A piezoelectric micromechanical speaker

Abstract

The present invention provides a piezoelectric micromechanical speaker, comprising: a base layer having a cavity, the cavity being located at one end of the base layer; a lower electrode layer disposed on the base layer and located at the other end of the base layer; a piezoelectric layer disposed on the lower electrode layer; and an upper electrode layer disposed on the piezoelectric layer, the edge of the upper electrode layer extending to the base layer, the edge of the upper electrode layer being alternately disposed with the edge of the lower electrode layer; and an isolation layer wrapped around the edge of the piezoelectric layer for isolating the upper electrode layer from the lower electrode layer. The present invention provides a piezoelectric micromechanical speaker that can ensure high consistency of vibration modes, improve the frequency response performance of the piezoelectric micromechanical speaker, and maintain insulation between the upper electrode layer and the lower electrode layer.

Description

Technical Field

[0001] The present invention relates to the technical field of loudspeakers, and in particular to a piezoelectric micromechanical loudspeaker. Background Art

[0002] Microelectromechanical systems (MEMS) is a device miniaturization technology that integrates micro-mechanical structures and circuit systems into a single chip. A speaker is a device that relies on the vibration of a diaphragm to squeeze the air to produce sound and transmit it to the surroundings. A piezoelectric MEMS speaker is a chip device that uses the piezoelectric effect to vibrate a tiny mechanical structure to produce sound. The traditional piezoelectric MEMS speaker structure is as follows Figure 1 As shown, the diaphragm area is a circular multi-layer structure, which is divided into a substrate layer a, a structural layer c, a lower electrode layer b, a piezoelectric layer e, and an upper electrode layer d. Since the upper electrode layer and the lower electrode layer are close to each other, short circuits are prone to occur.

[0003] The audio frequency range that the human ear hears is below 20kHz, and the resonant frequency of a general piezoelectric MEMS speaker should be set at 3-5kHz. The piezoelectric layer material of traditional piezoelectric MEMS speakers is mainly aluminum nitride (AlN). However, the resonant frequency of MEMS speakers based on the AlN piezoelectric layer is relatively high. When the resonant frequency should be set at 3-5kHz, the diameter of the diaphragm will reach 5mm. Since there is a hole area under the diaphragm, when the diaphragm diameter is too large, during the manufacturing process of the MEMS speaker, the internal stress will cause the diaphragm to bend, deform, or even collapse, resulting in performance degradation or even device damage.

[0004] On the other hand, in order to obtain a large output sound pressure, the piezoelectric MEMS speaker needs a light diaphragm and a large vibration amplitude. Figure 2 As shown in the figure, conventional piezoelectric MEMS speakers etch away non-structural layers in the diaphragm area, outside the center electrode, to reduce the diaphragm's mass. However, because the center electrode needs to be electrically connected to the substrate, a bridge structure f is required to connect the electrode to the substrate, so the piezoelectric layer must be retained at this bridge. Considering the overall device structure and diaphragm morphology, the remaining bridge structure inevitably disrupts the central symmetry of the MEMS speaker, causing deformation of the diaphragm's vibration pattern and resulting in a decrease in device performance. Summary of the Invention

[0005] The object of the present invention is to overcome the above problems existing in the prior art and to provide a piezoelectric micromechanical speaker having high output sound pressure and a centrally symmetrical device structure.

[0006] In order to achieve the above technical objectives and the above technical effects, the present invention is implemented through the following technical solutions:

[0007] The present invention provides a piezoelectric micromechanical speaker, comprising:

[0008] A base layer having a cavity, wherein the cavity is located at one end of the base layer;

[0009] a lower electrode layer, disposed on the base layer, and the lower electrode layer is located at the other end of the base layer;

[0010] a piezoelectric layer disposed on the lower electrode layer; and

[0011] an upper electrode layer, disposed on the piezoelectric layer, wherein an edge of the upper electrode layer extends to the base layer, and an edge of the upper electrode layer is alternately disposed with an edge of the lower electrode layer;

[0012] The isolation layer is wrapped around the edge of the piezoelectric layer and is used to isolate the upper electrode layer from the lower electrode layer.

[0013] In one embodiment of the present invention, the lower electrode layer comprises:

[0014] a lower center electrode, disposed on the base layer; and

[0015] At least two lower edge electrodes are disposed on the lower central electrode, and the lower edge electrodes are located on side walls of the lower central electrode.

[0016] In one embodiment of the present invention, the edge of the piezoelectric layer is arranged to be sloped.

[0017] In one embodiment of the present invention, the upper electrode layer comprises:

[0018] an upper central electrode, disposed on the piezoelectric layer; and

[0019] An upper edge electrode has one end connected to the side wall of the upper center electrode, and the other end of the upper edge electrode extends to the structural layer after passing through the edge of the piezoelectric layer.

[0020] In one embodiment of the present invention, the upper edge electrode is located between two adjacent lower edge electrodes, and a gap is formed between the upper edge electrode and the lower edge electrode.

[0021] In one embodiment of the present invention, one end of the isolation layer extends between the upper electrode layer and the piezoelectric layer, and the other end of the isolation layer extends between the lower central electrode and the upper edge electrode.

[0022] In one embodiment of the present invention, the base layer comprises:

[0023] a substrate layer; and

[0024] The buried oxide layer is disposed on the substrate layer, and the buried oxide layer is located at one end of the base layer.

[0025] In one embodiment of the present invention, the base layer further includes a structural layer, and the structural layer is located on an end of the buried oxide layer away from the substrate layer.

[0026] In summary, the present invention provides a piezoelectric micromechanical speaker, which completely removes the redundant piezoelectric layer and metal layer in the vibration area, maintains the central symmetry of the structure, ensures high consistency of the vibration mode, and improves the frequency response performance of the piezoelectric micromechanical speaker. The edge of the piezoelectric layer is set in a slope, the edge is routed, and an isolation layer is set at the edge of the piezoelectric layer to ensure that the upper electrode layer and the lower electrode layer are insulated during the process of leading out the central excitation electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of this application. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0028] Figure 1 It is a schematic diagram of the structure of a traditional piezoelectric MEMS speaker;

[0029] Figure 2 It is a schematic diagram of the structure of a traditional piezoelectric MEMS speaker;

[0030] Figure 3 This is a schematic diagram of the overall structure of the present invention from one angle;

[0031] Figure 4 This is a schematic diagram of the overall structure of the present invention from another angle;

[0032] Figure 5 This invention Figure 3 Structural explosion diagram;

[0033] Figure 6 It is a schematic diagram of the internal structure of the present invention;

[0034] Figure 7 This invention Figure 6 Front view of

[0035] Figure 8 It is a top view of the overall structure of the present invention;

[0036] Figure 9 This invention Figure 8 A magnified view of the structure at point A;

[0037] Figure 10 Schematic diagram of the structure of the substrate layer of the present invention;

[0038] Figure 11 is a flow chart of a method for manufacturing a piezoelectric micromechanical speaker according to one embodiment of the present invention;

[0039] Figure 12 It is a flow chart of a method for manufacturing a piezoelectric micromechanical speaker in another embodiment of the present invention.

[0040] Explanation of the numbers in the figure: 1-base layer, 10-substrate layer, 11-buried oxide layer, 12-structural layer, 13-cavity, 14-vibration area, 2-lower electrode layer, 20-lower edge electrode, 21-lower center electrode, 3-isolation layer, 4-upper electrode layer, 40-upper edge electrode, 41-upper center electrode, 5-piezoelectric layer, 51-annular groove. DETAILED DESCRIPTION

[0041] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments.

[0042] See also Figures 3 to 7 、 Figure 10 The present invention provides a piezoelectric micromechanical speaker having high output sound pressure and a centrally symmetrical device structure. Specifically, the piezoelectric micromechanical speaker comprises: a base layer 1, the base layer 1 having a cavity 13, the cavity 13 being located at one end of the base layer 1, and the vibrating region 14 of the piezoelectric micromechanical speaker being located above the cavity 13. In one embodiment of the present invention, the base layer 1 comprises a substrate layer 10, a buried oxide layer 11 and a structural layer 12, wherein the structural layer 12, the buried oxide layer 11 and the substrate layer 10 are formed as a whole in the form of silicon on insulating substrate (SOI), wherein the structural layer 12 and the substrate layer 10 may be made of single crystal silicon, and the buried oxide layer 11 may be made of silicon dioxide. The buried oxide layer 11 is located on the substrate layer 10, and the buried oxide layer 11 is located at one end of the substrate layer 10, and is used as a stop layer when the substrate layer 10 is etched. Cavity 13 is located within substrate layer 10 and buried oxide layer 11. Etching can begin at substrate layer 10 and continue through buried oxide layer 11, forming cavity 13. The radius of cavity 13 is r1, which is set to a reasonable value based on the actual application. Above cavity 13 is the vibration region 14 of the piezoelectric micromechanical speaker. Structural layer 12 is located on buried oxide layer 11, at the end of buried oxide layer 11 away from substrate layer 10.

[0043] Please refer to the figure, Figures 5 to 9In one embodiment of the present invention, the piezoelectric micromechanical speaker further includes a lower electrode layer 2, which is disposed on the base layer 1 and is located at the other end of the base layer 1. The lower electrode layer 2 serves as a ground electrode. The material of the lower electrode layer 2 is metal, for example, including but not limited to platinum (Pt), gold (Au), aluminum (Al), molybdenum (Mo), etc. The lower electrode layer 2 includes a lower center electrode 21 and a lower edge electrode 20. The lower center electrode 21 is located at the center of the structural layer 12, and the edge of the lower center electrode 21 is inclined. The lower edge electrode 20 is disposed on the lower center electrode 21 and is located on the side wall of the lower center electrode 21. The number of the lower edge electrodes 20 is at least two, for example, three, six or eight, and the multiple lower edge electrodes 20 are centrally symmetrically arranged. The angle between the two sides of the lower edge electrode 20 is θ1, and θ1 can be designed to be any appropriate angle according to actual conditions.

[0044] See also Figures 5 to 7 In one embodiment of the present invention, the piezoelectric micromechanical speaker further includes a piezoelectric layer 5 and an upper electrode layer 4. The piezoelectric layer 5 is disposed on the lower electrode layer 2. Specifically, the piezoelectric layer 5 is located on the lower center electrode 21, and the edge of the piezoelectric layer 5 is arranged in a sloped manner. The piezoelectric layer 5 can deform through the inverse piezoelectric effect, driving the vibration region 14 to vibrate. The sloped edge of the piezoelectric layer 5 allows the upper electrode layer 4 to be guided to the structural layer 12. The areas of the piezoelectric layer 5 not covered by the upper electrode layer 4 are completely etched away, thereby achieving a high output sound pressure of the piezoelectric micromechanical speaker. The radius of the piezoelectric layer 5 is r2, and the value of r2 is set to a reasonable value based on the actual application. The piezoelectric layer 5 is a piezoelectric material, and may include, for example, but not limited to, aluminum nitride (AlN), lead zirconate titanate (PZT), etc. It may also include doped piezoelectric materials formed by doping the aforementioned piezoelectric materials with different components, or may include piezoelectric materials with different crystal orientations, single crystals, or polycrystalline piezoelectric materials. An annular groove 51 is provided on one end of the piezoelectric layer 5 away from the lower electrode layer 2 .

[0045] See also Figure 3 、 Figures 5 to 9In one embodiment of the present invention, the upper electrode layer 4 is disposed on the piezoelectric layer 5, and the edge of the upper electrode layer 4 extends to the base layer 1, and the edge of the upper electrode layer 4 is arranged alternately with the edge of the lower electrode layer 2. The material of the upper electrode layer 4 can be metal, for example, including but not limited to platinum (Pt), gold (Au), aluminum (Al), molybdenum (Mo), etc. In addition, the upper electrode layer 4 can also be a region with the same pattern covered with multiple layers of different metals to improve the electrical and mechanical performance of the device. For example, the upper electrode layer 4 uses a Pt metal layer, and then a layer of Au metal layer with the same pattern is grown on the upper surface of the Pt metal layer. The upper electrode layer 4 serves as an excitation electrode. Specifically, the specific structure of the upper electrode layer 4 may include an upper center electrode 41 and an upper edge electrode 40. The upper center electrode 41 is located on the end of the piezoelectric layer 5 away from the lower electrode layer 2. The radius of the upper center electrode 41 is r3, and the value of r3 is set to a reasonable value according to the actual application. The upper edge electrode 40 is disposed on the sidewall of the upper center electrode 41. Specifically, one end of the upper edge electrode 40 is connected to the sidewall of the upper center electrode 41, and the other end of the upper edge electrode 40 extends through the edge of the piezoelectric layer 5 to the structural layer 12 and is located between two adjacent lower edge electrodes 20. The number of upper edge electrodes 40 is the same as the number of lower edge electrodes. The upper edge electrode 40 can be Z-shaped, but is not limited to this. A gap d is formed between the upper edge electrode 40 and the lower edge electrode 20. The angle between the two sides of the upper edge electrode 40 is θ2, which can be designed to any appropriate angle based on actual conditions.

[0046] See also Figure 3 、 Figures 5 to 8 In one embodiment of the present invention, since the upper and lower surfaces of the piezoelectric layer 5 are the upper electrode layer 4 and the lower electrode layer 2, respectively, when the upper electrode layer 4 passes through the slope of the edge of the piezoelectric layer 5, it is very easy to cause the upper electrode layer 4 and the lower electrode layer 2 to be connected, forming a short circuit. The piezoelectric micromechanical speaker also includes an isolation layer 3, which is wrapped around the edge of the piezoelectric layer 5 and is used to isolate the upper electrode layer 4 and the lower electrode layer 2, so that the upper electrode layer 4 is always on the surface of the isolation layer 3 during the process of extending toward the structural layer 12. One end of the isolation layer 3 extends to the inside of the annular groove 51 and is located between the upper electrode layer 4 and the piezoelectric layer 5. The other end of the isolation layer 3 extends to the side of the lower center electrode 21 and is located between the lower center electrode 21 and the upper edge electrode 40. The present application does not limit the material of the isolation layer 3. In one embodiment of the present invention, the material of the isolation layer 3 can be silicon dioxide, silicon nitride, or aluminum oxide.

[0047] The present invention also provides a method for processing a piezoelectric micromechanical speaker. Figure 5 、 Figure 10 、 Figure 11 In one embodiment of the present invention, the processing method includes steps S1-S6:

[0048] S1 prepares a commercial SOI wafer and grows the metal of the lower electrode layer 2 on the upper surface of the SOI wafer. The size of the SOI wafer is not limited. In one embodiment of the present invention, the SOI wafer can be two inches, four inches, six inches, or eight inches. The lower electrode layer 2 can be grown by electron beam evaporation or magnetron sputtering, but is not limited thereto.

[0049] S2 grows a piezoelectric layer 5 on the upper surface of the lower electrode layer 2, then performs photolithography and etching of the piezoelectric layer 5. The piezoelectric layer 5 can be grown by, but is not limited to, magnetron sputtering or a sol-gel method. Specifically, all areas of the piezoelectric layer 5 not covered by the upper electrode layer 4 within the vibration region 14 of the piezoelectric micromechanical speaker are etched away. The piezoelectric layer 5 is etched using a wet etching method, which facilitates forming a sloped structure.

[0050] S3: photolithography and etching of the lower electrode layer 2. The etching method of the lower electrode layer 2 can be reactive ion etching (RIE), inductively coupled plasma etching (ICP), or ion beam etching (IBE).

[0051] In step S4, an isolation layer 3 is grown at the edge and upper surface of the piezoelectric layer 5 and the edge of the lower electrode layer 2, and the isolation layer 3 is photoetched and etched. The isolation layer 3 can be grown by physical vapor deposition (PVD) or chemical vapor deposition (CVD), but is not limited thereto. The isolation layer 3 can be etched by reactive ion etching (RIE), inductively coupled plasma etching (ICP), or wet etching.

[0052] S5 grows the metal of the upper electrode layer 4, and then photolithographs and etches the upper electrode layer 4. The upper electrode layer 4 can be grown by electron beam evaporation or magnetron sputtering. The upper electrode layer 4 can be etched by reactive ion etching (RIE), inductively coupled plasma etching (ICP), or ion beam etching (IBE).

[0053] S6: Photolithography and etching of the SOI substrate layer 10 and buried oxide layer 11 are performed to obtain the piezoelectric micromechanical speaker of the present invention. The etching method for the substrate layer 10 is deep reactive ion etching (DRIE), but is not limited thereto. The etching method for the buried oxide layer 11 is reactive ion etching (RIE), but is not limited thereto.

[0054] Please participate Figure 5 、 Figure 10 、 Figure 12 In another embodiment of the present invention, the processing method includes steps S11-S71:

[0055] S11 prepares a commercial SOI wafer and grows the metal of the lower electrode layer 2 on the upper surface of the SOI wafer. The size of the SOI wafer is not limited. In one embodiment of the present invention, the SOI wafer can be two inches, four inches, six inches, or eight inches. The lower electrode layer 2 can be grown by electron beam evaporation or magnetron sputtering, but is not limited thereto.

[0056] S21 grows a piezoelectric layer 5 on the upper surface of the lower electrode layer 2. The piezoelectric layer 5 may be grown by magnetron sputtering or sol-gel method, but is not limited thereto.

[0057] S31: The metal of the upper electrode layer 4 is first grown, and the upper electrode layer 4 is photolithographically and etched. The upper electrode layer 4 can be grown by electron beam evaporation or magnetron sputtering. The upper electrode layer 4 can be etched by reactive ion etching (RIE), inductively coupled plasma etching (ICP), or ion beam etching (IBE). After etching, only the central circular region of the upper electrode layer 4 remains, i.e., the upper center electrode 41.

[0058] S41 photolithography and etching of the piezoelectric layer 5 and the lower electrode layer 2. The piezoelectric layer 5 is etched by wet etching, which facilitates the formation of a sloped structure. Specifically, all areas of the piezoelectric layer 5 not covered by the upper electrode layer 4 in the vibration region 14 of the piezoelectric micromechanical speaker are etched away. The lower electrode layer 2 can be etched by reactive ion etching (RIE), inductively coupled plasma etching (ICP), or ion beam etching (IBE). After etching, a complete pattern of the lower electrode layer 2 is formed.

[0059] After growing the isolation layer 3, photolithography and etching of the isolation layer 3 are performed in step S51. The isolation layer 3 may be grown by physical vapor deposition (PVD) or chemical vapor deposition (CVD), but is not limited thereto. The isolation layer 3 may be etched by reactive ion etching (RIE), inductively coupled plasma etching (ICP), or wet etching.

[0060] S61 is a second growth of the metal of the upper electrode layer 4. The growth method of the upper electrode layer 4 is lift-off. After the growth is completed, the growth of the upper electrode layer 4 is completed at the edge of the isolation layer 3 and the area between two adjacent lower edge electrodes 20.

[0061] S71 lithography and etching of the SOI substrate layer 10 and buried oxide layer 11 are performed to obtain the piezoelectric micromechanical speaker of the present invention. The etching method for the substrate layer 10 is deep reactive ion etching (DRIE), but is not limited thereto. The etching method for the buried oxide layer 11 is reactive ion etching (RIE), but is not limited thereto.

[0062] In summary, the present invention provides a piezoelectric micromechanical speaker, which completely removes the redundant piezoelectric layer and metal layer in the vibration area, maintains the central symmetry of the structure, ensures high consistency of the vibration mode, and improves the frequency response performance of the piezoelectric micromechanical speaker. The edge of the piezoelectric layer is set in a slope, the edge is routed, and an isolation layer is set at the edge of the piezoelectric layer to ensure that the upper electrode layer and the lower electrode layer are insulated during the process of leading out the central excitation electrode.

[0063] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention, and such changes and modifications fall within the scope of the invention as claimed.

Claims

1. A piezoelectric micromechanical speaker, characterized in that , the piezoelectric micromechanical speaker includes: A base layer having a cavity, wherein the cavity is located at one end of the base layer; a lower electrode layer, disposed on the base layer, and the lower electrode layer is located at the other end of the base layer; a piezoelectric layer, disposed on the lower electrode layer; an upper electrode layer, disposed on the piezoelectric layer, wherein an edge of the upper electrode layer extends to the base layer, and an edge of the upper electrode layer is alternately disposed with an edge of the lower electrode layer; and an isolation layer, wrapped around the edge of the piezoelectric layer and used to isolate the upper electrode layer from the lower electrode layer; Wherein, the lower electrode layer comprises: a lower center electrode, disposed on the base layer; and at least two lower edge electrodes, disposed on the lower central electrode, and the lower edge electrodes are located on side walls of the lower central electrode; The upper electrode layer comprises: an upper central electrode, disposed on the piezoelectric layer; and an upper edge electrode, one end of which is connected to the side wall of the upper center electrode, and the other end of which passes through the edge of the piezoelectric layer and extends to the structural layer; The upper edge electrode is located between two adjacent lower edge electrodes, and a gap is formed between the upper edge electrode and the lower edge electrode; One end of the isolation layer extends between the upper electrode layer and the piezoelectric layer, and the other end of the isolation layer extends between the lower central electrode and the upper edge electrode.

2. The piezoelectric micromechanical speaker according to claim 1, characterized in that , the edge of the piezoelectric layer is set to be sloped.

3. The piezoelectric micromechanical speaker according to claim 1, wherein , the base layer includes: a substrate layer; and The buried oxide layer is disposed on the substrate layer, and the buried oxide layer is located at one end of the base layer.

4. The piezoelectric micromechanical speaker according to claim 3, characterized in that The base layer also includes a structural layer, which is located on one end of the buried oxide layer away from the substrate layer.

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