MEMS structure and preparation method thereof, and ultrasonic transducer unit

Abstract

The invention relates to the technical field of ultrasonic transducers, in particular to an MEMS structure, a preparation method thereof and an ultrasonic transducer unit. The MEMS structure comprises a supporting structure, wherein a cavity is formed in the inner side of the supporting structure; a step structure is formed on the upper surface of the peripheral part; the piezoelectric composite layer is formed on the supporting structure, and in the horizontal direction, the first inner side part of the piezoelectric composite layer and the lower concave surface of the step structure form an annular groove; in the vertical direction, the piezoelectric composite layer comprises a mechanical layer, a bottom electrode, a piezoelectric layer and a top electrode. The capacitor structure comprises a bottom electrode and a top electrode, and the bottom electrode is formed on the lower concave surface of the step structure; the top electrode is formed on the bottom surface, facing the annular groove, of the mechanical layer and is relatively parallel to the bottom electrode, and an annular groove space between the bottom electrode and the top electrode serves as a capacitor air gap. According to the invention, the advantages of the PMUT and the CMUT are integrated, and the energy efficiency and the imaging quality are optimally balanced.

Description

Technical Field

[0001] This invention relates to the field of ultrasonic transducer technology, and in particular to a MEMS structure and its fabrication method, and an ultrasonic transducer unit. Background Technology

[0002] Piezoelectric micromechanical ultrasonic transducers (PMUTs) and capacitive micromechanical ultrasonic transducers (CMUTs) are novel microelectromechanical system (MEMS) ultrasonic transducers that have emerged in recent years. Compared with traditional bulk piezoelectric ceramic transducers, they have advantages such as miniaturization, ease of large-scale array integration, wider frequency bandwidth, compatibility with CMOS processes, reduced costs, and improved resolution. Therefore, they have shown broad application prospects in various scenarios such as flow velocity detection (e.g., ultrasonic Doppler three-dimensional flow velocity detectors), medical imaging (e.g., ultrasonic probes, wearable imaging devices), industrial inspection (non-destructive testing, liquid level measurement), fingerprint recognition, biosensing, and underwater communication. The advantage of PMUT is that it is directly driven by the piezoelectric effect without the need for bias voltage. The driving circuit is simple and has low power consumption, and it can generate strong sound pressure output. It is suitable for efficient transmission of ultrasonic signals in low-voltage, miniaturized devices. The disadvantage is that the bandwidth is relatively limited. The advantage of CMUT is that its capacitive structure brings ultra-wide bandwidth and high sensitivity. It is particularly suitable for capturing and resolving high-frequency detailed signals. At the same time, it can be highly integrated with CMOS circuits to realize large-scale array reception. However, its stability under high-voltage drive is relatively insufficient. Summary of the Invention

[0003] I. Technical problems to be solved

[0004] The present invention aims to at least partially solve one of the above-mentioned technical problems.

[0005] II. Technical Solution

[0006] A first aspect of the present invention provides a MEMS structure. The MEMS structure includes:

[0007] The supporting structure has a cavity formed on its inner side; the upper surface of its outer part forms a stepped structure, with the protruding surface of the stepped structure located on the outside of the concave surface.

[0008] The piezoelectric composite layer is formed on the supporting structure.

[0009] In the horizontal direction, the outer part of the piezoelectric composite layer is supported on the protruding surface of the stepped structure, the first inner part of which forms an annular groove with the concave surface of the stepped structure, and the second inner part of which is positioned towards the cavity.

[0010] In the vertical direction, the piezoelectric composite layer includes: a mechanical layer, the outer portion of which is supported by the protruding surface of the stepped structure; a bottom electrode, a piezoelectric layer, and a top electrode, which are formed sequentially on the front side of the mechanical layer;

[0011] The capacitor structure includes a bottom electrode and a top electrode, wherein the bottom electrode is formed on the concave surface of the stepped structure; the top electrode is formed on the bottom surface of the mechanical layer facing the annular groove, and is arranged parallel to the bottom electrode, and the annular groove space between the bottom electrode and the top electrode serves as the capacitor air gap.

[0012] In some embodiments of the present invention, the MEMS structure serves as an ultrasonic transducer. When the MEMS ultrasonic transducer is in the transmitting state, the bottom electrode of the piezoelectric composite layer is grounded, and the top electrode is loaded with an AC voltage. Under the action of the inverse piezoelectric effect, the piezoelectric layer generates lateral strain, causing the composite layer to bend and deform, and the piezoelectric composite layer emits ultrasonic waves. When the MEMS ultrasonic transducer is in the receiving state, the bottom electrode of the capacitor structure is grounded, and the top electrode is loaded with a DC bias voltage. The piezoelectric composite layer bends and deforms under the action of incident ultrasonic waves, changing the distance between the bottom electrode and the top electrode in the capacitor structure. The change in capacitance between the two reflects the physical characteristics of the incident ultrasonic waves.

[0013] In some embodiments of the present invention, the support structure is a substrate.

[0014] In some embodiments of the present invention, in the capacitor structure, the bottom electrode and the top electrode are positioned closer to the cavity side and further away from the protruding surface side of the stepped structure.

[0015] In some embodiments of the present invention, in the piezoelectric composite layer, the mechanical layer is made of one or more of the following materials: silicon, silicon nitride, silicon oxide, piezoelectric material; and / or, the piezoelectric layer is made of one or more of the following materials: aluminum nitride, scandium-doped aluminum nitride, zinc oxide, piezoelectric ceramic; and / or, the bottom electrode and / or top electrode are made of one or more of the following materials: molybdenum, gold, aluminum, chromium, doped polycrystalline silicon.

[0016] In some embodiments of the present invention, the thickness of the piezoelectric layer and the mechanical layer ranges from 0.1 μm to 10 μm; and / or, the thickness of the bottom electrode and the top electrode ranges from 20 nm to 200 nm; and / or, the depth of the annular groove space ranges from 0.05 μm to 5 μm.

[0017] In some embodiments of the present invention, the cavity and the annular groove on the inner side of the support structure are both regular N-gons in their horizontal projection, where N≥3; the first inner portion and / or the second inner portion of the piezoelectric composite layer are formed with an expansion slit of a quasi-regular N-gon, wherein for each side of the quasi-regular N-gon, the side is parallel to the corresponding side of the regular N-gon; the expansion slit includes: a first slit and a second slit, which extend from the vertex of the side toward the midpoint of the side, respectively, and are symmetrically arranged with a gap between them; and an intermediate slit, located inside or outside the gap between the first slit and the second slit.

[0018] In some embodiments of the present invention, N = 6.

[0019] In some embodiments of the present invention, the width of the widening slit ranges from 0.1 μm to 10 μm.

[0020] In some embodiments of the present invention, the expansion slit of the quasi-regular N-gon is located in the first inner portion, and the first inner portion and the second inner portion of the piezoelectric composite layer are formed with N stress-reducing slits. For each stress-reducing slit, it starts from the corresponding vertex of the quasi-regular N-gon and extends toward the center of the quasi-regular N-gon.

[0021] In some embodiments of the present invention, the expansion slit of the quasi-regular N-gon is located in the second inner portion, and the first inner portion and the second inner portion of the piezoelectric composite layer are formed with N stress-reducing slits. For each stress-reducing slit, it starts from the corresponding vertex of the quasi-regular N-gon and extends in the opposite direction toward the center of the regular N-gon.

[0022] In some embodiments of the present invention, in the region where the bottom electrode of the capacitor structure is located, an upper protrusion is formed on the concave surface of the stepped structure, extending through the bottom electrode and upward, and no electrode material is formed on the upper protrusion.

[0023] In some embodiments of the present invention, in the region where the top electrode of the capacitor structure is located, the piezoelectric composite layer has a lower protrusion extending downward through the top electrode and facing the bottom surface of the annular groove, and no electrode material is formed on the lower protrusion.

[0024] In some embodiments of the present invention, the depth h of the annular groove space in the vertical direction is 0.05μm-5μm; the height h1 of the upper and lower protrusions satisfies: h / 10≤h1≤h / 2.

[0025] A second aspect of the present invention provides a method for fabricating the above-described MEMS structure. The method for fabricating the MEMS structure includes:

[0026] Step A: Forming a groove on the substrate;

[0027] Step B: Deposit conductive material at the bottom of the groove and pattern the conductive material to form the bottom electrode of the capacitor structure;

[0028] Step C: Deposit a sacrificial layer in the groove, and then pattern the upper surface of the sacrificial layer to form a template structure for the top electrode of the capacitor structure;

[0029] Step D: Deposit conductive material over the sacrificial layer to form the top electrode of the capacitor structure;

[0030] Step E, depositing a mechanical layer;

[0031] Step F: Sequentially deposit the bottom electrode, the piezoelectric layer, and the top electrode of the piezoelectric composite layer above the mechanical layer;

[0032] Step G: Graphicalize the top electrode;

[0033] Step I: Deeply etch the back side of the substrate to form a back cavity;

[0034] Step J involves releasing the sacrificial layer through a buffered oxide etching solution to form the final MEMS structure.

[0035] In some embodiments of the present invention, in step D, the conductive material and the sacrificial layer are patterned sequentially to form a through hole penetrating the top electrode and a notch on the surface of the sacrificial layer; in step E, the material of the mechanical layer fills the notch on the surface of the sacrificial layer and the through hole penetrating the top electrode to form a lower protrusion structure.

[0036] In some embodiments of the present invention, the MEMS structure is the MEMS structure described above, and after step G, the method further includes step H, which involves sequentially patterning the piezoelectric layer, the bottom electrode, and the mechanical layer to form an expansion slit and a stress-reducing slit that penetrate the piezoelectric composite layer.

[0037] A third aspect of the present invention provides an ultrasonic transducer unit. The ultrasonic transducer unit includes:

[0038] The sensing module has the aforementioned MEMS structure;

[0039] The signal processing module connects the signals to the bottom and top electrodes of the piezoelectric composite layer in the MEMS structure; simultaneously, the signals are connected to the bottom and top electrodes of the capacitor structure.

[0040] III. Beneficial Effects

[0041] This invention combines the advantages of PMUT and CMUT, achieving an optimal balance between energy efficiency and imaging quality. This innovative design, which integrates PMUT transmission and CMUT reception, breaks through the performance limitations of traditional single transducers in ultrasonic imaging systems, ensuring both efficient ultrasonic output and high-sensitivity reception, making it suitable for various applications requiring high-performance ultrasonic detection. Attached Figure Description

[0042] Figure 1 This is a perspective view of the MEMS ultrasonic transducer according to the first embodiment of the present invention.

[0043] Figure 2 for Figure 1 The top view of the MEMS ultrasonic transducer shown.

[0044] Figure 3 for Figure 2 The diagram shows a cross-sectional view of the MEMS ultrasonic transducer along plane AA.

[0045] Figure 4A and Figure 4B They are respectively Figure 1The diagram shows the working mechanism of the MEMS ultrasonic transducer in ultrasonic transmission and ultrasonic reception states.

[0046] Figure 5 for Figure 1 The diagram shows the process flow chart for a MEMS ultrasonic transducer.

[0047] Figure 6 This is a top view of the MEMS ultrasonic transducer according to the second embodiment of the present invention.

[0048] Figure 7 for Figure 6 The diagram shows a cross-sectional view of the MEMS ultrasonic transducer along section AA. Detailed Implementation

[0049] This invention combines the advantages of PMUT and CMUT, proposing a piezoelectric transmitting and capacitive receiving MUT unit structure. Specifically, it uses a PMUT as the transmitting end to provide efficient, low-power ultrasound output, and a CMUT as the receiving end, achieving accurate signal detection and high-resolution imaging with high bandwidth and high sensitivity. This achieves an optimal balance between energy efficiency and image quality, making it particularly suitable for applications such as portable medical imaging, wearable health monitoring, and high-resolution ultrasound detection.

[0050] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0051] The first aspect of this invention provides a MEMS structure. In the following embodiments, this MEMS structure is described as an ultrasonic transducer, but those skilled in the art should understand that this MEMS structure can be used, but is not limited to, ultrasonic transducers, microphones, speakers, pressure sensors, or other actuators.

[0052] The first embodiment of the present invention is a MEMS ultrasonic transducer that integrates the advantages of both PMUT and CMUT. Figure 1 This is a perspective view of the MEMS ultrasonic transducer according to the first embodiment of the present invention. Figure 2 for Figure 1 The top view of the MEMS ultrasonic transducer shown. Figure 3 for Figure 2 The figure shows a cross-sectional view of the MEMS ultrasonic transducer along plane AA. Referring to the attached figure, the MEMS ultrasonic transducer of this embodiment includes:

[0053] The support structure 10 has a cavity 12 formed on its inner side; the upper surface of its outer peripheral portion 11 has a stepped structure, and the protruding surface of the stepped structure is located outside the concave surface.

[0054] A piezoelectric composite layer 20 is formed on the support structure.

[0055] In the horizontal direction, the outer portion of the piezoelectric composite layer is supported on the protruding surface of the stepped structure, and its first inner portion forms an annular groove with the concave surface of the stepped structure, and its second inner portion is disposed towards the cavity; in the vertical direction, the piezoelectric composite layer includes: a mechanical layer 21, the outer portion of which is supported on the protruding surface of the stepped structure; a bottom electrode 22, a piezoelectric layer 23, and a top electrode 24, which are sequentially formed on the front side of the mechanical layer;

[0056] The capacitor structure 30 includes a bottom electrode 31 and a top electrode 33, wherein the bottom electrode is formed on the concave surface of the stepped structure; the top electrode is formed on the bottom surface of the mechanical layer facing the annular groove, and is arranged parallel to the bottom electrode; the annular groove space 32 between the bottom electrode and the top electrode serves as the capacitor air gap.

[0057] The following is a detailed description of each component of the MEMS ultrasonic transducer in this embodiment.

[0058] In this embodiment, the support structure 10 is a processed substrate, i.e., a cavity and stepped structure are formed on the substrate, but the present invention is not limited thereto. In other embodiments of the present invention, the support structure may include two parts: a substrate and a material layer forming the stepped structure, which can also achieve the present invention and are also within the protection scope of the present invention.

[0059] In this embodiment, an annular groove is formed below the piezoelectric composite layer 20. This annular groove extends into the substrate 10 and serves to form a capacitor structure and act as an air gap for the capacitor structure. The horizontal projection of the hexagonal back cavity 12 falls within the horizontal projection of the annular groove. The presence of the back cavity 12 allows the piezoelectric composite layer to emit ultrasonic signals at maximum amplitude.

[0060] In this embodiment, the bottom electrode and top electrode are positioned closer to the cavity side and further away from the protruding surface of the stepped structure in the capacitor structure. This arrangement ensures that the diaphragm displacement on this side is maximized during reception, resulting in the highest receiving sensitivity. However, this invention is not limited to this. In other embodiments of this invention, the bottom electrode and top electrode can also be moved towards the protruding surface of the stepped structure, achieving the same result and falling within the scope of protection of this invention.

[0061] In the piezoelectric composite layer, the mechanical layer 21 can be silicon (Si), silicon nitride (Si3N4), silicon oxide (SiO2), and various piezoelectric materials. The piezoelectric layer 23 can be aluminum nitride (AlN), scandium-doped aluminum nitride (Sc), etc. x Al 1-xElectrodes 22, 24, 31, and 33 can be made of materials such as nitrogen (N), zinc oxide (ZnO), and piezoelectric ceramics (PZT), while electrodes 22, 24, 31, and 33 can be made of materials such as molybdenum (Mo), gold (Au), aluminum (Al), chromium (Cr), and doped polycrystalline silicon (DOPOS). The preferred thickness range for the piezoelectric and mechanical layers is 0.1 μm to 10 μm, the preferred thickness range for the electrode layers is 20 nm to 200 nm, and the preferred depth range for the annular groove space 32 is 0.05 μm to 5 μm.

[0062] In this embodiment, the substrate, cavity, diaphragm, and annular groove are all hexagonal, and each of their sides is parallel. The hexagonal design achieves optimal performance in terms of geometry, mechanics, acoustics, and manufacturing processes: its near-circular shape ensures more uniform stress distribution and higher reliability during operation, while also enabling efficient planar filling, resulting in a larger effective vibration area within the same chip area, thus improving transducer efficiency and sensitivity; at the array level, the hexagonal arrangement is equivalent to more uniform spatial sampling, significantly reducing beam sidelobes and improving directivity and imaging quality; in MEMS manufacturing, the compact and regular hexagonal structure facilitates photolithography and wiring, and makes fuller use of the silicon wafer area. Therefore, the hexagonal unit is one of the best geometric solutions balancing performance optimization and manufacturing feasibility.

[0063] It should be noted that although this embodiment uses a hexagon as an example, the present invention is not limited thereto. In other embodiments of the present invention, the substrate, cavity, diaphragm, and annular groove can also be other regular N-gons, where N≥3. Although their performance is slightly inferior to that of this embodiment, the present invention can still be achieved and is also within the scope of protection of the present invention.

[0064] Referring to the accompanying drawings, in this embodiment, the preferred side length of the hexagonal piezoelectric composite layer is 0.05 mm to 3 mm. A slit 25 penetrating the piezoelectric composite vibration layer is provided on the hexagonal piezoelectric composite layer. The preferred width of the slit 25 is 0.1 μm to 10 μm. This slit is divided into two types: expansion slits and stress-reducing slits. These will be described separately below.

[0065] (1) Widening slit

[0066] The first inner portion and / or the second inner portion of the piezoelectric composite layer are formed with an expanded slit resembling a regular N-gon. In this embodiment, the expanded slit is formed in the first inner portion of the piezoelectric composite layer. For each side of the regular N-gon, the side is parallel to the corresponding side of the regular N-gon.

[0067] The widening slit includes: a first slit and a second slit, which extend from the vertex of the edge toward the midpoint of the edge, respectively, and are symmetrically arranged with a gap between them; and an intermediate slit, located inside or outside the gap between the first slit and the second slit.

[0068] (2) Stress-reducing slit

[0069] The first and second inner portions of the piezoelectric composite layer have six stress-reducing slits. Each stress-reducing slit originates from a corresponding vertex of a quasi-regular N-gon and extends towards the center of the quasi-regular N-gon. The endpoints of the six stress-reducing slits form a new hexagon.

[0070] In this embodiment, the amplitude expansion slit and the stress reduction slit can effectively reduce the bending stiffness of the diaphragm edge and the whole, and can also effectively release residual stress, ultimately improving the amplitude and emission sensitivity.

[0071] Please refer to Figure 3 Below the mechanical layer 21 in the piezoelectric composite layer, there is a lower protrusion 26 that penetrates the top electrode 33 of the capacitor structure. No electrode material is formed on the lower protrusion. The depth h of the annular groove space in the vertical direction ranges from 0.05 μm to 5 μm; the height h1 of the lower protrusion satisfies: h / 10 ≤ h1 ≤ h / 2. This lower protrusion 26 mainly serves as a limiting element, effectively preventing the bottom electrode and top electrode from short-circuiting due to attraction.

[0072] This invention is not limited thereto. In other embodiments of this invention, in the region where the bottom electrode of the capacitor structure is located, an upper protrusion is formed on the concave surface of the stepped structure, penetrating the bottom electrode and extending upward, and no electrode material is formed on the lower protrusion. The function of the lower protrusion is similar to that of the upper protrusion in the above embodiments, and will not be repeated here.

[0073] Figure 4A and Figure 4B They are respectively Figure 1 The diagram shows the working mechanism of the MEMS ultrasonic transducer in ultrasonic transmission and ultrasonic reception states.

[0074] (1) Launch status

[0075] like Figure 4A As shown, in the emission state, the bottom electrode 22 of the piezoelectric composite layer is grounded, and an AC voltage is applied to the top electrode 24.

[0076] V = V DC +V AC sin(2πft)

[0077] Among them, V DC This is the DC bias voltage, which can be 0; V AC f is the AC voltage; f is the frequency of the AC voltage; and t is time.

[0078] The alternating voltage drives the piezoelectric layer 23 to produce transverse strain under the inverse piezoelectric effect, causing the composite layer to bend and deform, so that the piezoelectric composite layer 20 emits ultrasonic waves according to the required vibration mode.

[0079] (2) Receiving status

[0080] In the receiving state, the bottom electrode 31 of the capacitor structure is grounded, and a DC bias voltage -V is applied to the top electrode 33. DC The piezoelectric composite layer 20 undergoes bending deformation under the action of incident ultrasonic waves, changing the distance between the bottom electrode 31 and the top electrode 33 in the capacitor structure, thereby causing a change in capacitance. This converts the acoustic wave signal into an electrical signal output, and the change in capacitance reflects the physical characteristics of the incident ultrasonic waves.

[0081] This embodiment proposes a micromechanical ultrasonic transducer (MUT) unit structure employing piezoelectric transmission and capacitive reception. The PMUT serves as the transmitter, generating a powerful ultrasonic signal through its high efficiency and low power consumption. A CMUT, acting as the receiver, leverages its wide bandwidth and high sensitivity to achieve precise signal detection. This design combines the advantages of both PMUT and CMUT, achieving an optimal balance between energy efficiency and imaging quality. The PMUT generates ultrasonic waves through the mechanical vibration of piezoelectric materials, exhibiting low driving voltage and high conversion efficiency, significantly reducing energy consumption and making it ideal for portable devices or low-power applications. The CMUT, with its capacitive induction operating principle, provides a wide frequency response and excellent signal-to-noise ratio, supporting high-resolution signal acquisition and rapid response, meeting the requirements of high-precision imaging. This innovative design combining PMUT transmission and CMUT reception overcomes the performance limitations of traditional single transducers in ultrasonic imaging systems, ensuring both efficient ultrasonic output and high-sensitivity reception, making it suitable for various applications requiring high-performance ultrasonic detection.

[0082] The following describes the fabrication method of the MEMS ultrasonic transducer in this embodiment. Figure 5 for Figure 1 The diagram shows the process flow chart for a MEMS ultrasonic transducer. Figure 5 As shown, the preparation method includes:

[0083] Step A: A groove is formed on the upper surface of the substrate by dry etching, which serves as the air gap for the capacitor structure, such as... Figure 5 As shown in (a);

[0084] Step B involves depositing a layer of conductive material at the bottom of the aforementioned groove and patterning this conductive material to form the bottom electrode of the capacitor structure, as shown below. Figure 5 As shown in (b);

[0085] Step C involves depositing a sacrificial layer above the bottom electrode of the capacitor structure, and then patterning the upper surface of the sacrificial layer, as shown below. Figure 5 As shown in (c);

[0086] Step D involves depositing a conductive material layer over the sacrificial layer, followed by patterning the conductive material and the sacrificial layer sequentially to form the top electrode of the capacitor structure, a via penetrating the top electrode, and a shallow recessed opening on the surface of the sacrificial layer, as shown below. Figure 5 As shown in (d);

[0087] Step E involves depositing a mechanical layer and mechanically polishing it. The mechanical layer fills the notches on the surface of the sacrificial layer to form a lower protrusion, such as... Figure 5 As shown in (e);

[0088] Step F involves sequentially depositing a bottom electrode, a piezoelectric layer, and a top electrode of a piezoelectric composite layer above the mechanical layer, as shown below. Figure 5 As shown in (f);

[0089] Step G: Graphicalize the top electrode so that its projection in the horizontal plane coincides with the groove, as shown below. Figure 5 As shown in (g);

[0090] Step H involves sequentially patterning the piezoelectric layer, bottom electrode, and mechanical layer to form a slit-expansion slit and a stress-reducing slit penetrating the piezoelectric composite layer, as shown below. Figure 5 As shown in (h);

[0091] Step I: Deep silicon etching is performed on the substrate to form a back cavity, such as... Figure 5 As shown in (i);

[0092] Step J involves releasing the sacrificial layer through a buffered oxide etchant to form the final MUT structure, as shown below. Figure 5 As shown in (j).

[0093] Figure 6 This is a top view of the MEMS ultrasonic transducer according to the second embodiment of the present invention. Figure 7 for Figure 6 The diagram shows a cross-sectional view of the MEMS ultrasonic transducer along section AA. The difference between this embodiment and the first embodiment lies in the position of the slit 25. In the first embodiment, the slit 25 is located in the first inner portion of the piezoelectric composite layer (the portion above the stepped structure). In this embodiment, the slit is located in the second inner portion of the piezoelectric composite layer (the portion above the cavity).

[0094] Specifically, the stress-reducing slit in slit 25 originates at the apex of the hexagonal piezoelectric composite layer and extends towards the center of the diaphragm, ending at a point that forms a new hexagon. The expansion slit is located at the edge of this new hexagon and parallel to the six sides. In this embodiment, slit 25 effectively reduces the bending stiffness of the edge of the central hexagon of the diaphragm and the overall bending stiffness, and also effectively releases residual stress. In the firing state, the bending deformation of the six beams causes the central hexagon to translate, thereby increasing the amplitude and ultimately improving the firing sensitivity.

[0095] A second aspect of the present invention also provides an ultrasonic transducer unit. This ultrasonic transducer unit can be applied to ultrasonic devices such as ultrasonic Doppler three-dimensional flow velocity detectors.

[0096] In an exemplary embodiment of the present invention, the ultrasonic transducer unit includes: a sensing module, which is the aforementioned MEMS ultrasonic transducer; a signal processing module, which is connected to the bottom electrode and top electrode of the piezoelectric composite layer in the MEMS structure; and simultaneously, the signal is connected to the bottom electrode and top electrode of the capacitor structure.

[0097] This concludes the description of the various embodiments of the present invention. Based on the above description, those skilled in the art should have a clear understanding of the present invention.

[0098] It should be noted that for certain implementation methods, if they are not the key content of this invention and are well known to those skilled in the art, they are not described in detail in the accompanying drawings or text due to space limitations. In such cases, they can be understood by referring to the relevant prior art.

[0099] Unless explicitly stated otherwise, the numerical values ​​and ranges mentioned in this invention are approximate and can be changed according to the content of this invention. Specifically, all figures in the specification and claims indicating the content of composition, reaction conditions, etc., should be understood to be modified by the term "about" in all cases, meaning that they include variations of ±10% in certain embodiments.

[0100] The directional terms used in this invention, such as "center," "lateral," "longitudinal," "top," "bottom," "upper," "lower," "front," "rear," "left," "right," "inner," and "outer," indicate only the orientation or positional relationship shown in the accompanying drawings. These terms are used solely for the purpose of facilitating and simplifying the description of this invention, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention. Furthermore, throughout the accompanying drawings, the same elements are represented by the same or similar reference numerals. Also, the shapes and dimensions of the components in the drawings do not reflect actual size and proportion, but are only illustrative of embodiments of this invention.

[0101] The terms "connected" and "linked" used in this invention should be interpreted broadly unless otherwise explicitly specified and limited. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the connection of a portion of two components. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances.

[0102] Those skilled in the art will understand that in the claims and specification of this invention, the word "comprising" does not exclude the presence of elements (or steps) not listed in the claims. The word "a" or "an" preceding an element (or step) does not exclude the presence of a plurality of such elements (or steps).

[0103] Furthermore, the above embodiments are provided only to enable the invention to meet legal requirements, and the invention can be implemented in many different forms and should not be construed as limited to the embodiments set forth herein.

[0104] Similarly, it should be understood that, for the sake of brevity, in the above description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof. However, this method of invention should not be construed as reflecting an intention that the claimed invention requires more features than expressly recited in each claim. Rather, as reflected in the claims, the various inventive aspects consist of fewer than all the features of the preceding single embodiment. Furthermore, embodiments may be used in combination with each other or with other embodiments based on design and reliability considerations; that is, technical features from different embodiments can be freely combined to form more embodiments. Therefore, the claims following the detailed description are hereby expressly incorporated into that detailed description, wherein each claim itself is a separate embodiment of the invention.

[0105] The above specific embodiments have provided a detailed description of the purpose, technical means, and beneficial effects of the present invention. It should be understood that the purpose of the detailed description is to enable those skilled in the art to better understand the present invention, and it is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A MEMS structure, characterized by, The MEMS structure comprises: a support structure, an inner side of which forms a cavity; an upper surface of a peripheral part of the support structure forms a stepped structure, a convex surface of the stepped structure is located outside a concave surface of the stepped structure; a piezoelectric composite layer is formed on the support structure, in a horizontal direction, a peripheral part of the piezoelectric composite layer is supported on the convex surface of the stepped structure, a first inner side part of the piezoelectric composite layer forms an annular groove with the concave surface of the stepped structure, and a second inner side part of the piezoelectric composite layer is arranged towards the cavity; in a vertical direction, the piezoelectric composite layer comprises: a mechanical layer, a peripheral part of which is supported on the convex surface of the stepped structure; a bottom electrode, a piezoelectric layer, and a top electrode, which are sequentially formed on a front surface of the mechanical layer; a capacitor structure comprises: a bottom electrode and a top electrode, wherein the bottom electrode is formed on the concave surface of the stepped structure; the top electrode is formed on a bottom surface of the mechanical layer towards the annular groove, and is arranged in parallel with the bottom electrode; and an annular groove space between the bottom electrode and the top electrode serves as a capacitor air gap.

2. The MEMS structure of claim 1, wherein, The MEMS structure serves as an ultrasonic transducer, when the MEMS ultrasonic transducer is in a transmitting state, the bottom electrode of the piezoelectric composite layer is grounded, the top electrode is loaded with an alternating voltage, the piezoelectric layer generates a transverse strain under the action of the inverse piezoelectric effect, and the piezoelectric composite layer generates a bending deformation, so that the piezoelectric composite layer transmits ultrasonic waves; when the MEMS ultrasonic transducer is in a receiving state, the bottom electrode of the capacitor structure is grounded, the top electrode is loaded with a direct current bias voltage; the piezoelectric composite layer generates a bending deformation under the action of incident ultrasonic waves, the distance between the bottom electrode and the top electrode of the capacitor structure is changed, and the change in the capacitance between the bottom electrode and the top electrode reflects the physical characteristics of the incident ultrasonic waves.

3. The MEMS structure according to claim 1, wherein the support structure is a substrate; and / or in the capacitor structure, the bottom electrode and the top electrode are arranged close to the cavity and away from the convex surface of the stepped structure; and / or in the piezoelectric composite layer, the material of the mechanical layer is one or more of the following: silicon, silicon nitride, silicon oxide, and piezoelectric material; and / or the material of the piezoelectric layer is one or more of the following: aluminum nitride, scandium-doped aluminum nitride, zinc oxide, and piezoelectric ceramic; and / or the material of the bottom electrode and / or the top electrode is one or more of the following: molybdenum, gold, aluminum, chromium, and doped polysilicon; and / or the thickness of the piezoelectric layer and the mechanical layer ranges from 0.1 μm to 10 μm; and / or the thickness of the bottom electrode and the top electrode ranges from 20 nm to 200 nm; and / or the depth of the annular groove space ranges from 0.05 μm to 5 μm.

4. The MEMS structure according to claim 1, wherein the horizontal plane projections of the cavity in the support structure and the annular groove are both regular N-polygons, and N≥3; the first inner side part and / or the second inner side part of the piezoelectric composite layer forms a regular N-polygon-shaped widened slit, and for each side of the regular N-polygon-shaped widened slit, the side is parallel to a corresponding side of the regular N-polygon; and the regular N-polygon-shaped widened slit comprises: a first slit and a second slit, which respectively extend from a vertex of a side to a midpoint of the side, and are symmetrically arranged with a gap between the first slit and the second slit. a middle slit, located at the inner side or the outer side of the gap between the first slit and the second slit.

5. The MEMS structure of claim 4, wherein, N = 6; and / or the width of the widened slit ranges from 0.1 μm to 10 μm; and / or the widened slit of the quasi-N regular polygon is located at the first inner side portion, and the first inner side portion and the second inner side portion of the piezoelectric composite layer are formed with N stress-reducing slits, each of which extends from a corresponding vertex of the quasi-N regular polygon towards the center of the quasi-N regular polygon; and / or the widened slit of the quasi-N regular polygon is located at the second inner side portion, and the first inner side portion and the second inner side portion of the piezoelectric composite layer are formed with N stress-reducing slits, each of which extends from a corresponding vertex of the quasi-N regular polygon in a direction opposite to the center of the quasi-N regular polygon.

6. The MEMS structure of claim 1, wherein, an upper protrusion extending upwards through the bottom electrode and formed on the lower concave surface of the step structure is formed in the region of the bottom electrode of the capacitor structure, and no electrode material is formed on the upper protrusion; and / or a lower protrusion extending downwards through the top electrode and formed on the bottom surface of the annular groove is formed in the region of the top electrode of the capacitor structure, and no electrode material is formed on the lower protrusion.

7. The MEMS structure of claim 6, wherein, the depth h of the annular groove space in the vertical direction ranges from 0.05 μm to 5 μm; the height h1 of the upper protrusion and the lower protrusion satisfies: h / 10 ≤ h1 ≤ h / 2.

8. A method of producing the MEMS structure according to any one of claims 1 to 7, characterized by, comprising: Step A, forming a groove on a substrate; Step B, depositing a conductive material on the bottom of the groove, and patterning the conductive material to form a bottom electrode of a capacitor structure; Step C, depositing a sacrificial layer in the groove, and then patterning the upper surface of the sacrificial layer to form a template structure of a top electrode of the capacitor structure; Step D, depositing a conductive material above the sacrificial layer to form a top electrode of the capacitor structure; Step E, depositing a mechanical layer; Step F, sequentially depositing a bottom electrode, a piezoelectric layer and a top electrode of the piezoelectric composite layer above the mechanical layer; Step G, patterning the top electrode; Step I, deep etching the back surface of the substrate to form a back cavity; Step J, releasing the sacrificial layer by a buffer oxide etching solution to form a final MEMS structure.

9. The preparation method of claim 8, wherein, in the step D, the conductive material and the sacrificial layer are sequentially patterned to form a through hole through the top electrode and a notch on the surface of the sacrificial layer; and in the step E, the material of the mechanical layer fills the notch on the surface of the sacrificial layer and the through hole through the top electrode to form a lower protrusion structure; and / or the MEMS structure is the MEMS structure of claim 7, and the step G further comprises: Step H, sequentially patterning the piezoelectric layer, the bottom electrode and the mechanical layer to form widened slits and stress-reducing slits through the piezoelectric composite layer.

10. An ultrasound transducer unit, characterized by comprising: a sensing module, the MEMS structure of any one of claims 1 to 7; A signal processing module is connected to the bottom electrode and the top electrode of the piezoelectric composite layer in the MEMS structure, and is also connected to the bottom electrode and the top electrode of the capacitor structure.

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