Piezoelectric stack structure and MEMS acoustic device

Abstract

The invention provides a piezoelectric stack structure and an MEMS acoustic device, and relates to the technical field of semiconductors. The piezoelectric stack structure comprises at least two electrode layers arranged in a stacked mode in the first preset direction and a piezoelectric layer arranged between the two adjacent electrode layers, a slit is formed in the piezoelectric stack structure, and the slit penetrates through the two opposite surfaces of the piezoelectric stack structure in the first preset direction. The piezoelectric stack structure is divided into at least two cantilever beams; the slits comprise at least two first slits and at least one second slit, the number of the second slits is one less than that of the first slits, and the two opposite sides of the second slits in the first preset direction are connected with the first slits respectively. The width of the slit in the piezoelectric stack structure can be smaller than the minimum processing width of processing equipment, and the piezoelectric stack structure is easy to process.

Description

Technical Field

[0001] The present application relates to the field of semiconductor technology, and in particular to a piezoelectric stack structure and a MEMS acoustic device. Background Art

[0002] As an advanced acoustic sensor technology, cantilever microphones have been rapidly developed due to their many advantages such as low power consumption, fast response, and high reliability. A slit is provided on the piezoelectric stack structure of the cantilever microphone, and the slit runs through the piezoelectric stack structure to form a cantilever beam. The design of the slit has a great influence on the low-frequency response capability of the cantilever microphone. Among them, the slit width is a parameter that directly affects the low-frequency response of the cantilever microphone. The smaller the slit width, the lower the low-frequency response of the cantilever microphone and the wider the response range. A smaller slit width can help the cantilever microphone capture and reproduce low-frequency sounds more accurately, and achieve a wider frequency response to enable the cantilever microphone system to sense more natural and clear sounds.

[0003] However, in the actual process of preparing a cantilever microphone, the width of the slit depends on the minimum processing width of the processing equipment. In addition, the slit has a large aspect ratio and the piezoelectric stack structure contains piezoelectric materials that are difficult to etch. It is extremely difficult to obtain the smallest possible slit width. As the thickness of the cantilever beam increases, the difficulty of processing the slit increases further. Therefore, it is extremely difficult to process a slit with the smallest possible width using existing processes. Summary of the invention

[0004] The purpose of the present application is to provide a piezoelectric stack structure and a MEMS acoustic device in view of the above-mentioned deficiencies in the prior art, wherein the width of the slit can be smaller than the minimum processing width of the processing equipment and the device is easy to process.

[0005] To achieve the above purpose, the technical solution adopted in the embodiment of the present application is as follows:

[0006] According to one aspect of an embodiment of the present application, a piezoelectric stack structure is provided, comprising: at least two electrode layers stacked along a first preset direction and a piezoelectric layer arranged between two adjacent electrode layers, wherein a slit is provided in the piezoelectric stack structure, and the slit respectively penetrates two opposite surfaces of the piezoelectric stack structure in the first preset direction so as to divide the piezoelectric stack structure into at least two cantilever beams; the slit comprises at least two first slits and at least one second slit, the number of the second slits is one less than the number of the first slits, and the second slits are respectively connected to the first slits on two opposite sides of the first preset direction.

[0007] Optionally, the width of the first gap is greater than the depth of the second gap.

[0008] Optionally, a vertical distance between mutually adjacent side surfaces of two first gaps connected to the same second gap is greater than a depth of the first gap.

[0009] Optionally, a vertical distance between mutually adjacent side surfaces of two first slits connected to the same second slit is 10 times or more than 10 times the depth of the first slit.

[0010] Optionally, at least one of two side surfaces of the second slit that are opposite to each other in the first preset direction is connected to an end of the first slit.

[0011] Optionally, at least one of two opposite side surfaces of the second slit in a second preset direction is flush with a side surface of the first slit, and the second preset direction is perpendicular to the first preset direction.

[0012] Optionally, two opposite side surfaces of the second slit in the first preset direction are respectively connected to the ends of the first slit, two opposite side surfaces of the second slit in the second preset direction are respectively flush with the side surfaces of the first slit, and the second preset direction is perpendicular to the first preset direction.

[0013] Optionally, the number of the first gaps is two.

[0014] Optionally, a supporting layer is further included, and the electrode layer and the piezoelectric layer are both located on the supporting layer.

[0015] On the other hand, an embodiment of the present application provides a MEMS acoustic device, including: a substrate structure and a piezoelectric stack structure as any of the above items arranged on the substrate structure, the substrate structure is provided with a back cavity, the back cavity penetrates two surfaces of the substrate structure opposite to each other in a first preset direction, and the slit of the piezoelectric stack structure corresponds to and is connected to the back cavity position.

[0016] The beneficial effects of this application include:

[0017] The present application provides a piezoelectric stack structure, comprising: at least two electrode layers stacked along a first preset direction and a piezoelectric layer arranged between two adjacent electrode layers, a slit is provided in the piezoelectric stack structure, and the slits respectively penetrate two surfaces of the piezoelectric stack structure opposite to each other in the first preset direction, so as to divide the piezoelectric stack structure into at least two cantilever beams; the slits include at least two first slits and at least one second slit, the number of the second slits is one less than the number of the first slits, and the second slits are respectively connected to the first slits on two opposite sides in the first preset direction. In the above-mentioned piezoelectric stack structure, the slit does not extend in a straight line along the thickness direction (i.e., the first preset direction) of the piezoelectric stack structure, but at least two turns occur inside the piezoelectric stack structure to change the extension direction. The area between the sides of the two first slits connected to it that are close to each other on the second slit in the slit is the sound channel, and increasing the length of the sound channel (i.e., increasing the vertical distance between the sides of the two first slits connected to the same second slit that are close to each other) will increase the propagation path of the sound wave in the sound channel, thereby increasing the contact opportunity between the sound wave and the wall of the sound channel, increasing the viscosity, and making the acoustic impedance larger. Reducing the depth of the second slit will increase the velocity of the sound wave, increase viscosity, and thus increase the acoustic impedance. The greater the acoustic impedance, the more difficult it is for the sound to pass through the second slit, the less likely it is for the low-frequency signal to leak through the slit, and the piezoelectric stack structure has the opportunity to receive signals in a wider frequency range. The control of the channel length is related to the photolithography size, and it is easier to obtain a larger channel length in the process. The depth of the second slit is related to the film growth. By growing an extremely thin film and releasing it, a very small second slit depth can be achieved. Therefore, the slit width on the above-mentioned piezoelectric stack structure can be easily made as small as possible, thereby achieving better low-frequency response. In addition, the presence of the second slit causes the two cantilever beams to have a projection overlap area in the first preset direction. When the cantilever beam is deformed under the influence of the environment or the action of an external force, the above-mentioned piezoelectric stack structure can still maintain a small slit width to ensure the transmission effect of the low-frequency signal. In the piezoelectric stack structure in the prior art, the slit extends along a straight line, and when the cantilever beam is deformed under the influence of the environment or the action of an external force, the slit width will increase significantly. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0019] Figure 1 One of the structural schematic diagrams of the piezoelectric stack structure provided in the embodiment of the present application;

[0020] Figure 2 The second structural schematic diagram of the piezoelectric stack structure provided in the embodiment of the present application;

[0021] Figure 3 A schematic diagram of the deformation of the cantilever beam of the piezoelectric stack structure provided in an embodiment of the present application;

[0022] Figure 4 The third structural schematic diagram of the piezoelectric stack structure provided in the embodiment of the present application;

[0023] Figure 5 A fourth structural schematic diagram of a piezoelectric stack structure provided in an embodiment of the present application;

[0024] Figure 6 A fifth structural schematic diagram of a piezoelectric stack structure provided in an embodiment of the present application;

[0025] Figure 7 A schematic diagram of the structure of a MEMS acoustic device provided in an embodiment of the present application.

[0026] Icons: 10-piezoelectric stack structure; 11-electrode layer; 12-piezoelectric layer; 13-first protective layer; 14-support layer; 15-slit; 151-first gap; 152-second gap; 16-cantilever beam; 17-sound channel; 20-MEMS acoustic device; 21-substrate structure; 211-back cavity; 212-substrate layer; 213-second protective layer; X-first preset direction; Y-second preset direction; Z-third preset direction; B-width of the first gap; H-depth of the second gap; T-vertical distance between the sides of two first gaps connected to the same second gap that are close to each other; L-depth of the first gap. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. The components of the embodiments of the present application described and shown in the drawings here can be arranged and designed in various different configurations.

[0028] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. It should be noted that, in the absence of conflict, the various features in the embodiments of the present application can be combined with each other, and the combined embodiments are still within the scope of protection of the present application.

[0029] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0030] In the description of the present application, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, or the positions or positional relationships in which the product of the application is usually placed when in use. They are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific position, be constructed and operated in a specific position, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second", "third", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0031] In the description of this application, it should also be noted that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0032] In one aspect of the embodiment of the present application, please refer to Figure 1 and Figure 2 , a piezoelectric stack structure 10 is provided, comprising: at least two electrode layers 11 stacked along a first preset direction X and a piezoelectric layer 12 arranged between two adjacent electrode layers 11. The first preset direction X is preferably a direction perpendicular to the surface of the electrode layer 11. The electrode layer 11 and the piezoelectric layer 12 can be directly bonded, or other film layers can be arranged. Other film layers, such as a first protective layer 13, a support layer 14, etc., can be arranged on the side of the uppermost and lowermost electrode layers 11 away from the piezoelectric layer 12.

[0033] The piezoelectric stack structure 10 is provided with a slit 15, which respectively penetrates two surfaces of the piezoelectric stack structure 10 that are opposite to each other in the first preset direction X, so as to divide the piezoelectric stack structure 10 into at least two cantilever beams 16. It can be understood that when the number of the slit 15 is one, one slit 15 divides the piezoelectric stack structure 10 into two cantilever beams 16; when the number of the slit 15 is two or more, two or more slits 15 cooperate with each other to divide the piezoelectric stack structure 10 into two or more cantilever beams 16.

[0034] The slits 15 include at least two first slits 151 and at least one second slit 152, the number of the second slits 152 is one less than the number of the first slits 151, and the second slits 152 are respectively connected to the first slits 151 on opposite sides in the first preset direction X. In other words, at least two first slits 151 are arranged at intervals in the piezoelectric stack structure 10, and two adjacent first slits 151 are connected through the second slits 152. One surface of the piezoelectric stack structure 10 in the first preset direction X is penetrated by one first slit 151, and the other opposite surface is penetrated by another first slit 151.

[0035] It can be understood that the gap (the first gap 151 or the second gap 152) has dimensions in three directions, wherein the dimension of the gap in the first preset direction X is the depth of the gap, the dimension in the second preset direction Y is the width of the gap, and the dimension in the third preset direction Z is the length of the gap. The first preset direction X, the second preset direction Y, and the third preset direction Z are perpendicular to each other.

[0036] In the above-mentioned piezoelectric stack structure 10, the slit 15 does not extend in a straight line along the thickness direction (i.e., the first preset direction X) of the piezoelectric stack structure 10, but turns at least twice inside the piezoelectric stack structure 10 to change the extension direction. The area between the sides of the two first slits 151 connected to the same second slit 152 in the slit 15 that are close to each other is the sound channel 17 ( Figure 1 The area within the dotted box in the middle), increasing the length of the sound channel 17 (that is, increasing the vertical distance T between the sides of the two first slits connected to the same second slit that are close to each other) will increase the propagation path of the sound wave in the sound channel 17, thereby increasing the contact opportunity between the sound wave and the wall of the sound channel, increasing the viscosity, and increasing the acoustic impedance. Reducing the depth H of the second slit will increase the flow rate of the sound wave, increase the viscosity, and thus increase the acoustic impedance. The greater the acoustic impedance, the more difficult it is for the sound to pass through the second slit 152, and the possibility of low-frequency signals leaking through the slit 15 is smaller, and the piezoelectric stack structure 10 has the opportunity to receive signals in a wider frequency range. The control of the sound channel length is related to the photolithography size. It is easier to obtain a larger sound channel length in terms of technology. The depth H of the second slit is related to the growth of the film. By growing an extremely thin film and releasing it, a very small second slit depth H can be achieved. Therefore, the width of the slit 15 on the above-mentioned piezoelectric stack structure 10 can be easily made as small as possible, thereby achieving better low-frequency response. In addition, the existence of the second gap 152 enables the two cantilever beams 16 to have a projection overlap area in the first preset direction X ( Figure 1 The area within the dotted line frame) Figure 3When the cantilever beam 16 is deformed by the environment or external force, the piezoelectric stack structure 10 can still maintain a small slit 15 width to ensure the transmission effect of low-frequency signals. However, in the prior art piezoelectric stack structure 10 in which the slit 15 extends along a straight line, when the cantilever beam 16 is deformed by the environment or external force, the slit 15 width will increase significantly.

[0037] Optionally, the width B of the first gap is greater than the depth H of the second gap.

[0038] The processing of the first slit 151 is limited by the processing equipment, and its width is greater than or equal to the minimum processing width of the processing equipment. However, the depth H of the second slit is related to the film growth. By growing an extremely thin film and releasing it, a very small depth H of the second slit can be achieved. The minimum width of the slit 15 is determined by the depth H of the second slit. Therefore, limiting the depth H of the second slit to be less than the width B of the first slit can make the minimum width of the slit 15 smaller and achieve better low-frequency response.

[0039] Optionally, a vertical distance T between mutually adjacent side surfaces of two first gaps connected to the same second gap is greater than a depth L of the first gap.

[0040] Among them, the control of the vertical distance T between the sides of the two first gaps connected to the same second gap that are close to each other is related to the photolithography size, and it is easier to achieve a larger T in the process. The depth L of the first gap is related to the growth of the film. By growing an extremely thin film and releasing it, a very small depth L of the first gap can be achieved. When T>L, the overlapping area of ​​the projections of the two cantilever beams 16 in the first preset direction X is larger, and the piezoelectric stack structure 10 can still maintain a smaller slit 15 width when the cantilever beam 16 is deformed by the environment or external force, thereby ensuring the transmission effect of the low-frequency signal.

[0041] It should be noted that, in the present application, the sizes of at least two first slits 151 are not limited to be equal, nor are the sizes of at least two second slits 152 limited to be equal. Therefore, a certain parameter mentioned above may have multiple values, but all values ​​should satisfy the above size relationship. For example, when the number of first slits 151 is two and the widths B of the two first slits are not equal, the width B of the first slit has two values. At this time, the two values ​​of the width B of the first slit are both greater than the depth H of the second slit.

[0042] It can be understood that the smaller the depth H of the second gap is, the larger the vertical distance T between the sides of the two first gaps connected to the same second gap that are close to each other is, and the better the low-frequency response of the piezoelectric stack structure 10 is. Therefore, when B>>H and / or T>>L, the piezoelectric stack structure 10 can achieve better low-frequency response. However, the depth H of the second gap cannot be infinitely small, and the vertical distance T between the sides of the two first gaps connected to the same second gap that are close to each other cannot be infinitely large. Therefore, under the premise of taking into account the process difficulty, the size of the piezoelectric stack structure 10 and the low-frequency response, optionally, the vertical distance T between the sides of the two first gaps connected to the same second gap that are close to each other is 10 times or more than 10 times the depth L of the first gap.

[0043] Optionally, the number of the first slits 151 is two, and correspondingly, the number of the second slit 152 is one.

[0044] Such an arrangement can reduce the number of processing times while ensuring that the width of the slit 15 is as small as possible, thereby improving processing efficiency and reducing processing difficulty.

[0045] In the above embodiments, the specific connection position between the first slit 151 and the second slit 152 is not limited, and it is only required that each second slit 152 is provided with a first slit 151 on two opposite sides in the first preset direction X, and the first slit 151 is connected to the second slit 152. Several optional embodiments of the specific connection position between the first slit 151 and the second slit 152 are given below:

[0046] Optionally, see Figure 4 and Figure 5 At least one of the two opposite side surfaces of the second slit 152 in the first preset direction X is connected to the end of the first slit 151 .

[0047] The second slit 152 has two opposite side surfaces in the first preset direction X, wherein at least one side surface in the first preset direction X is connected to the end of the first slit 151. The second slit 152 whose side surface is connected to the end of the first slit 151 has no projection overlap area with the first slit 151 in the second preset direction Y.

[0048] Figure 4 In the illustrated embodiment, two side surfaces of the second slit 152 in the first preset direction X are connected to ends of the first slit 151 . Figure 5 In the illustrated embodiment, the lower side of the two side surfaces of the second slit 152 in the first preset direction X is connected to the end of the first slit 151, and the upper side is connected to the middle of the first slit 151. The second slit 152 whose side surface is connected to the middle of the first slit 151 has a projection overlap area with the first slit 151 in the second preset direction Y.

[0049] Optionally, see Figure 4 and Figure 6 At least one of the two opposite side surfaces of the second slit 152 in the second preset direction Y is flush with the side surface of the first slit 151 , and the second preset direction Y is perpendicular to the first preset direction X.

[0050] The second slit 152 has two opposite side surfaces in the second preset direction Y, wherein at least one side surface in the second preset direction Y is flush with the side surface of the first slit 151, i.e., located in the same plane. It can be understood that the first slit 151 and the second slit 152 refer to the first slit 151 and the second slit 152 that are connected to each other.

[0051] Figure 4 In the illustrated embodiment, two side surfaces of the second slit 152 in the second preset direction Y are flush with the side surfaces of the two first slits 151 , respectively. Figure 6 In the illustrated embodiment, of the two side surfaces of the second slit 152 in the second preset direction Y, the left side surface is flush with the side surface of the first slit 151 , and the right side surface is not flush with the side surface of the first slit 151 .

[0052] Optionally, see Figure 4 The two opposite side surfaces of the second slit 152 in the first preset direction X are respectively connected to the ends of the first slit 151 , and the two opposite side surfaces of the second slit 152 in the second preset direction Y are respectively flush with the side surfaces of the first slit 151 .

[0053] Such an arrangement allows the sound wave to propagate along a single path after entering the slit 15, thereby improving the transmission efficiency of the sound wave and reducing the loss of the sound wave.

[0054] There are many relative positional relationships between the first slit 151 and the second slit 152, which are not described in detail in this application. Since the first slit 151 and the second slit 152 can span multiple film layers, the first slit 151 and the second slit 152 can also be located in the same film layer. Figures 2 to 6 The specific membrane layers in the piezoelectric stack structure are not shown.

[0055] Optionally, see Figure 1 The piezoelectric stack structure 10 further includes a support layer 14 , and the electrode layer 11 and the piezoelectric layer 12 are both located on the support layer 14 .

[0056] The support layer 14 , as a part of the cantilever beam 16 , is disposed below the electrode layer 11 and the piezoelectric layer 12 , and can support and protect the electrode layer 11 and the piezoelectric layer 12 .

[0057] Optionally, the piezoelectric stack structure 10 further includes a first protective layer 13 , and the first protective layer 13 is located on the uppermost electrode layer 11 .

[0058] The first protective layer 13 , as a part of the cantilever beam 16 , is disposed above the uppermost electrode layer 11 , and can protect the electrode layer 11 and the piezoelectric layer 12 .

[0059] Please refer to Figure 7 This embodiment also provides a MEMS acoustic device 20, including a substrate structure 21 and a piezoelectric stack structure 10 as any of the above items arranged on the substrate structure 21, a back cavity 211 is provided on the substrate structure 21, the back cavity 211 penetrates two opposite surfaces of the substrate structure 21 in a first preset direction X, and the slit 15 of the piezoelectric stack structure 10 corresponds to and is connected to the back cavity 211.

[0060] The MEMS acoustic device 20 includes the same structure and benefits as the piezoelectric stack structure 10 in the aforementioned embodiment. The structure and benefits of the piezoelectric stack structure 10 have been described in detail in the aforementioned embodiment and will not be repeated here.

[0061] Optionally, the base structure 21 includes a substrate layer 212 and a second protective layer 213 disposed on the substrate layer 212 , the piezoelectric stack structure 10 is disposed on a surface of the second protective layer 213 facing away from the substrate layer 212 , and the back cavity 211 penetrates the substrate layer 212 and the second protective layer 213 .

[0062] When forming the back cavity 211, the back etching process is generally used to etch through the substrate layer 212, and then the thin film etching process is used to etch through the second protection layer 213. The second protection layer 213 can protect the piezoelectric stack structure 10 when the substrate layer 212 is etched.

[0063] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A piezoelectric stack structure, characterized in that: include: At least two electrode layers stacked along a first preset direction and a piezoelectric layer arranged between two adjacent electrode layers, wherein a slit is arranged in the piezoelectric stack structure, and the slit respectively penetrates two opposite surfaces of the piezoelectric stack structure in the first preset direction, so as to divide the piezoelectric stack structure into at least two cantilever beams; The slits include at least two first slits and at least one second slit, the number of the second slits is one less than the number of the first slits, and the second slits are respectively connected to the first slits on two opposite sides in the first preset direction.

2. The piezoelectric stack structure according to claim 1, wherein: The width of the first gap is greater than the depth of the second gap.

3. The piezoelectric stack structure according to claim 2, wherein: A vertical distance between mutually adjacent side surfaces of two first slits connected to the same second slit is greater than a depth of the first slit.

4. The piezoelectric stack structure according to claim 3, wherein: A vertical distance between mutually adjacent side surfaces of two first slits connected to the same second slit is 10 times or more than 10 times the depth of the first slit.

5. The piezoelectric stack structure according to claim 1, wherein: At least one of two side surfaces of the second slit that are opposite to each other in the first preset direction is connected to an end of the first slit.

6. The piezoelectric stack structure according to claim 1, wherein: At least one of two opposite side surfaces of the second slit in a second preset direction is flush with a side surface of the first slit, and the second preset direction is perpendicular to the first preset direction.

7. The piezoelectric stack structure according to claim 1, wherein: Two opposite side surfaces of the second slit in the first preset direction are respectively connected to the ends of the first slit, two opposite side surfaces of the second slit in the second preset direction are respectively flush with the side surfaces of the first slit, and the second preset direction is perpendicular to the first preset direction.

8. The piezoelectric stack structure according to claim 1, wherein: The number of the first gaps is two.

9. The piezoelectric stack structure according to claim 1, wherein: It also includes a supporting layer, on which the electrode layer and the piezoelectric layer are both located.

10. A MEMS acoustic device, characterized in that: It includes a base structure and a piezoelectric stack structure as described in any one of claims 1 to 9 arranged on the base structure, wherein a back cavity is provided on the base structure, and the back cavity runs through two surfaces of the base structure that are opposite to each other in a first preset direction, and the slit of the piezoelectric stack structure corresponds to and is connected to the back cavity position.

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