DE10249238A1 - Micro-mechanical differential pressure sensor, has two pressure measurement cavities linked by a channel and filled with incompressible liquid, with each covered by a membrane that deflects to enable pressure measurement - Google Patents

Abstract

Micro-mechanical differential pressure sensor has a substrate with first and second recesses that are linked by a channel (11) and filled with an incompressible liquid. Both cavities (9a, 9b) are sealed with an inelastic membrane that is deflected by a pressure change but not stretched. An electrically conducting electrode (4a, 4b) is applied to the top of each membrane so that two capacitors are formed between the electrodes and the respective bottoms of each cavity. The electrodes are connected to contacts (5) that are connected to an evaluation circuit. When used, one cavity is connected to each of the differing pressures.

Description

Technical application area

The invention relates to a Sensor chip for a differential pressure sensor, which is a substrate with a first recess has, which is covered by a first membrane sealing.

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

Usually feature such semiconductor pressure sensors both over a membrane, which consists of a or several, optionally doped or coated silicon layers exists as well piezoresistive elements used to sense the direction and / or the size of the deflection the membrane are provided. Such sensors convert those of Outside compressive forces acting on them into an electrical signal, which is then processed with an evaluation unit is evaluated.

In addition, these pressure sensors with an appropriate wrapping Mistake. The main one The task of wrapping is to protect the sensor from environmental influences, e.g. when used in aggressive media.

A special form of a pressure sensor is the so-called differential pressure sensor, with which the measurement of an between two volumes occurring pressure difference is possible. Such a sensor usually includes a silicon chip with a the pressure difference receiving membrane, which is operatively connected to piezoresistors. To the sensor from environmental influences to protect, it is poured into a casting 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 connections Pressure difference is measurable.

However, it can happen that the pressure at one of the two pressure connections is strong increases or decreases sharply, so a sudden, there is a strong pressure difference. For this reason, it is general It is important to design pressure sensors in such a way that they are ideal against overload pressures are insensitive. So can common today Semiconductor differential pressure sensors about two to three times the maximum working pressure at overload withstand without being damaged to become.

Frequently have to however also low differential pressures with high bilateral Pressure, the so-called offset pressure, can be measured. If the offset printing falls on one side, the sensor membrane must be subjected to extreme overpressure resist. A high overload resistance in such cases corresponding support structures, which are designed in the form of mechanical stops. This way, an overstretch or destruction prevents the membrane.

For example, describes US 5,969,591 a differential pressure sensor with one-sided overload protection, in which the two pressure connections are arranged on one side of the housing. The semiconductor pressure sensor has a silicon substrate, into which a recess is etched, which is covered by a membrane that is gas-tightly connected to the substrate at its membrane edges. An insulation layer and a protective layer are deposited on the membrane, a sensor element being integrated within the protective layer. A cavity is formed on both sides of the membrane, the cavity which is located above the membrane within a housing part constituting a pressure chamber. This pressure chamber is in turn connected to a first pressure connection via a pressure line arranged in the housing outer wall. A second pressure connection is connected via a second pressure line to a second pressure chamber, which is sealed gas-tight against the first pressure chamber. A pressure difference between the two pressure connections can be measured via the deflection of the membrane and the corresponding effects on the electrical properties of the sensor element. The overload protection, which is intended to protect the membrane from damage due to extreme overpressure, is realized with this differential pressure sensor by mechanical stops. In the event of an overload, the membrane lies, for example, against a boundary of the housing wall or the bottom of the recess in the substrate. In addition to the large freedom of movement of the membrane, it is disadvantageous that the overload protection is only guaranteed on one side. If the overpressure is on 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 double-sided overload protection. The differential pressure sensor has a deformable membrane which is attached to the top of a substrate and is tightly connected to the top of the substrate at its peripheral region. Provided within the substrate is a recess hermetically sealed by the membrane, which is designed in such a way 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 towards the substrate. With opposite movements, a nickel bridge limits the upward deflection of the membrane. The distance between the pressure relief bridge and the membrane and between the membrane and the bottom of the recess in the substrate is not more than 10 μm. In the differential pressure sensor described in this document, the two-sided overload protection is ensured by two different components. The method for producing such a semiconductor pressure sensor is correspondingly complicated.

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

Common to all these pressure sensors is that the protection of the sensor membrane against overload either only on one side or only by means of a large apparatus Effort guaranteed becomes.

Based on the known state of the Technology is therefore the object of the invention, a simple 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 done with the sensor chip according to claim 1 solved. Advantageous developments of the inventive concept are the subject of under claims as well as from the following description text and the exemplary embodiments remove.

The present sensor chip for one Differential pressure sensor has a substrate with a first recess on, which is sealed by a first membrane. The sensor chip is characterized in that the substrate has a second recess has a sealing membrane covered by a second is and about at least one channel is connected to the first recess, so that two cavities coupled together by a channel are formed be filled with an incompressible fluid, the membrane electrically conductive or conductive coated and electrically connected to a first contact, and on a footprint each recess is arranged at least one electrode, which is electrical is conductively connected to a second contact.

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

When using the sensor chip Differential pressure measurement, the two membranes are different Volumes connected, the pressure difference to be measured. Becomes one of the membranes above one of the cavities is more heavily loaded than the other, warped this membrane or this part of the membrane corresponding to the pressure load downward. In this process, part of the incompressible Fluids displaced through the channel into the adjacent cavity, so that the one above it Diaphragm or the membrane part warps upwards. Because of the deformation the membrane changes also the distance between the membrane and each on the base of the cavity located electrode. A change in capacity follows from this change in distance of the capacitor formed by the membrane and the electrode, so that the capacity of the capacitor with the diaphragm arched downwards and larger of the capacitor becomes smaller with the membrane curved upwards. The change the capacities, the so-called differential capacity, can be related to the pressure difference. Preferably the recesses of the sensor chip are identical and the capacities approximately the same in the idle state.

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

If the sensor chip described is overloaded, the construction and material properties of the membrane ensure that the membrane is not overstretched or even destroyed. In the event of an overpressure above or a strong pressure drop across the other cavity, one of the two membranes is arched downwards until it reaches the bottom of the cavity forming recess. The depth of the recesses is chosen so that the membrane is not overstretched or destroyed in this state. The recesses are preferably only a few μm deep. The overpressure present over a cavity is therefore not completely passed on to the other membrane via the incompressible fluid, so that this also arches upward only to the same extent as the first membrane. The same mechanism also applies if the excess pressure is present over the other cavity of the sensor chip. In this way, an easy to manufacture sensor chip is available that offers reliable double-sided overload protection. The sensor chip enables the attachment of both pressure connections on one side, so that the assembly of the sensor chip or a differential pressure sensor formed therefrom is simplified.

Preferably the first and the second membrane connected formed as a common membrane that connected to the channel Cavities covered. The membrane covers both cavities Completely and is in the area outside of the cavities preferably fixed to the substrate.

With a particularly suitable design of the sensor chips 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.

The membrane preferably consists made of silicon, metal or plastic. But it is also conceivable Use membrane made of other materials that make the cavities elastic but do not stretch extensively.

In a special embodiment the sensor chip has a cover that the first and the second or covers the common membrane at least in the area above the cavities. Furthermore has the lid preferably above each cavity via a lid recess two fluid-tight on a side of the membrane facing away from the substrate to form separate pressure chambers. With a design of the channel between the cavities as a trench in the surface of the Substrate is the lid in the area between the cavities the substrate so that it functions as an upper limit of the trench takes over and a warp the possibly existing common membrane over the trench prevented.

In a further special embodiment of the sensor chip according to the invention a pressure channel is formed in the cover, which is a fluid-tight connection between at least one cover recess and one of the substrate side facing away from the lid. Preferably located on this side of the cover facing away from the substrate, on which the Pressure channel adjacent to the environment, a pressure connection. Prefers is this pressure connection designed in such a way that any lines, e.g. over special coupling elements can be connected.

The lid can, for example Silicon, glass or plastic can be made. In an advantageous embodiment the lid and the substrate are anodically bonded to one another connected, the lid preferably being made of pyrex glass, that is fixed in this way on the wafer level. This enables one Fast, safe and high quality manufacture of a micromechanical Differential pressure sensor with the sensor chip according to the invention.

In one embodiment of the sensor chip is on the footprint only one electrode is arranged in each recess, which is electrically conductive with one from the outside of a housing for the sensor chip freely accessible electrical contact is connected. In this case it is preferable an evaluation unit is provided with which the two electrodes are separated are readable. In a further embodiment of the sensor chip according to the invention a large number of electrodes are provided on the base of each recess, which are separated from an appropriately designed evaluation unit are readable. Here you can For example, two electrodes are provided on the base of each cavity be evaluated separately with the evaluation unit, so that an error calculation and evaluation can follow and the failure of individual electrodes is not always a problem Incorrect measurement causes.

The wiring of the preferably contacts designed as bond pads for the electrodes and membrane can be done in different ways. So both on the base of the Recesses arranged electrodes as well as the membrane with each separate contacts to be electrically connected. Preferably if the membrane is connected to a common contact, this being the case when using a common membrane without further measures inevitably the case is. When using separate, isolated from each other Membranes it is also possible to connect the electrodes with a common contact and the Membrane with separate contacts.

The electrodes can be implanted directly into the substrate or be implemented as a metallic layer on an insulator, the on the footprint of the Recess is applied.

The present sensor chip preferably has receiving elements for fastening in a housing. These receiving elements have, for example, flat surfaces, so that the sensor chip can be glued into the housing with the aid of an adhesive. Excellent strength properties can also be achieved if the housing is preloaded. In comparison to a compressive strength of a differential pressure sensor limited by the strength values of the sensor materials, the preload tion of the housing achieves a significantly higher pressure resistance of the pressure sensor.

Brief description of the drawings The sensor chip according to the invention for one Differential pressure sensor is shown below without limitation general inventive idea based on an embodiment described again by way of example with reference to the drawings. It demonstrate:

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 the 1 ; and

3 a cross-sectional view through a differential pressure sensor with a sensor chip designed according to the invention.

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

There is also a connection which is also designed as a bond pad 14 provided the electrically conductive with one on the substrate 12 overlying membrane (not visible in this view) is connected. Because the membrane and that in the cavities 9a . 9b arranged electrodes 4a . 4b are not electrically conductively connected, they represent a capacitive resistor. The size of the capacitive resistor is via the contacts 5 and 14 readable with the help of an evaluation unit (not shown).

The 2 shows a cross-sectional view of the sensor chip 2 the 1 , In this illustration, the recesses are 8a . 8b in the substrate 12 to recognize the along with the the recesses 8a . 8b covering membrane 1 the cavities 9a . 9b form. In the base areas of the recesses 8a . 8b are the ones with the contacts 5 connected electrodes 4a . 4b implanted. The surface areas of the substrate 12 , in 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 cavity below the membrane 1 form. This cavity is with an incompressible fluid 13 filled in, which is indicated by hatching in the figure.

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

3 shows a cross-sectional view through a micromechanical differential pressure sensor with a sensor chip designed according to the invention 2 which is a substrate 11 has two recesses that over the channel 11 are interconnected. Furthermore, the sensor chip 2 a membrane 1 on the the recesses as well as the channel 11 spanned so that two by the channel 11 connected cavities 9a . 9b be formed. The sensor chip 2 indicates the in the 1 and 2 explained design on. It is also on the sensor chip 2 a lid chip 3 applied that in areas that are not the cavities 9a . 9b span, firmly on the membrane 1 rests.

The lid chip 3 has lid recesses 10a . 10b that are dimensioned so that the membrane 1 just over the cavities 9a . 9b is exposed 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 complete with an incompressible fluid 13 refilled. With the help of this incompressible fluid 13 becomes a hydraulic connection between the cavities 9a . 9b manufactured.

Will the membrane 1 above a cavity 9a through one on the pressure line 6 pressure P _{1 is present} , it bulges downwards. Part of the incompressible fluid 13 through the channel 11 into the neighboring cavity 9b displaced, so that the over this cavity 9b located diaphragm portion arched upwards. As a result, the capacitance of the electrode changes 5 and membrane 1 formed capacitor. The change in capacity becomes that between the pressure lines 6 and 7 applied pressure difference determined.

The construction of the pressure sensor from sensor chip 2 and lid chip 3 enables symmetrical overload protection on both sides. If the offset printing falls on one side, for example on the pressure line 6 out, becomes the membrane 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. Used for the membrane 1 If a silicon material is selected, this membrane can withstand pressures of several 10 ⁷ Pa (= 100 bar). When such an overpressure p _{1 is present} on one side, the membrane buckles 1 at the same time on the other side, in this case in the cover recess 8b , just by the displaced volume of the incompressible fluid 13 out. This ensures that the membrane 1 not overstretched even when there is a corresponding overpressure becomes.

The forces from the one-sided offset printing do not fall over the membrane 1 but the material between the pressure lines 6 and 7 and at the same time on the connection between the lid chip 3 and sensor chip 2 from. The pressure resistance of the pressure sensor shown is consequently not determined by the properties of the sensor chip 2 limited.

Since in the differential pressure sensor shown 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, this is due to the pressure lines 6 respectively. 7 applied pressure directly on the membrane 1 without a pressure being recorded via an additional medium provided in the sensor. The in 3 The sensor shown thus represents a media-decoupled differential pressure sensor, the use of which largely precludes incorrect measurements.

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 recess ( 8a ) having a first membrane ( 1 ) is sealingly covered, characterized in that the substrate ( 12 ) a second recess ( 8b ) having a second membrane ( 1 ) is sealingly covered and over at least one channel ( 11 ) with the first recess ( 8a ) communicates so that two through the channel ( 11 ) coupled cavities ( 9a . 9b ) that are formed with an incompressible fluid ( 13 ) are filled, whereby the membrane ( 11 ) 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 ( 11 ) are coherent as a common membrane. Sensor chip according to claim 1 or 2, characterized in that a cover ( 3 ) is provided, which the first and the second membrane ( 11 ) at least in one of the cavities ( 9a . 9b ) covers the opposite area. Sensor chip according to claim 3, characterized in that the cover ( 3 ) in the area of the cavities ( 9a . 9b ) one cover recess each ( 10a . 10b ), so that on a substrate ( 12 ) opposite side of the membrane ( 11 ) 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, which has a fluid-tight connection between at least one cover recess ( 10a . 10b ) and the substrate ( 12 ) opposite side of the cover ( 3 ) produces. 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 membrane ( 11 ) are made of silicon, metal or plastic. Sensor chip according to one of claims 1 to 8, characterized in that the first and the second membrane ( 10 ) in the area outside the cavities ( 9a . 9b ) on the substrate ( 11 ) lie on. 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 ) and the first and the second membrane ( 10 ) in the area outside the cavities ( 9a . 9b ) and the channel ( 11 ) on the substrate ( 11 ) lie on. 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 μm deep. Sensor chip according to one of claims 1 to 11, characterized in that an evaluation unit is provided with which the on the base areas of the recesses ( 8a . 8b ) arranged electrodes ( 4a . 4b ) can be read out 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 can be read out separately. Sensor chip according to one of claims 1 to 13, characterized in that the electrodes ( 4a . 4b ) into the substrate ( 12 ) 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 fastening 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 that is biased.