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Pressure sensor, especially pressure difference sensor

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Pressure sensor, especially pressure difference sensor


The pressure sensor of the invention includes at least one platform, at least one measuring membrane 30, and a transducer, wherein the measuring membrane comprises a semiconductor material, wherein the measuring membrane, enclosing a pressure chamber, is secured on the platform, wherein the measuring membrane is contactable with at least one pressure and is elastically deformable in a pressure-dependent manner, wherein the transducer provides an electrical signal dependent on deformation of the measuring membrane, wherein the platform has a membrane bed, on which the measuring membrane lies in the case of overload, in order to support the measuring membrane, wherein the membrane bed 21 has a glass layer 20, whose surface faces the measuring membrane and forms a wall of the pressure chamber, wherein the surface of the glass layer has a contour, which is suitable for supporting the measuring membrane 30 in the case of overload, characterized in that the contour of the membrane bed 21 is obtainable by a sagging of an unsupported region of a glass plate at increased temperature, due to the force of gravity on the unsupported region of the glass plate, and subsequent cooling of the glass plate.

Browse recent Endress + Hauser Gmbh + Co. Kg patents - Maulburg, DE
Inventors: Timo Kober, Michael Philipps, Dieter Stolze, Anh Tuan Tham, Roland Werthschutzky
USPTO Applicaton #: #20120279310 - Class: 73717 (USPTO) -


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The Patent Description & Claims data below is from USPTO Patent Application 20120279310, Pressure sensor, especially pressure difference sensor.

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The present invention relates to a pressure sensor, especially a pressure difference sensor.

Pressure sensors comprise a platform, a measuring membrane and a transducer, wherein the measuring membrane is secured on the platform, wherein the measuring membrane is contactable with at least one pressure and has a pressure-dependent elastic deformation, and wherein the transducer provides an electrical signal dependent on the deformation of the measuring membrane, wherein the platform, furthermore, has a membrane bed, on which the measuring membrane lies in the case of overload, in order to support the measuring membrane.

In such case, it is advantageous that the membrane bed has a contour approximating the natural pressure-dependent deformation, i.e. a contour matching that of the so-called deflection curve. It is difficult, however, to manufacture such a membrane bed in a reproducible and cost-effective manner.

The shaping of the bed as well as its manufacture depend on the material of the membrane bed and of the substrate, which bears the membrane bed, and what sort of joining technology is selected for joining the platform or the membrane bed with the membrane.

Especially suitable for pressure difference sensors are Si platforms, since these withstand the static pressure well. There exist various methods for connection of two silicon chips, such as, for example eutectic bonding or silicon direct bonding. In view of the requirements for a hermetically sealed and fixed connection of the components, which, in spite of this, has no major after-effects, these bonding methods according to the state of the art deliver a yield and reproducibility, which is still capable of improvement. Additionally, the manufacture of, for example, spherically concave beds according to U.S. Pat. No. 7,360,431 B2 of YAMATAKE is not directly possible in silicon. Currently known are either the non-established methods of gray scale lithography or a direct grinding/polishing of the silicon, which leads to reproducible results only with great effort.

The yet unpublished patent application DE 102008043171 discloses a pressure sensor comprising at least one platform, at least one measuring membrane and a transducer, wherein the measuring membrane comprises a semiconductor material (especially silicon), wherein the measuring membrane, enclosing a pressure chamber, is secured to the platform, wherein the measuring membrane is contactable with at least one pressure and is elastically deformable in a pressure-dependent manner, wherein the transducer provides an electrical signal dependent on the deformation of the measuring membrane, wherein the platform has a membrane bed, against which the measuring membrane lies in the case of overload, in order to support the measuring membrane, characterized in that the membrane bed has a glass layer, whose surface faces the measuring membrane and forms a wall of the pressure chamber. The surface of the glass layer is especially provided with a contour, which is suitable for supporting the measuring membrane in the case of overload. For this, the surface of the glass layer can be micromechanically processed. The glass layer can likewise have a surface contour, which is prepared by means of hot embossing. Furthermore, this patent application discloses that it is advantageous that the membrane bed has a surface contour, which is approximately the same as the deflection curve of the measuring membrane, or equals such.

Although this procedure leads to satisfactory results as regards the quality of the membrane beds, alternatives to the pressure sensors manufactured in such a way are still desired.

An object of the invention is to provide a pressure sensor, especially a pressure difference sensor, and a method for its manufacture, which can be implemented cost effectively and with improved yield and improved reproducibility.

The object is achieved according to the invention by the pressure sensor as defined in independent patent claim 1, and the methods as defined in independent patent claims 9 and 13.

The pressure sensor of the invention includes at least one platform, at least one measuring membrane, and a transducer, wherein the measuring membrane comprises a semiconductor material, wherein the measuring membrane, enclosing a pressure chamber, is secured to the platform, wherein the measuring membrane is contactable with at least one pressure and is elastically deformable in a pressure-dependent manner, wherein the transducer provides an electrical signal dependent on the deformation of the measuring membrane, wherein the platform a has a membrane bed, on which the measuring membrane lies in the case of overload, in order to support the measuring membrane, wherein the membrane bed has a glass layer, whose surface faces the measuring membrane and forms a wall of the pressure chamber, wherein the surface of the glass layer has a contour, which is suitable for supporting the measuring membrane in the case of overload, characterized in that the contour of the membrane bed is obtainable by a sagging of an unsupported region of a glass plate, which forms the glass layer at increased temperature, due to the force of gravity on the unsupported region of the glass plate and subsequent cooling of the glass plate.

In a further development of the invention, the platform comprises a substrate, which has a surface facing the glass layer, which supports the glass layer, wherein the surface has a cavity, via which the contour of the membrane bed is formed.

In given cases, the cavities of the side facing away from the membrane bed can be filled with a fill material, in order to prevent hollow spaces under the glass layer. The fill material can especially comprise a glass, which, for example, is applied in the form of glass frit, and which has a lower melting temperature than the glass of the glass layer. Additionally, the underside of substrate and glass facing away from the membrane bed can be leveled by grinding, lapping and/or polishing.

In an alternative embodiment of the invention, the leveling, lapping and/or polishing for leveling of the underside of substrate and glass facing away from the membrane bed can occur completely without prior filling of the unsupported region of the glass layer.

In a currently preferred embodiment, the glass of the glass layer or of the membrane bed includes a borosilicate glass, which is matched to the coefficient of expansion of the substrate material of the platform. Especially suitable glasses are, for example, Pyrex 7740, TEMPAX, Hoya SD-2, or Borofloat 33, which is obtainable from the firm, Schott.

The substrate material is preferably a semiconductor material, especially silicon.

According to a further development of the invention, the glass layer has a thickness of not less than 100 μm, preferably not less than 200 μm and further preferably not less than 400 μm.

According to a further development of the invention, the glass layer has a material thickness of no more than 2000 μm, preferably no more than 1400 μm and further preferably no more than 1000 μm.

Furthermore, it is currently preferable that the membrane bed has an aspherical surface contour, especially approximately the deflection curve of the measuring membrane, or equal thereto.

This results to a first approximation via the horizontal orientation of the supported region of the glass layer during a tempering of the glass layer, in order to allow the unsupported region of the glass layer to sink, and during the subsequent cooling of the glass layer.

For manufacture of the contour of the membrane bed, the glass layer can, for example, be connected in the planar state with a surface of the platform, which has the required cavities, or can be placed, non-affixed, on the surface, after which the glass layer is heated, in order to induce the sinking of the unsupported regions.

In the case of prior connection between glass layer and platform, this can be produced, for example, via anodic bonding.

To the extent that the glass layer is only placed non-affixedly, the connection between the platform and the glass layer can be produced during the heating via a silicon oxide layer on the surface of a silicon substrate.

Instead of preparing the membrane bed on the platform, the glass layer can be heated on a mold, which has corresponding cavities, in order for the unsupported regions to be caused to sink. Due to the multiple reuse of the mold, this justifies a greater effort for its manufacture. The means the cavities under the unsupported region can be embodied in such a manner, that the unsupported region, after a certain sag depth, can, for example, be locally supported, in order locally to limit the sinking. Fundamentally, it is, however, currently preferably, that the contour be formed without the influence of local support.

In a further development of the invention, at least the concave contour region of the membrane bed remains free of the influence of tools on the roughness of the surface of the glass layer facing the measuring membrane. The surface can nevertheless be largely smooth, and indeed, in the sense that no local raised portions or depressions occur, which could lead to local stresses and ultimately to a breaking of the measuring membrane to be supported.

Independently of whether the membrane bed is formed on a mold or on the platform, it can be advantageous to level the surface of the supported region of the glass layer, after the contour is formed in the unsupported region. The leveling can occur, for example, via grinding, lapping and/or polishing. A need for leveling can arise, for example, when, in the case of the sinking of the unsupported region of the glass plate, the upper side and the underside of the glass plate in the supported region different are exposed to boundary conditions, for example due to the underside lying on the substrate and the upper side being free, which leads to markedly different shear forces on the upper side and underside.

In a further development of the invention, it is consequently provided to lay a plate on the upper side of the glass plate, wherein this plate has cavities aligning with the cavities of the substrate, and lies on the supported regions of the glass body.

This plate can be removed again after preparation of the contour of the membrane bed. In a variant of the invention, the laid-on plate includes an opening with a greater inner cross section than the unsupported region, so that, in each case, an annular edge section of the supported region of the glass plate surrounds an unsupported region. This is sufficient, on the one hand, to effect a sufficiently planar upper side of the glass layer in the annular edge section of the supported region, and, on the other hand, the size of the edge region allows a measuring membrane to be secured thereon. In this way, the removal of the laid-on plate can be omitted.

With a membrane bed prepared according to the invention, the overload resistance of a pressure sensor can be increased significantly. For example, an Si measuring membrane with a measuring range of 10 mbar and with a material thickness of 30 pm and a diameter of, for instance, 5 mm in and of itself—that is without support—has an overload resistance of, for instance, 1 bar. When the measuring membrane can support itself on the membrane bed of the invention, the overload resistance rises therewith to at least 50 bar, especially to at least 100 bar, preferably to at least 140 bar and especially preferably to at least 160 bar.



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stats Patent Info
Application #
US 20120279310 A1
Publish Date
11/08/2012
Document #
13503804
File Date
10/07/2010
USPTO Class
73717
Other USPTO Classes
65107, 65 55
International Class
/
Drawings
3



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