Patent ID: 12196600

REFERENCE NUMERALS

1: anchoring unit;2: piezoelectric unit;21: lower electrode;22: piezoelectric material;221: first piezoelectric material;222: second piezoelectric material;23: upper electrode;24: middle electrode;3: support unit;4: hollow-out mechanical part;5: back cavity;6: groove, and7: sacrificial layer.

DESCRIPTION OF EMBODIMENTS

To make the objectives, technical solutions, and advantages of this application clearer, the following further describes embodiments of this application in detail with reference to the accompanying drawings.

Before embodiments of this application are described in detail, application scenarios in embodiments of this application are first described.

A microphone is an acoustic-electric energy conversion device that converts a sound signal into an electrical signal. Microphones are widely applied in mobile phones, noise reduction headsets, wireless Bluetooth earphones, smart speakers, and the like. Microphones are deeply rooted in every aspect of people's life. The following uses a mobile phone and a smart speaker as examples to describe an application of a microphone.

With rapid development of Internet technologies, a mobile phone has more functions and a higher integration level. Generally, a mobile phone has two microphones for sound pickup. One of the two microphones is a primary microphone, and is configured to pick up voice of a call. The other microphone is configured to pick up a background sound, and is usually installed on the back of the mobile phone and far away from the primary microphone. The two microphones are internally isolated by a mainboard. This design may effectively resist ambient noise interference around the mobile phone and greatly improve a quality of the call. In addition to the two microphones, another microphone may be disposed in the mobile phone. For example, a microphone may be disposed beside a rear-facing camera, so that sounds in different directions may be more easily received when a video is recorded by using the rear-facing camera. Certainly, a microphone may also be disposed beside the front-facing camera, so that sounds in different directions may be better picked up when a video is recorded by using the front-facing camera.

With emergence of the Internet of Things (IoT), smart home is becoming increasingly popular in daily life. Intelligent control has been applied to televisions, refrigerators, air conditioners, fans, and lights and other equipment. How to control these devices has become a topic of general concern. After independent remote control, built-in remote control of the mobile phone, and third-party remote control are experimented, the smart speaker can finally be controlled by voice. A microphone array including a plurality of microphones is disposed in the smart speaker. The microphone array may implement functions such as voice quality enhancement, acoustic source localization, dereverberation, and acoustic source signal extraction (separation). This makes it possible to perform voice control in a complex environment.

Piezoelectric microphones (namely, piezoelectric MEMS microphones) based on micro-electro-mechanical systems (MEMS) are widely used because of their advantages such as miniaturization, batch production and high performance. A piezoelectric acoustic sensor may be disposed in the piezoelectric MEMS microphones to collect sound, and the piezoelectric acoustic sensor has many advantages such as a high signal-to-noise ratio, low power consumption, and high sensitivity.

As electronic devices such as mobile phones and smart speakers have increasing requirements for directional sound pickup, more microphones need to be disposed in the electronic devices. To ensure a directional sound pickup effect, performance consistency of microphones in the electronic device needs to be maintained. In other words, performance consistency of piezoelectric acoustic sensors needs to be maintained.

However, a manufacturing process of the piezoelectric acoustic sensors has non-uniformity. Therefore, this results in that residual stresses of manufactured piezoelectric acoustic sensors cannot be consistent. Consequently, resonance frequencies of the piezoelectric acoustic sensors are inconsistent, and even sensitivity of the piezoelectric acoustic sensors is inconsistent. This further causes output response performance of the piezoelectric acoustic sensors to be inconsistent.

Therefore, an embodiment of this application provides a piezoelectric acoustic sensor, and a hollow-out mechanical part is designed, so that problems such as resonance frequency drift and sensitivity reduction caused by a residual stress can be solved, and performance consistency of the piezoelectric acoustic sensor can be improved.

The piezoelectric acoustic sensor provided in embodiments of this application is mainly applied to fields such as mobile phones, smart speakers, wireless Bluetooth headsets, noise reduction headsets, notebook computers, and automobiles, and is used as a sound pickup component. The piezoelectric acoustic sensor is mainly configured to restore a human voice or an ambient sound. For example, the piezoelectric acoustic sensor may complete human voice collection during a call of a mobile phone. For another example, a plurality of piezoelectric acoustic sensors may form an array to implement directional sound pickup of a smart speaker.

FIG.1is a schematic diagram of a sound pickup system according to an embodiment of this application. As shown inFIG.1, the sound pickup system includes a piezoelectric acoustic sensor100and an amplification circuit101. The piezoelectric acoustic sensor100may sense a sound, and convert a vibrating sound signal into an original electrical signal. Because the original electrical signal is weak and cannot be directly used, the amplification circuit101generally amplifies the original electrical signal, and the amplified electrical signal enters an audio system102for processing.

As shown inFIG.2andFIG.3(a metal housing201is not shown), the sound pickup system may be a closed sound cavity including the metal housing201and a printed circuit board (PCB)/ceramic board202. On the PCB/ceramic board202, the piezoelectric acoustic sensor100and the amplification circuit101(including but not limited to an application-specific integrated circuit (ASIC) chip) are arranged. The PCB/ceramic board202has a sound inlet hole2021, so that sound vibration may be transmitted to the piezoelectric acoustic sensor100. The piezoelectric acoustic sensor100is electrically connected to the amplification circuit101by using a lead. An acoustic electrical signal collected by the piezoelectric acoustic sensor100may be amplified by the amplification circuit101and then provided to the audio system102for processing.

FIG.4,FIG.5,FIG.6, orFIG.7is a schematic diagram of a structure of a piezoelectric acoustic sensor according to an embodiment of this application.FIG.5is specifically a sectional view of the piezoelectric acoustic sensor shown inFIG.4, andFIG.7is specifically a sectional view of the piezoelectric acoustic sensor shown inFIG.6. Refer toFIG.4toFIG.7. The piezoelectric acoustic sensor includes an anchoring unit1, a piezoelectric unit2, a support unit3, and a hollow-out mechanical part4.

A back cavity5is formed in the anchoring unit1. The piezoelectric unit2is configured to convert a sound signal that enters the back cavity5into an electrical signal. The support unit3covers the anchoring unit1and the piezoelectric unit2. The hollow-out mechanical part4is connected between the anchoring unit1and the piezoelectric unit2, and is embedded in the support unit3.

The following separately describes the anchoring unit1, the piezoelectric unit2, the support unit3, and the hollow-out mechanical part4.

The anchoring unit1is configured to fasten each component in the piezoelectric acoustic sensor, and another component in the piezoelectric acoustic sensor is formed on the anchoring unit1. The anchoring unit1includes the back cavity5, and the back cavity5is a sound inlet hole. The piezoelectric unit2is suspended above the back cavity5, and may convert a sound signal that enters the back cavity5into an electrical signal.

The anchoring unit1may include a substrate layer11and an insulation layer12, and the insulation layer12covers the substrate layer11. A material of the substrate layer11may be silicon, quartz, silicon-on-insulator (SOI), silicon carbide (SiC), or the like. A material of the insulation layer12may be silicon nitride or another dielectric material.

The piezoelectric unit2may be a piezoelectric stacked film, and may include the electrode and the piezoelectric material. A material of the electrode may be molybdenum, titanium, platinum, aluminum, or the like, and the piezoelectric material may be aluminum nitride, aluminum scandium nitride, lead zirconate titanate, or the like. The piezoelectric unit2may convert mechanical motion into an electrical signal. Specifically, when a sound signal causes the piezoelectric material to vibrate, an electric potential difference is generated between an upper electrode and a lower electrode in a stress-concentrated area in the piezoelectric material. In this way, the sound signal may be converted into the electrical signal for extraction.

In addition, a shape of the piezoelectric unit2may be set based on an actual requirement. For example, as shown inFIG.4orFIG.6, the piezoelectric unit2may be a circle. Alternatively, as shown inFIG.8orFIG.9, the piezoelectric unit2may be a polygon.

In a possible implementation, as shown inFIG.4,FIG.5, orFIG.8, the piezoelectric unit2may be a single piezoelectric wafer, and the piezoelectric unit2may include a lower electrode21, a piezoelectric material22, and an upper electrode23. The piezoelectric material22is located between the lower electrode21and the upper electrode23.

In another possible implementation, as shown inFIG.6,FIG.7, orFIG.9, the piezoelectric unit2may be a double piezoelectric wafer, and the piezoelectric unit2may include the lower electrode21, a first piezoelectric material221, a middle electrode24, a second piezoelectric material222, and the upper electrode23. The first piezoelectric material221is located between the lower electrode21and the middle electrode24, and the second piezoelectric material222is located between the middle electrode24and the upper electrode23.

The support unit3is configured to fasten positions of the anchoring unit1, the hollow-out mechanical part4, and the piezoelectric unit2, to enhance mechanical strength of the piezoelectric acoustic sensor. A material of the support unit3may be polycrystalline silicon, silicon nitride, silicon dioxide, or the like.

In addition, because the hollow-out mechanical part4is connected between the anchoring unit1and the piezoelectric unit2, after the support unit3covers the anchoring unit1and the piezoelectric unit2, the support unit3wraps the hollow-out mechanical part4. In other words, the hollow-out mechanical part4is embedded in the support unit3. In this way, the support unit3implements fastening positions of the anchoring unit1, the hollow-out mechanical part4, and the piezoelectric unit2.

In addition, the hollow-out mechanical part4is embedded in the support unit3, that is, the support unit3fills a hollow-out gap in the hollow-out mechanical part4. In this way, an intrinsic resonance frequency of the piezoelectric acoustic sensor may be adjusted, sound leakage caused by the hollow-out gap is reduced, and low-frequency response performance of the piezoelectric acoustic sensor is improved.

In a possible case, as shown inFIG.4,FIG.5, orFIG.8, when the piezoelectric unit2is a single piezoelectric wafer, an upper surface of the piezoelectric unit2is completely covered with the support unit3.

In this case, as shown inFIG.10, existence of the support unit3may enable a neutral axis m of the piezoelectric unit2to be far away from a center of the piezoelectric unit2(that is, far away from the piezoelectric material22), so that charge output and sensitivity of the piezoelectric acoustic sensor can be effectively improved.

In another possible case, as shown inFIG.6,FIG.7, orFIG.9, the piezoelectric unit2is a double piezoelectric wafer, and an upper surface of the piezoelectric unit2is partially covered with the support unit3. For example, an edge part of the upper surface of the piezoelectric unit2is covered with the support unit3, and a central part of the upper surface of the piezoelectric unit2is not covered with the support unit3. In other words, a central area of a part of the support unit3that is located above the piezoelectric unit2is hollowed out.

In this case, as shown inFIG.11, it may be ensured that the neutral axis m of the piezoelectric unit2is located in the middle electrode24of the piezoelectric unit2, so that charge output and sensitivity of the piezoelectric acoustic sensor are not affected.

The hollow-out mechanical part4is a mechanical structure in which some materials are removed, and has low rigidity and is easy to deform. For example, as shown inFIG.12, a shape of the hollow-out mechanical part4may be a bent shape, a width w1 of a bent part of the bent-shaped hollow-out mechanical part4may be from 1 to 10 micrometers, and a width w2 of a gap between bent parts may be greater than 0.5 micrometers. Alternatively, as shown inFIG.13, a shape of the hollow-out mechanical part4may be a hollow shape, a width w3 of a hollow-shaped part of the hollow-shaped hollow-out mechanical part4may be from 1 to 10 micrometers, and a width w4 of a hollow-out area may be greater than 2 micrometers. Alternatively, as shown inFIG.14, a shape of the hollow-out mechanical part4may be a grid shape, and a width w5 of a hollow-out area of the grid-shaped hollow-out mechanical part4may be greater than 1 micrometer.

It should be noted that the hollow-out mechanical part4is connected between the anchoring unit1and the piezoelectric unit2. In other words, a first end of the hollow-out mechanical part4may be fastened to an upper surface of the anchoring unit1(that is, an upper surface of the insulation layer12), and a second end of the hollow-out mechanical part4may be connected to the piezoelectric unit2.

In addition, the hollow-out mechanical part4may have a stress release function. A quantity of hollow-out mechanical parts4may be set based on a use requirement. To improve a stress release effect, the quantity of hollow-out mechanical parts4may be greater than or equal to 2. Further, at least two hollow-out mechanical parts4may be evenly distributed around the piezoelectric unit2. For example, as shown inFIG.15, there may be two hollow-out mechanical parts4, and the two hollow-out mechanical parts4may be evenly distributed around the piezoelectric unit2. Alternatively, as shown inFIG.16, there may be three hollow-out mechanical parts4, and the three hollow-out mechanical parts4may be evenly distributed around the piezoelectric unit2. Alternatively, as shown inFIG.17, there may be eight hollow-out mechanical parts4, and the eight hollow-out mechanical parts4may be evenly distributed around the piezoelectric unit2.

The hollow-out mechanical part4may be connected to at least one of the electrode or the piezoelectric material in the piezoelectric unit2. In addition, when the hollow-out mechanical part4is connected to the electrode in the piezoelectric unit2, the hollow-out mechanical part4and the electrode to which the hollow-out mechanical part4is connected may use a same material. When the hollow-out mechanical part4is connected to the piezoelectric material in the piezoelectric unit2, the hollow-out mechanical part4and the piezoelectric material to which the hollow-out mechanical part4is connected may use a same material. When the hollow-out mechanical part4is separately connected to the electrode and the piezoelectric material in the piezoelectric unit2, that is, when one part of the hollow-out mechanical part4is connected to the electrode in the piezoelectric unit2and another part is connected to the piezoelectric material in the piezoelectric unit2, a part of the hollow-out mechanical part4and the electrode to which the hollow-out mechanical part4is connected may use a same material, and the another part of the hollow-out mechanical part4and the piezoelectric material to which the hollow-out mechanical part4is connected may use a same material. In this case, the hollow-out mechanical part4may be a multi-layer structure, each layer of the hollow-out mechanical part4may be connected to the electrode or the piezoelectric material, and the electrode or the piezoelectric material connected to each layer of the hollow-out mechanical part4uses a same material.

In this way, when the electrode or the piezoelectric material in the piezoelectric unit2is manufactured, the hollow-out mechanical part4to which the electrode or the piezoelectric material is connected may also be manufactured. This simplifies a manufacturing process, and saves manufacturing costs and manufacturing time.

In a possible implementation, in the piezoelectric unit2shown inFIG.4,FIG.5, orFIG.8, that is, when the piezoelectric unit2includes three parts: the lower electrode21, the piezoelectric material22, and the upper electrode23, the hollow-out mechanical part4may be connected to any one of the three parts. In addition, when a quantity of hollow-out mechanical parts4is greater than or equal to 2, at least two hollow-out mechanical parts4may be connected to one part of the piezoelectric unit2, or each hollow-out mechanical part4may be connected to a different part of the piezoelectric unit2.

For example, as shown inFIG.5, the at least two hollow-out mechanical parts4are all connected to the lower electrode21in the piezoelectric unit2. Alternatively, as shown inFIG.18, at least one hollow-out mechanical part4in the at least two hollow-out mechanical parts4is connected to the upper electrode23in the piezoelectric unit2, and another hollow-out mechanical part4is connected to the lower electrode21in the piezoelectric unit2.

In another possible implementation, in the piezoelectric unit2shown inFIG.6,FIG.7, orFIG.9, that is, when the piezoelectric unit2includes five parts: the lower electrode21, the first piezoelectric material221, the middle electrode24, the second piezoelectric material222, and the upper electrode23, the hollow-out mechanical part4may be connected to any one of the five parts. In addition, when a quantity of hollow-out mechanical parts4is greater than or equal to 2, at least two hollow-out mechanical parts4may be connected to one part of the piezoelectric unit2, or each hollow-out mechanical part4may be connected to a different part of the piezoelectric unit2.

For example, as shown inFIG.7, the at least two hollow-out mechanical parts4are all connected to the lower electrode21in the piezoelectric unit2. Alternatively, as shown inFIG.19, at least one hollow-out mechanical part4in the at least two hollow-out mechanical parts4is connected to the middle electrode24in the piezoelectric unit2, and another hollow-out mechanical part4is connected to the lower electrode21in the piezoelectric unit2. Alternatively, as shown inFIG.20, at least one hollow-out mechanical part4in the at least two hollow-out mechanical parts4is connected to the upper electrode23in the piezoelectric unit2, and another hollow-out mechanical part4is connected to the lower electrode21in the piezoelectric unit2. Alternatively, as shown inFIG.21, the at least two hollow-out mechanical parts4are all connected to the middle electrode24in the piezoelectric unit2. Alternatively, as shown inFIG.22, the at least two hollow-out mechanical parts4are all connected to the upper electrode23in the piezoelectric unit2. Alternatively, as shown inFIG.23, at least one hollow-out mechanical part4in the at least two hollow-out mechanical parts4is connected to the upper electrode23in the piezoelectric unit2, and another hollow-out mechanical part4is connected to the middle electrode24in the piezoelectric unit2.

The following describes beneficial effects that can be achieved after the hollow-out mechanical part4is added to the piezoelectric acoustic sensor.

As shown inFIG.24orFIG.25, in a manufacturing process of the piezoelectric acoustic sensor, a sacrificial layer7is usually formed first, then the piezoelectric unit2is formed on the sacrificial layer7, and then the sacrificial layer7is removed. In this case, on one hand, the hollow-out mechanical part4may have a mechanical connection function. In a process of removing the sacrificial layer7below the piezoelectric unit2, the piezoelectric unit2may be connected to the anchoring unit1by using the hollow-out mechanical part4. This may prevent the piezoelectric unit2from falling off in the process of removing the sacrificial layer7. On the other hand, the hollow-out mechanical part4may have a stress release function. In the process of removing the sacrificial layer7below the piezoelectric unit2, the low-rigidity and deformable hollow-out mechanical part4allows the piezoelectric unit2to move (for example, bend up and down or extend horizontally) through a change of a hollow-out gap, and a residual stress of the piezoelectric unit2is released by the deformable hollow-out mechanical part4, to achieve zero residual stress. Since the residual stress of the piezoelectric unit2has been released, piezoelectric acoustic sensors of a same geometrical size have a same resonance frequency and sensitivity.

In this embodiment of this application, the piezoelectric acoustic sensor includes the anchoring unit1, the piezoelectric unit2, the support unit3, and the hollow-out mechanical part4. The back cavity5is formed in the anchoring unit1. The piezoelectric unit2is configured to convert a sound signal that enters the back cavity5into an electrical signal. The support unit3covers the anchoring unit1and the piezoelectric unit2. The hollow-out mechanical part4is connected between the anchoring unit1and the piezoelectric unit2, and is embedded in the support unit3. The residual stress of the piezoelectric unit2may be released by using the deformable hollow-out mechanical part4in a manufacturing process, to achieve zero residual stress. Therefore, this can avoid resonance frequency drift of the piezoelectric acoustic sensor, avoid sensitivity reduction of the piezoelectric acoustic sensor, and further help improve performance consistency of the piezoelectric acoustic sensor.

FIG.26is a flowchart of a method for manufacturing a piezoelectric acoustic sensor shown inFIG.4toFIG.25according to an embodiment of this application. Refer toFIG.26. The method includes the following steps.

Step2601: Provide an anchoring unit, and etch a groove on an upper surface of the anchoring unit.

As shown in a inFIG.27orFIG.28A, the anchoring unit1is provided, and then a groove6is etched on an upper surface of the anchoring unit1.

The anchoring unit1is configured to fasten each component in the piezoelectric acoustic sensor, and another component in the piezoelectric acoustic sensor may be formed on the anchoring unit1.

The anchoring unit1may include the substrate layer11and the insulation layer12. In this case, when the anchoring unit1is provided, the substrate layer11may be first provided, and then the insulation layer12is formed on the substrate layer11.

It should be noted that a material of the substrate layer11may be a material such as silicon, quartz, SOI, or SiC. A material of the insulation layer12may be silicon nitride or another dielectric material.

In addition, that the insulation layer12is formed on the substrate layer11may be depositing a material used to form the insulation layer12on an upper surface of the substrate layer11to obtain the insulation layer12.

When the groove6is etched on the upper surface of the anchoring unit1, a shape and a position of the groove6may be first defined on an upper surface of the insulation layer12, to determine an area in which the groove6is located on the upper surface of the insulation layer12. Then, an area other than the area in which the groove6is located on the upper surface of the insulation layer12is first protected by using a protective adhesive, and then the upper surface of the insulation layer12is etched to obtain the groove6on the upper surface of the insulation layer12.

It should be noted that the shape and the position of the groove6may be defined by using a photoetching process, for example, by using a photoetching process such as electron beam exposure or optical exposure.

In addition, the protective adhesive may be an anti-etching adhesive, a polymethyl methacrylate (PMMA), or the like.

In addition, when the upper surface of the insulation layer12is etched, etching may be performed by using a process such as reactive-ion etching (RIE) or oxygen plasma etching.

Step2602: Fill the groove with a sacrificial layer.

As shown in b inFIG.27orFIG.28A, the sacrificial layer7is filled in the groove6in the upper surface of the anchoring unit1. Specifically, a material used to form the sacrificial layer7may be deposited in the groove6on the upper surface of the anchoring unit1to obtain the sacrificial layer7. A material of the sacrificial layer7may be a material that is easily corroded by a chemical etching agent, such as silicon dioxide or phosphorus-doped silicon oxide.

Step2603: Form a piezoelectric unit on the sacrificial layer, and form a hollow-out mechanical part on the anchoring unit and the sacrificial layer.

As shown in c inFIG.27orFIG.28A, the piezoelectric unit2is formed on the sacrificial layer7, and the hollow-out mechanical part4is formed on the anchoring unit1and the sacrificial layer7.

It should be noted that the piezoelectric unit2may be a piezoelectric stacked film, and may include the electrode and the piezoelectric material. A material of the electrode may be molybdenum, titanium, platinum, aluminum, or the like, and the piezoelectric material may be aluminum nitride, aluminum scandium nitride, lead zirconate titanate, or the like. The piezoelectric unit2may convert mechanical motion into an electrical signal. Specifically, when a sound signal causes the piezoelectric material to vibrate, an electric potential difference is generated between an upper electrode and a lower electrode in a stress-concentrated area in the piezoelectric material. In this way, the sound signal may be converted into the electrical signal for extraction.

In addition, an area of a lower surface of the piezoelectric unit2is less than an area of an upper surface of the sacrificial layer7. In other words, the piezoelectric unit2is completely located on the upper surface of the sacrificial layer7.

When the piezoelectric unit2is formed on the sacrificial layer7, a shape and a position of the piezoelectric unit2may be defined on the upper surface of the sacrificial layer7to determine an area in which the piezoelectric unit2is located on the upper surface of the sacrificial layer7. Then, a material used to form the piezoelectric unit2is deposited on the area in which the piezoelectric unit2is located on the upper surface of the sacrificial layer7to obtain the piezoelectric unit2.

It should be noted that the shape and the position of the piezoelectric unit2may be defined by using a photoetching process, for example, by using a photoetching process such as electron beam exposure or optical exposure.

In a possible implementation, as shown inFIG.27, the piezoelectric unit2may be a single piezoelectric wafer, and the piezoelectric unit2may include the lower electrode21, the piezoelectric material22, and the upper electrode23. In this case, when the piezoelectric unit2is formed on the sacrificial layer7, the lower electrode21may be formed on the sacrificial layer7, the piezoelectric material22may be formed on the lower electrode21, and the upper electrode23may be formed on the piezoelectric material22.

In other words, a material used to form the lower electrode21may be deposited on the upper surface of the sacrificial layer7to obtain the lower electrode21, and then the piezoelectric material22is deposited on the upper surface of the lower electrode21. Finally, a material used to form the upper electrode23is deposited on an upper surface of the piezoelectric material22to obtain the upper electrode23.

In another possible implementation, as shown inFIG.28AandFIG.28B, the piezoelectric unit2may be a double piezoelectric wafer, and the piezoelectric unit2may include the lower electrode21, the first piezoelectric material221, the middle electrode24, the second piezoelectric material222, and the upper electrode23. In this case, when the piezoelectric unit2is formed on the sacrificial layer7, the lower electrode21may be formed on the sacrificial layer7, the first piezoelectric material221may be formed on the lower electrode21, the middle electrode24may be formed on the first piezoelectric material221, the second piezoelectric material222is formed on the middle electrode24, and the upper electrode23is formed on the second piezoelectric material222.

In other words, a material used to form the lower electrode21may be deposited on the upper surface of the sacrificial layer7to obtain the lower electrode21, and then the first piezoelectric material221is deposited on the upper surface of the lower electrode21. A material used to form the middle electrode24is deposited on an upper surface of the first piezoelectric material221to obtain the middle electrode24, then the second piezoelectric material222is deposited on an upper surface of the middle electrode24, and a material used to form the upper electrode23is deposited on an upper surface of the second piezoelectric material222to obtain the upper electrode23.

It should be noted that the hollow-out mechanical part4is a mechanical structure in which some materials are removed, and has low rigidity and is easy to deform. A shape of the hollow-out mechanical part4may be set based on a use requirement. For example, the shape of the hollow-out mechanical part4may be a bent shape, a hollow shape, a grid shape, or the like.

In addition, the hollow-out mechanical part4is connected between the anchoring unit1and the piezoelectric unit2. In other words, a first end of the hollow-out mechanical part4may be fastened to an upper surface of the anchoring unit1(that is, an upper surface of the insulation layer12), and a second end of the hollow-out mechanical part4may be connected to the piezoelectric unit2.

In addition, the hollow-out mechanical part4may have a stress release function. A quantity of hollow-out mechanical parts4may be set based on a use requirement. To improve a stress release effect, the quantity of hollow-out mechanical parts4may be greater than or equal to 2. Further, at least two hollow-out mechanical parts4may be evenly distributed around the piezoelectric unit2.

The hollow-out mechanical part4may be connected to at least one of the electrode or the piezoelectric material in the piezoelectric unit2. In addition, when the hollow-out mechanical part4is connected to the electrode in the piezoelectric unit2, the hollow-out mechanical part4and the electrode to which the hollow-out mechanical part4is connected may use a same material. When the hollow-out mechanical part4is connected to the piezoelectric material in the piezoelectric unit2, the hollow-out mechanical part4and the piezoelectric material to which the hollow-out mechanical part4is connected may use a same material. When the hollow-out mechanical part4is separately connected to the electrode and the piezoelectric material in the piezoelectric unit2, that is, when one part of the hollow-out mechanical part4is connected to the electrode in the piezoelectric unit2and another part is connected to the piezoelectric material in the piezoelectric unit2, a part of the hollow-out mechanical part4and the electrode to which the hollow-out mechanical part4is connected may use a same material, and the another part of the hollow-out mechanical part4and the piezoelectric material to which the hollow-out mechanical part4is connected may use a same material. In this case, the hollow-out mechanical part4may be a multi-layer structure, each layer of the hollow-out mechanical part4may be connected to the electrode or the piezoelectric material, and the electrode or the piezoelectric material connected to each layer of the hollow-out mechanical part4uses a same material.

In this way, when the electrode or the piezoelectric material in the piezoelectric unit2is manufactured, the hollow-out mechanical part4to which the electrode or the piezoelectric material is connected may also be manufactured. This simplifies a manufacturing process, and saves manufacturing costs and manufacturing time.

In a possible implementation, in the piezoelectric unit2shown inFIG.27, that is, when the piezoelectric unit2includes three parts: the lower electrode21, the piezoelectric material22, and the upper electrode23, the hollow-out mechanical part4may be connected to any one of the three parts. In addition, when a quantity of hollow-out mechanical parts4is greater than or equal to 2, at least two hollow-out mechanical parts4may be connected to one part of the piezoelectric unit2, or each hollow-out mechanical part4may be connected to a different part of the piezoelectric unit2.

For example, the at least two hollow-out mechanical parts4are all connected to the lower electrode21in the piezoelectric unit2. Alternatively, at least one hollow-out mechanical part4in the at least two hollow-out mechanical parts4is connected to the upper electrode23in the piezoelectric unit2, and another hollow-out mechanical part4is connected to the lower electrode21in the piezoelectric unit2.

In another possible implementation, in the piezoelectric unit2shown inFIG.28AandFIG.28B, that is, when the piezoelectric unit2includes five parts: the lower electrode21, the first piezoelectric material221, the middle electrode24, the second piezoelectric material222, and the upper electrode23, the hollow-out mechanical part4may be connected to any one of the five parts. In addition, when a quantity of hollow-out mechanical parts4is greater than or equal to 2, at least two hollow-out mechanical parts4may be connected to one part of the piezoelectric unit2, or each hollow-out mechanical part4may be connected to a different part of the piezoelectric unit2.

For example, the at least two hollow-out mechanical parts4are all connected to the lower electrode21in the piezoelectric unit2. Alternatively, at least one hollow-out mechanical part4in the at least two hollow-out mechanical parts4is connected to the middle electrode24in the piezoelectric unit2, and another hollow-out mechanical part4is connected to the lower electrode21in the piezoelectric unit2. Alternatively, at least one hollow-out mechanical part4in the at least two hollow-out mechanical parts4is connected to the upper electrode23in the piezoelectric unit2, and another hollow-out mechanical part4is connected to the lower electrode21in the piezoelectric unit2. Alternatively, the at least two hollow-out mechanical parts4are all connected to the middle electrode24in the piezoelectric unit2. Alternatively, the at least two hollow-out mechanical parts4are all connected to the upper electrode23in the piezoelectric unit2. Alternatively, at least one hollow-out mechanical part4in the at least two hollow-out mechanical parts4is connected to the upper electrode23in the piezoelectric unit2, and another hollow-out mechanical part4is connected to the middle electrode24in the piezoelectric unit2.

When the hollow-out mechanical part4is formed on the anchoring unit1and the sacrificial layer7, a shape and a position of the hollow-out mechanical part4may be defined on the upper surface of the anchoring unit1and the upper surface of the sacrificial layer7, to determine an area in which the hollow-out mechanical part4is located on the upper surface of the anchoring unit1and the upper surface of the sacrificial layer7. Then, a material used to form the hollow-out mechanical part4is deposited in the area in which the hollow-out mechanical part4is located to obtain the hollow-out mechanical part4.

It should be noted that the shape and the position of the hollow-out mechanical part4may be defined by using a photoetching process, for example, by using a photoetching process such as electron beam exposure or optical exposure.

Step2604: Remove the sacrificial layer.

As shown in d inFIG.27orFIG.28A, the sacrificial layer7may be removed. When the sacrificial layer7is removed, the sacrificial layer7may be corroded by using a chemical etching agent. For example, when a material of the sacrificial layer7is silicon dioxide, the silicon dioxide may be etched with liquid hydrofluoric acid to remove the silicon dioxide.

In this case, on one hand, the hollow-out mechanical part4may have a mechanical connection function. In a process of removing the sacrificial layer7below the piezoelectric unit2, the piezoelectric unit2may be connected to the anchoring unit1by using the hollow-out mechanical part4. This may prevent the piezoelectric unit2from falling off in the process of removing the sacrificial layer7. In this case, the piezoelectric unit2may be suspended above the groove6by using the hollow-out mechanical part4. On the other hand, the hollow-out mechanical part4may have a stress release function. In the process of removing the sacrificial layer7below the piezoelectric unit2, the low-rigidity and deformable hollow-out mechanical part4allows the piezoelectric unit2to move (for example, bend up and down or extend horizontally) through a change of a hollow-out gap, and a residual stress of the piezoelectric unit2is released by the deformable hollow-out mechanical part4, to achieve zero residual stress. Since the residual stress of the piezoelectric unit2has been released, piezoelectric acoustic sensors of a same geometrical size that are finally fabricated have a same resonance frequency and sensitivity.

Because the piezoelectric unit2is completely located on the sacrificial layer7in the foregoing steps, after the sacrificial layer7is removed, and after the residual stress of the piezoelectric unit2is released and each device (including the anchoring unit1, the piezoelectric unit2, and the hollow-out mechanical part4) is dried, due to gravity, the piezoelectric unit2drops into the groove6in which the original sacrificial layer7is located and is in contact with a bottom of the groove6. In other words, after the residual stress of the piezoelectric unit2is released and each device is dried, the piezoelectric unit2is attached to a surface of the anchoring unit1.

Step2605: When the piezoelectric unit is in contact with a bottom of the groove, a support unit is formed on the anchoring unit and the piezoelectric unit, and the support unit wraps the hollow-out mechanical part.

As shown in e inFIG.27orFIG.28A, when the piezoelectric unit2is in contact with the bottom of the groove6, the support unit3may be formed on the anchoring unit1and the piezoelectric unit2. In this case, the support unit3wraps the hollow-out mechanical part4.

It should be noted that the support unit3is configured to fasten positions of the anchoring unit1, the hollow-out mechanical part4, and the piezoelectric unit2, to enhance mechanical strength of the finally manufactured piezoelectric acoustic sensor. A material of the support unit3may be polycrystalline silicon, silicon nitride, silicon dioxide, or the like.

In addition, because the hollow-out mechanical part4is connected between the anchoring unit1and the piezoelectric unit2, after the support unit3is formed on the anchoring unit1and the piezoelectric unit2, the support unit3wraps the hollow-out mechanical part4. In other words, the support unit3covers the anchoring unit1and the piezoelectric unit2, and the hollow-out mechanical part4is embedded in the support unit3. In this way, the support unit3implements fastening positions of the anchoring unit1, the hollow-out mechanical part4, and the piezoelectric unit2.

In addition, the support unit3wraps the hollow-out mechanical part4, that is, the support unit3fills a hollow-out gap in the hollow-out mechanical part4. In this way, an intrinsic resonance frequency of a finally manufactured piezoelectric acoustic sensor may be adjusted, sound leakage caused by the hollow-out gap is reduced, and low-frequency response performance of the piezoelectric acoustic sensor is improved.

In a possible implementation, in the piezoelectric unit2shown inFIG.27, that is, when the piezoelectric unit2includes the lower electrode21, the piezoelectric material22, and the upper electrode23, the support unit3may be directly deposited on the upper surface of the anchoring unit1and the upper surface of the piezoelectric unit2. The deposited support unit3wraps the hollow-out mechanical part4.

In this case, the upper surface of the piezoelectric unit2is completely covered with the support unit3. In this way, existence of the support unit3may enable a neutral axis of the piezoelectric unit2to be far away from a center of the piezoelectric unit2(that is, far away from the piezoelectric material22), so that charge output and sensitivity of the finally manufactured piezoelectric acoustic sensor can be effectively improved.

When the support unit3is deposited on the upper surface of the anchoring unit1and the upper surface of the piezoelectric unit2, a shape and a position of the support unit3may be first defined on the upper surface of the anchoring unit1and the upper surface of the piezoelectric unit2, to determine an area in which the support unit3is located on the upper surface of the anchoring unit1and the upper surface of the piezoelectric unit2. Then, a material used to form the support unit3is deposited on the area in which the support unit3is located, to obtain the support unit3.

It should be noted that the shape and the position of the support unit3may be defined by using a photoetching process, for example, by using a photoetching process such as electron beam exposure or optical exposure.

In another possible implementation, in the piezoelectric unit2shown inFIG.28AandFIG.28B, that is, when the piezoelectric unit2includes the lower electrode21, the first piezoelectric material221, the middle electrode24, the second piezoelectric material222, and the upper electrode23, the support unit3may be first deposited on the upper surface of the anchoring unit1and the upper surface of the piezoelectric unit2. The deposited support unit3wraps the hollow-out mechanical part4, and then at least a part of the support unit3deposited on the upper surface of the piezoelectric unit2is removed.

In this case, the upper surface of the piezoelectric unit2is partially covered with the support unit3. For example, a part that is of the support unit3and that is deposited on the central part of the upper surface of the piezoelectric unit2may be removed. In this case, the support unit3is covered with an edge part of the upper surface of the piezoelectric unit2, and the support unit3is not covered with the central part of the upper surface of the piezoelectric unit2. In other words, a central area of the part above the piezoelectric unit2in the support unit3is hollowed out. In this way, it may be ensured that a neutral axis of the piezoelectric unit2is located in the middle electrode24of the piezoelectric unit2, so that charge output and sensitivity of the finally manufactured piezoelectric acoustic sensor are not affected.

When at least one part of the support unit3deposited on the upper surface of the piezoelectric unit2is removed, a shape and a position of a target part may be first defined on the upper surface of the support unit3, to determine an area in which the target part is located on the upper surface of the support unit3. The target part is at least a part deposited on the upper surface of the piezoelectric unit2. Then, an area other than the area in which the target part is located on the upper surface of the support unit3is first protected by using a protective adhesive, and then the upper surface of the support unit3is etched to remove the target part from the support unit3.

It should be noted that the shape and the position of the target part may be defined by using a photoetching process, for example, by using a photoetching process such as electron beam exposure or optical exposure.

In addition, when the upper surface of the support unit3is etched, etching may be performed by using a process such as reactive-ion etching or oxygen plasma etching.

Step2606: Etch a back cavity at a part between the bottom of the groove and a lower surface of the anchoring unit.

As shown in finFIG.27orFIG.28B, the back cavity5is etched at a part between the bottom of the groove6and the lower surface of the anchoring unit1. The back cavity5is a sound inlet hole. In this case, the piezoelectric unit2is suspended above the sound inlet hole, and may sense a sound.

In this embodiment of this application, an anchoring unit is provided, a groove is etched on an upper surface of the anchoring unit, and then a sacrificial layer is filled in the groove. A piezoelectric unit is formed on the sacrificial layer, a hollow-out mechanical part is formed on the anchoring unit and the sacrificial layer, and the hollow-out mechanical part is connected between the anchoring unit and the piezoelectric unit. Then, the sacrificial layer is removed. When the piezoelectric unit is in contact with a bottom of the groove, a support unit is formed on the anchoring unit and the piezoelectric unit, and the support unit wraps the hollow-out mechanical part. Finally, a back cavity is etched at a part between the bottom of the groove and a lower surface of the anchoring unit to obtain the piezoelectric acoustic sensor. In this manufacturing process, a residual stress of the piezoelectric unit may be released by using the deformable hollow-out mechanical part, to achieve zero residual stress. Therefore, this can avoid resonance frequency drift of the piezoelectric acoustic sensor, avoid sensitivity reduction of the piezoelectric acoustic sensor, and further help improve performance consistency of the piezoelectric acoustic sensor.

The foregoing description is embodiments provided in this application, but is not intended to limit this application. Any modification, equivalent replacement, or improvement made without departing from the spirit and principle of this application should fall within the protection scope of this application.