Diaphragm sensor for compensating for acceleration and corresponding operating method

Abstract

The invention claims a micromechanical diaphragm sensor, in particular a pressure sensor, and a method suitable for determining a sensor value and / or a sensor variable of a diaphragm sensor. The sensor value of the diaphragm sensor is determined in such a way that a gravitational force or other acceleration on the diaphragm is compensated to the greatest extent.

Description

Technical Field

[0001] The invention relates to a diaphragm sensor in which accelerations or weight forces acting on the diaphragm are taken into account when determining the sensor value, and to a corresponding operating method. Background Art

[0002] Micromechanical membrane sensors are usually directly exposed to the medium whose physical and / or chemical properties are to be detected. In this case, it can be provided that the membrane or at least the sensitive sensor structure located on the membrane is protected with a gel to prevent corrosion and / or unwanted adsorbent deposition. However, the use of a protective gel on the membrane surface can change the properties of the membrane (especially in the case of pressure sensors), which can lead to changes in the sensor variable to be detected or the sensor value determined with the membrane sensor.

[0003] In pressure sensors, covering the diaphragm with a protective gel results in a significant additional weight force on the diaphragm and thus in an orientation-dependent g-sensitivity or general acceleration sensitivity in the detection of the measured values. With increasing precision of the detected sensor value, the mass of the diaphragm or the combined mass of the diaphragm and (gel) covering represents a greater inaccuracy factor in determining the sensor value.

[0004] If, in addition to the membrane sensor, there is also a signal from an acceleration sensor, the orientation-dependent effect of the gravitational acceleration on the membrane can be calculated, as is the case with most smartphones. In order to implement this mathematical compensation, adjustments in production are necessary. In addition, the evaluation unit of the membrane sensor must be operated in addition to the compensation of the g-sensitivity, so additional computing power must be taken into account and additional energy expenditure is required. Summary of the invention

[0005] The invention claims a micromechanical diaphragm sensor, in particular a pressure sensor, and a method suitable for determining sensor values ​​and / or sensor parameters of a diaphragm sensor. The sensor value of the diaphragm sensor is determined in such a way that weight forces or other accelerations on the diaphragm are largely compensated.

[0006] This is achieved in that, in addition to the first sensor element, a second sensor element is provided, the first sensor element detecting a first sensor variable representing the movement of the diaphragm, the second sensor element detecting a second sensor variable based on a weight force or an acceleration. The core of the invention is that the second sensor element is configured in such a way that the second sensor variable detected and taken into account when determining the sensor value of the sensor assembly represents a weight force or an acceleration on the diaphragm. In particular, it is provided that the second sensor variable corresponds to the gravitational acceleration or the gravity of the total mass of the diaphragm and the additional covering or at least represents them. In addition, the structure according to the invention can also compensate for other accelerations that are not caused by gravity.

[0007] The advantage of this configuration or the separate detection of the influence of the gravitational acceleration as a function of the orientation is that interference effects which can lead to errors in the sensor measured values ​​due to the occupation of the membrane can be compensated without additional computer effort. In particular, in this case, with a corresponding configuration of the second sensor element with a variable measured value acquisition, aging effects which occur when the membrane or the gel layer thereon is occupied by the adsorbent can also be compensated.

[0008] In one embodiment of the invention, the second sensor element has a spring-mass system, wherein at least one first mass is connected to at least one spring element. Optionally, the first mass can have a movable electrode, which is part of a second capacitance measurement value detection device for detecting the compensation variable. Furthermore, it can be provided that the spring-mass system is fastened on one side to a rigid suspension.

[0009] Particularly advantageously, according to an embodiment of the invention, the second sensor element has a spring-mass system, in particular a spring-mass system in the form of a rocker structure. In particular, the spring-mass system can also have a second mass in addition to the first mass, which is also connected to at least one spring element. In one embodiment of the invention, the second mass and the first mass can be connected to the same spring element, in particular at two opposite ends or sides of the spring element. It is also conceivable that the second mass has a movable electrode, which is part of the third capacitance measurement value detection device. The first mass and the second mass have the same or significantly different masses. Here, the second mass can be 2, 5 or 10 times heavier than the first mass. This asymmetric configuration of the two masses can achieve that the second mass moves in the same direction as the diaphragm mass, whereby the first mass moves in the opposite or reverse direction due to the suspension of the second mass (for example in the form of a rocker structure). This results in a larger spacing of the electrodes in the second measuring capacitance of the first mass, whereby the detected sensor variable can be used as a measure of the applied weight force and for compensating the first sensor variable when the spring-mass system is dimensioned accordingly.

[0010] In a development of the invention, the second mass and / or the third measured value acquisition device can be actively controlled or influenced, so that the rigidity of the rocker structure is changed by this control.

[0011] The spring element can be arranged in the same plane as the two masses. It is also possible that the spring element is configured as a bending spring, a torsion spring or a bending beam. In addition, it can be provided that the mass is arranged in the same plane as the movable electrode of the first sensor element.

[0012] The first sensor element can have a first capacitance measurement value detection device, in which the bending of the membrane is detected by means of the useful signal based on the detected capacitance or the distance between the two electrodes. Optionally, the first sensor element can also have at least one capacitance reference measurement value detection device, which can generate a reference signal independently of the movement of the membrane. Other interfering influences on the useful signal, such as those caused by temperature effects, can be detected and compensated by means of the reference signal.

[0013] In addition to the useful signal, the second sensor signal of the second sensor element can be used as a weight force compensation variable. The second sensor signal can be detected separately and taken into account when evaluating the useful signal. Alternatively, the corresponding capacitances of the first measured value detection device, the reference measured value detection device, the second measured value detection device and the third measured value detection device can be electrically connected to each other in pairs or in sequence, so that a common sensor variable can be detected from at least two capacitance detection devices without the need for additional evaluation. It is conceivable that, for example, the useful capacitance of the first sensor element and the compensation capacitance of the second sensor element can be electrically connected to each other directly in a sensor structure, in particular a micromechanical structure, by suitable wiring, so that the useful capacitance and the compensation capacitance are summed directly in the MEMS chip plane.

[0014] Alternatively, the reference capacitance can also be corrected by means of a compensation capacitance. To this end, the compensation capacitance can be electrically connected to the reference capacitance so that the two capacitances are connected in parallel to produce the sensor variable. This circuit is particularly suitable if the useful capacitance and the compensation capacitance change in the same direction with the aid of acceleration.

[0015] In order to prevent resonance effects, in particular in the case of the second sensor element, it can be provided that the second sensor element is spatially and fluidically separated from the first sensor element, for example in a separate second cavity. Damping of the second sensor element can be achieved particularly advantageously in that the corresponding second cavity has a higher internal pressure. This damping can reduce amplitude overshoots in the case of coupling at the resonant frequency of the second sensor element. minimize.

[0016] Further advantages emerge from the following description of exemplary embodiments or from the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A first embodiment of the invention is shown, in which a second sensor element for compensating for weight forces is mounted in a separate or independent cavity. Figure 2 An embodiment is shown with a common cavity for the first and second sensor elements and for the alternative suspension of the spring-mass system. Figure 3 A further embodiment of the invention based on the first exemplary embodiment and in particular its production are shown. Figure 4 The embodiment shows an adjustable compensation of weight forces. Figure 5 The block diagram of FIG. 1 shows a possible evaluation and control unit of the membrane sensor according to the invention. Figure 6 The flow chart of FIG. 4 describes a possible method for adjusting the compensation by means of the second sensor element. DETAILED DESCRIPTION

[0018] As already mentioned at the outset, when the membrane sensor is rolled off, the weight of the membrane or the combined weight of the membrane and the covering can lead to interfering influences on the actual sensor signal. In particular, the orientation-dependent deflections caused by weight forces can have a negative impact on the quality of the detected sensor signal. According to an embodiment of the invention, a sensor structure is shown below, by means of which the influence of such orientation-dependent deflections can be compensated without requiring elaborate subsequent processing of the sensor signal. For this purpose, a second capacitive measuring sensor element is used, in particular in a micromechanical sensor structure, which generates a capacitance change that is dependent on the acting acceleration.

[0019] according to Figure 1 The typical structure of a micromechanical diaphragm sensor in the form of a pressure sensor is described, which has a first sensor element 180 to which, according to the invention, a second sensor element 200 is assigned in order to compensate for the influence of weight forces, gravitational acceleration or other accelerations.

[0020] For example, the structure of the pressure sensor consists of a substrate 100, on which an oxide layer 110 and a polysilicon layer 120 are applied. A first sensor element 180 is located on the polysilicon layer 120, which is constructed in a conventional layer structure 130, for example, in a sequence consisting of a plurality of polysilicon and oxide layers. In the present structure, a functional layer 135 is provided, from which an upper (movable) electrode 150 of a first measured value detection device or a first measuring capacitor and an upper electrode 160 of a reference capacitor are formed. Alternatively, the individual electrodes can also be formed by different layers or structures. The corresponding lower (rigid) electrode 155 of the first measured value detection device and the lower electrode 165 of the reference capacitor are applied directly to the polysilicon layer 120 and are electrically isolated from the substrate 100 by the oxide 110. Optionally, electrical connection lines for contacting the lower electrodes 155 or 165 can be arranged in the polysilicon layer 120 or the oxide layer 110. In the illustrated structure of the first sensor element 180, the upper electrode 150 is fastened directly to the diaphragm 180 of the diaphragm sensor. Therefore, when the diaphragm 140 is loaded with pressure, the distance between the two electrodes 150 and 155 changes, so that a measure of the bending of the diaphragm 140 can be derived from the resulting capacitance change. In contrast, the electrodes 160 and 165 of the reference capacitor are configured independently of the movement of the diaphragm 140, so that the reference capacitor can detect interfering influences acting on the entire system with the aid of the electrodes. Normally, in order to protect the electrical and / or sensor structures arranged on or in the diaphragm 140 from the influence of the medium abutting against the diaphragm, a non-conductive structure is arranged on the diaphragm 140. Figure 1 However, due to the gel covering, the diaphragm 140 is additionally provided with a mass which influences both the movement characteristics of the diaphragm and can be influenced by the effects of the gravitational acceleration g during the stationary phase of the pressure sensor.

[0021] exist Figure 1 In the exemplary embodiment shown, the second sensor element 200 for detecting the weight- or acceleration-dependent compensation is arranged directly next to the first sensor element 180 in the second cavity 160, but is nevertheless separated by a partition wall. The partition wall does not necessarily separate the first cavity 140, in which the first capacitance measurement value detection device or the reference capacitor is located, from the second cavity 260 in terms of fluid. Figure 1, the second sensor element 200 consists of a spring-mass system in the form of a rocker structure, wherein a first (seismic) mass 230 and a second (seismic) mass 235 are interconnected by a spring element 240, so that the masses 230 and 235 are configured to be movable upward 10 or downward 20, in particular perpendicular to the diaphragm 140, the functional layer 135 or the substrate 100. The situation in which the spring element 240 is suspended on a bracket in the second cavity 260 is not shown, but it can be known, for example, from the corresponding structures described in EP 0 244 581 B1 or EP 0 773443 B1. The spring element 240 can be configured as a bending spring, a bending beam or a torsion spring. For reasons of symmetry, the two masses can also be arranged separately on their own spring elements, in particular on a common central beam. Alternatively, the masses can also be connected to two sections on both sides of the spring element. Optionally, it can be provided, as in Figure 2 In the embodiment shown in FIG. 2 , only the first mass 230 is fastened to the spring element 240, while the movable second mass 235 is removed. The first mass 230 has an upper (movable) electrode 220 and a lower (rigid) electrode 225 located therebelow, in order to realize a second capacitance measurement value detection device within the framework of a compensation detection device. In this configuration, the lower electrode 225 is also mounted on the polysilicon layer 120. In addition, the lower electrode 225 can also be mounted on the substrate 100 in another form and, in particular, be electrically insulated from the substrate. Figure 1 In an embodiment of the present invention, the second mass 235 can be used as a vibration element, which reacts to the current acceleration or to the gravitational acceleration g in a static position. For this purpose, the second mass 235 is many times larger than the first mass 230, in particular 2, 5 or 10 times larger. Since the second mass 235 is of greater mass, it reacts more strongly to accelerations perpendicular to the substrate 100 or the diaphragm 140, so that the first mass 230, which is technically connected to the second mass 235 via the spring element 240, moves in the opposite direction or in the opposite direction. Optionally, it can be provided that the first mass 230, the second mass 235 and the spring element 240 can also be structured by the functional layer 135.

[0022] In the static phase of the pressure sensor, when no medium pressure is applied to the diaphragm 140, the diaphragm 140 bends downwards 20° due to the combined mass of the diaphragm 140 and the gel cover, which results in a reduction in the distance between the electrodes 150 and 155 and thus a change in the capacitance. Since this bending is independent of changes in the pressure applied to the diaphragm 140, the purpose of the design according to the invention of the second sensor element 200 is to detect compensation for such weight-based or generally acceleration-based disturbance variables. Figure 1Due to the asymmetric structure of the rocker structure, the second mass 235 is moved in the same direction as the diaphragm 140 by the gravitational acceleration g or generally the applied acceleration. Due to the rocker structure, the second sensor parameter representing the interference parameter can be detected by the movement of the first mass 230 in the opposite direction. The second sensor parameter can be generated by the corresponding configuration of the first and second masses or a properly selected mass ratio, and the second sensor parameter can be directly used as a compensation signal for the useful signal of the first sensor element 180. Alternatively, an additional compensation coefficient K can also be used, and the generated second sensor parameter is multiplied by the compensation coefficient to use the obtained parameter as a compensation parameter.

[0023] exist Figure 2 In the illustrated embodiment, the first sensor element 180 and the second sensor element 200 are mounted in a common cavity 175. Both sensor elements are exposed to the same direct environmental conditions through the common cavity 175. In addition, this structure enables the internal wiring and control of the sensor elements to be configured more simply and directly. In addition, Figure 2 2 shows another design of a spring-mass system of a second sensor element 200. In this case, only a first mass 230 is provided, which is fastened directly to the cavity bottom or substrate 100 via a spring element 240 on a suspension 250. In this design, therefore, only the first mass 230 is movable, wherein, due to the acceleration of gravity or other applied accelerations, the first mass 230 moves in the same direction as the diaphragm 140.

[0024] Figure 3The embodiment of the embodiment of the invention clearly describes the structure of the first cavity 170 and the second cavity 265 which are spatially and fluidically separated from each other. In order to prevent an amplitude overshoot of the second sensor element 200 or the spring-mass system or the rocker structure when a resonant oscillation occurs, the second cavity 265 can be purposefully provided with a higher pressure than the first cavity. For example, the pressure in the first cavity 170 is <5 kPa and the pressure in the second cavity 265 is 10-100 kPa. For this purpose, during the production of the sensor assembly, openings can be provided in the diaphragm 140 and in the cover 145 of the second cavity 265, through which the pressure in the cavity can be determined individually. After the internal pressure of the respective cavity has been determined, the diaphragm 140 can be closed with the first closure part 190 and the cover 145 can be closed with the second closure part 195. For example, it is conceivable that the first closure part 190 is first closed at a lower pressure during the joint processing of the structure of the pressure sensor, for example by means of a layer deposition process of an oxide or nitride layer. At a later point in time, the second closure part 195 can be closed at a higher ambient pressure by means of laser resealing. Due to the higher ambient pressure, the higher pressure present in second cavity 265 damps second sensor element 200 more strongly, so that lower resonant oscillations can be generated. However, it is also generally conceivable that second sensor element 200 is generally designed such that its resonant frequency lies outside / above the application range of the pressure sensor.

[0025] With the help of Figures 1 to 3 Some embodiments are shown in which the dimensions of the second sensor element 200 and thus the second sensor parameters are determined by manufacturing. Figure 4 An embodiment of the invention shows a structure in which the vibration characteristics of the spring-mass system or the rocker structure can also be changed after production. To this end, the second mass 235 has an electrode assembly consisting of an upper (movable) electrode 210 and a lower (rigid) electrode 215, wherein the latter can also be arranged on the substrate 100 or on a layer located thereon. The two electrodes 210 and 215 can be manipulated in the form of a tuning electrode assembly so that the movement characteristics of the second mass 235 are changed upward and downward or damped. By applying a direct voltage or a high-frequency pulse voltage to the electrodes, the rigidity of the spring-mass system can be purposefully adjusted via the value of the effective voltage. This effect is also referred to as the electrostatic spring softening effect. Optionally, a second measured value recording device having electrodes 220 and 225 can also be used as a tuning electrode assembly.

[0026] For example, when using a tuning electrode, you can use Figure 6. First, in a first step 400, the influence of the gravitational acceleration or other applied acceleration on the entire system consisting of the first and second sensor elements is detected without applying a tuning voltage to the electrodes. Subsequently, in a subsequent step 420, the capacitance change of the second sensor element 200 detected during this acceleration can be determined. Based on the capacitance change detected in this way, a corresponding voltage can be determined in a next step 440, wherein, if necessary, the second sensor element 200 can be used for compensation of the first sensor variable without a compensation factor K. For example, such an adjustment can be carried out during production, so that the tuning voltage to be adjusted can be determined in a targeted manner. Sufficiently known acceleration stimuli are applicable here, in particular the gravitational acceleration.

[0027] The tuning electrode can be operated at high frequencies, wherein the first part of the clock cycle is used to provide an effective voltage and produce a spring softening effect, wherein the capacitance is evaluated in the second part of the clock cycle. In this case, it is advantageous to connect the second sensor element to the reference sensor element in order to avoid possible negative effects of the electrical clock on the membrane (e.g. resonant excitation of membrane modes).

[0028] In another embodiment, the electrode assemblies 210 and 215 can also be used as a third capacitance measurement value detection device. For example, the detection of the second capacitance measurement value detection devices 220 and 225 can be supplemented, enhanced or checked with the aid of a second value.

[0029] The first sensor element consisting of the first measured value detection device 320 and the at least one reference measured value detection device 330 and the second sensor element with the second measured value detection device 340 can be controlled, queried or connected in different ways. Figure 5 The evaluation unit 300 shown in the block diagram of detects the sensor variables of the different detection devices 320 to 340 individually and interconnects them internally in order to generate acceleration- or weight-force-compensated sensor values ​​or pressure sensor values. The compensated sensor values ​​can then be transmitted to a further system 360 for further processing. In the case where the second sensor element has to be aligned during production, the evaluation unit 300 can additionally detect a predetermined or determinable acceleration signal of the corresponding acceleration sensor 350 in order to thereby determine a compensation factor K as a multiplier for the second sensor value. The compensation factor K can be stored in the memory 310 for further determination of the compensated sensor value. The alignment with the detected acceleration signal can also be used to control the tuning electrode 370 accordingly in order to adjust the stiffness of the spring-mass system in a targeted manner.

[0030] The evaluation unit 300 can also be used to detect sensor variables of the first and second sensor elements connected to each other. Therefore, it can be provided that the first measured value detection device 320, the at least one reference measured value detection device 330 and the second measured value detection device 340 or the third measured value detection device are at least partially directly electrically connected to each other in the structure of the micromechanical diaphragm sensor. For this purpose, wiring can be provided in the polysilicon layer 120, the oxide layer 110, the substrate 100 or other layers, so that the evaluation unit 300 can detect one or more detection units by means of sensor variables.

[0031] In this case, in a first embodiment, the first measured value detection device 320 (which represents the useful capacitance C by means of electrodes 150 and 155) 有用 ) and a second measured value detection device 340 (which represents a compensation capacitor C by means of electrodes 220 and 225) 补偿 ) are connected electrically in parallel with one another so that the evaluation unit can detect a common sensor variable. In addition, at least one separately detected reference measured value detection device 330 (which represents a reference capacitance C by means of electrodes 160 and 165) is used. 参考 ), the evaluation unit 300 changes the capacitance according to dC=(dC 有用 +dC 补偿 )-dC 参考 Determine the sensor value for weight force or acceleration compensation of the sensor assembly.

[0032] In another embodiment, the second measured value detection device 340 directly compensates the reference measured value detection device 330. In this case, the reference capacitance C 参考 and compensation capacitor C 补偿 Connect in parallel with each other and detect the useful capacitance C separately 有用 Therefore, the capacitance can be changed according to dC = dC 有用 -(dC 参考 +dC 补偿 )Determines the sensor value for weight force or acceleration compensation of the sensor assembly.

[0033] It should be expressly pointed out that the features of the above-described embodiments and configurations can be combined with one another.

Claims

1. A diaphragm sensor, especially a pressure sensor, having a first sensor element (180) which detects a first sensor variable as a function of the movement of the membrane (140), and a second sensor element (200) which detects a second sensor variable dependent on a weight force, It is characterized in that The second sensor element (200) is designed such that the second sensor variable represents a weight force acting on the membrane.

2. The diaphragm sensor according to claim 1, characterized in that: The second sensor element (200) has a spring-mass system in which at least one first mass (230) is connected to at least one spring element (240), wherein it is particularly provided that the first mass (230) has a movable electrode (220) of a second capacitance measured value detection device (220, 225).

3. The diaphragm sensor according to claim 1 or 2, characterized in that: The second sensor element (200) has a spring-mass system, in particular a spring-mass system in the form of a rocker structure, wherein the spring-mass system has a second mass (235) connected to a spring element (240), wherein it is particularly provided that the second mass (235) has a movable electrode (210) of an electrode assembly (210, 215), in particular a movable electrode of a third capacitance measurement value detection device.

4. The diaphragm sensor according to claim 3, characterized in that: The second mass (235) is greater than the first mass (230), in particular 2, 5 or 10 times greater.

5. The diaphragm sensor according to claim 3 or 4, characterized in that: At least one electrode of the electrode assembly (210, 215) is manipulated to change the stiffness of the spring-mass system.

6. The diaphragm sensor according to any one of claims 2 to 5, characterized in that: The spring element (240) comprises a bending spring or a torsion spring.

7. The film sensor according to any one of the preceding claims, characterized in that The first sensor element (180) generates a first useful signal according to the movement of the diaphragm (140) by means of a first capacitance measurement value detection device (150, 155) and generates a reference signal independent of the movement of the diaphragm (140) by means of at least one capacitance reference measurement value detection device (160, 165).

8. The diaphragm sensor according to claim 7, characterized in that: The measured value detection devices of the first and second sensor elements (180, 200) are electrically connected to one another, wherein in particular it is provided that the second capacitance measured value detection device is connected in parallel with the first capacitance measured value detection device or with the capacitance reference value detection device.

9. The membrane sensor according to any one of the preceding claims, characterized in that The first sensor element (180) is arranged in a first cavity (170), and the second sensor element (200) is arranged in a second cavity (260, 265) separated from the first cavity (170), wherein it is particularly provided that the second cavity (260, 265) is filled with a medium having a higher pressure than in the first cavity (170).

10. A method for determining a sensor value of a membrane sensor, in particular a sensor value of a membrane sensor according to any one of claims 1 to 9, wherein: The film sensor has a first sensor element (180) for detecting a first sensor variable in response to a movement of the membrane (140), and a second sensor element (200) for detecting a second sensor variable, the second sensor variable being representative of a weight force acting on the diaphragm, It is characterized in that The method determines the sensor value as a function of the first and second sensor variables.

11. The method according to claim 10, characterized in that The second sensor element (200) has a spring-mass system, in particular a spring-mass system in the form of a rocker structure, wherein the spring-mass system having a second mass connected to at least one spring element (240), and a movable electrode (210) having a capacitive electrode assembly (210, 215), in particular a movable electrode of a third capacitance measurement value detection device, The method manipulates the electrodes of the electrode assembly (210, 215) to change the stiffness of the spring-mass system.

12. The method according to any one of claims 10 or 11, characterized in that The second sensor parameter is multiplied by a compensation coefficient to determine the sensor value.

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