CN115706906A - Piezoelectric MEMS loudspeaker - Google Patents

Abstract

A piezoelectric MEMS speaker. The application discloses MEMS structure includes: the substrate comprises an inner ring body and an outer ring body which are connected through a connecting rod, wherein a first cavity is formed between the inner ring body and the outer ring body, and a second cavity is formed in the inner ring body; and a piezoelectric composite vibration layer formed over the substrate, including an edge portion formed over the outer ring and a center portion formed over the inner ring with a dividing gap therebetween. In summary, the present application provides a piezoelectric composite vibration layer of a piezoelectric MEMS speaker including an edge portion for generating a high frequency sound pressure level and a center portion for generating a low frequency sound pressure level. The combination of the edge part and the central part enables the piezoelectric MEMS loudspeaker to have a wider range of flatter sound pressure level frequency response curves, and the auditory effect of the whole frequency band is improved.

Description

A piezoelectric MEMS speaker

technical field

The present application relates to the technical field of micro-mechanics, in particular, to a piezoelectric MEMS (Micro-Electro-Mechanical System) speaker.

Background technique

Piezoelectric MEMS speaker is a small electroacoustic device that uses piezoelectric material as a sound conversion element. The principle is to use the inverse piezoelectric effect to input a voltage signal to the diaphragm with piezoelectric material to make the diaphragm vibrate, thereby driving The diaphragm and surrounding air vibrate to radiate sound. Compared with previous dynamic speakers, piezoelectric MEMS speakers have the advantages of small size, low power consumption, simple process, and low cost, and can be widely used in various portable electronic devices.

At present, the low-frequency response of most piezoelectric MEMS speakers is poor, and the output sound pressure level frequency response curve is not flat, which affects the user's listening experience.

Contents of the invention

In view of the problems in related technologies, the present application proposes a piezoelectric MEMS speaker, which can obtain a flat sound pressure level frequency response curve.

The technical scheme of the present application is realized like this:

According to one aspect of the present application, a MEMS structure is provided, comprising:

The substrate includes an inner ring body and an outer ring body connected by connecting rods, a first cavity is formed between the inner ring body and the outer ring body, and a second cavity is formed in the inner ring body;

a piezoelectric composite vibration layer formed above the substrate, including an edge portion formed above the outer ring body and a center portion formed above the inner ring body, between the edge portion and the center portion With split gap.

Wherein, the connecting rod is located at the bottom or the middle of the substrate.

Wherein, the division gap communicates with the first cavity.

Wherein, the fixed end of the edge portion is connected above the outer ring body, and the free end of the edge portion is suspended above the first cavity.

Wherein, the outer edge of the central part is connected and fixed above the inner ring body.

Wherein, the piezoelectric composite vibration layer includes:

a vibration support layer formed over the substrate;

a first electrode layer formed above the vibration support layer;

a first piezoelectric layer formed over the first electrode layer;

The second electrode layer is formed on the first piezoelectric layer.

Wherein, the area area of the vibration support layer in the central part is larger than the area area of the first electrode layer, and the area areas of the first electrode layer, the first piezoelectric layer and the second electrode layer are equal .

Wherein, the piezoelectric composite vibration layer also includes:

a second piezoelectric layer formed over the second electrode layer;

The third electrode layer is formed on the second piezoelectric layer.

Wherein, the division gap is less than or equal to 5 μm.

In summary, the piezoelectric composite vibration layer of the piezoelectric MEMS speaker provided by the present application includes an edge portion and a central portion, wherein the edge portion is used to generate high-frequency sound pressure levels, and the central portion is used to generate low-frequency sound pressure levels. The combination of the edge part and the central part makes the piezoelectric MEMS speaker have a wider and flatter sound pressure level frequency response curve, which improves the auditory effect of the entire frequency range.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the accompanying drawings required in the embodiments. Obviously, the accompanying drawings in the following description are only some of the present application. Embodiments, for those of ordinary skill in the art, other drawings can also be obtained based on these drawings without any creative effort.

Figure 1 shows a perspective view of a piezoelectric MEMS speaker structure provided according to some embodiments;

Figure 2 shows a cutaway perspective view of a piezoelectric MEMS speaker structure provided according to some embodiments;

Figure 3 shows a top view of a piezoelectric MEMS speaker structure provided in accordance with some embodiments;

Figure 4 illustrates a top view of a second substrate provided according to some embodiments;

Fig. 5 shows the sound pressure level frequency response curve corresponding to the edge part and the central part of the piezoelectric MEMS loudspeaker structure under specific materials and size parameters;

Fig. 6 shows the sound pressure level frequency response curve of the overall piezoelectric MEMS speaker structure under specific materials and size parameters.

Detailed ways

The following will clearly and completely describe the technical solutions in the embodiments of the application with reference to the drawings in the embodiments of the application. Apparently, the described embodiments are only some of the embodiments of the application, not all of them. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments in this application belong to the protection scope of this application.

Referring to FIG. 1 , FIG. 2 and FIG. 3 , according to the embodiment of the present application, a piezoelectric MEMS speaker is provided, which can improve the low-frequency sound pressure level and has a flatter sound pressure level frequency response curve with a wider range. The piezoelectric MEMS speaker can be used but not limited to other sensors or actuators, such as microphones, ultrasonic sensors. The piezoelectric MEMS speaker includes a substrate 10 , a piezoelectric composite vibration layer and a connecting rod 30 . Details will be described below.

The substrate 10 includes an inner ring body 12 and an outer ring body 11 connected by connecting rods 30 , a first cavity 13 is formed between the inner ring body 12 and the outer ring body 11 , and a second cavity 14 is formed in the inner ring body 12 . The connecting rod 30 is located at the bottom or middle of the substrate 10 for supporting and connecting the inner ring body 12 and the outer ring body 11 . FIG. 2 only shows an embodiment where the connecting rod 30 is located at the bottom of the substrate 10 . Substrate 10 comprises silicon or any suitable silicon-based compound or derivative (eg, silicon wafer, SOI, polysilicon on SiO2/Si).

A piezoelectric composite vibration layer is formed over substrate 10 . The piezoelectric composite vibration layer includes an edge portion 20 formed above the outer ring body 11 and a center portion 21 formed above the inner ring body 12 with a division gap 22 therebetween. The division gap 22 communicates with the first cavity 13 . Preferably, in order to prevent sound leakage caused by too large division gap 22, the division gap 22 is less than or equal to 5 μm.

The edge portion 20 is used to generate high frequency sound pressure levels. The fixed end of the edge portion 20 is connected above the outer ring body 11 , and the free end of the edge portion 20 is suspended above the first cavity 13 . The central part 21 is used to increase the low frequency sound pressure level and widen the flat range of the sound pressure level frequency response curve. The outer edge of the central part 21 is connected and fixed above the inner ring body 12 . The area area of the vibration supporting layer 23 of the central part 21 is greater than the area area of the first electrode layer 24, and the area areas of the first electrode layer 24, the first piezoelectric layer 25 and the second electrode layer 26 are equal, so as to produce a more Large diaphragm amplitude and sound pressure level.

In addition, an embodiment in which the substrate 10 and the piezoelectric composite vibration layer are circular is shown in FIGS. 1 , 2 and 3 . In other embodiments, the shapes of the substrate 10 and the piezoelectric composite vibration layer may be triangular, square, hexagonal or other suitable shapes.

The structure of the piezoelectric composite vibration layer will be specifically described below.

In the embodiment in which the piezoelectric composite vibration layer is a single wafer, the piezoelectric composite vibration layer includes a vibration support layer 23 formed above the substrate 10, a first electrode layer 24 formed above the vibration support layer 23, a first electrode layer 24 formed on the first The first piezoelectric layer 25 above the electrode layer 24 , and the second electrode layer 26 formed above the first piezoelectric layer 25 . The first piezoelectric layer 25 may convert electrical energy into acoustic energy, and the first electrode layer 24 and the second electrode layer 26 may provide voltage to the first piezoelectric layer 25 .

In the embodiment where the piezoelectric composite vibration layer is a bimorph, the piezoelectric composite vibration layer may further include a second piezoelectric layer (not shown) formed on the second electrode layer 26, formed on the second piezoelectric layer above the third electrode layer (not shown in the figure).

In some embodiments, the vibration supporting layer 23 includes a single-layer or multi-layer composite film structure composed of silicon nitride (Si ₃ N ₄ ), silicon oxide, single crystal silicon, polycrystalline silicon, or other suitable supporting materials.

In some embodiments, the materials of the first piezoelectric layer 25 and the second piezoelectric layer include zinc oxide, aluminum nitride, organic piezoelectric film, lead zirconate titanate (PZT), perovskite piezoelectric film or other suitable material. The first electrode layer 24 , the second electrode layer 26 and the third electrode layer include aluminum, gold, platinum, molybdenum, titanium, chromium and their composite films or other suitable materials.

It is worth noting that the MEMS structure without the connecting rod 30 and without the partition gap 22 at the vibration support layer 23 can be formed by existing processes. In other words, the only difference between this MEMS structure and the piezoelectric MEMS speaker shown in FIG. 2 is that the MEMS structure does not have a connecting rod 30 , and the vibration support layer 23 of the MEMS structure does not have a dividing gap 22 . Then, as shown in FIG. 4 , a second substrate with connecting rods 30 may be formed through photolithography and etching processes. The second substrate comprises an inner ring 32 and an outer ring 31 connected via connecting rods 30 . Then, the second substrate is bonded to the substrate 10 of the above-mentioned MEMS structure. Finally, the vibration supporting layer 23 having the division gap 22 is formed by etching to release the central portion 21 and the edge portion 20 . Thus, the piezoelectric MEMS speaker shown in Fig. 1 and Fig. 2 is finally obtained.

Figures 5 and 6 represent the sound pressure level frequency response curves corresponding to the low frequency part and high frequency part of the piezoelectric MEMS speaker and the total sound pressure level frequency response curve of the structure in Figure 1 under specific materials and size parameters. Wherein, the radius of the outer ring body 11 is 0.5 cm, the radius of the inner ring body 12 is 0.4 cm, the difference between the outer diameter and the inner diameter of the edge portion 20 is 0.1 cm, the width of the dividing gap 22 is 5 μm, and the thickness of the vibration supporting layer 23 is 7 μm, The thickness of the first piezoelectric layer 25 is 2 μm, and the thickness of the first electrode layer 24 and the second electrode layer 26 is 0.1 μm. Wherein, the radius of the first electrode layer 24 , the first piezoelectric layer 25 and the second electrode layer 26 of the central part 21 is 0.27 cm. The vibration supporting layer 23 of the central part 21 has a radius of 0.4 cm. The material of the vibration support layer 23 is silicon (Si), the material of the first piezoelectric layer 25 is piezoelectric ceramics (PZT), the material of the first electrode layer 24 and the second electrode layer 26 is aluminum (Al), and the magnitude of the applied voltage 2V, the sound pressure level was measured at 5 cm from the top surface of the central part of the piezoelectric MEMS speaker.

It can be seen from the sound pressure level frequency response curve in FIG. 5 that the sound pressure level corresponding to the edge part 20 in the high frequency band is relatively high, but has a large attenuation in the low frequency band. However, the sound pressure level corresponding to the central part 21 in the low frequency band is relatively high. Therefore, the two parts can work together, the working frequency of the central part 21 is 0 Hz-3900 Hz, and the working frequency of the edge part 20 is 3900 Hz-20000 Hz. Figure 6 corresponds to the sound pressure level frequency response curve of the overall structure. It can be seen that the sound pressure level in the low frequency band has increased by more than 20dB as a whole, and the output sound pressure level has reached more than 80dB at 1000Hz-20000Hz, which improves the auditory effect of the entire frequency band. .

The above is just a sound pressure level frequency response curve corresponding to a structure under a specific size and material parameters. Just to illustrate how it works and does not represent optimal results. Those skilled in the art can adjust the size parameters and material parameters of the structure as needed to obtain a higher sound pressure level output and a frequency response curve with a wider frequency range and a flatter sound pressure level.

In summary, the piezoelectric composite vibration layer of the piezoelectric MEMS speaker provided by the present application includes an edge portion 20 and a central portion 21 , wherein the edge portion 20 is used to generate high-frequency sound pressure levels, and the central portion 21 is used to generate low-frequency sound pressure levels. The combination of the edge portion 20 and the central portion 21 enables the piezoelectric MEMS speaker to have a wider and flatter sound pressure level frequency response curve, which improves the auditory effect of the entire frequency range.

The above are only preferred embodiments of the application, and are not intended to limit the application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the application shall be included in the scope of protection of the application. within.

Claims (9)

1. A MEMS structure, comprising:

the substrate comprises an inner ring body and an outer ring body which are connected through a connecting rod, wherein a first cavity is formed between the inner ring body and the outer ring body, and a second cavity is formed in the inner ring body;

and a piezoelectric composite vibration layer formed over the substrate, including an edge portion formed over the outer ring and a center portion formed over the inner ring with a dividing gap therebetween.

2. The MEMS structure of claim 1, wherein the tie bar is located at a bottom or middle portion of the substrate.

3. The MEMS structure of claim 1, wherein the separation gap is in communication with the first cavity.

4. The MEMS structure of claim 1, wherein a fixed end of the edge portion is connected above the outer ring, and a free end of the edge portion is suspended above the first cavity.

5. The MEMS structure, as set forth in claim 1, wherein the outer edge of the central portion is connectively fixed over the inner ring.

6. The MEMS structure of claim 1, wherein the piezoelectric composite vibrating layer comprises:

a vibrating support layer formed over the substrate;

a first electrode layer formed over the vibration support layer;

a first piezoelectric layer formed over the first electrode layer;

a second electrode layer formed over the first piezoelectric layer.

7. The MEMS structure of claim 6, wherein the area of the vibration support layer of the central portion is larger than the area of the first electrode layer, and the areas of the first electrode layer, the first piezoelectric layer, and the second electrode layer are equal.

8. The MEMS structure of claim 6, wherein the piezoelectric composite vibration layer further comprises:

a second piezoelectric layer formed over the second electrode layer;

a third electrode layer formed over the second piezoelectric layer.

9. The MEMS structure of claim 1, wherein the separation gap is less than or equal to 5 μ ι η.

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