MEMS Device

Abstract

A MEMS device is disclosed. In an embodiment a MEMS device includes a substrate having an active region and at least one integrated electrical and mechanical connection element configured to electrically and mechanically mount the MEMS device to a carrier, wherein the connection element comprises a stress-reducing structure.

Claims

1. A MEMS device comprising: a substrate comprising an active region; and at least one integrated electrical and mechanical connection element configured to electrically and mechanically mount the MEMS device to a carrier, wherein the connection element comprises a stress-reducing structure.

2. The MEMS device according to claim 1, wherein the connection element is at least partly formed by a part of the substrate.

3. The MEMS device according to claim 2, wherein the connection element comprises at least one contact pad at least partially surrounded by a trench in the substrate.

4. The MEMS device according to claim 3, wherein the contact pad is connected to the active region by a conductor track, the conductor track being arranged on a continuous path on the substrate which is free of the trench.

5. The MEMS device according to claim 3, wherein the trench is an interrupted trench partially surrounding the contact pad.

6. The MEMS device according to claim 5, further comprising a conductor track partly arranged on a fillet interrupting the trench.

7. The MEMS device according to claim 3, wherein the trench completely surrounds the contact pad.

8. The MEMS device according to claim 7, further comprising a conductor track partly arranged on a bridge element reaching over the trench.

9. The MEMS device according to claim 1, wherein the connection element comprises at least two associated contact pads.

10. The MEMS device according to claim 9, wherein each of the associated contact pads has an elongated cross-section.

11. The MEMS device according to claim 1, wherein the connection element comprises a metal mixed with a filler.

12. The MEMS device according to claim 11, wherein the metal is a solder metal.

13. The MEMS device according to claim 11, wherein the filler comprises a gas.

14. The MEMS device according to claim 11, wherein the filler comprises a plastic material.

15. The MEMS device according to claim 11, wherein the filler comprises a plurality of filler elements, each of the filler elements having a filler element diameter which is equal to or less than 1/10 of a connection element diameter.

16. The MEMS device according to claim 11, wherein the connection element has a solder-bump-like structure.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Further features, advantages and expediencies will become apparent from the following description of exemplary embodiments in conjunction with the figures.

[0024] FIGS. 1A and 1B show schematic drawings illustrating a MEMS device according to an embodiment,

[0025] FIG. 2 shows a schematic drawing illustrating a MEMS device according to a further embodiment,

[0026] FIGS. 3A and 3B show schematic drawings illustrating a MEMS device according to a further embodiment,

[0027] FIG. 4 shows a schematic drawing illustrating a MEMS device according to a further embodiment,

[0028] FIGS. 5 and 6 show schematic drawings illustrating MEMS devices according to further embodiments, and

[0029] FIGS. 7 and 8 show schematic drawings illustrating MEMS devices according to further embodiments.

[0030] In the figures, elements of the same design and/or function are identified by the same reference numerals. It is to be understood that the embodiments shown in the figures are illustrative representations and are not necessarily drawn to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0031] In the following, specific details are set forth, such as embodiments and features of the MEMS device as well as advantageous effects thereof, in order to provide a thorough understanding of embodiments of the invention. It will be apparent to one skilled in the art that embodiments of the invention may also be put into practice without these specific details.

[0032] The MEMS device 100 according to the embodiments shown in the figures is not restricted to a certain type of device but can comprise functionalities of one or more of a microphone, a SAW filter or resonator, a BAW filter or resonator, an accelerometer, a gyroscope, a micro tube, a sensor, a mirror, a resonator, a mechanical filter, a switch, a circuit, a cantilever beam, a bridge beam, a capacitor switch, a contact switch and a relay as well as of other devices of an acoustic type or a sensor type having one or several cavities with a controlled atmosphere or with a vacuum. Consequently, the MEMS device 100 according to the embodiments shown in the figures has an active region 2, which can comprise one or more active regions with one or more of the before-mentioned functionalities. Therefore, in the figures the MEMS device 100 and, in particular, the active region 2 are shown merely schematically.

[0033] The MEMS device 100 according to the embodiments shown in the figures is mountable on a carrier by means of an FCB process and comprises at least one integrated electrical and mechanical connection element 3 for electrically and mechanically mounting the MEMS device 100 to the carrier by such an FCB process. In particular, the MEMS device 100 according to the embodiments shown in the figures comprises a plurality of integrated electrical and mechanical connection elements 3. The position and the number of the integrated electrical and mechanical connection elements 3 shown in the figures are merely exemplary and can also deviate from the shown embodiments. In each embodiment shown in the figures, each of the integrated electrical and mechanical connection elements 3 comprises a stress-reducing structure 30, which is designed to reduce mechanical stress, for example, due to temperature changes of the MEMS device 100, that can have negative effects on the active region 2. In particular, the stress-reducing structures 30, which are integrated parts of the MEMS device 100, are designed to reduce the mechanical coupling of the active region 2 to a carrier onto which the MEMS device 100 is mounted via the integrated electrical and mechanical connection elements 3.

[0034] FIG. 1 shows schematic drawings of an embodiment of the MEMS device 100, wherein FIG. 1A shows a view of the MEMS device 100 onto a mounting side 10, which faces a carrier when the MEMS device 100 is mounted onto the carrier, while FIG. 1B shows a partial sectional view along the section plane BB indicated in FIG. 1A. The following description refers to both FIGS. 1A and 1B.

[0035] By way of example, the MEMS device 100 is embodied as a MEMS die having a substrate 1 with a quadratic cross-section, comprising an active region 2 and four integrated electrical and mechanical connection elements 3, which are connected to the active region 2 via conductor tracks 4.

[0036] The substrate 1or bulksubstantially comprises silicon. By means of structuring and applying suitable components and layers made from electrically conducting and/or electrically isolating materials, the active region 2 is formed.

[0037] As mentioned before, each of the integrated electrical and mechanical connection elements 3, in the following also denoted in short as connection elements 3, comprises a stress-reducing structure 30. Since all connection elements 3 are formed similarly, only one connection element 3 is provided with reference numerals in FIG. 1A. Each of the stress-reducing structures 30 is partly formed by a part of the substrate 1. In particular, the connection elements 3 and, in particular, the stress-reducing structures 30 comprise at least one contact pad 31, which can preferably be a solder pad and which is soldered to the carrier when mounting the MEMS device 100. The contact pads 31 can each have a diameter of several tens of micrometers, and typically of about 100 m.

[0038] The connection elements 3 and, in particular, the stress-reducing structures 30 further comprise a trench 32, wherein each of the trenches 32 partly surrounds the respective contact pad 31. Consequently, the substrate 1 is structured in the region of the connection elements 3 by forming the trenches, so that the contact pads 31 are positioned on column-like structures of the substrate 1 and at least partly and preferably as much as possible mechanically disconnected from the active region 2. The depth of the trenches 32 is preferably at least 30 m and equal to or less than a maximum depth, which corresponds to such depth that the residual thickness of the substrate 1, measured from a bottom surface of the trenches 32 to the outer surface of the substrate 1 remote from the mounting face 10, is at least 20 m or at least 30 m. The trenches 32 can preferably have a width of equal to or greater than 10 m and equal to or less than 100 m.

[0039] As indicated in FIG. 1A, the trenches 32 can have a round shape, which can for example, be circular or, alternatively, elliptical. The trenches 32 can be produced for instance by a deep-etching process or by etching with KOH (caustic potash). The trenches 32 are interrupted trenches, wherein each of the trenches 32 partially surrounds the respective contact pad 31, so that the trenches 32 do not form closed-ring-like structures around the contact pads 31 but are interrupted by a fillet 33. The fillets 33 provide paths on the mounting surface 10 between the contact pads 31 and the active region 2, on which for each of the connection elements 3 the respective conductor track 4 can be arranged. Consequently, the conductor tracks 4 can be arranged on continuous, trench-free paths on the mounting surface 10 from the contact pads 31 to the active region 2. It is also possible that the conductor tracks 4 are at least partly arranged below the mounting surface 10 and run in a deeper layer of the substrate.

[0040] By arranging the fillets 33 in suitable positions and directions, it can be possible that the resulting forces of the mechanical path between the connection elements 3 and the active region 2 do not focus toward the active region 2. As shown in FIG. 1A, the fillets 33 can be arranged in a substantially tangential direction with respect to the active region 2. With such preferable routing with the fillets 33 extending into a similar direction for each connection element 3, the resulting forces can act tangentially in a common rotational sense.

[0041] In FIG. 2 a further embodiment of the MEMS device 100 is shown, which represents a modification of the embodiment of FIGS. 1A and 1B. In contrast to the foregoing embodiment, the fillets 33 of the connection elements 3 and thus the remaining mechanical paths between the connection elements 3 and the active region 2 are oriented radially outward with respect to the active region 2, which can also help reducing stress-induced forces acting on the active region 2.

[0042] In FIGS. 3A and 3B, which show views corresponding to FIGS. 1A and 1B, a further embodiment of the MEMS device 100 is shown, which has, in contrast to the foregoing embodiments, connection elements 3 with stress-reducing structures 30 with trenches 32 which completely surround the respective contact pads 31. Consequently, the trenches 32 form closed-ring-like structures around the respective contact pads 31. In order to provide a continuous path between the contact pad 31 of a connection element 3 and the active region 2, on which the conductor track 4 can be arranged, each of the connection elements 3 and, in particular, each of the stress-reducing structures 30 comprises a bridge element 34 that reaches over the trench 32 from the column-like structure of the substrate 1, on which the contact pad 31 is arranged, to the surrounding mounting area 10. The bridge elements 34 can be produced for instance by a release etching process, wherein the trenches 32 can have a depth of several micrometers, for instance about 4 m, at least below the bridge elements 34. The remaining parts of the trenches 32 can either be also produced by release etching, or alternatively by the etching processes described in connection with the foregoing embodiments.

[0043] Similarly to the fillets described in connection with the foregoing embodiments, the bridge elements 34 can be arranged in suitable positions and directions, so that it can be possible that the resulting forces of the mechanical path between the connection elements 3 and the active region 2 do not focus toward the active region 2. As shown in FIG. 3A, the bridge elements 34 can be arranged in a substantially tangential direction with respect to the active region 2. Alternatively, as shown in a further embodiment in FIG. 4, the bridge elements 34 of the connection elements 3 and thus the remaining mechanical paths between the connection elements 3 and the active region 2 can be oriented radially with respect to the active region 2.

[0044] In FIGS. 5 and 6 further embodiments of the MEMS device 100 are shown. In contrast to the foregoing embodiments, each of the connection elements 3 comprises at least two associated contact pads 35 instead of only one contact pad 31, the at least two associated contact pads 35 of each of the connection elements 3 being part of the respective stress-reducing structure 30. Although in FIGS. 5 and 6 each of the connection elements 3 is shown with two associated contact pads 35, the connection elements 3 can also comprise more than two associated contact pads 35, respectively.

[0045] As explained in the general part of the description, the associated contact pads 35 are arranged in direct vicinity to each other and form a sub-structure, by means of which a single contact pad for a solder connection is replaced by the associated contact pads 35, forming correspondingly two or more solder connections which are electrically connected in parallel. When mounting the MEMS device 100 to a carrier, all associated contact pads 35 of each of the connection elements 3 can be connected to the same contact on the carrier, respectively. By means of individual conductor tracks 4, all associated contact pads 35 of a connection element 3 can be connected to the same part of the active region 2. Thus, by means of the associated contact pads 35, a single contact pad with a single conductor track 4 is split into two or more associated contact pads 35 with associated conductor tracks 4. Alternatively, the associated contact pads 35 of a connection element 3 can be connected to a common conductor track leading to the active region 2.

[0046] Preferably, each of the associated contact pads 35 has a smaller cross section than in the case of a connection element 3 with only one contact pad. As a consequence, the transfer of mechanical stress through the solder connection to the active region 2 is reduced without compromising the stability of the connection in case of mechanical shock events or temperature cycles. The associated contact pads 35 and thus the multiple solder connections of each of the connection elements 3 are preferably arranged such that the mechanical stress component critical to the active region's functionality is reduced. As shown in FIGS. 5 and 6, the associated contact pads 35 are preferably placed substantially tangentially with respect to the active region 2, so that stress on the active region 2 can be reduced.

[0047] As shown in FIG. 5, the associated contact pads 35 can have a shape with a circular cross-section. Alternatively, as shown in FIG. 6, each of the associated contact pads 35 can have an elongated cross-section. Such shape of the contact pads 35 can produce solder connections which can steer the active-region-affecting stress directions. Preferably, each of the associated contact pads 35 has a maximum extension direction which is oriented substantially tangentially in regard to the active region 2. As indicated in FIG. 6, each of the associated contact pads 35 can, for example, have an elliptical cross-section, wherein the longer axis is oriented substantially tangentially in regard to the active region 2.

[0048] FIGS. 7 and 8 show partial views of further embodiments of the MEMS device 100. In particular, both FIGS. 7 and 8 show a connection element 3 of the MEMS device 100, wherein the connection element 3 comprises a metal 36 mixed with a filler 37. In contrast to the embodiment of FIG. 7, FIG. 8 shows an embodiment of the MEMS device 100 mounted on a carrier 900.

[0049] The metal 36 comprises or is a solder metal and forms a solder-bump-like structure, which can be applied directly on the substrate 1, on a conductor track or, as shown in FIGS. 7 and 8, on a contact pad 31. The filler 37 comprises a plurality of filler elements 38, which are dispersed in the metal 36. Preferably, each of the filler elements 38 has a filler element diameter d which is equal to or less than 1/10 of a diameter of the connection element 3, which, in particular, can be given by the diameter D of the structure formed by the metal 36. Due to the filler 37 and, in particular, the dispersed filler elements 38 in the metal 36, the metal 36 can be rendered less rigid compared to the metal without the filler. This can reduce the maximum stress levels occurring in the event of thermal expansion or of other internal or external stress sources, thus increasing the critical temperature at which plastic deformation of the solder joint occurs or increasing the maximum stress at which plastic deformation occurs. Likewise, in case of plastic deformation, for instance during reflow soldering, the maximum stress transferred to the active region is reduced.

[0050] The filler 37 and, in particular, the filler elements 38 can comprise a gas. Consequently, the connection element 3 can contain a plurality of voids, which form the filler elements 38 and which are at least gas-filled. In order to produce such voids, a material chosen from an organic material, water, solder flux or the like is mixed to the metal 36, wherein the material produces a gas before and/or during a solder process, thereby forming the voids. Alternatively or additionally, the filler 37 and, in particular, the filler elements 38 can comprise a plastic material, for example a silicone, which can be added as powder or beads to the metal 36. In this case, the connection element 3 can comprise particles dispersed in the metal 36, the particles forming the filler elements 38.

[0051] Alternatively or additionally to the features described in connection with the figures, the embodiments shown in the figures can comprise further features described in the general part of the description. Moreover, features and embodiments of the figures can be combined with each other, even if such combination is not explicitly described.

[0052] The invention is not restricted by the description on the basis of the exemplary embodiments. Rather, the invention encompasses any new feature and also any combination of features, which in particular comprises any combination of features in the patent claims, even if this feature or this combination itself is not explicitly specified in the patent claims or exemplary embodiments.