Capacitive micro-machined ultrasonic transducer and manufacturing method thereof

Abstract

The invention discloses a capacitive micro-machined ultrasonic transducer and a manufacturing method thereof. The capacitive micro-machined ultrasonic transducer comprises a substrate; the supporting seat is arranged on the upper surface of the base, and a first cavity is formed in the supporting seat; the vibrating diaphragm is arranged on the upper surface of the supporting seat, the vibrating diaphragm comprises a vibrating diaphragm main body and a flexible supporting structure, the vibrating diaphragm main body is suspended above the first cavity, the periphery of the vibrating diaphragm main body is connected with the flexible supporting structure, and the flexible supporting structure is connected with the supporting seat and enables the first cavity to be sealed. According to the invention, the rigidity of the circumference of the vibrating diaphragm is reduced through the flexible supporting structure, so that the deformation of the vibrating diaphragm tends to a flat piston when the CMUT works, the emission sound pressure is effectively enhanced, and the emission performance is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of capacitive micromechanical ultrasonic transducers, and in particular relates to a capacitive micromechanical ultrasonic transducer and a manufacturing method thereof. Background Art

[0002] Capacitive micromachined ultrasonic transducer (CMUT) is a miniature ultrasonic sensor manufactured using MEMS technology. It can be mass-produced and form a high-density ultrasonic transducer array. CMUT has the advantages of large bandwidth, high sensitivity, and high electromechanical conversion efficiency, so it is widely used in medical imaging, non-destructive testing, and industrial control. Studies have shown that when the diaphragm movement approaches the piston state, CMUT can achieve the best transmission and reception performance. However, since the CMUT diaphragm is fixed on the circumference, the diaphragm is not flat when vibrating. Its maximum displacement occurs at the center of the circle, while the displacement on the circumference is zero. The entire diaphragm surface presents a convex or concave bridge shape, which seriously affects the transmission and reception performance.

[0003] Chinese invention patent CN108793061B discloses a method for preparing a CMUT device with a full-electrode convex structure. The CMUT with a full-electrode convex structure can work in a collapsed mode, effectively enhancing the output sound pressure.

[0004] Chinese invention patent CN115432662B discloses a micromechanical ultrasonic transducer with a centrally supported bottom electrode. The patent provides a new CMUT with a bendable bottom electrode. Under the action of electrostatic force, the diaphragm and the bottom electrode are deformed simultaneously and relatively parallel, thereby improving the transmitted sound pressure and receiving sensitivity.

[0005] Although the above existing technologies have made certain optimizations to the CMUT structure, they also bring about problems such as strong nonlinearity, low reliability, and low lifespan. Therefore, it is very necessary to design a low-support stiffness CMUT working in a non-collapse mode to achieve a diaphragm movement that is closer to a piston. Summary of the invention

[0006] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a capacitive micromechanical ultrasonic transducer and a method for manufacturing the same, which reduces the stiffness of the diaphragm at the circumference through a flexible support structure so that the deformation of the diaphragm when the CMUT is working is closer to a flat piston, effectively enhancing the emission sound pressure and improving the emission performance.

[0007] The present invention provides the following technical solutions: In a first aspect, a capacitive micromachined ultrasonic transducer is provided, comprising: substrate; A support seat, disposed on the upper surface of the base, wherein a first cavity is disposed in the support seat; The diaphragm is arranged on the upper surface of the support seat, and the diaphragm includes a diaphragm body and a flexible support structure. The diaphragm body is suspended above the first cavity, and the outer periphery of the diaphragm body is connected to the flexible support structure. The flexible support structure is connected to the support seat and seals the first cavity.

[0008] Furthermore, the diaphragm includes a second top silicon layer and a third top silicon layer symmetrically bonded to each other, and the second top silicon layer and the third top silicon layer are respectively provided with a first groove and a second groove corresponding to each other in position; When the second top silicon layer and the third top silicon layer are bonded together, the first groove and the second groove are connected to form a second cavity, so that the flexible support structure is a beam structure.

[0009] Further, it also includes an upper electrode and a lower electrode; The upper electrode is arranged on the upper surface or the lower surface of the diaphragm body; And / or, the lower electrode is disposed on the lower surface of the substrate or the first top silicon layer is used as the lower electrode.

[0010] Furthermore, an unetched pillar located below the first cavity is provided in the support seat, and a cavity isolation groove communicating with the first cavity is provided on the periphery of the unetched pillar.

[0011] Furthermore, the base comprises a first substrate and a first buried oxide layer, the first buried oxide layer is arranged on the upper surface of the first substrate, and the first buried oxide layer is connected to the support seat; And / or, the support seat includes a first top silicon layer and an oxide layer, the oxide layer is arranged on the upper surface of the first top silicon layer, and the oxide layer is connected to the diaphragm.

[0012] In a second aspect, a method for manufacturing a capacitive micromachined ultrasonic transducer is provided, comprising the following steps: Etching a first cavity on a first SOI wafer, wherein the periphery and bottom of the first cavity serve as a support seat; A semi-flexible support structure with the same structure is etched on a second SOI sheet and a third SOI sheet of the same specification, and then the second SOI sheet and the third SOI sheet are symmetrically bonded to connect the two semi-flexible support structures to form a flexible support structure, thereby obtaining a composite sheet layer with a diaphragm, wherein the diaphragm includes a diaphragm body and a flexible support structure connected to the periphery of the diaphragm body; Bonding the composite sheet with the diaphragm to the first SOI sheet with the first cavity, so that the diaphragm body is suspended above the first cavity, and the flexible support structure is connected to the support seat and seals the first cavity to obtain a transducer substrate; An upper electrode and a lower electrode are prepared on a transducer substrate to obtain a capacitive micromechanical ultrasonic transducer.

[0013] Furthermore, the first SOI sheet includes a first top silicon layer, a first buried oxide layer and a first substrate which are stacked; The method for etching a first cavity on a first SOI wafer comprises: Etching a first cavity on a first top silicon layer of a first SOI wafer, and then thermally oxidizing a surface of the first top silicon layer to form an oxide layer; Continue etching at the first cavity to make the first cavity reach a preset size, and at the same time etch a cavity isolation groove extending to the surface of the first buried oxide layer below the first cavity, and form an unetched pillar inside the cavity isolation groove; The oxide layer and the first top silicon layer serve as a support seat, and the first buried oxide layer and the first substrate serve as a base.

[0014] Further, the second SOI sheet includes a second top silicon layer, a second buried oxide layer, and a second substrate which are stacked, the third SOI sheet includes a third top silicon layer, a third buried oxide layer, and a third substrate which are stacked, and the thickness of the second top silicon layer and the third top silicon layer is half of the thickness of the first top silicon layer; The method of forming the flexible support structure comprises: Etching a first groove on the second top silicon layer of the second SOI wafer to form a semi-flexible support structure, and etching a second groove having the same structure as the first groove on the third top silicon layer of the third SOI wafer to form a semi-flexible support structure; The second SOI sheet and the third SOI sheet are symmetrically bonded to each other, so that the first groove and the second groove are connected to form a second cavity, and the two semi-flexible support structures are butted to form a flexible support structure of a beam structure; The depth of the first groove and the second groove is half of the thickness of the second top silicon layer and the third top silicon layer.

[0015] Furthermore, before bonding the composite sheet layer with the diaphragm to the first SOI sheet with the first cavity, the method further includes: removing the third buried oxide layer and the third substrate; And / or, after the composite sheet layer with the diaphragm is bonded to the first SOI sheet with the first cavity, the method further includes: removing the second buried oxide layer and the second substrate.

[0016] Furthermore, the method for preparing the upper electrode includes: preparing a metal layer as the upper electrode on the upper surface or the lower surface of the diaphragm body; And / or, the method for preparing the lower electrode comprises: preparing a metal layer as the lower electrode on the lower surface of the substrate or using the first top silicon layer as the lower electrode; The first top silicon layer is exposed by etching a third groove on the transducer substrate, and then a lower electrode pad is prepared at the exposed portion of the first top silicon layer, so that the first top silicon layer is used as a lower electrode, and the first top silicon layer is low-resistance silicon with a resistivity of ≤0.01Ω·cm.

[0017] Compared with the prior art, the present invention has the following beneficial effects: (1) The capacitive micromachined ultrasonic transducer provided by the present invention comprises a diaphragm body and a flexible support structure. The diaphragm body is suspended above the first cavity in the support seat. The outer periphery of the diaphragm body is connected to the flexible support structure. The flexible support structure is connected to the support seat and seals the first cavity. The flexible support structure reduces the stiffness of the diaphragm at the circumference, making the stiffness of the diaphragm from the center of the diaphragm to the boundary of the diaphragm more uniform, so that the deformation of the diaphragm when the CMUT is working tends to be more like a flat piston, which can effectively enhance the emission sound pressure and improve the emission performance; (2) The manufacturing method of the capacitive micromechanical ultrasonic transducer provided by the present invention is to etch a semi-flexible support structure with the same structure on a second SOI sheet and a third SOI sheet of the same specifications, and then symmetrically bond the second SOI sheet and the third SOI sheet to connect the two semi-flexible support structures to form a flexible support structure, thereby obtaining a diaphragm including a diaphragm body and a flexible support structure. The manufacturing method is simple, low-cost, and effectively improves the transmission performance of the CMUT. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a schematic diagram of a cross-sectional structure of a CMUT in an embodiment of the present invention; Figure 2 is a schematic diagram of the structure obtained in step S1 in Example 2 of the present invention; Figure 3 is a schematic diagram of the structure obtained in step S2 of Example 2 of the present invention; Figure 4 is a schematic diagram of the structure obtained in step S3 of Example 2 of the present invention; Figure 5 is a schematic top view of the structure obtained in step S3 of Example 2 of the present invention; Figure 6 is a schematic diagram of the structure obtained in step S4 in Example 2 of the present invention; Figure 7 is a schematic diagram of the structure obtained in step S5 in Example 2 of the present invention; Figure 8 is a schematic diagram of the structure obtained in step S6 of Example 2 of the present invention; Fig. 9 is a schematic diagram of the structure obtained in step S7 in Example 2 of the present invention; Fig.10 is a schematic diagram of the structure obtained in step S8 in Example 2 of the present invention; Fig.11 is a schematic diagram of the structure obtained in step S9 of Example 2 of the present invention; Fig.12is a schematic diagram of the structure obtained in step S10 in Example 2 of the present invention; Fig.13 is a finite element simulation comparison diagram of the emitted sound pressure of the CMUT structure in the embodiment of the present invention and the conventional CMUT structure under bias current; Markings in the figure are: 01, first top silicon layer; 02, first buried oxide layer; 03, first substrate; 04, oxide layer; 05, second top silicon layer; 06, second buried oxide layer; 07, second substrate; 08, third top silicon layer; 09, third buried oxide layer; 10, third substrate; 11, upper electrode; 12, lower electrode pad; 13, first groove; 14, second groove; 101, second cavity; 102, diaphragm; 1021, diaphragm body; 1022, flexible support structure; 103, first cavity; 104, base; 105, support seat; 106, unetched pillar; 107, third groove; 108, cavity isolation groove. DETAILED DESCRIPTION

[0019] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0020] It should be noted that, in the description of the present invention, the directions or positional relationships indicated by terms such as "front", "rear", "left", "right", "up", "down", "inside" and "outside" are based on the directions or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and do not require that the present invention must be constructed and operated in a specific direction. Therefore, they should not be understood as limitations on the present invention.

[0021] In the description of the present invention, it is to be understood that the terms "first", "second", etc. are used for descriptive purposes only and are not to be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first", "second", etc. may explicitly or implicitly include one or more of the feature. In the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0022] Example 1

[0023] like Figure 1 As shown, this embodiment provides a capacitive micromachined ultrasonic transducer, including a substrate 104, a support seat 105, a diaphragm 102, an upper electrode 11 and a lower electrode.

[0024] The support base 105 is disposed on the upper surface of the substrate 104 . When the CMUT is working, the support base 105 can be fixed by fixing the substrate 104 . A first cavity 103 is disposed in the support base 105 . The first cavity 103 is usually circular.

[0025] The diaphragm 102 is disposed on the upper surface of the support seat 105, and the diaphragm 102 includes a diaphragm body 1021 and a flexible support structure 1022; the diaphragm body 1021 is generally a thin disc-shaped structure, suspended above the first cavity 103; the outer periphery of the diaphragm body 1021 is connected to the flexible support structure 1022, and the flexible support structure 1022 is connected to the support seat 105 and seals the first cavity 103. When the support seat 105 is fixed, the circumference of the diaphragm 102 is fixed, and when the diaphragm 102 is subjected to force and vibrates, it will present a convex or concave shape.

[0026] In order to make the deformation of the surface of the diaphragm 102 flat so that the vibration of the diaphragm 102 is close to that of a piston, in this embodiment, the diaphragm 102 includes a second top silicon layer 05 and a third top silicon layer 08 that are symmetrically bonded, and the second top silicon layer 05 and the third top silicon layer 08 are respectively provided with a first groove 13 and a second groove 14 that correspond to the positions; when the second top silicon layer 05 and the third top silicon layer 08 are bonded, the first groove 13 and the second groove 14 are connected to form a second cavity 101, so that the flexible support structure 1022 is a beam structure, which reduces the stiffness at the circumference of the diaphragm 102, and makes the stiffness of the diaphragm 102 from the center of the diaphragm 102 to the boundary of the diaphragm 102 more uniform, and the deformation of the diaphragm 102 will be close to that of a piston when subjected to force.

[0027] The upper electrode 11 is distributed on the surface of the diaphragm body 1021 of the diaphragm 102. In this embodiment, the upper electrode 11 is disposed on the upper surface of the diaphragm body 1021, and the upper electrode 11 is connected to the external metal pad through a gold wire, so as to facilitate the application of voltage excitation to the upper electrode 11. In some other embodiments, the upper electrode can be disposed on the lower surface of the diaphragm body 1021, that is, the metal upper electrode is disposed inside the first cavity 103, which can reduce the distance between the upper electrode and the lower electrode and enhance the electrostatic force.

[0028] Typically, the lower electrode is disposed on the lower surface of the substrate 104. In order to reduce the distance between the upper electrode and the lower electrode, the first top silicon layer 01 in this embodiment is made of low-resistance silicon with a resistivity of ≤0.01Ω·cm, which is a good conductor and can be used as the lower electrode.

[0029] The support base 105 is provided with an unetched column 106 located below the first cavity 103, and the periphery of the unetched column 106 is provided with a cavity isolation groove 108 connected to the first cavity 103, and the cavity isolation groove 108 isolates the unetched column 106 from the support base 105, and the radius of the unetched column 106 plus the width of the cavity isolation groove 108 is the radius of the entire first cavity 103. The unetched column 106 can effectively reduce the depth of the first cavity 103. In a capacitor, the smaller the distance between the two electrode plates, the greater the capacitance, and the greater the electrostatic force. Therefore, when the lower electrode is provided on the lower surface of the substrate 104, the electrostatic force is enhanced by reducing the depth of the first cavity 103 through the unetched column 106, which plays a role in enhancing the emitted sound pressure.

[0030] In this embodiment, the base 104 is composed of a first substrate 03 and a first buried oxide layer 02 . The first buried oxide layer 02 is disposed on the upper surface of the first substrate 03 . The first buried oxide layer 02 is connected to the support seat 105 .

[0031] In this embodiment, the support base 105 is composed of a first top silicon layer 01 and an oxide layer 04 . The oxide layer 04 is disposed on the upper surface of the first top silicon layer 01 . The oxide layer 04 is connected to the diaphragm 102 . The oxide layer 04 prevents the CMUT from being broken down under a large voltage.

[0032] The present invention reduces the stiffness of the diaphragm 102 at the circumference through the flexible support structure 1022, making the stiffness of the diaphragm 102 from the center of the diaphragm 102 to the diaphragm boundary more uniform, so that the deformation of the diaphragm 102 when the CMUT is working is closer to a flat piston, which can effectively enhance the emission sound pressure and improve the emission performance.

[0033] Example 2

[0034] This embodiment provides a method for manufacturing a capacitive micromechanical ultrasonic transducer, and three SOI sheets are prepared in advance, namely, a first SOI sheet, a second SOI sheet, and a third SOI sheet. The first SOI sheet includes a first top silicon layer 01, a first buried oxide layer 02, and a first substrate 03 arranged in a stacked manner; the second SOI sheet includes a second top silicon layer 05, a second buried oxide layer 06, and a second substrate 07 arranged in a stacked manner, and the third SOI sheet includes a third top silicon layer 08, a third buried oxide layer 09, and a third substrate 10 arranged in a stacked manner. Among them, the thickness of the first top silicon layer 01 of the first SOI sheet is 2μm, the second SOI sheet and the third SOI sheet have the same specifications, and the thickness of the second top silicon layer 05 and the third top silicon layer 08 is half of the thickness of the first top silicon layer 01, that is, 1μm.

[0035] The method for manufacturing the capacitive micromachined ultrasonic transducer provided in this embodiment has the following specific steps: S1, such as Figure 2As shown, the first top silicon layer 01 of the first SOI wafer is patterned by dry etching to etch out the first cavity 103. At this time, the size of the first cavity 103 does not reach the preset size.

[0036] S2, such as Figure 3 As shown, an oxide layer 04, i.e., a SiO2 layer, is formed by thermal oxidation on the surface of the first top silicon layer 01. The thickness of the oxide layer 04 is usually designed to be a few tenths of a micron. In this embodiment, in order to prevent the CMUT from being broken down under a large voltage, the thickness of the oxide layer 04 is 0.25 μm, which can ensure that the CMUT is safe under a high voltage of 250 V.

[0037] S3, such as Figure 4 As shown, etching is continued at the first cavity 103 to make the first cavity 103 reach a preset size, and at the same time, a cavity isolation groove 108 extending to the surface of the first buried oxide layer 02 is etched below the first cavity 103, and an unetched pillar 106 is formed inside the cavity isolation groove 108 to obtain a first SOI wafer with a first cavity 103.

[0038] In the finished CMUT, the etched oxide layer 04 and the first top silicon layer 01 serve as a support seat, and the first buried oxide layer 02 and the first substrate 03 serve as a base.

[0039] For ease of presentation, Figure 4 The positional relationship of the first SOI slice in the two CMUT units is described, and their size, process and function are exactly the same. Figure 5 The figure shows a top view of the two first SOI wafers in this step, where the two unetched pillars 106 are connected through the middle channel. When the unetched pillars 106 are used as the lower electrode, the cavity isolation grooves 108 will play an isolating role, isolating the unetched pillars 106 from the support base 105, thus making the electrode area independent.

[0040] S4, such as Figure 6 As shown in (a), a first groove 13 is dry-etched on the second top silicon layer 05 of the second SOI wafer to form a semi-flexible support structure, as shown in FIG. Figure 6 As shown in (b), a second groove 14 having the same structure as the first groove 13 is etched on the third top silicon layer 08 of the third SOI wafer to form a semi-flexible support structure.

[0041] S5, such as Figure 7As shown, the second SOI sheet and the third SOI sheet are symmetrically bonded and connected, so that the first groove 13 and the second groove 14 are connected to form a second cavity 101, and the two semi-flexible support structures are connected to form a flexible support structure 1022 of a beam structure, and a complete diaphragm 102 is obtained, wherein the diaphragm 102 includes a diaphragm body 1021 and a flexible support structure 1022 connected to the periphery of the diaphragm body 1021. In this embodiment, the depth of the first groove 13 and the second groove 14 is half the thickness of the second top silicon layer 05 and the third top silicon layer 08, that is, the thickness of the flexible support structure 1022 on one side is 0.5 μm and the width is 4 μm.

[0042] S6, such as Figure 8 As shown, the third buried oxide layer 09 and the third substrate 10 are removed to expose the complete diaphragm 102, thereby obtaining a composite sheet layer with the diaphragm 102.

[0043] S7, such as Fig. 9 As shown, the composite sheet layer with the diaphragm 102 obtained in step S6 is bonded to the first SOI sheet with the first cavity 103 obtained in step S3, so that the diaphragm body 1021 is suspended above the first cavity 103, and the flexible support structure 1022 is connected to the support seat 105 and seals the first cavity 103.

[0044] S8, such as Fig.10 As shown, the second buried oxide layer 06 and the second substrate 07 are removed to expose the complete diaphragm 102, thereby obtaining a transducer substrate.

[0045] S9, such as Fig.11 As shown, a third groove 107 is etched on the transducer substrate, which penetrates the second top silicon layer 05, the third top silicon layer 08 and the oxide layer 04, to expose the first top silicon layer 01. In this embodiment, the first top silicon layer 01 is low-resistance silicon with a resistivity of ≤0.01Ω·cm, which can be used as a lower electrode. In some other embodiments, a metal can also be prepared on the lower surface of the first substrate 03 as a lower electrode.

[0046] S10, such as Fig.12 As shown, a metal layer is prepared on the upper surface of the diaphragm body 1021 of the diaphragm 102 as the upper electrode 11, and a lower electrode pad 12 is prepared in the third groove 107 and at the exposed part of the first top silicon layer 01, so as to obtain a CMUT.

[0047] Example 3

[0048] CMUT is a capacitor. After applying excitation to the upper electrode 11, an electrostatic force is formed between the upper electrode 11 and the lower electrode, causing the diaphragm 102 to move to the bottom of the first cavity 103. When the excitation is an AC voltage, the diaphragm 102 vibrates periodically, causing the diaphragm 102 to emit sound pressure outward. This is the transmitting mode of the CMUT. When the CMUT receives an external sound signal and causes the diaphragm 102 to vibrate, the capacitor generates current. This is the receiving mode of the CMUT.

[0049] The sound pressure emitted in the emission mode is determined by the vibration of the diaphragm 102, and the greater the emission sound pressure, the greater the received sound pressure is usually, because in the same medium, the attenuation of the sound pressure is certain.

[0050] In order to verify the advancedness of the CMUT structure in Example 1 or Example 2 of the present invention, this embodiment designs a CMUT with specific parameters and performs simulation comparison with the traditional model. The same excitation signal is used in the simulation to excite at the resonant frequency, and the CMUT structure design parameters are shown in Table 1.

[0051] Table 1 CMUT structural parameters

[0052] The results are as follows Fig.13 As shown, Fig.13 (a) is the emission sound pressure of the CMUT proposed in the present invention, and the peak value after stabilization is 1.86MPa. Fig.13 (b) is the emission sound pressure of the traditional CMUT, with a peak value of 1.50Mpa. From the simulation results, it can be seen that the CMUT structure proposed in the present invention has a significant advantage in emission sound pressure and can effectively improve the emission performance of the CMUT.

[0053] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A capacitive micromachined ultrasonic transducer, characterized in that: include: substrate; A support seat, disposed on the upper surface of the base, wherein a first cavity is disposed in the support seat; The diaphragm is arranged on the upper surface of the support seat, and the diaphragm includes a diaphragm body and a flexible support structure. The diaphragm body is suspended above the first cavity, and the outer periphery of the diaphragm body is connected to the flexible support structure. The flexible support structure is connected to the support seat and seals the first cavity.

2. The capacitive micromachined ultrasonic transducer according to claim 1, characterized in that: The diaphragm comprises a second top silicon layer and a third top silicon layer which are symmetrically bonded, and the second top silicon layer and the third top silicon layer are respectively provided with a first groove and a second groove which are located in corresponding positions; When the second top silicon layer and the third top silicon layer are bonded together, the first groove and the second groove are connected to form a second cavity, so that the flexible support structure is a beam structure.

3. The capacitive micromachined ultrasonic transducer according to claim 1, characterized in that: Also includes an upper electrode and a lower electrode; The upper electrode is arranged on the upper surface or the lower surface of the diaphragm body; And / or, the lower electrode is disposed on the lower surface of the substrate or the first top silicon layer is used as the lower electrode.

4. The capacitive micromachined ultrasonic transducer according to claim 1, characterized in that: An unetched pillar located below the first cavity is disposed in the support seat, and a cavity isolation groove communicating with the first cavity is disposed around the unetched pillar.

5. The capacitive micromachined ultrasonic transducer according to claim 1, characterized in that: The base comprises a first substrate and a first buried oxide layer, wherein the first buried oxide layer is arranged on the upper surface of the first substrate, and the first buried oxide layer is connected to the support seat; And / or, the support seat includes a first top silicon layer and an oxide layer, the oxide layer is arranged on the upper surface of the first top silicon layer, and the oxide layer is connected to the diaphragm.

6. A method for manufacturing a capacitive micromechanical ultrasonic transducer, characterized in that: The following steps are involved: Etching a first cavity on a first SOI wafer, wherein the periphery and bottom of the first cavity serve as a support seat; A semi-flexible support structure with the same structure is etched on a second SOI sheet and a third SOI sheet of the same specification, and then the second SOI sheet and the third SOI sheet are symmetrically bonded to connect the two semi-flexible support structures to form a flexible support structure, thereby obtaining a composite sheet layer with a diaphragm, wherein the diaphragm includes a diaphragm body and a flexible support structure connected to the periphery of the diaphragm body; Bonding the composite sheet with the diaphragm to the first SOI sheet with the first cavity, so that the diaphragm body is suspended above the first cavity, and the flexible support structure is connected to the support seat and seals the first cavity to obtain a transducer substrate; An upper electrode and a lower electrode are prepared on a transducer substrate to obtain a capacitive micromechanical ultrasonic transducer.

7. The method for manufacturing a capacitive micromachined ultrasonic transducer according to claim 6, characterized in that: The first SOI sheet includes a first top silicon layer, a first buried oxide layer and a first substrate which are stacked; The method for etching a first cavity on a first SOI wafer comprises: Etching a first cavity on a first top silicon layer of a first SOI wafer, and then thermally oxidizing a surface of the first top silicon layer to form an oxide layer; Continue etching at the first cavity to make the first cavity reach a preset size, and at the same time etch a cavity isolation groove extending to the surface of the first buried oxide layer below the first cavity, and form an unetched pillar inside the cavity isolation groove; The oxide layer and the first top silicon layer serve as a support seat, and the first buried oxide layer and the first substrate serve as a base.

8. The method for manufacturing a capacitive micromachined ultrasonic transducer according to claim 7, characterized in that: The second SOI sheet includes a second top silicon layer, a second buried oxide layer and a second substrate which are stacked, and the third SOI sheet includes a third top silicon layer, a third buried oxide layer and a third substrate which are stacked, and the thickness of the second top silicon layer and the third top silicon layer is half of the thickness of the first top silicon layer; The method of forming the flexible support structure comprises: Etching a first groove on the second top silicon layer of the second SOI wafer to form a semi-flexible support structure, and etching a second groove having the same structure as the first groove on the third top silicon layer of the third SOI wafer to form a semi-flexible support structure; The second SOI sheet and the third SOI sheet are symmetrically bonded to each other, so that the first groove and the second groove are connected to form a second cavity, and the two semi-flexible support structures are butted to form a flexible support structure of a beam structure; The depth of the first groove and the second groove is half of the thickness of the second top silicon layer and the third top silicon layer.

9. The method for manufacturing a capacitive micromachined ultrasonic transducer according to claim 8, characterized in that: Before bonding the composite sheet layer with the diaphragm to the first SOI sheet with the first cavity, the method further includes: removing the third buried oxide layer and the third substrate; And / or, after the composite sheet layer with the diaphragm is bonded to the first SOI sheet with the first cavity, the method further includes: removing the second buried oxide layer and the second substrate.

10. The method for manufacturing a capacitive micromachined ultrasonic transducer according to claim 7, characterized in that: The method for preparing the upper electrode comprises: preparing a metal layer as the upper electrode on the upper surface or the lower surface of the diaphragm body; And / or, the method for preparing the lower electrode comprises: preparing a metal layer as the lower electrode on the lower surface of the substrate or using the first top silicon layer as the lower electrode; The third groove and the first top silicon layer are exposed by etching on the transducer substrate, and then a lower electrode pad is prepared at the exposed portion of the first top silicon layer, so that the first top silicon layer is used as the lower electrode, and the first top silicon layer is low-resistance silicon with a resistivity of ≤0.01Ω·cm.

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