阅读说明：本技术 基于弹性梁结构的mems压电声压传感芯片 (MEMS piezoelectric sound pressure sensing chip based on elastic beam structure ) 是由 钱丽勋 李宏军 解涛 王胜福 杨志 郭松林 孙从科 徐佳 梁东升 丁现朋 于江涛 于 2020-05-25 设计创作，主要内容包括：本发明适用于水听器技术领域,提供了一种基于弹性梁结构的MEMS压电声压传感芯片,包括：键合连接的第一基片和第二基片；第一基片的键合面上设置一凹槽,与第二基片的键合面形成一真空腔；第二基片的第二面上与凹槽对应位置设置感应结构,第二基片的第二面为键合面对应的一面；第二基片的键合面上感应结构对应区域周围设置多个弹性梁结构,多个弹性梁结构位于真空腔的顶部,且多个弹性梁结构的边缘位置与真空腔的边缘位置对应。通过设置多个弹性梁结构,可以提高MEMS声压传感芯片的性能,且简化加工工艺、减小芯片体积。(The invention is suitable for the technical field of hydrophones, and provides an MEMS piezoelectric sound pressure sensing chip based on an elastic beam structure, which comprises: bonding the connected first substrate and second substrate; a groove is arranged on the bonding surface of the first substrate, and a vacuum cavity is formed between the groove and the bonding surface of the second substrate; an induction structure is arranged on the second surface of the second substrate corresponding to the groove, and the second surface of the second substrate is a surface corresponding to the bonding surface; a plurality of elastic beam structures are arranged around a corresponding area of the sensing structure on the bonding surface of the second substrate, the elastic beam structures are positioned at the top of the vacuum cavity, and the edge positions of the elastic beam structures correspond to the edge positions of the vacuum cavity. Through setting up a plurality of elastic beam structures, can improve MEMS acoustic pressure sensing chip's performance, and simplify processing technology, reduce the chip volume.)

1. The utility model provides a MEMS piezoelectricity acoustic pressure sensing chip based on elastic beam structure which characterized in that includes: bonding the connected first substrate and second substrate;

a groove is arranged on the bonding surface of the first substrate, and a vacuum cavity is formed between the groove and the bonding surface of the second substrate;

an induction structure is arranged on the second surface of the second substrate corresponding to the groove, and the second surface of the second substrate is a surface corresponding to the bonding surface; and a plurality of elastic beam structures are arranged around the corresponding area of the sensing structure on the bonding surface of the second substrate, the elastic beam structures are positioned at the top of the vacuum cavity, and the edge positions of the elastic beam structures correspond to the edge positions of the vacuum cavity.

2. The MEMS piezoelectric acoustic pressure sensing chip according to claim 1, wherein an overload protection structure is disposed at the bottom of the vacuum chamber in the first substrate, and the overload protection structure is connected to the bottom of the vacuum chamber.

3. The MEMS piezoelectric acoustic pressure sensing chip according to claim 2, wherein the overload protection structure comprises a plurality of supporting bodies connected to the bottom of the vacuum chamber.

4. The MEMS piezoelectric acoustic pressure sensing chip according to claim 3, wherein the plurality of supports are solid supports.

5. The MEMS piezoelectric acoustic pressure sensing chip based on an elastic beam structure according to claim 3, wherein the heights of the plurality of supporting bodies are lower than the height of the vacuum chamber.

6. The MEMS piezoelectric acoustic pressure sensing chip based on an elastic beam structure according to claim 1, wherein the first substrate and the second substrate are made of silicon.

7. The MEMS piezoelectric acoustic pressure sensing chip based on the elastic beam structure according to claim 1 or 6, wherein the number of the elastic beam structures is four, and the elastic beam structures are uniformly arranged around the corresponding area of the sensing structure;

each elastic beam structure comprises a first connecting end, a second connecting end and snakelike arranged beams, wherein the first connecting end is connected with one end of the snakelike arranged beams, and the second connecting end is connected with the other end of the snakelike arranged beams; the first connecting end or the second connecting end is connected with the edge of the corresponding area of the induction structure, and the second connecting end or the first connecting end is flush with the edge of the corresponding elastic beam structure.

8. The MEMS piezoelectric acoustic pressure sensing chip according to claim 1, wherein the sensing structure comprises an upper electrode, a lower electrode, an interlayer between the upper electrode and the lower electrode, a piezoelectric sensing layer on the upper electrode, and a piezoelectric layer under the lower electrode.

9. The MEMS piezoelectric acoustic pressure sensing chip according to claim 8, further comprising upper and lower electrode lead structures;

the upper electrode leading-out structure is connected with one end of the upper electrode and arranged in a first area on the piezoelectric sensing layer;

the lower electrode leading-out structure is connected with one end of the lower electrode and is arranged in a second area on the piezoelectric sensing layer; the first area and the second area are different in corresponding positions on the piezoelectric sensing layer.

10. The MEMS piezoelectric acoustic pressure sensing chip according to claim 9, wherein the upper and lower electrodes are made of Mo;

the interlayer between the upper electrode and the lower electrode, the piezoelectric sensing layer on the upper electrode and the piezoelectric layer on the lower surface of the lower electrode are made of AIN respectively;

the upper and lower electrode lead-out structure is made of Au.

Technical Field

The invention belongs to the technical field of hydrophones, and particularly relates to an MEMS piezoelectric sound pressure sensing chip based on an elastic beam structure.

Background

Hydrophones are devices that can measure the acoustic field in fluids, which are manufactured based on the principles of hydroacoustics. The hydrophone may be a device encapsulating the MEMS acoustic pressure sensing chip. The sound wave is transmitted in the form of longitudinal wave in water, sound pressure is generated in the transmission process, when the sound wave is transmitted to the MEMS miniature hydrophone, the sound pressure interacts with the packaging structure of the hydrophone at first, the sound pressure can penetrate through the MEMS miniature hydrophone almost without damage due to the fact that the packaging structure of the hydrophone is in a sound transmission design, the sound pressure penetrating through the packaging structure acts on an MEMS sound pressure sensing chip, and the sensing voltage signal is output due to the piezoelectric effect. The structure of the traditional MEMS sound pressure sensing chip mainly comprises a supporting substrate, a vacuum cavity and a piezoelectric sensing film, when sound pressure acts on the piezoelectric sensing film, the piezoelectric sensing film is deformed, and due to piezoelectric effect, the upper electrode and the lower electrode of the deformed piezoelectric film generate voltage difference, so that a sensing voltage signal is output. However, the performance of the existing MEMS acoustic pressure sensing chip is still insufficient, the processing technology is complex, and the chip volume is large.

Disclosure of Invention

In view of this, the embodiment of the invention provides an MEMS piezoelectric sound pressure sensing chip based on an elastic beam structure, and aims to solve the problems of poor performance, complex processing technology and large chip volume of the MEMS sound pressure sensing chip in the prior art.

In order to achieve the above object, a first aspect of the embodiments of the present invention provides a MEMS piezoelectric acoustic pressure sensing chip based on an elastic beam structure, including: bonding the connected first substrate and second substrate;

a groove is arranged on the bonding surface of the first substrate, and a vacuum cavity is formed between the groove and the bonding surface of the second substrate;

an induction structure is arranged on the second surface of the second substrate corresponding to the groove, and the second surface of the second substrate is a surface corresponding to the bonding surface; and a plurality of elastic beam structures are arranged around the corresponding area of the sensing structure on the bonding surface of the second substrate, the elastic beam structures are positioned at the top of the vacuum cavity, and the edge positions of the elastic beam structures correspond to the edge positions of the vacuum cavity.

As another embodiment of the present application, an overload protection structure is disposed at a bottom of the vacuum chamber in the first substrate, and the overload protection structure is connected to the bottom of the vacuum chamber.

As another embodiment of the present application, the overload protection structure includes a plurality of supporting bodies connected to the bottom of the vacuum chamber.

As another embodiment of the present application, the plurality of supports are solid supports.

As another embodiment of the present application, the plurality of supporters have a height lower than that of the vacuum chamber.

As another embodiment of the present application, the first substrate and the second substrate are made of silicon.

As another embodiment of the present application, the number of the elastic beam structures is four, and the elastic beam structures are uniformly arranged around the corresponding area of the sensing structure;

each elastic beam structure comprises a first connecting end, a second connecting end and snakelike arranged beams, wherein the first connecting end is connected with one end of the snakelike arranged beams, and the second connecting end is connected with the other end of the snakelike arranged beams; the first connecting end or the second connecting end is connected with the edge of the corresponding area of the induction structure, and the second connecting end or the first connecting end is flush with the edge of the corresponding elastic beam structure.

As another embodiment of the present application, the sensing structure includes an upper electrode, a lower electrode, an interlayer between the upper electrode and the lower electrode, a piezoelectric sensing layer on the upper electrode, and a piezoelectric layer under the lower electrode.

As another embodiment of the present application, the present application further includes an upper and lower electrode lead-out structure;

the upper electrode leading-out structure is connected with one end of the upper electrode and arranged in a first area on the piezoelectric sensing layer;

the lower electrode leading-out structure is connected with one end of the lower electrode and is arranged in a second area on the piezoelectric sensing layer; the first area and the second area are different in corresponding positions on the piezoelectric sensing layer.

As another embodiment of the present application, the upper and lower electrodes are made of Mo;

the interlayer between the upper electrode and the lower electrode, the piezoelectric sensing layer on the upper electrode and the piezoelectric layer on the lower surface of the lower electrode are made of AIN respectively;

the upper and lower electrode lead-out structure is made of Au.

Compared with the prior art, the embodiment of the invention has the following beneficial effects: compared with the prior art, the MEMS piezoelectric sound pressure sensing chip has the advantages that the plurality of elastic beam structures are arranged, so that the sensing structure deforms when sound waves act on the sensing structure, and the elastic beam structures generate tensile force along with the elastic beam structures, so that the nonlinearity of deformation caused by large deformation of the sensing structure is counteracted to a certain degree, the sensitivity of the MEMS piezoelectric sound pressure sensing chip is increased, the acceleration sensitivity of the MEMS piezoelectric sound pressure sensing chip is improved, and the consistency is improved. Meanwhile, the elastic beam structure is formed on the second substrate in an etching mode, so that the size of the MEMS piezoelectric sound pressure sensing chip can be reduced, and the cost is reduced. In addition, the vacuum cavity is extruded due to deformation of the sensing structure, and consistency with the MEMS piezoelectric sound pressure sensing chip is guaranteed, so that sensitivity of the MEMS piezoelectric sound pressure sensing chip can be improved.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the embodiments or the prior art descriptions will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without inventive exercise.

Fig. 1 is a schematic structural diagram of an MEMS piezoelectric acoustic pressure sensing chip based on an elastic beam structure according to an embodiment of the present invention;

fig. 2 is a schematic structural diagram of a MEMS piezoelectric acoustic pressure sensing chip based on an elastic beam structure according to another embodiment of the present invention;

FIG. 3 is a schematic diagram of a spring beam structure provided by an embodiment of the present invention;

FIG. 4 is an exemplary diagram of a sensing structure provided by an embodiment of the present invention;

FIG. 5 is a simplified model diagram of a MEMS piezoelectric acoustic pressure sensing chip according to an embodiment of the present invention;

fig. 6(1) is a schematic diagram of a relationship between a thickness of a piezoelectric sensing layer and an output of an induced voltage according to an embodiment of the present invention;

FIG. 6(2) is a schematic diagram illustrating a relationship between a thickness of a silicon supporting layer and an induced voltage output according to an embodiment of the present invention;

fig. 6(3) is a schematic diagram of a relationship between a sensing chip size and an induced voltage output according to an embodiment of the present invention;

fig. 6(4) is a schematic diagram of a relationship between a size of a sensing chip and an output voltage of the sensing chip before and after the elastic beam structure is introduced according to an embodiment of the present invention;

FIG. 7 is a schematic diagram illustrating the relationship between the thickness of the silicon support layer and the output of the acceleration induced voltage before and after the introduction of the elastic beam structure provided in the embodiment of the present invention;

fig. 8(1) is a schematic diagram of a frequency response range design model according to an embodiment of the present invention;

fig. 8(2) is a schematic diagram of a simulation result of the main mode shape according to an embodiment of the present invention;

FIG. 8(3) is a diagram illustrating a simulation result of the S parameter of the fundamental mode resonance output provided by the embodiment of the present invention;

FIG. 8(4) is a schematic diagram of the output voltage of the thin film according to the embodiment of the present invention;

fig. 9(1) is a schematic diagram of a maximum sound pressure design simulation model according to an embodiment of the present invention;

fig. 9(2) is a schematic diagram illustrating a relationship between a size of a sensing chip and a displacement of a silicon supporting layer according to an embodiment of the present invention;

fig. 10(1) is a schematic diagram of the relationship between sound pressure and induced voltage according to an embodiment of the present invention;

fig. 10(2) is a schematic diagram of the relationship between sound pressure and induced voltage according to another embodiment of the present invention.

Detailed Description

In the following description, for purposes of explanation and not limitation, specific details are set forth, such as particular system structures, techniques, etc. in order to provide a thorough understanding of the embodiments of the invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known systems, devices, circuits, and methods are omitted so as not to obscure the description of the present invention with unnecessary detail.

In order to explain the technical means of the present invention, the following description will be given by way of specific examples.

Fig. 1 is a schematic structural diagram of a MEMS piezoelectric acoustic pressure sensing chip based on an elastic beam structure according to an embodiment of the present invention, which is described in detail below.

Referring to fig. 1 to 3, the MEMS piezoelectric acoustic pressure sensing chip based on the elastic beam structure may include: the first substrate 100 and the second substrate 200 bonded together;

a groove is arranged on the first substrate 100, and a vacuum cavity 101 is formed between the groove and the bonding surface of the second substrate;

a sensing structure 201 is arranged on a second surface of the second substrate 200 corresponding to the vacuum chamber 101, and the second surface of the second substrate is a surface corresponding to the bonding surface; a plurality of elastic beam structures 202 are arranged around the corresponding area of the sensing structure 201 on the bonding surface of the second substrate 200, the elastic beam structures 202 are positioned at the top of the vacuum chamber 101, and the edge positions of the elastic beam structures 202 correspond to the edge position of the vacuum chamber 101.

The top of the vacuum cavity is positioned at the bonding position of the first substrate and the second substrate in the figure 1, the bottom of the vacuum cavity is a surface corresponding to the top of the vacuum cavity, and the bottom of the vacuum cavity is arranged in the first substrate.

Above-mentioned MEMS piezoelectricity acoustic pressure sensing chip based on elastic beam structure, through setting up a plurality of elastic beam structures, can be when the sound wave is used on the sensing structure, the sensing structure warp, makes the elastic beam structure produce the pulling force thereupon to offset the nonlinearity of the deformation that causes owing to the sensing structure warp greatly to a certain extent, increase MEMS piezoelectricity acoustic pressure sensing chip's sensitivity, improve MEMS piezoelectricity acoustic pressure sensing chip's acceleration sensitivity, improve the uniformity. Meanwhile, the elastic beam structure is formed on the second substrate in an etching mode, so that the size of the MEMS piezoelectric sound pressure sensing chip can be reduced, and the cost is reduced. In addition, the vacuum cavity is extruded due to deformation of the sensing structure, and consistency with the MEMS piezoelectric sound pressure sensing chip is guaranteed, so that sensitivity of the MEMS piezoelectric sound pressure sensing chip can be improved.

Optionally, fig. 1 is a longitudinal view of an MEMS piezoelectric acoustic pressure sensing chip based on an elastic beam structure, where the first substrate and the second substrate may be made of silicon, that is, the first substrate is a silicon substrate, the second substrate is a silicon supporting structure, and an induction structure is deposited on the silicon supporting structure. The grooves forming the vacuum chamber 101 are formed by etching the silicon substrate and the flexible beam structure 202 is formed by etching the silicon support structure.

Optionally, as shown in fig. 2, the first substrate 100 in the MEMS piezoelectric acoustic pressure sensing chip based on the elastic beam structure further includes an overload protection structure 102.

An overload protection structure is disposed at the bottom of the vacuum chamber 101 in the first substrate 100, and the overload protection structure 102 is connected to the bottom of the vacuum chamber 101. Optionally, when the overload protection structure is prepared, the overload protection structure can be directly prepared at the bottom of the vacuum cavity and connected with the vacuum cavity into a whole, so that the processing technology of the MEMS piezoelectric sound pressure sensing chip based on the elastic beam structure can be simplified, the production efficiency is improved, and a guarantee is provided for batch production. Alternatively, the vacuum chamber may be a circular chamber.

Optionally, the overload protection structure 102 includes a plurality of supporting bodies connected to the bottom of the vacuum chamber, that is, the overload protection structure is formed by a plurality of supporting bodies, that is, a plurality of supporting bodies are directly formed at the bottom of the vacuum chamber. The plurality of supports are solid supports. Optionally, the intervals between the plurality of supporting bodies are not limited in this embodiment, and the intervals between two supporting bodies may be uniform or non-uniform. The circumferences of the cross sections of the plurality of supports can be the same or different, namely the thicknesses of the supports can be different. The diameters of the plurality of support bodies are not limited in this embodiment. Alternatively, the cross section of the plurality of supports may have a circular shape, a square or a rectangular shape, or an irregular shape. For convenience in preparation, the cross-section of the plurality of supports may be in a regular pattern.

Optionally, the heights of the plurality of supporting bodies are lower than the height of the vacuum cavity so as to provide reliable support for the sensing structure.

Optionally, the plurality of supporting bodies may be perpendicular to the horizontal plane or may have an inclination angle with the horizontal plane, where the inclination angle refers to an included angle between the supporting body and the horizontal plane, and the included angle may be an acute angle or an obtuse angle. Alternatively, the support may be perpendicular to the horizontal plane, or have a small angle of inclination, in order to maximize the function of the support.

When the sound wave acts on the induction structure, the induction structure deforms and is in contact with the overload protection structure, so that the induction structure is protected from being damaged due to too large deformation, and when the sound pressure input disappears, the deformed induction structure recovers and is separated from the overload protection structure.

Optionally, as shown in fig. 3, the number of the elastic beam structures may be multiple, for example, the number of the elastic beam structures may be three, four, five, six, and the like, and is four as shown in fig. 3, a plurality of elastic beam structures may be uniformly disposed around the corresponding region of the sensing structure, and the plurality of elastic beam structures may improve the sensitivity and the uniformity of the MEMS piezoelectric acoustic pressure sensing chip.

Each elastic beam structure comprises a first connecting end, a second connecting end and snakelike arranged beams, wherein the first connecting end is connected with one end of the snakelike arranged beams, and the second connecting end is connected with the other end of the snakelike arranged beams; the first connecting end or the second connecting end is connected with the edge of the corresponding area of the induction structure, and the second connecting end or the first connecting end is flush with the edge of the corresponding elastic beam structure.

Optionally, the roof beam that snakelike was arranged can be arranged for the curve type, also can arrange for "bow" type, when the sound wave was used on the response structure, the response structure produces deformation, oppress silicon bearing structure, make the central zone shown in figure 3 produce the deformation of sound wave transmission direction, for example, produce decurrent deformation, then a plurality of elastic beam structures can produce the pulling force, deformation is big more, the pulling force that a plurality of elastic beam structures produced is also big more, can offset the nonlinearity of the deformation because piezoelectricity greatly causes this moment to a certain extent, thereby reduce the induced voltage linearity of MEMS piezoelectricity acoustic pressure sensing chip based on elastic beam structure, can increase sensing chip's sensitivity simultaneously, reduce MEMS piezoelectricity acoustic pressure sensing chip's acceleration sensitivity greatly, the improvement uniformity.

Optionally, as shown in fig. 1, fig. 2, or fig. 4, the sensing structure 201 is configured to receive sound pressure and generate deformation, and due to a piezoelectric effect, a voltage difference is generated between an upper electrode and a lower electrode of the deformed sensing structure, so as to output a sensing voltage signal. The sensing structure may include an upper electrode 2011, a lower electrode 2012, an interlayer 2013 between the upper and lower electrodes, a piezoelectric sensing layer 2014 on the upper electrode, and a piezoelectric layer 2015 under the lower electrode, with the opposite direction of the acoustic wave transmission direction as a reference direction. Optionally, the piezoelectric sensing layer 2014 on the upper surface of the upper electrode can be an AIN piezoelectric layer.

Optionally, the upper electrode 2011 and the lower electrode 2012 may be disposed in a disk shape, wherein a radius of the upper electrode 2011 is smaller than a radius of the lower electrode 2012, so that the electrode input and output terminals are conveniently disposed. Optionally, the sensing structure further includes an upper electrode lead-out structure 2016 and a lower electrode lead-out structure 2017.

The upper electrode leading-out structure is connected with one end of the upper electrode and arranged in a first area on the piezoelectric sensing layer;

the lower electrode leading-out structure is connected with one end of the lower electrode and is arranged in a second area on the piezoelectric sensing layer; the first area and the second area are different in corresponding positions on the piezoelectric sensing layer.

Optionally, as shown in fig. 4, the upper electrode leading-out structure is disposed on the left side of the piezoelectric sensing layer, and the lower electrode leading-out structure may be disposed on the right side of the piezoelectric sensing layer.

Optionally, the edge of the upper and lower electrode leading-out structure may be in a gentle slope shape.

Optionally, the upper and lower electrodes are made of Mo;

the interlayer between the upper electrode and the lower electrode, the piezoelectric sensing layer on the upper electrode and the piezoelectric layer under the lower electrode are made of AIN respectively;

the upper and lower electrode lead-out structure is made of Au.

Optionally, after the MEMS piezoelectric sound pressure sensing chip based on the elastic beam structure is prepared, a passivation layer may be further disposed on the outer surface of the MEMS piezoelectric sound pressure sensing chip based on the elastic beam structure, so that the surface of the MEMS piezoelectric sound pressure sensing chip based on the elastic beam structure is not easily oxidized, so as to protect the MEMS piezoelectric sound pressure sensing chip based on the elastic beam structure.

Above-mentioned MEMS piezoelectricity acoustic pressure sensing chip based on elastic beam structure, through setting up a plurality of elastic beam structures, can be when the sound wave is used on the sensing structure, the sensing structure warp, makes the elastic beam structure produce the pulling force thereupon to offset the nonlinearity of the deformation that causes owing to the sensing structure warp greatly to a certain extent, increase MEMS piezoelectricity acoustic pressure sensing chip's sensitivity, improve MEMS piezoelectricity acoustic pressure sensing chip's acceleration sensitivity, improve the uniformity. Meanwhile, the elastic beam structure is formed on the second substrate in an etching mode, so that the size of the MEMS piezoelectric sound pressure sensing chip can be reduced, and the cost is reduced. In addition, the vacuum cavity is extruded due to deformation of the sensing structure, and consistency with the MEMS piezoelectric sound pressure sensing chip is guaranteed, so that sensitivity of the MEMS piezoelectric sound pressure sensing chip can be improved. Through setting up overload protection structure, can provide reliable support for the response structure, reduce the damage probability of response structure, can simplify MEMS piezoelectricity acoustic pressure sensing chip's processing technology simultaneously, improve batch production reliability.

In order to verify the performance of the MEMS piezoelectric acoustic pressure sensing chip based on the elastic beam structure, the following simulation experiment was performed. The performance of the MEMS miniature sound pressure hydrophone is determined by an MEMS piezoelectric sound pressure sensing chip, an ASIC circuit, hydrophone packaging and the like, but the performance index of the MEMS miniature sound pressure hydrophone is based on the performance of the MEMS piezoelectric sound pressure sensing chip. Therefore, the design of the MEMS piezoelectric acoustic pressure sensing chip is one of the key technologies for the design of the hydrophone.

1) Sensitivity research of MEMS piezoelectric sound pressure sensing chip based on elastic beam structure

The sensitivity of a hydrophone refers to the ratio of open-circuit voltage of the hydrophone to sound pressure acting on a receiving surface of the hydrophone, and is generally expressed in dB, and the reference is 1V/uPa. The calculation formula is as follows:

wherein S is_PRepresenting the voltage output at which the hydrophone actually receives the sound pressure. From the above formula, when the hydrophone is subjected to a certain sound pressure, the higher the output voltage is, the higher the sensitivity is. According to the working principle of the MEMS miniature acoustic pressure hydrophone, when sound pressure acts on the MEMS piezoelectric sound pressure sensing chip, the sensing structure is deformed due to the piezoelectric effect, so that sensing voltage is output, namely under the same sound pressure, the sensing junction is ensuredThe larger the deformation is on the premise that the structure is not damaged, the larger the induction voltage output is, and the higher the sensitivity is. Based on the method, a simplified model of the MEMS piezoelectric sound pressure sensing chip is established for optimizing and calculating the sensitivity. A simplified model of a MEMS piezoelectric acoustic pressure sensing chip is shown in fig. 5. The influence factors of the sensitivity of the MEMS piezoelectric acoustic pressure sensing chip may include: the thickness of the silicon supporting layer, the thickness of the piezoelectric sensing layer, the size of the sensing chip and the like. Since the sensitivity of the hydrophone is proportional to the induced voltage of the sensing chip, we mainly focus on the magnitude of the induced voltage of the sensing chip.

With a conventional SOI wafer, the thickness of the silicon supporting layer is 5um, the radius of the sensing chip is 150um, and when 25000Pa sound pressure is input, the output of the sensing voltage is larger and larger as the thickness of the piezoelectric sensing layer is larger, but the increase rate is smaller and smaller, as shown in fig. 6(1) below. When the thickness of the piezoelectric sensing layer is 1.0um, the output of the induction voltage is 0.19V, when the thickness of the piezoelectric sensing layer is 1.5um, the output of the induction voltage is 0.25V, when the thickness of the piezoelectric sensing layer is 2.0um, the output of the induction voltage is 0.28V, and when the thickness of the piezoelectric sensing layer is 2.5um, the output of the induction voltage is 0.30V.

When the radius of the sensing chip is 150um, the thickness of the piezoelectric sensing layer is 1.5um, and 25000Pa sound pressure is input, the output of the sensing voltage becomes smaller and smaller as the thickness of the silicon supporting layer is thicker, as shown in fig. 6(2), when the thickness of the silicon supporting layer is 2um, the output of the sensing voltage is 0.65V, when the thickness of the silicon supporting layer is 3um, the output of the sensing voltage is 0.45V, when the thickness of the silicon supporting layer is 4um, the output of the sensing voltage is 0.32V, when the thickness of the silicon supporting layer is 5um, the output of the sensing voltage is 0.25V, when the thickness of the silicon supporting layer is 6um, the output of the sensing voltage is 0.18V, and.

By adopting a conventional SOI (silicon on insulator) sheet, the thickness of a silicon supporting layer is 5um, the thickness of a piezoelectric sensing layer is 1.5um, and when 25000Pa sound pressure is input, the larger the size of a sensing chip is, the larger the output of the sensing voltage is. As shown in fig. 6(3), the radius of the sensing chip is 100um, the output of the sensing voltage is 0.13V, the radius of the sensing chip is 150um, the output of the sensing voltage is 0.24V, the radius of the sensing chip is 200um, the output of the sensing voltage is 0.34V, the radius of the sensing chip is 250um, and the output of the sensing voltage is 0.45V.

In summary, the sensitivity of the MEMS piezoelectric sound pressure sensing chip gradually increases with the increase of the thickness of the piezoelectric sensing layer, the decrease of the thickness of the silicon supporting layer, and the increase of the size of the sensing chip. However, due to the limitations of multiple aspects such as process, reliability and cost, the sensitivity of the MEMS piezoelectric sound pressure sensing chip cannot be increased without limit. Therefore, in order to improve the sensitivity based on the original structure, an elastic beam structure is added to the MEMS piezoelectric acoustic pressure sensing chip, that is, the MEMS piezoelectric acoustic pressure sensing chip based on the elastic beam structure provided in the above embodiments of the present application.

When a conventional SOI (silicon on insulator) sheet is adopted, the thickness of a silicon supporting layer is 5um, the thickness of a piezoelectric layer is 1.5um, and 25000Pa sound pressure is input, before and after an elastic beam structure is introduced, along with the change of the size of a sensing chip, the output of induction voltage is improved by nearly 50% under the same size of the sensing chip, as shown in (4) of figure 6). The radius of the sensing chip is 100um, the output of the induced voltage is 0.13V before the elastic beam structure is introduced, and the output of the induced voltage is 0.17V after the elastic beam structure is introduced; the radius of the sensing chip is 150um, the output of the induced voltage is 0.24V before the elastic beam structure is introduced, and the output of the induced voltage is 0.35V after the elastic beam structure is introduced.

In the same way, the size of the sensing structure can be reduced under the same sensitivity, and according to the simulation result, the sensing voltage when the radius of the sensing chip is 200um is equivalent to the sensing voltage of the sensing chip with the radius of 140um after the elastic beam structure is introduced. Therefore, after the elastic beam is introduced, the size of the sensing chip (namely, the MEMS piezoelectric sound pressure sensing chip based on the elastic beam structure) can be reduced by 50%, so that the sensitivity of the MEMS piezoelectric sound pressure sensing chip is improved and the chip volume is reduced by introducing the elastic beam structure.

(2) Acceleration sensitivity design research of MEMS piezoelectric sound pressure sensing chip based on elastic beam structure

The acceleration sensitivity refers to that when the hydrophone is in an acceleration state, an induction structure of an MEMS piezoelectric sound pressure sensing chip (hereinafter referred to as a sensing chip) based on an elastic beam structure deforms due to the acceleration applied to the induction structure, so that induction voltage is outputAnd (6) discharging. Acceleration sensitivity unit is V/m/s²。

When the AlN piezoelectric thin film layer has a fixed structure, the thicker the silicon supporting layer is, the larger the area of the required sensing chip is to achieve the same sensitivity, and the acceleration sensitivity is also correspondingly increased at the moment. Under the condition that the sensing chip outputs the same sensing voltage, namely under the premise of the same sensitivity, the acceleration sensitivity of the device is continuously increased along with the increase of the thickness of the silicon supporting layer. To further reduce the acceleration sensitivity, a spring beam structure may be introduced in the silicon support layer, while shrinking the sensing chip size and reducing the acceleration sensitivity of the device. As shown in fig. 7, under the premise of the same silicon supporting layer thickness and the same sensitivity, after the elastic beam structure is introduced, the acceleration sensitivity of the MEMS piezoelectric acoustic pressure sensing chip can be greatly reduced. When the thickness of the silicon supporting layer is 2um, the output of the acceleration induction voltage is 3.40E before the elastic beam structure is introduced^-009V/m/s²After the elastic beam structure is introduced, the output of the induced voltage is 2.00E^-009V/m/s²When the thickness of the silicon supporting layer is 10um and before the elastic beam structure is introduced, the output of the acceleration induction voltage is 1.10E^-008V/m/s²After the elastic beam structure is introduced, the output of the induced voltage is 6.00E^-009V/m/s²。

(3) Frequency response range design research of MEMS piezoelectric sound pressure sensing chip based on elastic beam structure

The frequency response range of the sensing chip refers to the sound pressure frequency range in which the sensing chip can normally work. In order to ensure that the sensing chip can normally work in a certain frequency range, the mode of the sensing structure needs to be designed to be far away from the working frequency range.

Because the piezoelectric sensing layer of the sensing chip is in close contact with the package, the package can affect the resonance mode of the sensing chip to a certain extent, and therefore, when the resonance mode of the device is calculated, a sensing device model and a packaging structure need to be considered at the same time. Such as the frequency response range design model shown in fig. 8 (1). When calculating the mode of the model, the simulation result of the mode shape of the main mode is shown in fig. 8 (2). When the sound pressure frequency changes within the range of 10-20KHz, the simulation result of the main mode resonance output S parameter is shown in fig. 8(3), after the resonance mode of the device is optimized (i.e. the elastic beam is added), the film output voltage under the same sound pressure is shown in fig. 8(4) within the frequency response range of 10-20KHz, and the induced voltage of the sensing chip only changes very little along with the increase of the frequency, so the frequency response range of 10-20KHz can be completely realized through design.

(4) Maximum bearable sound pressure design of MEMS piezoelectric sound pressure sensing chip based on elastic beam structure

Maximum acceptable sound pressure means that the hydrophone will saturate or fail at an input that exceeds this sound pressure. The design of the maximum tolerable sound pressure needs to comprehensively consider factors such as the encapsulation of the hydrophone, the device structure and the like, and fig. 9(1) shows a simulation model of the maximum sound pressure design. When the sensing chip is under the action of sound pressure, the sensing structure of the sensing chip can deform, so that sensing voltage is generated.

When the input pressure is 25000Pa, the thickness of the silicon supporting layer is 5um, the thickness of the piezoelectric sensing layer is 1.5um, and the displacement of the silicon supporting layer corresponding to different sizes of the sensing chip is shown in fig. 9 (2). When the sensor chip radius is 150um, silicon supporting layer displacement volume is 0.1um, is 200um when the sensor chip radius, and silicon supporting layer displacement volume is 0.23um, is 250um when the sensor chip radius, and silicon supporting layer displacement volume is 0.35um, is 300um when the sensor chip radius, and silicon supporting layer displacement volume is 0.6um etc..

When the amount of deformation of the sensing structure is excessive, destructive failure of the sensing structure may be caused. It is believed that when the deformation amount of the sensing structure is larger than 1/3, the probability of the sensing structure breaking failure is high, and the piezoelectric sensing layer is thin, so that the deformation failure mainly comes from the silicon supporting layer. When the thickness of the silicon supporting layer is 5um, the deformation amount is less than 1.5um, which is the safe deformation amount. From the above results, it is found that the maximum safe radius of the sensing structure is 360um at a sound pressure input of 25000 Pa. Under the condition of 5um silicon support, when the radius of the sensing structure of the sensing chip is less than 360um, the sensing chip can bear the sound pressure below 25000 Pa.

In order to increase the reliability of a sensing chip and enable the sensing chip not to be damaged under the condition that the sensing chip bears the maximum bearable sound pressure which is larger than the maximum bearable sound pressure of the sensing chip, an overload protection structure is added into a designed sensing chip structure, when the input sound pressure is larger than 25000Pa, an induction structure is severely deformed, and when the deformation quantity is larger than 1.5um, the induction structure is contacted with the overload protection structure, so that the induction structure is not damaged due to too large deformation, and when the sound pressure input disappears, the induction structure is separated from the overload protection structure and returns to the original position again.

(5) Linear degree design of MEMS piezoelectric sound pressure sensing chip based on elastic beam structure

Linearity is the percentage of the maximum deviation between the hydrophone calibration curve and the fitted line to the full scale output. The final evaluation is the linearity of the hydrophone output at different sound pressure inputs.

The linearity of the MEMS miniature hydrophone is not only related to a hydrophone voltage amplifying circuit, but also related to the structure of the hydrophone, when the sound pressure input by the MEMS miniature hydrophone is small, the deformation degree of the induction structure is in a linear area, the induction voltage output is linear, when the sound pressure is gradually increased to a certain degree, the deformation degree of the induction structure is larger and larger, and the nonlinearity is more and more obvious, as shown in (1) of figure 10, when the sound pressure is within a range of 0-2500 Pa, the output of the induction voltage is linear, and then the nonlinearity is more and more obvious along with the continuous increase of the sound pressure. In order to further increase the degree of performance in the same dynamic range, the structure incorporating the elastic beam is optimized. As shown in fig. 10(2), after the sound pressure gradually increases to a certain degree, the deformation amount of the sensing structure becomes larger, and the larger the deformation amount of the sensing structure is, the larger the tensile force applied to the elastic beam becomes, and at this time, the nonlinearity of the deformation caused by the too large piezoelectric may be offset to a certain degree. In fig. 10(2), when the sound pressure is in the range of 20KPa to 30KPa, it is obvious that the output nonlinearity of the induced voltage becomes smaller. The small squares represent before the addition of the flexible beam and the origin represents after the addition of the flexible beam.

The above-mentioned embodiments are only used for illustrating the technical solutions of the present invention, and not for limiting the same; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; such modifications and substitutions do not substantially depart from the spirit and scope of the embodiments of the present invention, and are intended to be included within the scope of the present invention.