A MEMS speaker and its method for performance improvement

Abstract

The present invention discloses a MEMS speaker and a method for improving its performance. By applying a DC bias voltage to the peripherally clamped speaker, its linear working range is expanded, the output sound pressure level is increased, and the distortion rate is reduced. By applying the DC bias voltage, the speaker can be bent. As the DC bias voltage increases, the working mode transitions from the bending mode to the stretching mode, which can improve the driving efficiency of the speaker / correct the linearity of the speaker, allowing the speaker to generate a larger displacement and sound pressure level output under the same distortion rate requirement. By adjusting the magnitude of the DC bias voltage of the speaker, the linear working range of the speaker can be expanded, thereby reducing the total harmonic distortion of the speaker and increasing the output sound pressure level.

Description

Technical Field

[0001] The present invention belongs to the technical field of MEMS speakers, and more specifically, relates to a MEMS speaker and a method for improving its performance. Background Art

[0002] A speaker, an acoustic device that converts an electrical signal into an audio signal, is widely used in fields such as headphones, mobile phone speakers, wearable devices, medical auxiliary devices, and smart home devices. Compared with traditional electromagnetic speakers based on moving coil diaphragms and moving irons, MEMS speakers have the advantages of small size, light weight, and can be arrayed to achieve specific functions such as broadening the working frequency band and sound directional transmission; in addition, MEMS speakers are compatible with CMOS processes, do not require complex manual assembly steps, can be mass-produced, which is beneficial to controlling the product yield and reducing costs.

[0003] Piezoelectric MEMS speakers work by the inverse piezoelectric effect. In order to generate a high sound pressure level output, it is required that the piezoelectric multi-layer film structure generates a large bending deformation. Under large deformations, obvious geometric nonlinear effects will occur in the device. For a complete membrane structure with clamped-free boundaries, the geometric nonlinear effects are particularly obvious. This geometric nonlinear effect causes piezoelectric MEMS speakers to generate higher harmonic distortion and at the same time limits the further deformation and sound pressure level output of the device. Summary of the Invention

[0004] Aiming at the defects and improvement requirements of the existing technology, the present invention provides a MEMS speaker and a method for improving its performance. By applying a DC bias voltage to the MEMS speaker, the linear working area of the speaker is expanded, its sound pressure level output is increased, and the distortion rate is reduced.

[0005] To achieve the above object, in a first aspect, the present invention provides a MEMS speaker, including a piezoelectric multi-layer film with clamped-free boundaries and a substrate structure, and further including a driving unit. The driving unit is used to apply a DC bias voltage to one or more electrodes in the piezoelectric multi-layer film, and to apply an AC driving signal to one or more electrodes in the piezoelectric multi-layer film.

[0006] Further, the electrodes to which the DC bias voltage is applied cover a partial area of the surface of the piezoelectric layer in the piezoelectric multi-layer film.

[0007] Further, the electrodes to which the AC driving signal is applied cover a partial area or the entire area of the surface of the piezoelectric layer in the piezoelectric multi-layer film.

[0008] Further, when applying an AC driving signal to multiple electrodes in the piezoelectric multi-layer film, each of the AC driving signals is an AC driving signal with the same phase.

[0009] Further, the piezoelectric multi-layer film includes a support layer, a lower electrode layer, a piezoelectric layer, and an upper electrode layer from bottom to top, and the upper electrode layer includes a first upper electrode and a second upper electrode that are electrically isolated;

[0010] The driving unit is configured to apply a DC bias voltage to the first upper electrode; alternatively, apply a DC bias voltage to the second upper electrode; or apply DC bias voltages with opposite polarities to the first upper electrode and the second upper electrode simultaneously;

[0011] The driving unit is further configured to apply an AC driving signal to the first upper electrode; alternatively, apply an AC driving signal to the second upper electrode; or apply AC driving signals with the same phase to the first upper electrode and the second upper electrode simultaneously.

[0012] Further, the piezoelectric multi-layer film includes a lower electrode layer, a lower piezoelectric layer, an intermediate electrode layer, an upper piezoelectric layer, and an upper electrode layer from bottom to top, and the upper electrode layer includes a first upper electrode and a second upper electrode that are electrically isolated;

[0013] The driving unit is configured to apply a DC bias voltage to the first upper electrode; alternatively, apply a DC bias voltage to the second upper electrode; or apply DC bias voltages with opposite polarities to the first upper electrode and the second upper electrode simultaneously;

[0014] The driving unit is further configured to apply an AC driving signal to the first upper electrode; alternatively, apply an AC driving signal to the second upper electrode; or apply AC driving signals with the same phase to the first upper electrode and the second upper electrode simultaneously.

[0015] Further, the shape of the piezoelectric multi-layer film is polygonal or circular.

[0016] In a second aspect, the present invention provides a method for improving the performance of a MEMS speaker. The MEMS speaker includes a piezoelectric multi-layer film with a peripherally fixed support and a substrate structure. The method includes:

[0017] Applying a DC bias voltage to one or more electrodes in the piezoelectric multi-layer film;

[0018] Applying an AC driving signal to one or more electrodes in the piezoelectric multi-layer film;

[0019] Converting the working mode of the MEMS speaker from a bending mode to a stretching mode by adjusting the magnitude of the DC bias voltage.

[0020] Further, the piezoelectric multi-layer film includes a support layer, a lower electrode layer, a piezoelectric layer, and an upper electrode layer from bottom to top, and the upper electrode layer includes a first upper electrode and a second upper electrode that are electrically isolated;

[0021] The method includes:

[0022] The lower electrode layer is grounded;

[0023] Apply a DC bias voltage to the first upper electrode; or, apply a DC bias voltage to the second upper electrode; or, apply DC bias voltages with opposite polarities to the first upper electrode and the second upper electrode simultaneously;

[0024] Apply an AC driving signal to the first upper electrode; or, apply an AC driving signal to the second upper electrode; or, apply AC driving signals with the same phase to the first upper electrode and the second upper electrode simultaneously.

[0025] Furthermore, the piezoelectric multi-layer film includes a lower electrode layer, a lower piezoelectric layer, an intermediate electrode layer, an upper piezoelectric layer, and an upper electrode layer from bottom to top. The upper electrode layer includes electrically isolated first and second upper electrodes;

[0026] The method includes:

[0027] The intermediate electrode layer is grounded;

[0028] The lower electrode layer is floating;

[0029] Apply a DC bias voltage to the first upper electrode; or, apply a DC bias voltage to the second upper electrode; or, apply DC bias voltages with opposite polarities to the first upper electrode and the second upper electrode simultaneously;

[0030] Apply an AC driving signal to the first upper electrode; or, apply an AC driving signal to the second upper electrode; or, apply AC driving signals with the same phase to the first upper electrode and the second upper electrode simultaneously.

[0031] Generally speaking, through the above technical solutions conceived by the present invention, the following beneficial effects can be achieved:

[0032] Through the DC bias voltage in the present invention, the surface topography of the MEMS speaker is converted from a plane to a quasi-spherical surface, and the working mode transitions from a bending mode to a stretching mode, obtaining a larger linear working area and driving efficiency. Due to the limitation of the strain zero point in the bending mode, the electrodes of the MEMS speaker cannot cover the entire surface of the piezoelectric layer, and only partial coverage can be used to obtain the maximum driving efficiency; in contrast, the driving electrodes in the stretching mode can be fully covered, thereby obtaining the maximum driving efficiency. In addition, by selecting an appropriate DC bias voltage, the stress softening effect of the piezoelectric layer can be utilized to improve the device driving efficiency. By setting the magnitude and coverage area of the DC bias voltage, the linear working area of the speaker can be expanded, the driving efficiency can be improved, and the speaker is allowed to produce a high sound pressure level output at a low distortion rate. Description of the Drawings

[0033] To more clearly illustrate the technical solutions of the embodiments of the present application, the accompanying drawings of the embodiments will be briefly introduced below.

[0034] Figure 1 、 Figure 2 、 Figure 3 FIG. 9 is a schematic structural diagram of a MEMS speaker provided in Embodiment 1 of the present invention. Figure 1 It is a top view. Figure 2 It is a cross-sectional view. Figure 3 It is an isometric view, wherein the piezoelectric multilayer film is a quadrilateral film fixed at all four sides.

[0035] Figure 4 、 Figure 5 、 Figure 6 FIG. 23 is a schematic structural diagram of a MEMS speaker provided in Embodiment 2 of the present invention. Figure 4 It is a top view. Figure 5 It is a cross-sectional view. Figure 6 It is an isometric view, wherein the piezoelectric multilayer film is a circular film fixed at all four sides.

[0036] Figure 7 、 Figure 8 、 Figure 9 FIG. 37 is a schematic structural diagram of a MEMS speaker provided in Embodiment 3 of the present invention. Figure 7 It is a top view. Figure 8 It is a cross-sectional view. Figure 9 It is an isometric view, wherein the piezoelectric multilayer film is a circular film fixed at all four sides and includes two piezoelectric layers.

[0037] Figure 10 FIG. 47 is a curve showing the relationship between the air volume pushed by the quadrilateral MEMS speaker 301 provided in Embodiment 1 of the present invention and the AC drive voltage, obtained by simulation using the finite element method. Among them, the quadrilateral MEMS speaker 301 with a DC bias voltage has a larger linear working area and higher drive efficiency.

[0038] Figure 11 FIG. 51 is a curve of the sound pressure level spectral response of the quadrilateral MEMS speaker 301 provided in Embodiment 1 of the present invention, obtained by simulation in the human ear canal environment using the finite element method. Among them, the quadrilateral MEMS speaker 301 with a DC bias voltage has a larger sound pressure level output.

[0039] Figure 12 FIG. 55 is the sound pressure level and total harmonic distortion of the quadrilateral MEMS speaker 301 provided in Embodiment 1 of the present invention at 1 kHz under the conditions of having or not having a DC bias voltage and applying different AC drive voltages, obtained by simulation in the human ear canal environment using the finite element method.

[0040] Figure 13It is one of the curves showing the relationship between the air-pushing volume and the AC driving voltage of the circular MEMS speaker 601 provided in the second embodiment of the present invention obtained by simulation using the finite element method. Among them, the circular MEMS speaker 601 with a DC bias voltage has a larger linear working area and higher driving efficiency.

[0041] Figure 14 It is the sound pressure level spectrum response curve of the circular MEMS speaker 601 provided in the second embodiment of the present invention obtained by simulation in the human ear canal environment using the finite element method. Among them, the circular MEMS speaker 601 with a DC bias voltage has a larger sound pressure level output.

[0042] Figure 15 It is one of the results of the sound pressure level and total harmonic distortion of the circular MEMS speaker 601 provided in the second embodiment of the present invention obtained by simulation in the human ear canal environment using the finite element method under the conditions of having or not having a DC bias voltage and applying different AC driving voltages at 1 kHz. Among them, the circular MEMS speaker 601 with a DC bias voltage has a higher sound pressure level output and lower total harmonic distortion under the same AC driving voltage; and has a larger linear working area, allowing the circular MEMS speaker 601 to produce a higher sound pressure level output when the total harmonic distortion is <5%.

[0043] Figure 16 It is the second curve showing the relationship between the air-pushing volume and the AC driving voltage of the circular MEMS speaker 601 provided in the second embodiment of the present invention obtained by simulation using the finite element method. Among them, the circular MEMS speaker 601 with a DC bias voltage has a larger linear working area.

[0044] Figure 17 It is the second result of the sound pressure level and total harmonic distortion of the circular MEMS speaker 601 provided in the second embodiment of the present invention obtained by simulation in the human ear canal environment at 1 kHz using the finite element method. Among them, the circular MEMS speaker 601 with a DC bias voltage has a lower total harmonic distortion and a higher sound pressure level output.

[0045] Figure 18 It is the curve showing the relationship between the air-pushing volume and the AC driving voltage of the circular MEMS speaker 901 with a double piezoelectric layer provided in the third embodiment of the present invention obtained by simulation using the finite element method. Among them, the circular MEMS speaker 901 with a double piezoelectric layer and a DC bias voltage has a larger linear working area.

[0046] Figure 19The sound pressure level and total harmonic distortion of the circular MEMS speaker 901 with a double piezoelectric layer provided in the third embodiment of the present invention obtained by simulation in the human ear canal environment using the finite element method at 1 kHz. Among them, the circular MEMS speaker 901 with a double piezoelectric layer with a DC bias voltage has lower total harmonic distortion and higher sound pressure level output.

[0047] Figure 20 The structural dimension parameters of the quadrilateral MEMS speaker 301 in the finite element simulation are given.

[0048] Figure 21 The structural dimension parameters of the circular MEMS speaker 601 in the finite element simulation are given.

[0049] Figure 22 The structural dimension parameters of the circular MEMS speaker 901 with a double piezoelectric layer in the finite element simulation are given.

[0050] In all the drawings, the same reference numerals are used to represent the same elements or structures. Among them, for Figure 1 、 Figure 2 、 Figure 3 The quadrilateral MEMS speaker 301 shown: 201 - Si substrate; 202 - SiO2 substrate; 203 - Si support layer; 204 - lower electrode; 205 - piezoelectric layer; 206 - first upper electrode; 207 - second upper electrode; 208 - rear cavity; 301 - quadrilateral MEMS speaker.

[0051] For Figure 4 、 Figure 5 、 Figure 6 The circular MEMS speaker 601 shown: 501 - Si substrate; 502 - SiO2 substrate; 503 - Si support layer; 504 - lower electrode; 505 - piezoelectric layer; 506 - first upper electrode; 507 - second upper electrode; 508 - rear cavity; 601 - circular MEMS speaker.

[0052] For Figure 7 、 Figure 8 、 Figure 9 The circular MEMS speaker 901 with a double piezoelectric layer shown: 801 - Si substrate; 802 - SiO2 substrate; 803 - first lower electrode; 804 - second lower electrode; 805 - lower piezoelectric layer, 806 - intermediate electrode; 807 - upper piezoelectric layer; 808 - first upper electrode; 809 - second upper electrode; 810 - rear cavity; 901 - circular MEMS speaker with a double piezoelectric layer. Detailed implementation manners

[0053] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0054] In the present invention, terms such as "first" and "second" in the present invention and the accompanying drawings (if any) are used to distinguish similar objects and do not necessarily describe a specific order or sequence.

[0055] In the present invention, the MEMS speaker is fixedly supported at the periphery and has no free end. The piezoelectric multi-layer film is an integral body, and the geometric structure of the piezoelectric multi-layer film is not limited and can be any polygon structure, such as a triangular structure, a quadrilateral structure, a hexagonal structure to a circular structure. For a circular film with a peripherally fixed support of any geometric structure, when the deformation is too large, it will be restricted by the geometric non-linear effect, resulting in a large distortion rate during large displacement vibration.

[0056] In the present invention, the electrodes for applying the DC bias voltage cover a partial area on the surface of the piezoelectric layer and can be applied through a single electrode or multiple electrodes. The AC drive signal can be applied to a partial area or the entire area on the surface of the piezoelectric layer and can be applied through a single electrode or multiple electrodes. When the AC drive signal is applied to multiple electrodes, the AC drive signal is a in-phase signal. The AC drive signal and the DC bias voltage signal can share the electrodes or be independently applied.

[0057] Embodiment 1

[0058] Refer to Figure 1 、 Figure 2 、 Figure 3 The present invention provides a schematic structural diagram of a MEMS speaker, Figure 1 which is a top view, Figure 2 which is a cross-sectional view, Figure 3 which is an isometric view, wherein the piezoelectric multi-layer film is a quadrilateral film fixedly supported on all sides. The quadrilateral MEMS speaker 301 includes a Si substrate 201, a SiO2 substrate 202, a Si support layer 203, a lower electrode 204, a piezoelectric layer 205, a first upper electrode 206 and a second upper electrode 207 stacked in sequence, and a rear cavity 208. Among them, the first upper electrode 206 and the second upper electrode 207 are electrically connected with a slit therebetween.

[0059] The present invention does not limit the application position of the DC bias voltage. When the quadrilateral MEMS speaker 301 works, the lower electrode 204 is grounded. A driving signal with a DC bias voltage is applied to the first upper electrode 206, and the second upper electrode 207 is floating; alternatively, a driving signal with a DC bias voltage can be applied to the second upper electrode 207, and the first upper electrode 206 is floating; or DC bias voltages with opposite polarities are applied to the first upper electrode 206 and the second upper electrode 207.

[0060] Figures 10 to 12 This is the case where a driving signal with a DC bias voltage is applied to the first upper electrode 206, and the second upper electrode 207 is floating.

[0061] Embodiment 2

[0062] Refer to Figure 4 、 Figure 5 、 Figure 6 The present invention provides a schematic structural diagram of a MEMS speaker, Figure 4 which is a top view, Figure 5 which is a cross-sectional view, Figure 6 which is an isometric view, wherein the piezoelectric multilayer film is a circular film fixed at the periphery. The circular MEMS speaker 601 includes an Si substrate 501, an SiO2 substrate 502, an Si support layer 503, a lower electrode 504, a piezoelectric layer 505, a first upper electrode 506, a second upper electrode 507, and a back cavity 508 stacked in sequence. The first upper electrode 506 and the second upper electrode 507 are electrically connected with a slit therebetween.

[0063] For the circular MEMS speaker 601, it is also not necessary to limit the application position of the DC bias voltage.

[0064] Figures 13 to 15 This is the case where a driving signal with a DC bias voltage is applied to the first upper electrode 506, and the second upper electrode 507 is floating.

[0065] Figure 16 and Figure 17 This is the case where a DC bias voltage is applied to the first upper electrode 506, and AC driving signals with the same phase are applied to the first upper electrode 506 and the second upper electrode 507.

[0066] By adjusting the magnitude of the DC bias voltage, the piezoelectric multilayer film can be bent, and the speaker operates in the tensile mode. At the operating point, the speaker is less affected by the nonlinear effect, resulting in a larger linear region of the speaker and an improved driving efficiency. Specifically, how much the DC bias voltage is adjusted can be observed and analyzed with the aid of an electron microscope.

[0067] Embodiment 3

[0068] Refer to Figure 7 、 Figure 8 、Figure 9 , the present invention provides a schematic structural diagram of a MEMS speaker, Figure 7 which is a top view, Figure 8 which is a sectional view, Figure 9 which is an isometric view. The piezoelectric multi-layer film is a circular film fixed at its four sides and includes two piezoelectric layers. The circular MEMS speaker 901 with a double piezoelectric layer includes an Si substrate 801, an SiO2 substrate 802, a first lower electrode 803, a second lower electrode 804, a lower piezoelectric layer 805, an intermediate electrode 806, an upper piezoelectric layer 807, a first upper electrode 808 and a second upper electrode 809 stacked in sequence, and a rear cavity 810. The first lower electrode 803 and the second lower electrode 804 are electrically isolated from each other by a slit, and the first upper electrode 808 and the second upper electrode 809 are electrically isolated from each other by a slit.

[0069] For the circular MEMS speaker 901 with a double piezoelectric layer, there is also no need to define the application position of the DC bias voltage.

[0070] For example, when the circular MEMS speaker 901 with a double piezoelectric layer works, the first lower electrode 803, the second lower electrode 804 and the intermediate electrode 806 are grounded, a DC bias voltage is applied to the first upper electrode 808, and in-phase AC drive signals are applied to the first upper electrode 808 and the second upper electrode 809. By adjusting the magnitude of the DC bias voltage, the working mode of the speaker can be switched from the bending mode to the stretching mode. In this working mode, the speaker has a larger linear working area, allowing the speaker to generate a larger sound pressure level output under the same distortion rate requirement. The simulation results are as shown in Figure 18 and Figure 19 shown.

[0071] It is easy for those skilled in the art to understand that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A MEMS speaker, comprising a piezoelectric multi-layer film fixed at the periphery and a substrate structure, characterized in that, It further includes a driving unit, which is configured to apply a DC bias voltage to one or more electrodes in the piezoelectric multilayer film, and apply an AC driving signal to one or more electrodes in the piezoelectric multilayer film; by adjusting the magnitude of the DC bias voltage, the surface topography of the MEMS speaker is converted from a plane to a quasi-spherical surface.

2. The MEMS speaker according to claim 1, wherein The electrodes to which the DC bias voltage is applied cover a partial area of the surface of the piezoelectric layer in the piezoelectric multilayer film.

3. The MEMS speaker according to claim 1, wherein The electrodes to which the AC driving signal is applied cover a partial area or the entire area of the surface of the piezoelectric layer in the piezoelectric multilayer film.

4. The MEMS speaker according to claim 3, wherein When applying an AC driving signal to multiple electrodes in the piezoelectric multilayer film, each of the AC driving signals is an AC driving signal with the same phase.

5. The MEMS speaker according to claim 1, characterized in that, The piezoelectric multilayer film includes a support layer, a lower electrode layer, a piezoelectric layer, and an upper electrode layer from bottom to top, and the upper electrode layer includes an electrically isolated first upper electrode and a second upper electrode; The driving unit is configured to apply a DC bias voltage to the first upper electrode; or, apply a DC bias voltage to the second upper electrode; Or, apply DC bias voltages with opposite polarities to the first upper electrode and the second upper electrode simultaneously; The driving unit is further configured to apply an AC driving signal to the first upper electrode; Or, apply an AC driving signal to the second upper electrode; or, apply AC driving signals with the same phase to the first upper electrode and the second upper electrode simultaneously.

6. The MEMS speaker according to claim 1, characterized in that, The piezoelectric multilayer film includes a lower electrode layer, a lower piezoelectric layer, an intermediate electrode layer, an upper piezoelectric layer, and an upper electrode layer from bottom to top, and the upper electrode layer includes an electrically isolated first upper electrode and a second upper electrode; The driving unit is configured to apply a DC bias voltage to the first upper electrode; Or, apply a DC bias voltage to the second upper electrode; Or, apply DC bias voltages with opposite polarities to the first upper electrode and the second upper electrode simultaneously; The driving unit is further configured to apply an AC driving signal to the first upper electrode; Or, apply an AC driving signal to the second upper electrode; or, apply AC driving signals with the same phase to the first upper electrode and the second upper electrode simultaneously.

7. The MEMS speaker according to any one of claims 1 to 6, characterized in that, The shape of the piezoelectric multilayer film is polygonal or circular.

8. A method for improving the performance of a MEMS speaker, the MEMS speaker including a piezoelectric multilayer film fixed at the periphery and a substrate structure, characterized in that, The method includes: Applying a DC bias voltage to one or more electrodes in the piezoelectric multilayer film; Applying an AC driving signal to one or more electrodes in the piezoelectric multilayer film; By adjusting the magnitude of the DC bias voltage, the surface topography of the MEMS speaker is converted from a plane to a quasi-spherical surface.

9. The method for improving the performance of a MEMS speaker according to claim 8, wherein The piezoelectric multilayer film includes a support layer, a lower electrode layer, a piezoelectric layer, and an upper electrode layer from bottom to top, and the upper electrode layer includes an electrically isolated first upper electrode and a second upper electrode; The method includes: The lower electrode layer is grounded; Applying a DC bias voltage to the first upper electrode; or, applying a DC bias voltage to the second upper electrode; or, applying DC bias voltages with opposite polarities to the first upper electrode and the second upper electrode simultaneously; Applying an AC driving signal to the first upper electrode; or, applying an AC driving signal to the second upper electrode; or, applying AC driving signals with the same phase to the first upper electrode and the second upper electrode simultaneously.

10. The method for improving the performance of a MEMS speaker according to claim 8, characterized in that, The piezoelectric multilayer film includes, from bottom to top, a lower electrode layer, a lower piezoelectric layer, an intermediate electrode layer, an upper piezoelectric layer, and an upper electrode layer, and the upper electrode layer includes a first upper electrode and a second upper electrode that are electrically isolated; The method includes: The intermediate electrode layer is grounded; The lower electrode layer is suspended; Applying a DC bias voltage to the first upper electrode; or applying a DC bias voltage to the second upper electrode; or applying DC bias voltages with opposite polarities to the first upper electrode and the second upper electrode simultaneously; Applying an AC driving signal to the first upper electrode; or applying an AC driving signal to the second upper electrode; or applying AC driving signals with the same phase to the first upper electrode and the second upper electrode simultaneously.

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