Measuring and testing – Fluid pressure gauge – Diaphragm
Patent
1995-05-17
1996-12-10
Chilcot, Richard
Measuring and testing
Fluid pressure gauge
Diaphragm
73726, 73727, 73717, 73720, G01L 708, G01L 912, G01L 1500
Patent
active
055832962
DESCRIPTION:
BRIEF SUMMARY
Quite generally, the present invention deals with the field of pressure sensors. The invention deals in particular with a relative pressure sensor which can be implemented as a micromechanical structure having extremely small dimensions.
In other words, the present invention refers to a pressure sensor comprising a substrate and a layer defining together with said substrate a cavity, said layer including above said cavity a diaphragmlike area which is adapted to be acted upon by a first pressure prevailing outside of said cavity, according to the generic clause of patent claim 1. Pressure sensors which are adapted to be implemented by methods in the field of micromechanics and especially by methods in the field of surface micromechanics have been disclosed in a great number of manifestations in the more recent scientific literature and in the more recent patent literature.
The applicant's international patent application PCT/DE91/00107 (publication number W091/12507), for example, shows an absolute pressure sensor, which can be produced from a semiconductor material, especially from silicon, by micromechanical methods and which comprises a substrate having provided therein, by means of adequate doping, a conductive semiconductor region which is arranged such that it is insulated from the substrate, a pressure sensor structure being formed on this conductive semiconductor region in said semiconductor substrate by applying first a spacer layer to said substrate, whereupon a polycrystalline semiconductor layer is deposited on said spacer layer, whereupon the polycrystalline semiconductor layer is doped and the spacer layer, which can also be referred to as sacrificial layer, is removed by etching via suitable channels. Finally, the channels are closed by depositing a suitable material. The structure obtained is a capacitive pressure sensor structure in which the polycrystalline semiconductor layer defines together with the substrate a closed cavity, which can, for example, be evacuated or which can be filled with a gas having a predetermined pressure. Although such a pressure sensor is very advantageous insofar as it permits detection of an absolute pressure with high measurement accuracy as well as insofar as it is compatible with CMOS circuits due to the fact that the semiconductor region is insulated from the substrate, said pressure sensor is limited with respect to the fact that it only permits detection of an absolute pressure.
Relative pressure sensors and pressure sensors for differential pressure measurements, which have been realized by micromechanical techniques, are already known. For example, the technical publication Journal of Vacuum Science & Technology/A, Vol. 4, No. 3, May to June 1986, part 1, page 618, column 2, last paragraph to page 619, column 1, first paragraph, in connection with FIG. 3, shows a relative pressure sensor which is composed of semiconductor materials and which comprises a substrate and a polysilicon layer defining together with said substrate a cavity, said substrate being provided with a rear opening which has been formed by anisotropic etching from the back of the substrate to said cavity. In the course of the pressure sensor production process, a spacer layer or sacrificial layer is removed by etching through this rear opening by means of hydrofluoric acid for defining the future pressure sensor cavity. It turned out that such relative pressure sensors only show insufficient mechanical stability, in particular in the case of overload. In addition, it turned out that such relative pressure sensors show a spread with regard to their detection sensitivity; in the case of a capacitive relative pressure sensor, for example, a spread with respect to the quotient of the capacitance change related to the pressure change, such a spread occurring even within a single production lot.
It follows that, taking as a basis the above-described prior art, it is the object of the present invention to provide a pressure sensor by means of which a pressure difference can be measured and w
REFERENCES:
patent: 3930412 (1976-01-01), Mallon et al.
patent: 4276533 (1981-06-01), Tominaga et al.
patent: 4589054 (1986-05-01), Kuisma
patent: 4622856 (1986-11-01), Binder et al.
patent: 4790192 (1988-12-01), Knecht et al.
"The Role of Thin Films in Integrated Solid-State Sensors", K. Wise, 8257A rnl of Vacuum Science & Technology/A, 4 (1986) May-Jun., No. 3, Part 1, Woodbury, NY USA.
Amelung Jorg
Kandler Michael
Mokwa Wilfried
Chilcot Richard
Felber Joseph L.
Fraunhofer-Gesellschaft zur Forderung Der Angewandten Forschung
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