Ultrasonic transducer unit, array and preparation method thereof

Abstract

The invention discloses an ultrasonic transducer unit, an ultrasonic transducer array and a preparation method of the ultrasonic transducer unit, and relates to the technical field of sensors. The ultrasonic transducer unit sequentially comprises an upper electrode layer, a vibration film layer, a sealed cavity, a multi-step insulating layer, a substrate layer and a lower electrode layer from top to bottom; the side, facing the sealed cavity, of the multi-step insulating layer is of a multi-step structure from inside to outside from the center, and the sealed cavity is formed between the multi-step structure and the vibration film layer. The method has high detection sensitivity and can be used for weak ultrasonic signal detection.

Description

Technical Field

[0001] The present invention relates to the field of sensor technology, and in particular to an ultrasonic transducer unit, an array and a preparation method thereof. Background Art

[0002] A transducer is a device that converts mechanical vibration into electrical signals or generates mechanical vibration under the drive of an electric field. Currently, the most common ultrasonic transducer on the market is a piezoelectric ultrasonic transducer, which uses the piezoelectric effect to transmit and receive ultrasonic waves.

[0003] The piezoelectric ultrasonic transducer structure is composed of a multi-layer structure. Figure 1 FIG. 1 is a schematic diagram of the structure of a piezoelectric ultrasonic transducer in the prior art. Figure 1 As shown, the ultrasonic transducer is composed of an upper electrode layer 1001, a vibrating film layer 1002, a sealed cavity 1003, an insulating layer 1004, a substrate layer 1005 and a lower electrode layer 1006 from top to bottom. In the cavity structure of this ultrasonic transducer, the height of the cavity is consistent, and the cavity can be made by a single etching process. During operation, the cavity is in a vacuum state, and the top film is bent under atmospheric pressure. The figure shows a schematic diagram of the bending of the top film. A capacitor structure is formed between the bent film (upper electrode) and the bottom silicon substrate (lower electrode, which is highly doped silicon with good conductivity). In this movable capacitor structure, a vacuum medium is formed between the upper and lower electrodes in the cavity. In the ultrasonic transducer of this structure, the upper electrode layer and the vibrating film layer are movable structural layers, which realize the reception of ultrasonic signals by picking up external sound wave vibration signals and converting them into electrical signals. The detection of ultrasonic signals can be realized by detecting electrical signals; and by applying AC voltage to the upper and lower electrodes, the upper electrode layer and the vibrating film layer vibrate under AC excitation to generate ultrasonic signals.

[0004] The inventors of the present application have discovered that the piezoelectric ultrasonic transducer in the above-mentioned prior art has low sensitivity and is difficult to detect weak ultrasonic signals. Summary of the invention

[0005] The present invention provides an ultrasonic transducer unit, an array and a preparation method thereof, which have high ultrasonic detection sensitivity and can realize the detection of weak ultrasonic signals.

[0006] The present invention provides an ultrasonic transducer unit, which comprises, from top to bottom, an upper electrode layer, a vibration film layer, a sealed cavity, a multi-step insulating layer, a substrate layer and a lower electrode layer. The multi-step insulating layer adopts a multi-step structure from the center to the inside to the outside on the side facing the sealed cavity, and a sealed cavity is formed between the multi-step structure and the vibration film layer.

[0007] Optionally, a uniform thin insulating layer is also included between the upper electrode metal layer and the vibration film layer.

[0008] The present invention also provides an ultrasonic transducer array, comprising a plurality of array element structures, each of which is formed by closely arranging a plurality of the above-mentioned ultrasonic transducer units, and the ultrasonic transducer units in each array element structure are connected in parallel.

[0009] The present invention also provides a method for preparing an ultrasonic transducer unit, comprising:

[0010] Step 1, preparing a first substrate, wherein the first substrate comprises a multi-step insulating layer and a substrate layer connected together from top to bottom;

[0011] Step 2: bonding the multi-step insulating layer to the vibration film layer to form a sealed cavity between the multi-step structure of the multi-step insulating layer and the vibration film layer;

[0012] Step three, forming an upper electrode layer on the exposed surface of the vibration film layer;

[0013] Step 4: forming a lower electrode layer on the exposed surface of the substrate layer.

[0014] In the ultrasonic transducer unit, array and preparation method thereof provided by the embodiments of the present invention, the insulating layer forming the sealed cavity in the ultrasonic transducer is set to a multi-step structure to reduce the space occupied by the vacuum medium in the prior art, that is, part of the cavity area in the vacuum medium layer in the prior art is replaced by an insulating material, thereby reducing the size of the vacuum cavity, thereby increasing the capacitance value of the capacitor, that is, the absolute change in capacitance under unit sound pressure can be increased, thereby greatly improving the receiving sensitivity of the ultrasonic transducer. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0016] Figure 1 It is a structural schematic diagram of a piezoelectric ultrasonic transducer in the prior art;

[0017] Figure 2 A schematic structural diagram of an ultrasonic transducer unit provided in an embodiment of the present invention;

[0018] Figure 3 A schematic structural diagram of another ultrasonic transducer unit provided in an embodiment of the present invention;

[0019] Figure 4 Schematic diagram of an array element with a rectangular structure;

[0020] Figure 5 Schematic diagram of array element with square structure;

[0021] Figure 6 Schematic diagram of array elements of stacked structure;

[0022] Figure 7 Schematic diagram of array element with slotted structure;

[0023] Figure 8 A schematic diagram of a linear array structure formed by rectangular structure elements;

[0024] Fig. 9 A schematic diagram of a planar array structure formed by square structure elements;

[0025] Fig.10 Schematic diagram of the ring array structure formed by stacked structure elements;

[0026] Fig.11 A flowchart of a method for preparing an ultrasonic transducer unit provided by an embodiment of the present invention;

[0027] Fig.12 Schematic diagram of etching the first step;

[0028] Fig.13 Schematic diagram of etching the second step. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] In addition, the terms "first", "second", etc. are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. In the description of the following embodiments, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined.

[0031] exist Figure 1 In the prior art shown, in the transmitting state, a DC bias is applied between the upper and lower electrode plates, and through the superposition of AC voltage and DC bias voltage, the film produces simple harmonic vibration along with the AC signal, and the conversion of electrical energy into mechanical energy occurs, thereby generating ultrasonic waves; in the receiving state, a DC bias is applied between the upper and lower electrode plates, and the vibrating film vibrates due to the sound pressure of the ultrasonic wave, causing a change in the capacitance value, and the ultrasonic wave can be detected by detecting the change in capacitance.

[0032] The sensitivity calculation formula of the capacitance sensor is: S=ΔC / ΔX. Among them, S represents sensitivity, ΔC is the capacitance change, and ΔX is the displacement change of the capacitance electrode. Under the premise that the displacement change ΔX of the capacitance electrode is a constant, in the ultrasonic transducer structure design in the prior art, the sealed cavity is a vacuum, and the overall change in the capacitance value of the capacitor ΔC is small, which leads to poor sensitivity of the transducer and cannot meet the demand for high sensitivity in detecting weak signals in practical applications. To this end, an ultrasonic transducer unit, an array and a preparation method thereof are provided in an embodiment of the present invention. A sealed cavity is formed by adopting an insulating layer and a vibrating film layer with a multi-step structure to obtain a larger capacitance change, thereby improving the sensitivity of the ultrasonic transducer and realizing the detection of weak ultrasonic signals.

[0033] The following specific embodiments may be combined with each other, and the same or similar concepts or processes may not be described in detail in some embodiments. To make the technical solution of the present invention clearer, the embodiments of the present invention are described in detail below in conjunction with the accompanying drawings.

[0034] Figure 2 A schematic diagram of the structure of an ultrasonic transducer unit provided in an embodiment of the present invention is shown in FIG. Figure 2 As shown, the ultrasonic transducer unit of the structure includes, from top to bottom, an upper electrode layer 2001, a vibrating film layer 2002, a sealed cavity 2003, a multi-step insulating layer 2004, a substrate layer 2005, and a lower electrode layer 2006. The multi-step insulating layer adopts a multi-step structure from the center to the outside on the side facing the sealed cavity, and a sealed cavity is formed between the multi-step structure and the vibrating film layer. The number of steps of the multi-step insulating layer is a finite integer.

[0035] In order to improve the receiving sensitivity of the ultrasonic transducer, in the embodiment of the present invention, one side of the vacuum cavity in the prior art is improved into a multi-step shape, and a part of the space of the vacuum cavity is filled with a material with a larger dielectric constant, so as to achieve the effect of improving the receiving sensitivity of the transducer by increasing the change in the capacitance value of the capacitor. The specific principle of improving the sensitivity is analyzed as follows:

[0036] The calculation formula of capacitor capacitance C is:

[0037] C=εS / d

[0038] d=d1+d2 / ε ox

[0039] Among them, ε represents the relative dielectric constant, S is the coverage area of ​​the substrate, and d is the distance between the plates. d1 represents the thickness of the vacuum layer, d2 represents the thickness of the insulating layer, and ε ox It represents the dielectric constant of the insulating layer relative to the vacuum layer.

[0040] In an embodiment of the present invention,

[0041] d 阶梯 =d1-x+(d2+x) / ε ox =d-x+x / ε ox

[0042] Among them, d 阶梯 represents the average plate spacing, and x represents the average thickness of the steps.

[0043] Since the dielectric constant ε of the insulating material ox is often much larger than 1. For example, the relative dielectric constant of commonly used silicon dioxide material is 3.9. Therefore, the average plate spacing d in the embodiment of the present invention is 阶梯 Compared with the prior art, the plate spacing d is greatly reduced, and the capacitance of the capacitor is inversely proportional to the plate spacing. Therefore, the capacitance in the embodiment of the present invention is greatly increased.

[0044] Under the action of unit sound pressure, the deformation of the upper electrode vibration film remains unchanged. Therefore, under the premise that the displacement change ΔX of the capacitor electrode is a constant, the overall change ΔC of the capacitor capacitance value increases, thereby improving the receiving sensitivity of the transducer.

[0045] Specifically, in the ultrasonic transducer unit provided in the above embodiment, both the vibration film layer and the substrate layer can be made of single crystal silicon material. Since single crystal silicon is a highly doped material with excellent mechanical properties, it is widely used in micro sensors. As a deformation material, the single crystal silicon film layer can form a good ohmic contact with the upper electrode metal layer to achieve good bidirectional conductivity. The single crystal silicon substrate layer and the lower electrode metal layer can also form a good ohmic contact to achieve good bidirectional conductivity. Of course, as known to those skilled in the art, other materials can also be selected to form the above-mentioned vibration film layer and substrate layer according to the performance requirements of the ultrasonic transducer unit to be formed.

[0046] Specifically, in the ultrasonic transducer unit provided in the above embodiment, the multi-step insulating layer may be a silicon dioxide insulating layer to prevent the single crystal silicon thin film from contacting the single crystal silicon substrate layer, so as to prevent the upper and lower electrodes from being short-circuited due to breakdown. Of course, as known to those skilled in the art, other materials may also be selected to form the multi-step insulating layer according to the performance requirements of the ultrasonic transducer unit to be formed.

[0047] Furthermore, in order to increase the adhesion of metal on the film surface, improve the reliability of the device, and facilitate the adjustment of the driving voltage, another embodiment of the present invention also includes a uniform thin insulating layer between the upper electrode metal layer and the vibration film layer. Figure 3 A schematic diagram of the structure of another ultrasonic transducer unit provided in an embodiment of the present invention is shown in FIG. Figure 3As shown, the ultrasonic transducer unit in this embodiment includes, from top to bottom: an upper electrode layer 3001, a uniform film layer 3002, a vibration film layer 3003, a sealed cavity 3004, a multi-step insulating layer 3005, a substrate layer 3006 and a lower electrode layer 3007. The uniform thin insulating layer 3002 can be a silicon dioxide insulating layer. The silicon dioxide film has good insulation performance, good stability and a firm film layer. Of course, as known to those skilled in the art, other materials can also be selected to form the uniform thin insulating layer according to the performance requirements of the ultrasonic transducer unit to be formed.

[0048] The embodiment of the present invention arranges the inner wall of the insulating layer side that forms the sealed cavity in the prior art of the ultrasonic transducer as a multi-step insulating layer, so that part of the cavity area in the original vacuum cavity is replaced by an insulating layer with a larger relative dielectric constant, such as silicon dioxide material, to reduce the size of the vacuum cavity and increase the capacitance change, thereby improving the sensitivity of sound pressure detection using the ultrasonic transducer and realizing the detection of weak ultrasonic signals.

[0049] The above embodiments are the structure of a single ultrasonic transducer unit and the analysis of improving sensitivity. For applications in different fields, multiple ultrasonic transducer units are usually closely arranged and connected in parallel to form array elements to improve the signal acquisition effect, that is, the upper plate layers of the ultrasonic transducer units in the same array element are connected together, and the lower plate layers are connected together. Finally, multiple array elements of the same structural type are arranged in an array to form an ultrasonic transducer array structure for application in different occasions. The array element structure can be divided into a rectangular structure, a square structure, a stacked structure or a slotted structure according to different arrangement methods. Figure 4 It is a schematic diagram of the array element with a rectangular structure. Figure 5 Schematic diagram of the array element with a square structure. Figure 6 Schematic diagram of the stacked structure. Figure 7 Schematic diagram of the array element with slotted structure. Figure 4-Figure 7 The above diagrams show the arrangement of the ultrasonic transducer array elements. Figure 2 or Figure 3 The transducer units shown are arranged closely in sequence. As shown in the figure, a single circle represents a basic ultrasonic transducer unit, and the outer frame is the boundary of the corresponding array element structure.

[0050] The repeated arrangement of array elements of the same structural type constitutes various array structures. The repeated arrangement of array element structures of the same arrangement method forms an array structure of an ultrasonic transducer. For example, the repeated arrangement of array element structures of multiple rectangular structures can form a linear array, the repeated arrangement of array element structures of multiple slotted structures can also form a linear array, the repeated arrangement of array element structures of multiple square structures can form a planar array, and the repeated arrangement of array element structures of multiple stacked structures can form a circular array. Figure 8 Schematic diagram of the linear array structure formed by rectangular structure elements. Fig. 9 Schematic diagram of the surface array structure formed by square structure elements. Fig.10 Schematic diagram of the ring array structure formed by stacked structure elements, such as Figure 8-Figure 10 As shown in the figure, a single circle represents a basic ultrasonic transducer unit, and multiple circles covered by an outer frame are a corresponding array element structure. The above multiple array elements are repeatedly arranged to form various array structures. Rectangular structures and slotted structures are mostly used to form linear arrays, such as Figure 8 As shown in the figure, the slotted structure has a greater area utilization rate and has great advantages in the field of sensors with a large coverage area. The square structure is mostly used to form a surface array, such as Fig. 9 As shown in the figure, thanks to its equal length advantage, the surface array is evenly distributed and has a good signal collection effect. The stacking structure is often used to form a circular array, such as Fig.10 As shown, the structure has strong symmetry and maneuverability, and its signal transmission and reception effects are excellent when performing operations such as offset and rotation.

[0051] Corresponding to the above-mentioned ultrasonic transducer unit and array, the embodiment of the present invention also provides a corresponding preparation method. The preparation process is described in detail below using a single ultrasonic transducer unit. Based on the semiconductor device preparation process, the above-mentioned transducer array element or array can also be prepared by a similar method.

[0052] Fig.11 A flowchart of a method for preparing an ultrasonic transducer unit provided in an embodiment of the present invention is shown in FIG. Fig.11 As shown, the method for preparing the ultrasonic transducer unit provided in this embodiment includes the following steps:

[0053] Step S1, preparing a first substrate, the first substrate comprising a multi-step insulating layer and a substrate layer connected from top to bottom. Before using the first substrate, cleaning and other preparations are required.

[0054] In this step, the etching of the multi-step structure is mainly completed. Etching, in short, is to remove the thin film layer that is not masked by the resist, so as to obtain the same pattern on the thin film as on the resist film. The multi-step structure needs to be etched through multiple times with masks, layer by layer, and attention should be paid to controlling the time parameters during the process. If the etching time is too long, the steps will become thinner, or even be etched through, because the thickness of the insulating layer is originally very small, and if the etching time is too short, the step structure is not obvious, resulting in poor sensitivity improvement.

[0055] For the control of etching depth, there is the following analysis. Etching has three parameters, namely etching speed v (mm / min), etching depth h (mm), and etching time t. The three have a functional relationship of v = h / t, so v is constant. You only need to control the etching time parameter to control the etching depth. The specific etching type is divided into two types due to different structures, etching single crystal silicon and etching silicon dioxide.

[0056] In a specific application, a single crystal silicon substrate can be etched to form a multi-step structure, and then a silicon dioxide insulating layer can be formed on the surface of the multi-step structure; or a silicon dioxide substrate can be etched in multiple steps to form a multi-step structure, and then the surface facing away from the multi-step structure is bonded to a single crystal silicon substrate to form a first substrate. The process of preparing a first substrate having a multi-step structure is as follows: the step of etching a single crystal silicon wafer to form a multi-step structure includes:

[0057] Step 11, prepare a silicon wafer, and etch a multi-step structure on the first surface of the silicon wafer.

[0058] Step 12, oxidizing the multi-step structure surface of the silicon wafer to form a silicon dioxide insulating film layer on the surface as a multi-step insulating layer, and the rest of the silicon wafer as a substrate layer.

[0059] The steps of etching a silicon dioxide substrate to form a multi-step structure include:

[0060] Step 13, preparing a silicon dioxide substrate, and etching a multi-step structure on a first surface of the silicon dioxide substrate.

[0061] Step 14: Bonding the substrate layer to the second surface of the silicon dioxide substrate facing away from the multi-step structure to form a first substrate.

[0062] The above-mentioned etching of the multi-step structure is specifically as follows: multiple masks are used to sequentially etch out the outermost step, the second outermost step, ... the bottom of the innermost step of the multi-step structure, and the etching time of each layer is controlled to obtain a corresponding step depth.

[0063] The following is an example of etching single crystal silicon. Multiple masks are used to etch single crystal silicon to form a multi-step structure. Take a silicon wafer, expose the part to be etched, cover the other parts with a mask, place it in the etching solution for etching, and control the etching time to achieve the control of the etching depth. In this way, the first layer of steps, that is, the outermost layer of steps, can be obtained, and its structure is similar to that of an ordinary sensor structure. Repeat the above steps to obtain the second layer of steps, that is, the second outer layer of steps, and so on, to obtain multiple layers of steps until the specified target number of steps is reached. The obtained silicon wafer with a multi-step structure is heated to oxidize it, and a silicon dioxide protective film is obtained on the surface, that is, a multi-step insulating layer structure is formed. The unetched single crystal silicon is used as the substrate layer. The silicon dioxide protective film grown by this method is uniform and dense, and has good insulation and corrosion resistance.

[0064] Fig.12 This is the etching diagram of the first step. Fig.13 This is a schematic diagram of etching the second layer of steps. Etching of more layers is carried out in the same way, with multiple maskings layer by layer until the target number of steps is reached.

[0065] When etching a multi-step structure with a silicon dioxide substrate, the etching method is similar to the etching of single crystal silicon. After etching is completed, it is necessary to bond the substrate surface facing away from the multi-step structure with the single crystal silicon substrate layer. The chemical properties of silicon dioxide and single crystal silicon are used to bond their external electrons to form a covalent bond and form a stable structure. The specific implementation steps can use high-temperature pressing technology to press the silicon dioxide insulating layer and the single crystal silicon layer under high temperature conditions to achieve the purpose of combining the two.

[0066] Step S2 , bonding the multi-step insulating layer to the vibration film layer, so as to form a sealed cavity between the multi-step structure of the multi-step insulating layer and the vibration film layer.

[0067] The vibration film layer is bonded to the multi-step insulating layer. The bonding method is as described above. The chemical properties of silicon dioxide and single crystal silicon are utilized to perform a pressing process at high temperature so that the electronic bonding between the contact surfaces of the two forms a stable structure.

[0068] Step S3, forming an upper electrode layer on the exposed surface of the vibration film layer.

[0069] Step S4, forming a lower electrode layer on the exposed surface of the substrate layer.

[0070] The process of forming the electrode layer in steps S3 and S4 is the process of bonding single crystal silicon to the metal electrode. The available materials for the metal electrode are relatively wide. The present invention uses metal aluminum (AL) as an example. Silicon-aluminum alloy is an alloy material with excellent performance, and has the advantages of high strength, high hardness, high temperature resistance, corrosion resistance, etc., and has a natural advantage in the field of microsensors. Aluminum and silicon will generate silicon-aluminum alloy and silicon dioxide under high temperature conditions above 800°C. Therefore, the process conditions require a temperature of more than 800°C to make the metal layer and the single crystal silicon layer contact, and the use of a pressing process can make the two react and bond together.

[0071] In the above embodiment, a uniform thin film insulating layer may be formed between the formed upper electrode layer and the vibration film to improve the reliability of the device, that is, step three may specifically include:

[0072] Step 31, forming a uniform thin insulating layer on the exposed surface of the vibration film layer;

[0073] Step 32, forming an upper electrode metal layer on the exposed surface of the uniform thin insulating layer.

[0074] The uniform thin insulating layer can increase the adhesion of the metal on the film surface, improve the reliability of the device, and adjust the driving voltage. Specifically, the uniform thin insulating layer can be a silicon dioxide insulating layer. The silicon dioxide film has good insulation properties, good stability, and a strong film layer. Of course, as known to those skilled in the art, other materials can also be selected to form the uniform thin insulating layer according to the performance requirements of the ultrasonic transducer unit to be formed.

[0075] The preparation method of the ultrasonic transducer unit of this embodiment can be used to prepare the above Figure 2 or Figure 3 The ultrasonic transducer unit and the corresponding ultrasonic transducer array shown in the figure form a multi-step insulating layer to reduce the space occupied by the vacuum cavity in the prior art, thereby reducing the size of the vacuum cavity and improving the receiving sensitivity of the ultrasonic transducer. That is, the technical effect achieved is similar to the technical effect of the above-mentioned ultrasonic transducer unit and will not be repeated here.

[0076] Those skilled in the art will readily appreciate other embodiments of the present invention after considering the specification and practicing the invention disclosed herein. The present invention is intended to cover any variations, uses or adaptations of the present invention that follow the general principles of the present invention and include common knowledge or customary techniques in the art that are not disclosed by the present invention. The description and examples are to be considered exemplary only, and the true scope and spirit of the present invention is indicated by the following claims.

[0077] It should be understood that the present invention is not limited to the exact construction that has been described above and shown in the drawings, and that various modifications and changes may be made without departing from the scope thereof. The scope of the present invention is limited only by the appended claims.

Claims

1. An ultrasonic transducer unit, characterized in that: From top to bottom, it includes: an upper electrode layer, a vibration film layer, a sealed cavity, a multi-step insulating layer, a substrate layer and a lower electrode layer. The multi-step insulating layer adopts a multi-step structure from the center to the inside to the outside on the side facing the sealed cavity, and a sealed cavity is formed between the multi-step structure and the vibration film layer.

2. The ultrasonic transducer unit according to claim 1, characterized in that: A uniform thin insulating layer is also included between the upper electrode layer and the vibration film layer.

3. The ultrasonic transducer unit according to claim 1, characterized in that: The vibration film layer and the substrate layer are both made of single crystal silicon material.

4. The ultrasonic transducer unit according to any one of claims 1 to 3, characterized in that: The number of steps of the multi-step insulating layer is a finite integer.

5. An ultrasonic transducer array, characterized in that: It comprises a plurality of array element structures, each of which is formed by closely arranging a plurality of ultrasonic transducer units according to any one of claims 1 to 4, and the ultrasonic transducer units in each array element structure are connected in parallel.

6. The ultrasonic transducer array according to claim 5, characterized in that: The array element structure is arranged in a rectangular structure, a square structure, a stacked structure or a slotted structure; array element structures of the same arrangement are repeatedly arranged to form an array structure of an ultrasonic transducer, multiple rectangular structures or multiple slotted structures are repeatedly arranged to form a linear array, multiple square structures are repeatedly arranged to form a planar array, and multiple stacked structures are repeatedly arranged to form a circular array.

7. A method for preparing an ultrasonic transducer unit, characterized in that: include: Step 1, preparing a first substrate, wherein the first substrate comprises a multi-step insulating layer and a substrate layer connected together from top to bottom; Step 2: bonding the multi-step insulating layer to the vibration film layer to form a sealed cavity between the multi-step structure of the multi-step insulating layer and the vibration film layer; Step three, forming an upper electrode layer on the exposed surface of the vibration film layer; Step 4: forming a lower electrode layer on the exposed surface of the substrate layer.

8. The method according to claim 7, characterized in that The step three specifically includes: Step 31, forming a uniform thin insulating layer on the exposed surface of the vibration film layer; Step 32, forming an upper electrode metal layer on the exposed surface of the uniform thin insulating layer.

9. The method according to claim 7 or 8, characterized in that: The step one comprises: Step 11, preparing a silicon wafer, and etching a multi-step structure on a first surface of the silicon wafer; Step 12, oxidizing the multi-step structure surface of the silicon wafer to form a silicon dioxide insulating film layer on the surface as a multi-step insulating layer, and the rest of the silicon wafer as a substrate layer; or, Step 13, preparing a silicon dioxide substrate, and etching a multi-step structure on a first surface of the silicon dioxide substrate; Step 14: Bonding the substrate layer to the second surface of the silicon dioxide substrate facing away from the multi-step structure.

10. The method according to claim 9, characterized in that The etching of the multi-step structure is specifically as follows: The outermost step, the second outermost step, and the bottom of the innermost step of the multi-step structure are etched out in sequence using multiple masks. The etching time of each layer is controlled to obtain a corresponding step depth. The number of steps in the multi-step structure is a finite integer.

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