Micromechanical pressure sensor, method for producing same, and method for detecting a pressure variable

Abstract

The pressure sensor according to the invention has a diaphragm which stretches over a cavity. A first electrode is provided in or on the diaphragm in a central region, and a second electrode is provided on the cavity base so as to lie opposite the central region of the diaphragm or the first electrode. While the second electrode is arranged in a fixed and rigid manner, the first electrode in or on the diaphragm is designed so as to be able to flexibly bend together with the diaphragm and move towards the second electrode when a pressure is applied to the diaphragm. Together, the first and second diaphragm form a first measuring capacitor, by means of which a pressure can be detected up to a pressure threshold. When the pressure threshold is reached, the diaphragm is positioned on the second electrode such that an additional pressure increase does not result in an additional change in the capacitance. In order to allow even higher pressures to be detected, a second measuring capacitor is provided in the lateral region of the diaphragm. The second measuring capacitor is formed by an additional first electrode in or on the lateral region of diaphragm and an additional second electrode which is arranged on the cavity base opposite the additional first electrode. It is essential to the invention that the spacing of the electrodes of the second measuring capacitor is smaller than the spacing of the electrodes of the first measuring capacitor.

Description

[0001] Description

[0002] title

[0003] Micromechanical pressure sensor with and procedures for

[0004] The invention relates to a micromechanical capacitive pressure sensor, a corresponding micromechanical manufacturing method and a method for detecting or deriving a pressure sensor variable by means of the pressure sensor.

[0005] State of the art

[0006] Typical pressure sensors use a diaphragm above a cavity to detect pressure, which deflects when pressure is applied. Piezoelectric resistors and electrodes are used to measure the deflection of the diaphragm.

[0007] From the document DE 10 2009 001 924 Al a pressure sensor with two pressure characteristics is known, in which after the central part of the membrane has been placed on the cavern floor, the side areas can still be used for pressure detection.

[0008] From the unpublished document DE 10 2021 207 745 Al a

[0009] A pressure sensor is known in which lateral stamps are provided which, in the case of capacitive pressure detection, shorten the distance to the electrode when the membrane is bent.

[0010] The present invention is intended to describe a special construction of a pressure sensor that provides higher sensitivity in a second pressure range. Disclosure of the Invention

[0011] The present invention claims a micromechanical pressure sensor that derives a pressure sensor variable or a pressure sensor value from the deflection of a diaphragm using a capacitive measuring principle. For this purpose, a capacitance consisting of two electrodes is used, in which the distance between the two electrodes is reduced by an applied pressure. Furthermore, the invention claims a corresponding manufacturing method for this pressure sensor, in particular with micromechanical process steps. Furthermore, a method for operating the micromechanical pressure sensor or for detecting and deriving the pressure sensor variable as a function of the pressure applied to the diaphragm of the pressure sensor is also claimed.

[0012] The pressure sensor according to the invention has a membrane that spans a cavity. A first electrode is provided in or on the membrane in a central region. A second electrode is provided on the cavity floor, opposite the central region of the membrane or the first electrode. While the second electrode is fixed and rigidly arranged, the first electrode in or on the membrane is designed such that it can flexibly bend with the membrane and move towards the second electrode when pressure is applied to the membrane. Together, these first and second membranes form a first measuring capacitance with which a pressure up to a pressure limit value can be detected. When the pressure limit value is reached, the membrane rests on the second electrode so that there is no further change in capacitance if the pressure increases further.In order to be able to measure even higher pressures, according to the invention a second measuring capacitance is provided in the side region of the membrane. This second measuring capacitance is formed by an additional first electrode in or on the side region of the membrane and a further second electrode which is arranged on the cavern floor opposite the additional first electrode. The core of the invention is that the distance between the electrodes of the second measuring capacitance is smaller than the distance between the electrodes of the first measuring capacitance. The advantage of such a design is that two pressure ranges can be measured using the pressure sensor according to the invention. Since the second pressure range above the pressure limit value has a smaller contact surface for deflection on the membrane, significantly higher pressure values ​​can be measured with this second measuring capacitance.By reducing the distance between the electrodes of the second measuring capacitance, the resolution and responsiveness to deflection can be increased.

[0013] To achieve the smaller distance between the electrodes of the second measuring capacitance, the additional second electrode can be designed to be elevated relative to the second electrode in the central region relative to the cavern floor. This can be achieved by making the electrode thicker or by placing it on a pedestal.

[0014] Alternatively or additionally, an additional first electrode may be provided, which is arranged on the underside of the membrane in the side region. The additional first electrode can be attached directly to the membrane or, by means of a holding element, arranged at a distance from the membrane in the direction of the cavern floor or the further second electrode.

[0015] Advantageously, a reference electrode can also be provided, which is associated with at least one of the further rigid second electrodes. Thus, the reference electrode can be applied to the cavern floor or created in the underlying substrate, whereas the further second electrode is arranged or created above it at a distance from the reference electrode.

[0016] Further advantages emerge from the following description of embodiments and from the dependent patent claims.

[0017] Brief Description of the Drawings Figure 1 schematically shows the operation of a known capacitive pressure sensor. Figure 2 shows a first embodiment of the invention, and Figure 3 shows a second embodiment. Figure 4 shows a combination of the configurations of both embodiments.

[0018] Embodiments of the invention

[0019] In a pressure sensor with a capacitive measuring principle, as shown in Figure 1, a frame 130 with a membrane 140 is typically applied to a substrate 100 by means of a connecting layer 120. The frame 130 forms a cavity 110 with the substrate 100, which preferably has a substantially vacuum. When external pressure is applied, the membrane 140 bends, in extreme cases until it rests in a central region I in a membrane state 145 on the floor of the cavity 110, an electrode 150 located there, or the substrate 100. In particular, it is provided that the membrane 140 is designed with an insulating layer on the inside facing the cavity 110 in order to prevent a short circuit upon contact. Alternatively or additionally, the central electrode 150 can have an insulating layer.To detect the deflection of the membrane 140, a capacitive measuring principle provides that the membrane 140 is at least partially configured as a first flexible electrode with a first measuring capacitance. Furthermore, a second rigid electrode 150 of the first measuring capacitance is provided, particularly at the bottom 115 of the cavity 100, on or in the substrate 100 opposite the membrane 140 and / or the first electrode. If the distance between the first and second electrodes decreases due to the deflection of the membrane 140, a corresponding change in the detected capacitance can be recorded as a measure of the applied pressure.

[0020] In one possible embodiment of the capacitive pressure sensor, further pressure detection can occur even after the membrane 145 has been placed on the cavern floor 115 or the lower second electrode 150 at a limit pressure value. This is made possible by the fact that at pressures higher than the limit pressure value, the side regions II of the membrane 140 or 145 can be deflected further, whereby they also approach the cavern floor 115. In order to be able to detect this change in distance in the side region II of the membrane 140 above the limit pressure, it is necessary for the membrane 140 or 145 to be designed as a first electrode in this region as well, and for further second rigid or fixed electrodes 160 to be arranged on the cavern floor 115 in the side region II. This additional second measuring capacitance in the side region II makes it possible to realize a second pressure range separate from the first pressure range.Since the membrane 140 in side region II has a different deflection behavior due to its stiffer design, this second pressure range can be recognized in the recorded capacitance signal of the sensor by a pressure behavior that is different from the first pressure range. The design of the further second electrodes 160 can be provided so that they are electrically connected to the central second electrode 150 or electrically separated from it. This depends on the selected evaluation method, the respective options of the evaluation circuit and the respective application. It may be desired to map both pressure ranges via a characteristic curve. In this case, the electrodes 150 and 160 are electrically connected to one another. In another case, it may be desired to be able to switch between the two characteristic curves at any time. In this other case, the electrodes 150 and 160 are electrically separated from one another.

[0021] Since the distance between the membrane 140 in the side region II and the further second electrode 160 changes only slightly at a higher pressure applied to the membrane 140 above the limit pressure, it can be provided to bring the further electrode 165 closer to the first electrode in the membrane 140. Accordingly, Figure 2 shows a first exemplary embodiment of the invention, in which the further second electrode 165, which is arranged laterally to the central second electrode 150, is designed to be raised. Optionally, a reference electrode 170 can be arranged below the further second electrode 165, which, together with the rigid or permanently installed further second electrode 165 located above it, forms a reference capacitance. This can be used to implement the Wheatstone bridge circuit measuring principle common for pressure sensors.In a second embodiment, which is shown in Figure 3, the distance between the electrodes of the lateral second measuring capacitance can also be reduced by providing additional first electrodes 180 in the side region II, which are brought closer to the further second electrode 160, which is attached to the cavern floor 115, on stamp-shaped configurations or a holding element 185 on the membrane 140.

[0022] The configurations of the two above embodiments can also be combined, as shown in Figure 4.

[0023] The membrane 140 can be configured as a single first electrode, which interacts with the corresponding second electrodes as measuring capacitances both in the central region I and in the side regions II. Optionally, the central second electrode can be connected in parallel with the further second electrodes 160 and 165, respectively. This would create a common measuring capacitance that is essentially determined by the central electrodes in the central region I in a first pressure range until the limit pressure value is reached (=contact of the membrane 145 on the cavern floor 115 or on the first central electrode), and by the lateral electrodes above the limit pressure value.

[0024] Alternatively, however, it can also be provided that the membrane 140 has a central first electrode and an additional first electrode in each side region II. Furthermore, it can be provided that the second central electrode 150 and the laterally arranged further second electrodes 160 and 165 are electrically separated from one another and can also be read out separately. This makes it possible to realize, in addition to the central first measuring capacitance, a second laterally arranged measuring capacitance which is read out separately only for the second pressure range. Using the measures described in this patent, this capacitance can then be optimized specifically for the second pressure range with a sufficiently high sensitivity. Optionally, it can be provided that the additional first electrode is provided in the membrane 140 and the further second electrode 160 and 165 is provided only in one side region of the cavity.

Claims

1. Micromechanical capacitive pressure sensor with at least • a membrane (140, 145) spanning a cavern (110), • a flexible first electrode assigned to the central region (I) of the membrane (140, 145), • a rigid second electrode (150) opposite the central area (I) on the cavern floor (115), and • a flexible additional first electrode (180) assigned to the side region (II) of the membrane (140, 145), and • a rigid second electrode (160, 165) opposite the side region (II) on the cavern floor (115), wherein the distance between the additional first electrode and the further second electrode (160, 165) in the side region (II) is less than the distance between the first electrode and the second electrode (150) in the central region (I).

2. Micromechanical capacitive pressure sensor according to claim 1, characterized in that the at least one further second electrode (165) is arranged at least partially further away from the cavern floor (115) compared to the second electrode (150).

3. Micromechanical capacitive pressure sensor according to claim 1 or, characterized in that the at least one additional first electrode (180) is arranged spaced apart on the underside of the membrane (140, 145) by means of a retaining element (185).

4. Micromechanical capacitive pressure sensor according to one of the preceding claims, characterized in that a reference electrode (170) is assigned to the at least one further second electrode (165), wherein it is particularly provided that the reference electrode (170) is arranged on the cavern floor (115) and the further second electrode (165) is arranged spaced apart above the reference electrode (170). Method for manufacturing a micromechanical capacitive pressure sensor according to one of claims 1 to 4, wherein at least [number] micromechanical methods are used to manufacture a micromechanical capacitive pressure sensor. • a membrane (140, 145) spanning a cavern (110), • in or on a central region (I) of the membrane (140, 145) an associated flexible first electrode, • on the cavern floor (115) a rigid central area (I) opposite a second electrode (150), and • a flexible additional first electrode (180) associated with the side region (II) of the membrane (140, 145), and • a rigid second electrode (160, 165) opposite the side region (II) of the membrane (140, 145) is generated on the cavern floor (115), wherein the distance between the additional first electrode and the further second electrode (160, 165) in the side region (II) is smaller than the distance between the first electrode and the second electrode (150) in the central region (I).Method for detecting a pressure sensor signal with a micromechanical capacitive pressure sensor according to one of claims 1 to 4, wherein in a first pressure range up to a pressure limit value the derivation of the pressure quantity is carried out essentially by detecting the capacitance between the first and second electrode (150) in the central region (I) of the diaphragm (140, 145) and in a second pressure range above the pressure limit value the derivation is carried out essentially by detecting the capacitance between the additional first electrode (180) and the further second electrode (160, 165) in the side region (II) of the diaphragm (140, 145).

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