An acoustic sensor and a method of manufacturing the same

Abstract

The application discloses an acoustic sensor and a preparation method thereof. A substrate unit comprises a first silicon layer, a first oxide layer and a second silicon layer which are sequentially stacked from bottom to top, and a back cavity is formed in the substrate unit; a second oxide layer, a piezoelectric unit which is formed on the second oxide layer and comprises a first electrode layer, a piezoelectric layer and a second electrode layer which are sequentially stacked from bottom to top, and a slit and an opening are formed in the piezoelectric unit; a metal pad which is stacked on the first electrode layer at the opening; and an additional film layer which comprises a first part and a second part, the first part is laid on the second electrode layer and covers the slit, and the second part is laid on the metal pad. Compared with the prior art, the piezoelectric unit can move with maximum displacement and lowest limited vibration, thereby effectively improving SPL and structural reliability, the thickness of the additional film layer is uniformly distributed on the top surface of the piezoelectric unit, and the acoustic sensor is suitable for a larger area.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and in particular to an acoustic sensor and its fabrication method. Background Technology

[0002] Typical acoustic sensors utilize liquid or paste polymers to create additional film layers on piezoelectric units using a spin coating method. The polymer completely fills the accessible space on the patterned structure. However, there is a high risk that the spin coating material may be unevenly distributed on different surface topologies. In addition, the completely filled polymer may limit vibrational displacement and performance. Summary of the Invention

[0003] The purpose of this invention is to provide an acoustic sensor and its fabrication method to solve the technical problems in the prior art.

[0004] In a first aspect, the present invention provides an acoustic sensor, comprising:

[0005] A substrate unit includes a first silicon layer, a first oxide layer and a second silicon layer stacked sequentially from bottom to top. A back cavity is formed in the substrate unit, and the back cavity sequentially penetrates the first silicon layer and the first oxide layer. The second silicon layer is exposed through the back cavity.

[0006] A second oxide layer is formed on the substrate unit;

[0007] A piezoelectric unit is formed on the second oxide layer, and the piezoelectric unit includes a first electrode layer, a piezoelectric layer and a second electrode layer stacked sequentially from bottom to top.

[0008] A slit is formed in the middle of the second electrode layer, and the slit sequentially penetrates the second electrode layer, the piezoelectric layer, the first electrode layer, the second oxide layer, and the second silicon layer, and the slit is connected to the back cavity;

[0009] An opening is formed at the edge of the second electrode layer, and the opening sequentially penetrates the second electrode layer and the piezoelectric layer, with the first electrode layer exposed through the opening;

[0010] A metal pad, which is stacked on the first electrode layer at the opening;

[0011] An additional film layer includes a first portion and a second portion. The first portion is laid flat on the second electrode layer and covers the slit. The second portion is laid flat on the metal pad. A through groove is formed on the second portion, and the metal pad is positioned corresponding to the through groove. The metal pad is exposed through the through groove.

[0012] In the acoustic sensor described above, preferably, the first part and the second part have a height difference, with the second part located below the first part.

[0013] In the acoustic sensor described above, preferably, the first part and the second part have the same thickness, and the thickness is consistent at all points within the first part and the second part.

[0014] In the acoustic sensor described above, preferably, the thickness of the metal pad is less than the thickness of the piezoelectric layer.

[0015] In the acoustic sensor described above, preferably, there is a gap between the bottom surface of the second portion and the top surface of the first electrode layer, and the plane where the bottom surface of the second portion is located intersects with the piezoelectric layer.

[0016] In the acoustic sensor described above, preferably, the additional film layer is a photosensitive film.

[0017] Secondly, the present invention also provides a method for preparing an acoustic sensor, the method comprising:

[0018] A substrate unit is provided, the substrate unit comprising a first silicon layer, a first oxide layer and a second silicon layer stacked sequentially from bottom to top;

[0019] A second oxide layer, a first electrode layer, a piezoelectric layer, and a second electrode layer are formed sequentially from bottom to top on the second silicon layer;

[0020] A slit is etched in the middle of the second electrode layer and an opening is etched at the edge of the second electrode layer. The slit sequentially penetrates the second electrode layer, the piezoelectric layer, the first electrode layer, the second oxide layer, and the second silicon layer. The opening sequentially penetrates the second electrode layer and the piezoelectric layer. The first electrode layer is exposed through the opening.

[0021] A metal pad is formed on the first electrode layer at the opening;

[0022] An additional film layer is formed, a first portion of which is laid flat on the second electrode layer and covers the slit, and a second portion of which is laid flat on the metal pad. A through groove is formed on the second portion, the metal pad is positioned corresponding to the through groove, and the metal pad is exposed through the through groove.

[0023] A back cavity is formed by etching at the bottom of the first silicon layer, the back cavity passing through the first silicon layer and the first oxide layer in sequence, and the second silicon layer is exposed through the back cavity.

[0024] In the method for fabricating an acoustic sensor as described above, preferably, the additional diaphragm layer is formed by roll forming.

[0025] In the method for fabricating an acoustic sensor as described above, preferably, the additional film layer is formed by hot pressing.

[0026] In the method for fabricating an acoustic sensor as described above, preferably, the additional film layer is formed by plate printing.

[0027] In the method for fabricating an acoustic sensor as described above, preferably, the additional film layer is a photosensitive film.

[0028] In the method for fabricating an acoustic sensor as described above, preferably, the additional diaphragm layer is formed by roll forming.

[0029] In the method for fabricating an acoustic sensor as described above, preferably, the additional film layer is formed by hot pressing.

[0030] In the method for fabricating an acoustic sensor as described above, preferably, the through-groove is formed in the second part by a photolithography process.

[0031] Compared with the prior art, the present invention forms an additional film layer by rolling or hot pressing. The first part of the additional film layer is laid flat on the second electrode layer and covers the slit, and the second part of the additional film layer is laid flat on the metal pad. The piezoelectric unit can move with maximum displacement and minimize vibration, thereby effectively improving SPL and structural reliability. The thickness of the additional film layer is uniformly distributed on the top surface of the piezoelectric unit, which is suitable for acoustic sensors with a large area. Attached Figure Description

[0032] Figure 1 This is a cross-sectional schematic diagram of the acoustic sensor provided in the embodiment of the present invention;

[0033] Figures 2a-2e This is a flowchart illustrating the fabrication process of the acoustic sensor provided in this invention.

[0034] Explanation of reference numerals in the attached figures:

[0035] 10-Base unit, 11-Back cavity, 12-First silicon layer, 13-First oxide layer, 14-Second silicon layer;

[0036] 20 - Second oxide layer;

[0037] 30 - Piezoelectric unit, 31 - First electrode layer, 32 - Piezoelectric layer, 33 - Second electrode layer;

[0038] 40-slit;

[0039] 50-Opening;

[0040] 60 - Additional membrane layer; 61 - First part; 62 - Second part; 63 - Through groove;

[0041] 70-Metal pad. Detailed Implementation

[0042] The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0043] Figure 1 This is a cross-sectional schematic diagram of the acoustic sensor provided in the embodiment of the present invention, as shown below. Figure 1 As shown, an embodiment of the present invention provides an acoustic sensor, including a substrate unit 10, a second oxide layer 20, a piezoelectric unit 30, an additional film layer 60, and a metal pad 70, wherein:

[0044] The substrate unit 10 includes a first silicon layer 12, a first oxide layer 13, and a second silicon layer 14 stacked sequentially from bottom to top. A back cavity 11 is formed within the substrate unit 10. Preferably, the inner contour surface of the back cavity 11 is a circular groove structure. The back cavity 11 passes through the first silicon layer 12 and the first oxide layer 13 sequentially. The second silicon layer 14 is exposed through the back cavity 11. In one feasible embodiment, the first oxide layer 13 of SiO2 material is prepared on the first silicon layer 12 of silicon material using methods such as vapor deposition, thermal oxidation, or thermal decomposition. The second silicon layer 14 is formed on the first oxide layer 13 using methods such as vapor deposition, thermal oxidation, or thermal decomposition. The material of the second silicon layer 14 can be the same as that of the first silicon layer 12. The first oxide layer 13 is located below the second silicon layer 14 and has a significantly lower etching rate compared to the second silicon layer 14. When etching to form the slit 40 or the back cavity 11, it ensures that the etching stops relatively uniformly at the junction of the first oxide layer 13 and the second silicon layer 14.

[0045] The second oxide layer 20 is formed on the substrate unit 10. A second oxide layer 20 can be grown on the surface of the second silicon layer 14 by magnetron sputtering.

[0046] The piezoelectric element 30 is formed on the second oxide layer 20. The piezoelectric element 30 includes a first electrode layer 31, a piezoelectric layer 32, and a second electrode layer 33 stacked sequentially from bottom to top, wherein:

[0047] The first electrode layer 31 is formed on the second oxide layer 20 by electron beam stripping or magnetron sputtering, and the first electrode layer 31 is patterned by photolithography. The first electrode layer 31 is connected to the bottom electrode pad (not shown) through bottom electrode leads (not shown). The material of the first electrode layer 31 can be one or more of Al, Mo, W, Pt, Cu, Ag, Au, and ZrN, or other materials with good conductivity. In one feasible embodiment, the first electrode layer 31 is made of molybdenum (Mo).

[0048] A piezoelectric layer 32 is deposited on the first electrode layer 31. The piezoelectric layer 32 has the property of mechanical vibration in the presence of an electric field and generating an electric field if mechanical vibration occurs. The piezoelectric layer 32 can be made of lead zirconium titanate, aluminum nitride, or barium titanate or any other piezoelectric material. In one feasible embodiment, the piezoelectric layer 32 is made of aluminum nitride.

[0049] The second electrode layer 33 is formed on the piezoelectric layer 32 by electron beam stripping or magnetron sputtering, and the second electrode layer 33 is patterned by photolithography. The second electrode layer 33 is connected to the top electrode pad (not shown) through the top electrode lead (not shown). The material of the second electrode layer 33 can be one or more of Al, Mo, W, Pt, Cu, Ag, Au, and ZrN, or other materials with good conductivity. In one feasible embodiment, the second electrode layer 33 is made of molybdenum (Mo).

[0050] The piezoelectric unit 30 has a slit 40 and an opening 50. The slit 40 is located in the middle of the second electrode layer 33. Preferably, the inner contour surface of the slit 40 is a circular groove structure. The axis of the slit 40 coincides with the axis of the back cavity 11. The slit 40 passes through the second electrode layer 33, the piezoelectric layer 32, the first electrode layer 31, the second oxide layer 20, and the second silicon layer 14 in sequence until the slit 40 is connected to the back cavity 11. The opening 50 is located at the edge of the second electrode layer 33. Preferably, the opening 50 is an annular groove structure. The opening 50 passes through the second electrode layer 33 and the piezoelectric layer 32 in sequence. The first electrode layer 31 is exposed through the opening 50.

[0051] A metal pad 70 is stacked on the first electrode layer 31 at the opening 50 to be electrically connected to the first electrode layer 31. In this embodiment, a patterned hard mask is fabricated on the second electrode layer 33, and the opening 50 is etched at the edge of the second electrode layer 33 by dry etching or wet etching to expose part of the first electrode layer 31. The metal pad 70 is deposited on the first electrode layer 31 to form an electrical connection.

[0052] The additional film layer 60 includes a first part 61 and a second part 62. Preferably, the first part 61 and the second part 62 are integrally formed to facilitate molding and improve structural stability. The second part 62 is located at the outer edge of the first part 61. The size and shape of the first part 61 are adapted to the size and shape of the second electrode layer 33. The first part 61 is laid flat on the second electrode layer 33 and covers the slit 40. The size and shape of the second part 62 are adapted to the size and shape of the opening 50. The second part 62 is laid flat on the metal pad 70 and covers the opening 50. A through groove 63 is formed on the second part 62. The position of the metal pad 70 corresponds to the position of the through groove 63. The orthographic projection of the metal pad 70 in the thickness direction of the second part 62 falls in the through groove 63. The metal pad 70 is exposed through the through groove 63.

[0053] By covering the slit 40 with the additional membrane layer 60, the sound pressure loss caused by air leakage due to the slit 40 is reduced. The additional membrane layer 60 has certain tensile deformation properties. When the piezoelectric unit 30 vibrates, the additional membrane layer 60 undergoes bending motion, thereby reducing the restriction on the movement of the piezoelectric unit 30.

[0054] In this embodiment, an additional film layer 60 is formed by roll pressing or hot pressing. The additional film layer 60 is stacked on the piezoelectric unit 30 and the metal pad 70. The additional film layer 60 is a photosensitive film. In one feasible embodiment, roll pressing includes two or more rollers arranged in a certain pattern to press and stretch the additional film layer 60 material into an additional film layer 60 with a certain thickness and surface shape. Hot pressing includes a moving mold and a fixed mold, with a mold cavity between the moving mold and the fixed mold. After the additional film layer 60 material is placed in the mold cavity, it is hot pressed to form the shape of the mold cavity, thereby completing the forming of the additional film layer 60. Further, it also includes forming the additional film layer 60 by flatbed printing.

[0055] Compared to typical fully filled liquid types, the piezoelectric element 30 can effectively improve SPL and structural reliability by maximizing displacement and minimizing vibration.

[0056] In the embodiments provided in this application, reference is made to Figure 1 As shown, the first part 61 and the second part 62 have a height difference, with the second part 62 located below the first part 61. During the deformation of the piezoelectric unit 30, the height difference between the first part 61 and the second part 62 makes the deformation of the first part 61 more compliant, reducing the restriction on the movement of the piezoelectric unit 30 and further improving SPL and structural reliability.

[0057] Reference Figure 1As shown, the first part 61 and the second part 62 have the same thickness, and the thickness of each part 61 and the second part 62 is consistent. The deformation process of the piezoelectric unit 30 is a regular parabolic shape, which avoids the local deformation of the piezoelectric unit 30 being restricted due to the addition of the additional film layer 60, thereby improving the reliability of the acoustic sensor.

[0058] In the embodiments provided in this application, reference is made to Figure 1 As shown, the thickness of the metal pad 70 is less than the thickness of the piezoelectric layer 32. The plane where the bottom surface of the second part 62 is located intersects with the piezoelectric layer 32. There is a gap between the bottom surface of the second part 62 and the top surface of the first electrode layer 31. When the piezoelectric layer 32 is bent and deformed, the periphery is not subject to too much restriction, and the flexibility is better.

[0059] Figures 2a-2e This is a flowchart illustrating the fabrication process of the acoustic sensor provided in this invention. The fabrication method includes the following steps:

[0060] like Figure 2a As shown, a base unit 10 is provided. Specifically, a first silicon layer 12 is provided. A first oxide layer 13 of SiO2 material is prepared on the first silicon layer 12 using methods such as vapor deposition, thermal oxidation, or thermal decomposition. A second silicon layer 14 is formed on the first oxide layer 13 using methods such as vapor deposition, thermal oxidation, or thermal decomposition. The material of the second silicon layer 14 can be the same as that of the first silicon layer 12.

[0061] like Figure 2b As shown, a second oxide layer 20 is sputtered onto the surface of the second silicon layer 14 by magnetron sputtering.

[0062] Continue to refer to Figure 2b As shown, a piezoelectric unit 30 is formed on the second silicon layer 14. Specifically, a first electrode layer 31 is formed on the second oxide layer 20 by electron beam lift-off or magnetron sputtering, and the first electrode layer 31 is patterned using photolithography. The first electrode layer 31 is connected to the bottom electrode pad through bottom electrode leads. A piezoelectric layer 32 is deposited on the first electrode layer 31. A second electrode layer 33 is formed on the piezoelectric layer 32 by electron beam lift-off or magnetron sputtering, and the second electrode layer 33 is patterned using photolithography. The second electrode layer 33 is connected to the top electrode pad through top electrode leads.

[0063] like Figure 2cAs shown, a slit 40 is etched in the middle of the second electrode layer 33 and an opening 50 is etched at the edge of the second electrode layer 33. The slit 40 sequentially penetrates the second electrode layer 33, the piezoelectric layer 32, the first electrode layer 31, the second oxide layer 20, and the second silicon layer 14. The opening 50 sequentially penetrates the second electrode layer 33 and the piezoelectric layer 32. The first electrode layer 31 is exposed through the opening 50. Specifically, a patterned hard mask is fabricated on the second electrode layer 33, and the slit 40 is formed in the middle of the second electrode layer 33 and the opening 50 is etched at the edge of the second electrode layer 33 by dry etching or wet etching.

[0064] like Figure 2d As shown, a metal pad 70 is deposited on the first electrode layer 31 at the opening 50. Specifically, the metal pad 70 is deposited on the first electrode layer 31 by electron beam stripping or magnetron sputtering to form an electrical connection.

[0065] Continue to refer to Figure 2d As shown, an additional film layer 60 is formed by rolling or hot pressing. The first part 61 of the additional film layer 60 is laid flat on the second electrode layer 33 and covers the slit 40. The second part 62 of the additional film layer 60 is laid flat on the metal pad 70. A through groove 63 is formed on the second part 62. Preferably, the through groove 63 is formed by photolithography. The position of the metal pad 70 corresponds to the position of the through groove 63. The orthographic projection of the metal pad 70 in the thickness direction of the second part 62 falls in the through groove 63. The metal pad 70 is exposed through the through groove 63.

[0066] In one feasible embodiment, the additional film layer 60 is a photosensitive film, the rolling process includes two or more rollers arranged in a certain form to press and stretch the additional film layer 60 material into an additional film layer 60 with a certain thickness and surface shape, the hot pressing process includes a moving mold and a fixed mold, a mold cavity is provided between the moving mold and the fixed mold, and the additional film layer 60 material is placed in the mold cavity and then hot-pressed to form the shape of the mold cavity.

[0067] like Figure 2e As shown, a back cavity 11 is formed by etching at the bottom of the first silicon layer 12. The back cavity 11 passes through the first silicon layer 12 and the first oxide layer 13 in sequence. The second silicon layer 14 is exposed through the back cavity 11. Specifically, the back cavity 11 is formed by etching at the bottom of the first silicon layer 12 by dry etching or wet etching. The back cavity 11 passes through the first silicon layer 12 and the first oxide layer 13 in sequence.

[0068] The acoustic sensor prepared by the above method forms an additional film layer 60 by rolling or hot pressing. The first part 61 of the additional film layer 60 is laid flat on the second electrode layer 33 and covers the slit 40. The second part 62 of the additional film layer 60 is laid flat on the metal pad 70. The piezoelectric unit 30 can move with maximum displacement and minimize vibration, thereby effectively improving SPL and structural reliability. The thickness of the additional film layer 60 is uniformly distributed on the top surface of the piezoelectric unit 30, which is suitable for acoustic sensors with a large area.

[0069] The above description, based on the embodiments shown in the figures, details the structure, features, and effects of the present invention. The above description is only a preferred embodiment of the present invention, but the present invention is not limited to the scope of implementation shown in the figures. Any changes made in accordance with the concept of the present invention, or equivalent embodiments modified to have equivalent changes, that do not exceed the spirit covered by the specification and figures, should be within the protection scope of the present invention.

Claims

1. An acoustic sensor, characterized in that, include: A substrate unit includes a first silicon layer, a first oxide layer and a second silicon layer stacked sequentially from bottom to top. A back cavity is formed in the substrate unit, and the back cavity sequentially penetrates the first silicon layer and the first oxide layer. The second silicon layer is exposed through the back cavity. A second oxide layer is formed on the substrate unit; A piezoelectric unit is formed on the second oxide layer, and the piezoelectric unit includes a first electrode layer, a piezoelectric layer and a second electrode layer stacked sequentially from bottom to top. A slit is formed in the middle of the second electrode layer, and the slit sequentially penetrates the second electrode layer, the piezoelectric layer, the first electrode layer, the second oxide layer, and the second silicon layer, and the slit is connected to the back cavity; An opening is formed at the edge of the second electrode layer, and the opening sequentially penetrates the second electrode layer and the piezoelectric layer, with the first electrode layer exposed through the opening; A metal pad, which is stacked on the first electrode layer at the opening; An additional film layer includes a first portion and a second portion. The first portion is laid flat on the second electrode layer and covers the slit. The second portion is laid flat on the metal pad. A through groove is formed on the second portion, and the metal pad is positioned corresponding to the through groove. The metal pad is exposed through the through groove.

2. The acoustic sensor according to claim 1, characterized in that, The first part and the second part have a height difference, with the second part located below the first part.

3. The acoustic sensor according to claim 1, characterized in that, The first part and the second part have the same thickness, and the thickness of each part within the first part and the second part remains consistent.

4. The acoustic sensor according to claim 1, characterized in that, The thickness of the metal pad is less than the thickness of the piezoelectric layer.

5. The acoustic sensor according to claim 1, characterized in that, There is a gap between the bottom surface of the second part and the top surface of the first electrode layer, and the plane on which the bottom surface of the second part is located intersects with the piezoelectric layer.

6. The acoustic sensor according to claim 1, characterized in that, The additional film layer is a photosensitive film.

7. A method for fabricating an acoustic sensor, characterized in that, The method includes: A substrate unit is provided, the substrate unit comprising a first silicon layer, a first oxide layer and a second silicon layer stacked sequentially from bottom to top; A second oxide layer, a first electrode layer, a piezoelectric layer, and a second electrode layer are formed sequentially from bottom to top on the second silicon layer; A slit is etched in the middle of the second electrode layer and an opening is etched at the edge of the second electrode layer. The slit sequentially penetrates the second electrode layer, the piezoelectric layer, the first electrode layer, the second oxide layer, and the second silicon layer. The opening sequentially penetrates the second electrode layer and the piezoelectric layer. The first electrode layer is exposed through the opening. A metal pad is formed on the first electrode layer at the opening. An additional film layer is formed, a first portion of which is laid flat on the second electrode layer and covers the slit, and a second portion of which is laid flat on the metal pad. A through groove is formed on the second portion, the metal pad is positioned corresponding to the through groove, and the metal pad is exposed through the through groove. A back cavity is formed by etching at the bottom of the first silicon layer, the back cavity passing through the first silicon layer and the first oxide layer in sequence, and the second silicon layer is exposed through the back cavity.

8. The method for preparing an acoustic sensor according to claim 7, characterized in that, The additional film layer is a photosensitive film.

9. The method for preparing an acoustic sensor according to claim 8, characterized in that, The additional film layer is formed by rolling or hot pressing.

10. The method for preparing an acoustic sensor according to claim 8, characterized in that, The through-groove is formed in the second part by photolithography.

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