Pressure difference sensor and method for its manufacture

• US 9,442,033 B2
• Filed: 09/24/2013
• Issued: 09/13/2016
• Est. Priority Date: 10/09/2012
• Status: Active Grant

• Current Assignee: Endress + Hauser GmbH + Company KG (Endress+Hauser AG)
• Original Assignee: Endress GmbH & Co. KG.
• Inventors: Getman, Igor, Teipen, Rafael, Link, Thomas, Nommensen, Peter
• Primary Examiner(s): THOMPSON, JEWEL VERGIE
• Application Number:
  US14/434,172
• Publication Number:
  US 20150260598A1
• Time in Patent Office: 1,085 Days
• Field of Search: 737/24, 737/18, 737/16, 737/54, 735/143.2, 257/419, 216/2, 296/211
• US Class Current: 1/1
• CPC Class Codes: B81B 2201/0264 Pressure sensors
• CPC Class Codes: B81B 2203/0127 Diaphragms, i.e. structures separating two media that can control the passage from one medium to another; Membranes, i.e. diaphragms with filtering function
• CPC Class Codes: B81B 3/0027 Structures for transforming mechanical energy, e.g. potential energy of a spring into translation, sound into translation
• CPC Class Codes: B81C 1/00158 Diaphragms, membranes manufacture process for semi-permeable inorganic membranes B01D67/0039
• CPC Class Codes: B81C 1/00396 Mask characterised by its composition, e.g. multilayer masks
• CPC Class Codes: B81C 1/00531 Dry etching
• CPC Class Codes: G01L 13/025 using diaphragms
• CPC Class Codes: G01L 19/0618 Overload protection
• CPC Class Codes: G01L 9/0072 using variations in capacitance
• CPC Class Codes: G01L 9/0073 using a semiconductive diaphragm

Abstract

A pressure difference sensor includes a measuring membrane, which is arranged between two platforms and connected pressure-tightly with the platforms, in each case, via a first insulating layer for forming pressure chambers between the platforms and the measuring membrane. The insulating layer is especially silicon oxide, wherein the pressure difference sensor further includes an electrical transducer for registering a pressure dependent deflection of the measuring membrane. The platforms have support positions, against which the measuring membrane lies at least partially in the case of overload, wherein the support positions have position dependent heights, characterized in that the support positions are formed in the first insulating layer by isotropic etching, and the particular height h of a support position, in each case, is a function of a distance from a base of the support position in the reference plane.

Claims

1. A pressure difference sensor, comprising:

a measuring membrane;

a first platform;

a second platform; and

an electrical transducer for registering a pressure dependent deflection of the measuring membrane, wherein;

said measuring membrane is arranged between said first and said second platforms;

said measuring membrane is connected pressure-tightly with said first platform and said second platform, in each case, via a first insulating layer for forming a first, respectively second, pressure chamber between said platforms and said measuring membrane;

said insulating layer comprises especially silicon oxide;

wherein said first platform and/or said second platform have/has support positions, against which said measuring membrane lies at least partially in the case of unilateral overload;

said support positions have position dependent heights with respect to a reference plane, which extends parallel to a plane, which is defined by said measuring membrane;

said support positions are formed in said first insulating layer by isotropic etching, and the particular height of a support position, in each case, is a function of a distance from a base of said support position in the reference plane.

2. The pressure difference sensor as claimed in claim 1, wherein:

the height of a support position is a monotonic function of the respective minimum distance from the base of said support position in the reference plane to the location of the height of said support positions.

3. The pressure difference sensor as claimed in claim 1, wherein:

said measuring membrane includes a circular, deflectable region;

at least one support position has a circularly shaped or circular arc shaped curve coaxial with said measuring membrane, and

said support position has at least sectionally a constant height.

4. The pressure difference sensor as claimed in claim 1, wherein:

said measuring membrane has a circular, deflectable region;

at least one support position has, with reference to an axis extending perpendicular to the circular area through its midpoint, a radial course;

said support position has at least sectionally a height varying with radial position.

5. The pressure difference sensor as claimed in claim 1, wherein:

said support positions have in an inner radial region of the pressure chamber a circularly shaped or circular arc shaped curve and/or in an outer radial region of the pressure chamber a radial course.

6. The pressure difference sensor as claimed in claim 1, wherein:

said electrical transducer comprises a capacitive transducer, which includes at least one platform electrode, which is electrically isolated from said measuring membrane, and whose capacitance relative to said measuring membrane depends on a pressure difference to be measured.

7. The pressure difference sensor as claimed in claim 6, wherein:

said at least one platform electrode is surrounded by an annular space; and

said platform electrode is electrically isolated by the space from a part of the platform surrounding the space.

8. The pressure difference sensor as claimed in claim 7, wherein:

said annular space has a width, which amounts to at least 20-times, preferably at least 40-times and especially at least 80-times the distance between said platform electrode and said measuring membrane in the resting position of said measuring membrane.

9. The pressure difference sensor as claimed in claim 6, wherein:

said measuring membrane includes a deflectable region, whose diameter amounts to at least 200-times, especially at least 400-times and preferably at least 800-times the distance between said measuring membrane in the resting position and said at least one platform electrode.

10. The pressure difference sensor as claimed in claim 1, wherein:

the thickness of said first insulating layer amounts to no more than 16 μ

m, especially no more than 8 μ

m and preferably no more than 4 μ

m.

11. The pressure difference sensor as claimed in claim 6, wherein:

said platform has a layer structure with a first conductive layer and a second conductive layer, which are isolated from one another by a second insulating layer;

said first conductive layer faces said measuring membrane and comprises said platform electrode; and

said annular space extends through said first conductive layer to said second insulating layer.

12. The pressure difference sensor as claimed in claim 11, wherein:

said second insulating layer has a thickness, which amounts to not less than the thickness of said first insulating layer; and

said thickness of said second insulating layer especially amounts to not less than twice, preferably not less than triple, that of the first insulating layer.

13. The pressure difference sensor as claimed in claim 7, wherein:

said platform has a planar surface section, from which said support positions rise;

said planar surface section is limited by the space, the surface section has on no more than 20%, especially no more than 10% and preferably no more than 7.5% of its surface raised portions of support positions.

14. A method for preparing a platform for a pressure difference sensor, especially as claimed in one of the preceding claims, wherein the method comprises the steps of:

providing an at least sectionally conductive body, which has a cover layer of an electrically insulating material;

masking the cover layer with an etching mask, wherein the etching mask is to be at least sectionally underetched in a time governed, isotropic etching process, in order to remove the cover layer in a region of the body except for support positions with position dependent heights, wherein the etching mask has perforations, through which an etching solution can attack the cover layer, wherein the separation between neighboring perforations, between which support position are to be prepared, varies as a function of desired height, respectively desired height excursion, of the support position, wherein the separation increases with increasing height of the support position;

etching the cover layer through the etching mask;

stopping the etching procedure after a predetermined time; and

removing the etching mask.

15. The method as claimed in claim 14, wherein:

the conductive body is silicon and the cover layer is amorphous silicon dioxide.

16. The method as claimed in claim 14, wherein:

the mask is chromium or a photoresist, or it is a hardmask, especially a metal hardmask.

17. The method as claimed in claim 14, wherein:

the etching occurs by means of HF, said HF is provided especially, pure, diluted or sputtered.

18. The method as claimed in claim 14, wherein:

the etching includes a dry chemical etching method, especially RIE or DRIE.