An acoustic sensor and a method of manufacturing the same

Abstract

This invention discloses an acoustic sensor and its fabrication method. The acoustic sensor includes: a substrate unit comprising a first silicon layer, a first oxide layer, and a second silicon layer stacked sequentially from bottom to top, with a back cavity formed within the substrate unit; a second oxide layer; a piezoelectric unit comprising a first electrode layer, a piezoelectric layer, and a second electrode layer stacked sequentially from bottom to top, with a slit and an opening formed within the piezoelectric unit; a metal pad; and an additional film layer comprising a first part, a second part, and a third part. The first part is formed within the slit, with its sidewalls adhering to the inner wall of the slit, and its bottom wall covering the bottom opening of the slit. The sidewalls and bottom wall form a groove with a top opening. Compared with the prior art, this invention can effectively improve SPL and structural reliability. The thickness of the additional film layer is uniformly distributed on the surface of the piezoelectric unit, making it suitable for acoustic sensors with 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;

[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 part, a second part, and a third part. The first part is formed within the slit, with its sidewalls adhering to the inner wall of the slit. The bottom wall of the first part covers the bottom opening of the slit, and the sidewalls and the bottom wall form a groove with a top opening. The second part is formed on the second electrode layer. The third part is formed within the opening and encloses the metal pad. A through groove is formed on the third part, and the metal pad is positioned corresponding to the through groove, with the metal pad exposed through the through groove.

[0012] In the acoustic sensor described above, preferably, the first part, the second part, and the third part have the same thickness, and the thickness of the first part, the second part, and the third part is consistent at all points.

[0013] In the acoustic sensor described above, preferably, the thickness of the metal pad is less than the thickness of the piezoelectric layer.

[0014] In the acoustic sensor described above, preferably, the axis of the groove is coaxial with the axis of the back cavity.

[0015] In the acoustic sensor described above, preferably, the plane at the bottom of the groove intersects with the second silicon layer.

[0016] Secondly, the present invention also provides a method for preparing an acoustic sensor, the method comprising:

[0017] 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;

[0018] A second oxide layer, a first electrode layer, a piezoelectric layer, and a second electrode layer are sequentially deposited from bottom to top on the top of the second silicon layer;

[0019] 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.

[0020] A metal pad is formed on the first electrode layer at the opening;

[0021] An additional film layer is formed, wherein the sidewall of the first portion of the additional film layer covers the inner wall surface of the slit, the bottom wall of the first portion covers the first oxide layer, the sidewall and the bottom wall form a groove with a top opening, the second portion of the additional film layer is deposited on the second electrode layer, the third portion of the additional film layer is deposited in the opening and wraps the metal pad, a through groove is formed on the third portion, the position of the metal pad corresponds to the through groove, and the metal pad is exposed through the through groove;

[0022] 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.

[0023] In the method for fabricating an acoustic sensor as described above, preferably, the additional membrane layer is made of parylene.

[0024] In the method for fabricating an acoustic sensor as described above, preferably, the additional film layer is deposited by vapor deposition.

[0025] In the method for fabricating an acoustic sensor as described above, preferably, the vapor deposition method includes physical vapor deposition or chemical vapor deposition.

[0026] In the method for fabricating an acoustic sensor as described above, preferably, the piezoelectric layer is made of lead zirconate titanate, aluminum nitride, barium titanate, or a mixture of the above materials.

[0027] Compared with the prior art, the present invention forms an additional film layer by vapor deposition. The first part of the additional film layer is formed in the slit, the sidewall of the first part is attached to the inner wall of the slit, and the bottom wall of the first part covers the bottom opening of the slit. The sidewall and the bottom wall form a groove with a top opening. The second part of the additional film layer is formed on the second electrode layer, and the third part of the additional film layer is formed in the opening and wraps a metal pad. This allows the piezoelectric unit to move with maximum displacement and minimize vibration, thereby effectively improving SPL and structural reliability. Even on sharp corners (>85° sidewalls), the additional film layer can cover them. The thickness of the additional film layer is uniformly distributed on the surface of the piezoelectric unit, which is suitable for acoustic sensors with a large area. Attached Figure Description

[0028] Figure 1 This is a cross-sectional schematic diagram of the acoustic sensor provided in the embodiment of the present invention;

[0029] Figures 2a-2e This is a flowchart illustrating the fabrication process of the acoustic sensor provided in this invention.

[0030] Explanation of reference numerals in the attached figures:

[0031] 10-Base unit, 11-Back cavity, 12-First silicon layer, 13-First oxide layer, 14-Second silicon layer;

[0032] 20 - Second oxide layer;

[0033] 30 - Piezoelectric unit, 31 - First electrode layer, 32 - Piezoelectric layer, 33 - Second electrode layer;

[0034] 40-slit;

[0035] 50-Opening;

[0036] 60 - Additional membrane layer, 61 - First part, 62 - Second part, 63 - Third part, 64 - Groove, 65 - Through groove;

[0037] 70-Metal pad. Detailed Implementation

[0038] 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.

[0039] 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:

[0040] 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.

[0041] 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.

[0042] A piezoelectric unit 30 is formed on the substrate unit 10. The piezoelectric unit 30 includes a first electrode layer 31, a piezoelectric layer 32, and a second electrode layer 33 stacked sequentially from bottom to top, wherein:

[0043] 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).

[0044] 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.

[0045] 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).

[0046] 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.

[0047] 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.

[0048] The additional film layer 60 includes a first part 61, a second part 62, and a third part 63. Preferably, the first part 61, the second part 62, and the third part 63 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, and the third part 63 is located at the outer edge of the second part 62. The first part 61 is formed in the slit 40, and the bottom wall of the first part 61 covers the bottom opening of the slit 40. The side walls and the bottom wall form a groove 64 with a top opening. The second part 62 is deposited on the second electrode layer 24, and the third part 63 is deposited in the opening 50 and wraps around the metal pad 70. A through groove 65 is formed on the third part 63, and the metal pad 70 is positioned corresponding to the through groove 65. The orthographic projection of the metal pad 70 in the thickness direction of the third part 63 falls in the through groove 65, and the metal pad 70 is exposed through the through groove 65.

[0049] By covering the slit 40 with the additional film layer 60, the sound pressure loss caused by air leakage due to the slit 40 is reduced. The additional film layer 60 has certain tensile deformation properties. When the piezoelectric unit 30 vibrates, the additional film layer 60 undergoes bending motion, thereby reducing the restriction on the movement of the piezoelectric unit 30. In this embodiment, the additional film layer 60 is made of parylene and is formed by vapor deposition. Vapor deposition includes physical vapor deposition or chemical vapor deposition. Chemical vapor deposition (CVD) is a process in which gaseous or vaporized parylene reacts on the second electrode layer 33 and the metal pad 40 to form a thin film. Physical vapor deposition (PVD) uses physical methods (such as evaporation, sputtering, etc.) to vaporize parylene and deposit it on the surface of the second electrode layer 33 and the metal pad 40 to form a thin film. Both methods can achieve thin films with good thickness uniformity.

[0050] Compared to typical fully filled liquid types, the piezoelectric element 30 can withstand maximum displacement and minimal vibration, and the additional film layer 60 can cover even sharp corners (>85° sidewalls), thereby effectively improving SPL and structural reliability.

[0051] In the embodiments provided in this application, the first part 61, the second part 62, and the third part 63 have the same thickness, and the thickness of each part 61, the second part 62, and the third part 63 is consistent. The thickness of the additional film layer 60 is uniformly distributed on the surface of the piezoelectric unit 30, which is suitable for acoustic sensors with a large area. The deformation process of the piezoelectric unit 30 is a regular parabolic shape, which avoids the limitation of local deformation of the piezoelectric unit 30 due to the addition of the additional film layer 60, thereby improving the reliability of the acoustic sensor.

[0052] Reference Figure 1 As shown, the thickness of the metal pad 70 is less than the thickness of the piezoelectric layer 32. The axis of the groove 64 is coaxial with the axis of the back cavity 11. The groove 64 is located in the middle of the first part 61. The plane at the bottom of the groove 64 intersects with the second silicon layer 14, which makes the deformation of the first part 61 more flexible and reduces the restriction on the movement of the piezoelectric unit 30. When the piezoelectric layer 32 undergoes bending deformation, the periphery is not subject to excessive restriction, further improving SPL and structural reliability.

[0053] 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:

[0054] 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.

[0055] like Figure 2b As shown, a second oxide layer 20 is formed on the second silicon layer 14. Specifically, a second oxide layer 20 is sputtered on the surface of the second silicon layer 14 by magnetron sputtering.

[0056] Continue to refer to Figure 2b As shown, a first electrode layer 31, a piezoelectric layer 32, and a second electrode layer 33 are sequentially deposited from bottom to top on the second oxide layer 20. The first electrode layer 31 is formed on the second oxide layer 20 by electron beam lift-off or magnetron sputtering and is patterned using photolithography. The first electrode layer 31 is connected to the bottom electrode pad through bottom electrode leads. The piezoelectric layer 32 is deposited on the first electrode layer 31. The second electrode layer 33 is formed on the piezoelectric layer 32 by electron beam lift-off or magnetron sputtering and is patterned using photolithography. The second electrode layer 33 is connected to the top electrode pad through top electrode leads.

[0057] like Figure 2c As 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, the slit 40 is formed in the middle of the piezoelectric unit 30 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.

[0058] 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.

[0059] Continue to refer to Figure 2d As shown, an additional film layer 60 is formed by vapor deposition. The first part 61 of the additional film layer 60 is formed in the slit 40. The bottom wall of the first part covers the bottom opening of the slit 40. The side walls and the bottom wall form a groove 64 with a top opening. The second part 62 of the additional film layer 60 is deposited on the second electrode layer 24. The third part 63 of the additional film layer 60 is deposited in the opening 50 and wraps around the metal pad 70. A through groove 65 is formed on the third part 63. The position of the metal pad 70 corresponds to the position of the through groove 65. The orthographic projection of the metal pad 70 in the thickness direction of the third part 63 falls in the through groove 65. The metal pad 70 is exposed through the through groove 65.

[0060] In one feasible embodiment, the additional film layer 60 is made of parylene. Vapor deposition methods, including physical vapor deposition (PVD) and chemical vapor deposition (CVD), can both achieve good deposition results. In one feasible embodiment, the additional film layer 60 is made of parylene. Chemical vapor deposition (CVD) utilizes gaseous or vaporized parylene to react and form a thin film on the top surface of the second electrode layer 33, the top surface of the metal pad 40, and within the slit 40. Physical vapor deposition (PVD) uses physical methods (such as evaporation or sputtering) to vaporize parylene and deposit it as a thin film on the top surface of the second electrode layer 33, the top surface of the metal pad 40, and the inner surface of the slit 40.

[0061] like Figure 2eAs 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.

[0062] The acoustic sensor prepared by the above method has an additional film layer 60 deposited by vapor deposition. The piezoelectric unit 30 can move with maximum displacement and minimize vibration, thereby effectively improving SPL and structural reliability. Even at sharp corners (>85° sidewalls), the additional film layer 60 can cover the surface. The thickness of the additional film layer 60 is uniformly distributed on the surface of the piezoelectric unit 30, which is suitable for acoustic sensors with a large area.

[0063] 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 by The application relates to a piezoelectric element, comprising: a substrate unit comprising a first silicon layer, a first oxide layer and a second silicon layer stacked in sequence from bottom to top, a back cavity being formed in the substrate unit and penetrating the first silicon layer and the first oxide layer in sequence, the second silicon layer being exposed via the back cavity; a second oxide layer formed on the substrate unit; a piezoelectric unit formed on the second oxide layer, the piezoelectric unit comprising a first electrode layer, a piezoelectric layer and a second electrode layer stacked in sequence from bottom to top; a slit formed in the middle of the second electrode layer, the slit penetrating the second electrode layer, the piezoelectric layer, the first electrode layer, the second oxide layer and the second silicon layer in sequence; an opening formed in the edge of the second electrode layer, the opening penetrating the second electrode layer and the piezoelectric layer in sequence, the first electrode layer being exposed via the opening; a metal pad stacked on the first electrode layer at the opening; an additional film layer comprising a first part, a second part and a third part, the first part being formed in the slit, the side wall of the first part being attached to the inner wall surface of the slit, the bottom wall of the first part covering the bottom opening of the slit, the side wall and the bottom wall forming a groove with a top opening, the second part being formed on the second electrode layer, the third part being formed in the opening and wrapping the metal pad, a through groove being formed on the third part and penetrating the third part, the metal pad being exposed via the through groove; the thickness of the first part, the second part and the third part being the same, and the thickness of the first part, the second part and the third part being uniform. The thickness of the metal pad is smaller than the thickness of the piezoelectric layer. The axis of the groove is coaxial with the axis of the back cavity. The plane where the groove bottom is located intersects with the second silicon layer. The method comprises: providing a substrate unit comprising a first silicon layer, a first oxide layer and a second silicon layer stacked in sequence from bottom to top; sequentially depositing a second oxide layer, a first electrode layer, a piezoelectric layer and a second electrode layer on the top of the second silicon layer from bottom to top; etching a slit in the middle of the second electrode layer and an opening in the edge of the second electrode layer, the slit penetrating the second electrode layer, the piezoelectric layer, the first electrode layer, the second oxide layer and the second silicon layer in sequence, the opening penetrating the second electrode layer and the piezoelectric layer in sequence, the first electrode layer being exposed via the opening; forming a metal pad on the first electrode layer at the opening. ​ ​ ​ ​ 2. The acoustic sensor of claim 1, wherein, ​ 3. The acoustic sensor of claim 1, wherein, ​ 4. The acoustic sensor of claim 1, wherein, ​ 5. A method of manufacturing an acoustic sensor, characterized by ​ ​ ​ ​ ​ forming an additional film layer, a first portion of the additional film layer is deposited in the slit, a side wall of the first portion covers an inner wall surface of the slit, a bottom wall of the first portion of the additional film layer covers the first oxide layer, the side wall and the bottom wall enclose a groove with an open top, a second portion of the additional film layer is deposited on the second electrode layer, a third portion of the additional film layer is deposited in the opening and wraps the metal pad, a through slot is formed in the third portion and penetrates the third portion, the metal pad is exposed through the through slot; etching a back cavity at a bottom of the first silicon layer, the back cavity penetrates the first silicon layer and the first oxide layer in sequence, the second silicon layer is exposed through the back cavity; the additional film layer is deposited by a vapor deposition method, thicknesses of the first portion, the second portion and the third portion are the same, and thicknesses of the first portion, the second portion and the third portion are uniform.

6. The method of preparing an acoustic sensor according to claim 5, wherein, the additional film layer is made of poly-p-xylylene.

7. The method of claim 5, wherein the acoustic sensor is prepared by, the vapor deposition method includes a physical vapor deposition method or a chemical vapor deposition method.

8. The method of claim 5, wherein the acoustic sensor is prepared by, the piezoelectric layer is made of lead zirconate titanate, aluminum nitride, barium titanate or a mixture of the above materials.

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