Measuring and testing – Fluid pressure gauge – Electrical
Reexamination Certificate
1999-09-09
2001-05-22
Noori, Max (Department: 2855)
Measuring and testing
Fluid pressure gauge
Electrical
Reexamination Certificate
active
06234027
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a semiconductor pressure sensor.
European Patent No 0 146 709 describes a pressure sensor. The pressure sensor is based on a (001) oriented silicon wafer which has been thinned down, in a small region which represents the sensitive zone, to a membrane a few micrometers thick. This membrane deforms as a result of pressure admitted on one side. This deformation is measured utilizing the piezoresistive effect. For this purpose, there are located on the membrane four measurement resistors whose electrical resistance changes as a result of the deformation. The four measurement resistors are connected to electrodes which are located on the unthinned part of the substrate. These electrodes make possible a measurement of the electrical resistance of the measurement resistor, and thus also of the pressure acting on the membrane.
Due to temperature-related flow of the electrode material, however, it is possible with pressure sensors of this kind for changes dependent on temperature history (so-called hysteresis effects) to occur in the characteristic curve of the component.
SUMMARY OF THE INVENTION
A pressure sensor according to the present invention has an advantage in that the aforementioned hysteresis effects are compensated for.
It is particularly advantageous to arrange on the membrane four measurement resistors which are interconnected as a Wheatstone bridge. This arrangement results in a particularly sensitive measurement of the electrical resistance or the change therein resulting from the externally applied pressure.
It is additionally advantageous to produce the electrodes from aluminum, since aluminum is particularly easy to process. Furthermore, it offers the advantage of generating, because of its low flow limit, an internal mechanical interference stress that can be used for hysteresis compensation.
It is advantageous to associate a compensation resistor with each measurement resistor, since the greatest possible accuracy is obtained in this fashion. The use of a semiconductor substrate and the production of resistors by way of doped zones in the semiconductor results in a particularly economical capability for applying resistors onto a membrane. In addition, conventional capabilities of micromechanics and microelectronics are then available for production of the pressure sensor with hysteresis compensation.
It is particularly advantageous to use silicon as the semiconductor, since this material allows the sensor element and electronic analysis system to be integrated on one chip.
Lastly, it is particularly advantageous to use the silicon substrate in a (100) orientation, since this surface, on the one hand, allows easy manufacture of the membrane by potassium hydroxide etching, and, on the other hand, has two [011] directions in the substrate surface, in which conductivity reacts particularly sensitively to deformation.
REFERENCES:
patent: 4333349 (1982-06-01), Mallon
patent: 4622856 (1986-11-01), Binder et al.
patent: 4682503 (1987-07-01), Higashi
patent: 32 07 833 (1983-09-01), None
patent: 0 083 496 (1983-07-01), None
patent: 0 146 709 (1985-07-01), None
patent: 0 436 920 (1991-07-01), None
patent: 60-247129 (1985-12-01), None
J. Dziuban et al. “Self-Compensating Piezoresistive Pressure Sensor.” Sensors and Actuators A. vol. A42. No. 1/3. pp. 368-374 (Apr. 15, 1994).
Aw-Musse Abdullahi
Kenyon & Kenyon
Noori Max
Robert & Bosch GmbH
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