SENSOR SYSTEM, METHOD FOR OPERATING A SENSOR SYSTEM

Abstract

A sensor system including a chip arrangement, the chip arrangement including a sensor and an acceleration sensor, and the sensor system including a processor circuit. The processor circuit is configured in such a way that: one or multiple temperature-dependent variables and/or properties of the sensor are ascertained, and an offset of a signal of the acceleration sensor induced by a temperature gradient is corrected with the aid of the one or the multiple ascertained temperature-dependent variables and/or properties of the sensor.

Claims

1. A sensor system, comprising: a chip arrangement including a sensor and an acceleration sensor; and a processor circuit configured in such a way that: one or multiple temperature-dependent variables and/or properties of the sensor are ascertained, and an offset of a signal of the acceleration sensor induced by a temperature gradient is corrected with using the one or the multiple ascertained temperature-dependent variables and/or properties of the sensor.

2. The sensor system as recited in claim 1, wherein the chip arrangement includes a MEMS chip arrangement, the MEMS chip arrangement including at least one MEMS chip including the acceleration sensor.

3. The sensor system as recited in claim 2, wherein the offset of the signal of the acceleration sensor induced by the temperature gradient is caused by a temperature gradient in a perpendicular direction, perpendicular to a main extension plane of the MEMS chip including the acceleration sensor.

4. The sensor system as recited in claim 3, wherein the MEMS chip including the acceleration sensor has the temperature gradient in the perpendicular direction between a substrate and a cap of the MEMS chip.

5. The sensor system as recited in claim 3, wherein the chip arrangement includes an ASIC structure, the processor circuit is configured in such a way that the offset of the signal of the acceleration sensor induced by the temperature gradient is corrected in such a way that: with the aid of the one or the multiple ascertained temperature-dependent variables and/or properties of the sensor, a temperature difference between the ASIC structure and the sensor s ascertained and/or estimated, and the offset of the signal of the acceleration sensor induced by the temperature gradient is corrected with the aid of the ascertained and/or estimated temperature difference.

6. The sensor system as recited in claim 5, wherein the MEMS chip arrangement and the ASIC structure are situated offset in the perpendicular direction.

7. The sensor system as recited in claim 5, wherein the ASIC structure includes an integrated temperature sensor, or a temperature sensor is associated with the ASIC structure, the temperature sensor being configured in such a way that a temperature of the ASIC structure is ascertained using the temperature sensor, the processor circuit being configured in such a way that the temperature difference between the ASIC structure and the sensor is ascertained and/or estimated with the one or the multiple ascertained temperature-dependent variables and/or properties of the sensor and additionally with the aid of the ascertained temperature of the ASIC structure.

8. The sensor system as recited in claim 5, wherein the processor circuit is configured in such a way that the offset of the signal of the acceleration sensor induced by the temperature gradient is corrected with the aid of the following relationship:
Offset.sub.corrected=Offset.sub.measured−const.sub.TGO*dT, wherein: Offset.sub.corrected is the corrected offset of the signal of the acceleration sensor, Offset.sub.measured is a measured offset of the signal of the acceleration sensor, const.sub.TGO is a constant factor, dT is the temperature difference between the ASIC structure and the sensor, const.sub.TGO is a factor specific to a sensor type and/or a sensor channel.

9. The sensor system as recited in claim 8, wherein const.sub.TGO is ascertainable in a qualification phase and/or startup phase of the sensor system.

10. The sensor system as recited in claim 1, wherein the signal of the acceleration sensor is a signal of a first axis of the acceleration sensor, the acceleration sensor having at least one second axis, the processor circuit being configured in such a way that an offset of a further signal of the second axis of the acceleration sensor induced by a temperature gradient is corrected with using the one or the multiple ascertained temperature-dependent variables and/or properties of the sensor.

11. The sensor system as recited in claim 1, wherein the sensor is a rotation rate sensor.

12. The sensor system as recited in claim 11, wherein the one or the multiple temperature-dependent variables and/or properties include one or multiple of the following variables and/or properties: a drive frequency of the rotation rate sensor, a drive quality of a drive oscillation of the rotation rate sensor, a drive voltage required to obtain a fixed oscillation amplitude of a drive oscillation of the rotation rate sensor, a quadrature of the rotation rate sensor.

13. The sensor system as recited in claim 1, wherein the processor circuit includes a microcontroller or is a microcontroller.

14. A method for operating a sensor system, the sensor system including a chip arrangement including a sensor and an acceleration sensor and a processor circuit, the method comprising the following steps: in an ascertainment step, ascertaining one or multiple temperature-dependent variables and/or properties of the sensor; and in a correction step, correcting an offset of a signal of the acceleration sensor induced by a temperature gradient using the one or the multiple ascertained temperature-dependent variables and/or properties of the sensor.

15. The method as recited in claim 14, wherein the chip arrangement includes an ASIC structure), the ASIC structure (20) including an integrated temperature sensor or a temperature sensor being associated with the ASIC structure, and wherein, in an ASIC temperature ascertainment step, a temperature of the ASIC structure is ascertained using the temperature sensor, in a temperature difference ascertainment step, with the aid of the processor circuit, a temperature difference between the ASIC structure and the sensor is ascertained and/or estimated with using the one or the multiple ascertained temperature-dependent variables and/or properties of the sensor and using the ascertained temperature of the ASIC structure, and in the correction step, with the aid of the processor circuit, the correction of the offset of the signal of the acceleration sensor induced by the temperature gradient is carried out as a function of the temperature difference ascertained and/or estimated in the temperature difference ascertainment step.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0046] FIG. 1 shows a schematic representation of a heat source which causes a temperature gradient.

[0047] FIGS. 2a and 2b show schematic representations of chip arrangements according to different specific embodiments of the present invention.

[0048] FIG. 3 schematically shows a method according to one specific embodiment of the present invention.

[0049] FIG. 4 schematically shows an ascertainment of a temperature difference according to one specific embodiment of the present invention.

[0050] FIGS. 5a, 5b, and 5c show schematic views of a sensor system according to different specific embodiments of the present invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0051] In the various figures, identical parts are always provided with identical reference numerals and generally are therefore each also only named or mentioned once.

[0052] FIG. 1 shows a schematic representation of a heat source 103, which may cause a temperature gradient in a sensor or a chip arrangement 100. Chip arrangement 100 is located in the vicinity of heat source 103, for example in the vicinity of an application processor 103 on printed circuit board (PCB) 104 of a smart phone. Depending on the relative position of chip arrangement 100 in relation to heat source 103, a vertical or lateral temperature gradient or also a combination thereof will form in the sensor module. For example, for the case in which chip arrangement 100 is situated at a first position 101 according to FIG. 1, a vertical temperature gradient results within MEMS chip 100, symbolized by block arrow 101′. For the case in which chip arrangement 100 is situated at a second position 102 according to FIG. 1, a lateral temperature gradient results within MEMS chip 100, symbolized by block arrow 102′. In this case, chip arrangement 100 means the entire sensor or the entire sensors including MEMS chip, evaluation ASIC, and outer packaging, for example, LGA substrate and molding compound. Therefore, a temperature gradient also forms in MEMS chip 13, which includes acceleration sensor 11 and is part of chip arrangement 100. The temperatures of a movable structure of the acceleration sensor (for example a rocker structure) and of substrate 13′ of MEMS chip 13 are accordingly not in thermal equilibrium. Substrate 13′ including the base electrodes may, for example, be somewhat warmer than the movable structure of acceleration sensor 11. Movements of the gas particles in the sensor cavity are induced by the thermal gradient, the impacts of which with the movable sensor structure may result in measurable parasitic deflections of the movable sensor structure (for example the rocker) and thus in offset signals.

[0053] FIG. 2a shows a schematic representation of a chip arrangement 1 according to one specific embodiment of the present invention. FIG. 2a shows a MEMS chip arrangement 10 of a sensor 12 designed as a rotation rate sensor 12′ and an acceleration sensor 11. Rotation rate sensor 12′ and acceleration sensor 11 are situated here on the same MEMS chip 13. Chip arrangement 1 or MEMS chip arrangement 10 thus includes only one single MEMS chip 13, which in turn includes sensors 11, 12′. MEMS chip 13 includes a substrate 13′ and a cap 13″, with the aid of which cavities for sensors 11, 12′ are formed. MEMS chip 13 is connected mechanically, for example, via an adhesive, and electrically, for example, via bond wires (not shown in the figure) or alternatively solder balls to an evaluation ASIC structure 20. ASIC structure 20 is situated in a perpendicular direction 200, perpendicular to a main extension plane 210 of MEMS chip 13 (or perpendicular to a substrate plane), below MEMS chip 13. ASIC structure 20 is mechanically connected via a further adhesive layer 22 to substrate 21 of the LGA housing.

[0054] MEMS chip 13 and ASIC structure 20 are cast using a molding compound 25 for mechanical protection. Sensors 11, 12′ are mechanically and electrically connected to printed circuit board 204 via solder contacts 26 of LGA substrate 21. ASIC structure 20 includes an integrated temperature sensor 20′, using which a temperature of ASIC structure 20 may be ascertained or measured. FIG. 2b shows a schematic representation of a chip arrangement 1 according to another specific embodiment of the present invention. The further specific embodiment according to FIG. 2b differs from the specific embodiment shown in FIG. 2a in that sensor 12 designed as rotation rate sensor 12′ and acceleration sensor 11 are each situated in separate MEMS chips 13, 14. Chip arrangement 1 thus includes a MEMS chip arrangement 10, which includes a MEMS chip 13 including acceleration sensor 11 and a further MEMS chip 14 including rotation rate sensor 12′. Chip arrangement 1 or MEMS chip arrangement 10 thus includes two separate MEMS chips 13, 14, which are situated adjacent to one another. The two MEMS chips 13, 14 are jointly cast using molding compound 25.

[0055] FIG. 3 schematically shows a flowchart of a method according to one specific embodiment of the present invention, using which it is possible to compensate for or correct the TGO of acceleration sensor 11.

[0056] In an ASIC temperature ascertainment step 301, a temperature of ASIC structure 20 is ascertained with the aid of temperature sensor 20′ and read out by a processor circuit 40 (for example a microcontroller).

[0057] In an ascertainment step 302, before, during, and/or after ASIC temperature ascertainment step 301, one or multiple temperature-dependent variables and/or properties of rotation rate sensor 12′ are ascertained or read out by processor circuit 40. The one or the multiple temperature-dependent variables and/or properties may be, for example, a drive frequency of rotation rate sensor 12′. The following exemplary embodiment is explained on the basis of the drive frequency of rotation rate sensor 12′. However, the use of other temperature-dependent variables and/or properties of rotation rate sensor 12′ is alternatively or additionally also possible.

[0058] From the drive frequency of rotation rate sensor 12′, processor circuit 40 ascertains, in a temperature difference ascertainment step 303 with the aid of a stored algorithm, the local temperature in the area of the MEMS functional layer of rotation rate sensor 12′ or the temperature difference between the temperature of the MEMS functional layer T.sub.MEMS of rotation rate sensor 12′ and the temperature of the ASIC structure T.sub.ASIC.

[0059] The corresponding calculation may appear as follows, for example:

[00001]$dT=T_{MEMS}-T_{\mathrm{ASIC}}=\frac{Freq\left(T+dT\right)-Freq\left(T\right)}{\frac{dFreq\left(T\right)}{dT}}.$

[0060] In this case: [0061] Freq(T+dT) is the drive frequency presently read out by processor circuit 40, [0062] Freq(T) is the drive frequency which rotation rate sensor 12′ has in thermal equilibrium (ASIC temperature=MEMS temperature) at temperature T, and [0063] dFreq(T)/dT is the temperature dependence of the drive frequency in thermal equilibrium. This is dominant in a silicon-based MEMS rotation rate sensor 12′ over the above-mentioned temperature dependence of elasticity coefficient E, is determined by silicon, and is therefore (because of the relationship Freq˜E{circumflex over ( )}0.5) in the range of −30 ppm/K to 35 ppm/K.

[0064] Due to the arrangement of rotation rate sensor 12′ and acceleration sensor 11 on the same MEMS chip 13 or on different MEMS chips 13, 14 of the same MEMS chip arrangement 10, the MEMS functional layer of acceleration sensor 11 has a similar temperature as the MEMS functional layer of rotation rate sensor 12′, so that the local temperature of acceleration sensor 11 may also be inferred from the ascertained local temperature of rotation rate sensor 12′.

[0065] In a correction step 304, a corrected offset of acceleration sensor 11 is calculated in processor circuit 40 from ascertained temperature difference dT or the ascertained temperature difference between rotation rate sensor 12′ and ASIC structure 20, preferably a correction proportional with respect to the ascertained temperature difference according to

Offset.sub.corrected,i=Offset.sub.measured,i−const.sub.TGO,i*dT,

[0066] Offset.sub.corrected,i being the corrected offset of the signal of the acceleration sensor,

[0067] Offset.sub.measured,i being a measured offset of the signal of the acceleration sensor,

[0068] const.sub.TGO,i being a constant factor, in particular specific to the sensor type and/or the sensor channel,

[0069] dT being the temperature difference T.sub.MEMS−T.sub.ASIC between ASIC structure 20 and rotation rate sensor 12′. Factor const.sub.TGO,i may be determined in a qualification phase and/or startup phase of the sensor system. Index i in the above formula denotes possible detection axes or sensing directions x, y, z. Each channel of acceleration sensor 11 generally requires a separate correction coefficient.

[0070] Steps 301, 302, 303, 304 may preferably be carried out by or with the aid of a processor circuit 40 designed as a microcontroller.

[0071] FIG. 4 shows an ascertainment of a temperature difference dT between rotation rate sensor 12′ and ASIC structure 20 according to one specific embodiment of the present invention in a graph. The temperature of the ASIC structure is plotted on the x axis and the drive frequency of rotation rate sensor 12′ is plotted on the y axis. In thermal equilibrium (rotation rate sensor 12′ and ASIC structure 20 have an identical temperature), the drive frequency of rotation rate sensor 12′ follows characteristic curve 401. If value T.sub.1 is measured for the temperature of the ASIC structure, the drive frequency of rotation rate sensor 12′ would thus have to be at point 411. If a higher drive frequency of rotation rate sensor 12′ is actually measured/ascertained at point 412, this thus indicates that the local temperature in the MEMS functional layer of rotation rate sensor 12′ is lower than measured temperature value T.sub.1 of the ASIC structure. In thermal equilibrium between MEMS and ASIC, the measured drive frequency would result at a lower ASIC temperature T.sub.2 (point 413 on characteristic curve 401). Temperature difference dT=T.sub.2−T.sub.1 thus corresponds to the temperature difference between MEMS functional layer of rotation rate sensor 12′ and ASIC structure 20 and, due to the vertically stacked arrangement (thus in perpendicular direction 200) of ASIC structure 20 and MEMS chip arrangement 10, is also a measure of the local temperature gradient within MEMS chip 13 including acceleration sensor 11, which is responsible for the size of the parasitic TGO effects.

[0072] Ideally, it is possible that the correction coefficients or factors in the course of mass production are identical for all exemplars of the same sensor or sensor type. However, if fundamental properties change in the structure of the sensor, which may have an influence on the temperature distribution in the sensor, e.g., the thicknesses of ASIC structure 20, the MEMS substrate, or the molding compound above MEMS chips 13, 14, redetermining the correction coefficients is generally necessary or at least advantageous.

[0073] For precise direct measurement of the drive frequency of the rotation rate sensor, it may be advantageous for processor circuit 40 or the microcontroller, in addition to ASIC-internal variables, to also tap signals of an external clock generator, for example a frequency-stabilized oscillator, and compare them to the ASIC-internal signal. Such an oscillator would typically not be integrated in the sensor module itself.

[0074] In the course of FIGS. 3 and 4, a specific example embodiment of the method was described in which the drive frequency of rotation rate sensor 12′ was used as the temperature-dependent variable or property of rotation rate sensor 12′. However, alternatively or additionally to the drive frequency, other variables of a sensor 12 or a rotation rate sensor 12′ are also usable. Alternative variables or properties of rotation rate sensor 12′ for determining the local MEMS temperature may be, for example, the drive quality or drive voltage of rotation rate sensor 12′. In a sealed cavity, the quality of a mechanical resonator (thus also especially a rotation rate sensor 12′) varies proportionally with 1/square root (T) with temperature T. The drive voltage of the sensors is generally updated in the event of temperature changes in such a way that the oscillation amplitude remains constant, so that the mechanical and electrical sensitivity of the sensor remains unchanged. The drive voltage varies in this case according to T{circumflex over ( )}0.25, since the drive force is proportional to the square of the drive voltage. Therefore, the local temperature of the MEMS functional layer of the sensor may also be inferred by a precise measurement of the required drive voltage. In some rotation rate sensors, the quadrature (an interference signal phase shifted by 90° to the useful signal) varies with the temperature. If the relationship between quadrature and temperature is known, the local temperature of rotation rate sensor 12′ may also be inferred from the measurement of the quadrature (or the voltages or signals required for compensation of the quadrature).

[0075] If measured variables other than the drive frequency are used, the above formulas are adapted accordingly and other or new correction coefficients or factors are type-specifically ascertained.

[0076] A sensor system including a chip arrangement 1 may thus be implemented, chip arrangement 1 including a sensor 12 and an acceleration sensor 11, the sensor system including a processor circuit 40, so that processor circuit 40 is configured in such a way that: [0077] one or multiple temperature-dependent variables and/or properties of sensor 12 are ascertained, and [0078] with the aid of the one or the multiple ascertained temperature-dependent variables and/or properties of sensor 12, an offset of a signal of acceleration sensor 11 induced by a temperature gradient is corrected.

[0079] FIGS. 5a, 5b, and 5c show schematic representations of a sensor system 1 according to different specific example embodiments of the present invention, each in a top view of main extension plane 210. Processor circuit 40 is designed as a microcontroller in each case.

[0080] In FIG. 5a, the microcontroller for data correction is located outside chip arrangement 1, which includes MEMS chip arrangement 10 including sensor 12 and acceleration sensor 11. The microcontroller is mounted as a separate component 500 on application printed circuit board 30. Separate component 500, thus processor circuit 40, may be the application processor of a smart phone, for example.

[0081] In FIG. 5b, the microcontroller for data correction is located jointly with sensor 12 (or rotation rate sensor 12′) and acceleration sensor 11 in the same sensor module. In particular, the microcontroller may be integrated in ASIC structure 20 or the ASIC evaluation chip or may be connected to ASIC structure 20. The sensor module would then contain, for example, three chips 13, 14, 20.

[0082] A further alternative arrangement is shown in FIG. 5c. The microcontroller is integrated as an independent chip 520 separate from ASIC structure 20 or the ASIC evaluation chip in the same sensor module. The sensor module then contains four chips 13, 14, 20, 520. Alternatively, to the examples shown in FIGS. 5b and 5c, it is also possible in each case to integrate acceleration sensor 11 and sensor 12 on a shared MEMS chip 13.