Capacitive micro-machined ultrasonic transducer, manufacturing method and electrical product

Abstract

The invention provides a capacitive micro-machined ultrasonic transducer, a manufacturing method and an electrical product, and relates to the technical field of ultrasound. The capacitive micro-machined ultrasonic transducer comprises a plurality of ultrasonic transduction units which are arranged in an array mode. Each ultrasonic transduction unit comprises a vibrating membrane layer, a cavity, a stand column and a substrate which are sequentially arranged in a stacked mode. The vibrating membrane layer is bonded with the substrate through the stand columns, and the vibrating membrane layer, the substrate and the stand columns enclose to form the cavity; wherein the stand columns are support column bodies formed by the substrate through gaps at intervals, and are used for limiting the vibration membrane layer to be recessed towards the cavity when the vibration membrane layer is not naturally bent or not processed. According to the invention, the vertical columns are constructed in the cavity to support the vibrating membrane layer, so that the vibrating membrane layer cannot be recessed towards the cavity; therefore, the limitation of the cavity is relatively low, the height is extremely small, and the capacitive micro-mechanical ultrasonic transducer has extremely good emission sound pressure and acoustic sensitivity.

Description

Technical Field

[0001] The present application relates to the field of ultrasonic technology, and particularly to a capacitive micromachined ultrasonic transducer, a manufacturing method and an electrical product. Background Art

[0002] A micromachined ultrasonic transducer (MUT) is a MEMS ultrasonic device manufactured by using semiconductor micro-nano processing technology. Based on the electrostatic and piezoelectric principles, it can be divided into CMUT and PMUT. A capacitive micromachined ultrasonic transducer (CMUT) is a MEMS device that uses electrostatic force to drive a thin film to vibrate at a specific frequency to emit or receive ultrasonic signals. The emission and reception performance of CMUT are its key indicators, which determine the quality of the product. CMUT generally includes a bottom electrode, a vibrating film layer, a top electrode and a cavity. The cavity provides space for the vibration of the film layer. Since CMUT usually operates in the collapse mode, that is, the vibrating film layer is extremely close to or even contacts the electrode on the other side of the cavity, in order to avoid short circuit caused by the contact of the top and bottom electrodes, there is a dielectric film layer between the top and bottom electrodes. The acoustic emission and reception performance of CMUT are closely related to the cavity size, cavity height, diaphragm thickness and area. For example, when the cavity height of CMUT is smaller, its sensitivity is higher, and the thinner the diaphragm, the higher the sensitivity. The higher the vacuum degree in the cavity, the higher the sensitivity and performance.

[0003] When CMUT works, the DC bias voltage applied between the top and bottom electrodes determines the working mode of CMUT, including the normal mode, the collapse-fast recovery mode and the collapse mode. The magnitude of the bias voltage applied to CMUT is closely related to the film thickness and cavity height. The larger the film thickness and the higher the cavity height, the higher the bias voltage required. For example, limited by the wafer bonding manufacturing scheme, the obtained cavity height is usually several micrometers, such as 3um, 5um or even up to 10um, and the thickness of the vibrating film layer usually reaches 5um or even 10um; in order to achieve high sensitivity, a relatively high bias voltage needs to be applied, reaching 100V or even above 200V; it cannot meet the requirements of many scenarios for low bias voltage, such as scenarios where the bias voltage cannot be higher than 50V, or even 30V; at the same time, the relatively thick vibrating film layer also results in low sensitivity of the CMUT sensor. There is a need for a CMUT implementation scheme with a low cavity height and a thin diaphragm thickness to obtain excellent acoustic performance and a low bias voltage.

[0004] It should be noted that the above introduction of the technical background is only for the convenience of clearly and completely explaining the technical solutions of the present application and facilitating the understanding of those skilled in the art. It cannot be considered that the above technical solutions are well known to those skilled in the art just because these solutions are described in the background art part of the present application. Summary of the Invention

[0005] To solve at least one of the above problems existing in the prior art, an embodiment of the present application provides a capacitive micromachined ultrasonic transducer, a manufacturing method, and an electrical product.

[0006] According to a first aspect of the embodiments of the present application, the present application provides a capacitive micromachined ultrasonic transducer. The capacitive micromachined ultrasonic transducer includes a plurality of ultrasonic transducer units arranged in an array. The ultrasonic transducer unit includes a vibration film layer, a cavity, a pillar, and a substrate stacked in sequence. The vibration film layer is bonded to the substrate through the pillar and encloses the cavity with the substrate and the pillar. Among them, the pillar is a support pillar body formed by the substrate with gaps spaced apart, and is used to limit the vibration film layer from sagging into the cavity without natural bending or without processing.

[0007] In some embodiments, the vibration film layer includes a top electrode. The top electrode is a conductive thin film, and the conductive thin film includes low-resistance silicon, heavily phosphorus-doped silicon, boron-doped silicon, or a metal film layer. The substrate is a bottom electrode, and the bottom electrode includes silicon, low-resistance silicon, high-phosphorus and boron-doped silicon, highly conductive silicon, SOI, or a conductive metal film layer.

[0008] In some embodiments, the ultrasonic transducer unit further includes a dielectric thin film. The dielectric thin film is disposed on the side of the substrate opposite to the vibration film layer; or, the dielectric thin film is disposed on the side of the top electrode opposite to the substrate. Among them, the dielectric thin film includes a Si3N4, SiO2, AlN, Al2O3, or HfO2 film layer.

[0009] In some embodiments, it further includes electrical connection pads disposed on the top electrode and the bottom electrode, and the capacitive micromachined ultrasonic transducer is interconnected with an external circuit.

[0010] In some embodiments, the aspect ratio of the support pillar body is not less than 5.

[0011] In some embodiments, the support pillar body is a square pillar, a rectangular pillar, or a cylindrical pillar.

[0012] In some embodiments, the vibration film layer includes a rectangular thin film layer, a circular thin film layer, an elliptical thin film layer, a triangular thin film layer, or a polygonal thin film layer.

[0013] In some embodiments, a piston-shaped module is disposed on the other side of the vibration film layer relative to the substrate, for increasing the kinetic energy of the vibration film layer.

[0014] In some embodiments, it further includes a cavity height defining film layer. The cavity height defining film layer is disposed between the vibration film layer and the pillar, and both sides of the cavity height defining film layer are bonded to the vibration film layer and the pillar respectively. Among them, the cross-section of the vibration film layer is a flat structure.

[0015] According to the second aspect of the embodiments of the present application, the present application provides an electrical product including the above capacitive micromachined ultrasonic transducer.

[0016] According to the third aspect of the embodiments of the present application, the present application provides a method for manufacturing a capacitive micromachined ultrasonic transducer, the method including: forming columns by etching voids on one side of a substrate, and growing a sacrificial layer on the side of the substrate containing voids; patterning the sacrificial layer to generate a preset sacrificial layer pattern, and sequentially depositing a dielectric film layer and a conductive layer on the sacrificial layer; etching at the same positions of the dielectric film layer and the conductive layer to construct a sacrificial release channel, and using the sacrificial release channel to remove the sacrificial layer by etching to release a cavity formed by enclosing the dielectric film layer, the substrate, and the columns; filling the sacrificial release channel with a deposited material to physically isolate the cavity and the columns from the outside.

[0017] In some embodiments, patterning the sacrificial layer to generate a preset sacrificial layer pattern further includes: chemically mechanically polishing and planarizing the sacrificial layer outside the voids, and growing a sacrificial layer with a preset thickness on the void side of the substrate by a deposition method; patterning the sacrificial layer to generate a preset sacrificial layer pattern.

[0018] In some embodiments, using the sacrificial release channel to remove the sacrificial layer by etching to release the cavity and the columns includes: using the sacrificial release channel to remove the sacrificial layer by wet etching or dry etching to release the cavity and the columns.

[0019] In some embodiments, using the sacrificial release channel to remove the sacrificial layer by etching to release the cavity and the columns further includes: releasing a bottom electrode by etching the dielectric film layer and the conductive layer to form an electrical connection pad area.

[0020] According to the fourth aspect of the embodiments of the present application, the present application provides a method for manufacturing a capacitive micromachined ultrasonic transducer, the method including: generating a cavity height defining film layer on one side of a substrate, patterning the cavity height defining film layer to form a preset cavity height defining film layer pattern, and forming columns by etching voids on one side of the substrate; growing a sacrificial layer on the side of the substrate containing voids and on the other side of the height defining film layer relative to the substrate, and growing a dielectric film layer on the other side of the sacrificial layer relative to the substrate by vapor deposition; etching the dielectric film layer to construct a sacrificial release channel, and using the sacrificial release channel to remove the sacrificial layer by etching to release a cavity formed by enclosing the dielectric film layer, the substrate, and the columns; filling the sacrificial release channel with a deposited material to physically isolate the cavity and the columns from the outside, and depositing and generating a conductive layer and an electrical connection pad area on the other side of the dielectric film layer relative to the substrate and on the substrate.

[0021] In some embodiments, before growing a dielectric film layer on the other side of the sacrificial layer relative to the substrate by chemical vapor deposition, it further includes: chemically mechanically polishing a sacrificial layer with a preset thickness.

[0022] In some embodiments, when depositing and forming a conductive layer and an electrically connected pad region on the other side of the dielectric film layer relative to the substrate and the substrate, it further includes: when the conductive layer and the electrically connected pad region are made of different materials, depositing and patterning a conductive layer on the other side of the dielectric film layer relative to the substrate and the substrate; constructing an electrically connected pad region on the other side of the conductive layer relative to the dielectric film layer and the substrate.

[0023] In some embodiments, a piston-shaped module is disposed on the other side of the conductive layer relative to the dielectric film layer.

[0024] The manufacturing method of the capacitive micromachined ultrasonic transducer provided in this application can construct a CMUT device with an extremely small cavity height (for example, the cavity height is less than 500 nm, or even less than 100 nm); meanwhile, the pillar with a large aspect ratio has great flexibility and does not affect the vibration amplitude of the CMUT vibration film layer during operation. Moreover, using the sacrificial layer process to manufacture a super-large area CMUT with supporting pillars, this technology can manufacture CMUTs with cavities of any height and size and vibration film layers of any thickness. The supporting pillars and the vibration film layer are strongly bonded by chemical vapor deposition. Compared with the bonding process, the sacrificial layer process has almost no restrictions on the material of the vibration film layer; secondly, the capacitive micromachined ultrasonic transducer and electrical products provided in this application have excellent emission sound pressure and acoustic sensitivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The drawings described herein are used to provide a further understanding of this application, form a part of this application, and do not limit this application. In the drawings:

[0026] Figure 1a is a top view of a single CMUT provided by an embodiment of this application;

[0027] Figure 1b is along Figure 1a a cross-sectional schematic view in the AA direction in;

[0028] Figure 1c is a top view of the capacitive micromachined ultrasonic transducer provided by an embodiment of this application;

[0029] Figure 1d is a top view of the capacitive micromachined ultrasonic transducer provided by an embodiment of this application;

[0030] Figure 1eTop view of a capacitive micromachined ultrasonic transducer provided by an embodiment of the present application;

[0031] Figure 1f Schematic cross-sectional view along the Figure 1a AA direction provided by an embodiment of the present application;

[0032] Figure 1g Schematic cross-sectional view along the Figure 1a AA direction provided by an embodiment of the present application;

[0033] Figures 2 to 13 Schematic structural view of the preparation process of CMUT provided by an embodiment of the present application;

[0034] Figure 14 Schematic flow chart of the preparation method of CMUT provided by an embodiment of the present application;

[0035] Figure 15 Schematic flow chart of regrowth after planarization and polishing of the sacrificial layer provided by an embodiment of the present application;

[0036] Figure 16 Schematic flow chart of the preparation method of CMUT provided by an embodiment of the present application;

[0037] Figure 17 Schematic flow chart of the construction process of the electrical connection pad area provided by an embodiment of the present application;

[0038] Figures 18 to 28 Schematic structural view of the preparation process of CMUT provided by an embodiment of the present application

[0039] Figure 29 Schematic cross-sectional view along the Figure 1a AA direction provided by an embodiment of the present application;

[0040] Figure 30 Schematic cross-sectional view along the Figure 1a AA direction provided by an embodiment of the present application. Detailed implementation manners

[0041] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts shall fall within the protection scope of the present application.

[0042] Reference is made to the following description and the accompanying drawings, which disclose in detail specific embodiments of the present application and indicate the ways in which the principles of the present application can be employed. It should be understood that the embodiments of the present application are not limited in scope thereby. Within the spirit and terms of the appended claims, the embodiments of the present application include many modifications,

[0043] Features described and / or illustrated for one embodiment can be used in the same or similar manner in one or more other embodiments, combined with features in other embodiments, or substituted for features in other embodiments.

[0044] It should be emphasized that the term "comprising / including" as used herein refers to the presence of features, whole things, steps or components, but does not exclude the presence or addition of one or more other features, whole things, steps or components.

[0045] According to a first aspect of an embodiment of the present application, the present application provides a capacitive micromachined ultrasonic transducer, which includes a plurality of ultrasonically transducer units arranged in an array, and the ultrasonically transducer unit includes a vibrating membrane layer, a cavity, a pillar and a substrate stacked in sequence; the vibrating membrane layer is bonded to the substrate through the pillar, and together with the substrate and the pillar, encloses to form the cavity; wherein, the pillar is a support pillar body formed by the substrate with gaps spaced apart, and is used to limit the vibrating membrane layer from sagging into the cavity without natural bending or without processing.

[0046] In actual operation, to promote the mechanical stability and uniform vibration displacement of the ultra-thin CMUT vibrating membrane layer, the ultra-low cavity height and ultra-thin vibrating film enable the CMUT to reach the collapse mode at a very low bias voltage, obtaining a high emission sound pressure; in addition, the ultra-thin vibrating film is beneficial to obtaining a CMUT with higher sensitivity; to ensure the uniformity of the vibrating film displacement, the present application constructs pillars in the cavity to support the CMUT vibrating film so that it cannot sag towards the cavity; to avoid the pillars restricting the vibration of the vibrating film, the present application can construct pillars with a very small width or diameter or characteristic size (such as 1 μm), a very large height (such as 30 μm), and a very large ratio of length to cross-sectional size.

[0047] In some embodiments, the vibrating membrane layer includes a top electrode; the top electrode is a conductive film, and the conductive film includes low-resistance silicon, heavily phosphorus-doped, boron-doped silicon or a metal film layer; the substrate is a bottom electrode, and the bottom electrode includes silicon, low-resistance silicon, high-phosphorus and boron-doped silicon, highly conductive silicon, SOI or a conductive metal film layer. In actual operation, both the top electrode and the bottom electrode are conductive structures, which are the basic structural conditions of the capacitive micromachined ultrasonic transducer, and the present application will not elaborate on this here one by one.

[0048] Further, the ultrasonic transducer unit further includes a dielectric film, which is attached to the side of the substrate opposite to the vibrating film layer; or, the dielectric film is attached to the side of the top electrode opposite to the substrate; wherein, the dielectric film includes a Si3N4, SiO2, AlN, Al2O3 or HfO2 film layer. It should be noted that in actual work, the role of this dielectric film is to separate the top electrode and the bottom electrode to prevent short circuit. Therefore, those skilled in the art can choose to set the dielectric film on the substrate side or the conductive film side according to actual needs, and this application does not make further restrictions in this regard. In some other embodiments, the capacitive micromachined ultrasonic transducer provided in this application further includes electrical connection pads provided on the top electrode and the bottom electrode, and the capacitive micromachined ultrasonic transducer is interconnected with an external circuit.

[0049] For details, please refer to Figures 1a to 1b As shown, the capacitive micromachined ultrasonic transducer provided in this application can have an ultra-small cavity height, an ultra-thin vibrating film and high sensitivity; specifically, the CMUT structure includes a vibrating film layer composed of a substrate 100, a dielectric film 300 and a conductive film 400, and electrical connection pads 510 and 520 connecting the bottom electrode and the top electrode. Among them, the substrate 100 can be used as the bottom electrode, which can be a highly conductive material such as low-resistance silicon, heavily doped silicon, conductive metal, etc., and the conductive film 400 can be used as the top electrode, which can be low-resistance silicon, phosphorus or boron-doped silicon, metal, etc. The dielectric film layer 300 can be a high-quality dielectric film with high insulation such as Si3N4, SiO2, AlN, Al2O3, HfO2, etc. The cavity 201 provides the space required for the vibration of the vibrating film layer.

[0050] In some embodiments, the aspect ratio of the support column is not less than 5. Specifically, under the CMUT diaphragm provided in the present application, there are slender columns 110. There is a gap 101 between the columns and the substrate 100. The existence of the columns 110 can support the dielectric film 300 and the conductive film 400 of the CMUT with a large area, preventing them from sagging due to natural bending or the vacuum degree in the cavity 201 during processing, which would change the cavity height, resulting in design and actual deviations, and even the situation where the CMUT vibration film layer contacts the substrate and fails. Its size is very narrow, such as the width or diameter or characteristic size is less than 5 μm, less than 1 μm, or even less than 500 nm; its height is relatively large, such as greater than 3 μm, greater than 5 μm, greater than 10 μm, or even greater than 50 μm; the column 110 has a large aspect ratio of height to width, and its aspect ratio is preferably greater than 5, greater than 10, greater than 20, greater than 50, or even greater than 100. Therefore, the existence of the column 110 can keep the cavity size of the CMUT with a large-area vibration film stable; in addition, the column with a huge aspect ratio (such as >10) and an extremely fine structure (such as width <500 nm) has great flexibility and can minimize the restraint of the column on the vibration of the film layer when the CMUT dielectric film 300 and the conductive film 400 vibrate, enabling the CMUT with a large-area vibration film layer to exhibit excellent ultrasonic emission and reception performance.

[0051] Among them Figure 1a In the example, a single CMUT contains 3 columns 110, and a single CMUT vibration element is composed of vibration regions separated by four columns. Due to the extremely narrow and high columns with a large aspect ratio, they have great flexibility and basically do not affect Figure 1a the vibration of the overall film layer in the CMUT vibration element shown in, obtaining a great emitted sound pressure and acoustic sensitivity. Each independent CMUT unit is interconnected with the circuit through electrical connection pads 510-1 to 510-3 and electrical connection pads 520-1 to 520-3, realizing interconnection with circuits such as application-specific integrated circuits ASICs or printed circuit boards PCBs.

[0052] In the above embodiment, the cavity 201 is obtained by the sacrificial layer process, that is, a sacrificial layer film layer with a specific thickness is first grown, and its material can be Si, SiO2, phosphorus-doped SiO2, boron-doped SiO2, etc. Subsequently, it is released through a preset channel to form a cavity. After the release channel, it is filled by depositing the material 310, which can be silicon, Si3N4, etc. The height and size of the cavity obtained by this preparation method can be precisely controlled, and the cavity height can be very thin, such as less than 300 nm, less than 100 nm, or even less than 50 nm, less than 10 nm, etc. A smaller cavity height can significantly improve the sensitivity of the CMUT and reduce the bias voltage, etc. The specific preparation method will be described in detail in the subsequent embodiments and will not be elaborated here one by one.

[0053] In some embodiments, the support column can be a square column, a rectangular column or a cylindrical column. Specifically, please refer to Figure 1d as shown, in Figure 1d the column 110 is a square column, and the side length of its cross-section can be less than 5um, less than 3um, less than 1um, or even less than 500nm. Compared with Figures 1a to 1c , Figure 1d the overall size of the column cross-section in the example is smaller, and its overall rigidity is smaller. On the premise of supporting the CMUT vibration film layer and preventing it from naturally sagging, when the CMUT works, the vibration amplitude of the dielectric film 300 and the conductive film 400 is less restricted, and the CMUT with a super-large area vibration film has better acoustic performance. Among them, the functions of the void 101, the deposited material 310, the electrical connection pad 510, and the electrical connection pad 520 are the same as those in Figures 1a to 1c ; further, the column 110 can also be a cylindrical column, and its function is similar to that of a square column, which will not be elaborated here.

[0054] In some embodiments, the vibration film layer includes a rectangular film layer, a circular film layer, an elliptical film layer, a triangular film layer or a polygonal film layer. Specifically, please refer to Figure 1e as shown, in Figure 1e in addition to the vibration area of the CMUT being rectangularly arranged, the vibration film can be circular, elliptical or any other designed shape; the void 101, the deposited material 310, the electrical connection pad 510, and the electrical connection pad 520 can be set at corresponding positions according to actual needs, which will not be elaborated here.

[0055] In some embodiments, a piston-like module is provided on the other side of the vibration film layer relative to the substrate, for increasing the kinetic energy of the vibration film layer. Specifically, please refer to Figure 1f as shown, the vibration film is provided with a piston-like module 600. The piston-like module 600 can increase the kinetic energy of the vibration film and improve the acoustic emission and reception sensitivity of the CMUT; the functions of the substrate 100, the void 101, the column 110, the cavity 201, the deposited material 310, the electrical connection pad 510, and the electrical connection pad 520 are similar to those of the foregoing structures, which will not be elaborated here.

[0056] In some embodiments, the capacitive micromachined ultrasonic transducer provided by the present application further includes a cavity height defining film layer, the cavity height defining film layer is disposed between the vibration film layer and the column, and both sides of the cavity height defining film layer are adhesively bonded to the vibration film layer and the column respectively; wherein, the cross-section of the vibration film layer is a flat structure. Specifically, please refer to Figure 1g as shown, Figure 1g is a cross-sectional view along the AA direction in Figure 1a , and this structure is compared with Figure 1b andFigure 1f For the aforementioned structures such as the entire diaphragm layer, the electrode layer 510 connected thereto, and the piston-like module, there is no concave region equivalent to the height of the cavity 201 above the column 110. The movement edge of the dielectric film layer 300 and other film layers is formed by the cavity height defining the film layer 720. This structure makes the dielectric film layer 300 adjacent to the cavity integrated in the horizontal plane without structural mutations in the direction perpendicular to the plane. It increases the reliability of the CMUT diaphragm layer for long-term operation and improves the acoustic emission and reception performance of the entire CMUT diaphragm layer. Additionally, when the size of the column 110 is small enough, such as the size of a single cross-sectional direction being as small as 3 μm, less than 1 μm, or even less than 500 nm, the column 110 can exhibit the movement characteristics of a spring, assisting the integrated vibration of the entire diaphragm layer in the ultra-large-size vibrating thin-film CMUT of the present invention and improving the acoustic performance of the CMUT. Based on Figure 1g For the provided structure, the conductive thin film 400 connected to the cavity 201 is continuous in the horizontal plane without mutations. This structure can not only improve the reliability of the CMUT diaphragm layer for long-term operation but also assist the integrated vibration of the entire diaphragm layer, facilitating the CMUT to emit more uniform and high-intensity sound waves and also facilitating the reception of sound wave signals with high sensitivity.

[0057] According to the second aspect of the embodiments of the present application, the present application provides an electrical product including the above-mentioned capacitive micromachined ultrasonic transducer. In the structure of this electrical product, the performance of the capacitive micromachined ultrasonic transducer is mainly utilized, and thus a high-performance electrical product can be achieved. The structure of the piezoelectric micromachined ultrasonic transducer can refer to the embodiments of the first aspect of the present application and will not be elaborated here.

[0058] According to the third aspect of the embodiments of the present application, the present application provides a method for manufacturing a capacitive micromachined ultrasonic transducer. Specifically, please refer to Figure 14 As shown, the method includes:

[0059] S101: Form columns by etching voids on one side of the substrate, and grow a sacrificial layer on the substrate side containing voids;

[0060] S102: Pattern the sacrificial layer to generate a preset sacrificial layer pattern, and sequentially deposit a dielectric film layer and a conductive layer on the sacrificial layer;

[0061] S103: Etch at the same position of the dielectric film layer and the conductive layer to construct a sacrificial release channel, and use the sacrificial release channel to remove the sacrificial layer by etching to release the cavity surrounded by the dielectric film layer, the substrate, and the columns;

[0062] S104: Fill the sacrificial release channel with a deposited material to physically isolate the cavity and the columns from the outside.

[0063] Specifically, as Figure 2 and Figure 3 shown, the substrate 100 can be silicon, low-resistance silicon, high-phosphorus and boron-doped silicon, highly conductive silicon, SOI, etc., and silicon with high surface conductivity is preferably selected. A void 101 is etched on the substrate 100 to form a pillar 110 with an extremely high aspect ratio and extremely narrow width. The width, diameter, and cross-sectional size of the pillar are preferably less than 5 μm, less than 1 μm, and even less than 500 nm; its height is relatively large, such as greater than 3 μm, greater than 5 μm, greater than 10 μm, and even greater than 50 μm; the pillar 110 has a very high height-to-width ratio, and its height-to-width ratio is preferably greater than 5, greater than 10, greater than 20, greater than 50, and even greater than 100. The distance between the pillar 110 and the substrate 100 is relatively small. For example, it is less than 10 μm, less than 5 μm, and even less than 2 μm, which is more conducive to forming a stable electric field between the upper and lower electrodes of the CMUT and obtaining excellent CMUT acoustic performance.

[0064] In some embodiments, please refer to Figure 15 shown, patterning the sacrificial layer to generate a preset sacrificial layer pattern further includes:

[0065] S201: Chemically mechanically planarize and polish the sacrificial layer outside the voids, and grow a sacrificial layer with a preset thickness on the side of the voids of the substrate by a deposition method;

[0066] S202: Pattern the sacrificial layer to generate a preset sacrificial layer pattern.

[0067] Specifically, please refer to Figures 4 to 7 shown, based on Figure 3 the generated pillar 110 and void 101, a sacrificial layer material 200 can be grown on the substrate of the voids, and the material can be Si, SiO2, phosphorus-doped SiO2, boron-doped SiO2, etc. Please refer to Figure 5 shown again. The wafer with the sacrificial layer grown is ground and polished by chemical mechanical polishing (CMP) to form a structure as Figure 5 shown. Here, the sacrificial layer material only exists in the gap 101 and does not exist on the wafer surface. Of course, the remaining film thickness can be precisely controlled during polishing, and polishing can be stopped at a specific thickness to obtain a wafer with a sacrificial layer on the wafer surface as Figure 6 shown. However, it is very difficult to make the device surface retain a sacrificial layer film layer with a specific precise thickness by chemical mechanical polishing. Therefore, it can be selected to completely polish the sacrificial layer until it only exists in the voids. Then, a sacrificial layer with a specific thickness is grown on the wafer surface by a deposition method to form a pre-film layer of the cavity 210. Compared with the solution of removing part of the sacrificial layer on the wafer surface by CMP polishing to form a sacrificial layer film layer with a specific thickness, the solution of completely polishing and removing the sacrificial layer on the wafer surface and then growing a film layer with a specific thickness can well control the thickness of the sacrificial layer and the wafer-level uniformity.Figure 5 and Figure 6 ), so that the height and size of the CMUT cavity formed after the sacrificial layer is released can be precisely controlled to obtain CMUT units and arrays with uniform performance. Figure 7 As shown, the sacrificial layer 210 is patterned to form a predetermined sacrificial layer pattern 220 .

[0068] In some embodiments, removing the sacrificial layer release cavity and the pillar by etching using the sacrificial release channel includes: removing the sacrificial layer release cavity and the pillar by wet or dry etching using the sacrificial release channel. In some embodiments, removing the sacrificial layer release cavity and the pillar by etching using the sacrificial release channel also includes: releasing the bottom electrode by etching the dielectric film layer and the conductive layer to form an electrical connection pad area.

[0069] For details, please refer to Figures 8 to 13 As shown, based on Figure 7 The sacrificial layer pattern 220 formed in Figure 8 As shown, a dielectric film 300 and a conductive film 400 are deposited. The dielectric film 300 may be a high-quality dielectric film with high insulation properties such as Si3N4, SiO2, AlN, Al2O3, HfO2, etc. The conductive film 400 may be low-resistance silicon, heavily phosphorus or boron doped silicon, metal, etc. Thereafter, as Figure 9 As shown, a sacrificial layer release channel 301 is etched on the dielectric film 300 and the conductive film 400, and then the sacrificial layer material 220 is removed by wet or dry etching to release the pillar 110 and the cavity 201, as shown in FIG. Figure 10 Then, the dielectric film layer and the conductive layer are etched to release the bottom electrode electrical connection pad area, as shown in FIG. Figure 11 Then, a material 310 is deposited in the release channel to physically isolate the cavity 201 and the column channel 101 from the outside world, so that the cavity 201 and the gap 101 between the column and the substrate is in a vacuum state, so that the CMUT has better acoustic performance, such as Figure 12 As shown. Because of the existence of the pillars 110, when the cavity 201 and the gap 101 are in a vacuum state, the vibration film 300 and the conductive film 400 will not bend downward, causing the cavity size to be inconsistent with the design, thereby maintaining its acoustic performance. Finally, as Figure 13 As shown, top and bottom electrodes are deposited and patterned to electrically connect pads 510 and 520 .

[0070] According to the fourth aspect of the embodiment of the present application, the present application provides a method for preparing a capacitive micromechanical ultrasonic transducer. Figure 16 As shown, the method comprises:

[0071] In S301, a cavity height defining film layer is formed on one side of the substrate, the cavity height defining film layer is patterned to form a preset cavity height defining film layer pattern, and posts are formed by etching voids on one side of the substrate.

[0072] In S302, a sacrificial layer is grown on the side of the substrate with voids and on the other side of the height defining film layer relative to the substrate, and a dielectric film layer is grown on the other side of the sacrificial layer relative to the substrate by vapor deposition.

[0073] In S303, a sacrificial release channel is etched in the dielectric film layer, and the sacrificial layer is removed through the sacrificial release channel by etching to release the cavity formed by the enclosure of the dielectric film layer, the substrate, and the posts.

[0074] In S304, the sacrificial release channel is filled with a deposited material to physically isolate the cavity and the posts from the outside, and a conductive layer and an electrically connected pad region are deposited on the other side of the dielectric film layer relative to the substrate and on the substrate.

[0075] This preparation method is mainly for Figure 1g the preparation process of the capacitive micromachined ultrasonic transducer shown. The specific preparation process is as follows. Please refer to Figures 18 to 22 As shown, the substrate 100 can be silicon, low-resistivity silicon, high-phosphorus and boron-doped silicon, highly conductive silicon, SOI, etc. Through Figure 19 As shown, a cavity height defining film layer 700 is grown. This film layer can be a dielectric thin film layer, such as a high-quality dielectric thin film with high insulation such as Si3N4, SiO2, AlN, Al2O3, HfO2, etc.; it can also be a conductive thin film, such as metal, etc. Subsequently, through Figure 20 the cavity height defining film layer 700 is patterned in the illustrated manner to form a 710 pattern structure. Then, a void 101 is etched on the substrate 100 to form extremely narrow posts 110 with an extremely high aspect ratio, as Figure 21 shown. The width, diameter, and cross-sectional size of the posts are preferably less than 5 μm, less than 1 μm, and even less than 500 nm; their height is relatively large, such as greater than 3 μm, greater than 5 μm, greater than 10 μm, and even greater than 50 μm; the posts 110 have a very large height-to-width ratio, and the height-to-width ratio is preferably greater than 5, greater than 10, greater than 20, greater than 50, and even greater than 100. The distance between the posts 110 and the substrate 100 is relatively small. For example, less than 10 μm, less than 5 μm, and even less than 2 μm. This will be more conducive to forming a stable electric field between the upper and lower electrodes of the CMUT and obtaining excellent CMUT acoustic performance. Finally, a sacrificial layer material 200 is grown on the wafer to fill the void 101, and the material selection can be Si, SiO2, phosphorus-doped SiO2, boron-doped SiO2, etc., as Figure 22 shown.

[0076] In some embodiments, before growing a dielectric film layer on the other side of the sacrificial layer relative to the substrate by chemical vapor deposition, it further includes: chemically mechanically grinding and polishing a sacrificial layer with a preset thickness.

[0077] Specifically, please refer to Figure 23 As shown, in this embodiment, the wafer with the sacrificial layer 200 can be ground and polished by chemical mechanical polishing (CMP) to form a structure as shown in Figure 23 As shown. Here, it is necessary to precisely control the thickness of the cavity height defining film layer 710 and the sacrificial layer 200 during the polishing process, stop polishing at a specific thickness to obtain a sacrificial layer with a specific thickness, and then a cavity with a specific height can be obtained after release. Therefore, the thickness of the cavity height defining film layer 720 after polishing here will be less than or equal to the thickness of the initially grown film layer 700. Subsequently, a high-quality dielectric thin film 300 can be grown by chemical vapor deposition. As shown in Figure 24 As shown, the dielectric thin film 300 can be a high-quality dielectric thin film with high insulation such as Si3N4, SiO2, AlN, Al2O3, HfO2, etc. If the aforementioned cavity height defining film layer 720 also uses a dielectric thin film, the material of the dielectric thin film 300 can be the same as or different from that of the film layer 720. Then refer to Figures 25 to 28 As shown, the dielectric film layer 300 is etched to form a release channel 301 for releasing the sacrificial layer material 200; the sacrificial layer material 200 is released to form a cavity 201. A material 310 is deposited in the release channel to physically isolate the cavity 201 and the column channel 101 from the outside, make the gap 101 between the cavity 201 and the column and the substrate in a vacuum state, and enable the CMUT to have better acoustic performance. In addition, the presence of the cavity height defining film layer 720 makes the dielectric film layer 300 adjacent to the cavity continuously distributed on the entire horizontal plane, and there is no mutation position perpendicular to the horizontal plane, avoiding defects in the growth of the dielectric film layer 300 in the mutation region, and obtaining better acoustic emission, reception performance and long-term working stability. A deposition electrode layer is included, including a top electrode and pads for connecting the top and bottom electrodes to an external ASIC or PCB circuit. As shown in Figure 28 As shown, the substrate 100 itself or its surface is highly phosphorus or boron-doped silicon, which has high conductivity and serves as the bottom electrode of the CMUT. The bottom electrode pad 520 connects the bottom electrode to an ASIC or PCB circuit. The top electrode and the top electrode connection pad 510 are made of the same metal material, so that it covers the vibration film layer, and at the same time it is interconnected with the top electrode pad to connect the top electrode to an ASIC or PCB circuit.

[0078] Please refer to Figure 17 As shown, in some embodiments, when depositing a conductive layer and an electrically connected pad region on the other side of the dielectric film layer relative to the substrate and the substrate, it further includes:

[0079] S401 When the conductive layer and the electrical connection pad region are made of different materials, deposit and pattern a conductive layer on the other side of the dielectric film layer relative to the substrate and the substrate;

[0080] S402 Construct an electrical connection pad region on the other side of the conductive layer relative to the dielectric film layer and the substrate.

[0081] For details, please refer to Figure 29 As shown, in this embodiment, the top electrode layer and the electrode pad of the capacitive micromachined ultrasonic transducer prepared are not made of the same material. Deposit and pattern a conductive thin film 400, and the material of this layer can be selected from low-resistance silicon, heavily phosphorus- or boron-doped silicon, and metal, which acts as the top electrode and forms a vibrating thin film layer together with the dielectric film layer 300. Construct an electrical connection pad 510 for interconnecting the top electrode with ASIC or PCB on the conductive thin film 400. The electrical connection pad 510 and the electrical connection pad 520 constitute the pads for interconnecting the top and bottom electrodes with the drive and processing circuit.

[0082] In some embodiments, a piston-shaped module is provided on the other side of the conductive layer relative to the dielectric film layer. For details, please refer to Figure 30 As shown, an example of a CMUT structure variant with an ultra-small cavity height and an ultra-thin vibrating thin film containing a plunger module, where the vibrating thin film has a flat structure. Compared with the previous example Figure 29 in this example, the dielectric film layer 300 and the conductive thin film 400 are provided with a piston-shaped module 600, and the piston-shaped module 600 can increase the kinetic energy of the vibrating thin film and improve the acoustic emission and reception sensitivity of the CMUT.

[0083] The manufacturing method of the capacitive micromachined ultrasonic transducer provided by this application can construct CMUT devices with an extremely small cavity height (for example, the cavity height is less than 500 nm, even less than 100 nm); at the same time, the columns with a large aspect ratio have great flexibility and do not affect the vibration amplitude when the CMUT vibrating film layer works. Moreover, use the sacrificial layer process to manufacture a super-large-area CMUT containing support columns. This technology can manufacture CMUTs with cavities of any height and size and vibrating film layers of any thickness. Through the vapor deposition method, the support columns and the vibrating film layer are strongly bonded. And compared with the bonding process, the sacrificial layer process has almost no restrictions on the material of the vibrating film layer; secondly, the capacitive micromachined ultrasonic transducers, devices, and electrical products provided by this application have excellent emitted sound pressure and acoustic sensitivity.

[0084] It should be noted that in this text, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any 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, such that a process, method, article or device comprising a series of elements not only includes those elements but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising a..." does not exclude the presence of additional identical elements in the process, method, article or device comprising the said element. The orientation or positional relationship indicated by terms such as "upper", "lower", etc. is based on the orientation or positional relationship shown in the drawings, and 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 thus should not be construed as a limitation on the present application. Unless otherwise expressly specified and defined, the terms "mount", "connect" and "couple" shall be construed broadly. For example, it may be a fixed connection, a detachable connection or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the internal communication of two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific circumstances.

[0085] Each embodiment in this specification is described in a progressive manner, and the same or similar parts among the embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments. In the description of this specification, the description with reference to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the embodiments of this specification. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0086]

[0087] In this application, specific embodiments are used to elaborate on the principles and implementation manners of the application. The description of the above embodiments is only used to help understand the method and its core idea of the application; at the same time, for those of ordinary skill in the art, according to the idea of the application, there will be changes in the specific implementation manners and application scopes. In summary, the content of this specification should not be construed as a limitation to the application.

Claims

1. A capacitive micromachined ultrasonic transducer, the capacitive micromachined ultrasonic transducer comprising a plurality of ultrasonic transducer units arranged in an array, characterized in that, The ultrasonic transducer unit includes a vibration film layer, a cavity, a column, and a substrate that are sequentially stacked; The vibration film layer is bonded to the substrate through the column, and encloses the cavity with the substrate and the column; Wherein, the column is a support column formed by the substrate with gaps spaced apart, and is used to limit the vibration film layer from sagging into the cavity without natural bending or without processing.

2. The capacitive micromachined ultrasonic transducer according to claim 1, wherein The vibration film layer includes a top electrode; The top electrode is a conductive thin film, and the conductive thin film includes low-resistance silicon, heavily phosphorus-doped silicon, boron-doped silicon, or a metal film layer; The substrate is a bottom electrode, and the bottom electrode includes silicon, low-resistance silicon, highly phosphorus- and boron-doped silicon, highly conductive silicon, SOI, or a conductive metal film layer.

3. The capacitive micromachined ultrasonic transducer according to claim 2, wherein The ultrasonic transducer unit further includes a dielectric thin film, and the dielectric thin film is disposed on the side of the substrate opposite to the vibration film layer; or, the dielectric thin film is disposed on the side of the top electrode opposite to the substrate; wherein, the dielectric thin film includes a Si3N4, SiO2, AlN, Al2O3, or HfO2 film layer.

4. The capacitive micromachined ultrasonic transducer according to claim 2, characterized in that, It further includes electrical connection pads disposed on the top electrode and the bottom electrode, and the capacitive micromachined ultrasonic transducer is interconnected with an external circuit.

5. The capacitive micromachined ultrasonic transducer according to claim 1, wherein The aspect ratio of the support column is not less than 5.

6. The capacitive micromachined ultrasonic transducer according to claim 1, characterized in that, The support column is a square column, a rectangular column, or a cylindrical column.

7. The capacitive micromachined ultrasonic transducer according to claim 1, characterized in that, The vibration film layer includes a rectangular thin film layer, a circular thin film layer, an elliptical thin film layer, a triangular thin film layer, or a polygonal thin film layer.

8. The capacitive micromachined ultrasonic transducer according to claim 1, characterized in that, A piston-like module is disposed on the other side of the vibration film layer relative to the substrate, and is used to increase the kinetic energy of the vibration film layer.

9. The capacitive micromachined ultrasonic transducer according to claim 1, wherein It further includes a cavity height defining film layer, and the cavity height defining film layer is disposed between the vibration film layer and the column, and both sides of the cavity height defining film layer are respectively bonded to the vibration film layer and the column; wherein, the cross-section of the vibration film layer is a straight structure.

10. An electrical product, characterized in that, It includes the capacitive micromachined ultrasonic transducer according to any one of claims 1 to 9.

11. A method for fabricating a capacitive micromachined ultrasonic transducer, characterized in that, The method includes: Forming columns by etching gaps on one side of the substrate, and growing a sacrificial layer on the side of the substrate containing the gaps; Patterning the sacrificial layer to generate a preset sacrificial layer pattern, and sequentially depositing a dielectric film layer and a conductive layer on the sacrificial layer; Etching at the same position of the dielectric film layer and the conductive layer to construct a sacrificial release channel, and using the sacrificial release channel to remove the sacrificial layer by etching to release the cavity formed by enclosing the dielectric film layer, the substrate, and the column; Filling the sacrificial release channel with a deposited material to physically isolate the cavity and the column from the outside.

12. The manufacturing method of the capacitive micromachined ultrasonic transducer according to claim 11, characterized in that, Patterning the sacrificial layer to generate a preset sacrificial layer pattern further includes: Chemically mechanically polishing the sacrificial layer outside the gaps, and growing a sacrificial layer with a preset thickness on the gap side of the substrate by a deposition method; Patterning the sacrificial layer to generate a preset sacrificial layer pattern.

13. The manufacturing method of the capacitive micromachined ultrasonic transducer according to claim 11, characterized in that, Using the sacrificial release channel to remove the sacrificial layer by etching to release the cavity and the column includes: using the sacrificial release channel to remove the sacrificial layer by wet etching or dry etching to release the cavity and the column.

14. The method for manufacturing a capacitive micromachined ultrasonic transducer according to claim 11, wherein Removing the sacrificial layer through etching to release the cavity and the pillar by using the sacrificial release channel further includes: forming an electrical connection pad region by etching the dielectric film layer and the conductive layer to release the bottom electrode.

15. A preparation method of a capacitive micromachined ultrasonic transducer, characterized in that, The method includes: Generating a cavity height defining film layer on one side of the substrate, patterning the cavity height defining film layer to form a preset cavity height defining film layer pattern, and forming pillars by etching voids on one side of the substrate; Growing a sacrificial layer on the side of the substrate with voids and on the other side of the height defining film layer relative to the substrate, and growing a dielectric film layer on the other side of the sacrificial layer relative to the substrate by chemical vapor deposition; Etching the dielectric film layer to construct a sacrificial release channel, and removing the sacrificial layer through etching by using the sacrificial release channel to release the cavity surrounded by the dielectric film layer, the substrate, and the pillars; Filling the sacrificial release channel with a deposited material to physically isolate the cavity and the pillar from the outside, and depositing and generating a conductive layer and an electrical connection pad region on the other side of the dielectric film layer relative to the substrate and on the substrate; 16. The method for manufacturing a capacitive micromachined ultrasonic transducer according to claim 15, characterized in that, Before growing the dielectric film layer on the other side of the sacrificial layer relative to the substrate by chemical vapor deposition, it further includes: chemically mechanically polishing a sacrificial layer with a preset thickness.

17. The preparation method of the capacitive micromachined ultrasonic transducer according to claim 15, characterized in that, Depositing and generating a conductive layer and an electrical connection pad region on the other side of the dielectric film layer relative to the substrate and on the substrate further includes: When the conductive layer and the electrical connection pad region are made of different materials, depositing and patterning a conductive layer on the other side of the dielectric film layer relative to the substrate and on the substrate; Constructing an electrical connection pad region on the other side of the conductive layer relative to the dielectric film layer and on the substrate.

18. The method for fabricating a capacitive micromachined ultrasonic transducer according to claim 17, wherein, Providing a piston-shaped module on the other side of the conductive layer relative to the dielectric film layer.

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