Microelectromechanical system having at least one u-spring element with transverse stiffness in the z-direction, acceleration sensor, loudspeaker and optical sensor, in each case comprising at least two u-spring elements, and use of the at least one u-spring element in systems having movable masses

Abstract

The present invention relates to a microelectromechanical system (MEMS) (1) comprising a first functional layer (2) which spans an x-y plane and has a thickness d1 perpendicular to the x-y plane in the z-direction, at least one second functional layer (4) which is attached to the first functional layer (2) in such a way that there is a functional layer stack (6) having a height H in the z-direction, and at least one U-spring element (8). The at least one U-spring element (8) comprises a spring fastening (10) and a movable spring deflection part (12) which extends in the z-direction and has a transverse stiffness in the z-direction. The invention further relates to MEMS (1) according to the invention, which are designed as an acceleration sensor (100), as a loudspeaker (200) or as an optical sensor (300) and comprise at least two U-spring elements (8, 38). The invention also relates to the use of the MEMS (1) according to the invention in systems having movable mass bodies (30).

Description

[0001] R.415780

[0002] - 1 -

[0003] Description

[0004] title

[0005] Microelectromechanical system with at least one U-spring element with transverse stiffness in the z-direction, accelerometer, loudspeaker and optical sensor, each comprising at least two U-spring elements, and use of the at least one U-spring element in systems with movable mass bodies

[0006] Technical field

[0007] The present invention relates to a microelectromechanical system (MEMS) comprising a first functional layer spanning an xy-plane and having a thickness di perpendicular to the xy-plane in the z-direction, at least one second functional layer mounted on the first functional layer such that a functional layer stack with height H is present in the z-direction, and at least one U-spring element. The U-spring element comprises a spring mounting and a movable spring deflection part extending in the z-direction and exhibiting transverse stiffness in the z-direction. The invention further relates to MEMS according to the invention configured as an accelerometer, a loudspeaker, or an optical sensor, comprising at least two U-spring elements. The invention further relates to the use of the MEMS according to the invention in systems with movable masses.

[0008] State of the art

[0009] The form and functional elements present in microelectromechanical systems (MEMS) are predominantly two-dimensional structures extending in the chip plane (xy-plane). The functional layers of these components in the z-direction are usually of small thickness, meaning that the extent in the z-direction is many times smaller than that in the xy-direction. These form and functional elements can be understood as mass bodies that are fixed in the system by means of a spring suspension; they are therefore designed as mass-spring elements. In the simplest case, the springs are bidirectional.

[0010] - 2 -

[0011] Clamped bending beams are formed. However, such a simple arrangement has the disadvantage of a non-linear force deflection due to the resulting strain stiffening, which is undesirable.

[0012] The spring elements known from the prior art therefore mostly rely on so-called U-springs, which are firmly anchored in the xy-plane, i.e., in the chip substrate, via a spring attachment, and whose deflection extends horizontally in the xy-plane. Such U-springs allow translational movement of the mass bodies due to their compliance in the direction of use, which means that there is low spring stiffness in the xy-direction. The effect of strain stiffening can be avoided in such systems because the short spring arm in the U-shape, which is designed as a stiffener, is freely movable in the y-direction, resulting in a linear force deflection.

[0013] A disadvantage of such systems is that deflections in the z-direction can also occur, since the transverse stiffness in the z-direction is low due to the lever arm resulting from the entire length of the spring. These undesirable deflections in the z-direction pose the risk of damaging other components located in the chip plane, i.e., in the xy-plane, such as sensitive electrodes. This can be caused by particle formation, short circuits, or even direct contact with the electrodes.

[0014] This has a particularly negative impact on developments in MEMS, where newer manufacturing processes rely on more than one functional layer in the z-direction, ideally resulting in so-called layer stacks in the z-direction. The structure of such layer stacks allows for more complex and thicker form and functional elements at the chip level, which can often deliver higher performance.

[0015] DE 102012 223016 A1 discloses an inertial sensor with a substrate in the main extension plane, a first functional layer, and a second functional layer, the latter arranged parallel to one another. The inertial sensor includes a seismic mass formed in the first and second functional layers and spaced apart above the substrate. Furthermore, the inertial sensor comprises a torsion spring assembly connected to the substrate and the seismic mass by means of anchoring areas. The torsion spring assembly has a torsion axis arranged parallel to the main extension plane and a

[0016] - 3 -

[0017] The torsion spring assembly consists of a first spring element located in the first functional layer and a second spring element located in the second functional layer. The assembly is designed such that, during acceleration in direction x, parallel to the main plane of the substrate and perpendicular to the torsion axis y of the torsion spring assembly, a deflection in direction z, i.e., perpendicular to the main plane of the substrate, is suppressed.

[0018] DE 102008043524 A1 discloses an accelerometer in which a seismic mass and detection electrodes are integrated within a common functional layer. The sensor element is designed as a rocker that can rotate about an axis of rotation. The rocker has two wings that form an asymmetric mass distribution relative to each other with respect to the axis of rotation. Both the rocker body and the two electrode structures are implemented as self-supporting structures decoupled from the substrate. Two spring elements, designed as torsion bars, are arranged on either side of the rocker body to suspend it. The rocker body is preferably constructed in two layers.When accelerated in the direction orthogonal to the surface of the substrate, the rocker body rotates clockwise, so that the distance between the first electrode and an electrode area of ​​the right wing arranged above it decreases, while the distance between the second electrode structure and the electrode area of ​​the rocker below it increases.

[0019] While current state-of-the-art solutions aim to suppress deflections in the z-direction as much as possible, this is only possible in systems with a maximum of two functional layers. However, it would be desirable to enable more complex and thicker form and functional elements at the chip level in systems with higher layer stacks in the z-direction, without these elements being at risk of being damaged by deflections in the z-direction.

[0020] Accordingly, the demand for MEMS that enable spring suspension for form and function elements in a layer stack, without the disadvantages of the prior art and instead exhibiting sufficiently high stiffness in the z-direction, remains strong. R.415780

[0021] - 4 -

[0022] Disclosure of the invention

[0023] According to the invention, a microelectromechanical system (MEMS) is proposed which comprises a first functional layer, at least one second functional layer and at least one U-spring element. The first functional layer spans an xy-plane and has a thickness di perpendicular to the xy-plane in the z-direction.The at least one second, and in particular a plurality of further, functional layers are arranged on the first functional layer such that a functional layer stack with height H is present in the z-direction. The at least one U-spring element comprises a spring attachment and a movable spring deflection part, wherein the spring attachment is designed and configured to anchor the at least one U-spring element firmly in the first functional layer, i.e., in the xy-plane, and the movable spring deflection part extends in the z-direction and has a spring length L. In certain embodiments of the MEMS, the first functional layer can comprise the substrate or be designed as a substrate, wherein the substrate represents the support layer and is preferably made of silicon.

[0024] According to the invention, a U-spring element, also called a double spring, is understood to be a spring element in which the spring attachment is located at one end of the “non-shaped part” and the movable spring deflection part is formed from the “U” part itself.

[0025] In suitable embodiments, the movable spring deflection element comprises a spring base and two spring legs extending from the spring base. The first spring leg extends from the spring base to the spring mounting point, and the second spring leg extends from the spring base to a receiving element. Therefore, in a functional layer stack comprising a first and a second functional layer, the spring base is located within the second functional layer.

[0026] A movable spring deflection part is therefore understood to be the part of the U-spring element that is designed and configured to extend in the z-direction and also to retract again, while the spring mounting, on the other hand, is fixed in place, meaning it is not movable. R.415780

[0027] - 5 -

[0028] If the functional layer stack comprises n functional layers, the spring base is consequently located in the nth functional layer, and the spring length of the at least one U-spring element is determined by the number of functional layers, with the spring length L corresponding to (n-1) functional layers. In one embodiment of the MEMS according to the invention, the individual functional layers can have the same thicknesses d in the z-direction; however, in preferred systems, the n functional layers have different thicknesses di, d2, d n on.

[0029] The receiving element in the movable spring deflection part of the at least one U-spring is designed and configured according to the invention to receive a movable mass body, i.e. a form or functional element.

[0030] The MEMS according to the invention therefore also comprises at least one movable mass body, wherein the mass body is located in the (n-1)th functional layer of the functional layer stack.

[0031] In suitable embodiments of the MEMS according to the invention, the at least one U-spring element is designed as a double U-spring element. This means that, in a cross-section through the xy-plane, a U-spring element is present on virtually both sides in the z-direction. According to the invention, the double U-spring element comprises only a spring mounting, a receiving element, and two movable spring deflection parts. The spring base of the first spring deflection part is arranged in the first functional layer, and the spring base of the second spring deflection part is located in the nth functional layer.

[0032] According to the invention, the at least one U-spring element, whether designed as a simple U-spring element or as a double U-spring element, has a transverse stiffness in the z-direction, with a linear force-displacement ratio in the xy-plane.

[0033] According to the invention, a MEMS is further proposed which is configured as an accelerometer. The accelerometer comprises at least two previously described U-spring elements, each with a spring attachment, such that each of the two U-spring elements is separately anchored in the functional layer. Furthermore, the accelerometer according to the invention comprises two pairs of detection electrodes, wherein these are described in R.415780

[0034] - 6 -

[0035] The functional layer is firmly anchored by the two spring fixings. In the accelerometer according to the invention, the mass body is designed as a seismic mass, wherein the at least two U-spring elements are designed and configured such that when an acceleration acts on the MEMS, i.e., on the accelerometer, the seismic mass is moved relative to the detection electrode pairs, so that this deflecting movement can be detected.

[0036] A MEMS according to the invention is also proposed, which is designed as a loudspeaker.

[0037] In suitable embodiments, the loudspeaker according to the invention comprises at least two U-shaped spring elements according to the invention, each with a spring attachment, as well as two walls of two fluid chambers extending in the z-direction. The two walls of the fluid chambers extending in the z-direction are firmly anchored in the same functional layer in which the spring attachments are also firmly anchored. In suitable embodiments of the loudspeaker according to the invention, the mass body comprises at least parts of the two adjacent fluid chambers, wherein these parts do not include the two firmly anchored walls extending in the z-direction. According to the invention, each fluid chamber comprises at least one opening, in particular two openings.The at least two U-shaped spring elements are designed and configured such that, when a fluid flow enters the fluid chambers through an opening and exits them again, particularly through an opposite opening, the two adjacent fluid chambers are moved relative to the two firmly anchored walls, so that this deflecting movement can be detected.

[0038] A MEMS according to the invention is also proposed, which is designed as an optical sensor. The optical sensor according to the invention also comprises at least two U-spring elements, each with a spring attachment, which are firmly anchored in the functional layer. The mass body is designed as a reflective surface, wherein the at least two U-spring elements are designed and configured such that, when a light beam strikes the reflective surface, the reflective surface is deflected in the xy-plane, and this deflection can also be detected. R.415780

[0039] - 7 -

[0040] Furthermore, a use of the MEMS according to the invention in systems with movable mass bodies is proposed, wherein the mass bodies are designed and configured to perform a translational movement; in particular, a use in loudspeakers, inertial sensors and micromirrors is proposed.

[0041] Advantages of the invention

[0042] The MEMS according to the invention, comprising a first functional layer, at least a second functional layer, in particular a plurality of further functional layers n, such that a functional layer stack with height H is present in the z-direction, and at least one U-spring element, wherein its movable spring deflection part extends in the z-direction, can create a system with high transverse stiffness in the z-direction.

[0043] This minimizes, and preferably eliminates, unwanted deflections of the at least one U-spring element in the z-direction, thus preventing damage to other components, such as sensitive electrodes located in the chip plane. Despite the high transverse stiffness in the z-direction, the MEMS according to the invention exhibits a linear force-deflection ratio in the xy-plane without strain stiffening.

[0044] The U-shaped spring elements according to the invention are also intended to be used specifically in so-called 3D MEMS, which, due to new manufacturing processes, rely on higher functional layer stacks in order to enable more complex and thicker shape and functional elements at the chip level. These higher functional layer stacks also allow for greater spring lengths, further expanding the possibilities for designing different spring topologies.

[0045] Brief description of the drawings

[0046] Embodiments of the invention are explained in more detail with reference to the drawings and the following description.

[0047] It shows: R.415780

[0048] - 8 -

[0049] Figure 1 shows a schematic cross-sectional view in the z-direction of a U-spring element according to the invention;

[0050] Figure 2 shows a schematic top view of the xy-plane and a schematic cross-sectional view in the z-direction of a MEMS according to the invention;

[0051] Figure 3 shows a schematic top view of the xy-plane and a schematic cross-sectional view in the z-direction of an alternative MEMS according to the invention;

[0052] Figure 4 shows a schematic top view of the xy-plane and a schematic cross-sectional view in the z-direction of another alternative MEMS according to the invention;

[0053] Figure 5 shows a schematic cross-sectional view in the z-direction of an acceleration sensor according to the invention in the rest state and during acceleration;

[0054] Figure 6 shows a schematic cross-sectional view in the z-direction of a loudspeaker according to the invention in the idle state and during excitation and

[0055] Figure 7 shows a schematic cross-sectional view in the z-direction of an optical sensor according to the invention in the rest state and during excitation.

[0056] Embodiments of the invention

[0057] In the following description of embodiments of the invention, identical or similar elements are designated by the same reference numerals, and repeated descriptions of these elements are omitted in individual cases. The figures represent the subject matter of the invention only schematically.

[0058] Figure 1 shows the cross-section in the z-direction of a U-spring element 8 according to the invention, wherein the U-spring element 8 has a spring attachment 10 in the first functional layer 2, which forms a fixed anchorage 66 in the first functional layer 2. The receiving element 20 is also located in R.415780

[0059] - 9 -

[0060] The first functional layer 2 is designed and configured to accommodate a movable mass body 30 (not shown here). The first functional layer 2 spans an xy-plane and, in the illustrated embodiment, has a thickness di. Further functional layers 4, 22, 24, 26, 28 are attached to the first functional layer 2 such that a functional layer stack 6 is formed in the z-direction, which has a height H. The further functional layers 4, 22, 24, 26, 28 have different thicknesses d2, da, d n -2, d n -i and d n Starting from the spring mounting 10 and the receiving element 20, the movable spring deflection part 12 extends, having a length L in the z-direction, a spring base 14 and two spring legs 16, 18, the first spring leg 16 extending from the spring base 14 to the spring mounting 10 and the second spring leg 18 extending from the spring base 14 to the receiving element 20.

[0061] Figure 2 shows on the left a schematic top view of the xy-plane of a MEMS 1 according to the invention and on the right the corresponding cross-sectional view in the z-direction. The top view shows the four spring attachments 10 of the four U-spring elements 8 (not shown in the top view), which form fixed anchorages 66 in the xy-plane. The MEMS 1 also comprises a mass body 30, which can perform a translational movement 400. In the cross-sectional view, two U-spring elements 8, 38 (of the four U-spring elements in total) are visible. The U-spring elements 8, 38 are basically constructed as shown in Figure 2 and comprise a spring attachment 10, 40 in the first functional layer 2, each of which forms a fixed anchorage 66 in the xy-plane.In the illustrated embodiment, a functional layer stack 6 is formed in the z-direction from four functional layers 2, 4, 22, 28, such that the height H of the functional layer stack 6 corresponds to the sum of the thicknesses di, d2, da, d4 of the individual functional layers 2, 4, 22, 28. The spring length L of the two U-shaped double springs 8, 38 therefore corresponds to the sum of the thicknesses d2, da, d4 of the functional layers 4, 22, 28.

[0062] Figure 3 shows a schematic top view of the xy-plane and two schematic cross-sectional views in the z-direction of an alternative MEMS 1 according to the invention. This differs from the one shown in Figure 2 in that, in the positive z-direction, there is a first system of two U-spring elements 8, 38 with a mass body 30 attached to them, and in the negative z-direction, a second system of two U-spring elements 8, 38 with a mass body 30 attached to them. In the embodiment shown, the two R.415780

[0063] - 10 -

[0064] Systems are identically configured, which means that a functional layer stack 6 of the same height H is present (not shown for clarity) and therefore also the same number of functional layers.

[0065] Figure 4 shows a schematic top view of the xy-plane and a schematic cross-sectional view in the z-direction of another alternative MEMS 1 according to the invention. This differs from the MEMS 1 shown in Figure 2 in that only two (instead of four) U-spring elements 8, 38 are present, wherein the U-spring elements 8, 38 are each designed as a double U-spring element 32, which has only one spring attachment 10, 40, designed as a fixed anchor 66, and a receiving element 20 for receiving the movable mass body 30. The double U-spring element 32, however, comprises two spring deflection parts 12, 34, which extend along the z-direction in the negative and positive directions.

[0066] Figure 5 shows a schematic cross-sectional view in the z-direction of an accelerometer 100 according to the invention, shown on the left in its resting state and on the right during acceleration. In the illustrated embodiment, the accelerometer 100 comprises two U-shaped spring elements 8, 38, each with a spring attachment 10, 40, which is designed as a fixed anchor 66 in the xy-plane. Furthermore, the accelerometer 100 comprises two pairs of detection electrodes 42, 44, which are also fixedly anchored in the xy-plane. The mass body 30 is designed as a seismic mass 46. The two U-spring elements 8, 38 are designed and configured such that when an acceleration acts on the accelerometer 100, the seismic mass 46 is moved relative to the detection electrode pairs 42, 44, with the spring legs 16, 18 (not shown) moving towards each other or away from each other.

[0067] Figure 6 shows a schematic cross-sectional view in the z-direction of a loudspeaker 200 according to the invention, on the left in the rest state and on the right during excitation. In the embodiment shown, the loudspeaker 200 comprises two U-spring elements 8, 38, each with a spring attachment 10, 40, which is designed as a fixed anchor 66 in the xy-plane. Furthermore, the loudspeaker 200 comprises two walls 68, 70 extending in the z-direction of two fluid chambers 48, 50, which are located in the functional layer (not shown) with the spring attachments 10, 40 serving as a fixed anchor 66. The mass body 30 here comprises at least parts of the two adjacent R.415780

[0068] - 11 -

[0069] Fluid chambers 48, 50, wherein the parts of the fluid chambers 48, 50 do not include the two fixed walls 68, 70 extending in the z-direction. In the embodiment shown here, the two adjacent fluid chambers 48, 50 each comprise two openings 52, 54, 56, 58. The two U-shaped spring elements 8, 38 are designed and configured such that when a fluid flow 60 enters the fluid chambers 48, 50 through the two openings 54, 58 and exits again through the two openings 52, 56, the two adjacent fluid chambers 48, 50 are moved relative to the two fixed walls 68, 70 extending in the z-direction, with the spring legs 16, 18 (not shown) moving towards or away from each other.

[0070] Figure 7 shows a schematic cross-sectional view in the z-direction of an optical sensor 300 according to the invention, on the left in its resting state and on the right during excitation. In the illustrated embodiment, the optical sensor 300 comprises two U-shaped spring elements 8, 38, each with a spring attachment 10, 40, which is designed as a fixed anchor 66. The mass body 30 is designed as a reflective surface 62. When a light beam 64 strikes the reflective surface 62 in the resting state, the two U-shaped spring elements 8, 38 are deflected in the xy-plane, and the deflection is measurable.

[0071] The invention is not limited to the embodiments described here and the aspects highlighted therein. Rather, within the scope specified by the claims, a multitude of modifications are possible that fall within the bounds of what is considered skilled in the art.

Claims

R.415780 - 12 - Claims 1. Microelectromechanical system (MEMS) (1) comprising a first functional layer (2) which spans an xy-plane and has a thickness di perpendicular to the xy-plane in the z-direction, at least a second functional layer (4) which is attached to the first functional layer (2) in such a way that a functional layer stack (6) with height H is present in the z-direction, comprising at least one U-shaped spring element (8) a spring attachment (10) designed and configured to firmly anchor (66) the at least one U-spring element (8) in the first functional layer (2), and a movable spring deflection part (12) which extends in the z-direction and has a spring length L.

2. MEMS (1) according to claim 1, wherein the movable spring deflection part (12) comprises a spring base (14) and two spring arms (16, 18), wherein a first spring leg (16) extends from the spring base (14) to the spring attachment (10), wherein a second spring leg (18) extends from the spring base (14) to a receiving element (20), wherein the spring base (14) is located in the second functional layer (4).

3. MEMS (1) according to claim 1 or 2, comprising n functional layers (2, 4, 22, 24, 26, 28), wherein a functional layer stack (6) with n functional layers (2, 4, 22, 24, 26, 28) is present, wherein the spring base (14) is located in the nth functional layer (28), and wherein the spring length L corresponds to (n-1) functional layers (2, 4, 22, 24, 26, 28).

4. MEMS (1) according to claim 3, where the n functional layers (2, 4, 22, 24, 26, 28) have different thicknesses d x exhibit in the z-direction. R.415780 - 13 - 5. MEMS (1) according to at least one of the preceding claims, wherein the receiving element (20) is designed and configured to receive a movable mass body (30), wherein the mass body (30) is located in the (n- 1)th functional layer (2, 4, 22, 24, 26, 28).

6. MEMS (1) according to at least one of the preceding claims, wherein the at least one U-spring element (8) is designed as a double U-spring element (32), comprising a spring mounting (10), a receiving element (20) and two movable spring deflection parts (12, 34) wherein the spring base (14) of a first spring deflection part (12) is arranged in the first functional layer (2) and the spring base (36) of a second spring deflection part (34) is arranged in the nth functional layer (28).

7. MEMS (1) according to at least one of the preceding claims, wherein the at least one U-spring element (8, 32) has a transverse stiffness in the z-direction at a linear force-displacement ratio in the xy-plane.

8. MEMS (1) according to at least one of the preceding claims, wherein the MEMS (1) is designed as an acceleration sensor (100), comprising at least two U-spring elements (8, 38) each with a spring attachment (10, 40) and two detection electrode pairs (42, 44), wherein the detection electrode pairs (42, 44) are firmly anchored (66) in the functional layer (2) with the spring attachments (10, 40), wherein the mass body (30) is designed as a seismic mass (46), wherein the at least two U-spring elements (8, 38) are designed and arranged such that when an acceleration acts on the MEMS (1), the seismic mass (46) is moved relative to the detection electrode pairs (42, 44).

9. MEMS (1) according to at least one of the preceding claims, wherein the MEMS (1) is configured as a loudspeaker (200).

10. Loudspeaker (200) according to claim 9, comprising at least two U-spring elements (8, 38) each with a spring attachment (10, 40) and two walls (68, 70) extending in the z-direction of two fluid chambers (48, 50), wherein the walls (68, 70) of the fluid chambers (48, 50) are firmly anchored (66) in the functional layer (2) by the spring fixings (10, 40), R.415780 - 14 - wherein the mass body (30) comprises at least parts of the two adjacent fluid chambers (48, 50), wherein each fluid chamber (48, 50) comprises at least one opening (52, 54, 56, 58), wherein the at least two U-spring elements (8, 38) are designed and arranged such that when a fluid flow (60) enters the fluid chambers (48, 50), the two adjacent fluid chambers (48, 50) are moved relative to the walls (68, 70).

11. MEMS (1) according to at least one of the preceding claims, wherein the MEMS (1) is designed as an optical sensor (300), comprising at least two U-spring elements (8, 38) each with a spring attachment (10, 40) which are firmly (66) anchored in the functional layer (2), wherein the mass body (30) is designed as a reflective surface (62), wherein the at least two U-spring elements (8, 38) are designed and arranged such that when a light ray (64) hits the reflective surface (62), the reflective surface (62) is deflected in the xy-plane.

12. Use of the MEMS (1) according to any one of claims 1 to 7 in systems with movable mass bodies (30), designed and configured to perform a translational movement (400), in particular in loudspeakers (200), inertial sensors and micromirrors.

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