METHOD FOR TEMPERATURE COMPENSATION OF A MICROELECTROMECHANICAL SENSOR, AND MICROELECTROMECHANICAL SENSOR

Abstract

A method for temperature compensation of a MEMS sensor. The method includes: in a balancing step, a temperature gradient is produced by a thermal element and a first and a second temperature are determined at a first and a second temperature measurement point, wherein a deflection of a movable structure produced by the temperature gradient is measured and a compensation value is ascertained dependent on the first and second temperature and the deflection; in a measurement step, a physical stimulus is measured by way of a deflection of the movable structure and a third and fourth temperature is determined at the first and second temperature measurement points; in a compensation step, a measured value of the physical stimulus is ascertained dependent on the measured deflection, the third and fourth temperature and the compensation value. A method is also provided including: a regulation step, and a measurement step.

Claims

1. A method for temperature compensation of a microelectromechanical sensor, wherein the sensor has a movable structure configured to measure a physical stimulus and the method comprises the following steps: in a balancing step, producing a temperature gradient by at least one thermal element in such a way that a first and second partial region of the sensor are at different temperatures, wherein a first temperature is determined at a first temperature measurement point arranged in the first partial region and a second temperature is determined at a second temperature measurement point arranged in the second partial region, and wherein a deflection of the movable structure produced by the temperature gradient is measured and a compensation value is determined dependent on the first and second temperature and the deflection; in a measurement step, measuring the physical stimulus using a deflection of the movable structure, wherein a third temperature is determined at the first temperature measurement point and a fourth temperature is determined at the second temperature measurement point; and in a compensation step, ascertaining a measured value of the physical stimulus dependent on the measured deflection, the third and fourth temperatures, and the compensation value.

2. The method as recited in claim 1, wherein in the balancing step, a plurality of different temperature gradients are produced by the thermal element, with, for each temperature gradient, an associated deflection and temperatures at the first and second temperature measurement points being determined, the compensation value being ascertained dependent on the temperatures and deflections.

3. A method for temperature compensation of a microelectromechanical sensor, wherein the sensor has a movable structure for measuring a physical stimulus, and the method comprises the following steps: in a regulation step, determining a temperature difference between a first and a second temperature measurement point, the first and second temperature measurement points being spaced apart from one another, a local temperature increase within the sensor being brought about by at least one thermal element, regulation of the temperature increase taking place in such a way that the temperature difference between the first and second temperature measurement points is minimized; and in a measurement step, measuring the physical stimulus using a deflection of the movable structure.

4. The method as recited in claim 1, wherein the method further comprises: in an additional balancing step, increasing the temperature of the entire sensor by the thermal element to a plurality of temperature values, and for each temperature value, the physical stimulus is measured using the deflection of the movable structure, wherein a temperature dependency of an offset of the sensor, and/or of a sensitivity of the sensor is ascertained dependent on the temperature values and the deflections.

5. A microelectromechanical sensor, comprising: a movable structure; at least one thermal element; two temperature measurement elements; and an evaluation unit: wherein the movable structure is configured to measure a physical stimulus, and the sensor is configured to: produce a temperature gradient by at least one thermal element in such a way that a first and second partial region of the sensor are at different temperatures, wherein a first temperature is determined at a first temperature measurement point arranged in the first partial region and a second temperature is determined at a second temperature measurement point arranged in the second partial region, and wherein a deflection of the movable structure produced by the temperature gradient is measured and a compensation value is determined dependent on the first and second temperature and the deflection, measure the physical stimulus using a deflection of the movable structure, wherein a third temperature is determined at the first temperature measurement point and a fourth temperature is determined at the second temperature measurement point, and ascertain a measured value of the physical stimulus dependent on the measured deflection, the third and fourth temperatures, and the compensation value.

6. A microelectromechanical sensor, comprising: a movable structure; at least one thermal element; two temperature measurement elements; and an evaluation unit: wherein the movable structure is configured to measure a physical stimulus, and the sensor is configured to: determine a temperature difference between a first and a second temperature measurement point, the first and second temperature measurement points being spaced apart from one another, a local temperature increase within the sensor being brought about by at least one thermal element, regulation of the temperature increase taking place in such a way that the temperature difference between the first and second temperature measurement points is minimized; and measure the physical stimulus using a deflection of the movable structure.

7. The sensor as recited in claim 5, wherein the sensor has a first and a second partial element, the first and second partial elements being connected together and the movable structure being arranged in a cavity formed between the first and second partial elements.

8. The sensor as recited in claim 5, wherein the movable structure is an asymmetrical rocker structure having a first and a second rocker arm, the rocker structure being mounted rotatably about an axis of rotation and the first and second rocker arms being formed asymmetrically to each other with respect to the axis of rotation.

9. The sensor as recited in claim 7, wherein the thermal element is a resistance element arranged in the first partial region, the resistance element being configured to give off ohmic heat to the first partial region, the evaluation unit being configured to determine the first and third temperature using an electric resistance measurement of the resistance element.

10. The sensor as recited in claim 5, wherein the evaluation unit includes at least one CMOS structure, the CMOS structure having at least one temperature measurement element.

11. The sensor as recited in claim 5, wherein the thermal element is arranged in a vertical direction above the movable structure, the movable structure being formed from a first function layer of the sensor and the thermal element being formed from a second function layer of the sensor, each of the thermal element and the movable structure being connected mechanically to a common substrate using an anchor.

12. The sensor as recited in claim 6, wherein the sensor has a first and a second partial element, the first and second partial elements being connected together and the movable structure being arranged in a cavity formed between the first and second partial elements.

13. The sensor as recited in claim 6, wherein the movable structure is an asymmetrical rocker structure having a first and a second rocker arm, the rocker structure being mounted rotatably about an axis of rotation and the first and second rocker arms being formed asymmetrically to each other with respect to the axis of rotation.

14. The sensor as recited in claim 6, wherein the evaluation unit includes at least one CMOS structure, the CMOS structure having at least one temperature measurement element.

15. The sensor as recited in claim 6, wherein the thermal element is arranged in a vertical direction above the movable structure, the movable structure being formed from a first function layer of the sensor and the thermal element being formed from a second function layer of the sensor, each of the thermal element and the movable structure being connected mechanically to a common substrate using an anchor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] FIG. 1A shows a specific example embodiment of the sensor according to the present invention.

[0022] FIG. 1B illustrates the deflection caused by a temperature gradient.

[0023] FIG. 2 shows a further specific example embodiment of the sensor according to the present invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0024] FIG. 1 illustrates one specific embodiment of the sensor 1 according to the present invention, which is formed by a microelectromechanical structure that is arranged on a substrate 17. Below the substrate 17 there is arranged an ASIC 6 that is connected to the MEMS structure by way of a bonding wire connection 15. The MEMS structure comprises a movable structure 2 that here is formed as a rocker 2 suspended from a torsion spring 19. The rocker 2 consists of two rocker arms 11, 12, and has an additional mass 18 on the right-hand rocker arm 12, so that under a vertical acceleration applied from the outside, owing to the asymmetrical mass distribution, a torque is produced that brings about a deflection of the rocker 2 by way of which the external acceleration can be detected (Z-acceleration sensor). The movable structure 2 is arranged in a cavity 7 formed by a cap 10, in order to create a defined gas atmosphere that serves to damp the movements of the rocker 2.

[0025] If a temperature gradient is then applied to the sensor 1, as is caused for example by heat transfer from a printed circuit board lying under the sensor 1, a deflection of the movable structure 2 results even without external acceleration, solely due to the temperature gradient. This effect comes about substantially in that the impulse transfer of a particle striking an area depends on the temperature difference between the area and the gas, and the gas in the event of such a temperature difference thus exerts a slightly increased or reduced pressure on the area. In a perfectly symmetrical structure, the gas particles would exert forces of the same size on both rocker arms 11. Since, however, the two rocker sides 11, 12 are perforated differently for the etching process necessary to form the rocker 2, an asymmetrical moment that turns the structure 2 results.

[0026] In order to reduce or compensate for this measuring error, the sensor 1 according to the present invention has the following further structures: within the cavity 7, there are in this example two heating resistors 3, 3′, which by way of a measurement of the electrical resistance also function simultaneously as temperature measurement elements 4, 5. The upper heating structure 3 and the lower heating structure 3′ in the MEMS cavity 7 can be actuated and evaluated separately. Usually the ASIC 6 responsible for the evaluation lies below the MEMS structure and in this example it also has “top structuring” with a heating structure 3″. Since the latter in general is made of metal, this structure 3″ is more suitable for generating heat, but less so for measuring the temperature. There are better measuring options in the corresponding ASIC processes for measuring temperature, such as using diodes.

[0027] According to the present invention, the procedure may now be, for example, as follows: [0028] when calibrating the component 1, a temperature gradient is generated in a controlled manner by subjecting the structures 3, 3′, 3″ to a current so that the heating wires heat up and a first partial region 8 is at a different temperature than a second partial region 9 (indicated in FIG. 1b by different hatching). [0029] once the thermal time constants permit temperature control of the component, the change in the signal (i.e. the deflection) is measured relative to the change in the resistance. Delta ACC-Z:=DAZ, Delta Temp gradient=DTG. [0030] a compensation value K=−DAZ/DTG is calculated and programmed in the component for compensation, or alternatively made available to the end user in order to carry out the compensation outside the sensor 1. [0031] the ASIC 6 can now accordingly, with a suitable frequency (in general, thermal time constants are in the region of a few Hz), determine the gradient and calculate the updated values with K and add them to the digital acceleration value. [0032] a compensated value is then available at the output.

[0033] The influence of the temperature gradient can also be treated differently with the heating structure. For the example, the ASIC 6 is in direct contact with the printed circuit board (PCB) underneath, i.e. heating always takes place from underneath. The heating structure above the MEMS can now be heated in order to bring the gradient to zero in a control loop, and thus to remove or reduce the temperature gradient.

[0034] In FIG. 2, a particularly beneficial arrangement for MEMS components with two freely adjustable MEMS planes 21, 22 that lie one above another is proposed (the planes 21, 22 are marked by hatching). Such MEMS layers 21, 22 that lie one above another and can be freely coupled can be realized using MEMS production processes known from the prior art. A structure 3, 13 is proposed that is formed in the second MEMS layer 22 and is arranged in a free-floating manner above a partial region 25 of a movable structure 2. The movable structure 2 in this region is formed only in the first MEMS plane 21. This element 3, 13 can be anchored to the MEMS substrate 17 in an edge region or by way of a cutout 24 in the movable structure 2. At the same time, a heating and measuring element 3′, 13′ can be arranged below a partial region of the movable structure 2. In one particularly beneficial arrangement, the heating and measurement elements 3, 13, 3′, 13′ arranged above and below the movable structure 2 span the same partial region and are arranged symmetrically to each other. In the case of a movable structure 2 that can perform a rotary movement 23 about an axis lying parallel to the substrate surface, it is in addition beneficial to use in each case two pairs 3, 13 or 3′, 13′ of heating and measuring elements located above and below, which are arranged symmetrically to each other with respect to the axis of rotation. In a similar way, such a pair 3″, 13″ of heating elements may be provided as part of the ASIC 6.