DE10249238B4 - Sensor chip for a differential pressure sensor with double-sided overload protection - Google Patents

Abstract

sensor chip for one Differential pressure sensor comprising a substrate (12) having a first, a Recess in the substrate forming recess (8a), which of a first membrane (1) is sealingly covered, characterized in that the substrate (12) has a second, a depression in the substrate forming recess (8b), that of a second membrane (1) covered over is and about at least one channel (11) with the first recess (8a) in connection is so that two through the channel (11) with each other coupled Cavities (9a, 9b) filled with an incompressible fluid (13), wherein the membranes (1) coated electrically conductive or conductive and electrically conductively connected to a first contact (14) and on a floor space each recess (8a, 8b) at least one electrode (4a, 4b) is arranged is electrically connected to a second contact (5) is.

Description

Technical application

The The invention relates to a sensor chip for a differential pressure sensor, which has a substrate with a first recess, that of a first Membrane sealing covered is.

to Measurement of physical quantities, in particular of pressure, it is common today Use semiconductor sensors or load sensors. Typical for this Sensors is that these are an extremely small size as well an extremely high resistance across from from the outside forces acting on the sensors exhibit. For this reason, semiconductor sensors are particular in the field of pressure measurement of hydraulic and aerodynamic forces far common.

Usually feature Such semiconductor pressure sensors both via a membrane, which consists of a or more, possibly doped or coated silicon layers exists as well over piezoresistive elements used to detect the direction and / or the size of the deflection the membrane are provided. Such sensors convert from Outside pressure forces acting on them into an electrical signal, which is then connected to an evaluation unit is evaluated.

Furthermore These pressure sensors are provided with a corresponding envelope. The primary Task of serving it is the sensor against environmental influences, for example. When used in aggressive media, protect.

A special form of a pressure sensor is the so-called differential pressure sensor, with the measurement of a pressure difference occurring between two volumes possible is. Such a sensor usually includes a silicon chip with a pressure difference receiving membrane, with piezoresistors in Active compound is. To the sensor against environmental influences too protect, this is poured into a potting compound and together with the Potting compound in a housing used. On the outside of the housing are two pressure connections provided so that a prevailing between the pressure ports Pressure difference is measurable.

It However, it may happen that the voltage applied to one of the two pressure ports rises sharply or falls sharply, so that a sudden, strong pressure difference is applied. That's why it's general important to design pressure sensors such that they are as possible against overload pressures insensitive. So can in use today Semiconductor differential pressure sensors about two to three times the maximum working pressure at overload withstand without being damaged to become.

Often, though also low differential pressures at high two-sided printing, the so-called offset pressure, are measured. Falls here the offset printing on one side, so the sensor membrane a extreme overpressure resist. A high overload resistance gets through in such cases corresponding support structures, which are executed in the form of mechanical stops guaranteed. In this way, an overstretching or destruction prevents the membrane.

For example, describes the US 5,969,591 a differential pressure sensor with one-sided overload protection, in which the two pressure ports are arranged on one side of the housing. The semiconductor pressure sensor has a silicon substrate, in which a recess is etched, which is covered by a membrane at its membrane edges gas-tight connected to the substrate membrane. On the membrane, an insulating layer and a protective layer are deposited, wherein within the protective layer, a sensor element is integrated. On both sides of the membrane, a cavity is formed, wherein the cavity, which is located above the membrane within a housing part is a pressure chamber. This pressure chamber is in turn connected via a arranged in the housing outer wall pressure line with a first pressure port. A second pressure port is connected via a second pressure line to a second pressure chamber, which is sealed gas-tight against the first pressure chamber. By means of the deflection of the membrane and the corresponding effects on the electrical properties of the sensor element, a pressure difference located between the two pressure connections can be measured. The overload protection, which is intended to protect the diaphragm against damage due to extreme overpressure, is realized by mechanical stops in this differential pressure sensor. The membrane is in an overload occurring, for example. At a boundary of the housing wall or the bottom of the recess located in the substrate. A disadvantage is in addition to the large freedom of movement of the membrane that the overload protection is ensured only on one side. If the overpressure is applied to the "other" side of the membrane, it can be stretched even further and possibly destroyed.

The US 5,357,807 describes a micromechanical differential pressure sensor with a double-sided overload protection. The differential pressure sensor has a deformable membrane which is mounted on the top of a substrate and at its Um Catch area is tightly connected to the top of the substrate. Within the substrate is provided a hermetically sealed recess of the membrane, which is designed such that the membrane can perform a normal deflection movement, without touching the bottom of the recess. The bottom of the differential pressure sensor in this case represents an overpressure limitation for movements of the membrane in the direction of the substrate. With opposite movements, a nickel bridge limits the deflection of the membrane upwards. The distance between the pressure relief bridge and the membrane and between the membrane and the bottom of the recess of the substrate is not more than 10 microns. Thus, the double-sided overload protection is ensured by two different components in the differential pressure sensor described in this document. The method for manufacturing such a semiconductor pressure sensor is correspondingly complicated.

In addition, the describes US 4,072,057 a capacitive differential pressure sensor with double-sided overload protection. In this sensor, the sensor membrane used for the measurement is separated in the measuring chamber on both sides by flexible membranes from the outer medium. An incompressible oil in the measuring chamber ensures the pressure connection. In the event of overpressure, the respective outer separating membrane is pressed against a stop, so that only part of the load is transmitted to the sensor membrane serving for the measurement. This semiconductor differential pressure sensor is a sensor composed of a plurality of components, the structure of which becomes very complicated. Such a sensor is therefore hardly suitable for mass or mass production.

Together is all of these pressure sensors that protect the sensor membrane against overload either only one-sided or guaranteed only by means of a large amount of equipment becomes.

In the EP 0 639 761 A1 a sensor chip is described with a base substrate, which either itself represents an electrode or are applied to the two electrodes. On the electrodes there is a stencil-like intermediate layer with two openings, which is covered by corresponding membranes in order to produce the hydraulically connected cavities required for a differential pressure measurement.

The DE 197 50 131 A1 describes a micromechanical differential pressure sensor device in which two absolute pressure measuring devices are monolithically integrated on a carrier substrate. This is a differential pressure sensor composed of a multiplicity of micromechanical components, which is therefore complicated with respect to its production.

outgoing From the known prior art, the invention is therefore the task underlying, an easily manufacturable sensor chip for a Micromechanical differential pressure sensor with pressure connection options on one side of the case specify a reliable overload protection offers.

Presentation of the invention

The Task is solved with the sensor chip according to claim 1. advantageous Further developments of the inventive concept are the subject of the dependent claims and from the following description text and the exemplary embodiments remove.

Of the present sensor chip for a differential pressure sensor has a substrate with a first, a Recess in the substrate forming recess, which from a first Membrane sealing covered is. The sensor chip is characterized in that the substrate has a second recess forming a recess in the substrate, which is sealingly covered by a second membrane and at least over a channel communicates with the first recess, so that two cavities coupled to each other by a channel are formed, which are filled with an incompressible fluid, wherein the membranes electrically conductive or conductive coated and electrically connected to a first contact are, and on a floor space each recess is arranged at least one electrode which electrically is conductively connected to a second contact.

The used membrane is electrically conductive or conductive coated, so with the help of this membrane and the on the base of the respective cavity arranged electrode, a capacitor is formed, depending on Deflection of the membrane has a specific capacity. The membranes should preferably be elastic but not stretchable.

When using the sensor chip for differential pressure measurement, the two membranes are connected with different volumes whose pressure difference is to be measured. If in this case one of the membranes above one of the cavities is subjected to a greater load than the other, this membrane or this part of the membrane buckles down in accordance with the pressure load. In this process, a portion of the incompressible fluid through the Displaced channel in the adjacent cavity, so that the diaphragm located above or the membrane part bulges upwards. Due to the deformation of the membrane, the distance between the membrane and the respective electrode located on the base of the cavity also changes. From this change in the distance follows a change in capacitance of the capacitor formed by the membrane and electrode, so that the capacity of the condenser with downwardly curved membrane is larger and that of the condenser with an upwardly curved membrane smaller. The change in capacity, the so-called differential capacity, can be set in relation to the pressure difference. Preferably, the recesses of the sensor chip are formed identically and the capacity in the idle state approximately equal.

The Membrane covering the cavities exists preferably made of a material that is elastic but not stretchable is. This will ensure that the membrane, the above one of the cavities is loaded, but deformed but not stretched, so that Incorrect measurements of the differential pressure sensor can be largely avoided.

comes it overloads of the sensor chip described, is due to the structural design and the material properties of the membrane ensures that the Membrane not overstretched or even destroyed becomes. At an overpressure over one or a strong pressure drop over the other cavity one of the two membranes is bent down until they are at the bottom of the Forming a cavity Recess rests. The depth of the recesses is chosen so that the membrane is not overstretched or destroyed in this condition. Preferably the recesses are only a few microns deep. The over a cavity applied overpressure is thus over the incompressible fluid also not completely to the other membrane passed on, so that these only to the same extent as the first membrane arched upwards. The same mechanism also works when the pressure over the other cavity of the sensor chip is applied. In this way, an easy-to-manufacture sensor chip is available available the one reliable double-sided overload protection offers. The sensor chip allows the attachment of both pressure connections on one side, so that the assembly of the sensor chip or a differential pressure sensor formed therefrom simplified.

Preferably For example, the first and second membranes are contiguous as a common membrane formed, which covers the cavities connected to the channel. The membrane covers up both cavities Completely and is in the area outside the cavities preferably fixed to the substrate.

at a particularly suitable design of the sensor chip according to the invention is the channel between the cavities as a trench in the surface of the substrate trained and is also covered by the membrane sealing.

Preferably the membrane is made of silicon, metal or plastic. It is but also conceivable to use membranes made of other materials, the cavities span elastically but not stretchably.

In a special embodiment the sensor chip has a lid which is the first and the second or covering the common membrane at least in the area above the cavities. Furthermore has the lid is preferably above each cavity via a lid recess on a side facing away from the substrate of the membrane two fluid-tight to form separate pressure chambers. In one embodiment of the channel between the cavities as a trench in the surface of the Substrates the lid lies in the area between the cavities on the substrate, giving it the function of an upper limit the digging takes over and a warp the possibly existing common membrane over the trench prevented.

In another particular embodiment the sensor chip according to the invention is a pressure channel formed in the lid, which is a fluid-tight connection between at least one lid recess and one the substrate produces opposite side of the lid. Preferably is at this, the substrate facing away from the lid, on which the Pressure channel adjacent to the environment, a pressure port. Prefers this pressure connection is designed such that arbitrarily designed lines, for example, about special coupling elements, can be connected.

Of the Lid can be made of silicon, glass or plastic, for example be. In an advantageous embodiment, the lid and the substrate joined together by anodic bonding, the lid is preferably made of pyrex glass placed on top of it Way is fixed at the wafer level. This allows a fast, secure and high quality manufacturing of a micromechanical differential pressure sensor with the sensor chip according to the invention.

In one embodiment of the sensor chip, only one electrode is arranged on the base surface of each recess, which is electrically conductively connected to an electrical contact freely accessible from the outside of a housing for the sensor chip. Preferably, in this case, an evaluation unit is provided, with which the two Elek electrodes are readable separately. In a further embodiment of the sensor chip according to the invention, a multiplicity of electrodes are present on the base surface of each recess, which can be read out separately by a correspondingly formed evaluation unit. In this case, for example, two electrodes can be provided on the base of each cavity, which are evaluated separately with the evaluation unit, so that an error calculation and evaluation can follow and also the failure of individual electrodes does not cause a false measurement in each case.

The Wiring of the contacts, preferably designed as bond pads for the Electrodes and membranes can be done in different ways. So can both on the base the recesses arranged electrodes and the membranes be electrically connected to each separate contacts. Preferably, however, the membranes are in common contact this is when using a common membrane without further measures inevitably the Case is. When using separate, mutually insulated membranes it is also possible to connect the electrodes to a common contact and the Membranes with separate contacts.

The Electrodes can implanted directly into the substrate or as a metallic layer executed on an insulator be on the base of the Recess is applied.

Of the present sensor chip preferably has receiving elements for attachment in a housing on. These receiving elements have, for example, over level surfaces, so that the sensor chip with the aid of an adhesive in the housing is glued. Excellent strength properties are also achievable when the housing is biased. Compared to a through the strength characteristics of the Sensor materials limited compressive strength of a differential pressure sensor is due to the bias of the housing a much higher pressure resistance reached the pressure sensor.

Short description of drawings

Of the Sensor chip according to the invention for a differential pressure sensor is hereafter without limitation of the general inventive idea using an exemplary embodiment with reference to the drawings described again by way of example. Show it:

1 a plan view of an embodiment of a sensor chip according to the invention;

2 a cross-sectional view of the sensor chip of 1 ; and

3 a cross-sectional view through a differential pressure sensor with an inventively designed sensor chip.

Ways to execute the invention

In 1 is a plan view of an embodiment of a sensor chip according to the invention 2 shown. In a substrate 12 are cavities 9a . 9b formed by a channel 11 are connected with each other. On the bases of the cavities 9a . 9b forming recesses in the substrate 12 are electrodes 4a . 4b arranged, each with a trained as Bondpad contact 5 are electrically connected. The electrical contacts 5 are so on the substrate 12 arranged that they are freely accessible for contacting the sensor chip from the outside.

Furthermore, a likewise formed as a bond pad connection 14 provided, which is electrically conductive with one on the substrate 12 lying membrane (not visible in this view) is connected. As the membrane and in the cavities 9a . 9b arranged electrodes 4a . 4b are not electrically connected, they represent a capacitive resistance. The size of the capacitive resistance is via the contacts 5 and 14 with the help of an evaluation unit (not shown) readable.

The 2 shows a cross-sectional view of the sensor chip 2 of the 1 , In this illustration, the recesses 8a . 8b in the substrate 12 to recognize, together with the recesses 8a . 8b covering membrane 1 the cavities 9a . 9b form. In the bases of the recesses 8a . 8b are the ones with the contacts 5 connected electrodes 4a . 4b implanted. The surface areas of the substrate 12 into which no recesses are etched and that of the membrane 1 are covered with the membrane 1 firmly connected so that the cavities 9a . 9b and the cavities 9a . 9b connecting channel 11 a fluid-tight sealed cavity below the membrane 1 form. This cavity is filled with an incompressible fluid 13 filled in, hatched in the figure is indicated.

The membrane 1 and the electrodes 4a respectively. 4b each represent a capacitor whose capacity over the contacts 5 and a contact, not shown in this view 14 for the contacting of the membrane 1 is read out.

3 shows a cross-sectional view through a micromechanical differential pressure sensor with an inventively designed Sen sorchip 2 the one substrate 12 with two recesses over the channel 11 connected to each other. Furthermore, the sensor chip 2 a membrane 1 on which the recesses as well as the channel 11 spanned, leaving two by the channel 11 connected cavities 9a . 9b be formed. The sensor chip 2 has the in the 1 and 2 explained embodiment. Further, on the sensor chip 2 a lid chip 3 applied in areas that are not the cavities 9a . 9b straddle, firmly on the membrane 1 rests.

The lid chip 3 has lid recesses 10a . 10b , which are dimensioned so that the membrane 1 only over the cavities 9a . 9b is free or limited and in particular the cavities 9a . 9b connecting channel 11 is completely covered. The lid recess 10a is over the pressure line 6 and the lid recess 10b via the pressure line 7 connected to the environment.

The cavities 9a . 9b and the channel connecting the cavities 11 are completely filled with an incompressible fluid 13 refilled. With the help of this incompressible fluid 13 becomes a hydraulic connection between the cavities 9a . 9b produced.

Will the membrane 1 above a cavity 9a through one on the pressure line 6 pending pressure P ₁ charged, this warps down. This is part of the incompressible fluid 13 through the channel 11 in the neighboring cavity 9b displaced, so that the over this cavity 9b located membrane portion cambered upwards. As a result, the capacity of each electrode changes 4a respectively. 4b and membrane 1 formed capacitor. The change in capacity is between the pressure lines 6 and 7 applied pressure difference determined.

The structure of the pressure sensor made of sensor chip 2 and lid chip 3 enables bilateral, symmetrical overload protection. If offset printing falls on one side, for example on pressure line 6 out, the membrane becomes 1 into the corresponding cavity, which is only a few μm deep 9b pressed. The maximum expansion of the membrane is limited by the bottom of the cavity. Will for the membrane 1 selected a silicon material, this membrane can withstand pressures of several 10 ⁷ Pa (= 100 bar). If such overpressure p _{1 is present} on one side, the membrane will buckle 1 at the same time on the other side, in this case in the lid recess 8b only to the displaced volume of the incompressible fluid 13 out. This will ensure that the membrane 1 is not overstretched even with concerns about a corresponding overpressure.

The forces due to unilateral offset printing do not fall over the membrane 1 but on the material between the pressure lines 6 and 7 and at the same time also at the connection between cover chip 3 and sensor chip 2 from. The compressive strength of the illustrated pressure sensor is therefore not affected by the characteristics of the sensor chip 2 limited.

Since in the illustrated differential pressure sensor, a sensor chip 2 is provided, which is constructed symmetrically and with which a differential capacitance is measured, special temperature or stress-related drift effects can be eliminated in a simple manner. In addition, it is located on the pressure lines 6 respectively. 7 applied pressure directly on the membrane 1 on, without that a pressure is absorbed by an additionally provided in the sensor medium. The in 3 The sensor shown thus represents a media-decoupled differential pressure sensor, by the use of incorrect measurements are largely excluded.

1

membrane

2

sensor chip

3

chip cover

4a

electrode

4b

electrode

5

Contact

6

pressure line 1

7

pressure line 2

8a

first recess

8b

second recess

9a

cavity

9b

cavity

10a

Deckelausnehmung

10b

Deckelausnehmung

11

channel

12

substratum

13

incompressible fluid

14

connection for membrane

Claims (16)

Sensor chip for a differential pressure sensor, which is a substrate ( 12 ) with a first, a recess in the substrate forming recess ( 8a ) formed by a first membrane ( 1 ) is sealingly covered, characterized in that the substrate ( 12 ) a second, a recess in the substrate forming recess ( 8b ) separated from a second membrane ( 1 ) is sealingly covered and over at least one channel ( 11 ) with the first recess ( 8a ), so that two through the channel ( 11 ) with coupled cavities ( 9a . 9b ) formed with an incompressible fluid ( 13 ) are filled, the membranes ( 1 ) electrically conductive or conductive coated and electrically conductive with a first contact ( 14 ) are connected and on a base of each recess ( 8a . 8b ) at least one electrode ( 4a . 4b ) is arranged, which is electrically conductive with a second contact ( 5 ) connected is. Sensor chip according to claim 1, characterized in that the first and the second membrane ( 1 ) are formed coherently as a common membrane. Sensor chip according to claim 1 or 2, characterized in that a cover ( 3 ) is provided, the first and the second membrane ( 1 ) at least in one of the cavities ( 9a . 9b ) opposite area covered. Sensor chip according to claim 3, characterized in that the cover ( 3 ) in the area of the cavities ( 9a . 9b ) each have a lid recess ( 10a . 10b ), so that on a the substrate ( 12 ) facing away from the membrane ( 1 ) at least two fluid-tight separate pressure chambers are formed. Sensor chip according to claim 4, characterized in that at least one pressure channel ( 6 . 7 ) in the lid ( 3 ) is formed, the a fluid-tight connection between at least one Deckelausnehmung ( 10a . 10b ) and a substrate ( 12 ) facing away from the lid ( 3 ). Sensor chip according to one of claims 3 to 5, characterized in that the cover ( 3 ) consists of silicon, glass or plastic. Sensor chip according to one of claims 3 to 6, characterized in that the cover ( 3 ) and the substrate ( 12 ) are connected by anodic bonding. Sensor chip according to one of claims 1 to 7, characterized in that the membranes ( 1 ) are formed of silicon, metal or plastic. Sensor chip according to one of claims 1 to 8, characterized in that the first and the second membrane ( 1 ) in the area outside the cavities ( 9a . 9b ) on the substrate ( 12 ) rest. Sensor chip according to one of claims 1 to 8, characterized in that the channel ( 11 ) as a trench in a surface of the substrate ( 12 ) is formed and the first and the second membrane ( 1 ) in the area outside the cavities ( 9a . 9b ) and the channel ( 11 ) on the substrate ( 12 ) rest. Sensor chip according to one of claims 1 to 10, characterized in that the recesses ( 8a . 8b ) in the substrate ( 12 ) are only a few microns deep. Sensor chip according to one of claims 1 to 11, characterized in that an evaluation unit is provided, with which on the base surfaces of the recesses ( 8a . 8b ) arranged electrodes ( 4a . 4b ) are readable separately. Sensor chip according to one of claims 1 to 11, characterized in that on the base of each recess ( 8a . 8b ) at least two electrodes ( 4a . 4b ) are arranged and an evaluation unit is provided, with which a plurality of electrodes is read out separately. Sensor chip according to one of claims 1 to 13, characterized in that the electrodes ( 4a . 4b ) in the substrate ( 12 ) are implanted and / or formed as a metallic layer on an insulator. Sensor chip according to one of claims 1 to 14, characterized in that receiving elements for fixing the sensor chip ( 2 ) are provided in a housing. Sensor chip according to claim 15, characterized in that the sensor chip ( 2 ) is arranged in a housing which is biased.