DE102009046228A1 - Pressure sensor, in particular differential pressure sensor and a method for preparing a membrane bed for such a sensor - Google Patents

Abstract

Pressure sensor comprising at least one base body, at least one measuring diaphragm and a transducer, the measuring diaphragm in particular having a semiconductor material, the measuring diaphragm being attached to the base body including a pressure chamber, the measuring diaphragm being able to be acted upon by at least one pressure and being elastically deformable as a function of pressure, wherein the transducer provides an electrical signal dependent on the deformation of the measuring membrane, the base body having a membrane bed on which the measuring membrane rests in the event of an overload, whereby the measuring membrane is supported, the membrane bed having an aspherical contour concave in its center, which is suitable for supporting the measuring membrane in the event of an overload, the contour of the membrane bed being obtained by leveling the surface of an elastically pretensioned, curved disk and then letting the disk relax.

Description

The present invention relates to a pressure sensor, in particular a differential pressure sensor and a method for preparing a membrane bed for such a sensor.

Pressure sensors comprise a base body, a measuring diaphragm and a transducer, wherein the measuring diaphragm is fastened to the base body, wherein the measuring diaphragm is subjected to 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 diaphragm wherein the base body further comprises a membrane bed against which the measuring diaphragm rests in the event of an overload in order to support the measuring diaphragm.

It is advantageous if the membrane bed has a contour approximately the natural pressure-dependent deformation, the so-called bending line. The difficulty, however, is to produce such a membrane bed reproducible and inexpensive.

The design of the bed and its production depend on which material has the membrane bed and possibly a substrate which carries the membrane bed, and what is chosen for a connection technique of the main body or of the membrane bed with the membrane.

For differential pressure sensors in particular Si basic body are suitable because they withstand the static pressure well. For the connection of two silicon wafers, there are various methods, such as. B. eutectic bonding or silicon direct bonding.

The production of concave membrane beds in silicon is not readily possible, as in US 7 360 431 B2 is described. At present, either the non-established methods of gray-scale lithography or a direct spherical grinding / polishing of the silicon are known, which leads to reproducible results only at great expense.

The object of the invention is to provide a pressure sensor, in particular a differential pressure sensor and a method for its production, which can be carried out inexpensively with improved yield and improved reproducibility.

The object is achieved by the pressure sensor according to the independent claim 1 and by the method according to the independent claim. 8

The pressure sensor according to the invention comprises at least one main body, at least one measuring membrane, and a transducer, wherein the measuring membrane in particular has a semiconductor material, wherein the measuring membrane is attached to the base body including a pressure chamber, wherein the measuring membrane is acted upon by at least one pressure and elastically deformable pressure-dependent wherein the transducer provides an electrical signal dependent on the deformation of the measuring membrane, the base body having a membrane bed against which the measuring diaphragm bears in the event of overload, whereby the measuring diaphragm is supported, the diaphragm bed having an aspherical contour concave in its center which is suitable for supporting the measuring diaphragm in the event of an overload, characterized in that the contour of the diaphragm bed is obtainable by planarizing surface treatment of an elastically prestressed, curved disc and subsequent relaxing eat the slice.

In one development of the invention, the pressure sensor can be obtained by a method in which the disc is bent over at least one punch in such a way that the contour in this state of the disc at least partially corresponds to the negative of the desired membrane bed contour.

In a development of the invention, the pressure sensor can be obtained by a method in which the leveling surface treatment comprises grinding and / or lapping and / or polishing the disk in the tensioned state.

In a development of the invention, the pane comprises silicon, in particular in a thickness of between 200 μm and 1000 μm, preferably between 300 μm and 600 μm.

In one development of the invention, the contour has a depth of not more than 50 μm, preferably not more than 25 μm and more preferably not more than 12.5 μm. According to another aspect of the invention, the contour has a depth of not less than 4 μm, and preferably not less than 6 μm.

• (a) elastisches Spannen einer ebenen. Scheibe, insbesondere einer Siliziumscheibe, über mindestens einem Stempel mittels einer Scheibenaufnahme
• (b) zumindest abschnittsweises Einebnen jener Oberfläche der gespannten Scheibe, die der Scheibenaufnahme abgewandt ist, mittels Schleifen und/oder Läppen und/oder Polieren; und
• (d) Entspannenlassen der Scheibe

The method according to the invention for the preparation of an aspherical membrane bed of a pressure sensor according to the invention comprises the steps:

• (a) elastic tensioning of a plane. Disc, in particular a silicon wafer, via at least one punch by means of a disc holder
• (B) at least partially leveling that surface of the tensioned disc, which faces away from the disc holder, by means of grinding and / or lapping and / or polishing; and
• (d) releasing the disc

In one development of the invention, the at least one stamp has a height of at least 8 μm, in particular at least 16 μm and not more than 100 μm, in particular not more than 50 μm.

In a development of the invention, the invention is held by a pressure gradient. Ie. the prevailing pressure on the side facing away from the disc receiving side of the disc is greater than the disc receiving side facing the disc. For this purpose, the disc holder may have a surface with channels, via which the pressure between the disc holder and the disc can be controlled. In one embodiment of this development of the invention, the disc holder comprises a vacuum holder to which the disc is kept sucked.

In one development of the invention, the disc is stretched over a plurality of punches, wherein over each of the punches a membrane bed is manufactured by at least section-wise leveling of the surface portion of the disc stretched over the punch.

With such a prepared membrane bed, the overload resistance of a pressure sensor can be significantly increased. For example, a Si measuring membrane with a measuring range of 10 mbar with a material thickness of 30 microns and a diameter of about 5 mm per se, so without support an overload resistance of about 1 bar. If the measuring membrane can be supported on the membrane bed according to the invention, the overload resistance thus increases to at least 50 bar, in particular to at least 100 bar, preferably to at least and 140 bar and particularly preferably to at least 160 bar.

The mentioned pressure values relate in particular to a pressure sensor with a measuring range of 10 mbar. For larger measuring ranges, it is preferred if the overload resistance is also greater. For example, a pressure sensor with a measuring range of 500 mbar should have an overload resistance of at least 100 bar, preferably at least 300 bar, more preferably at least 420 bar, and particularly preferably 500 bar.

The pressure sensor of the present invention may be an absolute pressure sensor that measures a pressure against vacuum, or a relative pressure sensor that measures a pressure against the atmospheric pressure.

However, the present invention is particularly relevant for differential pressure sensors which detect the difference between a first pressure and a second pressure. Especially with differential pressure sensors, the risk of large static unilateral overloads is given, since the pressure difference to be measured is usually considerably smaller than a first or second pressure whose difference is to be detected. Therefore, the pressure sensor according to the invention in a presently preferred embodiment, a differential pressure sensor having a measuring diaphragm, a first base body and a second base body, wherein the measuring diaphragm between the first base body and the second base body arranged and with each of the two main body including a first pressure chamber and a second pressure chamber is connected, wherein the first pressure chamber and the second pressure chamber each have at least one channel through the first and second base body, wherein the measuring membrane can be acted upon by the channels with a first and a second pressure. The deflection of the membrane then depends on the difference between the first pressure and the second pressure.

The pressure sensor according to the invention may have any known to the expert transducer to convert a pressure-dependent or differential pressure-dependent deformation of the measuring diaphragm into an electrical signal. In particular, capacitive or (piezo) resistive converters should be mentioned here. For capacitive transducers electrodes are to be provided on the measuring membrane and on the membrane bed, which can be prepared by metallizing or by doping. Piezoresistive transducer structures can be produced, for example, by preparing the resistance elements of a full bridge by means of doping the membrane.

If a large number of sensors are produced in parallel in the wafer composite, finally a singulation of the sensors follows, for example by sawing.

The invention will now be explained with reference to an embodiment shown in the drawings.

It shows:

1 : A schematic sectional view of preparation steps for preparing the membrane beds and for producing a relative pressure sensor according to the invention; and

2 : A longitudinal section through an embodiment of a batch of differential pressure sensors according to the invention prior to singulation.

As in 1a shown is on a vacuum holder 10 on its surface 11 , Stamp 12 protrude, a silicon wafer 20 held, taking over the punches 12 the silicon wafer bulges 21 which form a contour, which essentially each form a negative of a desired membrane bed contour.

As in 1b shown, the protruding bulges 21 up to a contour line 30 removed by grinding and / or rag and / or polishing. The actual size ratios can be given as follows. The protruding bulges 21 have a height of, for example, about 20 microns to the minima of the surface of the silicon wafer. wherein the total thickness of the silicon wafer is for example a few hundred micrometers. By grinding, cloth or polishing more material is removed, as the height difference between the bulges and the minima is for example 30 microns.

After removing the silicon wafer from the vacuum holder 10 The silicon wafer can relax again, resulting in the positions of the abraded bulges now opposite the flat surface 22 , the silicon disk recesses 24 are formed, which have a contour which are the negative image of the bulges of the silicon wafer held on the vacuum holder, as in 1c is shown.

In 1d is the completion of relative pressure sensors sketched, in which case by the silicon wafer 20 channels 26 into the wells 24 to lead, and being another silicon wafer 40 , which is to form the measuring membranes of the individual relative pressure sensors, by means of a gold-silicon eutectic on the first silicon wafer 20 is attached. The relative pressure sensors are finally closed by sawing along the in 1d shown dashed vertical lines verzeinzelt.

2 shows one of the representation of 1d corresponding view of differential pressure sensors according to the invention, in which between two silicon wafers 120 which membrane beds 124 and print feed channels 126 have a third silicon wafer 140 is joined, which forms the measuring membranes of the differential pressure sensors. The differential pressure sensors are finally separated by sawing along dashed vertical lines.

Of course, both the relative pressure sensors and differential pressure sensors discussed here have suitable transducers, which may be, for example, capacitive or piezoresistive transducers which can be prepared in particular by doping and / or metallizing the measuring diaphragm and, in the case of a capacitive transducer, also of the membrane bed.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 7360431 B2 [0006]

Claims (11)

Pressure sensor, comprising at least one base body, at least one measuring membrane, and a transducer, wherein the measuring membrane in particular comprises a semiconductor material, wherein the measuring diaphragm is attached to the base body including a pressure chamber, wherein the measuring membrane is acted upon by at least one pressure and pressure-dependent elastically deformable wherein the transducer provides an electrical signal dependent on the deformation of the measuring diaphragm, the base body having a diaphragm bed against which the diaphragm rests in the event of overload, whereby the diaphragm is supported, the diaphragm bed having an aspherical contour concave in its center suitable for supporting the measuring membrane in the event of an overload, characterized in that the contour of the membrane bed is obtainable by planarizing surface treatment of an elastically prestressed, curved disk and then allowing the disk to relax. Pressure sensor according to claim 1, wherein the pressure sensor is obtainable by a method in which the disc is bent over at least one stamp in such a way that the contour corresponds in this state of the disc to the negative of the desired membrane bed contour. A pressure sensor according to claim 1 or 2, wherein the pressure sensor is obtainable by a method comprising grinding and / or lapping and / or polishing. Pressure sensor according to one of the preceding claims, wherein the disc comprises silicon. Pressure sensor according to one of the preceding claims, wherein the contour has a depth of not more than 50 microns, preferably not more than 25 microns and more preferably not more than 12.5 microns. A pressure sensor according to any one of the preceding claims, wherein the contour has a depth of not less than 4 μm, and preferably not less than 6 μm. Pressure sensor according to one of the preceding claims, wherein the pressure sensor is a differential pressure sensor in which a measuring diaphragm is arranged between two basic bodies, wherein both basic bodies each have a membrane bed with an aspherical, in the center concave contour. Process for the preparation of an aspherical membrane bed of a pressure sensor, in particular according to one of the preceding claims, comprising the steps: (A) elastic clamping a flat disc, in particular a silicon wafer, via at least one punch by means of a disc holder (B) at least partially leveling that surface of the tensioned disc, which faces away from the disc holder, by means of grinding and / or lapping and / or polishing; and (d) releasing the disc The method of claim 8, wherein the punch has a height of at least 8 microns, in particular at least 16 microns and not more than 100 microns, in particular not more than 50 microns. Method according to one of claims 8 to 9, wherein the disc is held by a pressure gradient, in particular on a vacuum holder. Method according to one of claims 8 to 10, wherein the disc is stretched over a plurality of punches, and wherein above each of the punches a membrane bed is made by at least section-wise leveling of the clamped over the stamp surface portion of the disc.

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