A sound producing device, a sound producing system and a method of manufacturing a sound producing device

Abstract

The present invention relates to a MEMS-based sound producing device (100) comprising a bonded chip stack with a first sound generating layer (20), a second sound generating layer (30) and an intermediate re-routing layer (40) The first sound generating layer (20) has a first support structure (200) forming an outer frame (201), being fixed to the periphery of at least one first sound generating element (210) and comprising at least one second opening (320). The second sound generating layer (30) has a second support structure (300) forming an outer frame (301), being fixed to the periphery of at least one second sound generating element (310) and comprising at least one second opening (320). Each re-routing layer (40) comprises at least one re- routing opening. The at least one second sound generating element (310), the at least one re-routing opening (420) and the at least one first opening (220) are arranged in the stack such that the inner walls of neighbouring openings overlap such that a sound-passing channel (70) for passing sound from the second sound generating element (310) to the first opening (220) is formed. The invention also relates to a method of manufacturing the sound producing device (100), and a sound producing system (110) comprising such a sound producing device.

Description

[0001] A SOUND PRODUCING DEVICE, A SOUND PRODUCING SYSTEM AND A METHOD OF MANUFACTURING A SOUND PRODUCING DEVICE

[0002] TECHNICAL FIELD

[0003] The present invention relates to a sound producing device. Preferably, the sound producing device is a micro speaker. More preferably, the sound producing device is a micro electromechanical system (MEMS) based micro speaker. Even more preferably, the sound producing device is a piezoelectric MEMS-based micro speaker.

[0004] The present invention also relates to a method of manufacturing such a sound producing device.

[0005] The present invention further relates to a sound producing system comprising such a sound producing device.

[0006] BACKGROUND

[0007] For sound generating devices, or speakers, generally, the acoustic output is related to the active area, with larger speaker sizes capable of producing more sound output. Several smaller speakers can also be combined into a combined device to create stronger sound output as well. However, in micro speaker applications, size is always a limiting factor, creating a challenge of producing adequate volume using a small active area.

[0008] In micro speaker applications such as in-ear headphones, several different acoustic drivers are typically combined, optimized for different frequency ranges. This removes the necessity of a full-range driver, but instead requires multiple units, creating even bigger demand for small form factors.

[0009] A piezoelectric MEMS speaker is a recent type of micro speaker with several advantages. However, like any other micro speaker they are generally limited by the available silicon substrate, or chip, area. With the aim of obtaining increased sound output from micro speakers, solutions exist for integrating several micro speakers on a single chip. One example of such integration is shown in the related art document US1 1172300 B2, which discloses two separate sound producing cells arranged side by side and being configured to produce sound on different audio bands, within different frequency ranges. As mentioned above, this solution removes the need for a full-range driver. However, even when several micro speakers are integrated in a single chip in this manner, the total active, sound-producing, area is still limited by the chip size and required dimensions of supporting structures to ensure the structural integrity of the chip. These dimensional limitations in turn set an upper limit to the highest possible sound output.

[0010] Hence, there is still a need to provide a micro speaker with an increased sound output compared to existing solutions.

[0011] SUMMARY

[0012] The object of the invention is to provide a sound producing device, e.g. a micro speaker, with an increased sound output compared to existing solutions, bearing in mind the problem that the active speaker area on a sound producing micro device, such as a microelectromechanical system (MEMS) micro speaker, is limited by the area of the chip / substrate size and the required dimensions of supporting structures to ensure the structural integrity of the chip and resulting device. A further object of the invention is to also enable sound output over different frequency ranges, within the limited area available, still having increased sound output compared to existing solutions.

[0013] This is achieved by a sound producing device, a sound producing system and a method of manufacturing a sound producing device, according to the appended independent claims.

[0014] The current invention relates to a sound producing device, preferably a MEMS based micro speaker, consisting of a bonded chip stack with micro speaker elements in several layers, where the acoustic output from one layer is routed through the other layers using sound passing channels leading the output around micro speaker elements in other layers. By the inventive use of sound producing devices in several layers in combination with the use of at least one intermediate layer and re-routing of sound through the sound passing channels of the stacked micro speaker, the active, sound producing, area of the sound producing device is increased compared to known single layer solutions. In other words, the active, sound producing, area of the inventive sound producing device is thereby enabled to exceed the maximum possible active area of a single layer micro speaker. The present invention also relates to a method of manufacturing such a sound producing device, and further to a sound producing system comprising such a sound producing device. In a first aspect of the invention, there is provided a sound producing device comprising a stack of a first sound generating layer, a second sound generating layer and at least one intermediate sound re-routing layer between the first sound generating layer and the second sound generating layer. The first sound generating layer comprises a first support structure forming an outer frame and being fixed to the periphery of at least one first sound generating element. The first support structure further comprises at least one first opening. The second sound generating layer comprises a second support structure forming an outer frame and being fixed to the periphery of at least one second sound generating element. The second support structure further comprises at least one second opening. Each of the at least one intermediate sound re-routing layer comprises a respective intermediate support structure forming a respective outer frame and having at least one re-routing opening. Each second sound generating element at least partially overlaps with at least one re-routing opening of each of the at least one intermediate support structure and said at least one re-routing opening at least partially overlaps with at least one first opening of the first support structure, such that the inner walls of the overlapping openings of the at least one intermediate support structure and the first support structure form a sound-passing channel for passing sound from the second sound generating element to the first opening. If there are two or more intermediate re-routing layers, each neighbouring pair of support structures in the stack will have at least partly overlapping second sound generating element and re-routing opening, re-routing opening and re-routing opening, or re-routing opening and first opening. Thereby, the inner walls of the pairwise overlapping openings of the support structures of all the layers in the stack form a sound-passing channel for passing sound from each second sound generating element to a first opening.

[0015] Suitably, the acoustic output from one layer is thereby routed through the other layers of the sound producing device using channels, typically etched channels, leading the sound output around micro speaker elements in other layers. Hence, the output sound from the second sound generating element in the second sound generating layer (the “bottom layer” or “bottom chip”) of the stack is directed past the at least one first sound generating element in the first sound generating layer (the “topmost layer” or “topmost chip”). Advantageously, the present invention thereby allows for larger effective micro speaker area in comparison the total chip area. Indeed, it is possible for the effective, sound producing, micro speaker area to exceed 100% of the total chip area since the micro speaker elements, or sound producing elements, are divided into different layers. Described differently, the output sound of both the first and second layer will be output, i.e., the sound waves of both layers will propagate, in the same direction from the sound producing device, from the first sound generating layer into the surrounding air, which is the intended sound output direction of the device. This is the direction from the sound producing device towards the intended user / listener. In the non-limiting example of an in-ear micro speaker, the output direction would be the direction from the first sound generating layer into the ear canal of a user, when the in-ear micro speaker is placed in the ear of the user.

[0016] Suitably, this also enables the integration of multiple micro speakers of varying shapes and sizes into a single unit, potentially replacing multiple discrete components in a speaker application.

[0017] Each sound passing channel may be symmetric or asymmetric with respect to the sound generating element from which it passes sound. Symmetrical is here understood as being symmetrical around an axis crossing the centre of the surface of the sound generating element that faces the sound passing channel and being perpendicular to said surface. By making channel symmetrical with respect to the sound generating element, the acoustic impedance between the air and the sound generating element will be likewise symmetrical, which contributes to smoother driving / actuation of the sound generating elements.

[0018] In the stack of the sound producing device, each first sound generating element may further at least partially overlap with at least one re-routing opening of each of the at least one intermediate support structure and said at least one re-routing opening at least partially overlaps with at least one second opening of the second support structure, such that the inner walls of the overlapping openings of the at least one intermediate support structure and the second support structure form a soundpassing channel for passing sound from the first sound generating element to the second opening. In this embodiment, if there are two or more intermediate re-routing layers, each neighbouring pair of support structures in the stack will have at least partly overlapping first sound generating element and re-routing opening, re-routing opening and re-routing opening, or re-routing opening and second opening. Thereby, the inner walls of the pairwise overlapping openings of the support structures of all the layers in the stack form a sound-passing channel for passing sound from each first sound generating element to a second opening. Hence, the output sound from the first sound generating element in the first sound generating layer (which may be referred to as the “topmost layer” or “topmost chip”) of the stack is directed past the at least one second sound generating element in the second sound generating layer (which may be referred to as the “bottom layer” or “bottom chip”). This allows the effective backside cavity size of the sound producing element to be defined outside of the chip stack, or the stack of layers, and can thus be made larger (or infinite, in the case of just connecting it to the atmosphere, or surrounding air), which reduces the acoustic impedance of the sound generation.

[0019] Preferably, at least one first sound generating element is partially or fully overlapping with at least one second sound generating element. In other words, the total size, or area, of the sound generating elements is not limited by the available area in a single layer but may be larger than what would have been possible for a single layer device. Advantageously, this increases total effective sound generating area available, and thus increases the possible sound output.

[0020] The stack may further comprise at least one additional sound generating layer. In this embodiment, each such additional sound generating layer comprises an additional support structure forming an outer frame and being fixed to the periphery of at least one additional sound generating element, wherein each additional support structure comprises at least one additional layer opening. Each of the at least one additional sound generating layer is then comprised between the first sound generating layer and the second sound generating layer, separated from each of the first and second sound generating layers by at least one intermediate sound rerouting layer, respectively.

[0021] Suitably, the total active area may thereby be increased even further compared to using two sound producing layers. Theoretically, a stack with a large number of layers is possible. However, the more sound-producing layers that are comprised in the stack, the more room is needed for sound passing channels, which gradually reduces the area available for sound producing elements in each layer.

[0022] In one or more embodiment, at least two of the sound generating elements in the first, second and / or additional layers are optimized for different frequency ranges.

[0023] Thereby, sound reproduction is suitably enabled over a larger frequency range, possibly the entire frequency range of interest, using a single sound generating device, while simultaneously achieving the advantage of increased sound output. This removes the necessity of a full-range driver.

[0024] The sound producing device may be a MEMS-based sound producing device.

[0025] Thereby, the sound producing device may advantageously be miniaturized. This enables application in for example wearable devices, on-ear headphones, earpieces, hearing aids, in-ear speakers, handheld devices such as mobile phones, and other applications which require small sized components.

[0026] The sound producing device may be a piezoelectric sound producing device, using a piezoelectric material as actuator.

[0027] Thereby, the power consumption may be reduced, which is a great advantage for small-sized applications and other applications which require low power consumption.

[0028] In a second aspect of the invention, there is provided a sound producing system comprising a sound producing device according to any of the embodiments described herein, that is in the description, the figures, or the claims, and further comprising a controller configured to generate at least one control signal that is configured to drive the sound generating elements of the sound producing device.

[0029] Suitably, the present invention thereby allows for larger effective micro speaker area in comparison the total chip area (the area in the x,y-plane), as described in connection with the first aspect. Furthermore, by the use of the controller, the generation of sound, i.e., driving the sound generating elements, may suitably be automatically controlled.

[0030] The sound producing device of the sound producing system may comprise N sound generating elements, wherein the controller is configured to drive the sound generating elements by generating N control signals, each control signal being configured to drive a sound generating element at frequencies within a frequency band determined by the control signal, wherein the frequency bands of at least two of the N control signals differ from each other. The controller is then configured to control each of the N sound generating elements based on a respective control signal, such that the sound generating elements are driven on at least two different frequency bands. Thereby, sound reproduction is suitably enabled over a larger frequency range, possibly the entire frequency range of interest, using a single sound generating device, while simultaneously achieving the advantage of increased sound output.

[0031] The controller may further be configured to receive an input audio signal and partition the audio band of the entire input audio signal into N audio sub-bands, each of the audio sub-bands covering a subrange of the frequencies of the entire input audio signal. In this embodiment, generating the respective control signal for each sound generating element comprises generating each control signal based on an individual one of the N audio bands.

[0032] Suitably, sound reproduction is thereby enabled over a larger part of or even the entire frequency range of the audio signal that is to be reproduced, using the single sound generating device, while simultaneously achieving the advantage of increased sound output.

[0033] For this purpose, the controller may comprise a crossover circuit that is coupled to the N sound generating elements and is configured to partition the audio band of the entire input audio signal into N audio sub-bands, thereby generating the N control signals, based on N-l preset crossover frequencies.

[0034] Suitably, the partition of the audio band of the input audio signal and the generation of control signals for driving the sound generating elements is achieved in an efficient manner.

[0035] A third aspect of the invention includes a method of manufacturing a sound producing device. The method comprises providing a first sound generating layer comprising a first support structure forming an outer frame and being fixed to the periphery of at least one first sound generating element. The first support structure comprises at least one first opening. The method further comprises providing a second sound generating layer comprising a second support structure forming an outer frame and being fixed to the periphery of at least one second sound generating element. The second support structure comprises at least one second opening. The method also comprises providing at least one intermediate sound re-routing layer comprising a respective intermediate support structure forming a respective outer frame and having at least two re-routing openings. The method further comprises stacking the first sound generating layer, the second sound generating layer, and the at least one intermediate sound re-routing layer between the first sound generating layer and the second sound generating layer, to form a sound producing device. The first, second and intermediate layers are stacked such that each second sound generating element at least partially overlaps with at least one re-routing opening of each of the at least one intermediate support structure and said at least one rerouting opening at least partially overlaps with at least one first opening of the first support structure. Thereby, the inner walls of the overlapping openings of the at least one intermediate support structure and the first support structure form a soundpassing channel for passing sound from the second sound generating element to the first opening. If there are two or more intermediate re-routing layers, the first, second and intermediate layers are stacked such that each neighbouring pair of support structures in the stack will have at least partly overlapping second sound generating element and re-routing opening, re-routing opening and re-routing opening, or rerouting opening and first opening. Thereby, the inner walls of the pairwise overlapping openings of the support structures of all the layers in the stack form a sound-passing channel for passing sound from each second sound generating element to a first opening.

[0036] Suitably, the present invention thereby allows for larger effective micro speaker area in comparison the total chip area, as described in connection with the first aspect.

[0037] Stacking the layers may further comprise stacking them such that each first sound generating element at least partially overlaps with at least one re-routing opening of each of the at least one intermediate support structure and said at least one rerouting opening at least partially overlaps with at least one second opening of the second support structure, so that the inner walls of the overlapping openings of the at least one intermediate support structure and the second support structure form a sound-passing channel for passing sound from the first sound generating element to the second opening. If there are two or more intermediate re-routing layers, the first, second and intermediate layers are in this embodiment stacked such that each neighbouring pair of support structures in the stack will have at least partly overlapping first sound generating element and re-routing opening, re-routing opening and re-routing opening, or re-routing opening and second opening. Thereby, the inner walls of the pairwise overlapping openings of the support structures of all the layers in the stack form a sound-passing channel for passing sound from each first sound generating element to a second opening. Hence, the output sound from the first sound generating element in the first sound generating layer (the “topmost layer” or “topmost chip”) of the stack is directed past the at least one second sound generating element in the second sound generating layer (the “bottom layer” or “bottom chip”). Suitably, this allows the effective backside cavity size of the sound producing element to be defined outside of the chip stack, or the stack of layers, and can thus be made larger (or infinite, in the case of just connecting it to the atmosphere, or surrounding air), which reduces the acoustic impedance of the sound generation.

[0038] Providing the first sound generating layer may comprise providing a first substrate and forming the first sound generating layer by patterning and etching said first substrate to provide a first support structure forming a first outer frame having at least one opening for fixation to the periphery of a respective at least one first sound generating element, and further having at least one first opening.

[0039] Similarly, providing the second sound generating layer may comprise providing a second substrate and forming the second sound generating layer by patterning and etching said second substrate to provide a second support structure forming a second outer frame having at least one opening for fixation to the periphery of a respective at least one second sound generating element, and further having at least one second opening.

[0040] Similarly to the embodiments for providing the first and / or second sound generating layers described above, providing the at least one intermediate substrate may comprise providing at least one intermediate substrate and, for each of the at least one intermediate substrate, forming an intermediate sound re-routing layer by patterning and etching said intermediate substrate to provide an intermediate support structure forming a respective outer frame and having at least one re-routing opening. This embodiment preferably comprises patterning and etching each of the at least one intermediate layer to provide an intermediate support structure having at least two re-routing openings. Thereby, at least one re-routing opening in each intermediate sound re-routing layer may become part of a sound passing channel for passing sound from the second sound generating element to a first opening, and at least one other re-routing opening may become part of a sound passing channel for passing sound from the first sound generating element to a second opening.

[0041] Stacking the first sound generating layer, the second sound generating layer, and the at least one intermediate sound re-routing layer between the first sound generating layer and the second sound generating layer may comprise bonding the adjacent layers in the stack to each other.

[0042] Thereby, a mechanically stable and hermetically sealed encapsulation is ensured. Any suitable bonding technique known in the art may be used.

[0043] The method may further comprise providing a carrier substrate, attaching the carrier substrate to the second substrate, providing an electrical connection between the carrier substrate and at least one of the first sound generating elements using a first electrically conductive wire, and providing a soldering connection between the carrier substrate and the second substrate, thereby electrically connecting the carrier substrate and the at least one second sound generating element.

[0044] Suitably, an electrical connection between the carrier substrate and the at least one second sound generating element is thereby achieved in an efficient manner, as the soldering connection in this embodiment may suitably provide both the attachment and the electrical connection between the carrier substrate and the second substrate.

[0045] In some embodiments the peripheral edge of the second substrate extends outside the peripheral edge of the intermediate substrate adjacent to it after stacking. In these embodiments, providing the second sound generating layer may further comprise patterning and etching said second substrate to form at least one through-silicon via from a part of the upper surface of the second substrate that is outside the peripheral edge of the intermediate substrate adjacent to it after stacking, such that the through-silicon via can be accessed after stacking, wherein each through-silicon via is in electrical contact with at least one second sound generating element. In these embodiments, the method further comprises providing a carrier substrate, attaching the carrier substrate to the second substrate, providing an electrical connection between the carrier substrate and at least one of the first sound generating elements using a first electrically conductive wire, and providing, for each of the at least one through-silicon via, a second electrically conductive wire between the carrier substrate and the through-silicon via, thereby electrically connecting the carrier substrate and the at least one second sound generating element.

[0046] Any advantage described in connection with one aspect of the invention, e.g. the sound producing device, is equally applicable to corresponding embodiments of other aspects of the invention, e.g. the sound producing system and the method for manufacturing the sound producing device. Many additional benefits and advantages of the present invention will be readily understood by the skilled person in view of the detailed description below.

[0047] DRAWINGS

[0048] The invention will now be described in more detail with reference to the appended drawings, wherein:

[0049] Figs, la-c schematically disclose a sound producing device according to a first embodiment, in a cross-sectional view;

[0050] Fig. 2 schematically discloses a sound producing system according to embodiments of the invention;

[0051] Figs. 3a-c schematically disclose a sound producing device according to the first embodiment, in a top view;

[0052] Figs. 4a-b schematically disclose a sound producing device according to a second embodiment, in a cross-sectional view;

[0053] Figs. 5a-c schematically disclose a sound producing device according to the second embodiment, in a top view;

[0054] Figs. 6a-c schematically disclose a sound producing device according to the second embodiment, in a top view;

[0055] Figs. 7a-c schematically disclose a sound producing device according to a third embodiment, in a top view;

[0056] Figs. 7d-e schematically disclose a sound producing device according to the third embodiment, in a cross-sectional view;

[0057] Figs. 8a-c schematically disclose a sound producing device according to a fourth embodiment, in a top view;

[0058] Figs. 8d-e schematically disclose a sound producing device according to the fourth embodiment, in a cross-sectional view;

[0059] Figs. 9a-b schematically disclose a sound producing device according to a fifth embodiment, in a cross-sectional view;

[0060] Figs. lOa-d schematically disclose a sound producing device according to the fifth embodiment, in a top view; Figs, l la-f schematically disclose a sound producing device according to a sixth embodiment, in a top view;

[0061] Figs. 12a-b schematically disclose a sound producing device according to the sixth embodiment, in a cross-sectional view;

[0062] Figs. 13a-c schematically disclose a sound producing device according to a seventh embodiment, in a top view;

[0063] Fig. 14 schematically discloses a sound producing device according to the seventh embodiment, in a cross-sectional view;

[0064] Figs. 15a-f schematically disclose a sound producing device according to an eighth embodiment, in a top view;

[0065] Fig. 16 schematically discloses a sound producing device according to the eighth embodiment, in a cross-sectional view;

[0066] Figs. 17a-c schematically disclose a sound producing device according to a nineth embodiment, in a top view;

[0067] Fig. 18 schematically discloses a sound producing device according to the nineth embodiment, in a cross-sectional view;

[0068] Figs. 19a-c schematically disclose a sound producing device according to a tenth embodiment, in a top view;

[0069] Fig. 20 schematically discloses a sound producing device according to the tenth embodiment, in a cross-sectional view;

[0070] Fig. 21 is a flow chart showing a method for manufacturing a sound producing device according to embodiments of the invention;

[0071] Fig. 22 is a flow chart showing a method for manufacturing a sound producing device according to an embodiment of the invention; and

[0072] Fig. 23 is a flow chart showing a method for manufacturing a sound producing device according to an embodiment of the invention.

[0073] All the figures are schematic, not necessarily to scale, and generally only show parts which are necessary in order to elucidate the respective embodiments, whereas other parts may be omitted or merely suggested. Any reference number appearing in multiple drawings refers to the same object or feature throughout the drawings, unless otherwise indicated.

[0074] DETAILED DESCRIPTION

[0075] There is provided a sound producing device, a sound producing system and a method for manufacturing a sound producing device to solve the problem of how to increase sound output compared to existing solutions, bearing in mind the problem that the active speaker area on a sound producing device, such as a microelectromechanical system (MEMS) micro speaker, is limited by the area of the substrate and the required dimensions of supporting structures to ensure the structural integrity of the chip and resulting device.

[0076] In other words, the inventive sound producing device according to embodiments herein comprises a bonded chip stack with micro speaker elements in several layers, where the acoustic output from one layer is routed through the other layers using etched channels leading the output around micro speaker elements in other layers.

[0077] It is noted that all sizes, angles, relations etc. given herein are not to be seen as only covering the exact given values but also include minor variations due to manufacturing tolerances. It is also to be noted that features from the various embodiments described herein may freely be combined, unless it is explicitly stated that such a combination would be unsuitable.

[0078] In a first aspect of the invention, a sound producing device 100 will first be described. The sound producing device 100 may be a MEMS-based sound producing device.

[0079] Figs, la-c and 3a-c schematically discloses such a sound producing device 100 according to a first embodiment. Figs. 3a-c show the different layers of the sound producing device 100 according to this first embodiment in a top view, while Figs, la- c show the stacked layers of the sound producing device 100 in a cross-sectional view of the stack taken along a cross-sectional line A-A’ shown in Figs. 3a-c.

[0080] It is noted that for the figures accompanying the embodiments of this first aspect of the invention, several figures show cross-sections of stacks along a respective selected axis. The selected axis could have been placed in an alternative location and / or angle. The skilled person understands from the figures the cross-sections that such alternative placement of the axis would render. It is further noted that a certain cross-section may be accomplished by many different layer designs. Finally, it is noted that the examples shown in the figures do not limit the invention but are merely illustrations of a number of different embodiments that are possible within the scope of the appended claims.

[0081] Turning first to Fig. la, there is shown a sound producing device 100 comprising a stack of a first sound generating layer 20, a second sound generating layer 30 and one intermediate sound re-routing layer 40. In this first embodiment, the stack of the sound producing device 100 comprises one re-routing layer 40. In other embodiments described herein the stack may instead comprise two or more intermediate layers 40, but always at least one intermediate re-routing layer 40. This at least one re-routing layer is what enables re-routing of sound around other elements of the sound producing device 100 and thereby enabling the use of a larger active area for sound generation compared to prior solutions without sound re-routing. The at least one intermediate sound re-routing layer 40 (the one re-routing layer 40 in this first embodiment) is arranged between the first sound generating layer 20 and the second sound generating layer 30 in the stack.

[0082] It is noted that the layers 20, 30, 40 and other layers described herein need not correspond to what is described by the term layers in MEMS processing. A layer as described herein may comprise several layers of the same or different material according to other, more detailed oriented, MEMS vocabulary. The layers 20, 30, 40 etc. described herein are used to provide an overview giving an easier understanding of the invention, and to illustrate the stacking relationship in different embodiments of the sound producing device 100.

[0083] As shown in the top view of the first sound generating layer 20 in Fig. 3a, the first sound generating layer 20 comprises a first support structure 200 forming an outer frame 201 and being fixed to the periphery of at least one, in this embodiment precisely one, first sound generating element 210. The first support structure 200 further comprises at least one first opening, in this embodiment four openings, 220.

[0084] As further shown in the top view of the intermediate re-routing layer 40 in Fig. 3b, the intermediate sound re-routing layer 40 comprises an intermediate support structure 400 forming an outer frame 401. The intermediate support structure 400 has at least one re-routing opening 420, in this first embodiment five re-routing openings 420. A re-routing opening is used for re-routing sound generated by the first sound generating layer 20, the second sound generating layer 30 and / or any additional sound generating layer in embodiments wherein at least one additional sound generating layer is included.

[0085] As can further be seen in the top view of the second sound generating layer 30 in Fig. 3c, the second sound generating layer 30 comprises a second support structure 300 forming an outer frame 301 and being fixed to the periphery of at least one second sound generating element 310. The second support structure 300 further comprises at least one second opening 320, in this first embodiment one second opening 320.

[0086] As illustrated in Figs, la to 1c, each second sound generating element 310 overlaps at least partially with at least one re-routing opening 420 of each of the at least one intermediate support structure 400 and the same at least one re-routing opening at least partially overlaps with at least one first opening 220 of the first support structure 200 when the layers 20, 30, 40 are stacked. Thereby, as shown in Figs, lb and 1c, the inner walls of the overlapping openings 420, 220, illustrated in the corresponding Fig. la, of the at least one intermediate support structure 400 and the first support structure 200 form at least one sound-passing channel 70, in this embodiment four sound passing channels 70, for passing sound from each of the second sound generating elements 310 to the first opening 220.

[0087] Overlapping openings is here understood as pairwise overlapping openings for each pair of neighbouring support structures in the stack. Thereby, the sound from both the first sound generating element 210 and the four second sound generating elements 310 will be output in the same direction from the sound producing device 100. In Figs, lb and 1c, this direction is referred to as DOUT and is indicated by arrows. The direction may also be described as directed out of the front side 101 of the sound producing device 100, as shown in Fig. 1c, which coincides with the front surface of the first sound generating layer 20. This is in contrast to the back side 102 of the sound producing device 100, which coincides with the back surface of the second sound generating layer 30. An increased sound output is thereby achieved.

[0088] Preferably, at least one first opening 220 also overlaps at least partially, preferably to a large degree, e.g. more than 50 %, with the corresponding second sound generating element 310 from which a sound passing channel 70 is formed to the first opening 220. Examples with different degree of overlap between the first opening 220 and a second sound generating element 310 connected thereto via a sound passing channel 70 are shown in Figs, la to 1c, 4a and 4b, 7d and 7e, 8d and 8e, 12b, 14, 16, 18 and 20. Advantageously, this achieves optimized sound pressure levels. However, the sound from a sound generating element 210, 310 may also be led around other elements in the stack if this design is preferable for a certain application. A nonlimiting example of such a stack design is e.g. illustrated for the fifth embodiment in Fig. 9b.

[0089] Since the layers 20, 30, 40 of the sound producing device 100 are stacked, the term overlapping when described features or elements of the stack is throughout this disclosure to be understood as overlapping as seen from a top view of the stack, e.g., in the view of Figs. 3a, 3b or 3c. In other words, features or elements described as overlapping herein have orthogonal projections that overlap when projected onto the x,y-plane or any two-dimensional plane parallel to the x,y-plane and the main extension of any of the layers 20, 30, 40 of the sound producing device 100.

[0090] Each first sound generating element 210 may further at least partially overlap with at least one re-routing opening 420 of each of the at least one intermediate support structure 400 and the same at least one re-routing opening 420 will then at least partially overlap with at least one second opening 320 of the second support structure 300, such that the inner walls of the overlapping openings 320, 420 of the at least one intermediate support structure 400 and the second support structure 300 form a sound-passing channel 71 for passing sound from the first sound generating element 210 to the second opening 320. Overlapping openings is here understood as pairwise over-lapping openings for each pair of neighbouring support structures in the stack. Advantageously, the at least one sound passing channel 71 leading sound to the second side, or backside, 102 of the sound producing device 100 allows the effective backside cavity size of the sound producing element to be defined outside of the chip stack, or the stack of layers, and can thus be made larger (or infinite, in the case of just connecting it to the atmosphere, or surrounding air), which reduces the acoustic impedance of the sound generation.

[0091] Similarly to what is described herein for any sound passing channel 70, optimized sound pressure levels is achieved in sound passing channels 71 if at least one second opening 320 also overlaps at least partially, preferably to a large degree, with the corresponding first sound generating element 210 from which a sound passing channel 71 is formed to the second opening 320.

[0092] In some embodiments, the layers may be designed and stacked such that the sound from at least one sound generating element 210, 310, 510 is passed through more than one sound passing channel 70, 71 to more than one opening 220, 320 on the front or back side of the sound producing device 100 if this design is preferable for a certain application. Examples of such stack designs are illustrated in Figs. 9b and 16.

[0093] Each of the at least one intermediate support structure 400 may have at least two rerouting openings 420. Thereby, at least one re-routing opening 420 in each intermediate sound re-routing layer 40 may become part of a sound passing channel 70 for passing sound from the second sound generating element 310 to a first opening 220, and at least one other re-routing opening 420 may become part of a sound passing channel 71 for passing sound from the first sound generating element 210 to a second opening 320. This is true for the first to sixth embodiments and the eighth to tenth embodiments described below. Sound passing channels 71 are illustrated in Figs, lb, 1c, 4a, 4c, 7d, 7e, 8d, 8e, 9a, 9b, 12a, 12b, 18 and 20 relating to the first to sixth embodiments and the ninth to tenth embodiments. In Fig. 16, relating to the eighth embodiment, no channel 71 is shown in the figure because the selected crosssection does not reveal such a channel. Also, there is no channel 71 for passing sound from the backside of the first sound generating element 210 to a second opening 320. As is clearly understood from the layers of Figs. 15a to f however, a different selection of cross-section through the stacked layers and a different viewpoint would show a channel 71 for passing sound from the back side of the additional sound generating element 510 of the additional sound generating layer 50 to a second opening 320 via pairwise at least partially overlapping openings in neighbouring support structures.

[0094] Second to tenth embodiments of this aspect of the invention will now be described with reference to Figs. 4a to 20. Each of these embodiments is similar to the first embodiment described above and will therefore be described mainly in those features that differ from the first embodiment. Anything not specifically said to be different when comparing any of the second to tenth embodiment to the first embodiment will be assumed to be similar, and it is to be noted that features from the different embodiments of an aspect of the invention may freely be combined unless such a combination is explicitly states as undesirable or disadvantageous. The same or very similar components are denoted by the same reference numerals.

[0095] Figs. 4a-b, 5a-c and 6a-c schematically disclose a sound producing device 100 according to a second embodiment. Figs. 5a-c show the different layers of the sound producing device 100 according to this second embodiment in a top view. Figs. 6a-c show an alternative design of the different layers of the sound producing device 100 according to this second embodiment in a top view. Figs. 4a-b show the stacked layers of the sound producing device 100 in a cross-sectional view of the stack taken along a cross-sectional line B-B’ shown in Figs. 5a-c or 6a-c. As shown in Figs. 4a and 4b, the sound passing channels 70, 71, which are formed when the layers shown in Figs. 3a to 3c are stacked, are in this embodiment symmetrical with respect to the first and second sound generating elements 210, 310. This is advantageous, because the acoustic impedance between the air and each first or second sound generating element 210, 310 will thereby likewise be symmetrical, which contributes to smoother driving of the sound generating elements 210, 310.

[0096] Figs. 7a-e schematically disclose a sound producing device 100 according to a third embodiment. Figs. 7a-c show the different layers of the sound producing device 100 according to this third embodiment in a top view. Figs. 7d-e show the stacked layers of the sound producing device 100 in a cross-sectional view of the stack taken along a cross-sectional line D-D’ shown in Figs. 7a-c.

[0097] Figs. 8a-e schematically disclose a sound producing device 100 according to a fourth embodiment. Figs. 8a-c show the different layers of the sound producing device 100 according to this fourth embodiment in a top view. Figs. 8d-e show the stacked layers of the sound producing device 100 in a cross-sectional view of the stack taken along a cross-sectional line E-E’ shown in Figs. 8a-c.

[0098] Figs. 9a-b and 10 a-d schematically disclose a sound producing device 100 according to a fifth embodiment. Figs. lOa-d show the different layers of the sound producing device 100 according to this fifth embodiment in a top view. Fig. 9a shows the stacked layers of the sound producing device 100 in a cross-sectional view of the stack taken along a cross-sectional line F-F’ shown in Figs. lOa-d, and Fig. 9b shows the stacked layers of the sound producing device 100 in a cross-sectional view of the stack taken along a cross-sectional line F”-F”’ shown in Figs. lOa-d.

[0099] Figs, l la-f and 12 a-b schematically disclose a sound producing device 100 according to a sixth embodiment. Figs, l la-f show the different layers of the sound producing device 100 according to this sixth embodiment in a top view. Fig. 12a shows the stacked layers of the sound producing device 100 in a cross-sectional view of the stack taken along a cross-sectional line G-G’ shown in Figs, l la-f, and Fig. 12b shows the stacked layers of the sound producing device 100 in a cross-sectional view of the stack taken along a cross-sectional line G”-G”’ shown in Figs, l la-f. The third, fourth, fifth and sixth embodiments, as well as all other embodiments herein, illustrate that the shape, number, and placement of sound generating elements 210, 310, 510 can be freely varied, as can the shape, number and placement of intermediate rerouting layers 40. In some cases, such as in the fifth embodiment, several intermediate re-routing layers 40 may be necessary. In addition, Figs, l la-f and 12a-b of the seventh embodiment illustrate that the number of sound generating layers 20, 30, 50 are not limited to only two, but may include additional sound generating layers 50 as described herein.

[0100] The great variability achieved by the embodiments of the present invention also enables the integration of multiple sound generating elements 210, 310, 510 of varying shapes and sizes into a single unit, such as a single sound producing device 100, potentially replacing multiple discrete components in a speaker application.

[0101] Figs. 13a-c and 14 schematically disclose a sound producing device 100 according to a seventh embodiment. Figs. 13a-c show the different layers of the sound producing device 100 according to this seventh embodiment in a top view. Fig. 14 shows the stacked layers of the sound producing device 100 in a cross-sectional view of the stack taken along a cross-sectional line H-H’ shown in Figs. 13a-c.

[0102] Similarly to the second embodiment, the sound passing channels 70, which are formed when the layers shown in Figs. 13a to 13c are stacked, are in this embodiment symmetrical, or substantially symmetrical, with respect to the second sound generating elements 310, thereby contributing to smoother driving of the second sound generating elements 310.

[0103] Figs. 15a-f and 16 schematically disclose a sound producing device 100 according to an eighth embodiment. Figs. 15a-f show the different layers of the sound producing device 100 according to this eighth embodiment in a top view. Fig. 16 shows the stacked layers of the sound producing device 100 in a cross-sectional view of the stack taken along a cross-sectional line I-F shown in Figs. 15a-f.

[0104] The first sound generating layer 20 of this embodiment, shown in Fig. 15a, comprises one large sound generating element 210 that overlaps all of the 8 second sound generating elements 310 of the second sound generating layer 30, shown in Fig. 15f, and the additional sound generating element 510 of the additional sound generating layer 50, shown in Fig. 15d. It can be clearly seen from the figures that the total active area of the sound generating elements 210, 310, 510 exceed the surface area of each of the layers 20, 30, 40, 50 in the stack. To enable sound passing channels 70 for passing sound from each of the second sound generating elements 310 to one of the first openings 220, around the first and additional sound generating elements 210, 510, two intermediate re-routing layers 400, shown in Figs. 15b and 15c, are needed between the first sound generating layer 20 and the additional sound generating layer 50, and a further intermediate re-routing layer 40, shown in Figs. 15e, is used between the additional sound generating layer 50 and the second sound generating layer 30. Thereby, the stack of Fig. 16 is obtained.

[0105] In contrast to the other embodiments, the first sound generating element 210 in the seventh as well as in the eighth embodiment is not connected to a sound passing channel 71 from its back side, i.e. a sound passing channel 71 for passing sound from the first sound generating element 210 to a second opening 320. Instead, the back side of the first sound generating element 210 faces a closed cavity. Although this will affect the performance of the first sound generating element 210 negatively to some degree, it will at the same time allow for increased active areas of the additional and second sound generating elements 510, 310, as less part of each layer needs to comprise openings compared to if there is a sound passing channel 71 going from the first sound generating element 210 to the second opening 320. To maximize the possible active area on the second sound generating layer 30, also the back side of the additional sound generating element 510 in this embodiment faces a closed cavity instead of a sound passing channel 71.

[0106] One or more closed cavity instead of a sound passing channel 71 leading sound towards second opening(s) on the back side 102 of the sound producing device 100 may be used in combination with any embodiment herein, to enable maximization of the total active area on the second sound generating layer 30 and any additional sound generating layer 50.

[0107] Figs. 17a-c and 18 schematically disclose a sound producing device 100 according to a ninth embodiment. Figs. 17a-c show the different layers of the sound producing device 100 according to this ninth embodiment in a top view. Fig. 18 shows the stacked layers of the sound producing device 100 in a cross-sectional view of the stack taken along a cross-sectional line J-J’ shown in Figs. 17a-c.

[0108] Fig. 18 also shows a first solution to the problem of getting drive signals, also referred to herein as actuation signals or control signals C, Cl, C2, C3, ..., CN to reach the sound generating elements 210, 310, 510 of different layers in the stack of the sound producing device 100. In Fig. 18, the layers 20, 30, 40 are represented as a first substrate 2 a second substrate 3 and an intermediate substrate 4. In this embodiment, the stack of the sound producing device 100 further comprises a carrier substrate 6 attached to the second substrate 6, i.e. attached to the back surface of the second sound generating layer 30 or second substrate 3, which is sometimes referred to herein as the back side 102 of the sound producing device 100. The sound producing device 100 further comprises an electrical connection between the carrier substrate 6 and at least one of the first sound generating elements 210 (in the example in Figs. 17a-c and 18 there is only one first sound generating element 210, but this solution is applicable to any other embodiment herein) in the form of a first electrically conductive wire 61. The sound producing device 100 in this embodiment also comprises a soldering connection 62 between the carrier substrate 6 and the second substrate 3, thereby electrically connecting the carrier substrate 6 also to the at least one second sound generating element 310. The electrical connection from any wire 61, 62 to relevant elements including the at least one first sound generating element 210 and second sound generating element 310, or a respective actuator thereof, may include using routing or any other suitable manner known in the art.

[0109] Figs. 19a-c and 20 schematically disclose a sound producing device 100 according to a tenth embodiment. Figs. 19a-c show the different layers of the sound producing device 100 according to this ninth embodiment in a top view. Fig. 20 shows the stacked layers of the sound producing device 100 in a cross-sectional view of the stack taken along a cross-sectional line K-K’ shown in Figs. 19a-c.

[0110] Fig. 20 shows a second solution to the problem of getting drive signals, also referred to herein as actuation signals or control signals C, Cl, C2, C3, ..., CN to reach the sound generating elements 210, 310, 510 of different layers in the stack of the sound producing device 100. In Fig. 20, similarly to Fig. 18, the layers 20, 30, 40 are represented as a first substrate 2, a second substrate 3 and an intermediate substrate 4. Unlike the ninth embodiment, the peripheral edge of the second substrate 3 extends outside the peripheral edge of the intermediate substrate 4 adjacent to it after stacking. Preferably, as shown in the figures, the peripheral edge of the second substrate 3 also extends outside the peripheral edge of any other substrate in the stack, in this example the first substrate 2. Thereby, other options for electrical connection are available. As shown in Fig. 20, the second substrate comprises at least one through-silicon via 63 outside the peripheral edge of the intermediate substrate 4 adjacent to it, and also outside the peripheral edge of the first substrate 2, as seen form a top view. Thereby, the through- silicon via 63 can be accessed after stacking. In this embodiment, each through-silicon via 63 is in electrical contact with at least one second sound generating element 310.

[0111] The sound producing device 100 in the tenth embodiment further comprises a carrier substrate 6 attached to the second substrate 6, i.e. attached to the back surface of the second sound generating layer 30 or second substrate 3, which is sometimes referred to herein as the back side 102 of the sound producing device 100. The sound producing device 100 further comprises an electrical connection between the carrier substrate 6 and at least one of the first sound generating elements 210 (in the example in Figs. 17a-c and 18 there is only one first sound generating element 210, but this solution is applicable to any other embodiment herein) in the form of a first electrically conductive wire 61. The sound producing device 100 in this embodiment also comprises, for each of the at least one through-silicon via 63, a second electrically conductive wire 62 forming an electrical connection between the carrier substrate 6 and through-silicon via 63. Thereby, the carrier substrate 6 is electrically connected also to the at least one second sound generating element 310. The electrical connection from any wire 61, 62 to relevant elements including the at least one first sound generating element 210 and second sound generating element 310, or a respective actuator thereof, may include using routing or any other suitable manner known in the art.

[0112] Further features are now described, relating to the sound producing device 100 of any or all of the first to tenth embodiments.

[0113] In embodiments wherein the sound producing device 100 comprises two or more intermediate re-routing layers 40, each intermediate re-routing layer 40 comprises a respective intermediate support structure 400 similar to the intermediate support structure 400 described for the first embodiment.

[0114] If there are two or more intermediate re-routing layers 40, the first, second and intermediate layers 20, 30, 40 are stacked such that each neighbouring pair of support structures 200, 300, 400 in the stack will have an at least partly overlapping second sound generating element 310 and re-routing opening 420, re-routing opening 420 and re-routing opening 420, or re-routing opening 420 and first opening 220. The inner walls of the pairwise overlapping openings 420, 220 of the support structures of the stack thereby form a sound-passing channel 70 for passing sound from each second sound generating element 310 to a first opening 220. The stacked layers may be rectangular, as illustrated in most of the examples of the figures but may have other shapes if suitable. Similarly, the shape, number and placement of sound producing elements 210, 310, 510, openings 220, 320, 420, 520 and any other elements of the layers may be varied freely. The examples shown in the first to tenth embodiments are illustrative examples only, and not limiting to the invention. The stacked layers may be equal in width (extension along the x-axis as indicated in the figures) and length (extension along the y-axis as indicated in the figures), within manufacturing tolerances. In other embodiments, if suitable, the width and / or length of at least one of the stacked layers may differ from that of at least one adjacent layer, so that one of the layers extend beyond the periphery of the other and the upper or lower surface of the layer extending beyond its adjacent layer can be accessed, e.g., for electrical connection as illustrated in Fig. 20.

[0115] The depth (extension along the z-axis as indicated in the figures) of the stacked layers may be the same or differ between layers, depending on the most preferable design for different applications. The stacked layers may be bonded together or attached in any suitable manner known in the art.

[0116] The sound generating elements 210, 310, 510 in any embodiment described herein may optionally comprise one or more slits, in different suitable configurations and design, used to change the deflection capacity and / or resonance frequency of the sound generating element. A non-limiting example of such slits is illustrated in Fig. 3a by the dashed lines 103. The term slit herein refers to a fine line cutting through the thickness, or part of the thickness, of a sound generating element, such as a membrane. The slit is typically very narrow. The pattern of slits affects the stiffness of the overall sound generating element, and hence the resonance frequency and deflectability thereof. The at least one slit may be made using to any suitable method known in the art At least one slit may be applied to any or all sound producing elements 210, 310, 510 in any embodiment presented herein.

[0117] Any sound generating element 210, 310, 510 herein may be a flexible membrane.

[0118] The sound producing device 100 may be a piezoelectric sound producing device. The actuator may in this case be a thin film actuator, such as a piezoelectric actuator. In an embodiment, the material may be made of lead zirconate titanate (PZT). The driving signal, herein referred to as a control signal C, Cl, C2, C3, ..., CN, causes deformation of the thin film actuator, which causes the sound generating element onto which the actuator is applied to move in the Z direction, i.e. deflect, and thereby generate sound pressure.

[0119] Thereby, the power consumption may be reduced, which is a great advantage for small-sized applications and other applications which require low power consumption.

[0120] The control signal C may comprise more than one control signal, configured to actuate a separate actuators and sound generating devices 210, 310, 510, via separate routings. Of course, the control signal C may comprise more than two signals, Cl, C2, C3, ..., CN, if this is required or desirable in a certain application, e.g. to drive N membranes that require separate drive signals, wherein N is a positive integer, preferably N > 2.

[0121] The sound generating elements may preferably be flexible membranes.

[0122] The support structures 200, 300, 500 are typically made of a semiconductor material, preferably silicon.

[0123] The openings in the different layers in the stack are etched openings that together with etched openings with which they overlap in the neighbouring layers form continuous channels leading the sound output from a sound generating element in the stack (which may be a micro speaker element, e.g. a flexible membrane) around sound generating elements in the other layers of the stack. Thereby sound is rerouted to the layer from which it is intended to be output. It is also noted that any opening 220, 320, 420, 520 in a layer described herein is a through opening through the entire thickness of the layer, as overlapping openings can form the sound passing channels 70, 71 described herein for passing sound from a sound generating element 210, 310, 510 through the stacked layers and into the surrounding air through the layer from which it is intended to be output. That each opening 220, 320, 420, 520 is a through opening is evident from the figures.

[0124] The number of first openings 220 in the first sound generating layer 20 may correspond to the number of second sound generating elements 310 in the second sound generating layer 30, and the number of second openings 320 in the second sound generating layer 30 may similarly correspond to the number of first sound generating elements 210 in the first sound generating layer 20. Several such examples are illustrated in the figures. It is also possible to achieve the advantages of the present invention using a different number of first and second openings 220, 320, respectively, in relation to the number of second and first sound generating elements 310, 210, respectively, as long as the neighbouring of relevant first, second and intermediate openings and sound generating elements in the stack are arranged such that they provide the required sound passing channels when the layers are stacked as described herein.

[0125] In some embodiments, at least one first sound generating element 210 is partially or fully overlapping with at least one second sound generating element 310 and / or at least one additional sound generating element 510, wherein at least one sound passing channel 70 leads the output sound from the second sound generating element 310 and / or the additional sound generating element 510 around the first sound generating element 210 to at least one first opening 220. Thereby, the total surface area of the first and second and / or additional sound producing elements 210, 310, 510 can be larger than the surface area of a sound generating element in a single layer micro speaker. Different non-limiting examples of stack designs with such overlapping first, second and / or additional sound generating elements 210, 310, 510 are shown in Figs. 4a and 4b, 7d and 7e, 8d and 8e, 9a and 9b, 12a and 12b, 14, 16, 18 and 20. The active area of each of these designs is impossible to achieve with a single layer micro speaker, and without the use of the inventive re-routing of sounds through a stack of layers. Depending on the size, design, placement, and number of the at least one first and at least one second sound producing elements 210, 310, and possibly also at least one additional sound producing element 510, the total surface area of all sound producing elements 210, 310, 510 can even be larger than the surface area of the micro speaker. Advantageously, embodiments herein thereby provide a sound producing device 100 that is able to achieve a higher output sound pressure per surface area unit compared to existing solutions.

[0126] The stack of the sound producing device 100 of any embodiment herein may further comprise at least one additional sound generating layer 50. The more sound generating layers that are added, the more active area, i.e. area of sound generating elements, may be used in the same sound producing device 100. Of course, the more sound generating elements 210, 310, 510 that are added, the more sound passing channels 70, 71 are needed to direct the output sound, and there will also be an increased need for intermediate re-routing layers 40 and possibly increasingly complex designs of the layers 20, 30, 40, 50 to achieve proper sound re-routing. As described herein in connection with Figs. 15a-f and 16, a combination of forward directed sound passing channels 70, backward directed sound passing channels 71 and closed cavities may be used, if this is suitable to enable a maximized total sound generation area, or maximized output sound pressure levels.

[0127] If at least one additional sound generating layer 50 is comprised in the stack, each additional sound generating layer 50 comprises an additional support structure 500 forming an outer frame 501 and being fixed to the periphery of at least one additional sound generating element 510, wherein each additional support structure 500 comprises at least one additional layer opening 520. Each additional support structure 500 may be obtained in a similar manner as described in connection with the first and second support structures, 200, 300, respectively. Each of the at least one additional sound generating layer 50 is then comprised between the first sound generating layer 20 and the second sound generating layer 30, separated from each of the first and second sound generating layers 20, 30 by at least one intermediate sound re-routing layer 40, as illustrated the exemplary embodiments in connection with Figs. 12a-b and 16.

[0128] In any embodiment herein, at least two of the sound generating elements 210, 310, 510 may be optimized for different frequency ranges. Thereby, multiple different acoustic drivers are combined in one sound producing device 100, the different acoustic drivers being optimized for different frequency ranges, to achieve sound reproduction over the entire frequency range of interest. Embodiments described herein may for example be used to produce a highly size efficient micro speaker capable of generating sounds of higher frequencies, as well as sounds of lower frequencies in a single device.

[0129] The first to tenth embodiments described herein show examples of possible designs of a sound producing device 100, with regard to number of layers, shape, size, and relative placement of the sound generating elements and openings, etc. Of course, a great number of alternative designs are possible with the scope of the invention according to the appended claims.

[0130] In a second aspect, the invention includes a sound producing system 110, which will now be described with reference to Fig. 2.

[0131] Fig. 2 shows a sound producing system 110 comprising at least one sound producing device 100 according to any embodiment herein, and a controller 120. The controller 120 is configured to generate at least one control signal C, Cl, C2, C3, ..., CN configured to drive the first, second, and in some cases also additional sound generating elements 210, 310, 510 of the at least one sound producing device 100. The sound producing system 110 may alternatively comprise more than one controller 120, wherein separate controllers are configured to drive separate or groups or sound generating elements 210, 310, 510. A controller 110 may also be referred to as a driver circuit.

[0132] In some embodiments of this second aspect of the invention, a sound producing device 100 of the sound producing system 110 comprises N sound generating elements 210, 310, 510. The controller 120 is in these embodiments configured to drive the sound generating elements 210, 310, 510 by generating N control signals Cl, C2, C3, ..., CN, each control signal Cl, C2, C3, ..., CN being configured to drive a first second or additional sound generating element 210, 310, 510 at frequencies within a frequency band, or frequency range, determined by the control signal Cl, C2, C3, ..., CN. The frequency bands of at least two of the N control signals Cl, C2, C3, ..., CN differ from each other. The controller 120 is then further configured to control each of the N first, second and possibly additional sound generating elements 210, 310, 510 based on a respective control signal Cl, C2, C3, ..., CN. Thereby, the sound generating elements 210, 310, 510 are driven on at least two different frequency bands. Suitably, this means that a larger range of frequencies can be reproduced by the sound producing element 100 and system 110. This removes the necessity of a full-range driver. For example, a first sound producing cell may comprise at least one sound generating element 210, 310, 510 configured to produce sound of higher register, and a second sound producing cell may comprise at least one sound generating element 210, 310, 510 configured to produce sound of lower register, compared to the first sound producing cell. Each sound generating element in the first and second sound producing cell is then controllable in response to a control signal Cl, C2, C3, ..., CN configured to drive the sound generating element in question in the desired frequency bad, or frequency range. A control signal may also be referred to as drive signal or an actuation signal.

[0133] The controller 120 may further be configured to receive an input audio signal S and partition the audio band of the entire input audio signal S into N audio sub-bands, each of the audio sub-bands covering a subrange of the frequencies of the entire input audio signal S. Generating the respective control signal Cl, C2, C3, ..., CN for each sound generating element 210, 310, 510 in this embodiment comprises generating each control signal Cl, C2, C3, ..., CN based on an individual one of the N audio bands. A frequency band may be referred to as a frequency range, an audio band, a subband, etc. All frequency ranges combined suitably covers the entire frequency range, or audio band, of the input audio signal S, based on which sound to be produced by the sound producing device and system according to embodiments herein. The frequency ranges may be partly overlapping or non-overlapping.

[0134] Partitioning the audio band into multiple frequency bands, or frequency ranges, suitably also enables optimizing the audio band of the input audio signal so as to balance factors such as the resonance frequency, compliance (stiffness), degrees of freedom and / or air leakage. Power consumption for producing the sound may also advantageously be reduced by driving different sound generating elements 210, 310, 510 in different frequency ranges, specifically for piezoelectric material driven MEMS micro speakers.

[0135] For the purpose of partitioning the audio band into multiple frequency ranges, the controller 120 may suitably comprise a crossover circuit that is coupled to the N sound generating elements 210, 310, 510, and is configured to partition the audio band of the entire input audio signal S into N audio sub-bands, thereby generating the N control signals Cl, C2, C3, ..., CN, based on N- l preset crossover frequencies.

[0136] In a third aspect of the invention and with reference to the flow diagram in Figs. 21, 22 and 23, we will now describe a method of manufacturing a sound producing device 100 according to any embodiment described in connection with Figs, la to c and 3a to 20. All embodiments and variations of the sound producing device 100 and its features and elements described herein are applicable to the method embodiments, where suitable.

[0137] The method illustrated in Fig. 21 comprises:

[0138] In step 2110: providing a first sound generating layer 20 comprising a first support structure 200 forming an outer frame 201 and being fixed to the periphery of at least one first sound generating element 210, wherein the first support structure 200 comprises at least one first opening 220.

[0139] Providing the first sound generating layer 20 may comprise providing a first substrate 2 and forming the first sound generating layer 20 by patterning and etching said first substrate 2 to provide a first support structure 200 forming a first outer frame 201 having at least one opening for fixation to the periphery of a respective at least one first sound generating element 210, and further having at least one first opening 220.

[0140] In step 2120: providing a second sound generating layer 30 comprising a second support structure 300 forming an outer frame 301 and being fixed to the periphery of at least one second sound generating element 310, wherein the second support structure 300 comprises at least one second opening 320.

[0141] Providing the second sound generating layer 30 may comprise providing a second substrate 3 and forming the second sound generating layer 30 by patterning and etching said second substrate 3 to provide a second support structure 300 forming a second outer frame 301 having at least one opening for fixation to the periphery of a respective at least one second sound generating element 310, and further having at least one second opening 320.

[0142] In step 2130: providing at least one intermediate sound re-routing layer 40 comprising a respective intermediate support structure 400 forming a respective outer frame 401 and having at least two re-routing openings 420.

[0143] Providing the at least one sound re-routing layer 40 comprises providing at least one intermediate substrate 4 and, for each of the at least one intermediate substrate 4, forming an intermediate sound re-routing layer 40 by patterning and etching said intermediate substrate 4 to provide an intermediate support structure 400 forming a respective outer frame 401 and having at least one re-routing opening 420.

[0144] In step 2140: stacking the first sound generating layer 20, the second sound generating layer 30, and the at least one intermediate sound re-routing layer 40 between the first sound generating layer 20 and the second sound generating layer 30, to form a sound producing device 100, wherein the layers 20, 30, 40 are stacked such that each second sound generating element 310 at least partially overlaps with at least one re-routing opening 420 of each of the at least one intermediate support structure 400 and said at least one re-routing opening 420 at least partially overlaps with at least one first opening 220 of the first support structure 200, such that the inner walls of the overlapping openings 220, 420 of the at least one intermediate support structure 400 and the first support structure 200 form a sound-passing channel 70 for passing sound from the second sound generating element 310 to the first opening 220. In some embodiments, stacking the layers 20, 30, 40 may further comprise stacking them such that each first sound generating element 210 at least partially overlaps with at least one re-routing opening 420 of each of the at least one intermediate support structure 400 and said at least one re-routing opening 420 at least partially overlaps with at least one second opening 320 of the second support structure 300, such that the inner walls of the overlapping openings 320, 420 of the at least one intermediate support structure 400 and the second support structure 300 form a sound-passing channel 70 for passing sound from the first sound generating element 210 to the second opening 320.

[0145] Stacking the first sound generating layer 20, the second sound generating layer 30, and the at least one intermediate sound re-routing layer 40 may comprise bonding the adjacent layers in the stack to each other. Alternatively, or additionally, any other suitable attachment means may be used.

[0146] Turning now to Fig. 22 with reference to Fig. 18, the method may further comprise:

[0147] In step 2210: providing a carrier substrate 6.

[0148] Step 2210 may be performed after step 2140, or at any suitable time between the steps of the method of Fig. 21.

[0149] In step 2220: attaching the carrier substrate 6 to the second substrate 3.

[0150] The attachment may be done in any suitable manner known in the art.

[0151] In step 2230: providing an electrical connection between the carrier substrate 6 and at least one of the first sound generating elements 210 using a first electrically conductive wire 61.

[0152] The first electrically conductive wire may be attached and connected to the surface on the first side, or front side, 101 of the sound producing device 100, which is also the front side of the first substrate 2 , from where electrical connection with relevant elements including the at least one first sound generating element 210, or a respective actuator thereof, can be achieved by routing or in any other suitable manner known in the art.

[0153] In step 2240: providing a soldering connection 62 between the carrier substrate 6 and the second substrate 3, thereby electrically connecting the carrier substrate 6 and the at least one second sound generating element 310. In Fig. 18, an example of a sound producing device 100 resulting from the manufacturing method of Fig. 22 is shown, wherein the sound producing device 100 is attached to, or comprises, a carrier substrate 6. In Fig. 18, a wire connection in the form of a first electrically conductive wire 61 and a soldering connection in the form of soldering balls 62 is shown.

[0154] Alternatively to the method embodiments described in connection with Fig. 22, the method described in connection with Fig. 21 may instead further comprise the steps shown in Fig. 23. In this embodiment, as illustrated in corresponding sound producing device 100 in Fig. 20, the peripheral edge of the second substrate 3 extends outside the peripheral edge of the intermediate substrate 4 adjacent to it after stacking. Thereby, alternative manners of providing an electrical connection to elements in the second substrate 3 are available compared to if the edges of the substrates were aligned, i.e. if the substrates were of equal size and shape (and concentrically arranged in the stack).

[0155] In the embodiment of Fig. 23, step 2120 of providing the second sound generating layer 30 further comprises, as shown in Fig. 20:

[0156] In step 2310: patterning and etching said second substrate 3 to form at least one through- silicon via 63 from a front side 401 of the second substrate 3 at a point that is outside the peripheral edge of the intermediate substrate 4 adjacent to it after stacking. Thereby, the through-silicon via 63 can be accessed after stacking.

[0157] Each through-silicon via 63 is further in electrical contact with at least one second sound generating element 310.

[0158] The method of Fig. 23 further comprises:

[0159] In step 2320: providing a carrier substrate 6.

[0160] Step 2210 may be performed after step 2140, or at any suitable time between the steps of the method of Fig. 21.

[0161] In step 2330: attaching the carrier substrate 6 to the second substrate 3.

[0162] Attaching may be done in any suitable manner known in the art, e.g., using glue 64, as illustrated in the non-limiting example of Fig. 20, or other adhesive means. In step 2340: providing an electrical connection between the carrier substrate 6 and at least one of the first sound generating elements 210 using a first electrically conductive wire 61.

[0163] The first electrically conductive wire may be attached and connected to the surface on the first side, or front side, 101 of the sound producing device 100, which is also the front side of the first substrate 2 , from where electrical connection with relevant elements such as the at least one first sound generating element 210, or a respective actuator thereof, can be achieved in any manner known in the art.

[0164] In step 2350: providing, for each of the at least one through-silicon via 63, a second electrically conductive wire 62 between the carrier substrate 6 and the through- silicon via 63, thereby electrically connecting the carrier substrate 6 and the at least one second sound generating element 310.

[0165] The second electrically conductive wire may be attached and connected to the surface on the front side 401 of the second substrate 3, from where electrical connection with relevant element, including the through-silicon via, can be achieved by routing or in any other suitable manner known in the art.

[0166] The carrier substrate 6 may be a printed circuit board (PCB).

[0167] The carrier substrate 6 may also comprise openings into which the sound passing channels 70, 71 of embodiments presented herein may extend.

[0168] Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

[0169] The term “comprises / comprising” when used in this specification is taken to specify the presence of stated features, integers, steps, or components. The term does not preclude the presence or addition of one or more additional elements, features, integers, steps or components or groups thereof. The indefinite article "a" or "an" does not exclude a plurality. In the claims, the word “or” is not to be interpreted as an exclusive or (sometimes referred to as “XOR”). On the contrary, expressions such as “A or B” covers all the cases “A and not B”, “B and not A” and “A and B”, unless otherwise indicated. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

[0170] It is also to be noted that features from the various embodiments described herein may freely be combined, unless it is explicitly stated that such a combination would be unsuitable.

[0171] The invention is not restricted to the described embodiments in the figures but may be varied freely within the scope of the claims.

Claims

CLAIMS1. A MEMS -based sound producing device (100) comprising a bonded chip stack with micro speaker elements in several layers including a first sound generating layer (20), a second sound generating layer (30) and at least one intermediate sound re-routing layer (40) between the first sound generating layer (20) and the second sound generating layer (30), wherein: the first sound generating layer (20) comprises a first support structure (200) forming an outer frame (201) and being fixed to the periphery of at least one first sound generating element (210), wherein the first support structure (200) further comprises at least one first opening (220); the second sound generating layer (30) comprises a second support structure (300) forming an outer frame (301) and being fixed to the periphery of at least one second sound generating element (310), wherein the second support structure (300) further comprises at least one second opening (320); each of the at least one intermediate sound re-routing layer (40) comprises a respective intermediate support structure (400) forming a respective outer frame (401) and having at least one re-routing opening (420); and wherein each second sound generating element (310) at least partially overlaps with at least one re-routing opening (420) of each of the at least one intermediate support structure (400) and said at least one re-routing opening (420) at least partially overlaps with at least one first opening (220) of the first support structure (200) as seen from a top view of the stack, such that the inner walls of the overlapping openings (220, 420) of the at least one intermediate support structure (400) and the first support structure (200) form a sound-passing channel (70) for passing sound from the second sound generating element (310) around micro speaker elements in other layers to the first opening (220).

2. The sound producing device (100) of claim 1, wherein each first sound generating element (210) at least partially overlaps with at least one rerouting opening (420) of each of the at least one intermediate supportstructure (400) and said at least one re-routing opening (420) at least partially overlaps with at least one second opening (320) of the second support structure (300), such that the inner walls of the overlapping openings (320, 420) of the at least one intermediate support structure (400) and the second support structure (300) form a sound-passing channel (71) for passing sound from the first sound generating element (210) around micro speaker elements in other layers to the second opening (320).

3. The sound producing device (100) of claim 1 or 2, wherein at least one first sound generating element (210) is partially or fully overlapping with at least one second sound generating element (210).

4. The sound producing device (100) of any one of the preceding claims, wherein the stack further comprises at least one additional sound generating layer (50), each comprising an additional support structure (500) forming an outer frame (501) and being fixed to the periphery of at least one additional sound generating element (510), wherein each additional support structure (500) comprises at least one additional layer opening (520), wherein each of the at least one additional sound generating layer (50) is comprised between the first sound generating layer (20) and the second sound generating layer (30), separated from each of the first and second sound generating layers (20, 30) by at least one intermediate sound re-routing layer (40).

5. The sound producing device (100) of any one of the preceding claims, wherein at least two of the sound generating elements (210, 310, 510) are optimized for different frequency ranges.

6. The sound producing device (100) of any one of the preceding claims, wherein the sound producing device (100) is a piezoelectric sound producing device.

7. A sound producing system (110) comprising a MEMS-based sound producing device (100) according to any one of the claims 1 to 6 and a controller (120) configured to generate at least one control signal (C, Cl, C2, C3, ..., CN) configured to drive the sound generating elements (210, 310, 510) of the sound producing device (100).

8. The sound producing system (110) of claim 7, wherein the sound producing device (100) comprising N sound generating elements (210, 310, 510),wherein N > 2, and wherein the controller (120) is configured to drive the sound generating elements (210, 310, 510) by: generating N control signals (Cl, C2, C3, ..., CN), each control signal (Cl, C2, C3, ..., CN) being configured to drive a sound generating element (210, 310, 510) at frequencies within a frequency band determined by the control signal (Cl, C2, C3, ..., CN), wherein the frequency bands of at least two of the N control signals (Cl, C2, C3, ... , CN) differ from each other; and controlling each of the N sound generating elements (210, 310, 510) based on a respective control signal (Cl, C2, C3, ..., CN), such that the sound generating elements (210, 310, 510) are driven on at least two different frequency bands.

9. The sound producing system (110) of claim 8, wherein the controller (120) further is configured to: receive an input audio signal (S); and partition the audio band of the entire input audio signal (S) into N audio sub-bands, each of the audio sub-bands covering a subrange of the frequencies of the entire input audio signal (S) ; wherein generating the respective control signal (Cl, C2, C3, ..., CN) for each sound generating element (210, 310, 510) comprises generating each control signal (Cl, C2, C3, ..., CN) based on an individual one of the N audio bands.

10. The sound producing system (110) of claim 9, wherein the controller (120) comprises a crossover circuit that is coupled to the N sound generating elements (210, 310, 510) and is configured to partition the audio band of the entire input audio signal (S) into N audio sub-bands, thereby generating the N control signals (Cl, C2, C3, ..., CN), based on N- l preset crossover frequencies.

11. A method of manufacturing a MEMS-based sound producing device (100), the method comprising: providing a first sound generating layer (20) comprising a first support structure (200) forming an outer frame (201) and beingfixed to the periphery of at least one first sound generating element (210), wherein the first support structure (200) further comprises at least one first opening (220); providing a second sound generating layer (30) comprising a second support structure (300) forming an outer frame (301) and being fixed to the periphery of at least one second sound generating element (310), wherein the second support structure (300) further comprises at least one second opening (320); providing at least one intermediate sound re-routing layer (40) comprising a respective intermediate support structure (400) forming a respective outer frame (401) and having at least two rerouting openings (420); and stacking the first sound generating layer (20), the second sound generating layer (30) , and the at least one intermediate sound rerouting layer (40) between the first sound generating layer (20) and the second sound generating layer (30) by bonding the adjacent layers in the stack to each other to form a sound producing device (100) with micro speaker elements in several layers, wherein the layers (20, 30, 40) are stacked such that each second sound generating element (310) at least partially overlaps with at least one re-routing opening (420) of each of the at least one intermediate support structure (400) and said at least one re-routing opening (420) at least partially overlaps with at least one first opening (220) of the first support structure (200) as seen from a top view of the stack, such that the inner walls of the overlapping openings (220, 420) of the at least one intermediate support structure (400) and the first support structure (200) form a sound-passing channel (70) for passing sound from the second sound generating element (310) around micro speaker elements in other layers to the first opening (220).

12. The method of claim 11, wherein stacking the layers (20, 30, 40) further comprises stacking them such that each first sound generating element (210) at least partially overlaps with at least one re-routing opening (420) of each of the at least one intermediate support structure (400) and said at least one re-routing opening (420) at least partially overlaps with at least one secondopening (320) of the second support structure (300), such that the inner walls of the overlapping openings (320, 420) of the at least one intermediate support structure (400) and the second support structure (300) form a sound-passing channel (71) for passing sound from the first sound generating element (210) around micro speaker elements in other layers to the second opening (320).

13. The method of claim 11 or 12, wherein providing the first sound generating layer (20) comprises providing a first substrate (2) and forming the first sound generating layer (20) by patterning and etching said first substrate (2) to provide a first support structure (200) forming a first outer frame (201) having at least one opening for fixation to the periphery of a respective at least one first sound generating element (210), and further having at least one first opening (220).

14. The method of any one of the claims 11 to 13, wherein providing the second sound generating layer (30) comprises providing a second substrate (3) and forming the second sound generating layer (30) by patterning and etching said second substrate (3) to provide a second support structure (300) forming a second outer frame (301) having at least one opening for fixation to the periphery of a respective at least one second sound generating element (310), and further having at least one second opening (320).

15. The method of any one of the claims 11 to 14, wherein providing the at least one sound re-routing layer (40) comprises providing at least one intermediate substrate (4) and, for each of the at least one intermediate substrate (4) , forming an intermediate sound re-routing layer (40) by patterning and etching said intermediate substrate (4) to provide an intermediate support structure (400) forming a respective outer frame (401) and having at least one re-routing opening (420).

16. The method of any one of the claims 11 to 15, further comprising: providing a carrier substrate (6); attaching the carrier substrate (6) to the second substrate (3);providing an electrical connection between the carrier substrate (6) and at least one of the first sound generating elements (210) using a first electrically conductive wire (61); and providing a soldering connection (62) between the carrier substrate (6) and the second substrate (3), thereby electrically connecting the carrier substrate (6) and the at least one second sound generating element (310).

17. The method of any one of the claims 11 to 15, wherein the peripheral edge of the second substrate (3) extends outside the peripheral edge of the intermediate substrate (4) adjacent to it after stacking, wherein providing the second sound generating layer (30) further comprises: patterning and etching said second substrate (3) to form at least one through- silicon via (63) from a front side (401) of the second substrate (3) at a point that is outside the peripheral edge of the intermediate substrate (4) adjacent to it after stacking, such that the through-silicon via (63) can be accessed after stacking, wherein each through-silicon via (63) is in electrical contact with at least one second sound generating element (310), wherein the method further comprises: providing a carrier substrate (6); attaching the carrier substrate (6) to the second substrate (3); providing an electrical connection between the carrier substrate (6) and at least one of the first sound generating elements (210) using a first electrically conductive wire (61); and providing, for each of the at least one through-silicon via (63), a second electrically conductive wire (62) between the carrier substrate (6) and the through-silicon via (63), thereby electrically connecting the carrier substrate (6) and the at least one second sound generating element (310).

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