A piezoelectric micromachined ultrasonic transducer structure and its manufacturing method

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 in the piezoelectric micromachined ultrasonic transducer structure includes at least one layer of AlScN layer. By doping Sc element into the traditional AlN layer to form the AlScN layer as a new type of piezoelectric material layer, and replacing Al element in the AlN layer with Sc element, the piezoelectric coefficient and the electromechanical coupling coefficient of the piezoelectric material layer can be significantly improved, the limitations of the AlN layer in various piezoelectric applications can be overcome, and at the same time, all the advantages of the matrix material system can still be benefited from, such as high-temperature stability, CMOS compatibility and good mechanical properties, thereby improving 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 specifically, to a piezoelectric micromachined 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 (UT for short), which is a transducer element that can be used to transmit and receive ultrasonic waves. When the UT is in the transmit mode, the electric 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 for short) 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 large influence by air.

[0003] In recent years, piezoelectric micromachined ultrasonic transducers (PMUT for short) have gradually attracted people's attention as a new type of MEMS device. This technology can vibrate the piezoelectric thin film through the piezoelectric effect of the piezoelectric material, thereby enabling the spontaneous transmission and reception of ultrasonic signals, and having 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 PMUTs usually use aluminum nitride (chemical formula: AlN) and lead zirconate titanate (chemical formula: PZT) as piezoelectric materials; the piezoelectric materials are 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, and the core reason is that the piezoelectric coefficients and electromechanical coupling coefficients of the AlN and PZT piezoelectric materials are relatively low. Therefore, how to improve the piezoelectric coefficients and electromechanical coupling coefficients of the 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 comprising:

[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 at least one AlScN layer.

[0010] Preferably, in the above piezoelectric micromachined ultrasonic transducer structure, the piezoelectric material layer includes one layer of the AlScN layer.

[0011] Preferably, in the above piezoelectric micromachined ultrasonic transducer structure, 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 the AlScN layer stacked in sequence in the first direction.

[0012] Preferably, in the above piezoelectric micromachined ultrasonic transducer structure, the thickness of the alternately stacked piezoelectric film layers in the first direction ranges from 8nm to 40nm.

[0013] Preferably, in the above piezoelectric micromachined ultrasonic transducer structure, the thickness of the AlN layer in the first direction ranges from 3nm to 20nm;

[0014] The thickness of the AlScN layer in the first direction ranges from 5nm to 20nm.

[0015] Preferably, in the above piezoelectric micromachined ultrasonic transducer structure, the total thickness of the piezoelectric material layer in the first direction ranges from 500nm to 1000nm.

[0016] Preferably, in the above piezoelectric micromachined ultrasonic transducer structure, 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.

[0017] Preferably, in the above piezoelectric micromachined ultrasonic transducer structure, the piezoelectric micromachined ultrasonic transducer structure further comprises:

[0018] A groove penetrating through the second metal layer and the piezoelectric material layer, the groove exposing a part of the first metal layer;

[0019] A first electrode located on the first metal layer;

[0020] A second electrode located on the second metal layer.

[0021] Preferably, in the above piezoelectric micromachined ultrasonic transducer structure, the substrate is a radio frequency SOI substrate.

[0022] 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 comprising:

[0023] Providing a substrate;

[0024] In a first direction, sequentially forming an oxide film layer, a first metal layer, a piezoelectric material layer, and a second metal layer on one side of the substrate, the first direction being perpendicular to the plane of the substrate and pointing from the substrate to the piezoelectric material layer; wherein, the piezoelectric material layer includes at least one AlScN layer.

[0025] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0026] The present invention provides a piezoelectric micromachined ultrasonic transducer structure and a method for manufacturing the same. 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 sequentially located on one side of the substrate, the first direction being perpendicular to the plane of the substrate and pointing from the substrate to the piezoelectric material layer; wherein, the piezoelectric material layer includes at least one AlScN layer. That is to say, by doping Sc elements into the traditional AlN layer to form an AlScN layer as a new piezoelectric material layer, replacing Al elements in the AlN layer with Sc elements can significantly improve the piezoelectric coefficient and electromechanical coupling coefficient of the piezoelectric material layer, overcome the limitations of the AlN layer in various piezoelectric applications, and at the same time still benefit from all the advantages of the parent material system, such as high temperature stability, CMOS compatibility, and good mechanical properties, thereby improving the sensitivity of the piezoelectric micromachined ultrasonic transducer structure. Description of the Drawings

[0027] 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 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, without creative efforts, other drawings can also be obtained according to the provided drawings.

[0028] Figure 1 One of the schematic structural diagrams of a piezoelectric micromachined ultrasonic transducer structure provided by an embodiment of the present invention;

[0029] Figure 2 Two of the schematic structural diagrams of a piezoelectric micromachined ultrasonic transducer structure provided by an embodiment of the present invention;

[0030] Figure 3 Three of the schematic structural diagrams of a piezoelectric micromachined ultrasonic transducer structure provided by an embodiment of the present invention;

[0031] Figure 4 Four of the schematic structural diagrams of a piezoelectric micromachined ultrasonic transducer structure provided by an embodiment of the present invention;

[0032] Figure 5 Five of the schematic structural diagrams of a piezoelectric micromachined ultrasonic transducer structure provided by an embodiment of the present invention;

[0033] Figure 6 Six of the schematic structural diagrams of a piezoelectric micromachined ultrasonic transducer structure provided by an embodiment of the present invention;

[0034] Figure 7 Flow schematic diagram of a preparation method of a piezoelectric micromachined ultrasonic transducer structure provided by an embodiment of the present invention;

[0035] Figures 8 - 15 For Figure 7 Partial structural schematic diagram corresponding to the shown preparation method. Detailed implementation manners

[0036] 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 shall fall within the protection scope of the present invention.

[0037] 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 with reference to the accompanying drawings and specific implementation manners.

[0038] Refer to Figure 1 , Figure 1FIG. 0 is one of the schematic structural diagrams of a piezoelectric micromachined ultrasonic transducer structure provided by an embodiment of the present invention. The piezoelectric micromachined ultrasonic transducer structure provided by the embodiment of the present invention includes: a substrate 11; an oxide film layer 12, a first metal layer 13, a piezoelectric material layer 14, and a second metal layer 15, which are sequentially located on one side of the substrate 11 in the first direction X. 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 at least one AlScN layer.

[0039] Specifically, in the embodiment of the present invention, as Figure 1 shown, the piezoelectric material layer 14 includes one layer of the AlScN layer, that is, one layer of the AlScN layer is used as the novel piezoelectric material layer 14. That is to say, by doping Sc elements into the traditional AlN layer to form the AlScN layer as the novel piezoelectric material layer 14, and replacing Al elements in the AlN layer with Sc elements, the piezoelectric coefficient and the electromechanical coupling coefficient of the piezoelectric material layer 14 can be significantly improved, which can overcome the limitations of the AlN layer in various piezoelectric applications, and at the same time still benefit from all the advantages of the matrix material system, such as high-temperature stability, CMOS compatibility, and good mechanical properties, thereby improving the sensitivity of the piezoelectric micromachined ultrasonic transducer structure.

[0040] Moreover, the AlScN layer as the novel piezoelectric material layer 14 can enhance the performance of radio frequency filters using bulk acoustic wave or surface acoustic wave resonators. In addition, energy harvesting and sensing applications can also benefit, and the higher pyroelectric coefficient enables new progress in fields such as infrared detectors.

[0041] Conventional aluminum nitride (chemical formula: AlN) piezoelectric materials have unique advantages in terms of longitudinal sound velocity v (11354 m / s), low frequency temperature coefficient (TCF, -25 ppm / °C), and acoustic and dielectric losses, and are applied to PMUT technology. However, its piezoelectric coefficient is relatively small, and aluminum scandium nitride (chemical formula: AlScN) materials have attracted extensive attention from researchers. This material is obtained by doping scandium elements into AlN piezoelectric materials, so that the piezoelectric coefficient and the electromechanical coupling coefficient of the device can be significantly improved.

[0042] Optionally, in another embodiment of the present invention, referring to Figure 2 , Figure 2 FIG. 18 is a second schematic structural diagram of a piezoelectric micromachined ultrasonic transducer structure provided by an embodiment of the present invention. 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 the AlScN layer 142 stacked in sequence in the first direction.

[0043] Specifically, in the embodiments 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 AlN layer 141 and the AlScN layer 142 are alternately stacked. AlN and AlScN are of the same type of semiconductor material, and their lattice mismatch is relatively small, making it easy to form a steep heterointerface. The AlN layer 141 serves as the barrier layer, and the AlScN 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 direction. The movement of carriers in the normal direction of the thin layer will be restricted and can only move freely within the thin layer plane. By means of the quantum effect, the piezoelectric coefficient and the electromechanical coupling coefficient of the piezoelectric material layer 14 can be significantly improved, and further the sensitivity of the piezoelectric micromachined ultrasonic transducer structure can be enhanced, and the electrical signal output of the piezoelectric micromachined ultrasonic transducer structure will be enhanced under the action of ultrasonic signals.

[0044] 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.

[0045] That is to say, in the embodiments 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.

[0046] 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.

[0047] That is to say, in the embodiments of the present invention, the number of periods of the piezoelectric material layer 14 can be from 25 to 60. An AlN layer 141 and an AlScN layer 142 adjacent to each other serve as a single period, and the total thickness of a single period in the first direction X ranges from 8 nm to 40 nm.

[0048] Optionally, the thickness of the AlN layer 141 in the first direction X ranges from 3 nm to 20 nm.

[0049] The thickness of the AlScN layer 142 in the first direction X ranges from 5 nm to 20 nm.

[0050] It should be noted that in some alternative embodiments of the present invention, refer to Figure 3 , Figure 3This is the third schematic structural diagram of a piezoelectric micromachined ultrasonic transducer structure provided by an 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 AlScN layers 142 located between adjacent two AlN layers 141. K≥2 and K is a positive integer. At this time, the purpose of sharing the AlScN layer 142 can be achieved.

[0051] Optionally, in another embodiment of the present invention, as Figures 1 - 3 shown, the oxide film layer 12 includes M sub-oxide film layers stacked in sequence in the first direction X. M≥2 and M is a positive integer.

[0052] Specifically, in the embodiment of the present invention, the traditional piezoelectric material layer is improved. A single-layer AlScN layer is used as the new piezoelectric material layer 14, that is, by doping Sc elements in the traditional AlN layer to form an AlScN layer as the new piezoelectric material layer 14, and replacing Al elements in the AlN layer with Sc elements, the piezoelectric coefficient and the electromechanical coupling coefficient of the piezoelectric material layer 14 can be significantly improved, the limitations of the AlN layer in various piezoelectric applications can be overcome, and at the same time, all the advantages of the matrix material system can still be benefited from, such as high-temperature stability, CMOS compatibility, and good mechanical properties. Furthermore, the sensitivity of the piezoelectric micromachined ultrasonic transducer structure can be improved.

[0053] Or, 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 layers 141 and the AlScN layers 142 are alternately stacked. AlN and AlScN 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 AlScN layer 142 serves as a quantum 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. With the help of the quantum effect, the piezoelectric coefficient and the electromechanical coupling coefficient of the piezoelectric material layer 14 can be significantly improved. 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 an ultrasonic signal.

[0054] Secondly, the traditional single-layer oxide film layer is improved. 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.

[0055] It should be noted that the resonator is used to enhance the interaction between sound waves and piezoelectric materials. Therefore, the M-layer sub-oxide film layer formed by laminating in the first direction X can also be called a resonator.

[0056] Optionally, the substrate 11 includes but is not limited to other substrates such as radio frequency SOI substrates. In the embodiments of the present invention, the radio frequency SOI substrate is used as the optimal embodiment for illustration. Since the frequency of the piezoelectric micromachined ultrasonic transducer structure is changed by changing the radius of the cavity and the thickness of the thin film, in the embodiments of the present invention, by changing the traditional substrate structure, that is, using a radio frequency SOI substrate, the frequency characteristics of the piezoelectric micromachined ultrasonic transducer structure are optimized, and the radio frequency loss is reduced, so that the sensitivity of the piezoelectric micromachined ultrasonic transducer structure is improved, and the imaging resolution of the piezoelectric micromachined ultrasonic transducer structure can also be improved.

[0057] It should be noted that theoretically, the M-layer sub-oxide film layer laminated in the first direction X can also be formed 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 radio frequency SOI substrate is used as the optimal embodiment for illustration.

[0058] As Figures 1 - 3 shown, the radio frequency SOI substrate includes a high-resistance Si substrate layer 111, a defect-rich layer 112, a buried oxide layer 113, and a Si layer 114 laminated in sequence in the first direction X. Almost no doping elements are present in the high-resistance Si substrate layer 111, which can improve the radio frequency characteristics; the defect-rich layer 112 can also be called a polysilicon layer, and its function is to capture charges, thereby improving the radio frequency characteristics; the buried oxide layer 113 can also be called an insulating layer; the Si layer 114 serves as a device functional layer.

[0059] Optionally, in another embodiment of the present invention, as Figures 1 - 3 shown, the oxide film layer 12 includes an M-layer sub-oxide film layer laminated in sequence in the first direction X. The material of each oxide film layer is the same, for example, SiO2 material or Al2O3 material and other oxide materials.

[0060] Optionally, in another embodiment 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 an embodiment of the present invention. Referring to Figure 5 , Figure 5 is the fifth structural schematic diagram of a piezoelectric micromachined ultrasonic transducer structure provided by an embodiment of the present invention. Referring to Figure 6 , Figure 6FIG. 6 is a schematic structural diagram of a piezoelectric micromachined ultrasonic transducer structure provided by an embodiment of the present invention. The oxide film layer 12 includes a first oxide film layer 121 and a second oxide film layer 122 that are alternately arranged in sequence in the first direction X.

[0061] 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.

[0062] 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. For example, three oxide film layers of different materials are alternately arranged in sequence in the first direction X, etc.

[0063] Optionally, in another embodiment of the present invention, the total thickness of the oxide film layer 12 provided by the embodiment of the present invention in the first direction X ranges from 50 nm to 400 nm, the number of periods can be 2 - 10, and the thickness of a single period in the first direction X ranges from 20 nm to 40 nm.

[0064] Optionally, in another embodiment of the present invention, as Figures 1 - 6 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.

[0065] A first electrode 16 located on the first metal layer 13.

[0066] A second electrode 17 located on the second metal layer 15.

[0067] Specifically, in the embodiment of the present invention, the design of the groove can form a step structure required for 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 both the first electrode 16 and the second electrode 17 are transparent electrode materials.

[0068] As Figures 1 - 6 shown, the side of the substrate 11 facing away from the piezoelectric material layer 14 has a patterned groove. When the substrate 11 is a radio frequency SOI substrate, the patterned groove penetrates through the high-resistance Si substrate layer 111 and exposes a part of the defect-rich layer 112.

[0069] As can be seen from the above description, in the embodiments of the present invention, the traditional piezoelectric material layer is first improved, and a single-layer AlScN layer is used as the new piezoelectric material layer 14. That is, by doping Sc elements into the traditional AlN layer to form the AlScN layer as the new piezoelectric material layer 14, and replacing Al elements in the AlN layer with Sc elements, the piezoelectric coefficient and electromechanical coupling coefficient of the piezoelectric material layer 14 can be significantly improved, which can overcome the limitations of the AlN layer in various piezoelectric applications, and at the same time still benefit from all the advantages of the matrix material system, such as high-temperature stability, CMOS compatibility, and good mechanical properties, thereby improving the sensitivity of the piezoelectric micromachined ultrasonic transducer structure.

[0070] Alternatively, N groups of alternately stacked piezoelectric film layers sequentially stacked in the first direction X are used as the new piezoelectric material layer. In the N groups of alternately stacked piezoelectric film layers, the AlN layer 141 and the AlScN layer 142 are alternately stacked. AlN and AlScN are the same type of semiconductor material, and their lattice mismatch is relatively small, making it easy to form a steep heterointerface. The AlN layer 141 serves as the barrier layer, and the AlScN layer 142 serves as the 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 directions. The movement of carriers in the normal direction of the thin layer will be restricted and can only move freely within the thin layer plane. By virtue of the quantum effect, the piezoelectric coefficient and electromechanical coupling coefficient of the piezoelectric material layer 14 can be significantly improved, thereby improving the sensitivity of the piezoelectric micromachined ultrasonic transducer structure, and enhancing the electrical signal output of the piezoelectric micromachined ultrasonic transducer structure under the action of ultrasonic signals.

[0071] Furthermore, the traditional single-layer oxide film layer is improved, and M sub-oxide film layers sequentially stacked 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.

[0072] 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.

[0073] Optionally, based on the above embodiments of the present invention, in another embodiment of the present invention, a method for manufacturing a piezoelectric micromachined ultrasonic transducer structure is further provided. Refer to Figure 7 , Figure 7 which is a schematic flowchart of a method for manufacturing a piezoelectric micromachined ultrasonic transducer structure provided by the embodiments of the present invention. The method for manufacturing a piezoelectric micromachined ultrasonic transducer structure provided by the embodiments of the present invention includes:

[0074] S101: As shown in Figure 8 , a substrate 11 is provided.

[0075] 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 at least one layer of AlScN layer.

[0076] Specifically, as shown in Figure 9 , the oxide film layer 12 is formed on one side of the substrate 11.

[0077] As shown in Figure 10 , the first metal layer 13 is formed on the side of the oxide film layer 12 away from the substrate 11.

[0078] As shown in Figure 11 , the piezoelectric material layer 14 is formed on the side of the first metal layer 13 away from the substrate 11.

[0079] As shown in Figure 12 , the second metal layer 15 is formed on the side of the piezoelectric material layer 14 away from the substrate 11.

[0080] As shown in Figure 13 , 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.

[0081] As shown in Figure 14 , a first electrode 16 is formed on the surface of the exposed first metal layer 13.

[0082] As shown in Figure 15 , a second electrode 17 is formed on the side of the second metal layer 15 away from the substrate 11.

[0083] It should be noted that the first electrode 16 and the second electrode 17 can also be prepared simultaneously in the same process.

[0084] As shown in Figure 1 , the substrate 11 is patterned on the side away from the piezoelectric material layer 14 to form a patterned groove. When the substrate 11 is a radio frequency SOI substrate, the patterned groove penetrates the high-resistance Si substrate layer 111 and exposes a part of the defect-rich layer 112.

[0085] The above has introduced in detail a piezoelectric micromachined ultrasonic transducer structure and a preparation method thereof 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.

[0086] It should be noted that the various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The same or similar parts among the various 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.

[0087] 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 such 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 identical 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 said element.

[0088] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but will conform to 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, and the substrate is a radio frequency SOI 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; 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 AlScN layer stacked in sequence in the first direction, and the surfaces of the AlN layer and the AlScN layer are in contact with each other.

2. The piezoelectric micromachined ultrasonic transducer structure according to claim 1, characterized in that, The piezoelectric material layer includes one layer of the AlScN layer.

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

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

5. The piezoelectric micromachined ultrasonic transducer structure according to claim 1, wherein The total thickness range of the piezoelectric material layer in the first direction is 500nm - 1000nm.

6. The piezoelectric micromachined ultrasonic transducer structure according to claim 1, characterized in that, 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.

7. A method for preparing a piezoelectric micromachined ultrasonic transducer structure, characterized in that, The preparation method of the piezoelectric micromachined ultrasonic transducer structure includes: providing a substrate, and the substrate is a radio frequency SOI 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 where the substrate is located, 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 AlScN layer stacked in sequence in the first direction, and the surfaces of the AlN layer and the AlScN layer are in contact with each other.

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