A piezoelectric micromachined ultrasonic transducer structure and a preparation method thereof

Abstract

The present invention provides a piezoelectric micromachined ultrasonic transducer structure and a preparation method thereof, relating to the technical field of semiconductor devices. The piezoelectric material layer includes N groups of alternately stacked piezoelectric film layers stacked in sequence in a first direction, where N≥2 and N is a positive integer. The alternately stacked piezoelectric film layers include an AlN layer and an AlGaN layer stacked in sequence in the first direction. AlN and AlGaN are the same type of semiconductor material, with a relatively small lattice mismatch and it is easy to form a steep heterointerface. The AlN layer serves as a barrier layer and the AlGaN layer serves as a well layer. The N groups of alternately stacked piezoelectric film layers have excellent quantum effects, resulting in the localization of the carrier wave function in one-dimensional direction. The movement of carriers in the normal direction of the thin layer will be restricted and they can only move freely within the thin layer plane, which can significantly improve the piezoelectric coefficient and electromechanical coupling coefficient of the piezoelectric material layer, and further improve the sensitivity of the piezoelectric micromachined ultrasonic transducer structure.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor devices, and more particularly, to a piezoelectric microelectromechanical ultrasonic transducer structure and a preparation method thereof. Background Art

[0002] Ultrasonic imaging technology has developed relatively maturely and is widely used in the medical field. An important component of medical ultrasonic equipment is the ultrasonic transducer (abbreviated as UT), which is a transducer element that can be used to transmit and receive ultrasonic waves. When the UT is in the transmit mode, the electrical potential energy is converted into the vibration of the transducer through electrostatic force or the inverse piezoelectric effect, thereby generating a radiation sound pressure; in the receive mode, the sound pressure acts on the surface of the transducer to cause it to vibrate, and the transducer then converts the vibration into a voltage. Currently, medical ultrasonic equipment mainly uses capacitive micro-machined ultrasonic transducers (CMUT) in capacitive MEMS (Micro Electromechanical System) ultrasonic transducers, resulting in disadvantages such as large volume of the ultrasonic inspection probe, low detection accuracy, poor sensitivity, large energy loss, and great influence by air.

[0003] In recent years, piezoelectric microelectromechanical ultrasonic transducers (PMUT) have gradually attracted people's attention as a new type of MEMS device. This technology can vibrate the piezoelectric film through the piezoelectric effect of the piezoelectric material, so that ultrasonic signals can be spontaneously transmitted and received, and has advantages such as high emission efficiency, high sensitivity, low internal resistance, and no need for high-voltage drive. In addition, PMUT has advantages such as a simple device structure, high compatibility with standard MEMS manufacturing processes, low manufacturing cost, high sensitivity, and high signal-to-noise ratio, and is suitable for large-scale applications. Commercial PMUT usually uses aluminum nitride (chemical formula: AlN) and lead zirconate titanate (chemical formula: PZT) as piezoelectric materials; the piezoelectric material is usually formed on a silicon or SOI (Silicon-On-Insulator) substrate, and this technical route is compatible with the mature CMOS (Complementary metal-oxide-semiconductor) process.

[0004] However, the sensitivity of the existing PMUT structure is relatively low. The core reason is that the piezoelectric coefficients and electromechanical coupling coefficients of AlN and PZT piezoelectric materials are relatively low. Therefore, how to improve the piezoelectric coefficients and electromechanical coupling coefficients of piezoelectric materials is the key to improving the sensitivity of the PMUT structure. Summary of the Invention

[0005] In view of this, to solve the above problems, the present invention provides a piezoelectric micromachined ultrasonic transducer structure and a preparation method thereof. The technical solutions are as follows:

[0006] A piezoelectric micromachined ultrasonic transducer structure, the piezoelectric micromachined ultrasonic transducer structure includes:

[0007] A substrate;

[0008] In a first direction, an oxide film layer, a first metal layer, a piezoelectric material layer, and a second metal layer are sequentially located on one side of the substrate. The first direction is perpendicular to the plane where the substrate is located and points from the substrate to the piezoelectric material layer;

[0009] Wherein, the piezoelectric material layer includes N groups of alternately stacked piezoelectric film layers stacked in the first direction, N≥2, and N is a positive integer. The alternately stacked piezoelectric film layers include an AlN layer and an AlGaN layer stacked in the first direction.

[0010] Preferably, in the above piezoelectric micromachined ultrasonic transducer structure, the thickness range of the N groups of alternately stacked piezoelectric film layers in the first direction is 500nm - 1000nm.

[0011] Preferably, in the above piezoelectric micromachined ultrasonic transducer structure, the thickness range of the alternately stacked piezoelectric film layers in the first direction is 8nm - 40nm.

[0012] Preferably, in the above piezoelectric micromachined ultrasonic transducer structure, the thickness range of the AlN layer in the first direction is 3nm - 20nm;

[0013] The thickness range of the AlGaN layer in the first direction is 5nm - 20nm.

[0014] Preferably, in the above piezoelectric micromachined ultrasonic transducer structure, the AlN layer is doped with Ga element.

[0015] Preferably, in the above piezoelectric micromachined ultrasonic transducer structure, the molar fraction of Al in the AlN layer is x, and the molar fraction of Ga is 1 - x;

[0016] Wherein, 0≤x≤30%.

[0017] Preferably, in the above piezoelectric micromachined ultrasonic transducer structure, the oxide film layer includes M sub-oxide film layers stacked in the first direction, M≥2, and M is a positive integer.

[0018] Preferably, in the above piezoelectric micromachined ultrasonic transducer structure, the piezoelectric micromachined ultrasonic transducer structure further includes:

[0019] a groove penetrating through the second metal layer and the piezoelectric material layer, the groove exposing a part of the first metal layer;

[0020] a first electrode located on the first metal layer;

[0021] a second electrode located on the second metal layer.

[0022] Preferably, in the above piezoelectric micromachined ultrasonic transducer structure, the substrate is a Si substrate or an SOI substrate.

[0023] The present application also provides a method for manufacturing a piezoelectric micromachined ultrasonic transducer structure, the method for manufacturing the piezoelectric micromachined ultrasonic transducer structure including:

[0024] providing a substrate;

[0025] In a first direction, an oxide film layer, a first metal layer, a piezoelectric material layer, and a second metal layer are sequentially formed on one side of the substrate, the first direction being perpendicular to the plane where the substrate is located and pointing from the substrate to the piezoelectric material layer; wherein, the piezoelectric material layer includes N groups of alternately stacked piezoelectric film layers sequentially stacked in the first direction, N≥2 and N is a positive integer, and the alternately stacked piezoelectric film layers include an AlN layer and an AlGaN layer sequentially stacked in the first direction.

[0026] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0027] The present invention provides a piezoelectric micromachined ultrasonic transducer structure and a preparation method thereof. The piezoelectric micromachined ultrasonic transducer structure includes: a substrate; in a first direction, an oxide film layer, a first metal layer, a piezoelectric material layer, and a second metal layer are sequentially located on one side of the substrate. The first direction is perpendicular to the plane where the substrate is located and points from the substrate to the piezoelectric material layer. Among them, the piezoelectric material layer includes N groups of alternately stacked piezoelectric film layers stacked in sequence in the first direction, N≥2 and N is a positive integer. The alternately stacked piezoelectric film layers include an AlN layer and an AlGaN layer stacked in sequence in the first direction. Since AlN and AlGaN are the same type of semiconductor material with a small lattice mismatch and it is easy to form a steep heterojunction interface, the AlN layer serves as a barrier layer and the AlGaN layer serves as a quantum well layer. The N groups of alternately stacked piezoelectric film layers stacked in sequence in the first direction have excellent quantum effects, resulting in the localization of the carrier wave function in one-dimensional direction. The movement of carriers in the normal direction of the thin layer will be restricted and they can only move freely within the plane of the thin layer. Compared with the scheme of using a single-layer AlN layer as the piezoelectric material layer, the piezoelectric coefficient and the electromechanical coupling coefficient of the piezoelectric material layer can be significantly improved, and thus the sensitivity of the piezoelectric micromachined ultrasonic transducer structure can be enhanced. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to the provided drawings without creative efforts.

[0029] Figure 1 FIG. 1 is one of the schematic structural diagrams of a piezoelectric micromachined ultrasonic transducer structure provided by an embodiment of the present invention;

[0030] Figure 2 FIG. 2 is another schematic structural diagram of a piezoelectric micromachined ultrasonic transducer structure provided by an embodiment of the present invention;

[0031] Figure 3 FIG. 3 is yet another schematic structural diagram of a piezoelectric micromachined ultrasonic transducer structure provided by an embodiment of the present invention;

[0032] Figure 4 FIG. 4 is still another schematic structural diagram of a piezoelectric micromachined ultrasonic transducer structure provided by an embodiment of the present invention;

[0033] Figure 5 FIG. 5 is a schematic flow diagram of a preparation method of a piezoelectric micromachined ultrasonic transducer structure provided by an embodiment of the present invention;

[0034] Figures 6 - 13For Figure 5 Partial structural schematic diagram corresponding to the preparation method shown. Specific implementation manners

[0035] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0036] To make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific implementation manners.

[0037] Referring to Figure 1 , Figure 1 is one of the structural schematic diagrams of a piezoelectric micromachined ultrasonic transducer structure provided by an embodiment of the present invention. A piezoelectric micromachined ultrasonic transducer structure provided by an embodiment of the present invention includes: a substrate 11; in the first direction X, an oxide film layer 12, a first metal layer 13, a piezoelectric material layer 14, and a second metal layer 15 are sequentially located on one side of the substrate 11. The first direction X is perpendicular to the plane where the substrate 11 is located and points from the substrate 11 to the piezoelectric material layer 14; wherein, the piezoelectric material layer 14 includes N groups of alternately stacked piezoelectric film layers stacked in sequence in the first direction X, N≥2, and N is a positive integer. The alternately stacked piezoelectric film layers include an AlN layer 141 and an AlGaN layer 142 stacked in sequence in the first direction X.

[0038] Specifically, in the embodiment of the present invention, N groups of alternately stacked piezoelectric film layers stacked in sequence in the first direction X are used as the novel piezoelectric material layer 14. In the N groups of alternately stacked piezoelectric film layers, the piezoelectric AlN layer 141 and the piezoelectric AlGaN layer 142 are alternately stacked. AlN and AlGaN are the same type of semiconductor material, and their lattice mismatch is relatively small, and it is easy to form a steep heterointerface. The AlN layer 141 serves as a barrier layer, and the AlGaN layer 142 serves as a well layer. The N groups of alternately stacked piezoelectric film layers stacked in sequence in the first direction X have excellent quantum effects, resulting in the localization of the carrier wave function in one-dimensional direction. The movement of carriers in the normal direction of the thin layer will be restricted and can only move freely in the plane of the thin layer. Compared with the solution of using a single-layer AlN layer as the piezoelectric material layer 14, the piezoelectric coefficient and the electromechanical coupling coefficient of the piezoelectric material layer 14 can be significantly improved by means of the quantum effect. Furthermore, the sensitivity of the piezoelectric micromachined ultrasonic transducer structure can be improved, and the electrical signal output of the piezoelectric micromachined ultrasonic transducer structure will be enhanced under the action of ultrasonic signals.

[0039] Optionally, in another embodiment of the present invention, the thickness of the N groups of alternately stacked piezoelectric film layers in the first direction X ranges from 500 nm to 1000 nm.

[0040] That is to say, in the embodiment of the present invention, the total thickness of the piezoelectric material layer 14 in the first direction X ranges from 500 nm to 1000 nm.

[0041] Optionally, in another embodiment of the present invention, N can range from 25 to 60, and the thickness of the alternately stacked piezoelectric film layers in the first direction X ranges from 8 nm to 40 nm.

[0042] That is to say, in the embodiment of the present invention, the number of periods of the piezoelectric material layer 14 can be from 25 to 60. An adjacent AlN layer 141 and an adjacent AlGaN layer 142 are used as a single period, and the total thickness of a single period in the first direction X ranges from 8 nm to 40 nm.

[0043] Optionally, the thickness of the AlN layer 141 in the first direction X ranges from 3 nm to 20 nm.

[0044] The thickness of the AlGaN layer 142 in the first direction X ranges from 5 nm to 20 nm.

[0045] It should be noted that in some optional embodiments of the present invention, referring to Figure 2 , Figure 2 is the second structural schematic diagram of a piezoelectric micromachined ultrasonic transducer structure provided by the embodiment of the present invention. The piezoelectric material layer 14 includes: K layers of AlN layers 141 stacked in sequence in the first direction X, and AlGaN layers 142 located between adjacent two AlN layers 141, where K≥2 and K is a positive integer. At this time, the purpose of sharing the AlGaN layer 142 can be achieved.

[0046] Optionally, in another embodiment of the present invention, the AlN layer 141 is doped with Ga element, and the molar fraction of Al in the AlN layer 141 is x, and the molar fraction of Ga is 1 - x; wherein, 0≤x≤30%.

[0047] Specifically, in the embodiment of the present invention, by doping the AlN layer 141 with Ga element, the piezoelectric coefficient and the electromechanical coupling coefficient of the AlN layer 141 are improved through the technology of doping Ga element, and further the piezoelectric coefficient and the electromechanical coupling coefficient of the piezoelectric material layer 14 are improved, so that the piezoelectric micromachined ultrasonic transducer structure can achieve higher receiving sensitivity.

[0048] And it is found in the inventive process of the present invention that when x is too large, the quality of the heterointerface between the AlN layer 141 and the AlGaN layer 142 will deteriorate, which is not conducive to the improvement of the piezoelectric coefficient and the electromechanical coupling coefficient of the piezoelectric material layer 14 stacked alternately by N groups. Therefore, in the embodiments of the present invention, 0≤x≤30% is defined.

[0049] Optionally, in another embodiment of the present invention, as Figure 1 and Figure 2 shown, the oxide film layer 12 includes M sub-oxide film layers stacked in sequence in the first direction X, where M≥2 and M is a positive integer.

[0050] Specifically, it is found in the inventive process of the present invention that the piezoelectric micromachined ultrasonic transducer structure in the prior art is to provide only a single-layer oxide film layer and a single-layer piezoelectric material layer on the SOI substrate. The single-layer design will limit the sensitivity and other indicators of the piezoelectric micromachined ultrasonic transducer structure. Therefore, in the embodiments of the present invention, the traditional single-layer piezoelectric material layer is first improved, and N groups of alternately stacked piezoelectric film layers stacked in sequence in the first direction X are used as the new piezoelectric material layer 14. In the N groups of alternately stacked piezoelectric film layers, the AlN layer 141 and the AlGaN layer 142 are alternately stacked. AlN and AlGaN are the same type of semiconductor material, and their lattice mismatch is relatively small, and it is easy to form a steep heterointerface. The AlN layer 141 serves as the barrier layer, and the AlGaN layer 142 serves as the well layer. The N groups of alternately stacked piezoelectric film layers stacked in sequence in the first direction X have excellent quantum effects, resulting in the localization of the carrier wave function in one-dimensional directions. The movement of carriers in the normal direction of the thin layer will be restricted and can only move freely in the plane of the thin layer. Compared with the scheme of using a single-layer AlN layer as the piezoelectric material layer, the piezoelectric coefficient and the electromechanical coupling coefficient of the piezoelectric material layer 14 can be significantly improved by means of the quantum effect, and further the sensitivity of the piezoelectric micromachined ultrasonic transducer structure can be improved, and the electrical signal output of the piezoelectric micromachined ultrasonic transducer structure will be enhanced under the action of ultrasonic signals.

[0051] Secondly, the traditional single-layer oxide film layer is improved, and M sub-oxide film layers stacked in sequence in the first direction X are used as the new oxide film layer 12. This design can not only reduce the leakage current of the piezoelectric micromachined ultrasonic transducer structure, but also improve the receiving sensitivity of the piezoelectric micromachined ultrasonic transducer structure.

[0052] It should be noted that the resonator is used to enhance the interaction between the acoustic wave and the piezoelectric material. Therefore, the M sub-oxide film layers stacked in sequence in the first direction X can also be called resonators.

[0053] Optionally, the substrate 11 includes, but is not limited to, other substrates such as Si substrates or SOI substrates. In the embodiments of the present invention, the Si substrate is taken as the optimal embodiment for elaboration. Forming M sub-oxide film layers stacked in the first direction X directly on the Si substrate has simple process steps and relatively low manufacturing costs.

[0054] It should be noted that theoretically, it is also possible to form M sub-oxide film layers stacked in the first direction X on other types of substrates. However, the lattice mismatch between the oxide film layer 12 and other types of substrates is relatively large, and the interface quality is not very good. Therefore, in the embodiments of the present invention, the Si substrate is taken as the optimal embodiment for elaboration.

[0055] Optionally, in another embodiment of the present invention, as Figure 1 and Figure 2 shown, the oxide film layer includes M sub-oxide film layers stacked in sequence in the first direction X. The material of each oxide film layer is the same, for example, other oxide materials such as SiO2 material or Al2O3 material.

[0056] Optionally, in another embodiment of the present invention, referring to Figure 3 , Figure 3 is the third structural schematic diagram of a piezoelectric micromachined ultrasonic transducer structure provided by the embodiments of the present invention. Referring to Figure 4 , Figure 4 is the fourth structural schematic diagram of a piezoelectric micromachined ultrasonic transducer structure provided by the embodiments of the present invention. The oxide film layer 12 includes a first oxide film layer 121 and a second oxide film layer 122 alternately arranged in sequence in the first direction X.

[0057] The material of the first oxide film layer 121 can be other oxide materials such as SiO2 material or Al2O3 material, and the material of the second oxide film layer 122 can be other oxide materials such as SiO2 material or Al2O3 material. The material of the first oxide film layer 121 is different from that of the second oxide film layer 122.

[0058] It should be noted that the oxide film layer 12 may also include multiple oxide film layers of different materials alternately arranged in sequence in the first direction X, such as three oxide film layers of different materials alternately arranged in sequence in the first direction X, etc.

[0059] Optionally, in another embodiment of the present invention, the total thickness of the oxide film layer 12 provided by the embodiments of the present invention in the first direction X ranges from 50 nm to 400 nm, the number of periods can be from 2 to 10, and the thickness of a single period in the first direction X ranges from 20 nm to 40 nm.

[0060] Optionally, in another embodiment of the present invention, as Figures 1 - 4 shown, the piezoelectric micromachined ultrasonic transducer structure further includes: a groove penetrating through the second metal layer 15 and the piezoelectric material layer 14, and the groove exposes a part of the first metal layer 13.

[0061] A first electrode 16 located on the first metal layer 13.

[0062] A second electrode 17 located on the second metal layer 15.

[0063] Specifically, in the embodiment of the present invention, the design of the groove can form the stepped structure required by the piezoelectric micromachined ultrasonic transducer structure. The materials of the first electrode 16 and the second electrode 17 can be the same or different. Optionally, the materials of the first electrode 16 and the second electrode 17 are both transparent electrode materials.

[0064] As Figures 1 - 4 shown, the side of the substrate 11 facing away from the piezoelectric material layer 14 has a patterned groove, and the patterned groove exposes a part of the oxide film layer 12.

[0065] It can be seen from the above description that in the embodiment of the present invention, the traditional single-layer piezoelectric material layer is first improved, and N groups of alternately stacked piezoelectric film layers are sequentially stacked in the first direction X as the new piezoelectric material layer 14. In the N groups of alternately stacked piezoelectric film layers, the AlN layer 141 and the AlGaN layer 142 are alternately stacked. AlN and AlGaN are the same type of semiconductor material, and their lattice mismatch is relatively small, and it is easy to form a steep heterointerface. The AlN layer 141 serves as a barrier layer, and the AlGaN layer 142 serves as a well layer. The N groups of alternately stacked piezoelectric film layers sequentially stacked in the first direction X have excellent quantum effects, resulting in the localization of the carrier wave function in one-dimensional direction. The movement of the carriers in the normal direction of the thin layer will be restricted and can only move freely in the plane of the thin layer. Compared with the scheme of using a single-layer AlN layer as the piezoelectric material layer, the piezoelectric coefficient and the electromechanical coupling coefficient of the piezoelectric material layer 14 can be significantly improved by means of the quantum effect, and further the sensitivity of the piezoelectric micromachined ultrasonic transducer structure can be improved, and the electrical signal output of the piezoelectric micromachined ultrasonic transducer structure will be enhanced under the action of ultrasonic signals.

[0066] Furthermore, the piezoelectric coefficient and the electromechanical coupling coefficient of the AlN layer 141 can be improved by doping Ga elements in the AlN layer 141, and further the piezoelectric coefficient and the electromechanical coupling coefficient of the piezoelectric material layer 14 can be improved, so that the piezoelectric micromachined ultrasonic transducer structure can achieve higher receiving sensitivity.

[0067] Further, the traditional single-layer oxide film layer is improved, and M sub-oxide film layers stacked in sequence in the first direction X are used as the novel oxide film layer 12. This design can not only reduce the leakage current of the piezoelectric micromachined ultrasonic transducer structure, but also improve the receiving sensitivity of the piezoelectric micromachined ultrasonic transducer structure.

[0068] Generally speaking, compared with the traditional Si-based or SiO-based piezoelectric micromachined ultrasonic transducer structures, the technical solution provided by the embodiments of the present invention contributes to the rapid development of piezoelectric micromachined ultrasonic transducer structures in ultrasonic detection.

[0069] Optionally, based on the above embodiments of the present invention, in another embodiment of the present invention, a preparation method of a piezoelectric micromachined ultrasonic transducer structure is further provided. Refer to Figure 5 , Figure 5 which is a schematic flowchart of a preparation method of a piezoelectric micromachined ultrasonic transducer structure provided by an embodiment of the present invention. The preparation method of a piezoelectric micromachined ultrasonic transducer structure provided by an embodiment of the present invention includes:

[0070] S101: As shown in Figure 6 , provide a substrate 11.

[0071] S102: In the first direction X, an oxide film layer 12, a first metal layer 13, a piezoelectric material layer 14, and a second metal layer 15 are sequentially formed on one side of the substrate 11. The first direction X is perpendicular to the plane where the substrate 11 is located and points from the substrate 11 to the piezoelectric material layer 14. Among them, the piezoelectric material layer 14 includes N groups of alternately stacked piezoelectric film layers stacked in sequence in the first direction X, N≥2 and N is a positive integer. The alternately stacked piezoelectric film layers include an AlN layer 141 and an AlGaN layer 142 stacked in sequence in the first direction X.

[0072] Specifically, as shown in Figure 7 , an oxide film layer 12 is formed on one side of the substrate 11.

[0073] As shown in Figure 8 , a first metal layer 13 is formed on the side of the oxide film layer 12 away from the substrate 11.

[0074] As shown in Figure 9 , a piezoelectric material layer 14 is formed on the side of the first metal layer 13 away from the substrate 11.

[0075] As shown in Figure 10 , a second metal layer 15 is formed on the side of the piezoelectric material layer 14 away from the substrate 11.

[0076] As shown in Figure 11As shown, the second metal layer 15 and the piezoelectric material layer 14 are processed to form a groove penetrating through the second metal layer 15 and the piezoelectric material layer 14, and the groove exposes a part of the first metal layer 13.

[0077] As Figure 12 shown, a first electrode 16 is formed on the surface of the exposed first metal layer 13.

[0078] As Figure 13 shown, a second electrode 17 is formed on the side of the second metal layer 15 away from the substrate 11.

[0079] It should be noted that the first electrode 16 and the second electrode 17 can also be prepared simultaneously in the same process.

[0080] As Figure 1 shown, the substrate 11 is patterned on the side away from the piezoelectric material layer 14 to form a patterned groove, and the patterned groove exposes a part of the oxide film layer 12.

[0081] The above has introduced in detail a piezoelectric micromachined ultrasonic transducer structure and its manufacturing method provided by the present invention. Specific examples are used in this article to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present invention.

[0082] It should be noted that the embodiments in this specification are all described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The same or similar parts among the embodiments can be referred to each other. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the description of the method part.

[0083] It should also be noted that in this article, 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 term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device that includes a series of elements includes not only those elements inherent to the process, method, article or device, but also other elements inherent to these process, method, article or device. Without further limitation, an element defined by the statement "including one..." does not exclude the existence of another identical element in the process, method, article or device that includes the element.

[0084] The foregoing description of the disclosed embodiments enables those skilled in the art to practice or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A piezoelectric micromachined ultrasonic transducer structure, characterized in that, The piezoelectric micromachined ultrasonic transducer structure includes: A substrate; In a first direction, an oxide film layer, a first metal layer, a piezoelectric material layer, and a second metal layer are sequentially located on one side of the substrate. The first direction is perpendicular to the plane of the substrate and points from the substrate to the piezoelectric material layer; Wherein, the oxide film layer includes M sub-oxide film layers stacked in sequence in the first direction, M≥2, and M is a positive integer; The piezoelectric material layer includes N groups of alternately stacked piezoelectric film layers stacked in sequence in the first direction, N≥2, and N is a positive integer. The alternately stacked piezoelectric film layers include an AlN layer and an AlGaN layer stacked in sequence in the first direction, and the surfaces of the AlN layer and the AlGaN layer are in contact with each other.

2. The piezoelectric micromachined ultrasonic transducer structure according to claim 1, wherein The thickness of the N groups of alternately stacked piezoelectric film layers in the first direction ranges from 500 nm to 1000 nm.

3. The piezoelectric micromachined ultrasonic transducer structure according to claim 1, wherein The thickness of the alternately stacked piezoelectric film layers in the first direction ranges from 8 nm to 40 nm.

4. The piezoelectric micromachined ultrasonic transducer structure according to claim 1, characterized in that The thickness of the AlN layer in the first direction ranges from 3 nm to 20 nm; The thickness of the AlGaN layer in the first direction ranges from 5 nm to 20 nm.

5. The piezoelectric micromachined ultrasonic transducer structure according to claim 1, characterized in that, The AlN layer is doped with Ga element.

6. The piezoelectric micromachined ultrasonic transducer structure according to claim 5, wherein, The molar fraction of Al in the AlN layer is x, and the molar fraction of Ga is 1 - x; Wherein, 0≤x≤30%.

7. The piezoelectric micromachined ultrasonic transducer structure according to claim 1, wherein The piezoelectric micromachined ultrasonic transducer structure further includes: A groove penetrating through the second metal layer and the piezoelectric material layer, and the groove exposes a part of the first metal layer; A first electrode located on the first metal layer; A second electrode located on the second metal layer.

8. The piezoelectric micromachined ultrasonic transducer structure according to claim 1, characterized in that The substrate is a Si substrate or an SOI substrate.

9. A preparation method for a piezoelectric micromachined ultrasonic transducer structure, characterized in that, The preparation method of the piezoelectric micromachined ultrasonic transducer structure includes: Providing a substrate; In a first direction, an oxide film layer, a first metal layer, a piezoelectric material layer, and a second metal layer are sequentially formed on one side of the substrate. The first direction is perpendicular to the plane of the substrate and points from the substrate to the piezoelectric material layer. Wherein, the oxide film layer includes M sub-oxide film layers stacked in sequence in the first direction, M≥2, and M is a positive integer; the piezoelectric material layer includes N groups of alternately stacked piezoelectric film layers stacked in sequence in the first direction, N≥2, and N is a positive integer. The alternately stacked piezoelectric film layers include an AlN layer and an AlGaN layer stacked in sequence in the first direction, and the surfaces of the AlN layer and the AlGaN layer are in contact with each other.

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