Light-transmitting micro-electromechanical ultrasonic transducer and method of manufacturing the same

Abstract

The application discloses a light-transmitting micro-electro-mechanical ultrasonic transducer and a preparation method thereof, and relates to the field of ultrasonic transducers. The method mainly comprises the following steps: depositing a common bottom electrode on a light-transmitting substrate; spin-coating a photosensitive polymer on the common bottom electrode and exposing and developing the same to form a photosensitive polymer light-transmitting substrate wafer with a cavity structure and a support structure; using a bonding machine and a wafer adhesion layer bonding technology, bonding and solidifying the photosensitive polymer light-transmitting substrate wafer and a silicon wafer with low-stress silicon nitride films deposited on both sides to obtain a bonded and solidified wafer; using a dry and wet etching method to remove the low-stress silicon nitride films on the outer surface of the bonded and solidified wafer and the silicon wafer, and retaining the low-stress silicon nitride films inside the bonded and solidified wafer; and depositing a common top electrode and a metal layer on the retained films, so that the obtained metal wires penetrate through the common top electrode. The application has the advantages of light-transmitting and not blocking the light path, and has a relatively large relative bandwidth.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of ultrasonic transducers, in particular to a light-transmitting ultrasonic transducer based on micro-electro-mechanical system (MEMS) technology and a preparation method thereof. BACKGROUND

[0002] An ultrasonic transducer is a device for converting ultrasonic waves and electrical signals. Ultrasonic transducers are widely used in industrial non-destructive testing, biomedical ultrasonic imaging, photoacoustic imaging, distance detection, underwater imaging, human-computer interaction, etc. The working frequency, bandwidth, energy conversion efficiency and noise of the ultrasonic transducer directly affect the optical resolution and the detection sensitivity of the photoacoustic microscopic imaging system. Currently, piezoelectric ultrasonic transducers based on piezoelectric materials are commonly used, which have a low bandwidth. The thickness of the piezoelectric material used as an ultrasonic transducer is half a wavelength. Taking a 50MHz piezoelectric ultrasonic transducer as an example, the thickness of the piezoelectric material is about 40μm. Such a thin thickness not only increases the energy conversion loss and the low electromechanical coupling coefficient, but also makes the structure fragile and difficult to cut into an ultrasonic transducer array.

[0003] With the development of micro-electro-mechanical system (MEMS) technology, capacitive micromachined ultrasonic transducers (CMUT) and piezoelectric micromachined ultrasonic transducers (PMUT) have emerged. However, PMUT has a low bandwidth and low energy conversion efficiency. CMUT has a wide working frequency range, high energy conversion efficiency, low thermal noise, and is easy to expand and design flexibly using photolithography technology, so it has a wide application prospect. Traditional CMUT is prepared on a silicon wafer, the support wall is silicon nitride or silicon dioxide, and doped silicon substrate or aluminum and gold are used as bottom electrodes, and aluminum or gold is used as top electrodes. The above-mentioned materials are not all light-transmitting, so the traditional CMUT does not have the light-transmitting function.

[0004] In the application scenarios of ultrasonic, such as photoacoustic microscopic imaging, human-computer interaction and underwater imaging, the light path will be blocked by the ultrasonic transducer, and special light paths need to be designed to bypass the ultrasonic transducer, which not only increases the complexity of the device structure, but also reduces the key technical indicators of the device. SUMMARY

[0005] The purpose of the present application is to provide a light-transmitting micro-electro-mechanical system (MEMS) ultrasonic transducer and a preparation method thereof. Compared with the existing ultrasonic transducers, the light-transmitting micro-electro-mechanical system (MEMS) ultrasonic transducer has the advantages of being light-transmitting and not blocking the light path, and can realize high-frequency devices (more than 30MHz) and also has a large relative bandwidth (6-dB relative bandwidth more than 80%).

[0006] To achieve the above-mentioned purpose, the present application provides the following solutions:

[0007] In a first aspect, the present application provides a light-transmitting micro-electro-mechanical ultrasonic transducer, comprising a plurality of light-transmitting CMUT array elements arranged in an array; the light-transmitting CMUT array element comprises a common top electrode, a light-transmitting substrate, a common bottom electrode arranged on the light-transmitting substrate, and a plurality of light-transmitting CMUT units arranged between the common top electrode and the common bottom electrode, and the light-transmitting CMUT units in the light-transmitting CMUT array element are electrically connected in parallel through the common top electrode and the common bottom electrode; the light-transmitting CMUT unit comprises a plurality of light-transmitting cavities of different sizes and shapes; wherein the light-transmitting CMUT array element is prepared based on a micro-electro-mechanical process.

[0008] The light-transmitting cavity comprises a cavity structure arranged on the common bottom electrode, a support structure arranged on the common bottom electrode and surrounding the cavity structure, and a vibrating diaphragm arranged on the cavity structure and capable of covering the cavity structure and the support structure.

[0009] Wherein, the common bottom electrode, the cavity structure, the support structure, the vibrating diaphragm and the common top electrode are all prepared from light-transmitting materials.

[0010] Optionally, the shape of the light-transmitting cavity is circular, rectangular or polygonal.

[0011] Optionally, the light-transmitting CMUT array element further comprises a metal wire led out from the common top electrode, a common top electrode pad connected to the metal wire, and a common bottom electrode pad connected to the common bottom electrode; wherein the metal wire penetrates through the common top electrode.

[0012] Optionally, the light-transmitting substrate is a glass wafer, the common bottom electrode is an indium tin oxide bottom electrode, the support structure is a support structure formed by a photosensitive polymer, the cavity structure is a vacuum-sealed cavity structure, the vibrating diaphragm is a low-stress silicon nitride diaphragm, and the common top electrode is an indium tin oxide top electrode.

[0013] Optionally, the light-transmitting substrate is a glass wafer with a thickness of 400 μm to 1 mm; the common bottom electrode is an indium tin oxide film with a thickness of 180 nm to 400 nm; and the common top electrode is an indium tin oxide film with a thickness of 180 nm to 400 nm.

[0014] In a second aspect, the present application provides a preparation method of the light-transmitting micro-electro-mechanical ultrasonic transducer of the first aspect, comprising:

[0015] Preparation of the light-transmitting CMUT array element by a micro-electro-mechanical process to obtain the light-transmitting micro-electro-mechanical ultrasonic transducer;

[0016] The light-transmitting CMUT array element is prepared by using a micro-electro-mechanical process, and specifically comprises the following steps:

[0017] A common bottom electrode is deposited on the light-transmitting substrate by using a magnetron sputtering method or an electron beam evaporation method.

[0018] A photosensitive polymer is spin-coated on the common bottom electrode, and the photosensitive polymer is exposed and developed through a mask plate to form a photosensitive polymer light-transmitting substrate wafer with a cavity structure and a support structure.

[0019] The photosensitive polymer light-transmitting substrate wafer is bonded and solidified with a silicon wafer having a low-stress silicon nitride film deposited on both the front and back surfaces by using a wafer adhesion layer bonding technology by using a bonder to obtain a bonded and solidified wafer.

[0020] The low-stress silicon nitride film and the silicon wafer located on the outer surface of the bonded and solidified wafer are removed by using a dry etching method and a wet etching method, and the low-stress silicon nitride film located in the interior of the bonded and solidified wafer is reserved; wherein the low-stress silicon nitride film located in the interior of the bonded and solidified wafer is a vibrating diaphragm.

[0021] A common top electrode is deposited on the vibrating diaphragm by using a magnetron sputtering method or an electron beam evaporation method.

[0022] A metal layer is deposited by using a magnetron sputtering method or an electron beam evaporation method, and a metal wire, a common top electrode pad and a common bottom electrode pad are formed by a stripping process; wherein the metal wire penetrates through the common top electrode, and the metal wire is connected with the common top electrode pad.

[0023] Optionally, a photosensitive polymer is spin-coated on the common bottom electrode, and the photosensitive polymer is exposed and developed through a first mask plate to form a photosensitive polymer light-transmitting substrate wafer with a cavity structure and a support structure, and specifically comprises the following steps:

[0024] The photosensitive polymer is exposed and developed by using a UV photolithography machine and a first mask plate after the photosensitive polymer is spin-coated on the common bottom electrode, a cavity structure is formed, and the remaining photosensitive polymer serves as a support structure of the cavity structure to obtain a photosensitive polymer light-transmitting substrate wafer with a cavity structure and a support structure.

[0025] Optionally, the photosensitive polymer light-transmitting substrate wafer is bonded and solidified with a silicon wafer having a low-stress silicon nitride film deposited on both the front and back surfaces by using a wafer adhesion layer bonding technology by using a bonder to obtain a bonded and solidified wafer, and specifically comprises the following steps:

[0026] A low-stress silicon nitride film is deposited on the front and back surfaces of a piece of silicon wafer by using a low-pressure chemical vapor deposition method.

[0027] Using a bonding machine, the one side of the photosensitive polymer spin-coated in the photosensitive polymer light-transmitting substrate wafer is bonded to the low-stress silicon nitride film on the front side of the silicon wafer to obtain a bonded and cured wafer by using the wafer adhesion layer bonding technology.

[0028] Optionally, the low-stress silicon nitride film and the silicon wafer located on the outer surface of the bonded and cured wafer are removed by using a dry etching method and a wet etching method, and the low-stress silicon nitride film located in the interior of the bonded and cured wafer is reserved, and the method specifically comprises the following steps.

[0029] The low-stress silicon nitride film located on the outer surface of the bonded and cured wafer is removed by using a reactive ion etching method or an inductively coupled plasma etching method.

[0030] The thickness of the silicon wafer in the bonded and cured wafer is thinned by using a reactive ion etching method or an inductively coupled plasma etching method, the remaining silicon wafer in the bonded and cured wafer is removed by using a wet etching method, and the low-stress silicon nitride film located in the interior of the bonded and cured wafer is reserved.

[0031] Optionally, the remaining silicon wafer in the bonded and cured wafer is removed by using a wet etching method, and the method specifically comprises the following steps.

[0032] Before being immersed in the potassium hydroxide solution, the target bonded and cured wafer is surrounded and protected by using a circular ring-shaped Teflon clamp, and then is entirely immersed in the potassium hydroxide solution, and after the remaining silicon wafer is entirely etched, the target bonded and cured wafer is taken out, cleaned and dried; the target bonded and cured wafer is the bonded and cured wafer from which the low-stress silicon nitride film on the outer surface is removed.

[0033] Alternatively, after a layer of polydimethylsiloxane film is deposited on the four sides and the bottom surface of the target bonded and cured wafer, the target bonded and cured wafer is entirely immersed in the potassium hydroxide solution, and after the remaining silicon wafer is entirely etched, the target bonded and cured wafer is taken out, cleaned, dried and the polydimethylsiloxane film is peeled off; the bottom surface of the target bonded and cured wafer is the light-transmitting substrate.

[0034] According to the specific embodiments of the present application, the following technical effects are provided.

[0035] Compared with the existing ultrasonic transducer technology, the ultrasonic transducer prepared from the light-transmitting material does not block the light path in the ultrasonic detection application. The device is prepared based on the micro-electromechanical technology, and is flexible and convenient to design, and can realize the ultrasonic transducer with high frequency (the center frequency is greater than 30 MHz), high bandwidth (the 6-dB relative bandwidth is greater than 80%) and large size. BRIEF DESCRIPTION OF DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed in the embodiments. Obviously, the drawings described below only illustrate some of the embodiments of the present application, and for those skilled in the art, other drawings can be obtained from these drawings without creative labor.

[0037] Figure 1 A structural schematic diagram of a light-transmitting micro-electro-mechanical ultrasonic transducer provided by an embodiment of the present application is shown in FIG. 1.

[0038] Figure 2 A structural schematic diagram of a light-transmitting cavity provided by an embodiment of the present application is shown in FIG. 2.

[0039] Figure 3 A structural schematic diagram of a circular light-transmitting CMUT cell provided by an embodiment of the present application is shown in FIG. 3.

[0040] Figure 4 A structural schematic diagram of a rectangular light-transmitting CMUT cell provided by an embodiment of the present application is shown in FIG. 4.

[0041] Figure 5 A structural schematic diagram of a polygonal light-transmitting CMUT cell provided by an embodiment of the present application is shown in FIG. 5.

[0042] Figure 6 A flowchart of a preparation method of a light-transmitting micro-electro-mechanical ultrasonic transducer provided by an embodiment of the present application is shown in FIG. 6.

[0043] Figure 7 A flowchart of a preparation method of a light-transmitting micro-electro-mechanical ultrasonic transducer provided by an embodiment of the present application is shown in FIG. 7.

[0044] Figure 8 A flowchart of a preparation method of a light-transmitting micro-electro-mechanical ultrasonic transducer provided by an embodiment of the present application is shown in FIG. 8.

[0045] Figure 9 A flowchart of a preparation method of a light-transmitting micro-electro-mechanical ultrasonic transducer provided by an embodiment of the present application is shown in FIG. 9.

[0046] Figure 10 A relationship diagram of a light-transmitting CMUT cell and electrode wiring and electrode pads provided by an embodiment of the present application is shown in FIG. 10. DETAILED DESCRIPTION

[0047] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments only represent some of the embodiments of the present application, and all other embodiments obtained by those skilled in the art without creative labor based on the embodiments in the present application also belong to the scope of protection of the present application.

[0048] In order to make the above objectives, characteristics and advantages of the present application more obvious and comprehensible, the present application will be further described in detail below with reference to the drawings and specific embodiments.

[0049] Embodiment One

[0050] As shown in Figure 1 and Figure 2 The light-transmitting micro-electro-mechanical ultrasonic transducer provided by the present embodiment comprises a plurality of light-transmitting CMUT array elements arranged in an array form in sequence; the light-transmitting CMUT array element comprises a common top electrode 6, a light-transmitting substrate 1, a common bottom electrode 2 arranged on the light-transmitting substrate 1, and a plurality of light-transmitting CMUT units arranged between the common top electrode 6 and the common bottom electrode 2, and the light-transmitting CMUT units in the light-transmitting CMUT array element are electrically connected in parallel through the common top electrode 6 and the common bottom electrode 2; the light-transmitting CMUT unit comprises a plurality of light-transmitting cavities with different sizes and shapes. The light-transmitting CMUT array element is prepared based on a micro-electro-mechanical process.

[0051] The light-transmitting cavity comprises a cavity structure 4 arranged on the common bottom electrode 2, a support structure 3 arranged on the common bottom electrode 2 and located around the cavity structure 4, and a vibrating diaphragm 5 arranged on the cavity structure 4 and capable of covering the cavity structure 4 and the support structure 3.

[0052] The light-transmitting substrate 1, the common bottom electrode 2, the cavity structure 4, the support structure 3, the vibrating diaphragm 5, and the common top electrode 6 are all prepared from light-transmitting materials.

[0053] Further, the light-transmitting CMUT array element further comprises a metal wire led out from the common top electrode 6, a common top electrode pad connected with the metal wire, and a common bottom electrode pad connected with the common bottom electrode 2; wherein the metal wire penetrates through the common top electrode.

[0054] Preferably, the light-transmitting substrate 1 is a glass wafer, the common bottom electrode 2 is an indium tin oxide (ITO) bottom electrode, the support structure 3 is a support structure formed by a photosensitive polymer, the cavity structure 4 is a vacuum-sealed cavity structure, the vibrating diaphragm 5 is a low-stress silicon nitride film, and the common top electrode 6 is an indium tin oxide top electrode.

[0055] Further, the light-transmitting substrate 1 is a glass wafer with a thickness of 400 μm to 1 mm; the common bottom electrode 2 is an indium tin oxide film with a thickness of 180 nm to 400 nm; and the common top electrode 6 is an indium tin oxide film with a thickness of 180 nm to 400 nm.

[0056] Further, the shape of the light-transmitting cavity is circular, rectangular, or polygonal.

[0057] Figure 3 Fig. 2 is a schematic diagram of a structure of a circular light-transmitting CMUT cell, as shown in Fig. 2, the circular light-transmitting CMUT cell is composed of four circular light-transmitting cavities with different radii, the large-size circular light-transmitting cavities are on the left side, and the other three circular light-transmitting cavities with different sizes are on the right side. Because the working frequency of the CMUT is related to the size of the vibrating diaphragm, the working frequency of the large-radius circular light-transmitting cavity is low, and the working frequency of the small-radius circular light-transmitting cavity is high, so the combined circular light-transmitting CMUT cell contains four different working frequencies, and a circular light-transmitting CMUT cell with a larger bandwidth can be obtained by selecting a suitable radius range. Figure 3

[0058] Fig. 3 is a schematic diagram of a structure of a rectangular light-transmitting CMUT cell, as shown in Fig. 3, the rectangular light-transmitting CMUT cell is composed of four rectangular light-transmitting cavities with different sizes, the large-size rectangular light-transmitting cavities are on the left side, and the other three rectangular light-transmitting cavities with different sizes are on the right side. A rectangular light-transmitting CMUT cell with a larger bandwidth can be obtained by selecting a suitable rectangular side length. Figure 4 Figure 4 Fig. 4 is a schematic diagram of a structure of a polygonal light-transmitting CMUT cell, as shown in Fig. 4, the polygonal light-transmitting CMUT cell is composed of four polygonal light-transmitting cavities with different sizes, the large-size polygonal light-transmitting cavities are on the left side, and the other three polygonal light-transmitting cavities with different sizes are on the right side. A polygonal light-transmitting CMUT cell with a larger bandwidth can be obtained by selecting a suitable polygonal side length.

[0059] Figure 5 It should be noted that, Figure 5 and

[0060] are only schematic diagrams of CMUT cells containing multiple cavities, the number, shape and position of each shape are not limited to the diagrams, and the light-transmitting CMUT array element can contain one or more light-transmitting CMUT cells with different shapes. Figure 3 Figure 4 Figure 5

[0061] Example Two

[0062] The embodiment provides a method for preparing the light-transmitting micro-electromechanical ultrasonic transducer.

[0063] The light-transmitting CMUT array element is prepared by using a micro-electromechanical process to obtain the light-transmitting micro-electromechanical ultrasonic transducer.

[0064] The light-transmitting CMUT array element is prepared by using a micro-electromechanical process, and specifically includes the following steps.

[0065] ​​​​S1: Depositing a common bottom electrode on a light-transmitting substrate using a magnetron sputtering method or an E-beam evaporation method.

[0066] S2: Spinning a photosensitive polymer on the common bottom electrode, exposing and developing the photosensitive polymer through a mask plate to form a photosensitive polymer light-transmitting substrate wafer with a cavity structure and a support structure.

[0067] S3: Bonding and curing the photosensitive polymer light-transmitting substrate wafer and a silicon wafer with low-stress silicon nitride films deposited on both sides using wafer adhesion layer bonding technology using a bonder to obtain a bonded and cured wafer.

[0068] S4: Removing the low-stress silicon nitride films and the silicon wafer on the outer surface of the bonded and cured wafer using a dry etching method and a wet etching method, and retaining the low-stress silicon nitride films inside the bonded and cured wafer; wherein the low-stress silicon nitride films inside the bonded and cured wafer are vibrating membranes.

[0069] S5: Depositing a common top electrode on the vibrating membranes using a magnetron sputtering method or an E-beam evaporation method.

[0070] S6: Depositing a metal layer using a magnetron sputtering method or an E-beam evaporation method to form metal wires, a common top electrode pad, and a common bottom electrode pad through a stripping process; wherein the metal wires pass through the common top electrode, and the metal wires are connected to the common top electrode pad.

[0071] In this embodiment, the preparation process of the light-transmitting CMUT element is as follows:

[0072] 1. Selecting a 4-inch glass wafer as a light-transmitting substrate 1, and the glass wafer can be BF33 or quartz glass, as shown in step (1) of Figure 6 The thickness of the glass wafer is between 400 μm and 1 mm.

[0073] 2. Depositing an indium tin oxide film as a common bottom electrode 2 on the upper surface of the glass wafer using a magnetron sputtering method or an E-beam evaporation method, and the thickness of the common bottom electrode 2 is between 180 nm and 400 nm. In order to reduce the sheet resistance of the indium tin oxide film and improve its light transmission rate, an annealing process is added after depositing the indium tin oxide film to reduce the sheet resistance to within 10 Ω / □, as shown in step (2) of Figure 6

[0074] 3. Spinning a photosensitive polymer on the common bottom electrode 2, and the thickness is between 200 nm and 600 nm, as shown in step (3) of Figure 6 ​Step (3) in FIG. 1. The photoresist is generally SU-8 photoresist or photo- sensitive benzocyclobutene (BCB), in particular, when SU-8 photoresist is SU-8 2000.5 or GM1020, and BCB is Cyclotene 4022-25, the photoresist layer can be spin-coated to a thickness of less than 500 nm.

[0075] 4. After the photoresist layer is exposed and developed using the first mask to define the CMUT cell, a cavity structure 4 is formed, and the remaining photoresist layer serves as a support structure 3 of the cavity structure 4, as shown in step (4a) in FIG. 1. Figure 6

[0076] 5. Low-pressure chemical vapor deposition (LPCVD) is used to deposit low-stress silicon nitride films 81 and 82 on the front and back surfaces of a 4-inch silicon wafer 7. The thickness of the silicon wafer 7 is between 200 μm and 525 μm, and the thickness of the low-stress silicon nitride film is between 400 nm and 600 nm, as shown in step (4b) in FIG. 1. Figure 6

[0077] 6. The wafer bonding technology using wafer adhesion layer is used to bond the side of the photoresist glass wafer spin-coated with the photoresist to the side of the low-stress silicon nitride film 81 of the silicon wafer 7, to achieve wafer bonding and curing, and obtain a bonded and cured wafer. Because the bonding pressure is very low, close to vacuum, the cavity structure 4 in the bonded and cured wafer is in a vacuum-tight state, as shown in step (5) in FIG. 1. Figure 7

[0078] 7. Dry etching technology such as reactive ion etching (RIE) or inductively coupled plasma etching (ICP) is used to remove the low-stress silicon nitride film 82 on the back surface of the bonded and cured wafer, as shown in step (6) in FIG. 1. Figure 7

[0079] 8. Dry etching technology such as reactive ion etching (RIE) or inductively coupled plasma etching (ICP) is used to thin the silicon wafer 7 to a thickness of about 100 μm. The residual silicon wafer 7 is removed using potassium hydroxide (KOH) wet etching technology. To protect the bonded photoresist from the potassium hydroxide solution, a circular-shaped Teflon clamp is used to surround and protect the bonded wafer before it is immersed in the potassium hydroxide solution. After the residual silicon wafer is completely etched, the bonded wafer is taken out, washed, and dried, as shown in step (7-1) in FIG. 1. Figure 7 Figure 7 ​​​​​71 is the thinned silicon wafer, and 91 is a Teflon fixture. If the Teflon fixture 91 is not used, a layer of polydimethylsiloxane (PDMS) film can be deposited around the bonded wafer and on the bottom of the glass wafer, and then the entire structure can be immersed in a potassium hydroxide solution until the residual silicon wafer is completely etched. After the residual silicon wafer is completely etched, the structure can be removed, cleaned, dried, and the PDMS film can be peeled off. Figure 8 Step (7-2) shown in FIG. 7B. Figure 7 71 is the thinned silicon wafer, and 92 is a PDMS film.

[0080] 9. After the silicon wafer 7 is completely removed, only the bonded wafer with the low-stress silicon nitride film 81 remains. The low-stress silicon nitride film 81 is the vibrating membrane 5, as shown in step (8) of FIG. 8. Figure 9 Step (8) shown in FIG. 8.

[0081] 10. An indium tin oxide film is deposited on the vibrating membrane 5 as a common top electrode 6 using a magnetron sputtering method or an electron beam evaporation method, and the thickness of the indium tin oxide film is between 180 nm and 400 nm. In order to reduce the sheet resistance of the indium tin oxide film and improve the light transmittance, an annealing process is added after the deposition of the indium tin oxide film, so that the sheet resistance of the indium tin oxide film is reduced to within 10 Ω / D, as shown in step (9) of FIG. 9. Figure 9 Step (9) shown in FIG. 9.

[0082] 11. Positive photoresist is spin-coated on the common top electrode 6, a second mask plate is used to define the shape of the common top electrode 6, and after exposure and development are performed using a photoetching machine, the indium tin oxide film outside the array element is etched using hydrochloric acid (HCL), as shown in step (10) of FIG. 10. Figure 9 Step (10) shown in FIG. 10.

[0083] 12. Positive photoresist is spin-coated, a third mask plate is used to define the common bottom electrode pad area, and after exposure and development are performed using a photoetching machine, the low-stress silicon nitride film and the photosensitive polymer outside the array element are sequentially etched using a reactive ion etching method, so that the common bottom electrode 2 is exposed, as shown in step (11) of FIG. 11. Figure 9 Step (11) shown in FIG. 11.

[0084] 13. Inverted photoresist is spin-coated, a fourth mask plate is used to define the top electrode metal wire, the common top electrode pad, and the common bottom electrode pad, and a composite metal layer composed of 20 nm of chromium and 180 nm of gold is sequentially deposited using an electron beam evaporation method. The metal wire 10 connected to the common top electrode 6 and the common bottom electrode pad 11 connected to the common bottom electrode 2 are prepared by a lift-off process, as shown in step (12) of FIG. 12. Figure 9 Step (12) shown in FIG. 12.

[0085] 14. The relationship between CMUT cell and electrode trace and electrode pad is shown in Fig. 13. Figure 10 Figure 10 CMUT cell 13, metal trace 10 from common top electrode 6, common bottom electrode pad 11 connecting common bottom electrode 2, and common top electrode pad 12.

[0086] Compared with the prior art, the present application has the following advantages:

[0087] 1. The light-transmitting substrate, common bottom electrode, cavity structure, support structure, vibrating membrane and common top electrode in the CMUT cell are all made of light-transmitting materials, so that the CMUT cell composed of CMUT units is light-transmitting, and the ultrasonic transducer composed of CMUT cells is also light-transmitting.

[0088] 2. One CMUT cell is composed of multiple CMUT units, and one CMUT unit is composed of multiple light-transmitting cavities of different sizes and shapes, so that the CMUT unit has high bandwidth.

[0089] 3. The cavity structure and support structure are formed by exposing and developing a photosensitive polymer to ultraviolet light, without using additional photoresist and dry etching process, thereby reducing the complexity of the preparation process.

[0090] 4. The glass wafer and silicon wafer are bonded and cured by wafer adhesion layer bonding technology to realize vacuum sealing of the CMUT cavity and improve reliability.

[0091] 5. The removal of the silicon wafer is divided into two steps: first, the thickness of the silicon wafer is thinned to about 100 μm using dry etching technology, and then the residual silicon wafer is completely etched away using potassium hydroxide (KOH) wet etching technology, and low-stress silicon nitride film is used as a barrier layer for potassium hydroxide wet etching.

[0092] 6. When etching the residual silicon wafer using potassium hydroxide (KOH), a circular Teflon clamp is used to surround and protect the bonded wafer. Alternatively, a layer of polydimethylsiloxane (PDMS) film is deposited on the side of the bonded wafer and the bottom of the glass wafer for protection.

[0093] 7. In order to reduce the resistance of the common top electrode, a metal trace is used to penetrate the common top electrode, and the metal trace connects the metal pad of the common top electrode. ​

[0094] The various embodiments described in this specification are presented for the purpose of illustrating the principles of the present application and its best mode of operation. Each of the embodiments described in this specification has been provided for the purpose of illustration and is not intended to limit the application.

[0095] The principles and operation of the present application have been explained so far with the help of specific examples. The examples have been provided only for the purpose of understanding the method of the present application and its core idea. However, the specific embodiments described above should not be construed as limiting the scope of the present application.

Claims

1. A light-transmitting microelectromechanical ultrasonic transducer, characterized by The light-transmitting CMUT array element comprises a plurality of light-transmitting CMUT elements arranged in an array; the light-transmitting CMUT element comprises a common top electrode, a light-transmitting substrate, a common bottom electrode arranged on the light-transmitting substrate, and a plurality of light-transmitting CMUT units arranged between the common top electrode and the common bottom electrode, and the light-transmitting CMUT units in the light-transmitting CMUT element are electrically connected in parallel through the common top electrode and the common bottom electrode; the light-transmitting CMUT unit comprises a plurality of light-transmitting cavities with different sizes and shapes; the light-transmitting cavities are circular, rectangular or polygonal in shape; wherein the light-transmitting CMUT array element is prepared based on a micro-electro-mechanical process; The light-transmitting CMUT array element further comprises a metal wire led out from the common top electrode, a common top electrode pad connected with the metal wire, and a common bottom electrode pad connected with the common bottom electrode; wherein the metal wire penetrates through the common top electrode; The light-transmitting cavities comprise a cavity structure arranged on the common bottom electrode, a support structure arranged on the common bottom electrode and located around the cavity structure, and a vibrating thin film arranged on the cavity structure and capable of covering the cavity structure and the support structure; Wherein, the common bottom electrode, the cavity structure, the support structure, the vibrating thin film and the common top electrode are all prepared from light-transmitting materials.

2. A light-transparent microelectromechanical ultrasonic transducer according to claim 1, characterized in that, The light-transmitting substrate is a glass wafer, the common bottom electrode is an indium tin oxide bottom electrode, the support structure is a support structure formed by a light-sensitive polymer, the cavity structure is a vacuum-sealed cavity structure, the vibrating thin film is a low-stress silicon nitride thin film, and the common top electrode is an indium tin oxide top electrode.

3. A light-transparent microelectromechanical ultrasonic transducer according to claim 2, characterized in that, The light-transmitting substrate is a glass wafer with a thickness of 400 μm to 1 mm; the common bottom electrode is an indium tin oxide thin film with a thickness of 180 nm to 400 nm; and the common top electrode is an indium tin oxide thin film with a thickness of 180 nm to 400 nm.

4. A method of manufacturing the light-transparent microelectromechanical ultrasonic transducer according to any one of claims 1 to 3, characterized in that, The light-transmitting CMUT array element is prepared by a micro-electro-mechanical process to obtain a light-transmitting micro-electro-mechanical ultrasonic transducer; The light-transmitting CMUT array element is prepared by a micro-electro-mechanical process, specifically including: A common bottom electrode is deposited on the light-transmitting substrate by a magnetron sputtering method or an electron beam evaporation method; A light-sensitive polymer is spin-coated on the common bottom electrode, the light-sensitive polymer is exposed and developed through a mask plate to form a light-sensitive polymer light-transmitting substrate wafer with a cavity structure and a support structure; A bonding machine is used to bond and solidify the light-sensitive polymer light-transmitting substrate wafer and a silicon wafer with low-stress silicon nitride thin films deposited on both sides by wafer adhesion layer bonding technology to obtain a bonded and solidified wafer; A dry etching method and a wet etching method are used to remove the low-stress silicon nitride thin film and the silicon wafer on the outer surface of the bonded and solidified wafer, and to retain the low-stress silicon nitride thin film inside the bonded and solidified wafer; wherein the low-stress silicon nitride thin film inside the bonded and solidified wafer is a vibrating thin film; A common top electrode is deposited on the vibrating thin film by a magnetron sputtering method or an electron beam evaporation method; ​ The metal layer is deposited by using a magnetron sputtering method or an electron beam evaporation method, and the metal wires, the common top electrode pad and the common bottom electrode pad are formed by a stripping process; wherein the metal wires penetrate the common top electrode, and the metal wires are connected with the common top electrode pad.

5. A method of fabricating a light-transparent microelectromechanical ultrasonic transducer according to claim 4, wherein, The photosensitive polymer is spin-coated on the common bottom electrode, the photosensitive polymer is exposed and developed by using a first mask plate to form a photosensitive polymer light-transmitting base wafer with a cavity structure and a support structure, specifically including: The photosensitive polymer is spin-coated on the common bottom electrode, and after the photosensitive polymer is exposed and developed by using a UV photolithography machine and a first mask plate, the cavity structure is formed, and the remaining photosensitive polymer serves as the support structure of the cavity structure, thereby obtaining the photosensitive polymer light-transmitting base wafer with the cavity structure and the support structure.

6. A method of fabricating a light-transparent microelectromechanical ultrasonic transducer according to claim 4, wherein, The photosensitive polymer light-transmitting base wafer is bonded and solidified with the silicon wafer on which the low-stress silicon nitride film is deposited on both sides by using a wafer adhesion layer bonding technology of a bonder, thereby obtaining a bonded and solidified wafer, specifically including: The low-stress silicon nitride film is deposited on the front side and the back side of a silicon wafer by using a low-pressure chemical vapor deposition method; The photosensitive polymer light-transmitting base wafer is bonded and solidified with the low-stress silicon nitride film on the front side of the silicon wafer by using a wafer adhesion layer bonding technology of a bonder, thereby obtaining a bonded and solidified wafer.

7. A method of fabricating a light-transparent microelectromechanical ultrasonic transducer according to claim 6, wherein, The low-stress silicon nitride film and the silicon wafer located on the outer surface of the bonded and solidified wafer are removed by using a dry etching method and a wet etching method, and the low-stress silicon nitride film located in the interior of the bonded and solidified wafer is retained, specifically including: The low-stress silicon nitride film located on the outer surface of the bonded and solidified wafer is removed by using a reactive ion etching method or an inductively coupled plasma etching method; The thickness of the silicon wafer in the bonded and solidified wafer is thinned by using a reactive ion etching method or an inductively coupled plasma etching method, the remaining silicon wafer in the bonded and solidified wafer is removed by using a wet etching method, and the low-stress silicon nitride film located in the interior of the bonded and solidified wafer is retained.

8. A method of fabricating a light-transparent microelectromechanical ultrasonic transducer according to claim 7, wherein, The remaining silicon wafer in the bonded and solidified wafer is removed by using a wet etching method, specifically including: Before being immersed in the potassium hydroxide solution, the target bonded and solidified wafer is surrounded and protected by using a circular ring-shaped Teflon clamp, and then is entirely immersed in the potassium hydroxide solution, until the remaining silicon wafer is completely etched, and then is taken out for cleaning and drying; the target bonded and solidified wafer is the bonded and solidified wafer from which the low-stress silicon nitride film on the outer surface is removed; Or, a layer of polydimethylsiloxane film is deposited on the four sides and the bottom surface of the target bonded and solidified wafer, and then the target bonded and solidified wafer is entirely immersed in the potassium hydroxide solution, until the remaining silicon wafer is completely etched, and then is taken out for cleaning, drying and peeling off the polydimethylsiloxane film; the bottom surface of the target bonded and solidified wafer is the light-transmitting base.

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