip Circuitry,” by Susumu Sugiyama et al., PROCEEDINGS OF THE 3RD SENSOR SYMPOSIUM (1983).
As another example of a conventional technique, a similar structure is disclosed in JP-A-3-76139 (UM) as well. Furthermore, a semiconductor pressure sensor based upon the piezoresistance effect is disclosed in JP-B-60-32993 as well, which corresponds to U.S. patent application Ser. No. 619,866 filed on Oct. 6, 1975.
SUMMARY OF THE INVENTION
In theses techniques, however, two piezoresistive elements are connected in series in an n-type substrate having the same potential. Therefore, the potential difference between the resistance region and the substrate differs from piezoresistive element to piezoresistive element. Due to the difference in influence of the potential of the substrate exerted upon the resistance region, it was difficult to realize the same resistance value.
An object of the present invention is to provide a semiconductor composite sensor capable of having high accuracy and high reliability.
In accordance with the present invention, a semiconductor composite sensor includes at least two piezoresistive elements connected together, the two piezoresistive elements being identical in shape, and semiconductor regions having respective individual potential values and respectively surrounding the two piezoresistive elements, potential difference values between the two piezoresistive elements and the semiconductor regions being respectively made constant.
In order to provide two semiconductor regions with respective indidividual potential values, the semiconductor regions are disposed so as not to cause electric interference between the semiconductor regions and the semiconductor regions are supplied respectively with voltages from different supply sources.
In forming a bridge circuit by using the above described piezoresistive elements, at least two piezoelectric elements connected in series are made identical in shape, and a semiconductor region surrounding one piezoresistive element located on the voltage supply source side is supplied with the voltage of the voltage supply source whereas a semiconductor region surrounding the other piezoresistive element is supplied with the voltage of the voltage supply source minus a voltage drop across the piezoresistive element located on the voltage supply source side.
When at least two identical piezoresistive elements are to be connected in series, they are disposed so as to be covered by electrodes located on the negative side of the piezoresistive elements or electrodes located on the positive side of the piezoresistive elements. If one piezoresistive element is covered by an electrode of negative side at this time, the other piezoresistive element is also covered by an electrode of negative side. The same holds true for the electrodes of positive sides as well.
According to the present invention, semiconductor regions surrounding two or more piezoresistive elements are provided for respective piezoresistive elements and semiconductor regions are disposed so as not to cause mutual electric interference. Therefore, each semiconductor region is able to have an individual potential. No matter what potential each piezoresistive element has, therefore, the reverse bias voltage between the piezoresistive element and the semiconductor region can be made equal by making the potential difference with respect to each semiconductor region surrounding each piezoresistive element constant. Therefore, the width of a depletion layer appearing between the piezoresistive element and the semiconductor region can be made identical. That is to say, the width of the depletion layer interferring with the piezoresistive element can also be made constant. Especially when the same resistive elements are used, therefore, a change of resistance caused by influence of the depletion layer can be made constant.
According to the present invention, an input or output terminal electrode of piezoresistive elements is disposed so as to cover each of two identical piezoresistive elements connected in series. Therefore, accumulation layers are formed between the electrodes and the piezoresistive elements. Voltage drop values across two piezoresistive elements and influence of electrodes exerted upon piezoresistive elements can be made constant. The width of the appearing accumulation layers can be made constant. With respect to the electric influence of the surface of the semiconductor layer, therefore, the electrodes serve as shields and changes of piezoresistive elements caused by influence of the accumulation layers can be made constant.
According to the present invention, when a bridge circuit is formed by uisng four piezoresistive elements, at least two piezoresistive elements connected in series in the bridge circuit are made identical. Potential difference values with respect to semiconductor regions respectively surrounding two piezoresistive elements are made equal by applying a voltage equal to a voltage applied to a piezoresistive element located on an electrically positive side to a semiconductor region surrounding the piezoresistive element of the positive side and included in two semiconductor regions and applying the voltage applied to the positive side minus a voltage drop across the piezoresistive element of positive side to a semiconductor region surrounding a piezoresistive element of negative side.
Thus, a semiconductor composite sensor having not only high accuracy but also high reliability and a reduced output drift is obtained. Furthermore, in forming a bridge, all piezoresistive elements, semiconductor regions surrounding the piezoresistive elements, and electrodes disposed on the piezoresistive elements are made identical and subjected to the same voltage condition. By doing so, all resistance values can be made equal under any condition and environment of use. Therefore, an output correction circuit becomes unnecessary, and a highly accurate, highly reliable semiconductor composite sensor is obtained.
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patent: 35 43 261 (1987-06-01), None
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patent: 3-76139 U (1991-07-01), None
“Miniature Piezoresistive Strain and Pressure Sensors with On-Chip Circuitry”, by Sugiyama et al., Proceedings of the 3rd Sensor Symposium, 1983, pp. 209-213.
Murakami Susumu
Shimada Satoshi
Shimizu Shuichi
Takahashi Yukio
Ugai Seiichi
Easthom Karl D.
Hitachi , Ltd.
Kenyon & Kenyon
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