Piezoelectric micromechanical ultrasonic transducer, manufacturing method and electrical product

Abstract

The invention discloses a piezoelectric micromechanical ultrasonic transducer, a manufacturing method and an electrical product, and relates to the technical field of ultrasound. The piezoelectric micromechanical ultrasonic transducer comprises a substrate, a vibrating membrane layer and a flexible membrane layer which are sequentially stacked, the flexible film layer is integrally connected with the surface film layer of the vibrating film layer in a solid state through a chemical bonding mode, and the surface film layer is an outermost film structure, deviating from the substrate, of the vibrating film layer; a first through opening is pre-formed in the flexible film layer in the thickness direction, and a bonding pad, which is in circuit connection with the outside, on the vibrating film layer is exposed through the first through opening. The flexible film layer is integrally connected with the surface film layer of the vibrating film layer in a solid state through a chemical bonding mode, and the first through opening for exposing the bonding pad is formed in the flexible film layer in advance in the thickness direction, so that the bonding pad, which is in circuit connection with the outside, on the vibrating film layer is not blocked, and the surface of the bonding pad is naturally exposed.

Description

Technical Field

[0001] This application relates to the field of ultrasonic technology, and particularly to a piezoelectric micromachined ultrasonic transducer, a manufacturing method, and an electrical product. Background Art

[0002] A piezoelectric micromachined ultrasonic transducer (PMUT) is a MEMS device that uses the direct and converse piezoelectric effects of piezoelectric materials to vibrate a piezoelectric thin film layer, thereby transmitting or receiving ultrasonic signals. The PMUT can be used as both an actuator to emit sound waves and a sensor to receive sound waves. Moreover, mass production and wafer-level packaging based on MEMS standard processes have greatly reduced the cost of PMUTs, making them very suitable for large-scale commercial applications. PMUTs have good application prospects in ultrasonic ranging, ultrasonic imaging, ultrasonic non-destructive testing, ultrasonic fingerprint recognition, ultrasonic flow detection, ultrasonic mechanical feedback, etc. For example, they are used in specific products and scenarios such as ultrasonic imagers, ultrasonic radars, sonar detectors, floor cleaning robots, ultrasonic smoke alarms, ultrasonic flow meters, etc.

[0003] When the PMUT is used as an ultrasonic sensor, a matching / coupling layer is required to achieve the most efficient transmission of the ultrasonic waves emitted by the vibrating thin film to the object to be measured, and the most efficient transmission of the ultrasonic waves returning from the object to be measured to the vibrating thin film, so as to obtain an ultrasonic signal with a high signal-to-noise ratio. Although the PMUT does not need to construct multiple layers of matching layers of various materials on the surface of the block like traditional piezoelectric ceramic block sensors, it also requires an appropriate matching / coupling layer to achieve efficient signal transmission.

[0004] Usually, these materials are thick colloids formed by liquid casting and curing. However, one of the advantages of the PMUT is the use of MEMS processes for wafer-level mass manufacturing. The wafer-level manufacturing of the PMUT's matching / coupling layer is an essential step in realizing the overall wafer-level manufacturing of the PMUT sensor.

[0005] As Figure 1a shown, each independent PMUT device 600 on the PMUT wafer 001 includes a functional area 610. The film layer in the functional area 610 vibrates through the piezoelectric / converse piezoelectric effect to transmit or receive ultrasonic waves. Whether transmitting or receiving ultrasonic waves, the vibrating film layer needs to be electrically connected to the excitation source or the receiving end. Therefore, each independent PMUT device 600 includes a circuit pad 620 for realizing interconnection with the outside world.

[0006] As Figure 1bAs shown, if a matching / coupling layer 700 is formed by pouring on the wafer 500, the pads 620 on the PMUT device 600 will undoubtedly be covered. It is necessary to remove the material above the pads 620 to expose the pads 620 for electrical interconnection with an external excitation source or a receiving end. However, this layer of colloid is usually thick, reaching hundreds of micrometers or even several millimeters. It is almost impossible to remove such a thick colloid film layer without damaging the pad surface.

[0007] Thinner film layers can be obtained by methods such as vapor deposition or liquid spin coating. However, their thickness is usually thin, typically about a few micrometers. The matching and coupling effect of this film layer is limited. In addition, this step will also cover the pads, and an additional step is required to remove the surface material to expose them. Due to the lack of a suitable mask protection scheme, the etching of wafer-level colloid materials is a world problem in semiconductor processing, and there is currently no suitable technology to achieve it.

[0008] It should be noted that the above introduction of the technical background is only for the convenience of clearly and completely explaining the technical solutions of the present application and facilitating the understanding of those skilled in the art. It cannot be considered that the above technical solutions are well known to those skilled in the art just because these solutions are described in the background art part of the present application. Summary of the Invention

[0009] To solve at least one of the above problems existing in the prior art, an embodiment of the present application provides a piezoelectric micromachined ultrasonic transducer, a manufacturing method, and an electrical product.

[0010] According to the first aspect of the embodiments of the present application, the present application provides a piezoelectric micromachined ultrasonic transducer, including a substrate, a vibration film layer, and a flexible film layer that are sequentially stacked; wherein,

[0011] The flexible film layer is integrally connected to the surface film layer of the vibration film layer in a solid state by chemical bonding, and the surface film layer is the outermost thin film structure of the vibration film layer facing away from the substrate;

[0012] A first through opening is pre-formed in the flexible film layer in the thickness direction, and the pads for circuit connection between the vibration film layer and the outside are exposed through the first through opening.

[0013] In some embodiments, the surface film layer is a SiO2, Si3N4, or Si-based film layer, and the flexible film layer is a silicone-based film layer.

[0014] In some embodiments, the vibration film layer includes a bottom electrode, a piezoelectric thin film layer, a top electrode, and a support layer that are sequentially stacked; wherein, the bottom electrode is connected to the substrate, and the support layer is the surface film layer of the vibration film layer.

[0015] In some embodiments, the vibrating membrane layer includes a support layer, a bottom electrode, a piezoelectric thin film layer, a top electrode, and a surface film layer that are sequentially stacked; wherein, the support layer is connected to the substrate.

[0016] In some embodiments, the vibrating membrane layer is a relaxed vibrating membrane layer structure with voids in the thickness direction.

[0017] In some embodiments, the flexible membrane layer completely covers the voids on the vibrating membrane layer.

[0018] In some embodiments, the thickness of the flexible membrane layer is between nanometers and millimeters.

[0019] In some embodiments, a cavity is provided on the substrate, and the portion of the vibrating membrane layer opposite to the cavity is in a curved surface form.

[0020] In some embodiments, the portion of the vibrating membrane layer opposite to the cavity bends away from the cavity; or

[0021] The portion of the vibrating membrane layer opposite to the cavity bends towards the cavity.

[0022] In some embodiments, after the flexible membrane layer is integrally connected to the surface film layer of the vibrating membrane layer in a solid state by chemical bonding, the surface of the flexible membrane layer facing away from the vibrating membrane layer is flat.

[0023] In some embodiments, the side of the flexible membrane layer facing away from the surface film layer includes a non-planar structure for physically contacting the surface of the object to be measured.

[0024] In some embodiments, a non-planar structure layer is connected to the side of the flexible membrane layer facing away from the surface film layer, and the side of the non-planar structure layer facing away from the flexible membrane layer includes a non-planar structure for physically contacting the surface of the object to be measured.

[0025] In some embodiments, the non-planar structure is in a spherical array, a needle-like array, or an irregular shape.

[0026] In some embodiments, the cavity provided on the substrate has an opening, the opening of the cavity faces the vibrating membrane layer, and the cavity is obtained by a sacrificial layer process; or

[0027] The cavity provided on the substrate penetrates the substrate, and the cavity is obtained by a backside etching process.

[0028] According to the second aspect of the embodiments of the present application, the present application also provides a manufacturing method of a piezoelectric micromachined ultrasonic transducer, including:

[0029] Integrally attach a flexible film layer having a first through-opening in the thickness direction to the surface of a piezoelectric micromachined ultrasonic transducer wafer, and align the first through-opening with the pads on the piezoelectric micromachined ultrasonic transducer wafer so that the pads leak out through the first through-opening;

[0030] Bond the flexible film layer to the surface of the piezoelectric micromachined ultrasonic transducer wafer using a chemical bonding technique;

[0031] Split the overall structure formed by bonding the flexible film layer to the surface of the piezoelectric micromachined ultrasonic transducer wafer into independent piezoelectric micromachined ultrasonic transducers.

[0032] In some embodiments, a second through-opening is also pre-formed in the thickness direction of the flexible film layer;

[0033] When integrally attaching the flexible film layer to the surface of the piezoelectric micromachined ultrasonic transducer wafer, also align the second through-opening with the boundary position of the piezoelectric micromachined ultrasonic transducer on the piezoelectric micromachined ultrasonic transducer wafer.

[0034] According to the third aspect of the embodiments of the present application, the present application also provides an electrical product, including the piezoelectric micromachined ultrasonic transducer described in any of the above embodiments.

[0035] In the present application, the flexible film layer is integrally connected to the surface film layer of the vibrating film layer in a solid state by a chemical bonding method, and a first through-opening for leaking out the pads is pre-formed in the thickness direction of the flexible film layer. Therefore, the pads for circuit connection with the outside on the vibrating film layer will not be blocked, and the surfaces of the pads are naturally exposed. There is no need for other etching means to open the pads, greatly reducing the manufacturing difficulty and cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings. In the drawings:

[0037] Figure 1a It is a top view of a PMUT wafer provided by the present application.

[0038] Figure 1b It is in Figure 1a The structural schematic diagram after pouring and forming a matching / coupling layer on the PMUT wafer shown.

[0039] Figure 2aIt is a top view of a piezoelectric micromachined ultrasonic transducer provided by this application.

[0040] Figure 2b It is a schematic cross-sectional view along the Figure 2a AA direction in [].

[0041] Figure 2c It is a schematic cross-sectional view along the Figure 2a BB direction in [].

[0042] Figures 3a - 3b It is a cross-sectional view of a piezoelectric micromachined ultrasonic transducer provided by this application in two different directions.

[0043] Figures 4a - 4b It is a cross-sectional view of a piezoelectric micromachined ultrasonic transducer provided by this application in two different directions.

[0044] Figure 5a It is a top view of a piezoelectric micromachined ultrasonic transducer provided by this application.

[0045] Figure 5b It is a schematic cross-sectional view along the Figure 5a AA direction in [].

[0046] Figure 5c It is a schematic cross-sectional view along the Figure 5a BB direction in [].

[0047] Figures 6a - 6b It is a cross-sectional view of a piezoelectric micromachined ultrasonic transducer provided by this application in two different directions.

[0048] Figures 7a - 7b It is a cross-sectional view of a piezoelectric micromachined ultrasonic transducer provided by this application in two different directions.

[0049] Figures 8a - 8b It is a cross-sectional view of a piezoelectric micromachined ultrasonic transducer provided by this application in two different directions.

[0050] Figures 9a - 9b It is a cross-sectional view of a piezoelectric micromachined ultrasonic transducer provided by this application in two different directions.

[0051] Figure 10a It is a schematic diagram of the outer surface of the flexible film layer of a piezoelectric micromachined ultrasonic transducer provided by this application presenting a spherical array.

[0052] Figure 10b It is a schematic diagram of the outer surface of the flexible film layer of a piezoelectric micromachined ultrasonic transducer provided by this application presenting a needle-like array.

[0053] Figure 10cSchematic diagram of the outer surface of the flexible film layer of a piezoelectric micromachined ultrasonic transducer provided by this application being in an irregular shape.

[0054] Figure 10d Schematic diagram of a non-planar structure layer being superimposed on the upper surface of the flexible film layer of a piezoelectric micromachined ultrasonic transducer provided by this application.

[0055] Figure 11 Schematic flow diagram of a manufacturing method of a piezoelectric micromachined ultrasonic transducer provided by this application.

[0056] Figure 12 Schematic diagram of the structure of a flexible film layer provided by this application.

[0057] Figure 13 For Figure 12 Top view of the overall structure formed after the flexible film layer in is bonded to the surface of the PMUT wafer shown in Figure 1.

[0058] Figure 14a Schematic diagram of a method for bonding / fitting a flexible film layer to the surface film layer of a PMUT provided by this application.

[0059] Figure 14b Schematic diagram of a method for bonding / fitting a flexible film layer to the surface film layer of a PMUT provided by this application. Detailed implementation mode

[0060] Next, the technical solutions in the embodiments of this application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of this application. Obviously, the described embodiments are only a part of the embodiments of this application, rather than all the embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of this application.

[0061] Referring to the following description and the accompanying drawings, specific implementation modes of this application are disclosed in detail, indicating the ways in which the principles of this application can be adopted. It should be understood that the implementation modes of this application are not limited thereby. Within the spirit and terms of the appended claims, the implementation modes of this application include many changes, modifications, and equivalents.

[0062] Features described and / or illustrated for one implementation mode can be used in the same or similar manner in one or more other implementation modes, combined with the features in other implementation modes, or replace the features in other implementation modes.

[0063] It should be emphasized that the term "including / containing" when used herein refers to the presence of features, whole parts, steps, or components, but does not exclude the presence or addition of one or more other features, whole parts, steps, or components.

[0064] To solve at least one of the above problems existing in the prior art, in a first aspect, the present application provides a piezoelectric micromachined ultrasonic transducer. As Figures 2a - 2c shown, a piezoelectric micromachined ultrasonic transducer 002 provided by the present application includes a substrate 100, a vibrating membrane layer 200, and a flexible membrane layer 300 that are sequentially stacked; wherein, the flexible membrane layer 300 is integrally connected to the surface membrane layer (support layer 240) of the vibrating membrane layer 200 in a solid state by chemical bonding, and the surface membrane layer is the outermost thin film structure of the vibrating membrane layer 200 facing away from the substrate 100 (not limited to the support layer 240); a first through-opening 301 is pre-formed in the flexible membrane layer 300 in the thickness direction, and a pad 201 for electrical connection with the outside on the vibrating membrane layer 200 leaks out through the first through-opening 301.

[0065] Among them, the flexible membrane layer 300 has good flexibility and deformability, and can achieve gapless fitting with the surface membrane layer with various surface topographies (flat surface, curved surface, uneven surface, etc.). The material and thickness of the flexible membrane layer 300 can be designed according to requirements. The first through-opening 301 can be formed when the flexible membrane layer 300 is cast by a mold, or can be formed by many economical and effective methods such as laser cutting and mechanical cutting after the overall flexible membrane layer 300 is formed; the first through-opening 301 pre-formed on the flexible membrane layer 300 exposes the electrical connection pads 201 on the surface of the PMUT, facilitating subsequent electrical connection. Specifically, the PMUT needs to be electrically interconnected with an external circuit such as a PCB. Therefore, in the PMUT stacked structure, the top electrode 230 and the bottom electrode 210 will be connected to the external circuit through the pad 201. When forming the flexible membrane layer 300, the pad 201 needs to be exposed so that the pad 201 can be connected to the external circuit by means such as wire bonding. The matching / coupling layer grown by chemical vapor deposition will cover the entire surface of the PMUT. Extra means such as etching are required to remove the matching / coupling layer material on the surface of the pad 201, or the opening is made on the back, increasing the manufacturing difficulty and cost. In the embodiment of the present application, the first through-opening 301 is pre-formed on the flexible membrane layer 300, and then the flexible membrane layer 300 containing the first through-opening 301 is bonded / fitted to the surface membrane layer of the PMUT, so that the surface of the pad 201 is naturally exposed, and no other etching means are required to open the pad 201, greatly reducing the manufacturing difficulty and cost.

[0066] For the piezoelectric micromachined ultrasonic transducer 002 provided by the present application, the flexible membrane layer 300 is integrally connected to the surface membrane layer of the vibrating membrane layer in a solid state by chemical bonding, and a first through-opening 301 for leaking out the pad 201 is pre-formed in the flexible membrane layer 300 in the thickness direction. Therefore, the pad 201 for electrical connection with the outside on the vibrating membrane layer 200 will not be blocked.

[0067] As Figure 2b shown, in some embodiments, the material properties of the flexible film layer 300 match those of the surface film layer (support layer 240), enabling the flexible film layer 300 to chemically bond with the surface film layer (support layer 240), thereby ensuring that the bonding interface between the flexible film layer 300 and the surface film layer (support layer 240) has a sufficiently high bonding strength, and the PMUT maintains reliable performance during long-term use. However, in other embodiments, a surface matching layer may also be provided on the side of the surface film layer facing away from the substrate 100. In this case, it is required that the material properties of the surface matching layer match those of the flexible film layer 300, without necessarily requiring the material properties of the surface film layer to match those of the flexible film layer 300. The surface film layer and the surface matching layer can be two materials, that is to say, the surface film layer and the surface matching layer are two film layers, which can be grown by chemical vapor deposition respectively to obtain a uniform, high-quality, and dense thin film.

[0068] In some embodiments, when the entire flexible film layer 300 is connected to the surface film layer of the vibrating film layer 200 in a solid state by chemical bonding, the surface film layer can be SiO2, Si3N4, or a Si-based film layer, and the flexible film layer 300 can correspondingly be a silicone-based film layer, such as PDMS and its composites.

[0069] In some embodiments, when chemically bonding between the flexible film layer 300 and the surface film layer, the bonding surface between the flexible film layer 300 and the surface film layer is activated by plasma. Specifically, during operation, the bonding surface of the flexible film layer 300 and the surface film layer can be activated by UV light, oxygen plasma, etc. The activated surface is chemically bonded to achieve long-term reliable bonding. For example, after the surface of a Si, SiO2, or Si3N4 surface film layer is activated by O2 plasma, -OH is formed on the surface. After the silicone flexible film layer 300 is activated by O2 plasma, -OH can also be formed on the surface. An -O- chemical bond can be formed between -OH and -OH, enabling the surface film layer and the flexible film layer 300 to be bonded together by chemical bonds, ensuring that the performance of the PMUT vibrating film layer remains stable during long-term vibration.

[0070] In some embodiments, the surface film layer and the flexible film layer 300 can be grown by chemical vapor deposition respectively. In this case, after the flexible film layer 300 is grown into a solid film layer by chemical vapor deposition, it needs to be attached to the surface of the surface film layer and chemically bonded to the surface film layer.

[0071] As Figures 2b - 2cAs shown, in some embodiments, the vibrating membrane layer 200 includes a bottom electrode 210, a piezoelectric thin film layer 220, a top electrode 230, and a support layer 240 that are sequentially stacked; wherein, the bottom electrode 210 is connected to the substrate 100, and the support layer 240 is the surface film layer of the vibrating membrane layer 200. As Figures 3a - 3b shown, in some embodiments, the surface film layer 250 may also be a separate layer structure connected to the support layer 240.

[0072] As Figure 4a and Figure 4b shown, in some embodiments, the vibrating membrane layer 200 includes a support layer 240, a bottom electrode 210, a piezoelectric thin film layer 220, a top electrode 230, and a surface film layer 260 that are sequentially stacked; wherein, the support layer 240 is connected to the substrate 100. At this time, the surface film layer 250 is a separate layer structure.

[0073] It should be noted that the surface film layer of the vibrating membrane layer 200 is not limited to the support layer 240 or a separate layer structure pointed out in the above embodiments, and the surface film layer of the vibrating membrane layer 200 is determined according to the actual PMUT structure.

[0074] In any of the above embodiments, the function of the support layer 240 is to offset the mass center of the piezoelectric micromachined ultrasonic transducer 002 from the central axis of the piezoelectric thin film layer 220, so as to realize the bending vibration of the PMUT vibrating membrane layer 200.

[0075] As Figures 2a - 2c shown, in some embodiments, the vibrating membrane layer 200 may be a relaxed vibrating membrane layer structure with a gap 202 provided in the thickness direction, or a non-relaxed vibrating membrane layer structure without the gap 202. When the vibrating membrane layer 200 is a relaxed vibrating membrane layer structure with a gap 202 provided in the thickness direction, as Figure 2b shown, the flexible membrane layer 300 may completely cover the gap 202 on the vibrating membrane layer 200. Specifically, as Figures 2a - 2c shown, the relaxed PMUT includes a substrate 100, a cavity 110, a bottom electrode 210, a piezoelectric thin film layer 220, a top electrode 230, and a support layer 240, wherein the cavity 110 provides space for the PMUT vibration, and the support layer 240 offsets the mass center of the PMUT from the central axis of the piezoelectric thin film layer 220, so as to realize the bending vibration of the PMUT vibrating membrane structure.

[0076] Compared with the structure in which the PMUT vibrating membrane layer is completely clamped at the cavity edge, Figures 2a - 2c the PMUT in Figures 2a - 2bThe shown gap 202 can significantly reduce the constraint of the vibration film layer 200 by the substrate 100, enabling the vibration film layer 200 to obtain a larger vibration displacement, sound pressure, and ultrasonic emission and reception sensitivity, significantly improving the acoustic performance of the PMUT. Such a vibration film layer 200 can be called a relaxed vibration film layer structure.

[0077] However, as Figure 2b shown, the release of the edge part of the vibration film layer 200 causes the PMUT cavity 110 to be directly connected to the external environment through the gap 202, which hinders the application of the PMUT in many environments, especially in liquid environments, fluid environments, and even high-pressure gas environments. Sealing the edge-released PMUT with the flexible film layer 300 to effectively isolate the cavity 110 from the external environment is an effective means to maintain the intrinsic performance of the PMUT and improve the ultrasonic sensitivity and performance of the relaxed PMUT.

[0078] In addition, due to the stacked structure of the PMUT, including the patterned bottom electrode 210, piezoelectric thin film layer 220, top electrode 230, support layer 240, etc., the surface of the surface film layer may not be flat. The flexible film layer 300 needs to be effectively and closely attached to all regions of the surface film layer to ensure that there is no gap between the flexible film layer 300 and the surface film layer, and to avoid the obstruction of ultrasonic wave propagation caused by the existence of air bubbles, thereby reducing the emission and reception performance of the PMUT. Therefore, the flexibility and deformability of the flexible film layer 300 enable it to closely adhere to the uneven surface film layer.

[0079] As Figure 2b shown, in some embodiments, when observed from a direction perpendicular to the substrate 100, the gap 202 is vertically arranged on the vibration film layer 200, and the gap 202 penetrates the vibration film layer 200 and is connected to the cavity 110. In other embodiments, when observed from a direction perpendicular to the substrate, the gap 202 can be vertically arranged on a part of the film layer of the vibration film layer 200 without penetrating the vibration film layer 200, and one end of the gap 202 facing away from the cavity 110 is connected to the external environment. For example, the gap 202 is formed on the support layer 240, top electrode 230, piezoelectric thin film layer 220, etc. At this time, the gap 202.

[0080] As Figures 2a - 2b shown, in some embodiments, when observed from a direction perpendicular to the substrate 100, the gap 202 straddles the junction of the cavity 110 and the substrate 100.

[0081] As Figures 2a - 2b shown, in some embodiments, when observed from a direction perpendicular to the substrate 100, when the gap 202 straddles the junction of the cavity 110 and the substrate 100, and the gap 202 is formed along the junction line of the cavity 110 and the substrate 100, the gap 202 provided on the vibration film layer 200 can be symmetric about the axis of the vibration film layer 200.

[0082] As Figures 5a - 5c shown, in some embodiments, when observed from a direction perpendicular to the substrate 100, at least one void 202 is formed on the vibrating membrane layer 200. Each void 202 is formed along the diameter of the vibrating membrane layer 200, and each void 202 straddles the junction of the cavity 110 and the substrate 100. When the number of voids 202 is two or more, each void 202 divides the vibrating membrane layer 200 into a petal-like shape. Specifically, different from the void 202 shown in Figure 2a , Figures 5a - 5c the void 202 is not formed at the boundary position between the substrate 100 and the cavity 130, but is formed along the diameter of the vibrating membrane layer 200, making the vibrating membrane layer 200 no longer integral, but instead forming multiple vibrating units similar to petals; the formation scheme of the flexible membrane layer 300 proposed in this application does not impose any restrictions on the size of the void 202, and has good universality.

[0083] As Figures 6a - 6b shown, in some embodiments, the void 202 is completely located inside the boundary of the cavity 110. At this time, if the junction line between the cavity 110 and the substrate 100 is circular as shown in Figure 2a , the number of voids 202 can be at least two, and each void 202 is an arc parallel to the junction line between the cavity 110 and the substrate 100; in other words, at this time, the shape of the void 202 can refer to the shape of the void 202 in Figure 2a , and the position of the void 202 is completely moved inside the boundary of the cavity 110 compared to the position of the void 202 in Figure 2a .

[0084] In some embodiments, the thickness of the flexible membrane layer 300 is between nanometers and millimeters. Specifically, the selection of the thickness of the flexible membrane layer 300 has a very large free space, and the thickness can be freely changed between nanometers and millimeters. The final thickness of the flexible membrane layer 300 is determined by the ultrasonic use scenario and requirements. Compared with the gas-phase deposition scheme for obtaining a matching / coupling layer, the thickness operation degree of freedom of the flexible membrane layer 300 proposed in this application is stronger.

[0085] As Figures 6a - 6b , Figures 7a - 7b shown, in some embodiments, a cavity 110 is provided on the substrate 100, and the portion of the vibrating membrane layer 200 opposite to the cavity 110 is in a curved surface form. Specifically, compared with the PMUT in which the vibrating membrane layer 200 is in a planar form in the foregoing embodiments, the curved vibrating membrane layer 200 structure enables the PMUT to exhibit better ultrasonic emission and reception sensitivity. In addition, as shown in Figure 6b and Figure 7b , releasing the bound boundary portion of the PMUT vibrating membrane layer 200 will further improve the acoustic performance of the PMUT.

[0086] As Figures 6a - 6b 、 Figures 7a - 7b shown, in some embodiments, when the portion of the vibrating membrane layer 200 facing the cavity 110 is in a curved surface form, after the flexible membrane layer 300 is integrally connected to the surface membrane layer of the vibrating membrane layer 200 in a solid state by chemical bonding, the surface of the flexible membrane layer 300 facing away from the vibrating membrane layer 200 is flat. Specifically, the vibrating membrane layer 200 of the PMUT itself is usually rigid and has a curved surface structure with relatively high rigidity, which is not conducive to the PMUT device being closely attached to the object to be measured, resulting in a gap between the device and the object to be measured and causing attenuation of the acoustic signal. It is necessary to fill the height difference of this part. However, it is difficult to fill the height difference of the rigid curved surface by depositing the matching / coupling layer in a gas phase manner. By bonding the flexible membrane layer 300 (matching / coupling layer) to the surface of the PMUT device proposed in this application, when the height of the curved surface and the thickness of the matching layer are appropriate, a PMUT device with a flat surface as shown in Figures 6a - 6b 、 Figures 7a - 7b can be formed to avoid the limitation of the rigid curved surface vibrating membrane layer on the usability of the sensor. As Figures 6a - 6b and Figures 7a - 7b shown, in some embodiments, the portion of the vibrating membrane layer 200 facing the cavity 110 bends away from the cavity 110.

[0087] As Figures 8a - 8b shown, in some embodiments, the portion of the vibrating membrane layer 200 facing the cavity 110 bends towards the cavity 110.

[0088] As Figures 6a - 6b 、 Figures 7a - 7b and Figures 8a - 8b shown, in some embodiments, the cavity 110 provided on the substrate 100 has an opening, that is to say, the cavity 110 only occupies a part of the substrate 100 area and does not penetrate the entire substrate 100; the opening of the cavity 110 faces the vibrating membrane layer 200, and the cavity 110 can be obtained by a sacrificial layer process.

[0089] As Figure 9a and Figure 9b shown, in some embodiments, the cavity 110 provided on the substrate 100 penetrates the substrate 100, and the cavity 110 can be obtained by a back etching process.

[0090] In addition, when there are uneven structures on the surface of the object to be measured, the surface of the matching / coupling layer is preferably in an uneven structure matching the surface topography of the object to be measured, so that the PMUT can be completely attached to the object to be measured, increasing the acoustic propagation efficiency and obtaining an ultrasonic signal with a high signal-to-noise ratio.

[0091] Specifically, as Figures 10a - 10cAs shown, in some embodiments, one side of the flexible film layer 300 facing away from the surface film layer includes a non-planar structure 310 for physically contacting the surface of the object to be measured. As Figure 10d As shown, in some other embodiments, a non-planar structure layer 400 is connected to one side of the flexible film layer 300 facing away from the surface film layer. One side of the non-planar structure layer 400 facing away from the flexible film layer 300 includes a non-planar structure 410 for physically contacting the surface of the object to be measured.

[0092] As Figures 10a - 10d As shown, in some embodiments, the non-planar structure 310 / 410 is in a spherical array, a needle-like array or an irregular shape. Specifically, as Figures 10a - 10c As shown, the surface of the flexible film layer 300 facing away from the surface film layer can be a non-planar structure, for example, including various surface structures such as a spherical array, a needle-like array, and / or a non-uniform curved surface. The non-planar structure helps to form better physical contact on the surface of the object to be measured during the use of the PMUT, and obtain excellent ultrasonic measurement performance. In addition, as Figure 10d As shown, a non-planar structure layer 400 can also be added to the surface of the flexible film layer 300, wherein a reliable integral film layer is formed between the flexible film layer 300 (such as silicone) and the non-planar structure layer 400 (such as a silicone composite material) through chemical bonding to ensure the long-term reliability of the PMUT during use. Figures 10a - 10d The matching / coupling layer structure shown cannot be realized by traditional methods such as chemical vapor deposition and liquid casting. The present application provides an effective solution to realize this structure.

[0093] According to the second aspect of the embodiments of the present application, the present application also provides a manufacturing method of a piezoelectric micromachined ultrasonic transducer. As Figure 11 As shown, a manufacturing method of a piezoelectric micromachined ultrasonic transducer provided by the present application includes:

[0094] S101. Integrally attach a flexible film layer having a first through-opening in the thickness direction to the surface of a piezoelectric micromachined ultrasonic transducer wafer, and align the first through-opening with the pads on the piezoelectric micromachined ultrasonic transducer wafer so that the pads leak out through the first through-opening;

[0095] In step S101, as Figure 12 As shown, a first through-opening 301 is pre-formed in the thickness direction of the flexible film layer 300; as Figure 13As shown, when the flexible film layer 300 is integrally bonded to the surface of the piezoelectric micromachined ultrasonic transducer wafer 001, the first through-opening 301 is aligned with the pad 201 on the piezoelectric micromachined ultrasonic transducer wafer 001. When a second through-opening 302 is also pre-formed in the thickness direction of the flexible film layer 300, when the flexible film layer 300 is integrally bonded to the surface of the piezoelectric micromachined ultrasonic transducer wafer 001, the second through-opening 302 is also aligned with the boundary position (dicing lane) of the piezoelectric micromachined ultrasonic transducer 600 on the piezoelectric micromachined ultrasonic transducer wafer 001.

[0096] S102. Bond the flexible film layer to the surface of the piezoelectric micromachined ultrasonic transducer wafer by using a chemical bonding technique;

[0097] In step S102, as Figure 14a shown, in some embodiments, the flexible film layer 300 can be bonded to the surface film layer of the vibration film layer 200 by a way of approaching uniformly as a whole. As Figure 14b shown, in other embodiments, the flexible film layer 300 can be fixed by first contacting a part of the surface film layer of the vibration film layer 200, and then further increasing the contact area with the surface film layer until it is completely bonded to the surface film layer to realize the connection with the surface film layer. Of course, the flexible film layer 300 as a whole can also be bonded to the surface film layer of the vibration film layer 200 by other means, and the embodiments of the present application do not limit this.

[0098] When the flexible film layer 300 is bonded to the surface film layer of the vibration film layer 200 by the method shown in Figure 14a or Figure 14b shown, during the bonding operation, it can be gently pressed under pressure to make the flexible film layer 300 closely bonded to the surface film layer, avoid the existence of air bubbles at the interface, thereby reducing the acoustic loss and enabling the PMUT to maintain excellent acoustic performance.

[0099] The flexible film layer, as a matching / coupling film layer, realizes intermolecular interconnection with the surface of the PMUT vibration thin film through chemical bonding, ensuring the bonding strength and reliability. The flexible film layer and the PMUT surface need to be seamlessly and reliably bonded, and the flexible film layer will not separate from the surface of the PMUT vibration thin film during operation.

[0100] S103. Split the overall structure formed by bonding the flexible film layer to the surface of the piezoelectric micromachined ultrasonic transducer wafer into independent piezoelectric micromachined ultrasonic transducers.

[0101] In step S103, as Figure 13As shown, in the dicing stage, at the junction of every two piezoelectric micromachined ultrasonic transducers 600 (PMUT units) on the piezoelectric micromachined ultrasonic transducer wafer 001, the piezoelectric micromachined ultrasonic transducer wafer 001 is diced into independent PMUT units. For example, using a cutting technique, the thicker colloidal film layer and the substrate film layer can be split. After being diced into independent PMUT units, the pads of the PMUT can be electrically connected to the signal source or the receiving end directly through wire bonding, ball bonding and other solutions.

[0102] The manufacturing method of the piezoelectric micromachined ultrasonic transducer provided by the embodiment of the present application can realize the wafer-level manufacturing of the piezoelectric micromachined ultrasonic transducer with a flexible film layer. Since the flexible film layer is integrally bonded to the surface of the piezoelectric micromachined ultrasonic transducer wafer in a solid form, it has requirements only for the surface film material of the vibration film layer of the piezoelectric micromachined ultrasonic transducer on the piezoelectric micromachined ultrasonic transducer wafer, and there is no limitation on the structure of the vibration film layer of the piezoelectric micromachined ultrasonic transducer.

[0103] According to the third aspect of the embodiment of the present application, the present application also provides an electrical product, including the piezoelectric micromachined ultrasonic transducer described in any of the above embodiments.

[0104] In the structure of this electrical product, the performance of the piezoelectric micromachined ultrasonic transducer is mainly utilized, and thus a high-performance electrical product can be realized. The structure of the piezoelectric micromachined ultrasonic transducer can refer to the embodiment of the first aspect of the present application, and will not be elaborated here.

[0105] It should be noted that in this text, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, such that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising a..." does not exclude the presence of additional identical elements in the process, method, article or device comprising the said element. The orientation or positional relationship indicated by terms such as "above", "below", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation of the present application. Unless otherwise clearly specified and defined, the terms "mounted", "connected" and "coupled" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, and can be the internal communication of two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific circumstances.

[0106] The various embodiments in this specification are described in a progressive manner. For the parts that are the same or similar among the various embodiments, reference can be made to each other. Each embodiment focuses on the differences from other embodiments. In the description of this specification, the description with reference to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the embodiments of this specification. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0107] In this application, specific embodiments are used to elaborate on the principles and implementation manners of the application. The description of the above embodiments is only used to help understand the method and its core idea of the application; at the same time, for those of ordinary skill in the art, according to the idea of the application, there will be changes in the specific implementation manners and application scopes. In summary, the content of this specification should not be construed as a limitation to the application.

Claims

1. A piezoelectric micromachined ultrasonic transducer, characterized in that, It includes a substrate, a vibrating film layer, and a flexible film layer that are stacked in sequence; wherein, The flexible film layer is integrally connected to the surface film layer of the vibrating film layer in a solid state by chemical bonding, and the surface film layer is the outermost thin film structure of the vibrating film layer facing away from the substrate; A first through-opening is pre-formed in the flexible film layer in the thickness direction, and the pads for electrical connection with the outside on the vibrating film layer leak out through the first through-opening.

2. The piezoelectric micromachined ultrasonic transducer according to claim 1, wherein The surface film layer is a SiO2, Si3N4, or Si-based film layer, and the flexible film layer is a silica gel-based film layer.

3. The piezoelectric micromachined ultrasonic transducer according to claim 1, characterized in that, The vibrating film layer includes a bottom electrode, a piezoelectric thin film layer, a top electrode, and a support layer that are stacked in sequence; wherein, the bottom electrode is connected to the substrate, and the support layer is the surface film layer of the vibrating film layer.

4. The piezoelectric micromachined ultrasonic transducer according to claim 1, characterized in that, The vibrating film layer includes a support layer, a bottom electrode, a piezoelectric thin film layer, a top electrode, and a surface film layer that are stacked in sequence; wherein, the support layer is connected to the substrate.

5. The piezoelectric micromachined ultrasonic transducer according to claim 1, wherein The vibrating film layer is a relaxed vibrating film layer structure with voids provided in the thickness direction.

6. The piezoelectric micromachined ultrasonic transducer according to claim 5, wherein, The flexible film layer completely covers the voids on the vibrating film layer.

7. The piezoelectric micromachined ultrasonic transducer according to claim 1, characterized in that, The thickness of the flexible film layer is between nanometers and millimeters.

8. The piezoelectric micromachined ultrasonic transducer according to claim 1, wherein A cavity is provided on the substrate, and the part of the vibrating film layer opposite to the cavity is in a curved surface form.

9. The piezoelectric micromachined ultrasonic transducer according to claim 8, characterized in that, The part of the vibrating film layer opposite to the cavity bends away from the cavity; or The part of the vibrating film layer opposite to the cavity bends towards the cavity.

10. The piezoelectric micromachined ultrasonic transducer according to claim 8, wherein After the flexible film layer is integrally connected to the surface film layer of the vibrating film layer in a solid state by chemical bonding, the surface of the flexible film layer facing away from the vibrating film layer is flat.

11. The piezoelectric micromachined ultrasonic transducer according to claim 1, characterized in that, One side of the flexible film layer facing away from the surface film layer includes a non-planar structure for physical contact with the surface of the object to be measured.

12. The piezoelectric micromachined ultrasonic transducer according to claim 1 or 10, wherein A non-planar structure layer is connected to one side of the flexible film layer facing away from the surface film layer, and one side of the non-planar structure layer facing away from the flexible film layer includes a non-planar structure for physical contact with the surface of the object to be measured.

13. The piezoelectric micromachined ultrasonic transducer according to claim 11, characterized in that, The non-planar structure is in a spherical array, a needle-like array, or an irregular shape.

14. The piezoelectric micromachined ultrasonic transducer according to claim 8 or 9, characterized in that, The cavity provided on the substrate has an opening, the opening of the cavity faces the vibrating film layer, and the cavity is obtained by a sacrificial layer process; or The cavity provided on the substrate penetrates the substrate, and the cavity is obtained by a back etching process.

15. A manufacturing method of a piezoelectric micromachined ultrasonic transducer, characterized in that, It includes: Integrally attaching a flexible film layer with a first through-opening in the thickness direction to the surface of a piezoelectric micromachined ultrasonic transducer wafer, and aligning the first through-opening with the pads on the piezoelectric micromachined ultrasonic transducer wafer so that the pads leak out through the first through-opening; Bonding the flexible film layer to the surface of the piezoelectric micromachined ultrasonic transducer wafer together using a chemical bonding technique; Splitting the overall structure formed after bonding the flexible film layer to the surface of the piezoelectric micromachined ultrasonic transducer wafer into independent piezoelectric micromachined ultrasonic transducers.

16. The method according to claim 15, wherein A second through-opening is also pre-formed in the thickness direction of the flexible film layer; When integrally attaching the flexible film layer to the surface of the piezoelectric micromachined ultrasonic transducer wafer, the second through-opening is also aligned with the boundary position of the piezoelectric micromachined ultrasonic transducer on the piezoelectric micromachined ultrasonic transducer wafer.

17. An electrical product, characterized in that, A piezoelectric micromachined ultrasonic transducer comprising any one of the piezoelectric micromachined ultrasonic transducers described in claims 1 to 14 above.

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