Micromechanical sensor and method for manufacturing a micromechanical sensor

Abstract

Micromechanical sensor (200), comprising: - a substrate (1); - a movable mass element (10) sensitive in three spatial directions (x, y, z); - two x-electrode backs (20) with x-electrode fingers (21) arranged on them in a third functional layer of the sensor (200) for detecting lateral x-displacement of the movable mass element (10); two fastening elements (40, 50) with x-electrode fingers (22) arranged on them in the third functional layer for detecting lateral x-deflection of the movable mass element (10), two y-electrode backs (30) with y-electrode fingers (31) arranged on them in the third functional layer for detecting lateral y-displacement of the movable mass element (10), two fastening elements (60, 70) with y-electrode fingers (32) arranged on them in the third functional layer for detecting lateral y-deflection of the movable mass element (10), - z-electrodes (33, 34) for detecting a z-displacement of the movable mass element (10); wherein - each lateral electrode (20, 21, 22, 30, 31, 32) is attached to the substrate (1) by means of a fastening element (40, 50, 60, 70); wherein - the fastening elements (40, 50, 60, 70, 120, 130) of all electrodes (20, 21, 22, 30, 31, 32, 33, 34) are formed close to a connecting element (13) of the movable mass element (10) to the substrate (1).

Description

[0001] The invention relates to a micromechanical sensor. The invention further relates to a method for producing a micromechanical sensor. State of the art

[0002] Typically, acceleration sensors are designed as separate cores for each of the three Cartesian detection directions x, y, and z. The x- and y-channels are typically mass-spring structures that experience linear in-plane motion due to in-plane acceleration. Z-channel acceleration sensors are typically spring-mass structures that experience rotational motion around a rotation axis defined by torsion springs due to out-of-plane acceleration. An alternative to saving chip space is to implement a core that can detect all three acceleration directions with a single seismic mass.

[0003] Such structures, often referred to as single-mass oscillators, are known, for example, from DE 10 2008 001 442 A1 and DE 10 2012 200 740 A1. These propose a single-mass oscillator with only two spring elements, which are subjected to bending or rotation in specific directions or around specific axes depending on the direction of the acceleration vector. A suitable electrode arrangement thus enables detection of all three acceleration directions with a single movable mass. The structures shown are relatively sensitive to mechanical or thermomechanical stress, since the suspension points of the electrodes experience a slightly different displacement upon substrate stretching or curvature than a suspension point of the mass. This can lead to false signals, in particular to undesired offset signals.

[0004] DE 10 2012 200 740 A1 emphasizes the advantage of mounting the fixed electrodes as centrally as possible, as this can reduce the influence of substrate distortions, which can occur, for example, during circuit board assembly. The disclosed sensors exhibit inadequate offset performance during circuit board assembly or even after assembly when exposed to temperature changes. The problem of non-differential electrode cells is solved by implementing self-supporting fixed electrodes with a fully differential arrangement using a second detachable micromechanical functional layer.

[0005] The second micromechanical functional layer is arranged below the first micromechanical functional layer and is typically, but not necessarily, thinner than it. The widely projecting support arms for x- and y-detection, as well as the arrangement of the x- and y-electrode anchors, which are not aligned with the mass suspension, also make this arrangement sensitive to certain substrate deformations and to material-intrinsic changes in the thermomechanical properties of the two micromechanical layers. For example, the lower micromechanical layer may expand slightly differently over temperature than the upper micromechanical layer due to different manufacturing conditions (e.g., different doping, different crystal structure, etc.). This can lead to undesirable relative displacements between fixed and movable electrode fingers when the temperature changes, and thus to offset signals.

[0006] The subsequently published patent application DE 10 2015 222 532 A1 discloses a micromechanical structure for an acceleration sensor.

[0007] The published patent application JP 2010-71912 A discloses a MEMS sensor.

[0008] The patent EP 2 462 408 B1 discloses a micromechanically manufactured inertial sensor device. Disclosure of the invention

[0009] It is therefore an object of the present invention to provide a micromechanical sensor that is improved compared to the above-mentioned concepts and a method for producing a micromechanical sensor.

[0010] The object is achieved according to a first aspect with a micromechanical sensor according to claim 1.

[0011] Due to this specific design of the detection elements, the micromechanical sensor is advantageously less sensitive to substrate deformation. This advantageously improves the sensing characteristics and offset performance of the micromechanical sensor.

[0012] According to a second aspect, the object is achieved by a method for producing a micromechanical sensor according to claim 5.

[0013] Preferred embodiments of the micromechanical sensor are the subject of dependent claims.

[0014] An advantageous refinement of the micromechanical sensor is characterized by the fact that the electrode backs of the lateral electrodes are short relative to the sensor's longitudinal dimension. This allows the support arms of the lateral electrodes' detection fingers to be short, which ultimately supports the insensitivity of the entire sensor to substrate deformation.

[0015] A further advantageous development of the micromechanical sensor provides for the length of the electrode backs to be approximately one-third of half the sensor's longitudinal dimension. This achieves a favorable size ratio for the electrode backs relative to the overall dimensions of the sensor.

[0016] A further advantageous development of the micromechanical sensor is characterized in that conducting elements for the electrodes are formed in a first and second functional layer of the sensor. This allows the micromechanical sensor to be manufactured according to proven principles of surface micromechanics.

[0017] A further advantageous development of the micromechanical sensor is characterized by the fact that the detection fingers and the electrode backs of the lateral electrodes are formed in a third functional layer of the sensor. This also supports the simple manufacturability of the sensor using proven surface micromechanical processes.

[0018] The invention is described in detail below with further features and advantages using several figures. All disclosed features, regardless of their reference in the patent claims and regardless of their representation in the description and figures, form the subject matter of the present invention. Identical or functionally equivalent elements have the same reference numerals. The figures are intended in particular to clarify the principles essential to the invention and are not necessarily to scale.

[0019] Disclosed method features result analogously from corresponding disclosed device features, and vice versa. This means, in particular, that features, technical advantages, and embodiments relating to the micromechanical sensor result analogously from corresponding embodiments, features, and advantages relating to the method for producing a micromechanical sensor, and vice versa.

[0020] In the figures shows: Fig. 1 a movable mass element of a conventional micromechanical z-acceleration sensor; Fig. 2 a plan view of an embodiment of a micromechanical sensor according to the invention; Fig. 3 a plan view of a bottom layer of an embodiment of the micromechanical sensor according to the invention; Fig. 4 a plan view of an embodiment of the micromechanical sensor according to the invention with a further functional layer; Fig. 5 a perspective view of an embodiment of the micromechanical sensor according to the invention; Fig. 6 a sectional view along a section AA of Fig. 2; Fig. 7 a sectional view along a section BB of Fig. 2; Fig. 8 a sectional view along a section CC of Fig. 2; Fig. 9 a sectional view along a section DD of Fig. 2; Fig. 10 is a plan view of an alternative embodiment of the micromechanical sensor; Fig. 11 is a plan view of another alternative embodiment of the micromechanical sensor; and Fig. 12 shows a basic sequence of a method for producing a micromechanical sensor according to the invention. Description of embodiments

[0021] A fundamental idea of ​​the present invention is to design and arrange suspension and mounting structures for all electrodes of a micromechanical acceleration sensor as close to the center as possible. In this way, substrate deflections have as little impact as possible on the sensor's sensing characteristics, which can significantly improve the sensor's offset performance. All electrodes of the sensor are designed according to the well-known fully differential principle, in which capacitance changes due to the displaced, movable seismic mass are recorded and evaluated.

[0022] The proposed solution combines a suitable spring-mass structure, sensitive to accelerations in all three spatial directions, with a special fully differential arrangement of the electrodes for both x-, y-, and z-detection. At least two suspensions are provided for each polarity for the suspension and arrangement of the lateral fixed electrodes, both for the x-axis and the y-axis. This allows for better symmetry conditions between the electrode and mass suspension and better compensation for certain substrate deformations. Furthermore, the support arms or the electrode backs of the fixed electrodes are designed to be short relative to the overall length, so that any deformations occurring in the anchoring area or in the micromechanical layers themselves have a significantly lower impact on changes in the distances between the movable and fixed electrodes than in the prior art.This results in a significantly improved offset performance of the acceleration sensor.

[0023] Fig. 1 shows a perspective view of a movable seismic mass element 10 in the form of a rocker, which is attached or connected to a substrate 1 by means of a central connection element 13. A seismic mass of the left rocker arm is greater than a mass of the right rocker arm, thus realizing a mass asymmetry of the movable mass element 10. A spring 11 oriented in the y-direction is arranged on the connection element 13. The mass element 10 is arranged on the outside of the spring 11 in the form of a frame with asymmetrically distributed mass. Detection fingers 12 for detecting lateral acceleration in the x- and y-directions are located on both sides of the spring 11. A micromechanical functional layer (not shown) arranged underneath is used for detecting the out-of-plane channel z.

[0024] Fig. 2 shows a top view of an embodiment of the micromechanical sensor 200 according to the invention. Four section lines AA, BB, CC, and DD are visible, which are explained in more detail in subsequent figures. It can be seen that x-electrode fastening elements 40, 50 and y-electrode fastening elements 60, 70 are arranged on the central connection element 13 for the movable mass element 10. Thus, for the lateral x- and y-electrodes ("in-plane electrodes"), two mutually separate fastening elements 40, 50 are arranged close to the central connection element 13 for the movable mass element 10. Furthermore, the two z-electrodes 33, 34 ("out-of-plane electrodes") are also arranged close to the central connection element 13. As a result, all electrodes are connected to the substrate 1 close to the central connection element 13, which advantageously realizes a compact design of the micromechanical sensor 200.

[0025] Fig. Figure 3 shows routings of conductive elements 80...130 for implementing electrical connections of the aforementioned electrodes. All of the aforementioned conductive elements 80...130 are formed in a first or lowermost micromechanical functional layer (preferably made of polysilicon) of the micromechanical sensor 200. The conductive elements 80, 90 and 100, 110 for the lateral x-electrodes and for the lateral y-electrodes are each formed in duplicate.

[0026] The conducting elements 80, 90 have suitable electrical potentials so that a movement of the detection fingers 12 between lateral x-electrode fingers can be detected. The conducting elements 100, 110 have suitable electrical potentials so that a movement of the detection fingers 12 between lateral y-electrode fingers can be detected. The conducting elements 120, 130 have suitable electrical potentials for detecting a deflection of the seismic mass element 10 in the z-direction.

[0027] Fig. Figure 4 shows the structure of the micromechanical sensor 200 with an additional micromechanical functional layer in the region of the conducting elements 80, 90, 100, 110, 120, 130. It can be seen that the conducting elements 80, 90, 110 are L-shaped near the central connection element 13, thus establishing an electrical connection of the lateral x- and y-electrodes. These L-shaped elements are formed in a second micromechanical functional layer (preferably made of polysilicon) of the micromechanical sensor 200, which is arranged on the lowest functional layer.

[0028] Fig. Figure 5 shows a perspective view of an embodiment of the proposed micromechanical sensor 200 with all micromechanical functional layers. For detecting acceleration in the x-direction, x-electrode fingers 21, 22 are shown, each interacting with a movable detection finger 12 of the mass element 10. It can be seen that two such structures are arranged diagonally offset from one another with respect to the central connection element 13. Furthermore, y-electrode fingers 31, 32 are provided for detecting the lateral y-deflection, each interacting with a movable detection finger 12 of the mass element 10. The lateral electrodes 20, 21, 22 and 30, 31, 32 are arranged diagonally offset from one another with respect to the central connection element 13.

[0029] Two x-electrode backs 20 can be seen, on which the x-electrode fingers 21, 22 are arranged, with a detection finger 12 of the movable mass element 10 being arranged between each two x-electrode fingers 21, 22. For detecting a deflection of the movable mass element 10 in the y-direction, two y-electrode backs 30 with y-electrode fingers 31, 32 formed thereon are provided, with each two y-electrode fingers 31, 32 interacting with a respective movable detection finger 12. The y-electrode structure can be suitably applied with potential by means of the conduction elements 100, 110, just as the x-electrode structure can be applied with the conduction elements 80, 90. Depending on the application, the electrode backs 20, 30 can have the same or different electrical potentials.

[0030] One dimension of the electrode backs 20, 30 is approximately one-third of half the length of the micromechanical sensor 200. The two z-electrodes 33, 34 are arranged between two lateral electrodes each, so that in this way a compact detection structure for the micromechanical sensor 200 is implemented.

[0031] Fig. 6 is a representation of a sectional view through the proposed micromechanical sensor 200 of Fig. 2 along section AA. It can be seen that the z-electrodes 33, 34 are connected to the lowest micromechanical functional layer of the sensor 200 via conduction elements 130, 120. The fully differential design of the z-electrodes 33, 34 is also evident here, with a conduction element 120 with the electrical potential of the z-electrode 34 being formed below the z-electrode 33. A detection finger 12 of the movable mass element 10 is arranged between each of the z-electrodes 33, 34 and the conduction elements 120, 130.

[0032] Fig. Figure 7 shows a sectional view through the proposed sensor 200 of Fig. 2 along section BB. The conductive elements 80, 90, 100, 110 can be seen in the lowest functional layer for the electrical connection of the lateral x- and y-electrodes. It can also be seen that the z-electrodes 33, 34, as well as the lateral electrode backs 20, 30, together with the L-shaped fastening elements 40, 50, 60, and 70, are arranged close to the central connection element 13 or the spring 11.

[0033] Fig. Figure 8 shows a sectional view through the proposed structure of Fig. 2 along the section line CC. The x-electrode fingers 21, 22 of the lateral x-electrode and the y-electrode fingers 31, 32 of the lateral y-electrode can be seen, each arranged on an L-shaped fastening element 50 or 70 formed in the second functional layer.

[0034] A sectional view of the micromechanical sensor 200 along the section line DD is shown in Fig. 9. In addition to the elements of Fig. 8 shows the detection fingers 12 of the movable mass element 10. Also visible here are the conducting elements 120, 130 in the second micromechanical functional layer of the sensor 200, wherein the conducting element 130 is provided for the electrical connection of the z-electrode 33 and the conducting element 120 for the electrical connection of the z-electrode 34.

[0035] Fig. Fig. 10 shows a plan view of a first alternative of the proposed micromechanical sensor 200. In this case, the x-electrode backs 20 are not arranged diagonally with respect to the central connection element 13, but opposite each other, as are the y-electrode backs 30. Structurally, there is a difference compared to the arrangements of the Fig. 5 to 9, there is no difference, but here one of the electrode backs 30 has the electrical potential of the conduction element 100 and the other electrode back 30 has the electrical potential of the conduction element 110. The two electrode backs 20 both have the same electrical potential of the conduction element 90.

[0036] Fig. 11 shows a plan view of a second alternative of the micromechanical sensor 200 according to the invention. In this case, the two L-shaped fastening elements 50 of the lateral x-electrodes are subjected to the electrical potential of the conduction elements 80, and the two L-shaped fastening elements 40 of the lateral x-electrodes are subjected to the electrical potential of the conduction elements 90. The fastening elements 60 of the two lateral y-electrodes are subjected to the electrical potential of the conduction elements 100, and the fastening elements 70 of the two lateral y-electrodes are subjected to the electrical potential of the conduction elements 110.

[0037] From the variants of Fig. 10 and Fig. 11 it can be seen that the electrode backs 20, 30 can be advantageously and easily supplied with suitable electrical potentials of the conduction elements 80 to 110.

[0038] Which of the Fig. 5, Fig. 10, Fig. Whether the electrode configurations shown in Figure 11 are particularly resistant to substrate deflection ultimately depends on the type of substrate deflection, which can vary depending on the sensor core's installation position in the chip and the various package variants. Therefore, depending on the package's boundary conditions, the optimal electrode configuration can be selected for a specific product.

[0039] Fig. 12 shows a basic flow of the proposed procedure: In a step 300, a substrate 1 is provided. In a step 310, a movable mass element 10 sensitive in three spatial directions x, y, z is provided. In a step 320, two x-lateral electrodes 20, 21, 22 are formed. In a step 330, two y-lateral electrodes 30, 31, 32 are formed. In a step 340, two z-electrodes are formed. In a step 350, all electrodes 20, 21, 22, 30, 31, 32, 33, 34 are attached close to a connection element 13 of the movable mass element 10 to the substrate 1.

[0040] The order of the steps can also be changed.

[0041] In summary, the present invention proposes a micromechanical sensor that can be manufactured using a surface micromechanical process. This advantageously achieves optimized sensing behavior by arranging all detection-relevant elements as close as possible to a mass suspension. This allows the substrate to warp as similarly as possible to the movable mass element. As a result, the insensitivity of the acceleration sensor to substrate deflection is advantageously increased.

[0042] As a result, an acceleration sensor is provided as a single-mass oscillator, which enables the detection of x-, y-, and z-accelerations in a single core and which, at the same time, has excellent robustness against substrate bending, i.e., good offset performance during circuit board assembly as well as under thermomechanical stress in the sensor housing.

[0043] Although the invention has been described above with reference to concrete application examples, a person skilled in the art can also implement embodiments not disclosed or only partially disclosed without deviating from the essence of the invention.

Claims

[1] Micromechanical sensor (200), comprising: - a substrate (1); - a movable mass element (10) sensitive in three spatial directions (x, y, z); - two x-electrode backs (20) with x-electrode fingers (21) arranged thereon in a third functional layer of the sensor (200) for detecting lateral x-deflection of the movable mass element (10); two fastening elements (40, 50) with x-electrode fingers (22) arranged thereon in the third functional layer for detecting lateral x-deflection of the movable mass element (10), two y-electrode backs (30) with y-electrode fingers (31) arranged thereon in the third functional layer for detecting lateral y-deflection of the movable mass element (10), two fastening elements (60, 70) with y-electrode fingers (32) arranged thereon in the third functional layer for detecting lateral y-deflection of the movable mass element (10), - z-electrodes (33, 34) for detecting a z-deflection of the movable mass element (10); wherein - each lateral electrode (20, 21, 22, 30, 31, 32) is fixed to the substrate (1) by means of a fixing element (40, 50, 60, 70); - the fastening elements (40, 50, 60, 70, 120, 130) of all electrodes (20, 21, 22, 30, 31, 32, 33, 34) are formed close to a connecting element (13) of the movable mass element (10) to the substrate (1). [2] Micromechanical sensor (200) according to claim 1, characterized by that electrode backs (20, 30) of the lateral electrodes (20, 21, 22, 30, 31, 32) are short in relation to a longitudinal dimension of the sensor (200). [3] Micromechanical sensor (200) according to claim 2, characterized bythat lengths of the electrode backs (20, 21, 22, 30, 31, 32) are approximately one third of half a longitudinal dimension of the sensor (200). [4] Micromechanical sensor (100) according to one of the preceding claims, characterized by that conducting elements (80, 90, 100, 110, 120, 130) for the electrodes (20, 21, 22, 30, 31, 32, 33, 34) are formed in a first and second functional layer of the sensor (200). [5] Method for producing a micromechanical sensor (200), comprising the steps: - Providing a substrate (1); - Providing a movable mass element (10) sensitive in three spatial directions (x, y, z); - forming two x-electrode backs (20) with x-electrode fingers (21) arranged thereon in a third functional layer of the sensor (200) for detecting lateral x-deflection of the movable mass element (10); Forming two fastening elements (40, 50) with x-electrode fingers (22) arranged thereon in the third functional layer for detecting lateral x-deflection of the movable mass element (10), Forming two y-electrode backs (30) with y-electrode fingers (31) arranged thereon in the third functional layer for detecting lateral y-deflection of the movable mass element (10), - Forming two fastening elements (60, 70) with y-electrode fingers (32) arranged thereon in the third functional layer for detecting lateral y-deflection of the movable mass element (10) - forming two z-electrodes (33, 34); and - Attaching all electrodes (20, 21, 22, 30, 31, 32, 33, 34) close to a connection element (13) of the movable mass element (10) to the substrate (1). [6] The method of claim 5, wherein lengths of electrode backs (20, 30) of the lateral electrodes (20, 21, 22, 30, 31, 32) are formed to be approximately one-third as long as half a longitudinal dimension of the sensor (200). [7] Method according to claim 5 or 6, wherein conduction elements (80, 90, 100, 110, 120, 130) for the electrodes (20, 21, 22, 30, 31, 32, 33, 34) are formed in a first and second functional layer of the sensor (200).

Images