MEMS piezoelectric speaker with soft support structure and preparation method thereof

Abstract

The present invention discloses a MEMS piezoelectric speaker with a soft support structure and a preparation method thereof. The MEMS piezoelectric speaker includes: a substrate, the central area of ​​which is a hollow area; a composite dielectric film layer, located above the substrate, and containing an annular groove inside, the annular groove being located above the hollow area; a piezoelectric unit, located above the composite dielectric film layer on the inner side of the annular groove; and a soft support film layer, covering the annular groove; wherein the composite dielectric film layer, the piezoelectric unit and the soft support film layer located on the inner side of the annular groove constitute a composite piezoelectric vibration film with a soft support structure. The vibration film stress of the MEMS piezoelectric speaker with a soft support structure is released, the vibration amplitude is large during operation, it has high sensitivity, and the preparation process is simple.

Description

Technical Field

[0001] The present invention belongs to the technical field of micro-electromechanical systems, and relates to a MEMS piezoelectric speaker with a soft support structure and a preparation method thereof. Background Art

[0002] Microelectromechanical systems (MEMS) are developed on the basis of microelectronics technology, integrating lithography, corrosion, thin film, LIGA, silicon micromachining, non-silicon micromachining and precision machining technologies. Microphones in mobile communication devices such as mobile phones and tablets have been miniaturized using MEMS technology.

[0003] MEMS speakers mainly include MEMS electromagnetic speakers and piezoelectric speakers. Among them, piezoelectric speakers have the advantages of relatively low power consumption and simple processing technology. Compared with traditional speakers, MEMS speakers have the advantages of small size and low power. The industrialization of MEMS speakers in mobile phones, tablets and other devices will bring about great changes in the design concepts of these communication devices, thereby accelerating the rapid upgrading of these devices. The low sensitivity of MEMS speakers is currently a major obstacle to their industrialization. Therefore, how to improve the sensitivity of MEMS speakers through structural and process improvements is a technical problem that urgently needs to be solved in the industrialization of MEMS speakers. Summary of the invention

[0004] 1. Technical issues to be resolved

[0005] The present disclosure provides a MEMS piezoelectric speaker with a soft support structure and a preparation method thereof, so as to at least partially solve the technical problems raised above.

[0006] (II) Technical solution

[0007] According to one aspect of the present disclosure, a MEMS piezoelectric speaker with a soft support structure is provided, comprising: a substrate, wherein the central area of ​​the substrate is a hollow area; a composite dielectric film layer, located above the substrate and comprising an annular groove therein, wherein the annular groove is located above the hollow area; a piezoelectric unit, located above the composite dielectric film layer on the inner side of the annular groove; and a soft support film layer, covering the annular groove; wherein the composite dielectric film layer, the piezoelectric unit and the soft support film layer located on the inner side of the annular groove constitute a composite piezoelectric vibration membrane with a soft support structure.

[0008] In some embodiments of the present disclosure, the piezoelectric unit includes, from bottom to top, a bottom electrode, a piezoelectric layer, and a top electrode.

[0009] In some embodiments of the present disclosure, the material of the piezoelectric layer is one of the following materials: zinc oxide, aluminum nitride, lead zirconate titanate, perovskite-type piezoelectric material, relaxor-type piezoelectric material, or organic piezoelectric material; and / or the bottom electrode and the top electrode are: a metal single-layer film, a metal multilayer film, a non-metallic conductive film, or a combination of metal and non-metallic conductive films.

[0010] In some embodiments of the present disclosure, the thickness of the piezoelectric layer is between 0.01 μm and 60 μm; and / or the thickness of the bottom electrode and the top electrode is between 0.01 μm and 5 μm.

[0011] In some embodiments of the present disclosure, the thickness of the annular groove is the same as the thickness of the composite dielectric film layer, and the width of the ring in the annular groove is between 0.01 μm and 1000 μm.

[0012] In some embodiments of the present disclosure, the composite dielectric film layer includes, from bottom to top: a first silicon nitride layer, a silicon oxide layer, and a second silicon nitride layer; and / or the thicknesses of the first silicon nitride layer, the silicon oxide layer, and the second silicon nitride layer are respectively between 0.01 μm and 30 μm; or the composite dielectric film layer includes, from bottom to top: a first silicon oxide layer, a silicon nitride layer, and a second silicon oxide layer; and / or the thicknesses of the first silicon oxide layer, the silicon nitride layer, and the second silicon oxide layer are respectively between 0.01 μm and 30 μm; or The composite dielectric film layer includes, from bottom to top: a silicon layer, an oxide layer, or an oxide layer, a silicon layer, and an oxide layer; and / or the thickness of the silicon layer and the oxide layer are respectively between 0.01 μm and 30 μm; or the composite dielectric film layer is a single-layer or multi-layer structure comprising one of a silicon nitride layer, a silicon oxide layer, polycrystalline silicon, phosphosilicate glass, and borosilicate glass, or any combination of two or more thereof, and / or the thickness of the silicon nitride layer, the silicon oxide layer, polycrystalline silicon, phosphosilicate glass, and borosilicate glass are respectively between 0.01 μm and 30 μm.

[0013] In some embodiments of the present disclosure, the material of the soft supporting film layer is an organic thin film material, including: polyimide, polyparaxylene, polyurethane, or other organic thin films; and / or the thickness of the soft supporting film layer is between 0.01 μm and 30 μm.

[0014] In some embodiments of the present disclosure, the MEMS piezoelectric speaker further includes: a mask layer located on the back side of the substrate.

[0015] According to another aspect of the present disclosure, a method for preparing a MEMS piezoelectric speaker with a soft support structure is provided, comprising: growing a composite dielectric film layer on the front side of a substrate; growing a patterned piezoelectric unit above the composite dielectric film layer; etching away the composite dielectric film layer in the surrounding area below the piezoelectric unit to form an annular groove; preparing a soft support film layer above the annular groove; and forming a mask layer with a hollow central area on the back side of the substrate, and performing body etching by a wet or dry method to remove the central area of ​​the substrate to release a composite piezoelectric vibration film with a soft support structure; wherein the composite piezoelectric vibration film comprises: a composite dielectric film layer located on the inner side of the annular groove, a piezoelectric unit, and a soft support film layer; the mask layer used for body etching is retained or removed in the final device.

[0016] In some embodiments of the present disclosure, the step of preparing a soft supporting film layer above the annular groove includes: filling a filling sacrificial layer in the annular groove; growing a soft supporting film layer above the composite dielectric film layer and the filling sacrificial layer; and removing the filling sacrificial layer in the annular groove.

[0017] (III) Beneficial effects

[0018] It can be seen from the above technical solutions that the MEMS piezoelectric speaker with a soft support structure and the preparation method thereof provided by the present disclosure have the following beneficial effects:

[0019] (1) A composite vibration membrane layer in the central area is composed of a piezoelectric layer and a composite dielectric membrane layer. The composite vibration membrane layer in the central area is surrounded by an annular groove and a soft support membrane layer located thereon, forming a soft support structure at the edge, which helps to release the stress of the composite vibration membrane layer, increase the vibration amplitude and radiation sound pressure, thereby improving the sensitivity of the MEMS piezoelectric speaker, and the preparation process is simple;

[0020] (2) An organic film is used as the soft supporting film layer, which has good elasticity and sealing properties, forming a structure in which the central area is made of hard material and the edge supporting area is made of flexible material. While increasing the vibration amplitude, it also prevents the problems of "sound leakage" and reduction of radiation area. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1A Schematic cross-sectional view of a MEMS piezoelectric speaker with a soft support structure according to an embodiment of the present disclosure.

[0022] Figure 1B FIG. 4 is a top view of a MEMS piezoelectric speaker with a soft support structure according to an embodiment of the present disclosure.

[0023] Figure 2 The present invention is a flow chart of a method for preparing a MEMS piezoelectric speaker with a soft support structure according to an embodiment of the present invention.

[0024] Figure 3A-3K A schematic diagram of the structures corresponding to the various steps of preparing a MEMS piezoelectric speaker with a soft support structure.

[0025] Figure 3A It is a schematic cross-sectional view after the oxide layer is grown on the substrate.

[0026] Figure 3B It is a cross-sectional schematic diagram of growing a composite dielectric film layer on the front side of a substrate.

[0027] Figure 3C It is a schematic cross-sectional view after the bottom electrode is grown on the composite dielectric film layer.

[0028] Figure 3D It is a schematic cross-sectional view after the piezoelectric layer is grown on the bottom electrode.

[0029] Figure 3E Schematic diagram of the cross section after the top electrode is grown on the piezoelectric layer.

[0030] Figure 3F This is a schematic cross-sectional view of the composite dielectric film layer after an annular groove is formed by etching.

[0031] Figure 3G It is a cross-sectional schematic diagram after a filling sacrificial layer is formed in the annular groove.

[0032] Figure 3H It is a cross-sectional schematic diagram of forming a soft supporting film layer above the composite dielectric film layer and the filling sacrificial layer.

[0033] Fig. 3I A schematic cross-sectional view of etching the oxide layer on the back side of the substrate to form a mask layer.

[0034] Figure 3J A schematic cross-sectional view after substrate etching to form a hollow area.

[0035] Figure 3K This is a schematic cross-sectional view after the filling sacrificial layer is etched away.

[0036]

Explanation of symbols

[0037] 10-base;

[0038] 20-composite dielectric film layer;

[0039] 21- a first silicon nitride layer; 22- a silicon oxide layer;

[0040] 23- a second silicon nitride layer;

[0041] 30- piezoelectric unit;

[0042] 31- bottom electrode; 32- piezoelectric layer;

[0043] 33-top electrode;

[0044] 40-annular groove; 41-filling sacrificial layer;

[0045] 50-soft supporting film layer;

[0046] 60-mask layer; 70-hollow area. DETAILED DESCRIPTION

[0047] The present disclosure provides a MEMS piezoelectric speaker with a soft support structure and a preparation method thereof, wherein a composite vibration membrane layer in a central area is composed of a piezoelectric layer and a composite dielectric membrane layer, the composite vibration membrane layer in the central area is surrounded by an annular groove and a soft support membrane layer located thereon, forming a soft support structure at the edge, which helps to release the stress of the composite vibration membrane layer, increase the vibration amplitude and the radiated sound pressure, thereby improving the sensitivity of the MEMS piezoelectric speaker, and the preparation process is simple; in addition, an organic membrane is used as the soft support membrane layer, which has good elasticity and sealing, forming a structure in which the central area is made of hard material and the edge support area is made of flexible material, which prevents the problems of "sound leakage" and reduced radiation area while increasing the vibration amplitude.

[0048] In order to make the objectives, technical solutions and advantages of the present disclosure more clearly understood, the present disclosure is further described in detail below in combination with specific embodiments and with reference to the accompanying drawings.

[0049] In the present disclosure, the terms "hard" and "soft" refer to the properties of a material, "hard" means greater hardness and strength; "soft" means better flexibility of the material; and the numerical range "between" includes the endpoint values.

[0050] In a first exemplary embodiment of the present disclosure, a MEMS piezoelectric speaker is provided.

[0051] Figure 1A FIG1B is a cross-sectional schematic diagram of a MEMS piezoelectric speaker with a soft support structure according to an embodiment of the present disclosure. FIG1B is a top view of a MEMS piezoelectric speaker with a soft support structure according to an embodiment of the present disclosure. Figure 1A For along Figure 1B A cross-sectional view after the section shown by AA is cut open.

[0052] Reference Figure 1A and Figure 1BAs shown, the MEMS piezoelectric speaker with a soft support structure disclosed in the present invention includes: a substrate 10, whose central area is a hollow area; a mask layer 60, located on the back side of the substrate 10; a composite dielectric film layer 20, formed above the substrate 10, and comprising an annular groove 40 inside, wherein the annular groove 40 is located above the hollow area; a piezoelectric unit 30, located above the composite dielectric film layer 20 on the inner side of the annular groove 40; and a soft support film layer 50, covering the annular groove 40; wherein the composite dielectric film layer 20, the piezoelectric unit 30 and the soft support film layer 50 located on the inner side of the annular groove 40 constitute a composite piezoelectric vibration film with a soft support structure.

[0053] The various parts of the MEMS piezoelectric speaker with a soft support structure disclosed in the present invention are described in detail below with reference to the accompanying drawings.

[0054] In this embodiment, the substrate 10 is a silicon substrate, but the substrate 10 disclosed in the present invention is not limited to the examples in the embodiments, and may also be an SOI substrate or other substrates. In order to obtain different composite dielectric film layers 20, the substrate 10 is selected according to actual needs.

[0055] Reference Figure 1A As shown, in this embodiment, the composite dielectric film layer 20 includes, from bottom to top, a first silicon nitride layer 21, a silicon oxide layer 22, and a second silicon nitride layer 23, wherein the silicon oxide layer is preferably a silicon oxide layer grown under low temperature conditions. The thickness of the first silicon nitride layer 21, the silicon oxide layer 22, and the second silicon nitride layer 23 are respectively between 0.01 μm and 30 μm.

[0056] It should be noted that the number of layers of the composite dielectric film layer 20 disclosed in the present invention is not limited, and the material of each layer is not limited to the above embodiments. The number of layers and the materials of each layer of the composite dielectric film layer can be selected according to actual needs. For example, in one example, the composite dielectric film layer 20 includes: a first silicon oxide layer, a silicon nitride layer, and a second silicon oxide layer from bottom to top. Preferably, the thickness of the first silicon oxide layer, the silicon nitride layer, and the second silicon oxide layer is between 0.01 μm and 30 μm, respectively. Or in one example, the composite dielectric film layer includes: a silicon layer and an oxide layer from bottom to top. Or in one example, the composite dielectric film layer includes: an oxide layer, a silicon layer, and an oxide layer from bottom to top. Preferably, the thickness of the silicon layer and the oxide layer is between 0.01 μm and 30 μm, respectively. Or in one example, the composite dielectric film layer is a single-layer or multi-layer structure including one or any two of a silicon nitride layer, a silicon oxide layer, polycrystalline silicon, phosphosilicate glass, and borosilicate glass. Preferably, the thickness of the silicon nitride layer, the silicon oxide layer, the polysilicon, the phosphosilicate glass, and the borosilicate glass is respectively between 0.01 μm and 30 μm.

[0057] Reference Figure 1A and Figure 1B As shown, in this embodiment, the piezoelectric unit 30 includes, from bottom to top, a bottom electrode 31, a piezoelectric layer 32, and a top electrode 33. In other embodiments, an insulating isolation layer may also be included between the electrode and the piezoelectric layer of the piezoelectric unit. The bottom electrode 31 and the top electrode 33 are: a metal single-layer film, a metal multilayer film, a non-metallic conductive film, or a combination of a metal and a non-metallic conductive film. In this embodiment, the material of the piezoelectric layer 32 may be selected from but not limited to one or more of the following materials: zinc oxide, aluminum nitride, lead zirconate titanate, relaxor piezoelectric material, perovskite piezoelectric material or organic piezoelectric material; the thickness of the piezoelectric layer is between 0.01 μm and 60 μm. The material of the bottom electrode 31 and the top electrode 33 may be selected from but not limited to one or a combination of the following materials: aluminum, copper, gold, platinum, molybdenum, chromium, titanium, lanthanum nickelate (LNO) and other metal or non-metallic conductive films. When the bottom electrode and the top electrode are metal or non-metallic conductive films, the thickness is between 0.01 μm and 5 μm. When the bottom electrode or the top electrode is a composite layer, and its adhesion layer is a chromium layer, a titanium layer or other conductive film layer, the thickness is between 0.01 μm and 1 μm. In one embodiment, the bottom electrode or the top electrode is: a gold / chromium composite layer, or a platinum / titanium composite layer. Preferably, the thickness of the aluminum electrode is between 0.01 μm and 5 μm, the thickness of the chromium layer or the titanium layer is between 0.01 μm and 1 μm, and the thickness of the gold layer or the platinum layer is between 0.01 μm and 5 μm.

[0058] Reference Figure 1B As shown, in this embodiment, in order to facilitate the electrical connection between the top electrode 33 and the bottom electrode 31 in the device, an opening is etched out of the part of the soft support film layer 50 above the bottom electrode 31, so that the bottom electrode 31 is exposed as a bottom electrode pressure welding hole; a top electrode pressure welding hole is drawn out outside the circular top electrode 33, and the shape is as follows Figure 1B Of course, according to actual needs, the shape of the electrode is not limited to the circle shown in this embodiment, and the lead-out method of the electrode can also be adaptively adjusted according to actual needs.

[0059] In this embodiment, the material of the soft supporting film layer 50 may be selected from but not limited to one of the following materials: polyimide, polyparaxylene, polyurethane, or other organic films; the thickness of the soft supporting film layer 50 is between 0.01 μm and 30 μm.

[0060] In this embodiment, the annular groove 40 is obtained by etching part of the composite dielectric film layer above the hollow area. The projection of the hollow area on the plane where the composite dielectric film layer is located can be square, circular or other shapes. The shape of the annular groove 40 can be circular, square or rectangular or other shapes, and the internal shape of the annular groove can be set according to actual needs. In this embodiment, a circular annular groove or a square (including a rectangular or square) annular groove is preferred. The thickness of the annular groove 40 is the same as the thickness of the composite dielectric film layer 20, that is, the sum of the thicknesses of the first silicon nitride layer 21, the silicon oxide layer 22, and the second silicon nitride layer 23. The width of the ring of the annular groove 40 is between 0.1μm and 1000μm. In this embodiment, for a circular annular groove, the width of the ring represents the distance between two concentric circles; for a square annular groove, the width of the ring represents the distance between the edge of the middle square and the outer circle in the diameter direction.

[0061] In this embodiment, the thickness of the mask layer 60 is between 0.01 μm and 20 μm. In this embodiment, the mask layer 60 is an oxide layer, which is used as a mask for forming a hollow area during the preparation of the MEMS piezoelectric speaker. Here, the oxide layer is used as an example, and the mask layer disclosed in the present invention is not limited thereto.

[0062] In this embodiment, the composite dielectric film layer 20, the piezoelectric unit 30 and the soft support film layer 50 located on the inner side of the annular groove 40 together constitute a composite piezoelectric vibration film with a soft support structure. When a voltage is loaded on the piezoelectric unit, the composite piezoelectric vibration film with a soft support structure undergoes bending vibration, thereby radiating sound pressure. Since the MEMS piezoelectric speaker has an annular groove and a soft support film layer located above it, the annular groove 40 and the soft support film layer 50 above it release the stress of the composite piezoelectric vibration film. The composite dielectric film layer 20 has a higher hardness and strength, which is the central area of ​​the composite piezoelectric vibration film, while the soft support film layer 50 has better flexibility and better sealing, which is the edge area of ​​the composite piezoelectric vibration film. The combination of the two forms a MEMS speaker vibration film with a "hard" middle and a "soft" edge, thereby increasing the radiated sound pressure under the same voltage, improving the sensitivity of the MEMS speaker, and avoiding the problems of "sound leakage" and reduced radiated sound pressure.

[0063] The preparation process of the soft support film layer 50 includes depositing a filling sacrificial layer 41 in the annular groove 40, and then depositing the soft support film 50 on the composite dielectric film layer and the filling sacrificial layer, and then removing the filling sacrificial layer 41 by a dry or wet etching process to release the soft support film layer 50. The present disclosure does not limit the height of the filling sacrificial layer, as long as the filling can be achieved in the actual process and a soft support film layer can be formed on it, it is within the protection scope of the present disclosure.

[0064] In a second exemplary embodiment of the present disclosure, a method for preparing a MEMS piezoelectric speaker is provided.

[0065] Figure 2 The present invention is a flow chart of a method for preparing a MEMS piezoelectric speaker with a soft support structure according to an embodiment of the present invention. Figure 3A-3K A schematic diagram of the structures corresponding to the various steps of preparing a MEMS piezoelectric speaker with a soft support structure.

[0066] Reference Figure 2 , Figure 3A-3K As shown, the method for preparing the MEMS piezoelectric speaker with a soft support structure disclosed in the present invention comprises:

[0067] Step S202: growing a mask layer on the back side of the substrate;

[0068] In this embodiment, an oxide layer is used as the mask layer 60 for illustration. The mask layer disclosed in the present invention may also be other mask layers, and is not limited thereto.

[0069] The step S202 includes: depositing oxide layers on the upper and lower surfaces of the substrate, and then removing the oxide layer on the upper surface to obtain a substrate with an oxide layer on the back side.

[0070] Figure 3A It is a schematic cross-sectional view after the oxide layer is grown on the substrate.

[0071] In this embodiment, the composite dielectric film layer 20 is a first silicon nitride layer 21, a silicon oxide layer 22, and a second silicon nitride layer 23. The substrate 10 is selected and it is determined that the substrate 10 is made of silicon material. First, the substrate silicon is cleaned using a standard cleaning method, and is respectively boiled and cleaned using an acid cleaning solution and an alkaline cleaning solution, and then cleaned with deionized water, and finally dried with nitrogen gas; then, an oxide layer is deposited on the front and back sides of the substrate silicon 10 using a thermal oxidation furnace as a mask layer 60, see Figure 3A As shown, photoresist is coated on the mask layer 60 on the back side of the substrate silicon, the mask layer 60 on the front side is removed by a wet process, and finally the photoresist on the mask layer 60 on the back side is removed.

[0072] However, the substrate 10 disclosed in the present invention is not limited to the examples in the embodiments, and may also be an SOI substrate or other substrates. The substrate 10 and the composite dielectric film layer 20 are matched and selected according to the bonding state between the composite dielectric film layer 20 and the substrate 10, the difficulty of preparation, and other effects.

[0073] In this embodiment, the thickness of the mask layer 60 is between 0.01 μm and 20 μm.

[0074] In some examples, the thickness of the mask layer 60 is 0.2 μm, 0.5 μm, 1 μm, 1.5 μm, 3 μm, or 3.5 μm.

[0075] Step S204: growing a composite dielectric film layer on the front surface of the substrate;

[0076] Figure 3B It is a cross-sectional schematic diagram of growing a composite dielectric film layer on the front side of a substrate.

[0077] Reference Figure 3B As shown, a first silicon nitride layer 21, a silicon oxide layer 22, and a second silicon nitride layer 23 are sequentially deposited on the front surface of the substrate silicon by a plasma chemical vapor deposition (PECVD) method to form a composite dielectric film layer 20, wherein the silicon oxide layer 22 is preferably grown under low temperature conditions. For the materials of the composite dielectric film layers of other embodiments, they are also sequentially deposited according to a thin film deposition technique such as a PECVD method, which belongs to a conventional preparation process and will not be described in detail here.

[0078] In this embodiment, the thicknesses of the first silicon nitride layer 21 , the silicon oxide layer 22 , and the second silicon nitride layer 23 are respectively between 0.01 μm and 30 μm.

[0079] In some instances, the thickness of the first silicon nitride layer 21 and the second silicon nitride layer 23 are both 0.5 μm, and the thickness of the silicon oxide layer 22 prepared at low temperature is 0.2 μm; or the thickness of the first silicon nitride layer 21 and the second silicon nitride layer 23 are both 1 μm, and the thickness of the silicon oxide layer 22 prepared at low temperature is 0.5 μm; or the thickness of the first silicon nitride layer 21, the second silicon nitride layer 23 and the silicon oxide layer 22 prepared at low temperature are all 0.5 μm; or the thickness of the first silicon nitride layer 21 and the second silicon nitride layer 23 are both 1.5 μm, and the thickness of the silicon oxide layer 22 prepared at low temperature is 0.2 μm; or the thickness of the first silicon nitride layer 21 and the second silicon nitride layer 23 are both 1 μm, and the thickness of the silicon oxide layer 22 prepared at low temperature is 0.2 μm, etc.

[0080] Step S206: growing a bottom electrode on the composite dielectric film layer;

[0081] Figure 3C It is a schematic cross-sectional view after the bottom electrode is grown on the composite dielectric film layer.

[0082] Reference Figure 3C As shown, a bottom electrode film is deposited on the second silicon nitride layer 23 using a metal thin film deposition technique, and the bottom electrode film is patterned using a standard photolithography and etching process to form a bottom electrode 31; or a photoresist is coated on the second silicon nitride layer, and the photoresist is patterned using a standard photolithography process, and then a bottom electrode metal film is deposited, and finally the photoresist is etched away using a stripping technique to form a bottom electrode 31.

[0083] In this embodiment, the bottom electrode 31 has a circular pattern, but the present disclosure is not limited thereto.

[0084] In this embodiment, the material of the bottom electrode 31 may be selected from but is not limited to one of the following materials or a combination thereof: aluminum, copper, gold, platinum, molybdenum, chromium, titanium, lanthanum nickel oxide (LNO), and other metals or non-conductive films, wherein it may be a composite metal layer, such as: a gold / chromium composite layer, or a platinum / titanium composite layer, wherein, preferably, the thickness of the aluminum electrode is between 0.01 μm and 5 μm, the thickness of the chromium layer or the titanium layer is between 0.01 μm and 1 μm, and the thickness of the gold layer or the platinum layer is between 0.05 μm and 5 μm.

[0085] In some instances, the bottom electrode 31 is an aluminum electrode with a thickness of 0.2μm or 0.3μm; or the bottom electrode 31 is a gold / chromium composite layer with a thickness of 0.2μm / 0.02μm or 0.3μm / 0.05μm respectively; or the bottom electrode 31 is a platinum / titanium composite layer with a thickness of 0.2μm / 0.05μm or 0.3μm / 0.05μm, etc.

[0086] Step S208: growing a piezoelectric layer on the bottom electrode;

[0087] Figure 3D It is a schematic cross-sectional view after the piezoelectric layer is grown on the bottom electrode.

[0088] Reference Figure 3D As shown, in this embodiment, an organic piezoelectric film is deposited on the bottom electrode 31, and a patterned piezoelectric layer 32 is formed by using a standard photolithography process or a lift-off process.

[0089] The material of the piezoelectric layer 32 may be selected from but not limited to one or a combination of the following materials: zinc oxide, aluminum nitride, lead zirconate titanate, relaxor piezoelectric material, perovskite piezoelectric material or organic piezoelectric material; the thickness of the piezoelectric layer is between 0.01 μm and 60 μm.

[0090] In this embodiment, the pattern of the piezoelectric layer 32 is as shown in FIG. Figure 1B As shown, the pattern is the same as that of the top electrode 33, which is a circular shape with a lead-out welding hole. The area of ​​the piezoelectric layer 32 is smaller than that of the bottom electrode 31, so that the bottom electrode 31 and the top electrode 33 deposited later can be exposed.

[0091] In some instances, the piezoelectric layer 32 is made of zinc oxide with a thickness of 1 μm, 2 μm or 3 μm; or the piezoelectric layer 32 is made of lead zirconate titanate with a thickness of 4 μm; or the piezoelectric layer 32 is made of organic piezoelectric material with a thickness of 1 μm or 2 μm; or the piezoelectric layer 32 is made of relaxor ferroelectric material with a thickness of 1 μm; or the piezoelectric layer 32 is made of aluminum nitride with a thickness of 2 μm, etc.

[0092] Step S210: growing a top electrode on the piezoelectric layer;

[0093] Figure 3E Schematic diagram of the cross section after the top electrode is grown on the piezoelectric layer.

[0094] Reference Figure 3E As shown, in this embodiment, a top electrode film is deposited on the piezoelectric layer 32 using a metal thin film deposition technique, and the top electrode film is patterned using a standard photolithography etching process to form a top electrode 33. Alternatively, a photoresist is coated on the piezoelectric layer 32, and the photoresist is patterned using a standard photolithography process, and then a top electrode metal film is deposited, and finally a lift-off technique is used to pattern the top electrode 33.

[0095] In this embodiment, the pattern of the top electrode 33 is as shown in FIG. Figure 1B As shown, the pattern of the piezoelectric layer 32 is the same as that of a circle with a lead-out bonding hole.

[0096] The bottom electrode 33 is: a metal single-layer film, a metal multilayer film, a non-metallic conductive film, or a combination of a metal and a non-metallic conductive film. In this embodiment, the material of the top electrode 33 may be selected from but not limited to one of the following materials or a combination thereof: aluminum, copper, gold, platinum, molybdenum, chromium, titanium, lanthanum nickel oxide (LNO), and other metal or non-metallic conductive films, which may be a composite metal layer, such as: a gold / chromium composite layer, or a platinum / titanium composite layer. Preferably, the thickness of the aluminum electrode is between 0.01 μm and 5 μm, the thickness of the chromium layer or the titanium layer is between 0.01 μm and 1 μm, and the thickness of the gold layer or the platinum layer is between 0.05 μm and 5 μm.

[0097] In some instances, the top electrode 33 is an aluminum electrode with a thickness of 0.2 μm or 0.3 μm; or the top electrode 33 is a platinum / titanium composite layer with a thickness of 0.2 μm / 0.05 μm respectively; or the top electrode 33 is a gold / chromium composite layer with a thickness of 0.2 μm / 0.05 μm or 0.3 μm / 0.05 μm, etc.

[0098] Step S212: etching away the composite dielectric film layer in the surrounding area below the bottom electrode to form an annular groove;

[0099] Figure 3F This is a schematic cross-sectional view of the composite dielectric film layer after an annular groove is formed by etching.

[0100] Reference Figure 3F As shown, the composite dielectric film layer 20 in the surrounding area below the bottom electrode is etched away by a dry or wet process to form an annular groove 40. The thickness of the annular groove 40 is the same as the sum of the thicknesses of the first silicon nitride layer 21, the silicon oxide layer 22, and the second silicon nitride layer 23.

[0101] In this embodiment, the shape of the annular groove obtained by etching is: the outer layer is circular, and the inner layer is circular or square, and the square includes a square or a rectangle.

[0102] In this embodiment, the width of the annular groove 40 is between 0.1 μm and 1000 μm. In this embodiment, for a circular annular groove, the width of the ring represents the distance between two concentric circles; for a square annular groove, the width of the ring represents the distance between the edge of the middle square and the outer circle in the diameter direction.

[0103] In some examples, the width of the ring in the circular or square annular groove is 10 μm, 30 μm, 50 μm, 60 μm, 80 μm, 100 μm, 200 μm, 300 μm, 500 μm, 600 μm or 700 μm, etc.

[0104] Step S214: filling the sacrificial layer into the annular groove;

[0105] Figure 3G It is a cross-sectional schematic diagram after a filling sacrificial layer is formed in the annular groove.

[0106] Reference Figure 3G As shown, in this embodiment, zinc oxide is used as the filling sacrificial layer 41, and zinc oxide is filled in the annular groove using a standard photolithography process. The material of the filling sacrificial layer can be selected but not limited to: metal oxide, porous silicon, polycrystalline silicon, etc. The present disclosure does not limit the height of the filling sacrificial layer, as long as the filling can be achieved in the actual process and a soft support film layer can be formed on it, it is within the protection scope of the present disclosure.

[0107] Step S216: growing a soft support film layer on the composite dielectric film layer and the filling sacrificial layer;

[0108] Figure 3H It is a cross-sectional schematic diagram of forming a soft supporting film layer above the composite dielectric film layer and the filling sacrificial layer.

[0109] In this embodiment, a soft support film layer 50 is deposited on the composite dielectric film layer and the filling sacrificial layer, and is patterned as follows: Figure 1B The shape shown in FIG. 5 is formed by the pattern of the soft supporting film layer 50 and the shape formed by the top electrode 33 and the bottom electrode 31 are complementary patterns. At the same time, in order to allow the bottom electrode 31 to lead out a welding hole, the part of the soft supporting film layer 50 covering the bottom electrode 31 is patterned to make an opening to expose the bottom electrode 31. Figure 1B shown.

[0110] Reference Figure 3HAs shown, the soft supporting film layer 50 spans the annular groove 40, covers a portion of the bottom electrode 31, connects the composite dielectric film layer on the periphery of the annular groove with the bottom electrode on the inside of the annular groove and the composite dielectric film layer thereunder, and together with the composite dielectric film layer 20 on the inside of the annular groove 40 and the piezoelectric unit 30 above the composite dielectric film layer 20, constitutes a composite piezoelectric vibration film with a soft supporting structure, and forms the edge structure of the composite piezoelectric vibration film.

[0111] It should be noted that the pattern of the soft supporting film layer in this embodiment is only an example, and any structure as long as the soft supporting film layer can cover the annular groove is within the protection scope of the present disclosure.

[0112] In this embodiment, the material of the soft supporting film layer 50 may be selected from but not limited to one of the following materials: polyimide, polyparaxylene, polyurethane, or other organic films; the thickness of the soft supporting film layer 50 is between 0.01 μm and 30 μm.

[0113] In some examples, the organic vibration film layer 50 is made of polyimide with a thickness of 1 μm, 1.5 μm or 2 μm; or the organic vibration film layer 50 is made of polyparaxylene, polyurethane, or other organic films with a thickness of 1 μm, 1.5 μm or 2 μm.

[0114] Step S218: pattern-etching the mask layer on the back side of the substrate, and further etching the substrate to form a hollow area;

[0115] Fig. 3I A schematic cross-sectional view of etching the oxide layer on the back side of the substrate to form a mask layer. Figure 3J A schematic cross-sectional view after substrate etching to form a hollow area.

[0116] Reference Fig. 3I As shown, in this embodiment, a photoresist is coated on the mask layer 60 on the back of the substrate, and the photoresist is patterned using double-sided exposure technology and standard photolithography technology. The back mask layer 60 is patterned and etched using a dry or wet etching process, and the photoresist is removed to form a patterned mask layer 60. The patterned mask layer 60 includes a hollow area corresponding to the outer edge diameter of the annular groove 40. Using the patterned mask layer 60 as a mask, the central area of ​​the substrate is further etched using a wet or dry etching process to obtain a hollow area 70. The result is shown in FIG. Figure 3J shown.

[0117] Step S220: removing the filling sacrificial layer in the annular groove to complete the preparation of the MEMS piezoelectric speaker;

[0118] Figure 3K This is a schematic cross-sectional view after the filling sacrificial layer is etched away.

[0119] Reference Figure 3K As shown, the filling sacrificial layer 41 in the annular groove 40 can be removed by dry etching or wet etching. In this embodiment, the filling sacrificial layer 41 is removed by wet etching to obtain a released composite vibration membrane layer.

[0120] In summary, the present disclosure provides a MEMS piezoelectric speaker with a soft support structure and a preparation method thereof, wherein a composite vibration membrane layer in the central area is composed of a piezoelectric layer and a composite dielectric membrane layer, and the composite vibration membrane layer in the central area is surrounded by an annular groove and a soft support membrane layer located thereon, forming a soft support structure at the edge, which helps to release the stress of the composite vibration membrane layer, increase the vibration amplitude and the radiated sound pressure, thereby greatly improving the sensitivity of the MEMS piezoelectric speaker and the preparation process is simple; in addition, an organic film is used as the soft support membrane layer, which has good elasticity and sealing, forming a structure in which the central area is a hard material and the edge support area is a flexible material, which improves the vibration amplitude while preventing the problems of "sound leakage" and reduced radiation area.

[0121] Of course, according to actual needs, the MEMS piezoelectric speaker with a soft support structure and the preparation method thereof disclosed in the present invention also include other processes and steps, which are irrelevant to the innovation of the present invention and will not be repeated here. It should also be noted that the directional terms mentioned in the embodiments, such as "up", "down", "front", "back", "left", "right", etc., are only reference directions of the accompanying drawings, and are not used to limit the scope of protection of the present invention. Throughout the accompanying drawings, the same elements are represented by the same or similar figure marks. Conventional structures or constructions will be omitted when they may cause confusion in the understanding of the present invention. And the shapes and sizes of the components in the figures do not reflect the actual size and proportion, but only illustrate the contents of the embodiments of the present invention. In addition, in the claims, any reference symbols between brackets should not be constructed as limitations on the claims.

[0122] The ordinal numbers used in the specification and claims, such as "first", "second", "third", etc., to modify the corresponding elements, do not themselves mean that the elements have any ordinal numbers, nor do they represent the order of one element and another element, or the order in the manufacturing method. The use of these ordinal numbers is only used to clearly distinguish a component with a certain name from another component with the same name.

[0123] In addition, unless the steps are specifically described or must occur in sequence, the order of the above steps is not limited to the above list, and can be changed or rearranged according to the required design. And the above embodiments can be mixed and matched with each other or with other embodiments based on design and reliability considerations, that is, the technical features in different embodiments can be freely combined to form more embodiments.

[0124] The specific embodiments described above further illustrate the purpose, technical solutions and beneficial effects of the present disclosure. It should be understood that the above description is only a specific embodiment of the present disclosure and is not intended to limit the present disclosure. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present disclosure should be included in the protection scope of the present disclosure.

Claims

1. A MEMS piezoelectric speaker with a soft support structure, comprising: the base, whose central region is a hollow area; A composite dielectric film layer is located above the substrate and contains an annular groove therein, the annular groove is located above the hollow area, and the annular groove is obtained by etching a portion of the composite dielectric film layer above the hollow area; A piezoelectric unit is located above the composite dielectric film layer inside the annular groove, and the piezoelectric unit includes, from bottom to top, a bottom electrode, a piezoelectric layer, and a top electrode; and A soft supporting film layer covers the annular groove and connects the composite dielectric film layer on the outer side of the annular groove with the composite dielectric film layer on the inner side of the annular groove, wherein the material of the soft supporting film layer is an organic thin film material; Wherein, the composite dielectric film layer, the piezoelectric unit and the soft support film layer located on the inner side of the annular groove constitute a composite piezoelectric vibration film with a soft support structure; When a voltage is applied to the piezoelectric unit, the composite piezoelectric diaphragm with a soft support structure undergoes bending vibration, thereby radiating sound pressure.

2. The MEMS piezoelectric speaker according to claim 1, wherein: The piezoelectric unit has at least one insulating isolation layer between the bottom electrode and the piezoelectric layer or between the top electrode and the piezoelectric layer.

3. The MEMS piezoelectric speaker according to claim 2, wherein: The material of the piezoelectric layer is one or more of the following materials: zinc oxide, aluminum nitride, lead zirconate titanate, perovskite-type piezoelectric material, relaxor-type piezoelectric material, or organic piezoelectric material; and / or The materials of the bottom electrode and the top electrode are: a metal single-layer film, a metal multi-layer film, a non-metallic conductive film, or a combination of a metal and a non-metallic conductive film.

4. The MEMS piezoelectric speaker according to claim 3, wherein: The thickness of the piezoelectric layer is between 0.01 μm and 60 μm; and / or The thickness of the bottom electrode and the top electrode is between 0.01 μm and 5 μm.

5. The MEMS piezoelectric speaker according to claim 1, wherein: The thickness of the annular groove is the same as the thickness of the composite dielectric film layer, and the width of the ring in the annular groove is between 0.01 μm and 1000 μm.

6. The MEMS piezoelectric speaker according to claim 1, wherein: The composite dielectric film layer includes, from bottom to top, a first silicon nitride layer, a silicon oxide layer, and a second silicon nitride layer; and / or the thicknesses of the first silicon nitride layer, the silicon oxide layer, and the second silicon nitride layer are respectively between 0.01 μm and 30 μm; Or the composite dielectric film layer includes, from bottom to top, a first silicon oxide layer, a silicon nitride layer, and a second silicon oxide layer; and / or the thicknesses of the first silicon oxide layer, the silicon nitride layer, and the second silicon oxide layer are respectively between 0.01 μm and 30 μm; Or the composite dielectric film layer includes, from bottom to top, a silicon layer, an oxide layer, or an oxide layer, a silicon layer, and an oxide layer; and / or the thickness of the silicon layer and the oxide layer are respectively between 0.01 μm and 30 μm; Or the composite dielectric film layer is a single-layer or multi-layer structure comprising one of a silicon nitride layer, a silicon oxide layer, polycrystalline silicon, phosphosilicate glass, and borosilicate glass, or any combination of two or more of them, and / or the thickness of the silicon nitride layer, silicon oxide layer, polycrystalline silicon, phosphosilicate glass, and borosilicate glass is respectively between 0.01 μm and 30 μm.

7. The MEMS piezoelectric speaker according to claim 1, wherein: The organic film material includes: polyimide, polyparaxylene, polyurethane, or other organic films; and / or the thickness of the soft support film layer is between 0.01 μm and 30 μm.

8. The MEMS piezoelectric speaker according to any one of claims 1 to 7, further comprising: The mask layer is located on the back side of the substrate.

9. A method for preparing a MEMS piezoelectric speaker with a soft support structure, comprising: Growing a composite dielectric film layer on the front side of the substrate; Growing a patterned piezoelectric unit on the composite dielectric film layer, the piezoelectric unit comprising, from bottom to top, a bottom electrode, a piezoelectric layer, and a top electrode; Etching away the composite dielectric film layer in the surrounding area below the piezoelectric unit to form an annular groove; A soft supporting film layer is prepared above the annular groove, the soft supporting film layer covers the annular groove, spans the annular groove, covers a portion of the bottom electrode, connects the composite dielectric film layer outside the annular groove with the bottom electrode inside the annular groove and the composite dielectric film layer below the annular groove, and the material of the soft supporting film layer is an organic thin film material; and A mask layer with a hollow central region is formed on the back of the substrate, and the central region of the substrate is removed by body etching using a wet method or a dry method to release a composite piezoelectric vibration film having a soft support structure; Wherein, the composite piezoelectric vibration film comprises: a composite dielectric film layer located inside the annular groove, a piezoelectric unit, and a soft support film layer; the mask layer on the back of the substrate is retained or removed in the final device; When a voltage is applied to the piezoelectric unit, the composite piezoelectric diaphragm with a soft support structure undergoes bending vibration, thereby radiating sound pressure.

10. The preparation method according to claim 9, wherein: The step of preparing a soft supporting film layer above the annular groove comprises: Filling the sacrificial layer in the annular groove; growing a soft support film layer on the composite dielectric film layer and the filling sacrificial layer; and The sacrificial layer filled in the annular groove is removed.

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