Piezoelectric micromechanical ultrasonic transducer, array and manufacturing method

Abstract

The invention provides a piezoelectric micro-mechanical ultrasonic transducer, an array and a manufacturing method, and belongs to the technical field of micro electro mechanical systems, the piezoelectric micro-mechanical ultrasonic transducer comprises a substrate layer and a stacking structure arranged on the substrate layer, the substrate layer comprises a substrate area, a first cavity area and a second cavity area, and the first cavity area and the second cavity area are surrounded by the substrate area; the orthographic projection area of the first cavity region on the stacked structure is larger than that of the second cavity region on the stacked structure, and the suspended part of the stacked structure on the substrate layer is a vibrating diaphragm of the ultrasonic transducer. According to the invention, the boundary of the diaphragm of the PMUT is accurately defined by using the silicon surface cavity, and the pressed diaphragm damping is reduced by combining the bulk silicon back etching structure, so that the performance of the PMUT is improved; besides, the bandwidth and sensitivity of the PMUT can be regulated and controlled by adjusting the size ratio of the second cavity area to the first cavity area, so that the corresponding bandwidth and sensitivity can be set according to different application requirements, and the PMUT can be widely applied to the fields of distance measuring sensors, flow meters, liquid level meters, material identification and the like.

Description

Technical Field

[0001] The present application belongs to the field of micro-electromechanical technology, and specifically, relates to a piezoelectric micro-mechanical ultrasonic transducer, an array, and a manufacturing method. Background Art

[0002] Piezoelectric Micromachined Ultrasonic Transducer (PMUT) is a type of MEMS device that transmits or receives ultrasonic signals by vibrating a piezoelectric film through the forward and reverse piezoelectric effects of piezoelectric materials.

[0003] In the prior art, the piezoelectric micromechanical ultrasonic transducer, on the one hand, has a silicon surface cavity structure realized based on micro-surface processing technology, which has limited depth and will lead to large squeeze-film damping in the cavity; on the other hand, the cavity structure realized based on bulk silicon back-etching technology has the disadvantage of being unable to accurately define the PMUT diaphragm boundary. Summary of the invention

[0004] In response to the problems existing in the prior art, the present application provides a piezoelectric micromechanical ultrasonic transducer, an array and a manufacturing method, which can accurately define the PMUT diaphragm boundary according to the silicon surface cavity, and at the same time combine the bulk silicon back-etching structure to reduce the squeeze film damping to improve the PMUT performance.

[0005] According to a first aspect of the present application, a piezoelectric micromechanical ultrasonic transducer is provided, the ultrasonic transducer comprising:

[0006] substrate layer, and

[0007] A stacked structure is provided on the substrate layer, wherein:

[0008] The substrate layer comprises a substrate region and a first cavity region and a second cavity region surrounded by the substrate region;

[0009] The orthographic projection of the first cavity region on the stacked structure covers the orthographic projection of the second cavity region on the stacked structure, and the suspended portion of the stacked structure on the substrate layer is the diaphragm of the ultrasonic transducer.

[0010] In some optional aspects of this embodiment, the stacking structure includes:

[0011] A support layer, a first electrode layer, a first piezoelectric layer and a second electrode layer are stacked on the substrate layer, wherein the orthographic projection of the second electrode layer on the support layer falls within the orthographic projection of the first electrode layer on the support layer, and the thickness of the first electrode layer is the same as the thickness of the second electrode layer.

[0012] In some optional aspects of this embodiment, the stacking structure includes:

[0013] A third electrode layer, a second piezoelectric layer and a fourth electrode layer are stacked on the substrate layer, wherein the orthographic projection of the fourth electrode layer on the second piezoelectric layer falls within the orthographic projection of the third electrode layer on the second piezoelectric layer, and the thickness of the fourth electrode layer is greater than the thickness of the third electrode layer.

[0014] In some optional aspects of this embodiment, the stacking structure includes:

[0015] A fifth electrode layer, a third piezoelectric layer, a sixth electrode layer, a fourth piezoelectric layer and a seventh electrode layer are stacked on the substrate layer, wherein the orthographic projections of the sixth electrode layer and the seventh electrode layer on the third piezoelectric layer fall within the orthographic projection of the fifth electrode layer on the third piezoelectric layer.

[0016] In some optional embodiments of this embodiment, a release hole is further included that passes through the stacking structure, and the release hole is configured to form a slit in the stacking structure, wherein both ends of the slit protrude from the second cavity area, and / or both ends of the slit protrude from the first cavity area.

[0017] In some optional embodiments of this embodiment, the size of the first cavity area in a direction horizontal to the substrate layer is a first cavity horizontal size, the size of the second cavity area in a direction horizontal to the substrate layer is a second cavity horizontal size, and the second cavity horizontal size is smaller than the first cavity horizontal size.

[0018] In some optional embodiments of this embodiment, the sensitivity of the ultrasonic transducer is positively correlated with the ratio of the second cavity horizontal size to the first cavity horizontal size; the bandwidth of the ultrasonic transducer is negatively correlated with the ratio of the second cavity horizontal size to the first cavity horizontal size.

[0019] In some optional embodiments of this embodiment, when the ratio is 1, the sensitivity of the ultrasonic transducer is the upper limit of sensitivity; when the ratio is greater than 0.3 and less than 1, the sensitivity of the ultrasonic transducer is not less than one tenth of the upper limit of sensitivity.

[0020] In some optional aspects of this embodiment, the bandwidth of the ultrasonic transducer is greater than 5 kHz and less than 20 kHz; the sensitivity of the ultrasonic transducer is greater than 0.6 μm / V and less than 3.5 μm / V.

[0021] In some optional embodiments of this embodiment, the size of the first cavity region in a direction perpendicular to the substrate layer is the first cavity vertical size, and when the ratio of the second cavity horizontal size to the first cavity horizontal size is constant, the sensitivity of the ultrasonic transducer is positively correlated with the first cavity vertical size; the bandwidth of the ultrasonic transducer is negatively correlated with the first cavity vertical size.

[0022] In some optional aspects of this embodiment, when the ratio is not greater than 0.5, the vertical dimension of the first cavity is greater than 0.5 μm and less than 5 μm.

[0023] In some optional aspects of this embodiment, the bandwidth of the ultrasonic transducer is greater than 12.5 kHz and less than 35 kHz; the sensitivity of the ultrasonic transducer is greater than 0.45 μm / V and less than 1.4 μm / V.

[0024] In some optional embodiments of this embodiment, when the sensitivity obtains a lower limit value of sensitivity, the bandwidth obtains an upper limit value of bandwidth; and when bandwidth regulation is performed, the sensitivity is not less than one tenth of the upper limit value of sensitivity.

[0025] In some optional methods of this embodiment, the vertical dimension of the first cavity and the ratio satisfy a linear relationship, and the intersection of the linear relationship and the cavity depth coordinate axis is h, and the intersection of the linear relationship and the ratio coordinate axis is k. An arbitrary combination of cavity depth and ratio is selected outside the area formed by the h point, the k point and the origin so that the sensitivity is not less than one tenth of the upper limit of the sensitivity.

[0026] According to a second aspect of the present application, a method for manufacturing the piezoelectric micromechanical ultrasonic transducer of the first aspect is provided, the method comprising:

[0027] Etching a first cavity region on the substrate layer, and forming a sacrificial layer on the substrate layer, wherein the sacrificial layer covers the substrate layer;

[0028] performing a planarization process on the sacrificial layer to remove the sacrificial layer outside the first cavity region;

[0029] forming a stacked structure above the exposed substrate layer and the sacrificial layer, wherein the stacked structure covers the sacrificial layer and the exposed substrate layer;

[0030] Performing back etching on the substrate layer at a side of the substrate layer away from the stacking structure to form a second cavity region;

[0031] Release the sacrificial layer in the first cavity area to connect the first cavity area with the second cavity area, wherein the outside of the first cavity area and the second cavity area is a substrate area, the orthographic projection of the first cavity area on the stacked structure covers the orthographic projection of the second cavity area on the stacked structure, and the suspended part of the stacked structure on the substrate layer is the diaphragm of the ultrasonic transducer.

[0032] In some optional aspects of this embodiment, forming a stacked structure on the exposed substrate layer and the sacrificial layer further includes:

[0033] forming a support layer over the exposed substrate layer and the sacrificial layer;

[0034] forming a first electrode layer on the support layer;

[0035] forming a first piezoelectric layer on the first electrode layer;

[0036] A second electrode layer is formed on the first piezoelectric layer, wherein the orthographic projection of the second electrode layer on the supporting layer falls within the orthographic projection of the first electrode layer on the supporting layer, and the thickness of the first electrode layer is the same as that of the second electrode layer.

[0037] In some optional aspects of this embodiment, forming a stacked structure on the exposed substrate layer and the sacrificial layer further includes:

[0038] forming a third electrode layer over the exposed substrate layer and the sacrificial layer;

[0039] forming a second piezoelectric layer on the third electrode layer;

[0040] A fourth electrode layer is formed on the second piezoelectric layer, wherein an orthographic projection of the fourth electrode layer on the second piezoelectric layer falls within an orthographic projection of the third electrode layer on the second piezoelectric layer, and a thickness of the fourth electrode layer is greater than a thickness of the third electrode layer.

[0041] In some optional aspects of this embodiment, forming a stacked structure on the exposed substrate layer and the sacrificial layer further includes:

[0042] forming a fifth electrode layer over the exposed substrate layer and the sacrificial layer;

[0043] forming a third piezoelectric layer on the fifth electrode layer;

[0044] forming a patterned sixth electrode layer on the third piezoelectric layer;

[0045] forming a fourth piezoelectric layer on the sixth electrode layer and covering the sixth electrode layer;

[0046] A seventh electrode layer is formed on the fourth piezoelectric layer, wherein the orthographic projections of the sixth electrode layer and the seventh electrode layer on the third piezoelectric layer fall within the orthographic projection of the fifth electrode layer on the third piezoelectric layer.

[0047] In some optional aspects of this embodiment, the manufacturing method further includes:

[0048] A release hole is formed through the stacking structure, wherein the release hole is configured to form a slit in the stacking structure, two ends of the slit protrude from the second cavity area, and / or two ends of the slit protrude from the first cavity area.

[0049] According to a third aspect of the present application, a piezoelectric micromechanical ultrasonic transducer array is provided, the ultrasonic transducer array comprising: an acoustic coupling medium and a plurality of piezoelectric micromechanical ultrasonic transducers as described in the first aspect above, wherein:

[0050] The piezoelectric micromechanical ultrasonic transducer receives or transmits an ultrasonic signal through the acoustic coupling medium.

[0051] The present application provides a piezoelectric micromechanical ultrasonic transducer, array and manufacturing method, which have a dual release structure of silicon surface cavity and back engraving, and use the silicon surface cavity to accurately define the PMUT diaphragm boundary, while combining the bulk silicon back-engraving structure to reduce the squeeze film damping to improve the performance of the PMUT; in addition, by adjusting the size ratio of the second cavity area and the first cavity area, the bandwidth and sensitivity of the PMUT can be controlled, so that the corresponding bandwidth and sensitivity can be set according to different application requirements, and it is widely used in ranging sensors, flow meters, level meters, material identification and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0053] Figure 1a to Figure 1b is a schematic diagram of a piezoelectric micromechanical ultrasonic transducer in the prior art;

[0054] Figure 2 is a schematic structural diagram of a piezoelectric micromechanical ultrasonic transducer according to an embodiment of the present application;

[0055] Figure 3 is a flowchart of manufacturing a piezoelectric micromechanical ultrasonic transducer according to an embodiment of the present application;

[0056] Figure 4This is one of the schematic diagrams for manufacturing a piezoelectric micromechanical ultrasonic transducer according to an embodiment of the present application;

[0057] Figure 5 is a schematic structural diagram of a piezoelectric micromechanical ultrasonic transducer according to another embodiment of the present application;

[0058] Figure 6 This is a second schematic diagram of manufacturing a piezoelectric micromechanical ultrasonic transducer according to an embodiment of the present application;

[0059] Figure 7 is a schematic structural diagram of a piezoelectric micromechanical ultrasonic transducer according to another embodiment of the present application;

[0060] Figure 8 The third schematic diagram of manufacturing a piezoelectric micromechanical ultrasonic transducer according to an embodiment of the present application;

[0061] Fig. 9 is a schematic structural diagram of a piezoelectric micromechanical ultrasonic transducer according to another embodiment of the present application;

[0062] Fig.10 is one of the schematic diagrams of the slit structure according to an embodiment of the present application;

[0063] Fig.11 This is a second schematic diagram of a slit structure according to an embodiment of the present application;

[0064] Fig.12 This is one of the schematic diagrams of the morphology of the first cavity region and the second cavity region according to an embodiment of the present application;

[0065] Fig.13 This is a second schematic diagram of the morphology of the first cavity region and the second cavity region according to an embodiment of the present application;

[0066] Fig.14 This is one of the schematic diagrams for regulating bandwidth and sensitivity according to an embodiment of the present application;

[0067] Fig.15 The second schematic diagram of bandwidth and sensitivity regulation according to an embodiment of the present application;

[0068] Fig.16 The third schematic diagram of bandwidth and sensitivity regulation according to an embodiment of the present application;

[0069] Fig.17 Schematic diagram of the structure of a piezoelectric micromechanical ultrasonic transducer array according to an embodiment of the present application. DETAILED DESCRIPTION

[0070] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only 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.

[0071] It should be noted that the terms “on…”, “formed on…” and “disposed on…” described herein may indicate that one layer is directly formed or disposed on another layer, or may indicate that one layer is indirectly formed or disposed on another layer, i.e., there are other layers between the two layers. In this article, unless otherwise specified, the term “located on the same layer” used means that two layers, parts, components, elements or parts can be formed by the same patterning process, and the two layers, parts, components, elements or parts are generally formed of the same material. In this article, unless otherwise specified, the expression “patterning process” generally includes steps such as coating, exposure, development, etching and stripping of photoresist. The expression “one-time patterning process” means a process of forming patterned layers, parts, components, etc. using a mask.

[0072] Currently, PMUT has potential applications in biometric sensors such as fingerprint sensors, gesture detection, microphones and speakers, ultrasonic imaging, and chemical sensors. PMUT generally includes a cavity and a stacked structure suspended on the cavity, such as a support layer, a piezoelectric layer, and a patterned or unpatterned electrode layer on each side of the piezoelectric layer. In the prior art, PMUT is as follows Figure 1a-1b Two common cavity structures are shown, specifically:

[0073] like Figure 1a As shown, the silicon surface cavity realized based on micro-surface processing technology can accurately define the diaphragm boundary of PMUT, for example Figure 1a The two ends of the dotted line are the boundaries of the diaphragm, and the cavity depth h is generally less than 10 microns. Due to the limited depth, a large squeeze-film damping will be generated in the cavity, and the squeeze-film damping is difficult to accurately control, resulting in a decrease in the performance of the PMUT.

[0074] like Figure 1b As shown, the cavity realized based on the bulk silicon back etching technology can release the back space and reduce the compression film damping in the cavity. When the back is etched, the diaphragm boundary of the cavity in the ideal state is the boundary shown by the short dashed line. However, due to the problems of uneven etching amount and over-etching in the back etching process in the actual manufacturing process, it is difficult to control the back etching process. Figure 1b The over-engraving amplitude indicated by the arrow makes it difficult to accurately control the PMUT diaphragm boundary.

[0075] For this reason, Figure 2As shown, one embodiment of the present application provides a novel piezoelectric micromechanical ultrasonic transducer, which includes:

[0076] The substrate layer 10, and

[0077] The stacked structure 20 is arranged on the substrate layer 10, wherein:

[0078] The substrate layer 10 includes a substrate region 101 and a first cavity region 102 and a second cavity region 103 surrounded by the substrate region 101;

[0079] The orthographic projection area of ​​the first cavity region 102 on the stacked structure 20 is larger than the orthographic projection area of ​​the second cavity region 103 on the stacked structure 20 , and the suspended portion of the stacked structure on the substrate layer is the diaphragm of the ultrasonic transducer.

[0080] In this embodiment, the substrate layer is generally a silicon wafer, such as Figure 2 As shown, the suspended portion 20' of the stacked structure 20 on the substrate layer 10 is a diaphragm. Figure 2 a and b in the figure are the diaphragm boundaries of the ultrasonic transducer. It should be noted that the upper boundary ab of the silicon surface cavity (the first cavity region 102) is coplanar (i.e., in the same horizontal plane) with the upper boundary of the base silicon (substrate layer 10), so that the PMUT diaphragm will not produce a step difference at the boundary of the silicon surface cavity, and the boundary of the PMUT diaphragm can be accurately defined, further improving the controllability of the PMUT resonant frequency and sensitivity.

[0081] The piezoelectric micromachined ultrasonic transducer provided in this embodiment has a double release structure of silicon surface cavity and back engraving, and uses the silicon surface cavity to accurately define the PMUT diaphragm boundary, while combining the bulk silicon back engraving structure to reduce the squeeze film damping to improve the performance of the PMUT.

[0082] In some optional embodiments of this embodiment, Figure 2 As shown, the stacked structure includes a support layer 201, a first electrode layer 202A, a first piezoelectric layer 203 and a second electrode layer 202B stacked on the substrate layer 10, wherein the orthographic projection of the second electrode layer 202B on the support layer 201 falls into the orthographic projection of the first electrode layer 202A on the support layer 201, and the thickness of the first electrode layer 202A is the same as the thickness of the second electrode layer 202B.

[0083] The following is an example of making a piezoelectric micromechanical ultrasonic transducer of this embodiment. The specific manufacturing process is as follows: Figure 3 As shown, including:

[0084] S10, etching a first cavity region on the substrate layer, and forming a sacrificial layer on the substrate layer, wherein the sacrificial layer covers the substrate layer.

[0085] In a specific example, a cavity is etched on the surface of a silicon wafer, such as Figure 4 As shown in FIG. 1 (a), a first cavity region 102 is etched on the substrate layer 10, and then a releasable sacrificial material is grown to fill it. Figure 4 As shown in FIG. 2( b ), a sacrificial layer 30 is formed on the substrate layer 10 , wherein the sacrificial layer 30 covers the substrate layer 10 , and wherein the sacrificial layer is a releasable sacrificial material, generally phosphosilicate glass.

[0086] It should be noted that the substrate refers to the base on which the piezoelectric film grows. In order to ensure the oriented growth of the wafer-level piezoelectric material, no matter what substrate material is selected, a seed layer or a buffer layer needs to be grown on the substrate when growing the piezoelectric material. Therefore, the choice of substrate material is mainly determined by the process and device design, and has no direct relationship with the piezoelectric material.

[0087] With the development of MEMS process technology and manufacturing equipment, surface micro-machining and bulk micro-machining devices tend to be specialized in process routes. In device and process design, the choice of substrates has begun to develop in two directions: single-layer substrates represented by silicon wafers and multi-layer substrates represented by SOI (Silicon-On-Insulator).

[0088] In addition, in addition to the common substrates mentioned above, there are some materials that can also be used as substrate materials in piezoelectric MEMS processes, such as: silicon carbide (SiC), silicate (SixOy), Parylene (polyparaxylene), PI (Polyimide) and PDMS (Polydimethylsiloxane), etc., which are not limited in this application.

[0089] S11, performing planarization processing on the sacrificial layer to remove the sacrificial layer outside the first cavity area.

[0090] In a specific example, if Figure 4 As shown in FIG. 7( c ), the sacrificial layer outside the first cavity region is removed, for example, the surface of the wafer is polished flat using a CMP process, and only the sacrificial material 301 in the first cavity region is retained.

[0091] Among them, the CMP process, namely Chemical-Mechanical Planarization, is a technology in the semiconductor device manufacturing process, which uses chemical corrosion and mechanical force to planarize silicon wafers or other substrate materials during the processing.

[0092] S12. Forming a stacked structure above the exposed substrate layer and the sacrificial layer, wherein the stacked structure covers the sacrificial layer and the exposed substrate layer.

[0093] In this embodiment, the growth and patterning of the diaphragm thin film material are carried out, wherein the diaphragm thin film material is a stacked structure. Since the CMP process is performed on the wafer surface, the formation of large gradient steps during the film growth process is avoided, thereby avoiding the introduction of stress concentration points in the thin film structure and thus reducing the structural reliability.

[0094] In a specific example, forming a stacked structure above the exposed substrate layer and the sacrificial layer further includes:

[0095] S121 , forming a support layer on the exposed substrate layer and the sacrificial layer.

[0096] In a specific example, if Figure 4 As shown in FIG. 2( d ), a support layer 201 is formed on the exposed substrate layer 10 and the sacrificial material 301. The support layer, also known as a mechanical layer, may be one or more of epoxy resin, resin, glass fabric, matte glass, carbon fiber, and polyester fiber.

[0097] S122, forming a first electrode layer on the support layer.

[0098] In a specific example, if Figure 4 As shown in FIG. 8( e ), a first electrode layer 202A is formed on the support layer 201 .

[0099] S123. Form a first piezoelectric layer on the first electrode layer.

[0100] In a specific example, if Figure 4 As shown in FIG. (f), a first piezoelectric layer 203 is formed on the first electrode layer 202A. It should be noted that the piezoelectric material used in PMUT manufacturing is a piezoelectric film that can be manufactured at the wafer level, rather than using traditional bulk piezoelectric ceramics for miniaturization. The manufacturing process of wafer-level piezoelectric films is fully compatible with MEMS processes.

[0101] S124. Form a second electrode layer on the first piezoelectric layer.

[0102] In a specific example, if Figure 4 As shown in Figure (g), a second electrode layer 202B is formed on the first piezoelectric layer 203, wherein the orthographic projection of the second electrode layer 202B on the supporting layer 201 falls into the orthographic projection of the first electrode layer 202A on the supporting layer 201, and the thickness of the first electrode layer 202A is the same as the thickness of the second electrode layer 202B.

[0103] At this point, the production of the front structure of the piezoelectric micromechanical ultrasonic transducer is completed.

[0104] Step S13: performing back etching on the substrate layer at a side of the substrate layer away from the stacking structure to form a second cavity region.

[0105] After the front structure of the piezoelectric micromechanical ultrasonic transducer is fabricated, in a specific example, Figure 4 As shown in FIG. 1 (h), the back of the substrate layer 10 is etched on the side of the substrate layer 10 away from the stacked structure 20. It should be noted that the entire substrate layer is not etched, but the substrate layer is partially etched based on a certain etching size to form Figure 4 The second cavity region 103 is shown in FIG.

[0106] Step S14, releasing the sacrificial layer in the first cavity region to connect the first cavity region with the second cavity region, wherein the area outside the first cavity region and the second cavity region is a substrate region.

[0107] In a specific example, if Figure 4 As shown in Figure (i), the sacrificial material in the first cavity area is released, the first cavity area 102 is connected to the second cavity area 103, and the outside of the first cavity area 102 and the second cavity area 103 is the substrate area 101. At this time, the substrate layer 10 includes the substrate area 101 and the first cavity area 102 and the second cavity area 103 surrounded by the substrate area 101.

[0108] At this point, the manufacturing of the piezoelectric micromechanical ultrasonic transducer is completed. In some optional methods of this embodiment, such as Figure 5 As shown, the stacking structure includes:

[0109] A third electrode layer 202A', a second piezoelectric layer 203' and a fourth electrode layer 202B' are stacked on the substrate layer, wherein the orthographic projection of the fourth electrode layer 202B' on the second piezoelectric layer 203' falls within the orthographic projection of the third electrode layer 202A' on the second piezoelectric layer 203', and the thickness of the third electrode layer 202A' is greater than the thickness of the fourth electrode layer 202B'.

[0110] The following is an example of making a piezoelectric micromechanical ultrasonic transducer of this embodiment. The specific manufacturing process is as follows: Figure 3 As shown, including:

[0111] S10, etching a first cavity region on the substrate layer, and forming a sacrificial layer on the substrate layer, wherein the sacrificial layer covers the substrate layer.

[0112] In a specific example, if Figure 6 As shown in FIG. 1 (a), a first cavity region 102 is etched on the substrate layer 10. Figure 6 As shown in FIG. (b), a sacrificial layer 30 is formed on the substrate layer 10, wherein the sacrificial layer 30 covers the substrate layer 10. Figure 6 For the description of Figures (a) and (b) of Figure 4 The description of Figures (a) to (b) of the present application will not be described in detail here.

[0113] S11, performing planarization processing on the sacrificial layer to remove the sacrificial layer outside the first cavity area.

[0114] In a specific example, if Figure 6 As shown in FIG. 5( c ), the sacrificial layer 30 is planarized to remove the sacrificial layer 30 outside the first cavity region and retain the sacrificial material 301 in the first cavity region. Figure 6 The description of Figure (c) can be found in Figure 4 The description of Figure (c) will not be described in detail in this application.

[0115] S12. Forming a stacked structure above the exposed substrate layer and the sacrificial layer, wherein the stacked structure covers the sacrificial layer and the exposed substrate layer.

[0116] In a specific example, forming a stacked structure above the exposed substrate layer and the sacrificial layer further includes:

[0117] S121 ′, forming a third electrode layer on the exposed substrate layer and the sacrificial layer.

[0118] In a specific example, if Figure 6 As shown in FIG. 5( d ) , a third electrode layer 202A′ is formed on the exposed substrate layer 10 and the sacrificial material 301 .

[0119] It should be noted that Figure 2 The difference between the embodiments is that the thickness of the third electrode layer in this embodiment is higher than that in the aforementioned Figure 2 In the embodiment, the thickness of the first electrode layer 202A is such that the thickened third electrode layer 202A′ can serve as a bottom electrode and a supporting layer. Figure 2 Embodiment: This embodiment does not require an additional support layer, which saves costs and simplifies the process.

[0120] S122', forming a second piezoelectric layer on the third electrode layer.

[0121] In a specific example, if Figure 6As shown in FIG. (e), a second piezoelectric layer 203' is formed on the third electrode layer 202A'. Figure 6 The description of Figure (e) can be found in Figure 4 The description of Figure (f) will not be described in detail in this application.

[0122] S123', forming a fourth electrode layer on the second piezoelectric layer.

[0123] In a specific example, if Figure 6 As shown in FIG. (f), a fourth electrode layer 202B' is formed on the second piezoelectric layer 203'. The orthographic projection of the fourth electrode layer 202B' on the second piezoelectric layer 203' falls within the orthographic projection of the third electrode layer 202A' on the second piezoelectric layer 203', and the thickness of the third electrode layer 202A' is greater than the thickness of the fourth electrode layer 202B'.

[0124] In this example, Figure 6 The description of Figure (f) can be found in Figure 4 The description of Figure (g) will not be described in detail in this application.

[0125] At this point, the production of the front structure of the piezoelectric micromechanical ultrasonic transducer is completed.

[0126] Step S13: performing back etching on the substrate layer at a side of the substrate layer away from the stacking structure to form a second cavity region.

[0127] After the front structure of the piezoelectric micromechanical ultrasonic transducer is fabricated, in a specific example, Figure 6 As shown in FIG. 5( g ), the substrate layer 10 is back-etched on a side of the substrate layer 10 away from the stacking structure 20 to form a second cavity region 103 .

[0128] In this example, Figure 6 The description of Figure (g) can be found in Figure 4 The description of Figure (h) will not be described in detail in this application.

[0129] Step S14, releasing the sacrificial layer in the first cavity region to connect the first cavity region with the second cavity region, wherein the area outside the first cavity region and the second cavity region is a substrate region.

[0130] In a specific example, if Figure 6As shown in Figure (h), the sacrificial material in the first cavity area 102 is released, the first cavity area 102 is connected to the second cavity area 103, and the outside of the first cavity area 102 and the second cavity area 103 is the substrate area 101. At this time, the substrate layer 10 includes the substrate area 101 and the first cavity area 102 and the second cavity area 103 surrounded by the substrate area 101.

[0131] At this point, the production of the piezoelectric micromechanical ultrasonic transducer is completed.

[0132] In some optional embodiments of this embodiment, Figure 7 As shown, the stacking structure includes:

[0133] A fifth electrode layer 202A", a third piezoelectric layer 203A", a sixth electrode layer 202B", a fourth piezoelectric layer 203B" and a seventh electrode layer 202C" are stacked on the substrate layer, wherein the orthographic projections of the sixth electrode layer 202B" and the seventh electrode layer 202C" on the third piezoelectric layer 203A" fall within the orthographic projection of the fifth electrode layer on the third piezoelectric layer 203A".

[0134] S10, etching a first cavity region on the substrate layer, and forming a sacrificial layer on the substrate layer, wherein the sacrificial layer covers the substrate layer.

[0135] In a specific example, if Figure 8 As shown in FIG. (a), a first cavity region is etched on the substrate layer 10, as shown in FIG. Figure 8 As shown in FIG. (b), a sacrificial layer 30 is formed on the substrate layer 10, wherein the sacrificial layer 30 covers the substrate layer 10. Figure 8 For the description of Figures (a) and (b) of Figure 4 The description of Figures (a) to (b) of the present application will not be described in detail here.

[0136] S11, performing planarization processing on the sacrificial layer to remove the sacrificial layer outside the first cavity area.

[0137] In a specific example, if Figure 8 As shown in FIG. 5( c ), the sacrificial layer 30 is planarized to remove the sacrificial layer 30 outside the first cavity region and retain the sacrificial material 301 in the first cavity region. Figure 8 The description of Figure (c) can be found in Figure 4 The description of Figure (c) will not be described in detail in this application.

[0138] S12. Forming a stacked structure above the exposed substrate layer and the sacrificial layer, wherein the stacked structure covers the sacrificial layer and the exposed substrate layer.

[0139] In a specific example, forming a stacked structure above the exposed substrate layer and the sacrificial layer further includes:

[0140] S121 ”, forming a fifth electrode layer on the exposed substrate layer and the sacrificial layer.

[0141] In a specific example, if Figure 8 As shown in FIG. 5( d ) , a fifth electrode layer 202A is formed on the exposed substrate layer 10 and the sacrificial material 301 .

[0142] S122”, forming a third piezoelectric layer on the fifth electrode layer.

[0143] In a specific example, if Figure 8 As shown in FIG. 5( e ) , a third piezoelectric layer 203A” is formed on the fifth electrode layer 202A”.

[0144] S123”, forming a patterned sixth electrode layer on the third piezoelectric layer.

[0145] In a specific example, if Figure 8 As shown in Figure (f), a patterned sixth electrode layer 202B" is formed on the third piezoelectric layer 203A", wherein the orthographic projection of the sixth electrode layer 202B" on the third piezoelectric layer 203A" falls within the orthographic projection of the fifth electrode layer 202A" on the third piezoelectric layer 203A". The patterning is a prior art and will not be described in detail in this application.

[0146] S123", forming a fourth piezoelectric layer on the sixth electrode layer and covering the sixth electrode layer.

[0147] In a specific example, if Figure 8 As shown in FIG. 2( g ), a fourth piezoelectric layer 203B” is formed on the sixth electrode layer 202B” and covers the sixth electrode layer.

[0148] It should be noted that Figure 2 The difference between the embodiments is that in this embodiment, a dual piezoelectric layer structure including a third piezoelectric layer 203A" and a fourth piezoelectric layer 203B" is provided. On this basis, the dual piezoelectric layer structure can enhance the performance of converting the returned ultrasonic signal into an electrical signal on the one hand, and can also serve as a supporting layer on the other hand. Therefore, compared with the aforementioned Figure 2 Embodiment: This embodiment does not require an additional support layer, which saves costs and simplifies the process.

[0149] S124", forming a seventh electrode layer on the fourth piezoelectric layer.

[0150] In a specific example, if Figure 8As shown in Figure (h), a seventh electrode layer 202C" is formed on the fourth piezoelectric layer 203B", wherein the orthographic projection of the seventh electrode layer 202C" on the third piezoelectric layer 203A" falls within the orthographic projection of the fifth electrode layer 202A" on the third piezoelectric layer 203A".

[0151] At this point, the production of the front structure of the piezoelectric micromechanical ultrasonic transducer is completed.

[0152] Step S13: performing back etching on the substrate layer at a side of the substrate layer away from the stacking structure to form a second cavity region.

[0153] After the front structure of the piezoelectric micromechanical ultrasonic transducer is fabricated, in a specific example, Figure 8 As shown in FIG. 1 (i), the substrate layer 10 is back-etched on a side of the substrate layer 10 away from the stacked structure 20 to form a second cavity region 103.

[0154] In this example, Figure 8 The description of Figure (i) can be found in Figure 4 The description of Figure (h) will not be described in detail in this application.

[0155] Step S14, releasing the sacrificial layer in the first cavity region to connect the first cavity region with the second cavity region, wherein the area outside the first cavity region and the second cavity region is a substrate region.

[0156] In a specific example, if Figure 8 As shown in Figure (j), the sacrificial material in the first cavity area 102 is released, the first cavity area 102 is connected to the second cavity area 103, and the outside of the first cavity area 102 and the second cavity area 103 is the substrate area 101. At this time, the substrate layer 10 includes the substrate area 101 and the first cavity area 102 and the second cavity area 103 surrounded by the substrate area 101.

[0157] At this point, the production of the piezoelectric micromechanical ultrasonic transducer is completed.

[0158] In some optional embodiments of this embodiment, the piezoelectric micromechanical ultrasonic transducer also includes a release hole passing through the stacking structure, and the release hole is configured to form a slit in the stacking structure, wherein both ends of the slit protrude out of the second cavity area, and / or both ends of the slit protrude out of the first cavity area.

[0159] In a specific example, Figure 7 The piezoelectric micromechanical ultrasonic transducer of the embodiment shown in the figure is used as an example for explanation. Figure 8 After the (j) graph, Fig. 9As shown, the invention further includes: forming a release hole 40 penetrating the stack structure 20, wherein the release hole 40 is configured to form a slit (in Fig. 9 The slit structure is not shown in the front view).

[0160] Hence, see Fig.10 and Fig.11 , which shows a simplified schematic diagram of a top view of a piezoelectric micromechanical ultrasonic transducer, as shown Fig.10 and Fig.11 As shown in FIG. 1 , the dotted ellipse is the release hole 40, and the structure extending around the release hole 40 is a slit. In the actual process design, on the one hand, the size of the slit can exceed the back engraving size (the horizontal size of the second cavity), that is, Fig.10 At the solid line ellipse shown in FIG. 1 , both ends of the slit protrude from the second cavity region 103. At this time, the portion of the slit that exceeds the second cavity region 103 can release the air gap, thereby reducing the squeeze film damping caused by the size difference between the back engraving size and the first cavity region size. On the other hand, the size of the slit can exceed the horizontal size of the first cavity, that is, Fig.11 At the solid line ellipse shown, both ends of the slit protrude from the first cavity area 102. At this time, the portion of the slit that exceeds the first cavity area 102 can release the air gap. On the basis that both ends of the slit protrude from the first cavity area and the second cavity area, Fig.11 The slit structure shown can achieve a better effect of releasing the damping of the die.

[0161] Further, in the piezoelectric micromechanical ultrasonic transducer of the aforementioned embodiment, Figure 2 , Figure 5 and Figure 7 As shown, the size of the first cavity area in a direction horizontal to the substrate layer is a first cavity horizontal size S1, and the size of the second cavity area in a direction horizontal to the substrate layer is a second cavity horizontal size S2, and the second cavity horizontal size S2 is smaller than the first cavity horizontal size S1.

[0162] In actual process design, due to the phenomenon of over-etching and uneven etching amount in the back-etching process, it is necessary to ensure that there is an excess value L between the silicon surface cavity radius (silicon surface cavity, i.e., the first cavity area) and the back-etching radius. By adjusting the excess value L, the size ratio between the first cavity horizontal size S1 and the second cavity horizontal size S2 can be determined, such as Figure 2 , Figure 5 and Figure 7 As shown, the cavity radius is half of the horizontal dimension S1 of the first cavity, that is, S1 / 2; and the back engraving radius is half of the horizontal dimension of the second cavity, that is, S2 / 2.

[0163] It should be noted that the present application does not limit the morphology of the first cavity region and the second cavity region, except for the aforementioned embodiments (e.g. Figure 2 , Figure 5 and Figure 7 ) is shown in the structural schematic diagram of the piezoelectric micromechanical ultrasonic transducer, in some optional embodiments of this embodiment, taking the stacked structure including the support layer, the first electrode layer, the first piezoelectric layer and the second electrode layer as an example, the first cavity region and the second cavity region may also have the following Fig.12 The morphologies shown in Figures (a) to (d).

[0164] exist Fig.12 In Figures (a) to (d), the first cavity region and the second cavity region also satisfy the relationship described in the aforementioned embodiment, wherein the maximum size of the first cavity region 102 in the direction horizontal to the substrate layer is greater than the maximum size of the second cavity region 103 in the direction horizontal to the substrate layer, and the remaining repetitive parts are not repeated. Fig.13 As shown, when the first cavity region is etched by micromachining technology, the top view of the first cavity region can be circular or square, and when the substrate layer is back-etched, the top view of the second cavity region obtained by back-etching can be square or circular. Fig.13 As shown in Figures (a) and (b), the substrate region 101 surrounds the first cavity region 102 and the second cavity region 103, and the orthographic projection area of ​​the first cavity region 102 on the stacking structure is larger than the orthographic projection area of ​​the second cavity region 103 on the stacking structure.

[0165] It should be noted that those skilled in the art can set the morphology and etching pattern of the first cavity area and the second cavity area according to actual needs, and this application does not limit this.

[0166] In this embodiment, the applicant found that by adjusting the excess value L so that the first cavity horizontal dimension S1 is greater than the second cavity horizontal dimension S2, the first cavity region can produce a precisely controllable amount of squeeze film damping, thereby regulating the bandwidth and sensitivity of the ultrasonic transducer. In other words, the sensitivity and bandwidth of the ultrasonic transducer are related to the ratio S2 / S1 of the second cavity horizontal dimension S2 to the first cavity horizontal dimension S1, the sensitivity of the ultrasonic transducer is positively correlated with the ratio S2 / S1 of the second cavity horizontal dimension to the first cavity horizontal dimension, and the bandwidth of the ultrasonic transducer is negatively correlated with the ratio S2 / S1 of the second cavity horizontal dimension to the first cavity horizontal dimension.

[0167] See also Fig.14, which shows a schematic diagram of how the piezoelectric micromechanical ultrasonic transducer adjusts the excess value L at a frequency of 600kHz, changes the ratio S2 / S1 of the second cavity horizontal size to the first cavity horizontal size, and finally regulates the bandwidth and sensitivity. Fig.14 As shown, the sensitivity of the ultrasonic transducer is positively correlated with the ratio S2 / S1 of the second cavity horizontal dimension to the first cavity horizontal dimension, that is, the larger the ratio S2 / S1 of the second cavity horizontal dimension S2 to the first cavity horizontal dimension S1, the higher the sensitivity; the bandwidth of the ultrasonic transducer is negatively correlated with the ratio S2 / S1 of the second cavity horizontal dimension to the first cavity horizontal dimension, that is, the larger the ratio S2 / S1 of the second cavity horizontal dimension S2 to the first cavity horizontal dimension S1, the lower the bandwidth.

[0168] In a specific example, when the ratio S2 / S1 is 1, the sensitivity of the ultrasonic transducer is the upper limit of sensitivity; when the ratio S2 / S1 is greater than 0.3 and less than 1, the sensitivity of the ultrasonic transducer is not less than one tenth of the upper limit of sensitivity; the bandwidth of the ultrasonic transducer is greater than 5 kHz and less than 20 kHz; the sensitivity of the ultrasonic transducer is greater than 0.6 μm / V and less than 3.5 μm / V.

[0169] Depend on Fig.14 It can be seen that when the ratio S2 / S1 of the second cavity horizontal dimension S2 and the first cavity horizontal dimension S1 is 1, the bandwidth of the ultrasonic transducer obtains the lower limit value of the bandwidth, and the sensitivity of the ultrasonic transducer obtains the upper limit value of the sensitivity. By adjusting the excess value L, the values ​​of the bandwidth and sensitivity can be adjusted to achieve precise control of the bandwidth and sensitivity.

[0170] It should be noted that the frequency of the above-mentioned ultrasonic transducer is exemplary. In fact, for an ultrasonic transducer at any frequency, its bandwidth and sensitivity and the ratio S2 / S1 all satisfy the above-mentioned relationship, that is, the sensitivity of the ultrasonic transducer is positively correlated with the ratio S2 / S1 of the second cavity horizontal size to the first cavity horizontal size, and the bandwidth of the ultrasonic transducer is negatively correlated with the ratio S2 / S1 of the second cavity horizontal size to the first cavity horizontal size.

[0171] Further, in some optional embodiments of this embodiment, such as Figure 2 , Figure 5 and Figure 7As shown, the size of the first cavity region 102 in a direction perpendicular to the substrate layer 10 is the first cavity vertical size h1. The applicant has found that when the ratio S2 / S1 of the second cavity horizontal size to the first cavity horizontal size is constant, the sensitivity and bandwidth of the ultrasonic transducer are related to the first cavity vertical size h1. Specifically, the sensitivity of the ultrasonic transducer is positively correlated with the first cavity vertical size; and the bandwidth of the ultrasonic transducer is negatively correlated with the first cavity vertical size.

[0172] Still taking the aforementioned piezoelectric micromechanical ultrasonic transducer at 600kHz as an example, Fig.15 As shown, it shows a schematic diagram of the regulation of bandwidth and sensitivity by different first cavity vertical dimensions h1 when the ratio S2 / S1 of the second cavity horizontal dimension to the first cavity horizontal dimension is 0.5. Fig.15 As shown, the sensitivity of the ultrasonic transducer is positively correlated with the first cavity vertical dimension h1, that is, the larger the first cavity vertical dimension h1 is, the higher the sensitivity of the ultrasonic transducer is; the bandwidth of the ultrasonic transducer is negatively correlated with the first cavity vertical dimension h1, that is, the larger the first cavity vertical dimension h1 is, the lower the bandwidth of the ultrasonic transducer is.

[0173] In a specific example, when the ratio S2 / S1 is not greater than 0.5, the vertical dimension of the first cavity is greater than 0.5 μm and less than 5 μm; the bandwidth of the ultrasonic transducer is greater than 12.5 kHz and less than 35 kHz; the sensitivity of the ultrasonic transducer is greater than 0.45 μm / V and less than 1.4 μm / V.

[0174] It should be noted that the ratio S2 / S1 of the horizontal dimension of the second cavity to the horizontal dimension of the first cavity is exemplary. In fact, for an ultrasonic transducer under any fixed ratio S2 / S1, its bandwidth and sensitivity satisfy the above relationship, that is, the sensitivity of the ultrasonic transducer is positively correlated with the vertical dimension of the first cavity; the bandwidth of the ultrasonic transducer is negatively correlated with the vertical dimension of the first cavity.

[0175] It should be understood that different applications, such as ranging sensors, flow meters, liquid level meters, material identification, etc., have different requirements for bandwidth and sensitivity. Therefore, based on the above description, the applicant has found that the bandwidth and sensitivity of the ultrasonic transducer are in a trade-off relationship. The corresponding bandwidth and sensitivity can be set by adjusting the ratio S2 / S1 according to different application requirements, thereby applying the piezoelectric micromechanical ultrasonic transducer of this embodiment to applications such as ranging sensors, flow meters, liquid level meters, and material identification.

[0176] In some optional methods of this embodiment, when bandwidth regulation is performed, it is necessary to ensure that the sensitivity is not less than one tenth of the upper sensitivity limit. For applications with higher sensitivity requirements, when bandwidth regulation is performed, it is necessary to ensure that the sensitivity is not less than one fifth of the upper sensitivity limit.

[0177] Specifically, taking the case where the sensitivity is not less than one tenth of the upper limit of the sensitivity when the bandwidth is controlled as an example, the method of controlling the bandwidth and sensitivity by adjusting the ratio S2 / S1 in the present application is described as follows:

[0178] First, according to the above discussion, for an ultrasonic transducer at any frequency, its bandwidth and sensitivity and the ratio S2 / S1 all satisfy the following: Fig.14 The relationship shown in FIG. 1 can be used to determine the schematic diagram of bandwidth, sensitivity and ratio S2 / S1 at the frequency, and the upper limit of sensitivity can be determined; further, it is also possible to determine the upper limit of sensitivity at each ratio S2 / S1, such as Fig.15 Schematic diagram of the first cavity vertical dimension h1, bandwidth and sensitivity.

[0179] Secondly, when the vertical dimension h1 of the first cavity is determined, the ratio S2 / S1 that satisfies "the sensitivity is not less than one tenth of the upper limit of the sensitivity when bandwidth regulation is performed" can be determined. For example, Fig.14 and Fig.15 For example, the upper limit of sensitivity is about 3.25. When the ratio S2 / S1 is 0.5 and the vertical dimension h1 of the first cavity is 0.5 μm, the lower limit of sensitivity is about 0.425. Therefore, "the sensitivity is not less than one tenth of the upper limit of sensitivity" is satisfied. Then, the schematic diagrams of the remaining ratios S2 / S1 and the vertical dimension h1 of the first cavity are traversed to determine the critical value of the ratio S2 / S1 that satisfies "the sensitivity is not less than one tenth of the upper limit of sensitivity when bandwidth control is performed".

[0180] Finally, the above operation is performed on each first cavity vertical dimension h1 to determine the critical value of the ratio S2 / S1 that satisfies "the sensitivity is not less than one tenth of the upper sensitivity limit when bandwidth regulation is performed" for each first cavity vertical dimension h1, and the critical value is organized into a curve graph accordingly.

[0181] In a specific example, the performance regulation of the piezoelectric micromechanical ultrasonic transducer of this embodiment is described by taking the PMUT at resonant frequencies of 40kHz, 100kHz, 300kHz, 500kHz and 1MHz, the vertical dimension h1 of the first cavity being 0.1μm to 10μm, and the ratio S2 / S1 being 0.1 to 1 as an example. As can be seen from the foregoing, the vertical dimension of the first cavity and the ratio satisfy a linear relationship. Fig.16In the curve graph shown, the intersection of the linear relationship and the cavity depth axis is h, and the intersection of the linear relationship and the ratio S2 / S1 axis is k. Any combination of cavity depth and ratio selected outside the region formed by point h, point k and the origin can make the sensitivity not less than one tenth of the upper sensitivity limit value, that is, Fig.16 The black slash filled area in the upper right corner is an optional area for the ratio S2 / S1 and the vertical dimension h1 of the first cavity when the sensitivity is not less than one tenth of the upper limit of the sensitivity during process design.

[0182] It should also be noted that the prior art separates the substrate and the diaphragm by an anchoring structure. On the one hand, since the diaphragm cannot directly contact the substrate, the reliability and heat dissipation performance of the diaphragm are impaired; on the other hand, since the values ​​of the cavity depth and the proportional radius are affected by both the anchoring structure and the substrate, and these two structures are often affected by different material parameters, thermal expansion coefficients, etching morphologies and rates, the cavity depth and proportional radius are not accurately controlled or change over time, which in turn affects the PMUT performance.

[0183] Different from the prior art, the process of forming the first cavity area and the second cavity area through the aforementioned embodiments of the present application, a and b are the diaphragm boundaries of the ultrasonic transducer, wherein the upper boundary ab of the silicon surface cavity (the first cavity area 102) is coplanar (that is, in the same horizontal plane) with the upper boundary of the base silicon (substrate layer 10), that is, the diaphragm is in direct mechanical contact with the substrate area, and the reliability and heat dissipation performance of the diaphragm are good; in addition, since the values ​​of the cavity depth and the proportional radius (equivalent to the ratio S2 / S1) are both formed and controlled by a single material of the substrate, the present application can accurately control the values ​​of the cavity depth and the proportional radius to expand the application field of the PMUT, and the values ​​of the cavity depth and the proportional radius do not change with time, which is beneficial to improving the stability of the PMUT.

[0184] A piezoelectric micromechanical ultrasonic transducer proposed in this embodiment has a double release structure of a silicon surface cavity and a back-engraving. The silicon surface cavity is used to accurately define the PMUT diaphragm boundary, and the bulk silicon back-engraving structure is combined to reduce the squeeze film damping to improve the performance of the PMUT. In addition, the bandwidth and sensitivity of the PMUT can be controlled by adjusting the size ratio of the second cavity area and the first cavity area, so that the corresponding bandwidth and sensitivity can be set according to different application requirements. It is widely used in the fields of ranging sensors, flow meters, liquid level meters, and material identification.

[0185] Based on the above-mentioned piezoelectric micromechanical ultrasonic transducer, an embodiment of the present application further provides a method for manufacturing the above-mentioned piezoelectric micromechanical ultrasonic transducer, such as Figure 3 As shown, the method includes:

[0186] S10, etching a first cavity region on the substrate layer, and forming a sacrificial layer on the substrate layer, wherein the sacrificial layer covers the substrate layer;

[0187] S11, performing planarization processing on the sacrificial layer to remove the sacrificial layer outside the first cavity area;

[0188] S12, forming a stacked structure above the exposed substrate layer and the sacrificial layer, wherein the stacked structure covers the sacrificial layer and the exposed substrate layer;

[0189] S13, performing back etching on the substrate layer at a side of the substrate layer away from the stacking structure to form a second cavity region;

[0190] S14. Release the sacrificial layer in the first cavity area to connect the first cavity area with the second cavity area, wherein the area outside the first cavity area and the second cavity area is a substrate area, the orthographic projection of the first cavity area on the substrate layer covers the orthographic projection of the second cavity area on the substrate layer, and the suspended part of the stacked structure on the substrate layer is the diaphragm of the ultrasonic transducer.

[0191] The ultrasonic transducer obtained by the method for manufacturing a piezoelectric micromechanical ultrasonic transducer proposed in this embodiment has a double release structure of a silicon surface cavity and a back-engraving. The silicon surface cavity is used to accurately define the PMUT diaphragm boundary, and the bulk silicon back-engraving structure is combined to reduce the squeeze film damping to improve the performance of the PMUT. In addition, the bandwidth and sensitivity of the PMUT can be controlled by adjusting the size ratio of the second cavity area and the first cavity area, so that the corresponding bandwidth and sensitivity can be set according to different application requirements. It is widely used in the fields of ranging sensors, flow meters, liquid level meters, and material identification.

[0192] Since the manufacturing method provided in the embodiment of the present application corresponds to the piezoelectric micromechanical ultrasonic transducer provided in the above embodiment, the previous implementation is also applicable to the manufacturing method provided in this embodiment and will not be described in detail in this embodiment.

[0193] Based on the above-mentioned piezoelectric micromechanical ultrasonic transducer, an embodiment of the present application further provides a piezoelectric micromechanical ultrasonic transducer array, such as Fig.17 As shown, the ultrasonic transducer array comprises: an acoustic coupling medium and a plurality of piezoelectric micromechanical ultrasonic transducers as described in the first aspect above, wherein:

[0194] The n piezoelectric micromechanical ultrasonic transducers receive or transmit ultrasonic signals through the acoustic coupling medium.

[0195] It should be understood that the various forms of processes shown above can be used to reorder, add or delete steps. For example, the steps recorded in this disclosure can be executed in parallel, sequentially or in different orders, as long as the desired results of the technical solution of this disclosure can be achieved, and this document is not limited here.

[0196] In the description of the present application, it should be noted that the orientation or position relationship indicated by the terms "upper", "lower", etc. is based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present application. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to the specific circumstances; relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such a process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "including one..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0197] The above specific implementations do not constitute a limitation on the protection scope of the present disclosure. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present disclosure shall be included in the protection scope of the present disclosure.

Claims

1. A piezoelectric micromechanical ultrasonic transducer, characterized in that: include: substrate layer, and A stacked structure is provided on the substrate layer, wherein: The substrate layer comprises a substrate region and a first cavity region and a second cavity region surrounded by the substrate region; The orthographic projection area of ​​the first cavity region on the stacked structure is greater than the orthographic projection area of ​​the second cavity region on the stacked structure, and the suspended portion of the stacked structure on the substrate layer is the diaphragm of the ultrasonic transducer.

2. The ultrasonic transducer according to claim 1, characterized in that: The stacking structure comprises: A support layer, a first electrode layer, a first piezoelectric layer and a second electrode layer are stacked on the substrate layer, wherein the orthographic projection of the second electrode layer on the support layer falls within the orthographic projection of the first electrode layer on the support layer, and the thickness of the first electrode layer is the same as the thickness of the second electrode layer.

3. The ultrasonic transducer according to claim 1, characterized in that: The stacking structure comprises: A third electrode layer, a second piezoelectric layer and a fourth electrode layer are stacked on the substrate layer, wherein the orthographic projection of the fourth electrode layer on the second piezoelectric layer falls within the orthographic projection of the third electrode layer on the second piezoelectric layer, and the thickness of the fourth electrode layer is greater than the thickness of the third electrode layer.

4. The ultrasonic transducer according to claim 1, characterized in that: The stacking structure comprises: A fifth electrode layer, a third piezoelectric layer, a sixth electrode layer, a fourth piezoelectric layer and a seventh electrode layer are stacked on the substrate layer, wherein the orthographic projections of the sixth electrode layer and the seventh electrode layer on the third piezoelectric layer fall within the orthographic projection of the fifth electrode layer on the third piezoelectric layer.

5. The ultrasonic transducer according to claim 1, characterized in that: It also includes a release hole that passes through the stacking structure, and the release hole is configured to form a slit in the stacking structure, wherein two ends of the slit protrude from the second cavity area, and / or two ends of the slit protrude from the first cavity area.

6. The ultrasonic transducer according to claim 1, characterized in that: The size of the first cavity region in a direction horizontal to the substrate layer is a first cavity horizontal size, the size of the second cavity region in a direction horizontal to the substrate layer is a second cavity horizontal size, and the second cavity horizontal size is smaller than the first cavity horizontal size.

7. The ultrasonic transducer according to claim 6, characterized in that: The sensitivity of the ultrasonic transducer is positively correlated with the ratio of the second cavity horizontal size to the first cavity horizontal size; the bandwidth of the ultrasonic transducer is negatively correlated with the ratio of the second cavity horizontal size to the first cavity horizontal size.

8. The ultrasonic transducer according to claim 7, characterized in that: When the ratio is 1, the sensitivity of the ultrasonic transducer is the upper limit of sensitivity; when the ratio is greater than 0.3 and less than 1, the sensitivity of the ultrasonic transducer is not less than one tenth of the upper limit of sensitivity.

9. The ultrasonic transducer according to claim 8, characterized in that: The bandwidth of the ultrasonic transducer is greater than 5 kHz and less than 20 kHz; the sensitivity of the ultrasonic transducer is greater than 0.6 μm / V and less than 3.5 μm / V.

10. The ultrasonic transducer according to claim 6, characterized in that: The size of the first cavity area in a direction perpendicular to the substrate layer is the first cavity vertical size. When the ratio of the second cavity horizontal size to the first cavity horizontal size is constant, the sensitivity of the ultrasonic transducer is positively correlated with the first cavity vertical size; the bandwidth of the ultrasonic transducer is negatively correlated with the first cavity vertical size.

11. The ultrasonic transducer according to claim 10, characterized in that: When the ratio is not greater than 0.5, the vertical dimension of the first cavity is greater than 0.5 μm and less than 5 μm.

12. The ultrasonic transducer according to claim 11, characterized in that: The bandwidth of the ultrasonic transducer is greater than 12.5 kHz and less than 35 kHz; the sensitivity of the ultrasonic transducer is greater than 0.45 μm / V and less than 1.4 μm / V.

13. The ultrasonic transducer according to claim 10, characterized in that: When the sensitivity obtains a lower limit value of sensitivity, the bandwidth obtains an upper limit value of bandwidth; and when bandwidth regulation is performed, the sensitivity is not less than one tenth of the upper limit value of sensitivity.

14. The ultrasonic transducer according to claim 13, characterized in that: The vertical dimension of the first cavity and the ratio satisfy a linear relationship, and the intersection of the linear relationship and the cavity depth coordinate axis is h, and the intersection of the linear relationship and the ratio coordinate axis is k. Any combination of cavity depth and ratio is selected outside the area formed by the h point, the k point and the origin so that the sensitivity is not less than one tenth of the upper limit of the sensitivity.

15. A method for manufacturing a piezoelectric micromechanical ultrasonic transducer as claimed in any one of claims 1 to 14, characterized in that: include: Etching a first cavity region on the substrate layer, and forming a sacrificial layer on the substrate layer, wherein the sacrificial layer covers the substrate layer; performing a planarization process on the sacrificial layer to remove the sacrificial layer outside the first cavity region; forming a stacked structure above the exposed substrate layer and the sacrificial layer, wherein the stacked structure covers the sacrificial layer and the exposed substrate layer; Performing back etching on the substrate layer at a side of the substrate layer away from the stacking structure to form a second cavity region; Release the sacrificial layer in the first cavity area to connect the first cavity area with the second cavity area, wherein the outside of the first cavity area and the second cavity area is a substrate area, the orthographic projection of the first cavity area on the stacked structure covers the orthographic projection of the second cavity area on the stacked structure, and the suspended part of the stacked structure on the substrate layer is the diaphragm of the ultrasonic transducer.

16. The manufacturing method according to claim 15, characterized in that: The forming of a stacked structure on the exposed substrate layer and the sacrificial layer further comprises: forming a support layer over the exposed substrate layer and the sacrificial layer; forming a first electrode layer on the support layer; forming a first piezoelectric layer on the first electrode layer; A second electrode layer is formed on the first piezoelectric layer, wherein the orthographic projection of the second electrode layer on the supporting layer falls within the orthographic projection of the first electrode layer on the supporting layer, and the thickness of the first electrode layer is the same as that of the second electrode layer.

17. The manufacturing method according to claim 15, characterized in that: The forming of a stacked structure on the exposed substrate layer and the sacrificial layer further comprises: forming a third electrode layer over the exposed substrate layer and the sacrificial layer; forming a second piezoelectric layer on the third electrode layer; A fourth electrode layer is formed on the second piezoelectric layer, wherein an orthographic projection of the fourth electrode layer on the second piezoelectric layer falls within an orthographic projection of the third electrode layer on the second piezoelectric layer, and a thickness of the fourth electrode layer is greater than a thickness of the third electrode layer.

18. The manufacturing method according to claim 15, characterized in that: The forming of a stacked structure on the exposed substrate layer and the sacrificial layer further comprises: forming a fifth electrode layer over the exposed substrate layer and the sacrificial layer; forming a third piezoelectric layer on the fifth electrode layer; forming a patterned sixth electrode layer on the third piezoelectric layer; forming a fourth piezoelectric layer on the sixth electrode layer and covering the sixth electrode layer; A seventh electrode layer is formed on the fourth piezoelectric layer, wherein the orthographic projections of the sixth electrode layer and the seventh electrode layer on the third piezoelectric layer fall within the orthographic projection of the fifth electrode layer on the third piezoelectric layer.

19. The manufacturing method according to claim 15, characterized in that: Also includes: A release hole is formed through the stacking structure, wherein the release hole is configured to form a slit in the stacking structure, two ends of the slit protrude from the second cavity area, and / or two ends of the slit protrude from the first cavity area.

20. A piezoelectric micromechanical ultrasonic transducer array, characterized in that: include: An acoustic coupling medium and a plurality of piezoelectric micromechanical ultrasonic transducers as claimed in any one of claims 1 to 14, wherein: The piezoelectric micromechanical ultrasonic transducer receives or transmits an ultrasonic signal through the acoustic coupling medium.

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