Device for measuring strain and inclination

Abstract

The invention relates to a microelectromechanical strain sensor (100) for measuring strains, inclinations, and curvature on a test object, and further relates to a method for testing, manufacturing, and assembling such a sensor, wherein the sensor comprises contact points (201, 202) or contact surfaces (203), a capacitive transducer (400), a capacitive-to-digital converter (600), and a signal processor (700). The invention further relates to a method for self-testing the device with a self-test mechanism (500) by which a strain effect on the sensor is simulated by an electrical test signal.

Description

Technical area of ​​the invention

[0001] The present invention relates to a microelectromechanical strain sensor, a method for mounting a strain sensor on a test object, and the performance of strain measurements and functional tests. Background and state of the art

[0002] Strain gauges are used, among other things, to measure forces, weights, and torques. Strain gauges, often foil- or semiconductor-based, are frequently used for strain measurement. These measure strain by detecting changes in electrical resistance.

[0003] The electrical resistance of strain gauges is generally more sensitive to temperature changes than to strain changes. For this reason, strain gauges are often connected in a Wheatstone bridge to compensate for the temperature effect. Strain gauges initially only provide an electrical resistance value. To evaluate the resistance changes or the bridge voltage, additional complex analog circuits such as measuring amplifiers are required. The electrical data processing and analysis then typically takes place outside the measuring point using sophisticated evaluation electronics.

[0004] Another disadvantage is that strain gauges cannot be directly soldered or welded, as the sensors are made of a thin polymer-based film.

[0005] Another disadvantage of strain gauges is that they often consist of a meandering conductor track, which can unintentionally act as an antenna and is sensitive to electromagnetic waves. Consequently, an external electromagnetic field can induce a voltage across the strain gauge, causing additional noise. Furthermore, strain gauges offer no way to verify the quality of the installation or the functionality of the strain gauge through a self-test. Calibration data cannot be stored directly on the strain gauge itself, but only in external evaluation electronics.

[0006] Mounting strain gauges is complex, as they require gluing and wiring. Automated assembly is often impossible and not cost-effective for small production runs.

[0007] WO 2005 / 068960 A1 describes a capacitive strain sensor with parallel finger electrodes forming a capacitor. Strain on the test object causes a displacement of the finger electrodes, thus changing the capacitance. The strain is then determined by evaluating the capacitance. The device also features articulated beams that amplify an applied strain signal. However, the amplification via the articulated beams is non-linear and requires subsequent correction of the measurement signal. A major disadvantage of the invention is that the amplification mechanism is not decoupled from the rest of the micromechanical system by the articulated beams. Consequently, even an obliquely applied strain signal can distort the device, resulting in an erroneous measurement signal. Furthermore, the non-linear nature of the articulated beams introduces ambiguity into the measurement signal when the strain is applied obliquely.Furthermore, an integrated functional test of the mechanism is not possible.

[0008] Further sensors for strain measurement are described in DE 69822097T2, DE 102016202769 A1, WO 2016 / 092475 A1, US 5109701 A, WO 2005 / 068960 A1, EP 000003822577 B1.

[0009] The devices known from the prior art do not allow for direct serial digital output of the strain, nor for direct calibration of the strain via an integrated signal processor. The measurement data is typically digitized and processed / calibrated decentrally, i.e., via external evaluation electronics. Calibration directly on the chip or measuring strip is not possible.

[0010] Furthermore, the strain is initially converted directly into an electrical quantity (e.g., a change in resistance) using the known devices. Signal amplification then only occurs in the electrical domain. Consequently, electrical noise is also amplified and must be filtered.

[0011] The current state of the art does not provide for any verification of the sensor's functionality or its assembly quality. To verify the functionality of known strain gauges, only direct loading of the test object followed by strain measurement is conceivable, or an indirect verification of the sensor's functionality, e.g., by electrically measuring the resistance at the strain gauge. Rigid test objects, such as bridges, tunnels, or steel beams, on which strain gauges are to be mounted, are often difficult to subject to a defined test strain. For this reason, it is helpful to provide a sensor that itself generates a small test force with which a strain measurement at the sensor can be simulated.

[0012] Another disadvantage of existing strain gauges, especially DMS, is that they can only measure the strain on the surface of a test object, not the bending line, inclination, or curvature. Thus, strain measurement does not provide information about the type of stress, such as bending or tension. Summary of the invention

[0013] One object of the present invention was to overcome the known disadvantages of the prior art and to provide, as an alternative to classical resistance-based strain gauges, a novel micromechanical strain sensor which measures a strain and directly outputs a digital value of the strain or a value associated with the strain.

[0014] A further object of the present invention was to provide the strain sensor with a mechanically acquired and mechanically amplified strain signal. Because the amplified signal is mechanical rather than electrical, the influence of electrical noise on the measured quantity is reduced, resulting in a higher signal-to-noise ratio. In a subsequent step, the mechanically amplified strain measurement data is digitized at the measuring device and read out by a digital signal processor on the measuring system. The digital signal processor processes and / or corrects the incoming measured values ​​using predefined calibration data and by applying a transfer function. Finally, the signal processor outputs the revised or corrected digital strain values.

[0015] Furthermore, the strain sensor is configured to store application-specific calibration data and, depending on the application, to apply an application-specific transfer function to the raw strain measurement data received via the signal processor. This enables the direct digital output of application-specific measured values ​​(such as weight, torque, angle) via the strain sensor.

[0016] Another object of the present invention was to ensure that the strain sensor, in addition to the strain, also detects the temperature and corrects the influence of temperature on the strain measurement via a signal processor.

[0017] A further object of the present invention is to test the functionality of the strain sensor via a self-test, wherein a test force is applied to the measuring device according to the invention, simulating an applied strain. The self-test function can also be used to assess the quality of the chip's mounting on a test object and, if necessary, to determine whether the sensor has become detached or has been damaged during operation.

[0018] In a preferred embodiment, the device according to the invention allows, in addition to measuring the strain in one direction, also the measurement of the inclination or curvature of the test object. The device thus makes it possible to perform measurements that allow conclusions to be drawn about the cause of the strain, for example, the type of stress (tension, compression, bending, torsion).

[0019] The system according to the invention can be mounted onto a test object in the form of a chip, either materially bonded or form-fitted, to measure strain. The measurement is based on the principle that the strain causes at least two contact points of the microsystem to be displaced relative to each other. This relative displacement is amplified by a micromechanical differential amplifier and converted into a larger displacement. This amplified displacement is then transmitted to a capacitive transducer, which converts the displacement into a change in capacitance. A capacitance-to-digital converter transforms this change in capacitance into a digital value, which is then forwarded to a digital signal processor that corrects or processes the value using calibration data.

[0020] The device according to the invention has the advantage over other strain measurement systems that a strain signal is first mechanically acquired and amplified before being converted into an electrical quantity. Parasitic electrical effects such as thermal noise, high cross-sensitivity to temperature, or electromagnetic fields are reduced. The signal is already amplified before parasitic electrical effects can influence the measurement signal. Furthermore, the mechanical signal amplification also allows for higher measurement sensitivity and a higher signal-to-noise ratio than with direct conversion of the strain into an electrical (resistance or capacitance) quantity; electronic signal amplification can also be used.

[0021] A further advantage of the device according to the invention is that digitization, signal processing, and measurement correction are performed directly at the strain sensor, eliminating the need for external evaluation electronics, as these are already integrated and partially implemented mechanically. The sensor itself provides a digital signal, thus reducing the influence of disturbances such as electromagnetic radiation on the measurement chain. Another advantage of the device according to the invention is that the sensor's functionality can be verified by performing an integrated self-test. Furthermore, the self-test function on the sensor can be used to check the mounting quality of the chip on the test object or to determine the stiffness of the test object. In addition, the strain sensor can be mounted automatically, for example, using a mounting device as described below.

[0022] The described technical problems are solved by the devices or methods according to the independent claims of the present invention. The dependent claims describe preferred embodiments. Value ranges limited by numerical values ​​should always include the stated limit values. Description of the drawings Fig. 1: Block diagram of the microelectromechanical strain sensor (100) according to the invention for pure strain measurement. Fig. 2: Block diagram of the microelectromechanical strain sensor according to the invention with curvature electrodes (410) for strain measurement and curvature measurement. Fig. 3: Illustration of a bent test object (805) under A) pure bending and B) combined stress of tension and bending. Fig. 4: Illustration of the curvature electrodes (410) at A) no bending and at B) bending present. Fig. 5: Illustration of the operating principle of the capacitive curvature electrodes (410) on a curved test object (800). Fig. 6: Block diagram of the microelectromechanical strain sensor according to the invention with curvature electrodes (410) for pure curvature measurement. Fig. 7: Block diagram of a preferred embodiment of the microelectromechanical strain sensor for pure strain measurement with temperature sensor (A) and processor (B). Fig. 8: Components and structure of the micromechanical part of the strain sensor (101) in the undisplaced state (A) and in the deflected state as a result of strain acting on the contact points (B). Fig. 9: Components and structure of the micromechanical part of the strain sensor (101) with tilt electrodes (410) for detecting the tilt of the stretched test object. Fig. 10: Components and structure of the micromechanical part of the strain sensor (101) in the deflected state as a result of a force applied by the electromechanical actuator (510). Fig. 11: Illustration of the micromechanical part of the strain sensor (101) with defective lever (305). Fig. 12: Illustration of the micromechanical part of the strain sensor (101) with a conductor loop (550) that is part of the self-test mechanism (500). Fig. 13: Exemplary representation of a break in the strain sensor and separation of the conductor loop. Fig. 14: Illustration of the micromechanical part of the strain sensor (101) with defective capacitive transducer (400). Fig. 15: Representation of the micromechanical part of the strain sensor (101) during the performance of a dynamic self-test (A) when applying a voltage step, shown in (B) and recording the time-dependent step response (C) and the distribution of the vibration components (D). Fig. 16: Preferred embodiment of the mechanical part of the strain sensor (101) with electromechanical actuator (510) in the form of an integrated electrostatic actuator (520) during the performance of a dynamic self-test (A), representation of a voltage step (B), representation of an exemplary step response (C) and representation of the division of the vibration components of the step response (D). Fig. 17: Representation of stiffnesses at the strain sensor (100), wherein the bonding layer (900) and the test object (800) are separated from each other. Fig. 18: Representation of stiffnesses at the strain sensor (100), wherein the bonding layer (900) and the test object (800) are connected to each other. Fig. 19: Illustration of the connection of a strain sensor (100) with a test object via a closed and functional connection layer (A) and a defective connection layer (B) and sketched results of a self-test in each case. Fig. 20: Illustration of the connection of a strain sensor (100) with a first test object (A) and second test object (B) with different moduli of elasticity, as well as sketched results of a dynamic self-test. Fig. 21: Exemplary representation of a characteristic frequency spectrum. Fig. 22: Exemplary embodiment of the self-test mechanism with electrothermal actuator (530). Fig. 23: Exemplary embodiment of the self-test mechanism with electrothermal actuator (530) and conductor loop (550). Fig. 24: Exemplary embodiment of the self-test mechanism with bi-directional electrothermal actuator (530). Fig. 25: Exemplary embodiment of the electrothermal actuator (530) wherein the pre-steered spring (406) itself is the electrical heating resistor (531). Fig. 26: Exemplary embodiment of the electrothermal actuator (530) wherein the actuator is located outside the guide mechanism (401) and comprises a clamped buckling spring (532). Fig. 27: Exemplary embodiment of the electrothermal actuator (530) wherein the actuator is located outside the guide mechanism (401) and is mechanically decoupled from the runner (402). Fig. 28: Exemplary embodiment of the self-test mechanism with electrostatic actuator (520). Fig. 29: Block diagram illustrating the relationship between the individual components in a self-test. Fig. 30: Preferred embodiment of a mounting device (1000) with strain sensor (100) and test object (800). Fig. 31: Illustration of the mounting of a strain sensor (100) on a test object (800) via the mounting device (1000), wherein a solder layer is melted via a heater (1310). Fig. 32: Illustration of the mounting of a strain sensor (100) on a test object (800) via the mounting device (1000), wherein a solder layer is melted by an electric current flowing through the test object, solder layer and strain sensor. Fig. 33: Illustration of a preferred embodiment of the mounting device with a joint. Fig. 34: Simplified circuit diagram for the instantaneous provision of ignition energy by discharging a capacitor. Fig. 35: Illustration of the positive-locking mounting of a strain sensor (100) on a test object (800) by melting the test object made of plastic (850). Fig. 36: Preferred process plan for the manufacture of the micromechanical part of the strain sensor according to the invention. Fig. 37: Illustration of supplementary manufacturing steps: A) Deposition of a compound layer (900) on the chip package (150); B) Deposition of a separator layer (910) on the chip package and C) Deposition of a separator layer (910) and adhesive layer (900) on the chip package. Fig. 38: Illustration of a supplementary manufacturing step: Etching cavities (980) into the chip package (150). Fig. 39: Illustration of a preferred embodiment of the microelectromechanical strain sensor (100) according to the invention shown in a possible cross-section. Fig. 40: Example of using the strain sensor as a force sensor. (A) shows a deformation body (810) with a strain sensor (100) according to the invention. (B) outlines the calibration by a signal processor (700). Fig. 41: Example of using the strain sensor as a scale. (A) shows a deformation body (810) with a strain sensor (100) according to the invention and a weight. (B) outlines the calibration by a signal processor (700). Fig. 42: Illustration of the calibration of the measuring device for an application as a scale. (A) shows a deformation body (820) in the unloaded state. (B) shows the deformation body in the loaded state and (C) shows a diagram. Detailed description of the invention

[0023] Before the invention is described in detail, it should be noted that it is not limited to the specific components of the described devices or the described manufacturing steps of the methods, as these may vary. Furthermore, it is emphasized that the terminology is used only to describe certain embodiments and is not intended to be restrictive.

[0024] It should be noted that in the description and the appended claims, terms such as "a" or "the" include both singular and plural forms, unless the context clearly indicates otherwise. If a parameter range is specified, the stated limits are to be understood as part of the specified or claimed range.

[0025] The invention relates in particular to a microelectromechanical strain sensor (100), hereinafter also referred to as measuring system or strain sensor, which is designed to be mounted on a test object (800) in order to measure, process and provide as a measured value the existing strain and / or inclination, curvature. Furthermore, in a preferred embodiment, the invention comprises a method and a device for performing self-tests on the strain sensor in order to test the functionality and quality of the sensor as well as the quality of the sensor mounting on the test object and / or to identify the material of a test object.

[0026] A preferred embodiment of the microelectromechanical measuring system (100) comprises a capacitive transducer (400) in the form of a tilt electrode pair (410) consisting of at least two electrodes (411, 412) which together form a capacitor; a contact surface (203) which is directly or indirectly mechanically connected to at least one of the electrodes (411) of the tilt electrode pair (410) and the test object (800) and is designed to accommodate the tilt and / or curvature of the test object. It further comprises a capacitive-to-digital converter (600) designed to convert the capacitance change of the capacitive transducers (400) into an electrical digital signal. For processing the digitized electrical signal, the device preferably also includes a digital signal processor (700).

[0027] In a further preferred embodiment of the measuring device according to the invention, it comprises at least two contact points (201, 202), wherein at least one of the contact points is connected to a micromechanical differential amplifier (300); a micromechanical differential amplifier (300) for amplifying the signal of the strain-induced mechanical distance change of the contact points (201, 202); a capacitive transducer (400) for converting the amplified mechanical displacement of the micromechanical differential amplifier into a change in capacitance; a capacitive-to-digital converter (600) configured to convert the change in capacitance of the capacitive transducer (400) into an electrical digital signal; and a signal processor (700) for adapting and processing the electrical digital signal of the capacitive-to-digital converter (400).

[0028] In a further preferred embodiment, the measuring device according to the invention comprises both the contact points (201, 202), the differential amplifier (300) and a first capacitive transducer (400) for converting the amplified mechanical displacement into a change in capacitance C for measuring a strain, as well as a further capacitive transducer (400) in the form of a tilt electrode pair (410) for simultaneously measuring the tilt.

[0029] A preferred aspect of the present invention is said microelectromechanical measuring system, which further comprises a self-test mechanism (500) configured to effect a mechanical displacement and / or force on the capacitive transducer (400) by applying a test signal, in order to simulate a strain measurement on the measuring device. The self-test mechanism (500) comprises an electromechanical actuator (510). In a preferred embodiment, said electromechanical actuator (510) is an electrothermal actuator (530). In another preferred embodiment, the electromechanical actuator (510) is an electrostatic actuator (520), which may also be part of the capacitive transducer.

[0030] In the context of the present invention, "contact points" are understood to be a micromechanical component or geometry that serves as the direct or indirect connection between the micromechanical differential amplifier and the test object under investigation. The contact points have fixed positions and distances on the measuring system. The contact points are designed to detect any displacement caused by strain on the measuring system at the position of the contact points.

[0031] A “micromechanical differential amplifier” within the meaning of the present invention is understood to be a component whose function is to convert an initially small translational displacement into a translational displacement with a high amplitude, in order to enable sensitive resolution of the strain. In particular, the function of the micromechanical differential amplifier is to amplify the relative displacement and / or displacement difference of the contact points.

[0032] A “movable frame” within the meaning of the present invention is understood to be a part of the micromechanical differential amplifier which can be moved relative to the housing of the sensor and whose function is to receive a first relative displacement via one of the contact points.

[0033] An “input element” within the meaning of the present invention is understood to be a part of the micromechanical differential amplifier which can be displaced relative to the movable frame and whose function is to receive a second relative displacement via one of the contact points.

[0034] An “output element” within the meaning of the present invention is understood to be a part of the micromechanical differential amplifier, the function of which is to provide an amplified mechanical displacement implemented by the micromechanical differential amplifier to a further micromechanical component.

[0035] A "capacitive transducer" within the meaning of the present invention is understood to be a component whose function is to convert the displacement at the output of the micromechanical differential amplifier or the curvature or inclination introduced into the measuring system into an electrical change in capacitance. In particular, it refers to plate capacitors with a variable plate spacing and / or variable electrode overlap, thereby changing the capacitance.

[0036] A “micromechanical actuator” within the meaning of the present invention is understood to be a component whose function is to generate a displacement or force based on an electrical signal, wherein the displacement or force can be static or dynamic.

[0037] A “capacitance-to-digital converter” within the meaning of the present invention is understood to be an electrical or electronic component designed to convert the capacitance or change in capacitance at the capacitive converter into a digital electrical quantity.

[0038] A "signal processor" within the meaning of the present invention is understood to be an electrical or electronic component whose function is to process and modify the digital measurement signal of the capacitive-to-digital converter. In particular, a modification consists of linearizing the measurement signal or applying a transfer function to the measurement signal in such a way that a temperature influence on the measurement can be factored out or calibration values ​​can be applied to the measurement signal.

[0039] In the sense of the invention, a “test object”, “test specimen” or “measurement object” is understood to be a body, object or item that can or should be subjected to strain measurement or strain monitoring.

[0040] In the context of the invention, a "characteristic stiffness" is understood to be the mechanical resonance frequency that can be excited at and acts upon the device according to the invention by an electromechanical actuator. The characteristic stiffness results combinatorially from the mechanical connection and interconnection of the components and their stiffnesses on the measuring system according to the invention, the connection of the measuring system to the test object, in particular from the stiffness of the interconnecting layer, and the stiffness of the test object, provided the measuring system is mounted on the test object.

[0041] A “characteristic frequency spectrum y” is defined as follows: c(f)“ in the sense of the invention, the resulting frequency spectrum of the displacement y c (f) understood that excitation via the electromechanical actuator results in a frequency- and / or time-dependent displacement y at the capacitive transducer c (f) can be detected. The characteristic frequency spectrum results in particular from the combination of the stiffnesses and masses of the measuring system, as well as from the stiffness of the connection of the measuring system to the test object and the stiffness of the test object, provided that the measuring device is mounted on the test object.

[0042] A "self-test" in the sense of the invention is understood to be a method in which the functionality of the sensor is tested by applying an electrical signal, in particular in the form of a voltage or a current. A self-test particularly includes the direct or indirect measurement of the acting stiffnesses at the sensor system by evaluating displacement and force amplitudes or by a dynamic analysis of resonance frequencies or vibration spectra.

[0043] A "self-test mechanism" as defined in the invention comprises the micromechanical and electrical components involved in performing a self-test. These include, in particular, electromechanical actuators and conductor loops.

[0044] In the sense of the invention, an "algorithm" is understood to be a sequence of individual steps that follows a fixed pattern, wherein the individual steps particularly include instructions, calculations, and the storage of data values. The execution of these individual steps can, in particular, be controlled and / or regulated by a processor.

[0045] In the context of the invention, a "digital value" is understood to be a digital numerical value that can be processed by a processor or a digital signal processor. In particular, the digital value can be a binary code.

[0046] In the sense of the invention, a "solder layer" is understood to be a layer or several layers of an alloy, a metal or alternating metal layers or alloy layers, the purpose of which is to connect the electromechanical measuring system to a test object by soldering or welding in a metallurgically bonded manner by melting.

[0047] In the context of the invention, "ignition energy" is understood to be a form of energy capable of melting a solder layer. In particular, ignition energy can be provided by an electric current, by temperature, by an electrical spark discharge, or by light or laser radiation.

[0048] In the sense of the invention, an “assembly force” is understood to be a force with which the measuring device according to the invention is pressed against a test object during the execution of an assembly process.

[0049] A “curvature electrode pair” in the sense of the invention is understood to be a plate capacitor in which the capacitance changes depending on the imprinted curvature and / or inclination of the electrodes.

[0050] The term "separation layer" refers to a structured layer made of a material with which the connecting layer cannot be bonded in a material-bonded manner, or at all.

[0051] In a preferred embodiment of the present invention, the contact points (201, 202) are arranged at a known distance on the measuring system, wherein at least one connecting element is directly or indirectly connected to the input of the micromechanical differential amplifier and at least one further contact point is directly or indirectly connected to the movable frame of the micromechanical differential amplifier. Furthermore, the device according to the invention comprises a micromechanical differential amplifier configured to convert the relative displacement of the contact points into a larger displacement, and further comprising a capacitive transducer configured to convert the amplified displacement into a capacitance or change in capacitance.

[0052] In a further preferred embodiment, the capacitive transducer (400) of the present invention is designed as a pair of curvature electrodes (410) in which the capacitance changes depending on the curvature of the object being measured, thus providing information about the curvature of the object being measured.

[0053] In a further preferred embodiment, the measuring device comprises several capacitive transducers (400) and contact points and contact surfaces to measure both strain and curvature simultaneously.

[0054] In a further preferred embodiment, the device according to the invention also comprises a capacitive-to-digital converter which is configured to digitize the capacitance or capacitance change present at the capacitive converter and to provide a digital value of the capacitance or capacitance change.

[0055] Another preferred embodiment of the device according to the invention comprises, in addition to the components mentioned above, a temperature sensor for measuring the temperature.

[0056] In a further preferred embodiment, the device according to the invention further comprises a signal processor configured to process the digital value at the capacitive-to-digital converter. This processing can, in particular, consist of filtering the digital measured values ​​entering the signal processor and / or applying a transfer function to the values ​​and / or determining an average / moving average and / or calibrating the measured values. Furthermore, the signal processor, in combination with a temperature measurement at the temperature sensor, can be used to compensate for temperature-related measurement effects during strain measurement by means of a transfer function.

[0057] In a further preferred embodiment, the device according to the invention also includes a self-test mechanism designed to test the functionality of the device. The self-test mechanism comprises an electromechanical actuator that can be excited by an electrical signal and causes a defined displacement or force on the micromechanical differential amplifier and / or the capacitive transducer. Among other things, the actuator produces a similar effect on the sensor as could be caused externally by applying strain to the sensor.

[0058] In a further preferred embodiment, the device according to the invention, as part of the self-test mechanism, comprises, in addition to the electromechanical actuator, a conductor loop which is configured to detect a break / crack or other damage to the sensor by changing its electrical resistance when the sensor is damaged.

[0059] The present invention further relates to a method for measuring the inclination of a measuring object using a microelectromechanical measuring system according to the present invention, comprising at least the following steps: (i) Connecting the measuring system (100) to the surface of a test object (800) on which the strain and / or inclination is to be measured; (ii) Measurement of the distance between the electrodes (411, 412) of the tilt electrode pair (410); (iii) Conversion of the change in distance into a change in capacitance at the tilt electrode pair (410); (iv) Conversion of the capacitance change into a digital value via a capacitance-to-digital converter, wherein the digital value represents a measure of the inclination and / or strain of the test object; (v) Calculation of the inclination and / or strain of the test object (800) from the digital value of the change in distance of the electrodes (411, 412) determined in the previous steps.

[0060] The present invention further relates to a method for measuring the strain of a measuring object using a microelectromechanical measuring system according to the present invention, comprising at least the following steps: (vi) Connecting the measuring system (100) to the surface of a test object (800) on which the strain is to be measured; (vii)Measurement of the strain-induced change in distance of the contact points (201, 202) on the measuring system (100) and amplification of this change in distance via a mechanical differential amplifier (300) which provides at the amplifier output (308) an amplified displacement dependent on the change in distance; (viii) Conversion of the amplified displacement signal into a change in capacitance via a capacitive converter (400); (ix) Conversion of the change in capacitance into a digital value via a capacitance-to-digital converter, the digital value being a measure of the change in distance of the contact points; (x) Calculation of the strain of the object being measured from the known distance of the connecting elements (201, 202) and the digital value of the change in distance determined in the previous steps.

[0061] The method for measuring strain and / or inclination can further include measuring the temperature of the test object (800) via a temperature sensor (750) on the measuring system (100).

[0062] Furthermore, the method according to the invention can include a further step between said steps (iv) and (v), namely the processing / correction of the digital value of the capacitive-to-digital converter via a signal processor, relating in particular to: the correction of an offset, the application of a predefined transfer function for linearizing the measurement, the application of a transfer function for correcting a cross-sensitivity of the measurement to temperature.

[0063] Another object of the present invention is a method for self-testing the microelectromechanical measuring system according to the present invention, comprising at least the following steps: (i) Applying an electrical test signal to the electromechanical actuator (510); (ii) Measurement of the time-dependent and / or time-independent displacement at the capacitive transducer (400) in response to the applied electrical test signal; (iii) Determination of the characteristic stiffness and / or the characteristic frequency spectrum; (iv) Evaluation of the functionality of the sensor based on comparative data of the characteristic stiffness and / or the characteristic frequency spectrum.

[0064] The method according to the invention can comprise a further step prior to said step (i), namely applying an electrical voltage or an electric current to a conductor loop and determining the integrity of the conductor loop by measuring its electrical resistance. Alternatively, the conductor loop can be connected to the electromechanical actuator to provide the electrical test signal to the actuator via the conductor loop. If the conductor loop is interrupted, the self-test will also fail.

[0065] Furthermore, the method according to the invention can include a further step between said steps (ii) and (iii), namely determining the mechanical resonance frequencies and / or the frequency components of the mechanical vibration spectrum at the capacitive transducer, in particular using a Fourier transform.

[0066] The method according to the invention can include a further step before the last step, namely determining the resulting mechanical stiffness of the micromechanical components based on the measured change in capacitance and / or the determined resonance frequency(ies) and / or the determined vibration characteristics.

[0067] The method according to the invention can, after the last step, include a further step, namely evaluating the assembly quality of the microelectromechanical strain sensor on the test object using comparative data.

[0068] In a preferred embodiment, the method according to the invention is controlled by an algorithm on the processor (760).

[0069] The present invention further relates to a method for manufacturing a microelectromechanical measuring system according to the present invention, comprising at least the following steps: (1) Providing a handle layer (2300) and a buried oxide layer (2200); (2) Providing a further layer ‘Devicelayer’ (2100) containing the mechanical and electromechanical components of the micromechanical measuring system; (3) Undercutting the movable mechanical structures (2101) on the device layer by partially removing the sacrificial layer below the moving components; (4) Encapsulation of the micromechanical components by means of a lid (2400) using a bonding process; (5) Providing vias (2450) through the cover (2400) to the device layer (2100) and (6) Thinning of the carrier layer (2300).

[0070] The manufacturing method according to the invention can, after the last step, comprise a further step, namely the assembly of the mechanical part of the measuring device (101) and the electrical part (102) in a common sensor housing (103).

[0071] The contact points (201, 202) are attached to the “Devicelayer” and the “Buried Oxide Layer” and connect the Devicelayer to the Handlelayer.

[0072] In a preferred embodiment, the micromechanical measuring system according to the present invention is manufactured by means of lithography and / or by anisotropic etching and / or wafer bonding.

[0073] In another preferred embodiment of the method, the surface of the housing (150) is structured by etching or laser structuring.

[0074] Furthermore, in a preferred embodiment, the manufacture of the micromechanical measuring system according to the present invention is extended by applying a bonding layer (900) e.g. in the form of a solder layer or adhesive layer to the thinned handle layer.

[0075] In another preferred embodiment of the method, a separation layer is deposited and structured on the housing, which is designed to mask the surface of the housing and to enable a material-bonded connection through a bonding layer only at defined positions.

[0076] The present invention further relates to a method for mounting a microelectromechanical measuring system according to the present invention on a test object, comprising at least the following steps: a) Providing a connection layer (900) at the microelectromechanical measuring system (100); b) Providing an assembly device (1000) which is configured to provide a defined assembly force and ignition energy; c) Contacting the microelectromechanical measuring system (100) with a test object (800), applying a mounting force between the measuring system (100) and the test object (800) via the mounting device (1000) and providing the ignition energy to melt a solder layer (950) on the microelectromechanical measuring system (100) and / or melting the surface of the test object (800); d) Termination of the provision of ignition energy and assembly force at the measuring system (100).

[0077] In a preferred embodiment of the assembly method, the ignition energy is provided either by heat via a heater (1310) on the assembly device, by an electric current, or by an ignition spark.

[0078] Furthermore, the ignition energy is preferably provided in a short time interval and only when a defined assembly force is provided.

[0079] In a preferred embodiment of the assembly method, the ignition energy provided in step c) is supplied by heat via a heater at the assembly device.

[0080] In another preferred embodiment of the assembly method, the ignition energy provided in step c) is supplied by an electric current flow via the discharge of an energy storage device at the assembly device.

[0081] In another preferred embodiment of the assembly method, the ignition energy provided in step c) is supplied by an electrically generated ignition spark.

[0082] The present invention also relates to a device for mounting the microelectromechanical measuring system (100) comprising a) a sensor mount (1200) designed to fix the micromechanical measuring device (100); b) a power generator (1100) for generating an assembly force; c) an ignition device (1300) for providing ignition energy;

[0083] The assembly device preferably further comprises an assembly housing (1400) and a switch (1350) or a switching device designed to provide the ignition energy as soon as the assembly force is reached.

[0084] In a preferred embodiment, the ignition device comprises a heater (1310) which is designed to melt the compound layer (900) on the measuring system (100) by providing heat to the measuring system (100) when the ignition energy is supplied.

[0085] The invention is described below with reference to figures, and the operating principle is explained.

[0086] Fig. Figure 1 shows the main components of the microelectromechanical strain measurement system (100). The components of the measurement system (100) can be divided into a micromechanical part (101) and an electronic part (102). The micromechanical part (101), also referred to as MEMS, comprises at least the following components: contact points (200), a micromechanical differential amplifier (300), and a capacitive transducer (400). In a preferred embodiment, the micromechanical part (101) further includes a self-test mechanism (500). The electronic part (102), also referred to as ASIC, comprises at least the following components: a capacitive-to-digital converter (600) and a signal processor (700). The sequence and arrangement of the main components may vary.

[0087] The measuring device can be mounted on a test object (800) for strain measurement. A strain ε on the test object is detected via the contact points (200) at at least two positions, i.e., via at least two contact points (201, 202), and causes a change in distance Δy between the contact points. This change in distance Δy is amplified by a gain factor A via a micromechanical differential amplifier (300) and supplied to the capacitive transducer (400). The capacitive transducer (400) converts the amplified change in distance into a change in capacitance ΔC or capacitance C. The capacitance-to-digital converter (600) converts the analog quantity change in capacitance ΔC or capacitance into a digital numerical value D1.The signal processor (700) processes and / or modifies the digital numerical value D1 using an algorithm with the help of further data D3, such as calibration values, function parameters, correction values ​​or further measured values ​​such as temperature, and represents the processed and / or modified numerical value in the form of D. out ready.

[0088] In a preferred embodiment, the signal processor (700) comprises an electronic memory (710). The signal processor (700) is configured to calculate the strain ε from the digital value of the capacitance change D1 using an algorithm. For this purpose, the signal processor accesses the electronic memory (710) to apply a transfer function to the incoming measurement data D1 using stored function parameters D3. The stored parameters include the geometric dimensions of the sensor, in particular the distance a0 between the contact points, the transfer parameters of the capacitive transducer (e.g., number of electrodes), and calibration data to account for the material of the test object.

[0089] The measuring device (100) can also be subjected to a functional test. The purpose of such a functional test is to verify whether the components of the measuring device are functioning correctly, whether manufacturing tolerances were exceeded during the production of the measuring system, or whether the measuring device has been damaged. For this purpose, the measuring system (100) includes a self-test mechanism (500) designed to check the function of the measuring system.

[0090] In a preferred embodiment, the self-test mechanism (500) comprises an electromechanical actuator (510), for example, in the form of an electrostatic actuator (520) or an electrothermal actuator (530). To perform a self-test in the preferred embodiment, a voltage signal is applied to the electromechanical actuator (510), which causes the actuator to generate an actuator force F. The actuator force F is transmitted to at least one of the micromechanical components (differential amplifier, contact points, and / or capacitive transducer) and causes a displacement of the capacitive transducer (400). Finally, the capacitance or change in capacitance at the capacitive transducer is evaluated. Based on the change in capacitance at a given input signal Ut at the electromechanical actuator (510), it can be determined whether the measuring system is functioning correctly.In particular, conclusions can be drawn about the stiffness of the micromechanical components and thus whether a defect exists, a component is missing, or there is a deviation in manufacturing tolerances. The evaluation of the capacitance change for a given test signal Ut can be performed both statically and dynamically, especially by determining the resonant frequency of the connected mechanical components (contact points, differential amplifiers, capacitive transducers).

[0091] Fig. Figure 2 shows a preferred embodiment of the measuring device comprising pairs of curvature electrodes (410) as a special embodiment of a capacitive transducer (400), and a contact point or contact surface of the curvature electrodes (203) via which the curvature or inclination is mechanically coupled into the measuring system. With the aid of the pairs of curvature electrodes, in addition to pure strain measurement, the inclination ω' and curvature ω'' of the object being measured can also be determined. The curvature electrodes are plate capacitors whose capacitance changes as a result of curvature or inclination. The change in capacitance is evaluated via a capacitance-to-digital converter (600).

[0092] Fig. 3 explains the technical problem that is to be solved via the curvature electrode pairs (410). Fig. Figure 3A shows the cross-section of a bending beam (805) clamped at one end and subjected to a force Fz. Bending occurs, resulting in elongation ε. b on the beam surface. Fig. Figure 3B, however, shows the same beam under combined loading. In addition to bending, the beam is subjected to tension by the force Fx. A combined strain (ε) occurs at the surface. b +ε z A strain sensor mounted on the beam surface can only measure strain and cannot distinguish between combined stress (tension + bending) and pure bending stress. A second sensor, for example on the opposite surface, would be required for this. However, measuring the inclination allows conclusions to be drawn about the type and distribution of the stress.

[0093] Fig. Figure 4 shows a preferred embodiment of the curvature electrode pairs (410), consisting of two electrically insulated electrodes (411 and 412) which are connected to each other via a mechanical anchoring (413). Fig. Figure 4A shows the electrodes (411 and 412) arranged in parallel with a constant plate separation zs,0. Fig. Figure 4B shows how the lower plate tilts due to a curvature of the measuring device, thus changing the plate distance z. s (x s ,ω'(x)) of the two electrodes as a function of the inclination ω'(x) at position x s It changes. Consequently, the capacity also changes.

[0094] Fig. Figure 5 shows the mounting of the curvature electrode pairs (410) on a curved test object (800) and how the capacitance C is z changes as a result of the bend.

[0095] It is assumed for simplicity that the inclination of the test object at the position of the measuring device corresponds to an angle θ between the two electrodes (411, 412), i.e. θ=ω' If this is the case, the capacitance of the curvature electrode in the illustrated embodiment can be calculated as follows: ΔCz=t ε0θ(Log(d0+L θ)−Log(d0))

[0096] where L is the length of the overlapping electrodes, t is the depth of the electrodes, and d0 is the initial plate distance.

[0097] Inclination, curvature, and elongation are directly related and can be converted into one another, provided the boundary conditions of the test object are known.

[0098] Fig. Figure 6A shows a block diagram of another preferred embodiment of the measuring device (100). The micromechanical part of the measuring device (101) consists of at least one contact point or contact surface (203) and pairs of curved electrodes (410). The electrical part of the device (102) comprises a capacitive digital-to-analog converter (600) and a digital signal processor (700).

[0099] Fig. Figure 6B shows a top view of a preferred embodiment of the mechanical part of the measuring device according to the invention, which is mounted on a test object to measure the curvature and elongation based on bending. Fig. Figure 6C shows the arrangement in cross-section. The device comprises a pair of curvature electrodes (410) consisting of two parallel electrodes (411, 412) which are mechanically connected to each other at specific points via a mechanical anchor (413). The pair of curvature electrodes is connected to a test object (800) via a contact surface (203). If the test object bends, the first electrode (412) is deformed, causing a change in the distance to the second electrode. This results in a change in capacitance between the electrode pair.

[0100] Fig. Figure 7A shows another preferred embodiment of the microelectromechanical measuring system in which a temperature sensor (750) is additionally integrated. The temperature sensor (750) is designed to measure the temperature at the device or on the test object and convert it into a digital value D2, and to transmit the digital value of the temperature D2 to the signal processor (700). Using the detected and digitized change in capacitance D1 and the digitized measured value of the temperature D2, as well as optionally further parameters D3, the signal processor (700) calculates the strain ε at the test object via a transfer function. Temperature-related influences on the strain measurement can be corrected or compensated for by the additional temperature measurement.In particular, parasitic thermal effects such as changes in relative permittivity, changes in linearity at the capacitive-to-digital converter, or the effect of different coefficients of thermal expansion between the sensor material and the test object can be corrected.

[0101] Fig. Figure 7B shows an extended preferred embodiment of the microelectromechanical measuring system, in which the test signal U t The self-test mechanism can be switched via a processor (760) of the electronic part (102) of the measuring device. The self-test is triggered, or the test signal is switched, for example, by an external command D. in The self-test is then performed by executing an algorithm on the processor (760). The algorithm includes applying a test signal to the electromechanical actuator, as well as initiating measurements of the capacitance change at the capacitive transducer (400).

[0102] Fig. Figure 8A shows a preferred embodiment of the micromechanical part (101). The components shown are: contact points (200), a micromechanical differential amplifier (300), a capacitive transducer (400), and an electromechanical self-test mechanism in the form of an electromechanical actuator (510). The components are preferably arranged in a mirror-symmetrical manner. Furthermore, the device includes contact electrodes (450) for connecting the MEMS (101) to the electrical or electronic part (102) of the sensor.

[0103] The micromechanical differential amplifier (300) comprises a movable frame (301) which is connected on one side to one of the contact points (201) and is supported on the other side by springs (310). Due to the connection with the contact point (201), the frame assumes the displacement value of the connected contact point (201) relative to the second contact point (202), particularly when a strain ε is applied to the measuring system.

[0104] A lever mechanism (302) is mounted on the movable frame (301) via solid-body joints (306). The lever mechanism consists of at least one lever (305). In the embodiment shown here, the symmetrically constructed lever mechanism (302) comprises two levers (305) on each side, which are cascaded via a connector (304). A second contact point (202) is mounted at the input (307) of the lever mechanism. The input of the lever mechanism thus assumes the displacement value of the second contact point (202).

[0105] The contact points (201 and 202) are arranged at a defined distance from each other. When a strain ε is applied to the measuring system, the two contact points (201 and 202) are displaced relative to each other, resulting in a change in their distance. This change in distance is transmitted to a micromechanical differential amplifier (300) via the connection of the contact points to the movable frame (301) and the input of the lever mechanism (307). The lever mechanism (302) then converts the change in distance into a larger displacement at the output (308) of the lever mechanism.

[0106] In the preferred embodiment in Fig. 8A is located at the output of the lever mechanism of the capacitive transducer (400). The capacitive transducer comprises a guide mechanism (401), at least one paired arrangement of frame-fixed finger electrodes (403) and movable finger electrodes (404), and a frame or runner (402) on which the movable finger electrodes (404) are mounted.

[0107] When the measuring system is subjected to strain, the increased displacement at the output of the lever mechanism (308) is transmitted to the frame or runner (402) of the capacitive transducer (400), and the movable finger electrodes (404) are displaced relative to the frame-fixed finger electrodes (403). Due to the change in the overlap area of ​​the finger electrode pairs, a change in capacitance at the capacitive transducer (400) is caused. The capacitance and the change in capacitance at the capacitive transducer (400) can be provided to the electronic part of the measuring system (102) via the contact electrodes (450). The capacitance can be read out, for example, at the contact electrodes (451, 452, 453) relative to the contact electrodes (455 and / or 454).

[0108] In a preferred and in Fig. In the embodiment shown in Figure 8A, the fixed and movable finger electrodes are arranged in pairs, forming two capacitors. The capacitance change of the first capacitor increases when the rotor (402) is moved in a first direction, while the capacitance change of the second capacitor decreases. Of course, a single pairing of finger electrodes is also possible.

[0109] Fig. Figure 8B shows a preferred embodiment of the micromechanical part (101) of the measuring system (100), illustrating how the contact points (201 and 202) are slightly displaced relative to each other by Δy due to an externally applied strain ε. The initial distance between the contact points is a0. The strain-induced change in distance Δy is amplified by the micromechanical differential amplifier (300) by the gain factor A and transmitted at the output (308) of the differential amplifier to the capacitive transducer (400). The displacement of the finger electrodes (403 and 404) changes the capacitance of the capacitive transducer (400). The change in capacitance is then digitized by a capacitive-to-digital converter (600) and transferred to a signal processor (700) for further processing. The signal processor then calculates the strain from the digital values ​​of the change in capacitance using a transfer function.One possible transfer function, with respect to the exemplary embodiment, could look like this: ε(ΔC)=ΔC1a0d0A ε0 t nK1+K2

[0110] Here, a0 is the initial distance between the contact points, d0 is the distance between the finger electrodes (404, 403) on the capacitive transducer, A is the gain factor of the micromechanical differential amplifier, ε0 is the dielectric constant, t is the depth of the finger electrodes, and n is the number of finger electrode pairs. K1 and K2 are exemplary calibration parameters for correcting slope and offset.

[0111] Also shown in Fig. 8A and B is an electromechanical actuator (510) in the form of an electrothermal actuator, which is integrated as part of the guide mechanism (401). In the illustrated embodiment, it is a geometrically pre-displaced beam. When a current is passed through this beam, thermal heating occurs, resulting in a thermally induced deflection of the beam in a preferred direction. The electromechanical actuator generates a force against the connected micromechanical components. Depending on the spring stiffness of the guide mechanism (401), the lever mechanism (302), and the connection of the contact points (201, 202), a deflection occurs at the capacitive transducer (400), similar to the effect of a strain signal.The target deflection of the capacitive transducer (400) and the associated measurable change in capacitance as a function of the test signal applied to the electromechanical actuator (510) are known through dimensioning, simulation, and / or experimentation. A deviation in the resulting change in capacitance can be interpreted as a malfunction of the measuring device. The test current can, for example, be introduced into the actuator via the contact electrodes (454 and 455).

[0112] Fig. Figure 9 shows a preferred embodiment of the measuring device with an additional pair of tilt electrodes (410). The tilt measurement is carried out by the electrodes (411, 412) moving relative to each other in the z-direction, thereby changing the capacitance C z changes.

[0113] Fig. Figure 10 shows in a preferred embodiment the function of the self-test mechanism: A test voltage U is applied to the electrodes (454) and (455). tapplied. As a result of the applied test voltage, a current flows through the electromechanical actuator (510), here in the form of an electrothermal actuator, which generates a force F that acts against the spring stiffnesses of the guide mechanism (401) and the differential amplifier (300) and results in a displacement y. t at the capacitive transducer (400), in particular at the rotor (402), and causes a change in capacitance ΔC at the capacitive transducer. By measuring the change in capacitance ΔC, e.g., via the contact electrodes (451 and 455), the achieved displacement y can be determined. t to be determined.

[0114] Fig. 11 shows the same preferred embodiment. Fig. 10. The effect of an exemplary defective component on the micromechanical part of the measuring system. Here, a lever (305) on the micromechanical differential amplifier is broken as an example. Due to the defect, the stiffness of the differential amplifier is reduced, so that the actuator force F of the micromechanical actuator (510) results in a higher displacement y. t at the capacitive transducer (400) when it is in an intact device (see Fig. 10) would be present. The characteristic stiffness k c The force acting on the actuator is therefore lower. The characteristic stiffness can be determined by measuring the displacement y. t The force F applied to the capacitive transducer and to the electromechanical actuator can be calculated as follows: kc=Fyt

[0115] Determining the force F from the test signal U t (t) results from a transfer function F(U) depending on the dimensioning and design of the actuator. t(t)). Likewise, the measurement of the displacement y at the capacitive transducer results from the dimensioning and the geometric design of the capacitive transducer and can be calculated from the measured capacitance change ΔC(t) using a transfer function y(ΔC(t)).

[0116] Fig. Figure 12 shows a further preferred embodiment of the micromechanical part of the strain sensor (101), further comprising a conductor loop (550) that preferably runs around the critical mechanical structures. The conductor loop serves to detect a break in the sensor. If a break occurs in the sensor and the area of ​​the break is covered by the conductor loop, the conductor is interrupted and / or the electrical resistance of the conductor loop is changed. In the embodiment shown, the conductor loop is electrically connected to the electromechanical actuator (510). A test signal U tThe current is routed through the conductor loop (550) to the electromechanical actuator (510). If the line is interrupted, the actuator (510) cannot exert any force or displacement, so that no deflection of the capacitive transducer (400) occurs during a self-test. Thus, it can be clearly determined that there is a defect in the measuring device.

[0117] In Fig. Figure 13 shows an example of a break at the differential amplifier (300) and at the conductor loop (550).

[0118] Fig. Figure 14 shows another fault that can be detected by the self-test. In this example, the micromechanical measuring system (101) is shown, where the differential amplifier and the guide mechanism are fault-free, but the finger electrodes (403, 404) are missing. In this case, the test voltage U would t The electromechanical actuator generates a force and a displacement y tcause the same change in capacitance ΔC as is achieved in the fault-free state, however, due to the faulty finger electrodes, the achieved change in capacitance ΔC deviates from the standard value and the device can be identified as faulty.

[0119] Fig. Figure 15A shows how the electromechanical actuator can be used to perform a dynamic self-test instead of a static one. For this purpose, a time-dependent voltage signal is provided to the electromechanical actuator, here, for example, in the form of a voltage jump at time t = 0. The voltage jump is then... Fig. 15B illustrates this.

[0120] The moving components of the microsystem, in particular the capacitive transducer (400) and the differential amplifier (300), begin to oscillate. The resonance frequency f is determined from the measurement of the time-dependent displacement yt(t) via a time-dependent capacitance measurement ΔC(t). rand / or the vibration spectrum is determined, for example, by Fourier transformation.

[0121] Fig. Figure 15C shows, as an example, the oscillation of the displacement y. t (t) on the microsystem. Fig. Figure 15D shows an example of how to determine the frequency components as a function of the frequency f of the oscillation, e.g., after performing a fast Fourier transform. This results in the characteristic frequency spectrum y. c (f) By comparing the frequencies and the stiffnesses that can be determined from them at the sensor with known standard values ​​of the resonance frequency and / or the vibration components in the characteristic frequency spectrum, or by prior determination of the stiffness and comparison with standard values ​​of stiffness, it is possible to conclude that there is a malfunction or deviation in the function of the measuring device.

[0122] Fig. Figure 16A shows another preferred embodiment in which the electromechanical actuator is designed as an electrostatic actuator (520). Here, the electrostatic actuator is integrated on the capacitive transducer (400). For a self-test, a static or time-dependent test voltage U(t) is applied to the electrostatic actuator (520), causing the actuator to generate a force. In this embodiment, the execution of a time-dependent self-test is shown with reference to the graphs presented. At time t = 0, the voltage U is applied to the electrostatic actuator via the contact electrodes (454, 451). t applied. The step response of the time-dependent shift y t (t) is recorded, for example, by measuring the time-dependent change in capacitance. The mechanical components of the MEMS oscillate, and the characteristic frequency spectrum y is recorded. c (f) and the resonance frequency f rThe resonance frequency is determined because it depends on both the mass and the stiffness of the micromechanical components. This allows the stiffness of these components to be calculated from the resonance frequency. A comparison with standard values ​​then reveals whether there is a deviation from the target value of the resonance frequency or stiffness. Such a deviation indicates a defective component, for example, caused by breakage, a deviation from the manufacturing tolerance, or jamming of the moving structures.

[0123] The advantage of this embodiment is that the same micromechanical components can be used for the capacitive transducer and the self-test mechanism.

[0124] A particular advantage of the device according to the invention is that the micromechanical differential amplifier is designed to also amplify forces and stiffnesses. When the electromechanical actuator is arranged at the output of the differential amplifier, the differential amplifier amplifies a small actuator force into a larger force and makes this available at the input of the differential amplifier. Accordingly, an amplified actuator force also acts at the contact points, which pushes the contact points (201, 202) apart or together. The contact points are resiliently mounted and act with a stiffness against the amplified actuator force.

[0125] Fig. Figure 17 shows, by way of example, some stiffnesses in the measuring system, the assignment of which to the respective components of the measuring system is represented by a simplified spring model. The stiffness of the contact points depends, among other things, on the suspension of the contact points on the housing (150), on the stiffness of the differential amplifier, as well as on the indirect connection of the contact points on the test object (800) and the stiffness of the bonding layer (900) with which the measuring device is mounted on the test object (800).

[0126] The self-test mechanism can also be used to examine the quality of the assembly of the microelectromechanical measuring system (100) on a test object (800). According to the invention, this is done by the self-test mechanism through a direct or indirect measurement of the stiffness of the microsystem using the electromechanical actuator (510) and the capacitive transducer (400). The actuator generates a force F and the resulting displacement y. t The force is measured at the capacitive transducer. The resulting stiffness k can be determined from the force-to-displacement ratio. g close. The overall stiffness k g The force against which the actuator (510) exerts a force is composed, on the one hand, of the combined stiffnesses of the micromechanical components; such as the stiffness k fl of the guide mechanism (401) on the capacitive transducer (400) and the stiffness k outat the output (308) of the micromechanical differential amplifier (300) and on the other hand from the stiffness k V the connection of the contact points (201, 202) to the test object (800). The stiffness k V symbolizes the connection of the contact points (201, 202) with the housing (150). The stiffness k resulting at the electromechanical actuator (510) g is a function of the individual stiffnesses on the measuring system k g = f (k out , k f1 , k f2 , k v , k M ...).

[0127] The stiffness shown k V This symbolizes the stiffness between the contact points (201 and 202). It is influenced by the housing (150) and / or the substrate (900) to which the contact points are mounted. k M This refers to the stiffness of the bonding layer and stiffness k. E symbolizes the stiffness of the test object (800).

[0128] Will be like in the model in Fig. 18. If the measuring system is mounted on a test object, the stiffness between the contact points (200, or 201 and 202) is determined by the stiffness of the test object k. E This increases the overall stiffness k. g compared to the electromechanical actuator (510). The force generated by the actuator (510) consequently causes a smaller displacement at the capacitive transducer (400).

[0129] A bonding layer (900), e.g. in the form of an adhesive or solder, is used to connect the measuring device (100) to the test object (800). The strength of the connection can be determined by its stiffness k. M can be modeled. If the connection between the measuring device and the test object is soft, this corresponds to a low stiffness k. M A fixed, rigid connection has a high stiffness k. M before. The stiffness k MThis also contributes to the overall stiffness k g A measurement of the overall stiffness via the self-test mechanism thus allows for an evaluation of the assembly quality and / or a determination of the stiffness of the test object. To unambiguously determine the assembly quality, it is helpful to measure the stiffness k. g to determine the measurement system before and after assembly with a test object.

[0130] Fig. Figure 19 shows a simplified cross-section of a mounted strain gauge (100) on a test object with a bonding layer (900). Fig. Figure 19A shows a continuous, homogeneous bonding layer. The sketched, measurable displacement y is obtained as a result of a self-test. ı at the capacitive converter (400) as a function of the test voltage U t . Fig. Figure 19B shows an incomplete connection between the strain sensor (100) and the test object (800). The connection layer (900) is interrupted. Consequently, the stiffness of the connection is lower than in Figure A. When performing a self-test and determining the stiffness k g This allows us to determine that the overall stiffness of the sensor is lower when it is incompletely mounted than when it is fully mounted on the test object. The stiffness can be determined either statically or dynamically. Applying a constant test voltage U t is the measured displacement y l at the capacitive converter (400) consequently with incomplete connection ( Fig. 19B) larger than with full connection ( Fig. 19A).

[0131] Fig. Figure 20 shows an embodiment in which the stiffness of the test object (800) and / or the material of the test object can be determined using the self-test. Fig. Figure 20A shows by way of example the cross-section of the strain sensor (100) according to the invention which is mounted on a test object with a first modulus of elasticity (801) via a connecting layer (900). Fig. Figure 20B shows the same arrangement, but with a different test object (802) exhibiting a second modulus of elasticity. By applying a test signal to the electromechanical actuator (510) and measuring the stiffness of the microsystem, the stiffness of the test object can also be determined. The stiffness of the test object is preferably determined by comparison with reference values. For this purpose, several sensors are experimentally mounted on different test objects, each with a known modulus of elasticity, and stiffnesses are determined using the self-test mechanism. The determined stiffness values ​​serve as a reference for future measurements.

[0132] Fig. Figure 21A shows an example of a characteristic frequency spectrum that results from performing a dynamic self-test on a measuring system. Fig. Figure 21B shows, as a reference, a characteristic frequency spectrum of an ideal measuring system with ideal mounting on a test object. By comparing the two characteristic frequency spectra, defects can be detected and identified.

[0133] The following figures show examples of preferred embodiments of the electromechanical actuator (510).

[0134] In Fig. Figure 22 shows an embodiment of the electromechanical actuator (510) in the form of an electrothermal actuator (530). The actuator is integrated directly into the guide mechanism (401) of the capacitive transducer (400). The actuator is based on a pre-loaded spring (406) which includes a heating resistor (531). When current flows due to a test signal U t(t) The heating resistor (531) is heated by the heating element, causing the pre-extended spring to expand. This exerts a force on the rotor (402) of the capacitive transducer. The rotor is pushed upwards, and the capacitance of the capacitive transducer changes. The rotor (402) is connected to the micromechanical differential amplifier (300) and, indirectly, to the contact points (201, 202), and, in turn, indirectly to the test object (800) and the interconnect layer (900). Consequently, the actuator force is counteracted not only by the stiffness of the guide mechanism (401) but also by the overall stiffness k. s of the connected components. The resulting displacement at the capacitive transducer divided by the actuator force corresponds here to the characteristic stiffness.

[0135] Fig. Figure 23 shows an embodiment in which the self-test mechanism (500) comprises a conductor loop (550) in addition to the electrothermal actuator (530), the conductor loop being guided along the mechanical structures. The source (560) for the test signal U t (t) is connected in series with the electrothermal actuator (530) via the conductor loop. If the conductor loop is interrupted due to damage, the actuator cannot be controlled. Consequently, there is then a defect in the measuring device (100). The symbolic spring (115) with stiffness k g represents, by way of example, the stiffness acting on the electromechanical actuator (510) and which results summarily from the stiffnesses of the individual components of the measuring system.

[0136] Fig. Figure 24 shows a bi-directional embodiment of the electrothermal actuator (530).

[0137] Fig. Figure 25 shows an embodiment of the electrothermal actuator (530) in which current does not flow through an additional heating resistor (531), but in which the forward-deflection spring (406) itself forms the heating resistor (531).

[0138] Fig. Figure 26 shows another possible embodiment of the electrothermal actuator (530), wherein, in contrast to the previous examples, the electrothermal actuator is not directly integrated into the guide mechanism (401) of the capacitive transducer (400), but is connected to the runner (402) outside the guide mechanism in the form of a hinged beam (532).

[0139] Fig. Figure 27 shows another possible embodiment of the electrothermal actuator (530) wherein the electrothermal actuator (530) is mechanically decoupled from the capacitive transducer (400).

[0140] Fig. Figure 28 shows an embodiment of an electrostatic actuator (520) which is mounted outside the capacitive transducer (400) on the runner (401).

[0141] A preferred coupling of the individual components during a self-test is described in Fig. Figure 29 shows that the processor (760) executes a self-test algorithm. For this purpose, it controls a test signal Ut(t), which is output to the self-test mechanism (500). The self-test mechanism, comprising an electromechanical actuator (510), exerts an actuator force F(t) on the capacitive transducer (400). The capacitive transducer (400), in particular the rotor (402), is in turn directly and indirectly connected to the micromechanical differential amplifier (300), the contact points (200), and via these to the interconnect layer (900) and the test object (800), each of which has a stiffness and a mass, and whose combined stiffness and mass effect is present on the capacitive transducer (400). From the applied actuator force F(t) and the combined stiffness k gIn the dynamic case, the mass effect results in a displacement yt(t) at the capacitive converter, causing a change in capacitance ΔC(t). This change in capacitance is preferably converted into a digital signal D1 via the capacitive-to-digital converter (600), optionally processed by the digital signal processor (700) (e.g., offset correction), and either directly output externally as a digital signal D out The data is output or forwarded to the processor (760). The processor (760) processes the measurement data using an algorithm, calculates the characteristic stiffness and / or the characteristic frequency spectrum (if not already done by the digital signal processor), and evaluates the result of the self-test. An evaluation of the self-test can consist of determining whether a defect is present, what type of defect it is, and / or what the elastic modulus of the test object is.

[0142] The following figures describe preferred embodiments of the mounting device as well as preferred mounting methods for the measuring device (100) and the test object (800): Fig. Figure 30 shows a preferred embodiment of a mounting device (1000) for mounting the micromechanical measuring system (100) on a test object. The measuring device comprises at least one force generator (1100), here in the form of a spring, a sensor mount (1200), an ignition device (1300), and a mounting housing (1400).

[0143] To mount the measuring device (100) on a test object (800), the measuring device (100) is preferably first fixed to the sensor receptacle (1200) of the mounting device (1000) and pressed onto the surface of the test object with the mounting device. For this purpose, the mounting housing (1400) is connected to the sensor receptacle (1200) via a bearing (1450), so that the mounting housing (1400) can be displaced relative to the sensor receptacle. A force F is applied via the force generator / spring (1100). z This force is generated when the housing (1400) is displaced relative to the sensor mount. The force presses the measuring device onto the surface of the test object.

[0144] As soon as a defined spring deflection and thus the assembly force is reached, the ignition energy from an energy source (1380) is transferred to the ignition device (1300) via a switch (1350), so that the solder layer (900) between measuring device (100) and test object (800) melts and connects the measuring device and test object in a material-bonded and / or form-bonded manner.

[0145] Fig. Figure 31 shows how, in a preferred embodiment, a displacement z is applied to the housing (1400) of the mounting device, causing the spring (1200) to compress and thus exerting a force Fz on the measuring device. In the preferred embodiment, the ignition device is a heat source (1310) configured to transfer heat to the measuring device in order to melt the solder layer.

[0146] Instead of the heat source (1310) as in Fig. As shown in Figure 31, to activate via a switch (1350), it is also conceivable to operate the heat source continuously and to initiate the ignition process by ensuring that the heat source only comes into contact with the measuring device when the mounting force is reached.

[0147] Fig. Figure 32 shows a further preferred embodiment of the assembly device and the assembly method, in which an electric current is used as the ignition source, causing the solder layer to melt. The current flows through the measuring device according to the invention. For this purpose, the energy source (1380) is connected directly to the test object via at least one contact pin (1390), and another contact of the energy source is connected to the measuring system (100), so that current flows through the measuring device (100) and through the bonding layer (900) as soon as the assembly force is reached. In this embodiment, the activation of the ignition energy is also initiated by a switch when a defined assembly force is reached. Naturally, the assembly device can be extended by a circuit that enables the current flow via an electronic circuit, e.g., using a transistor.

[0148] The interconnect layer in the measuring device according to the invention is preferably a reactive metal layer consisting of several metal layers, such as aluminum and nickel. The flow of current heats the metal layer, causing it to alloy, thereby inducing an exothermic reaction and enabling a high melting point to be achieved.

[0149] Another preferred embodiment is described in Fig. Figure 33 shows that the housing of the mounting device (1400) includes an additional ball joint (1402) to correct obliquely introduced displacements via the upper part of the housing (1401).

[0150] To make the ignition energy available at the measuring system for only a short time, the following is suitable, for example: Fig. Figure 34 shows a preferred connection between the energy source (1380) and the switch (1350). The energy source, for example a battery, charges capacitors. As soon as the critical mounting force F is reached... M When this point is reached, a signal is sent to ignite the ignition. th The power is provided by a physical switch / button. The switch / button activates an electrically controlled switching element T and closes the circuit between capacitors and the heater (1310), here in the form of a resistor R. L . Capacitor C discharges suddenly and for a short duration.

[0151] Instead of the capacitor C discharging via the heater (1310), it can also be discharged directly via the measuring device (100), which melts a solder layer or ignites a reactive metal layer.

[0152] Fig. Figure 35 shows a further preferred embodiment of the method for mounting the strain sensor (100) on a plastic test object (850) by means of a positive-locking connection. For this purpose, the strain sensor has a roughened surface with cavities (980). Under the influence of the mounting force F M The strain gauge (100) is pressed onto the test specimen. By briefly switching on a heater (1310), the sensor and the test specimen are heated locally at their connection point. As the plastic test specimen (850) softens or melts, it flows into the cavities on the strain gauge, thus forming a positive-locking connection between the strain gauge and the test specimen.

[0153] Fig. Figure 36 shows a preferred method for manufacturing the measuring device according to the invention. Step A shows the preparation of a carrier layer (2300), also referred to as the handle layer; a sacrificial layer (2200), also referred to as the buried oxide layer; and a layer that carries the mechanical structures, also referred to as the device layer (2100). In step B, the device layer (2100) is structured with the mechanical components of the measuring system by etching. These include, in particular, the contact points (200) as well as all movable micromechanical components (2101). In step C, the movable components (2101) of the measuring system are exposed from the carrier layer (2300) by partially undercutting the sacrificial layer (2200). However, the contact points (200) remain connected to the carrier layer via the sacrificial layer (2200).In step D, a cover (2400) is bonded to the device layer (2100), thus enabling a hermetic seal of the moving components on the device layer. In a preferred embodiment, the cover includes cavities (2460) to be mechanically separated from the moving structures. Furthermore, in a preferred embodiment, vias (2450) are provided on the cover to electrically contact the device layer through the cover.

[0154] In step D, the substrate layer is thinned by etching and / or grinding and / or polishing.

[0155] Fig. Figure 37 shows an extension of the preferred manufacturing steps from Fig. 36, wherein in A) an additional compound layer (900) is deposited on the housing of the strain sensor (150). In B), however, a separating layer (910) is selectively deposited and structured. The separating layer serves as a mask for the selective coating of a compound layer (900) on the measuring device. The separating layer prevents or reduces a metallurgical bond between the test object and the measuring system via a compound layer (910), as in Fig. 37C shown.

[0156] Fig. Figure 38 shows a further preferred addition to the manufacturing steps from Fig. 36, wherein the outer surface of the housing (150) is structured by etching or laser ablation, thus creating cavities (980) for a subsequent positive connection to the housing of the measuring system.

[0157] Fig. Figure 39 shows a preferred embodiment of the microelectromechanical measuring device (100) comprising the micromechanical part (101), the electronic part (102), and the connection of both parts via a sensor housing (105). The components are electrically interconnected via vias (105). For communication and output of measurement results, the electronic part (102) is connected to the outside via external electrodes (104).

[0158] The figures described below show application examples relating to the calibration of the measuring device for various measured quantities.

[0159] Fig. Figure 40A shows an exemplary application of a bending beam as a deformation body (810) for measuring a force P pThe measuring device (100) according to the invention is mounted on the beam (810). The force applied bends the deformation body, causing it to stretch at the position of the measuring device (100). The purpose of the measurement using the measuring device is to determine the acting force P. p The measurement of the strain ε serves only as an auxiliary quantity. The resulting strain is determined by the force, but also depends on the geometry and material of the deformed body (810), as well as the position of the measuring device and the point of force application on the deformed body.

[0160] As in Fig. As outlined in Figure 40B, the device according to the invention is able to directly determine the desired measured quantity of force Pp from the strain measurement data by applying a transfer function to the digital signal processor (700). For this purpose, a transfer function is applied to the measurement data D1 provided by the capacitive-to-digital converter, whereby application-specific calibration data D3 are incorporated into the transfer function. This allows, among other things, the slope and offset in the transfer function to be set for the specific application, and the output data D out directly describes the force to be measured in the desired unit.

[0161] An example of a transfer function would be: doubt(d1)=d3,1∗d1+d3,2

[0162] Here, d1 is a value of the measurement data D1, d 3,1 and d 3,2 are calibration data and d out(d1) is the measured value corrected for offset and slope as a function of d1. The calibration data are application-specific and must be determined specifically for each application. They can be permanently stored in the memory (710) of the measuring device.

[0163] According to the principle from Fig. 41 shows Fig. 42 how a weight measurement can be implemented using the measuring device (100). The required calibration data D3 for calculating a weight from a strain measurement are first determined and stored in the memory (710). During a weight measurement, the resulting strain on the deformed body is first determined using the measuring device, and the weight is then calculated using the calibration data.

[0164] In this way, it is possible to measure not only force and weight, but also other physical quantities that cause elongation in a deformed body. These include, for example, torsion, torque, pressure, or acceleration.

[0165] Fig. Figure 42 shows a preferred method for calibrating and adapting the measuring device for a specific application. The particular advantage of the measuring device according to the invention is, among other things, that it can be adapted for different applications by calibration. Here, the determination of the calibration data D3 using a two-point calibration is shown. The measuring device is shown here in Fig. 42A is mounted on a deformation body (820). The deformation body (820) serves as a fixture for a weight measurement. First, a strain measurement is performed on the measuring system, whereby the deformation body is not subjected to any weight. A first data point d is recorded. b determined.

[0166] Then, as in Fig. Figure 42B shows the deformation body with a known test weight m p0 (821) loaded and another strain measurement was performed with the measuring system and a second data point d a determined. From the data points, it is possible to determine, as in Fig. 42C now shows the slope (d a -d b / (m p0 -0)) and the offset d b The calibration values ​​slope and offset are now stored in the memory (710) of the measuring device. When determining an unknown weight, the transfer function is applied to the measured quantity D1, so that the measuring device directly outputs the calculated weight instead of or in addition to the strain. Reference symbol list 100 microelectromechanical strain measurement system 101 micromechanical part of the measuring system, MEMS 102 Electronic part of the measuring system, ASIC 103 Sensor housings 104 external electrodes 105 Vias 115 symbolic feathers to represent a summary stiffness k s 150 chip packages / MEMS packages 200 contact points 201 first contact points 202 second contact points 203 Contact point or contact surface of the curvature electrodes 300 micromechanical differential amplifiers 301 movable frame of the micromechanical differential amplifier 302 Lever mechanism 304 connectors 305 levers 306 solid body joints 307 Input of the differential amplifier / lever mechanism 308 Output of the differential amplifier / lever mechanism 310 Guide spring on the movable frame of the differential amplifier 400 capacitive transducers 401 Guide mechanism 402 Runner / Frame of the capacitive converter 403 frame-mounted finger electrodes 404 movable finger electrodes 405 Guide spring of the guide mechanism 406 angled spring of the guide mechanism 407 rigid connector of the guide mechanism 410 pairs of curved electrodes 411 first curvature electrode 412 second curvature electrode 413 mechanical anchoring of the curvature electrodes 450 contact electrodes 451 first contact electrodes 452 second contact electrodes 453 third contact electrodes 454 fourth contact electrodes 455 fifth contact electrodes 500 self-test mechanism 510 electromechanical actuator 520 electrostatic actuator 521 movable finger electrode on the electrostatic actuator 522 Frame-mounted finger electrode on the electrostatic actuator 530 electrothermal actuator 531 Electrical heating resistor made of metal or semiconductor material / electrical conductor 532 clamped buckling spring 533 heated bending beam 550 conductor loop 560 Test signal source 561 Illustration of an electrical connection / connections 600 Capacitance Digital Converter 700 Digital Signal Processor 710 electronic storage 750 temperature sensor 760 processor 800 test object, measuring object, test piece 801 Test object with a first modulus of elasticity 802 Test object with a second modulus of elasticity 805 bending beams 810 Deformation bodies for measuring a force P p 820 deformation bodies for measuring a weight m p 821 Test weight with defined mass 830 Deformation bodies for measuring a torque M z 850 test object made of plastic 900 compound layer 910 Separation layer / Separation layer 980 roughened surface of the chip housing for form-fitting assembly 1000 assembly device 1100 power generator 1150 spring 1200 sensor recording 1300 Ignition device 1310 stokers 1350 switches 1380 Energy source 1390 Contact pin 1400 Housing of the mounting device 1401 upper part of the housing of the mounting device 1402 ball bearings 1450 bearings for shifting the housing relative to the chip holder 2100 Devicelayer 2101 movable structure at the device layer 2200 Sacrificial layer, Buried Oxide Layer 2300 Carrier layer, Handle layer 2400 lid wafers 2450 through-hole plating 2460 cavity 2460 connection electrodes QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] WO 2005 / 068960 A1 [0007, 0008] DE 69822097T2

[0008] DE 102016202769 A1

[0008] WO 2016 / 092 475 A1

[0008] US 5 109 701 A

[0008] EP 000003822577 B1

[0008]

Claims

[1] Microelectromechanical measuring system (100) for measuring strains, inclination and curvatures on a test object (800) comprising a) at least one capacitive transducer (400) in the form of a tilting electrode pair (410), consisting of at least two electrodes (411, 412) which together form a capacitor; b) at least one contact surface (203) which is directly or indirectly mechanically connected to one of the electrodes (411) of the tilt electrode pair (410) and the test object (800) and is designed to accommodate the tilt and / or curvature of the test object; c) a capacitive-to-digital converter (600) designed to convert the capacitance change of the capacitive converter(s) (400) into an electrical digital signal and d) a signal processor (700) for processing the electrical digital signal of the capacitive-to-digital converter (400). [2] Microelectromechanical measuring system according to claim 1, further comprising a) at least two further contact points (201, 202) which are arranged at a defined distance from each other, wherein at least one of the contact points is connected to a micromechanical differential amplifier (300); b) a micromechanical differential amplifier (300) designed to convert the change in distance of the contact points (201, 202) into an amplified mechanical displacement and c) a further capacitive transducer (400) for converting the amplified mechanical displacement of the micromechanical differential amplifier into a further change in capacitance. [3] Microelectromechanical measuring system according to claim 2, further comprising a self-test mechanism (500) comprising at least one electromechanical actuator (510) configured to effect a mechanical displacement and / or force on the capacitive transducer (400) by applying a test signal. [4] Microelectromechanical measuring system according to claim 3, wherein the electromechanical actuator (510) is designed as an electrostatic actuator (520). [5] Microelectromechanical measuring system according to claim 4, wherein the self-test mechanism (500) further comprises a conductor loop (550) arranged along the measuring device. [6] Microelectromechanical measuring system according to any one of claims 1 to 5, further comprising a temperature sensor (750) for measuring the temperature on the test object (800). [7] Microelectromechanical measuring system according to any one of claims 1 to 6, further comprising a processor (760) configured to control an algorithm for performing a self-test. [8] Microelectromechanical measuring system according to any one of claims 1 to 7, further comprising a connecting layer (900) which is configured to connect the measuring system to a test object (800) in a metallurgical manner. [9] Method for measuring inclination and / or strain on a test object (800) using a microelectromechanical measuring system (100) according to any one of claims 1-8, comprising at least the following steps: (i) Connecting the measuring system (100) to the surface of a test object (800) on which the strain and / or inclination is to be measured; (ii) Measurement of the distance between the electrodes (411, 412) of the tilt electrode pair (410); (iii) Conversion of the measured change in distance into a change in capacitance at the tilt electrode pair (410); (iv) Conversion of the capacitance change into a digital value via a capacitance-to-digital converter, wherein the digital value represents a measure of the inclination and / or strain of the test object; (v) Calculation of the inclination and / or strain of the test object (800) from the digital value of the change in distance of the electrodes (411, 412) of the tilt electrode pair determined in the previous steps. [10] Method for strain measurement according to claim 9, comprising the following further steps: (vi) Measurement of the strain-induced change in distance of the contact points (201, 202) on the measuring system (100) and amplification of this change in distance via a mechanical differential amplifier (300) which provides at the amplifier output (308) an amplified displacement dependent on the change in distance; (vii) Conversion of the amplified displacement signal into a change in capacitance via a capacitive converter (400); (viii) Conversion of the capacitance change into a digital value via a capacitance-to-digital converter, wherein the digital value represents a measure of the distance change of the contact points; (ix) Calculation of the strain of the object being measured from the known distance of the connecting elements (201, 202) and the digital value of the change in distance of the connecting elements (201, 202) determined in the previous steps. [11] Method for strain measurement according to one of claims 9 or 10, further comprising a measurement of the temperature of the test object (800) via a temperature sensor (750) on the measuring system (100). [12] Method for strain measurement according to one of claims 9 or 10, comprising, after the last step, the following further step: Application of a transfer function to the digital value of the measured capacitance change via a digital signal processor. [13] Method for strain measurement according to claim 12, wherein said transfer function is designed to compensate for the temperature influence on the strain measurement via the measured temperature (D2) and the determined digitized capacitance change (D1).

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