DIRECTIONAL MEMS MICROPHONE

A directional microelectromechanical systems (MEMS) microphone, including a first layer, a second layer, and a third layer stacked in sequence and multiple adhesive members formed between the first layer, the second layer, and the third layer, is provided. The adhesive members include an outer adhesive member disposed surrounding a periphery of the first layer, the second layer, and the third layer and an inner adhesive member disposed within a range surrounded by the outer adhesive member. The outer adhesive member and the inner adhesive member form at least two slits between the first layer, the second layer, and the third layer. An external sound is transmitted to a sound sensing element after passing through two receiving holes of the directional MEMS microphone respectively along two paths. One of the two paths passes through the at least two slits.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Taiwan application serial no. 112112472, filed on Mar. 31, 2023. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.

BACKGROUND

Technical Field

The disclosure relates to a directional microphone, and in particular to a directional microelectromechanical systems (MEMS) microphone.

Description of Related Art

Under the thinning trend of electronic products, the thickness of the MEMS microphone package must also be thinned accordingly. Therefore, how to maintain good sound quality when the MEMS microphone package is thinned has become an important key technology in the development of MEMS microphone elements.

In particular, as the size of the condenser microphone changes to become thinner and smaller, the directivity and the signal-to-noise ratio deteriorate accordingly, which cannot meet the complex and changing requirements of the usage environment of the current electronic products. Therefore, how to combine MEMS technology to manufacture a compact condenser microphone with high directivity and signal-to-noise ratio is an issue that persons skilled in the art need to face and solve.

SUMMARY

The disclosure provides a directional MEMS microphone, which forms a sound path difference in an internal space of a monomer to achieve good directivity.

A directional MEMS microphone of the disclosure includes a first layer, a second layer, and a third layer stacked in sequence and multiple adhesive members formed between the first layer, the second layer, and the third layer. The adhesive members include an outer adhesive member disposed surrounding a periphery of the first layer, the second layer, and the third layer and an inner adhesive member disposed within a range surrounded by the outer adhesive member, and the outer adhesive member and the inner adhesive member form at least two slits between the first layer, the second layer, and the third layer. An external sound is transmitted to a sound sensing element after passing through two receiving holes of the directional MEMS microphone respectively along two paths. One of the two paths passes through the slits.

Based on the above, the directional MEMS microphone forms the monomer structure of the microphone by the first layer, the second layer, and the third layer stacked in sequence and the adhesive members formed between the first layer, the second layer, and the third layer. More importantly, in the monomer structure formed above, the adhesive members are further divided into the outer adhesive member and the inner adhesive member. The outer adhesive member is disposed surrounding the periphery of the first layer, the second layer, and the third layer, and the inner adhesive member is disposed within the range surrounded by the outer adhesive member.

At the same time, the adhesive members further form the at least two slits. The same external sound respectively passes through the two receiving holes along the two paths and enters the monomer structure and is transmitted to the sound sensing element according to the above component configuration, and one of the two paths passes through the slits. In this way, the sound passing through the slits along one of the paths is limited by the internal structure of the monomer to have a longer sound transmission path, and an obvious path difference is generated for the same sound due to the transmission path, causing difference in reception between the front end (0 degrees) and the rear end (180 degrees), so as to improve the unidirectionality of the microphone to the sound.

DETAILED DESCRIPTION OF DISCLOSED EMBODIMENTS

FIG.1is an exploded view of a directional MEMS microphone according to an embodiment of the disclosure.FIG.2is a top view of the directional MEMS microphone ofFIG.1.FIG.3is a cross-sectional view of the directional MEMS microphone ofFIG.2along a section line A-A′. Please refer toFIG.1toFIG.3at the same time. In the embodiment, a directional MEMS microphone100includes a first layer110, a second layer120, and a third layer130stacked in sequence and multiple adhesive members140formed between the first layer110, the second layer120, and the third layer130. The adhesive members140include outer adhesive members141and142disposed surrounding a periphery of the first layer110, the second layer120, and the third layer130and inner adhesive members143to146disposed within a range surrounded by the outer adhesive members141and142, and the outer adhesive members141and142and the inner adhesive members143to146form at least two slits SL1and SL2between the first layer110, the second layer120, and the third layer130. An external sound is transmitted to a sound sensing element150after passing through two receiving holes131and132of the directional MEMS microphone100respectively along two paths (a first path L1and a second path L2). One of the first path L1and the second path L2passes through the slits SL1and SL2. In the embodiment, the widths of the slits SL1and SL2are greater than or equal to 20 μm, so as to prevent resonance of sounds below 10 KHz.

Further, in the embodiment, the first layer110, the second layer120, and the third layer130are respectively printed circuit boards, and the adhesive members140are solder paste, silicone, or epoxy. In other words, as shown inFIG.1toFIG.3, a monomer structure of the directional MEMS microphone100is formed during the manufacturing process, wherein the third layer130is provided with the sound sensing element150and related electronic elements and has the two receiving holes131and132. Here, the first layer110and the third layer130are respectively boards, and the second layer120is a constant-height layer with a thickness greater than those of the first layer110and the third layer130, there are multiple partitions121and122therein to separate the inside of the monomer structure into multiple chambers, and the chambers are in air communication with each other by the slits SL1and SL2. In another unillustrated embodiment, the first layer and the third layer are respectively printed circuit boards, and the second layer is a metal plate. In addition, in another unillustrated embodiment, the first layer and the third layer respectively have the receiving holes131and132. In short, the receiving hole131or the receiving hole132may be disposed on the first layer according to requirements.

The inner adhesive member143is adhered between the partition122and the first layer110, and the inner adhesive member145is adhered between the partition122and the third layer130, wherein the inner adhesive member143covers an entire top surface of the partition122, and the inner adhesive member145is only adhered to a partial bottom surface of the partition122, so the slit SL2is formed between the partition122and the third layer130, and is substantially formed on the side of the inner adhesive member145.

Furthermore, the inner adhesive member144is adhered between the partition121and the first layer110, and the inner adhesive member146is adhered between the partition121and the third layer130, wherein the inner adhesive member146covers an entire bottom surface of the partition121, and the inner adhesive member144is only connected to a partial top surface of the partition121, so the slit SL1is formed between the partition121and the first layer110, and is substantially formed on the side of the inner adhesive member144.

Relatively speaking, in another unillustrated embodiment, the inner adhesive member is adhered between the partition and the first layer110to form the slit between the partition and the third layer130or the inner adhesive member is adhered between the partition and the third layer130to form the slit between the partition and the first layer110, which is also applicable to the disclosure.

On the other hand, the directional MEMS microphone100of the embodiment also includes a sound damping member160disposed in one of the two receiving holes (taking the receiving hole131as an example here), so that the second path L2passing through the slits SL1and SL2also passes through the sound damping member160, so as to delay the transmission of sound along the second path L2, which is equivalent to increasing the transmission length.

FIG.4Ais a sound cardioid polar pattern showing a corresponding relationship between path difference and directivity. Please refer toFIG.3andFIG.4Aat the same time. In the embodiment, the second path L2passes through the two slits SL1and SL2, but the first path L1does not pass through the slits SL1and SL2, and the length of the second path L2is greater than five times the length of the first path L1. Preferably, the length of the second path L2is greater than eighteen times to twenty-five times the length of the first path L1. As shown in the cardioid polar pattern ofFIG.4A, a curve SN1represents that the length of the second path L2is eighteen times that of the first path L1, and a curve SN2represents that the length of the second path L2is twenty-five times that of the first path L1. In this way, an obvious path difference is generated for the same sound due to the transmission path, causing difference in reception between the front end (0 degrees) and the rear end (180 degrees), so as to improve the unidirectionality of the microphone to the sound.

FIG.4Bis a sound cardioid polar pattern showing a corresponding relationship between the number of partitions and directivity. Please refer toFIG.4Band respectively compareFIG.4BwithFIG.3andFIG.4A. A curve SN4shown inFIG.4Brepresents that the second layer120ofFIG.3has the partitions121and122and the slits SL1and SL2, and a curve SN3represents that the second layer ofFIG.3only has the partition121and the slit SL1. As such, it can be clearly seen that the number of partitions and slits obviously affects the cardioid polar pattern of the sound, wherein the directivity of the curve SN4is obviously better than that of the curve SN3.

In other words, it can be clearly seen from the above sound cardioid polar pattern that in order to effectively improve the directivity of the sound, in a preferred embodiment of the disclosure, the length of the second path L2is required to be more than eighteen times the length of the first path L1, and at least two partitions (or at least two slits) are required.

FIG.5is an exploded view of a directional MEMS microphone according to another embodiment of the disclosure.FIG.6is a top view of the directional MEMS microphone ofFIG.5.FIG.7is a side view of the directional MEMS microphone ofFIG.5. Please refer toFIG.5toFIG.7at the same time. The difference from the foregoing embodiment is that in a directional MEMS microphone200of the embodiment, a second layer220has three partitions221,222, and223, and the adhesive member240also includes multiple inner adhesive members243to248in addition to the outer adhesive members141and142, wherein the inner adhesive members244,246, and248respectively cover an entire top surface of the partition222, an entire bottom surface of the partition223, and an entire bottom surface of the partition221, and the inner adhesive members243,245, and247respectively cover a partial top surface of the partition223, a partial top surface of the partition221, and a partial bottom surface of the partition222, thereby forming a bent second path L4as shown inFIG.6, thus increasing the path length difference between a first path L3and the second path LA, so as to improve the directivity of the microphone.

FIG.8is a cross-sectional view of a directional MEMS microphone according to another embodiment of the disclosure, wherein the same components as those of the foregoing embodiments will not be described again. Please refer toFIG.8. The difference from the foregoing embodiments is that a directional MEMS microphone300of the embodiment is changed to form recesses R1to R3on a first layer310and a third layer330, and the second layer320is not provided with the adhesive member on the partition corresponding to the recesses R1to R3, so that the partition not covered with the adhesive member can further form the slits with the recesses R1to R3for the sound to pass through the slits formed by the partition and the recesses R1and R2of the first layer310and the partition and the recess R3of the third layer330when being transmitted along a second path L6. Furthermore, the sound when being transmitted along the second path L6causes a path difference from the sound when being transmitted along a first path L5, so as to achieve the required directivity.

FIG.9is a cross-sectional view of a directional MEMS microphone according to another embodiment of the disclosure. Please refer toFIG.9. In a directional MEMS microphone400of the embodiment, the difference from the foregoing embodiments is the formation structure of the slits. As shown inFIG.9, a second layer420has opening structures, thereby forming, for example, a slit421aon a partition421, a slit422aon a partition422, and a slit423aon a partition423, so that chambers separated by the partitions421to423can be in air communication with each other through the opening structures. As such, when the sound is transmitted along a second path L8, a greater path difference is generated compared with a first path L7, so as to achieve the requirement of improving sound directivity. Different from the foregoing embodiments in which the second layer120or the second layer220is a constant-height layer, a second layer420of the embodiment has a structure with different heights due to the opening structures. For example, the partition423forms a height difference due to the opening structure. In other words, in the embodiment, the slits for the sound to pass through are formed through structure of the second layer420.

In summary, in the foregoing embodiments of the disclosure, the directional MEMS microphone forms the monomer structure of the microphone by the first layer, the second layer, and the third layer stacked in sequence and the adhesive members formed between the first layer, the second layer, and the third layer. More importantly, in the monomer structure formed above, the adhesive members are further divided into the outer adhesive member and the inner adhesive member, wherein the outer adhesive member is disposed surrounding the periphery of the first layer, the second layer, and the third layer, and the inner adhesive member is disposed within the range surrounded by the outer adhesive member.

At the same time, the adhesive members further form the at least two slits. The same external sound respectively passes through the two receiving holes along the two paths and enters the monomer structure and is transmitted to the sound sensing element according to the above component configuration, and one of the two paths passes through the slits.

The layers and the adhesive members can be matched with each other to form the required slits accordingly. In an embodiment, the constant-height second layer can enable the partition not provided with the adhesive member to form the slit with the opposite first layer or third layer according to whether there is the adhesive member on the two opposite sides. In another embodiment, the recesses of the first layer and the third layer or the opening structures of the second layer are matched to form the required slits.

In this way, the sound passing through the slits along one of the paths is limited by the internal structure of the monomer, including staggered configuration of the partitions with the inner adhesive members, to have a longer sound transmission path, and an obvious path difference is generated for the same sound due to the transmission path, causing difference in reception between the front end (0 degrees) and the rear end (180 degrees), so as to improve the unidirectionality of the microphone to the sound.