Method and device for measuring voltage

Abstract

A method of measuring a voltage using a micro-electro-mechanical system, namely a MEMS (100), comprising: a sample mass (110) supported above a substrate by means of mechanical spring elements (120) in such a way as to be movable relative to the substrate along a vibration direction (x); a trimming electrode (130) adapted, when applied with a voltage, to generate an electrostatic force on the sample mass (110) against a mechanical spring force generated by the spring element (120) when the sample mass (110) is shifted along the vibration direction (x); a drive electrode (140) adapted to place the sample mass (110) in a movement along the vibration direction (x); and a readout electrode (150) adapted to measure a vibration frequency of a vibration of the sample mass (110) generated in this way, the method comprising: applying a voltage to be measured to the trimming electrode (130); measuring the magnitude of the voltage to be measured from the measured vibration frequency of the sample mass (110); and detecting a change in the voltage to be measured based on a change in the measured vibration frequency.

Description

Technical Field

[0001] The invention relates to a method for measuring a voltage by means of a micro-electromechanical system and to such a micro-electromechanical system. Background Art

[0002] Reference voltage sources are used in various electronic applications to predetermine a voltage based on which further operations are performed. For example, reference voltages are used in analog-to-digital converters for sampling analog signals. Other parameters used in corresponding electronic components, such as voltage values ​​or current variables, are also confirmed or calculated based on the reference voltage.

[0003] In particular, in the case of acceleration or angular velocity sensors designed as microelectromechanical systems, MEMS, a reference voltage is required in order to set the drive and / or readout voltage to a predetermined or predeterminable value. For example, the measurement accuracy of an acceleration sensor is usually proportional to the voltage applied between the vibrating mass of the sensor and its drive / readout electrode in a quadratic manner. Therefore, the so-called proportionality factor, which converts the measurable change in capacitance or charge caused by the deflection of the sample mass into an actual acceleration of interest, is quadratically related to this drive readout voltage. Since this in turn is generated or set based on the reference voltage, the proportionality factor is quadratically related to the magnitude of the reference voltage.

[0004] High-performance components, such as high-precision acceleration or angular rate sensors, are subject to the requirement that they are long-term stable, i.e. their calculation or measurement results have the same quality over a very long time, e.g. over 10 years or more, and in particular there is no time drift, i.e. no continuous increase or decrease.

[0005] Here, when, for example, operating and environmental conditions are maintained constant during the product life cycle of the acceleration sensor, a deviation of less than 100 ppm per year is acceptable for the proportionality factor of the acceleration sensor, i.e., at the beginning of the product life cycle, the deviation is only 100 millionth of the proportionality factor.

[0006] However, typical reference voltage sources only achieve an accuracy of the order of magnitude of, for example, 50 ppm per year. Due to the quadratic dependence of the scale factor on the reference voltage, this already results in a change of the scale factor of 100 ppm per year. If the aging effects of other components are also taken into account, this results in a drift of the scale factor and therefore also of the measured value of at least 300 ppm per year for a conventionally realizable acceleration sensor. This also affects the accuracy of the measurement via the displacement / offset of the sensor to values ​​of 50 to 100 μg, which is too much for an uncorrected high-precision acceleration sensor.

[0007] In a similar way, inaccuracies of other electronic components that occur over time can also be estimated. Here, too, the time drift of the reference voltage is often the main cause of the drift of the entire component.

[0008] In this process, an improvement of the accuracy of the reference voltage source is not possible or is only possible in a complicated manner. In addition, there is the problem that the direct measurement of the reference voltage is affected by similar time drifts or inherent measurement inaccuracies, which are similar in magnitude to the drift of the reference voltage. Summary of the invention

[0009] Therefore, the object of the present invention is to provide a method for measuring a voltage, in particular a reference voltage, which method is accurate enough to detect long-term drifts of the voltage. The object of the present invention is also to provide an apparatus that can implement such a method.

[0010] This object is achieved by the subject matter of the following technical solution. Advantageous improvements are defined in the following technical solution.

[0011] In particular, the method for measuring voltage uses a micro-electromechanical system, or MEMS. The MEMS has: a sample mass, which is mounted above a substrate in a manner movable relative to the substrate along a vibration direction by means of a mechanical spring element; a trimming electrode, which is suitable for generating an electrostatic force on the sample mass when a voltage is applied, which electrostatic force opposes the mechanical spring force generated by the spring element when the sample mass is deflected along the vibration direction; a drive electrode, which is suitable for placing the sample mass in a movement along the vibration direction; and a readout electrode, which is suitable for measuring the vibration frequency of the vibration of the sample mass generated in this way. The method comprises: applying a voltage to be measured to the trimming electrode; measuring the magnitude of the voltage to be measured from the measured vibration frequency of the sample mass; and detecting a change in the voltage to be measured based on a change in the measured vibration frequency.

[0012] The detection of the voltage to be measured is thus achieved by determining the vibration frequency of the vibration system. Since the vibration frequency can be determined significantly more accurately than the voltage, this already makes a decisive contribution to the above-mentioned purpose. In addition, by applying the voltage to be measured to the trimming electrode, it is achieved that the voltage has a significant influence on the vibration characteristics of the sample mass. The voltage applied to the trimming electrode effectively changes the spring constant of the vibration system. A suitable design of the MEMS, i.e. in particular a suitable design of the mechanical spring constant, allows setting an effective spring constant, which is particularly advantageous for detecting frequency changes caused by changes in the voltage to be measured. Therefore, by applying the voltage to be measured to the trimming electrode, the measurement accuracy can be further improved.

[0013] Advantageously, the voltage to be measured is a reference voltage, the magnitude of which is the basis for further measurement and / or calculation operations. The method then further comprises: correcting further measurement and / or calculation operations by replacing the expected reference voltage with the measured reference voltage. Thus, additional operations such as analog-to-digital conversion, determination of the measured value by means of a scaling factor, etc. are not performed using the reference voltage specified when the reference voltage source is produced, but using the measured voltage value. Similarly, the value of a variable derived (e.g., simulated) from the reference voltage is updated or corrected based on the measured value of the reference voltage. This improves the result of the further measurement and / or calculation operation.

[0014] By applying the voltage to be measured to the trimming electrode, a mechanical spring force of between 50% and 90%, preferably between 60% and 80%, more preferably 75%, is compensated. These compensation values ​​are particularly advantageous for the magnitude of the frequency variation of the voltage variation to be measured. This increases the accuracy of the measurement. Once the magnitude of the voltage to be measured is known, the magnitude of the compensation can be achieved by a suitable design of the MEMS, i.e. in particular the trimming electrode and / or the spring element and the spring constant specified by them. In this way, a particularly sensitive MEMS can be produced which is set to a specific voltage value.

[0015] The method can be performed in particular when the MEMS is stationary, i.e. when there are no strong vibrations or linear accelerations. This avoids disturbances caused by excessive movements. For example, the method can always be performed as long as the electronic component whose reference voltage is to be measured is activated. In particular, if this is an acceleration sensor, the MEMS can be expected to be stationary or almost stationary. This makes it possible to obtain a reliable value for the voltage to be measured.

[0016] A micro-electromechanical system, or MEMS, for measuring voltage has: a sample mass, which is mounted above a substrate in a manner movable relative to the substrate along a vibration direction by means of mechanical spring elements; a trimming electrode, which is suitable for generating an electrostatic force on the sample mass when a voltage is applied, which electrostatic force opposes the mechanical spring force generated by the spring element when the sample mass is deflected along the vibration direction; a drive electrode, which is suitable for placing the sample mass in a movement along the vibration direction; and a readout electrode, which is suitable for measuring the vibration frequency of the vibration of the sample mass generated in this way. The MEMS also includes a control unit, which is suitable for controlling the MEMS in such a way that it performs the above method.

[0017] The above-mentioned positive effects can be achieved by utilizing such MEMS.

[0018] The MEMS can be designed so that, when the trimming electrode is applied with the voltage to be measured, the resonant frequency of the vibration of the sample mass changes by a value in the range from 100 ppm to 1000 ppm of the resonant frequency in the case of a change in voltage of 1 mV. Thus, the MEMS is designed so that a relatively small change in the voltage applied to the trimming electrode in the millivolt range, i.e., for example, about 100 ppm at a voltage of 10 V, causes a change in the resonant frequency that is significantly greater than the stability fluctuation of the resonant frequency of less than 10 ppm. This then enables high accuracy when measuring the change in the resonant frequency, which enables high accuracy when measuring the change in the voltage applied to the trimming electrode.

[0019] In this process, the change of the resonant frequency with the change of voltage may not be linearly related to the offset of the sample mass and / or the resonant frequency may vary with the ambient temperature. The control unit is then adapted to take these correlations into account by calibration when detecting the voltage to be measured. The magnitude of the vibration amplitude of the sample mass and the temperature changes of the components of the MEMS (e.g. due to fluctuations in ambient temperature) can both affect the mechanical spring constant and the electrostatic spring constant generated by the trimming electrode. Due to the changing voltage at the trimming electrode, different offsets of the sample mass and / or different temperatures within the MEMS lead to various degrees of change in the resonant frequency. This relationship is generally not linear.

[0020] Thus, the control unit can be adapted to perform a calibration of the system, for example by modifying known variations of the voltage at the electrodes at different vibration amplitudes or temperatures and determining the resulting variation of the resonant frequency. The relationship obtained in this way can be used directly to correct the measured values ​​to specific standard values ​​of vibration amplitude and / or temperature during operation. Conversely, the temperature and / or vibration amplitude can also be determined by using known voltage variations from the measured values ​​for variations of the resonant frequency. For example, calibration is not necessary when the vibration amplitude is kept constant and / or measurements are performed only within a predetermined temperature range.

[0021] The MEMS can be designed so that when the trimming electrodes are applied with the voltage to be measured, the vibration system generated by the vibration of the sample mass has a performance index greater than 1000. This makes it particularly easy to measure changes in the resonant frequency.

[0022] The sample mass, spring element, trimming electrode, drive electrode and readout electrode can be evacuated in the process, for example by encapsulating them in a common evacuated housing. This achieves an improvement in the performance of the system due to the elimination of air resistance, which in turn improves the measurement accuracy.

[0023] The acceleration sensor for measuring acceleration may include a MEMS as described above. In the process, the MEMS is suitable for measuring the acceleration acting on the acceleration sensor along the vibration direction of the sample mass by measuring the vibration frequency of the sample mass. Therefore, the vibration system of the MEMS is not only used to detect the change of the voltage applied to the trimming electrode, but also mainly used to measure the change of the vibration caused by the acceleration applied to the sample mass. In the process, the two signals can be easily distinguished based on different time constants. The change of the voltage to be measured has a very long time constant, such as months or years, while the acceleration naturally has a short-term effect, that is, in the range of seconds, minutes or hours.

[0024] In the process, the voltage to be measured can be equal to a reference voltage for determining an operating voltage applied to the drive electrode and / or the readout electrode. This means that the voltage to be measured is the voltage that determines the scale factor of the acceleration measurement. This makes it possible to detect and correct for changes in the scale factor due to drift of the reference voltage. In the process, it is particularly advantageous that this can be performed using existing components that can be used for acceleration measurement, thereby preventing the addition of additional components or structures. In this way, a highly accurate, compact and long-term stable acceleration sensor can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The invention will be further described below with reference to the accompanying drawings. This description is to be understood as purely exemplary. The invention is limited only by the claims.

[0026] Figure 1 A schematic diagram of a micro-electromechanical system, or MEMS, for measuring voltage is shown;

[0027] Figure 2 A schematic flow chart of a method for measuring voltage by means of MEMS is shown;

[0028] Figure 3 shows a schematic diagram of a MEMS for measuring a reference voltage;

[0029] Figure 4 shows a schematic diagram of another MEMS for measuring voltage;

[0030] Figure 5 shows a schematic diagram of an acceleration sensor including a MEMS for measuring drive and / or readout voltage;

[0031] Figure 6 A schematic diagram showing another MEMS for measuring voltage; and

[0032] Figure 7 A schematic diagram of another MEMS for measuring voltage is shown. DETAILED DESCRIPTION

[0033] Figure 1 Schematic diagram of a micro-electromechanical system, ie, a MEMS 100 , for measuring a voltage U. The MEMS 100 comprises a sample mass 110 , a mechanical spring element 120 and a trimming electrode 130 .

[0034] The sample mass 110 is mounted above the substrate by means of a mechanical spring element 120 so that it can be moved relative to the substrate along the vibration direction x. Figure 1 In the example shown, the substrate is parallel to the plane of the drawing, for example below the sample mass 110. In principle, the sample mass 110 can have any shape as long as it can be used to achieve the effects described below. Typically, the sample mass 110 will have an extension relative to the plane of the substrate, i.e. the dimension parallel to the substrate is much larger than the extension perpendicular to the substrate.

[0035] The spring element 120 is Figure 1 1 is shown purely symbolically and can in principle assume any shape which allows linear guidance of the sample mass 110 along a specific vibration direction x. Vibrations in a plurality of different vibration directions are also possible. Preferably, however, the spring element 120 only allows the sample mass 110 to vibrate along the vibration direction x, i.e. the sample mass 110 is free to move in the vibration direction x except for being constrained by the restoring spring force, while the movement perpendicular to the vibration direction x is strongly suppressed and therefore negligibly small in comparison. The spring element 120 is connected to the substrate via an anchor 125.

[0036] For example, by supplying electric charge to the trimming electrode 130 and / or the sample mass 110, a voltage U may be applied to the trimming electrode 130 relative to the sample mass 110. The magnitude of the voltage U may be known in the process.

[0037] like Figure 1 As shown, the sample mass 110 may include a counter electrode 112. The voltage U may then be applied only between the trimming electrode 130 and the corresponding counter electrode 112. The counter electrode 112 may be made of the same material as the rest of the sample mass 110 and be conductively connected to the sample mass. However, the counter electrode 112 may also be electrically insulated from the rest of the sample mass 110.

[0038] The voltage U generates an electrostatic force on the sample mass 110. In the process, the tuning electrode 130 is designed or configured relative to the sample mass 110 so that when the sample mass 110 is deflected along the vibration direction x, the electrostatic force resists the mechanical spring force generated by the spring element 120. Therefore, when the spring element 120 moves the sample mass back to its initial position, i.e., to the left, in the case of a rightward deflection, for example, a force in the deflection direction, i.e., to the right, is generated between the tuning electrode 130 and the sample mass 110. Therefore, by changing the voltage U at the tuning electrode 130, the effective spring constant of the entire vibration system can be changed, depending on which part of the mechanical spring force is compensated by the electrostatic spring force. Similarly, in the case where the voltage U is fixed to a specific range, a specific compensation ratio can be achieved by the construction of the MEMS 100 (i.e., in particular the sample mass 110, the spring element 120 and / or the tuning electrode 130). The effective spring constant or the difference between the mechanical spring force and the electrostatic force then naturally determines the resonant frequency of the vibration of the sample mass 110 along the vibration direction x.

[0039] The MEMS 100 may have drive electrodes adapted to put the sample mass 110 into motion along the vibration direction x. The MEMS 100 may also include readout electrodes adapted to measure the vibration frequency of the vibrations of the sample mass 110 generated in this way. However, the sample mass 110 may also be put into vibration in other ways, for example by movement of the MEMS 100 or by coupling to other vibration systems. Therefore, the drive electrodes are not absolutely necessary and are therefore not included in the description. Figure 1 Shown in.

[0040] It is also possible to dispense with a special readout electrode, since the vibration frequency can also be detected via the trimming electrode 130. For example, at a constant voltage U, the change in capacitance of the capacitor formed by the trimming electrode 130 and the counter electrode 112 can be determined via a charge measurement. This enables the determination of a distance, the time course of which enables the determination of the vibration frequency. However, other readout schemes are also conceivable. In this case, at least one trimming electrode 130 serves as a readout electrode.

[0041] Furthermore, the MEMS 100 has a control unit (not shown) which is adapted to control the MEMS 100 in such a way that it performs a method for measuring a voltage U applied between the trimming electrode 130 and the sample mass 110. In this process, the control unit can be formed on the substrate of the MEMS 100. However, the control unit can also be configured externally. The method performed by the MEMS 100 can be referred to Figure 2 This is schematically summarized as follows.

[0042] At S110 , a voltage U to be measured is applied to the trimming electrode 130 , thereby generating an electrostatic force on the sample mass 110 , which partially compensates for the mechanical spring force.

[0043] At S120, the magnitude of the voltage U to be measured is determined from the measured vibration frequency of the sample mass 110. Since the mechanical properties of the MEMS 100 are in principle predetermined by the manufacturing process and are thus known, the influence of the voltage U on the effective spring constant and thus on the vibration frequency of the sample mass 110 can be determined. In addition, the vibration frequency with and without the voltage U applied to the trimming electrode 130 can be measured under otherwise constant operating parameters. The magnitude of the voltage U can also be inferred by comparing the measurement results.

[0044] At S130, a change in the voltage U to be measured is determined based on the change in the measured vibration frequency. In particular, small changes in the voltage U in the millivolt range that occur over a long period of time, for example, over 1 year or 10 years, can be determined via the change in the vibration frequency with higher accuracy than direct voltage measurement because the change in the vibration frequency can be determined with high accuracy.

[0045] In this way, small changes in a voltage that is assumed to be constant can be accurately determined over a long period of time. Preferably, between 50% and 90%, preferably between 60% and 80%, more preferably 75% of the mechanical spring force is compensated by applying the voltage U to the trimming electrode 130. As will be explained further below, with this parameter selection or this layout of the MEMS 100, the MEMS 100 is sufficiently sensitive to changes in the voltage U to be measured.

[0046] The method is preferably performed when the MEMS 100 is stationary or when it can be expected to be in a stationary position, such as during the start of operation of the MEMS 100 or of the device in which the voltage U to be measured is used. In principle, the method is based on detecting a change in the effective spring constant, which is reflected in a change in the vibration performed. Since the movement of the MEMS 100 and in particular the acceleration can disturb such vibrations, the operation is preferably stationary for reliable results. Otherwise, it is necessary to detect and compensate for the disturbance.

[0047] like Figure 3As shown schematically, the voltage U to be measured can be a reference voltage, the size of which is the basis for further measurement and / or calculation operations. In this process, the reference voltage U is required for the operation of the electronic component 200, such as a voltage converter, an analog-to-digital converter, a sensor (e.g., an acceleration sensor), and is generated by a reference voltage source 210. The electronic component 200 performs measurement and / or calculation operations based on the reference voltage U. For example, the reference voltage U can be used as a reference or comparison value for various voltage and / or current variables used in the electronic component 200. As described above, the measurement results of the electronic component 200 constructed as a sensor can also be related to the size of the reference voltage. In this process, the MEMS 100, which is also supplied with the reference voltage U, can be part of the electronic component 200 or can be used as a separate component.

[0048] like Figure 2 As symbolically indicated by the dashed line in , the method may then optionally further comprise, at S140 , correcting further measurement and / or calculation operations by replacing the expected reference voltage with the measured reference voltage U. This then enables long-term stable operation of the reference voltage-based functions of the electronic component 200 .

[0049] Particularly preferred is a configuration of the MEMS in which, when the trimming electrode 130 is applied with the voltage U to be measured, the resonant frequency of the vibration of the sample mass 110 changes by a value in the range of 100 ppm to 1000 ppm of the resonant frequency with a change in voltage of 1 mV. This enables particularly accurate and reliable measurement of the voltage U.

[0050] For example, in Figure 4 A schematic diagram of the design of a MEMS 100 that can meet the above requirements is shown in . For example, all components are made of silicon.

[0051] like Figure 4 As shown, the sample mass 110 can be designed as a rectangular perforated structure, in which the trimming electrode 130 is arranged. Therefore, the trimming electrode 130 forms a plate capacitor with the side of the recess in the sample mass 110 in a space-saving manner.

[0052] The sample mass 110 is mounted in a symmetrical manner at its four corners above the base plate via spring elements 120 which are configured as folded bending beam springs. In the process, the bending beam springs extend perpendicularly to the vibration direction x and thus allow the sample mass 110 to vibrate in this direction, while the movement in other directions is suppressed to a negligible extent.

[0053] The vibration of the sample mass 110 is driven by a drive electrode 140 arranged laterally in the vibration direction x, which drive electrode is engaged in the counter electrode 114 of the sample mass 110. The vibration parameter is read out via the trimming electrode 130, which therefore also serves as a readout electrode 150. However, the drive electrode 140 can also serve as the readout electrode 150, or a separate readout electrode 150 can be provided.

[0054] The force acting between the trim electrode 130 and the sample mass 110 produces an electrostatic spring constant for the vibration of the sample mass, which is defined as follows:

[0055]

[0056] Where N is the number of trimming electrodes, h is their height perpendicular to the substrate, L is their length parallel to the substrate and perpendicular to the vibration direction x, and d is the gap distance between the sample mass 110 and the trimming electrode 130 at rest.

[0057] This results in the effective spring constant k eff Determine the resonant frequency:

[0058]

[0059] Where m represents the mass of the sample mass 110, and the mechanical spring constant k m is given as:

[0060]

[0061] Where n is the number of spring elements, E Si is the elastic modulus of silicon, h is the height of the spring elements 120 perpendicular to the substrate, b is their width in the vibration direction x, and l is their length parallel to the substrate and perpendicular to the vibration direction x.

[0062] Then, the sensitivity of the resonant frequency to the change of the voltage U is:

[0063]

[0064] If the compensation factor β is introduced, it satisfies: β·k m =g·U 2 .

[0065] Thus, a high sensitivity can be achieved, for example, by a relatively large voltage U or a large factor, i.e. the largest possible effective trimming electrode area N·L·h with the smallest possible gap distance d. It is also possible to achieve a small mass m of the sample mass 110 and a small mechanical spring constant k m , that is, high sensitivity is achieved through small width b and large length l.

[0066] If the resolvable change in voltage is quantified as a fraction of the voltage U to be measured using dU=α·U, the resulting relationship between the resulting change in frequency df and the output frequency f is as follows:

[0067]

[0068] The relative frequency stability is about 10ppm, that is, a frequency change of the order of 10ppm of the output frequency cannot be quickly identified as a measurement signal. Therefore, it should be satisfied:

[0069]

[0070] For example, if α=50ppm is selected, that is, the drift of the reference voltage within one year is already very low, then the resulting compensation factor β is:

[0071] β>0.828

[0072] If β is known, then considering that β·k must satisfy m =k el The fact that you can adjust Figure 4 The various parameters of MEMS100 are set to the following specifications:

[0073]

[0074] Based on these setting specifications, MEMS 100 can in principle be adapted to any voltage U to be measured, ie MEMS 100 can be configured for measuring a specific reference voltage with a known value range. In this way, a high-precision voltmeter can be realized for slowly changing voltages.

[0075] Furthermore, it helps in this process that MEMS 100 is configured so that when the voltage U to be measured is applied to trim electrode 130 , the vibration system generated by the vibration of sample mass 110 has a performance index greater than 1000. This makes the resonant frequency of the system particularly easy to measure.

[0076] For this purpose, but also to protect the components of the MEMS 100, the MEMS 100 may have a housing 160, which is Figure 4 1 and 2. The housing 160 is symbolically depicted as a dotted fence of the MEMS components. In particular, the housing 160 includes the sample mass 110, the spring element 120, the trim electrode 130, the drive electrode 140 and the readout electrode 150. The housing 160 and thus the MEMS components therein can be evacuated. This eliminates air resistance and the resulting damping, thereby (further) improving the performance of the system.

[0077] Of particular interest is the use of the above techniques in an acceleration sensor 400. Such an acceleration sensor 400 is Figure 5 It is schematically shown in FIG.

[0078] The acceleration sensor 400 includes a MEMS 100 adapted to measure the acceleration acting on the acceleration sensor 300 along the vibration direction x of the sample mass 110 by measuring the vibration frequency of the sample mass 110. For this purpose, the trimming electrode 130 may be used as a readout electrode 150, such as Figure 4 However, it may also be advantageous to detect the vibrations of the sample mass 110 via separate readout electrodes 150. They may be arranged together with the drive electrodes 140 on the side of the sample mass 110, as shown in FIG. Figure 5 However, the lateral electrodes can be operated as both drive electrodes and readout electrodes by time division multiplexing.

[0079] In this way, any acceleration sensor 400 constructed according to the above considerations can also be used as a device for voltage measurement if a separate connection of the trim electrode 130 to a voltage source is possible. This allows implementing additional functionality with the acceleration sensor 400 beyond just acceleration measurement.

[0080] Also like Figure 5 As shown, the voltage U to be measured is preferably equal to a reference voltage for determining an operating voltage applied to the drive electrode 140 or the readout electrode 150. This means that the acceleration sensor 400 includes a reference voltage source 410. The reference voltage generated by this reference voltage source 410 is applied to the trimming electrode 130 and the voltage generator 420. The voltage generator 420 generates an operating voltage for the drive electrode 140 and / or the readout electrode 150 from the reference voltage, for example by proportionally adjusting and / or modulating the reference voltage U, for example in the form of a sinusoidal modulation.

[0081] As described above, the proportionality factor that converts the measured vibration into acceleration is quadratically related to the operating voltage and, therefore, also to the reference voltage U. By applying the reference voltage U to the trimming electrode 130 and monitoring the effect of possible changes in the reference voltage U on the vibration system, drift of the proportionality factor can be detected and corrected. In this way, a highly accurate and long-term stable acceleration sensor 400 can be provided.

[0082] The configuration of the MEMS 100 described above is purely exemplary. A large number of alternative configurations are possible, as long as the goal of causing an accurate measurable change in the vibration of the sample mass 110 by changing the voltage at the trim electrode 130 is achieved. The correct layout of such a sensor can be derived by a person skilled in the art in a manner similar to the considerations made above.

[0083] Figure 6 and Figure 7 An example of this alternative configuration is shown. Figure 6 As shown, the MEMS 100 may have a sample mass 110 which is configured as a beam extending mainly in the deflection direction x. At each of its ends, the sample mass 110 is connected to a substrate via two spring elements 120 which are configured as folded bending beam springs.

[0084] A row of drive electrodes 140 and readout electrodes 150 configured as comb electrodes is also mounted on the substrate, wherein the same electrode comb can be used as both the drive electrode 140 and the readout electrode 150. The drive / readout electrodes 140, 150 are joined in a counter electrode 116 configured in the form of a comb electrode on the sample mass 110. By applying a voltage between the drive / readout electrodes 140, 150 and the counter electrode 116, the sample mass 110 can be placed in vibration along the vibration direction x. For example, the vibration can be determined by detecting the charge on the electrode at a constant voltage or by detecting the voltage at a constant charge (i.e., when the current flowing to the electrode is interrupted).

[0085] The trimming electrode 130 is mounted on the back side of the counter electrode 116 and resists the mechanical spring force when a voltage is applied to them. As mentioned above, the trimming electrode 130 can also be used as a readout electrode 130.

[0086] Figure 7 shows a schematic configuration of a MEMS 100, which is basically derived from Figure 4 The setup of the MEMS 100 shown is replicated. In this process, two sample masses 110 share a set of centrally arranged drive / readout electrodes 140, 150. In this area, the two sample masses 110 are connected by a coupling spring 122, which allows the two sample masses 110 to vibrate along the vibration direction x (also in opposite directions). In other aspects, Figure 7 Each half of the MEMS 100 is configured to correspond to Figure 4 Therefore, no further description is necessary.

[0087] As with many other possible constructions, Figure 6 and Figure 7 Both configurations also make it possible to measure a voltage (in particular a reference voltage) by applying a voltage to the trimming electrode 130 and monitoring the effect on the vibration characteristics. Thus, a person skilled in the art has several possibilities for solving the initially mentioned problem within the scope of the present technical solution.

Claims

1. A method for measuring voltage by means of a microelectromechanical system, i.e., MEMS (100), said microelectromechanical system comprising: a sample mass (110) mounted above the substrate by means of a mechanical spring element (120) so as to be movable relative to the substrate along a vibration direction (x); a trimming electrode (130) adapted to generate an electrostatic force on the sample mass (110) when a voltage is applied, the electrostatic force resisting the mechanical spring force generated by the spring element (120) when the sample mass (110) is deflected along the vibration direction (x); a drive electrode (140) adapted to place the sample mass (110) in motion along the vibration direction (x); and a readout electrode (150) adapted to measure the vibration frequency of the vibration of the sample mass (110) generated in this way, wherein the method comprises: applying a voltage (U) to be measured to the trimming electrode (130); measuring the magnitude of the voltage (U) to be measured from the measured vibration frequency of the sample mass (110); and detecting a change in the voltage (U) to be measured based on a change in the measured vibration frequency.

2. The method according to claim 1, wherein the voltage (U) to be measured is a reference voltage, the magnitude of which is the basis for further measurement and / or calculation operations; and the method further comprises: correcting the further measurement and / or calculation operations by replacing the expected reference voltage with the measured reference voltage.

3. The method according to any one of the preceding claims, wherein, by applying the voltage (U) to be measured to the trimming electrode (130), between 50% and 90%, preferably between 60% and 80%, more preferably 75% of the mechanical spring force is compensated.

4. The method according to any one of the preceding claims, wherein the method is performed when the MEMS (100) is stationary.

5. A microelectromechanical system, i.e., MEMS (100), for measuring voltage, comprising: a sample mass (110) mounted above the substrate by means of a mechanical spring element (120) so as to be movable relative to the substrate along a vibration direction (x); a trimming electrode (130) adapted to generate an electrostatic force on the sample mass (110) when a voltage is applied, the electrostatic force resisting the mechanical spring force generated by the spring element (120) when the sample mass (110) is deflected along the vibration direction (x); a drive electrode (140) adapted to place the sample mass (110) in motion along the vibration direction (x), and a readout electrode (150) adapted to measure the vibration frequency of the vibration of the sample mass (110) generated in this way; and a control unit adapted to control the MEMS (100) in such a way as to perform the method according to any one of the preceding claims.

6. The MEMS (100) according to claim 5, wherein the MEMS (100) is designed such that when the trimming electrode (130) is applied with the voltage (U) to be measured, in the case where the change in voltage is 1 mV, the resonant frequency of the vibration of the sample mass (110) changes by a value within the range of 100 ppm to 1000 ppm of the resonant frequency.

7. The MEMS (100) according to claim 6, wherein the change in the resonant frequency with respect to the change in voltage is not linearly correlated with the offset of the sample mass (110); and / or the resonant frequency changes with the ambient temperature; and the control unit is adapted to take these correlations into account by calibration when detecting the voltage (U) to be measured.

8. The MEMS (100) according to any one of claims 5 to 7, wherein the MEMS (100) is designed such that when the trimming electrode (130) is applied with the voltage (U) to be measured, the vibration system generated by the vibration of the sample mass (110) has a performance index greater than 1000.

9. The MEMS (100) according to any one of claims 5 to 8, wherein the sample mass (110), the spring element (120), the trimming electrode (130), the drive electrode (140) and the readout electrode (150) are evacuated.

10. An acceleration sensor (400) for measuring acceleration, comprising: the MEMS (100) according to any one of claims 5 to 9, wherein the MEMS (100) is adapted to measure the acceleration acting on the acceleration sensor (300) along the vibration direction (x) of the sample mass (110) by measuring the vibration frequency of the sample mass (110).

11. The acceleration sensor (300) according to claim 10, wherein the voltage (U) to be measured is equal to the reference voltage for determining the operating voltage applied to the drive electrode (140) and / or the readout electrode (150).

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