A MEMS ultrasonic transducer and its manufacturing method and ultrasonic transducer array

Abstract

The present invention belongs to the field of MEMS ultrasonic transducers and three-dimensional micro-nano manufacturing technology, and specifically relates to a MEMS ultrasonic transducer, a preparation method thereof, and an ultrasonic transducer array. The conformal electrode in the present invention can significantly enhance the electric field strength outside the central area of ​​the chamber, thereby significantly improving the sensitivity and reducing the driving voltage; the TGV glass substrate can significantly reduce parasitic capacitance and improve sensitivity. Furthermore, the material of the conformal electrode and the resonant plate or resonant membrane of the present invention can be metal or alloy, which can significantly improve the mechanical life and reliability of the device compared with traditional materials such as single crystal silicon or silicon nitride. The present invention also provides a preparation method for the MEMS ultrasonic transducer. The preparation method provided by the present invention can achieve high-precision 3D processing of conformal electrodes with good consistency and low cost, and is suitable for large-scale array wafer-level manufacturing. It is also compatible with ASIC technology and is easy to achieve 3D integration with ASIC.

Description

Technical Field

[0001] The present invention belongs to the field of MEMS ultrasonic transducers and three-dimensional micro-nano manufacturing technology, and particularly relates to a MEMS ultrasonic transducer and a preparation method thereof, as well as an ultrasonic transducer array. Background Art

[0002] Capacitive MEMS ultrasonic transducers (CMUTs) are electrostatic conversion ultrasonic sensors that utilize microelectromechanical (MEMS) technology and capacitive sensing principles to achieve high-precision ultrasonic detection and high-pressure ultrasonic output. CMUTs offer significant advantages, including high sensitivity, high output sound pressure, wide bandwidth, ease of large-scale array fabrication, and ease of integration with ASICs. They are widely used in medical imaging diagnostics and treatment, high-intensity focused ultrasound (HIFU), handheld personal medical ultrasound equipment, chemical sensing, and applications using gas as a propagation medium, becoming a powerful alternative to piezoelectric transducers.

[0003] A traditional CMUT is a parallel plate capacitor consisting of a resonant plate or membrane, a movable electrode, and a fixed electrode. When ultrasound acts on the resonant plate or membrane, it changes the capacitance of the capacitor, generating an electrical signal. When an AC signal is applied, the resonant plate or membrane vibrates under the action of electrostatic force, emitting ultrasound. However, the performance of the traditional CMUT is limited by the planar electrode structure. Only the central area, where the vibration amplitude is the largest and accounts for about 20% of the size, has a high electric field strength and electromechanical conversion efficiency. Its sensitivity is limited and the driving voltage is high. At the same time, the receiving sensitivity is also limited by parasitic capacitance, which affects the imaging quality. Summary of the Invention

[0004] The present invention aims to provide a MEMS ultrasonic transducer, a method for fabricating the same, and an ultrasonic transducer array. This invention proposes a novel CMUT (Combined Mean Time Unit) with a novel structure and materials, along with a corresponding fabrication method. These methods aim to improve the CMUT's receiving sensitivity, reduce driving voltage, enhance imaging quality and reliability, and improve device processing accuracy and consistency, while reducing manufacturing costs.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] A MEMS ultrasonic transducer comprises a substrate unit and a structural unit;

[0007] The substrate unit includes a TGV glass substrate, a metal bottom electrode located on the upper surface of the TGV glass substrate, an insulating layer covering the upper surface of the metal bottom electrode, a first bump bottom UBM layer and a second bump bottom UBM layer located on the lower surface of the TGV glass substrate, a first ball grid electrode located on the lower surface of the first bump bottom UBM layer, and a second ball grid electrode located on the lower surface of the second bump bottom UBM layer;

[0008] The TGV glass substrate is provided with a first through-hole electrode and a second through-hole electrode that vertically penetrates the TGV glass substrate; the metal bottom electrode is in ohmic contact with the first through-hole electrode; the area of ​​the insulating layer is larger than the area of ​​the metal bottom electrode; the first bump bottom UBM layer is in ohmic contact with the first through-hole electrode; the first ball grid electrode is in ohmic contact with the first bump bottom UBM layer; the second bump bottom UBM layer is in ohmic contact with the second through-hole electrode; and the second ball grid electrode is in ohmic contact with the second bump bottom UBM layer.

[0009] The structural unit includes a resonant plate or a resonant membrane, a conformal electrode, and a metal upper electrode; the lower surface of the conformal electrode is a special-shaped surface, and the edge of the lower surface is bonded to the upper surface of the TGV glass substrate to form a micro-nano cavity; the metal lower electrode and the insulating layer are located in the micro-nano cavity, and the insulating layer and the conformal electrode do not contact each other;

[0010] A gap is provided at the edge of the conformal electrode at a position corresponding to the second through-hole electrode, and the metal top electrode is provided in the gap, located on the surface of the conformal electrode between the surface of the TGV glass substrate and the sidewall of the gap; the metal top electrode and the second through-hole electrode are in ohmic contact, and the edge of the metal top electrode contacts the edge of the conformal electrode, so that the conformal electrode and the second through-hole electrode are electrically connected;

[0011] The resonant plate or resonant film is arranged on the upper surface of the conformal electrode;

[0012] The metal lower electrode and the metal upper electrode form a pair of driving electrodes.

[0013] Preferably, the conformal electrode is made of silicon, which is single crystal silicon or polycrystalline silicon; and the resonant plate or resonant film is made of a material different from that of the conformal electrode.

[0014] Preferably, the resonant plate or the resonant membrane is made of a non-metallic material or a metal material; the non-metallic material includes silicon nitride, silicon oxide, silicon carbide or diamond; the metal material is a metal element or an alloy.

[0015] Preferably, the conformal electrode is made of silicon, which is single crystal silicon or polycrystalline silicon, and the resonant plate or resonant film is made of the same material as the conformal electrode; the conformal electrode and the resonant plate or resonant film form an integral structure.

[0016] Preferably, the MEMS ultrasonic transducer further includes a bonding dielectric layer; the bonding dielectric layer is arranged between the contact positions of the substrate unit and the conformal electrode.

[0017] Preferably, the upper surface of the conformal electrode is flat, and the resonant plate or resonant film is a planar resonant plate or a planar resonant film.

[0018] Preferably, the material of the conformal electrode is a non-silicon material, and the non-silicon material is a metal or a semiconductor material; the metal is a metal element or an alloy; and the MEMS ultrasonic transducer includes a bonding dielectric layer; the bonding dielectric layer is arranged between the contact position of the substrate unit and the conformal electrode.

[0019] Preferably, the material of the resonant plate or the resonant membrane is non-metal or metal, the non-metal includes silicon nitride, silicon oxide, silicon carbide or diamond; the metal is a metal element or an alloy.

[0020] Preferably, the conformal electrode is made of metal, and the resonant plate or resonant membrane is made of the same material as the conformal electrode; the conformal electrode and the resonant plate or resonant membrane form an integral structure, and the metal upper electrode is omitted.

[0021] Preferably, the conformal electrode is made of metal, and the metal has the function of a bonding dielectric layer, and the bonding dielectric layer is omitted.

[0022] Preferably, the upper surface of the conformal electrode is a special-shaped surface, and the resonant plate or the resonant film is a special-shaped resonant plate or a special-shaped resonant film.

[0023] Preferably, the diameters of the first through-hole electrode and the second through-hole electrode are independently 1 μm to 1 mm; the materials of the first through-hole electrode and the second through-hole electrode independently include metal or non-metal; the metal is a metal element or an alloy; the non-metal includes single crystal silicon or polycrystalline silicon.

[0024] Preferably, the thickness of the metal upper electrode and the metal lower electrode is 10 nm to 1 μm; the material of the metal upper electrode and the metal lower electrode is metal;

[0025] The thickness of the insulating layer is 10 nm to 1 μm; the material of the insulating layer includes one or more of silicon oxide, silicon nitride, aluminum oxide, aluminum nitride, hafnium oxide, zirconium oxide and tantalum oxide.

[0026] Preferably, the surface of the structural unit is coated with a passivation layer; the thickness of the passivation layer is 0 to 10 μm; the material of the passivation layer includes one or more of silicon nitride, silicon oxide, aluminum oxide, phosphate glass and polyimide.

[0027] Preferably, the thickness of the bonding dielectric layer is 10 nm to 10 μm; the material of the bonding dielectric layer is metal, polymer or semiconductor material.

[0028] The present invention also provides a method for preparing the MEMS ultrasonic transducer described in the above scheme (method 1), comprising the following steps:

[0029] (1) providing a TGV glass substrate having a first through-hole electrode and a second through-hole electrode; sequentially preparing a metal bottom electrode and an insulating layer at a position on the surface of the TGV glass substrate corresponding to the first through-hole electrode to obtain a substrate to be bonded;

[0030] (2) Providing an SOI wafer; the SOI wafer includes a device layer, a buried oxide layer, and a substrate layer stacked in layers; preparing a mask layer on the surface of the device layer in an area corresponding to the bonding position with the TGV glass substrate, and then performing a thermal oxidation treatment on the SOI wafer, and then removing the mask layer and the silicon dioxide generated by the thermal oxidation to obtain a plate to be bonded; the mask layer is a silicon dioxide mask layer or a composite mask layer; the composite mask layer includes a silicon nitride layer and a silicon dioxide layer stacked in sequence from top to bottom;

[0031] (3) bonding the electrode plate to be bonded and the substrate to be bonded to form a micro-nano chamber, removing the substrate layer, the buried oxide layer and part of the device layer to obtain a conformal electrode;

[0032] (4) preparing a resonant plate or a resonant film on the upper surface of the conformal electrode, then etching the resonant plate or the resonant film to expose a portion of the conformal electrode, and then etching the conformal electrode to expose the second through-hole electrode of the TGV glass substrate;

[0033] (5) preparing a metal top electrode at a position on the surface of the TGV glass substrate corresponding to the second through-hole electrode, and making the edge of the metal top electrode contact the edge of the conformal electrode;

[0034] (6) sequentially preparing a first bump bottom UBM layer and a first ball grid electrode on the lower surface of the first through-hole electrode of the TGV glass substrate, and sequentially preparing a second bump bottom UBM layer and a second ball grid electrode on the lower surface of the second through-hole electrode to obtain the MEMS ultrasonic transducer;

[0035] There is no time sequence restriction for steps (1), (2) and (6).

[0036] The present invention also provides a method for preparing the MEMS ultrasonic transducer described in the above scheme (Method 2), comprising the following steps:

[0037] (1) providing a TGV glass substrate having a first through-hole electrode and a second through-hole electrode; sequentially preparing a metal bottom electrode and an insulating layer at a position on the surface of the TGV glass substrate corresponding to the first through-hole electrode to obtain a substrate to be bonded;

[0038] (2) Providing an SOI wafer; the SOI wafer includes a device layer, a buried oxide layer, and a substrate layer stacked in layers; the thickness of the device layer is greater than the total thickness of the conformal electrode and the resonant plate; preparing a mask layer on the surface of the device layer in an area corresponding to the bonding position with the TGV glass substrate, and then performing a thermal oxidation treatment on the SOI wafer, and then removing the mask layer and the silicon dioxide generated by the thermal oxidation to obtain a plate to be bonded; the mask layer is a silicon dioxide mask layer or a composite mask layer; the composite mask layer includes a silicon nitride layer and a silicon dioxide layer stacked in sequence from top to bottom;

[0039] (3) bonding the electrode plate to be bonded and the substrate to be bonded to form a micro-nano chamber, removing the substrate layer and the buried oxide layer, and controlling the thickness of the remaining device layer to be the total thickness of the conformal electrode and the resonant plate to obtain an integrated structure of the conformal electrode and the resonant plate;

[0040] (4) etching the integrated structure of the conformal electrode and the resonant plate to expose the second through-hole electrode of the TGV glass substrate;

[0041] (5) preparing a metal top electrode at a position on the surface of the TGV glass substrate corresponding to the second through-hole electrode, and making the metal top electrode cover the conformal electrode and the integrated structure of the resonant plate;

[0042] (6) sequentially preparing a first bump bottom UBM layer and a first ball grid electrode on the lower surface of the first through-hole electrode of the TGV glass substrate, and sequentially preparing a second bump bottom UBM layer and a second ball grid electrode on the lower surface of the second through-hole electrode to obtain the MEMS ultrasonic transducer;

[0043] There is no time sequence restriction for steps (1), (2) and (6).

[0044] The present invention also provides a method for preparing the MEMS ultrasonic transducer described in the above scheme (method three), comprising the following steps:

[0045] Providing a TGV glass substrate with a first through-hole electrode and a second through-hole electrode; sequentially preparing a metal bottom electrode and an insulating layer at a position on the surface of the TGV glass substrate corresponding to the first through-hole electrode, and depositing a bonding dielectric layer at the device edge of the TGV glass substrate to obtain a substrate to be bonded;

[0046] The MEMS ultrasonic transducer is prepared according to steps (2) to (6) in method one, or prepared according to steps (2) to (6) in method two to obtain the MEMS ultrasonic transducer.

[0047] The present invention also provides a method for preparing the MEMS ultrasonic transducer described in the above scheme (method four), comprising the following steps:

[0048] (1) providing a TGV glass substrate with a first through-hole electrode and a second through-hole electrode; sequentially preparing a metal bottom electrode and an insulating layer at a position corresponding to the first through-hole electrode on the surface of the TGV glass substrate, and depositing a bonding dielectric layer at the device edge of the TGV glass substrate to obtain a substrate to be bonded;

[0049] (2) Providing an SOI wafer; the SOI wafer includes a device layer, a buried oxide layer, and a substrate layer stacked in layers; preparing a mask layer on the surface of the device layer in an area corresponding to the bonding position with the TGV glass substrate, and then performing a thermal oxidation treatment on the SOI wafer, and then removing the mask layer and the silicon dioxide generated by the thermal oxidation to obtain a silicon-based mold with a special-shaped surface; the mask layer is a silicon dioxide mask layer or a composite mask layer; the composite mask layer includes a silicon nitride layer and a silicon dioxide layer stacked in sequence from top to bottom;

[0050] (3) sequentially preparing a barrier layer, a resonant film, and a conformal electrode on the irregular surface of the irregular surface silicon-based mold to obtain a plate to be bonded;

[0051] (4) bonding the electrode plate to be bonded and the substrate to be bonded to form a micro-nano chamber, and removing the substrate layer, buried oxide layer, device layer and barrier layer; etching the resonant film to expose the conformal electrode; then etching the conformal electrode and the bonding dielectric layer to expose the second through-hole electrode of the TGV glass substrate;

[0052] (5) preparing a metal top electrode at a position on the surface of the TGV glass substrate corresponding to the second through-hole electrode, and making the edge of the metal top electrode contact the edge of the conformal electrode;

[0053] (6) sequentially preparing a first bump bottom UBM layer and a first ball grid electrode on the lower surface of the first through-hole electrode of the TGV glass substrate, and sequentially preparing a second bump bottom UBM layer and a second ball grid electrode on the lower surface of the second through-hole electrode to obtain the MEMS ultrasonic transducer;

[0054] There is no time sequence restriction for steps (1), (2) and (6).

[0055] The present invention also provides a method for preparing the MEMS ultrasonic transducer described in the above scheme (Method 5), comprising the following steps:

[0056] (1) providing a TGV glass substrate with a first through-hole electrode and a second through-hole electrode; sequentially preparing a metal bottom electrode and an insulating layer at a position corresponding to the first through-hole electrode on the surface of the TGV glass substrate, and depositing a bonding dielectric layer at the device edge of the TGV glass substrate to obtain a substrate to be bonded;

[0057] (2) Providing an SOI wafer; the SOI wafer includes a device layer, a buried oxide layer, and a substrate layer stacked in layers; preparing a mask layer on the surface of the device layer in an area corresponding to the bonding position with the TGV glass substrate, and then performing a thermal oxidation treatment on the SOI wafer, and then removing the mask layer and the silicon dioxide generated by the thermal oxidation to obtain a silicon-based mold with a special-shaped surface; the mask layer is a silicon dioxide mask layer or a composite mask layer; the composite mask layer includes a silicon nitride layer and a silicon dioxide layer stacked in sequence from top to bottom;

[0058] (3) sequentially preparing a barrier layer, a resonant film, and a conformal electrode integrated structure layer on the irregular surface of the irregular surface silicon-based mold to obtain a plate to be bonded;

[0059] (4) bonding the electrode plate to be bonded and the substrate to be bonded to form a micro-nano chamber, and contacting the resonant film and conformal electrode integrated structure layer with the second through-hole electrode of the TGV glass substrate; removing the substrate layer, buried oxide layer, device layer and barrier layer; etching the resonant film and conformal electrode integrated structure layer and the bonding dielectric layer to expose the TGV glass substrate at the edge of the device;

[0060] (5) sequentially preparing a first bump bottom UBM layer and a first ball grid electrode on the lower surface of the first through-hole electrode of the TGV glass substrate, and sequentially preparing a second bump bottom UBM layer and a second ball grid electrode on the lower surface of the second through-hole electrode to obtain the MEMS ultrasonic transducer;

[0061] There is no time sequence restriction for steps (1), (2) and (5).

[0062] The present invention also provides a method for preparing the MEMS ultrasonic transducer described in the above scheme, which is characterized by comprising the following steps: preparing according to steps (1) to (6) in method four, only omitting the bonding medium layer.

[0063] Preferably, before preparing the first bottom bump UBM layer, the first ball grid electrode, the second bottom bump UBM layer and the second ball grid electrode, the method further comprises preparing a passivation layer on the surface of the obtained structural unit.

[0064] The present invention also provides a capacitive MEMS ultrasonic transducer array, comprising a plurality of transducer units distributed in an array structure; the transducer unit is the MEMS ultrasonic transducer described in the above scheme or a MEMS ultrasonic transducer prepared by the preparation method described in the above scheme.

[0065] Preferably, the substrate unit of the plurality of transducer units distributed in an array structure forms an integral structure;

[0066] The second through-hole electrode and the second ball grid electrode in each transducer unit in the array are omitted, and a total through-hole electrode is provided at the edge of the capacitive MEMS ultrasonic transducer array, and a ball grid electrode is provided at the bottom of the total through-hole electrode; each transducer unit in the array is electrically connected to the total through-hole electrode through a metal top electrode.

[0067] The present invention provides a MEMS ultrasonic transducer. The present invention adopts a conformal electrode with a special-shaped surface structure, so that the transducer has a non-uniform cavity height. Outside the 20% central area with the largest vibration amplitude, the cavity height gradually decreases. Therefore, the electric field strength outside the central area is significantly enhanced, thereby significantly improving the sensitivity and reducing the driving voltage compared to traditional planar electrodes. At the same time, the resonant plate or resonant membrane can be deformed under the drive of an AC signal to obtain a relatively uniform cavity height, maintaining the maximum resonance amplitude and output sound pressure. The present invention adopts a glass substrate with a through hole (TGV, Through-Glass Via). Compared with traditional silicon-based substrates that require an insulating layer for electrical isolation in the bonding area, the TGV glass substrate does not require an insulating layer in the bonding area and is not limited by the thickness of the insulating layer. It can eliminate the influence of parasitic capacitance and significantly improve the receiving sensitivity. Furthermore, the material of the conformal electrode and the resonant plate or resonant membrane of the present invention can be metal or alloy, which can significantly improve the mechanical life and reliability of the device compared with traditional materials such as single crystal silicon or silicon nitride.

[0068] The present invention also provides a method for preparing the MEMS ultrasonic transducer. The present invention adopts TGV glass substrate and SOI wafer, and realizes the preparation of MEMS ultrasonic transducer by local oxidation of silicon (LOCOS) and bonding technology. The present invention prepares a mask layer on the SOI wafer device layer, and then forms a special-shaped surface structure of the device layer of the SOI wafer through means such as thermal oxidation treatment. When the material of the conformal electrode is single crystal silicon, the SOI device layer with a special-shaped surface can be directly used to prepare the conformal electrode. When the conformal electrode is made of other materials, the SOI wafer with a special-shaped surface can be used as a mold, and the conformal electrode can be prepared by combining sputtering, electroplating, deposition and other methods. The preparation method provided by the present invention can achieve high-precision 3D processing of conformal electrodes with good consistency and low cost, and is suitable for large-scale array wafer-level manufacturing. It is also compatible with ASIC technology and is easy to achieve 3D integration with ASIC. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Figure 1 Schematic diagram of the structure of a MEMS ultrasonic transducer when the upper surface of the conformal electrode is flat and the resonant plate or resonant membrane is a flat resonant plate or resonant membrane;

[0070] Figure 2 Schematic diagram of the structure of a MEMS ultrasonic transducer when the upper surface of the conformal electrode is flat and the resonant plate or resonant membrane is integrated with the conformal electrode;

[0071] Figure 3 Schematic diagram of the structure of a MEMS ultrasonic transducer when the upper surface of the conformal electrode is a curved surface, and the resonant plate or resonant membrane is a curved resonant plate or a curved resonant membrane;

[0072] Figure 4 Schematic diagram of the structure of a MEMS ultrasonic transducer in which the upper surface of the conformal electrode is a curved surface, the resonant plate or resonant membrane is a curved resonant plate or a curved resonant membrane, the metal upper electrode is omitted, and the resonant plate or resonant membrane and the conformal electrode are integrated into one;

[0073] Figure 5 is a schematic diagram of the principle when the MEMS ultrasonic transducer is used as a receiver;

[0074] Figure 6 is a schematic diagram showing the principle when the MEMS ultrasonic transducer is used as a transmitter;

[0075] Figure 7 is a flow chart of the preparation process when the structure of the MEMS ultrasonic transducer belongs to situation 1;

[0076] Figure 8 This is a flow chart of the preparation process when the structure of the MEMS ultrasonic transducer belongs to case 1, and the conformal electrode and the resonant plate or resonant membrane are integrated into one.

[0077] Figure 9 1 is a flow chart of a preparation process when the structure of the MEMS ultrasonic transducer belongs to case 1 and is further provided with a bonding dielectric layer;

[0078] Figure 10 is a flow chart of the preparation process when the structure of the MEMS ultrasonic transducer belongs to case 2;

[0079] Figure 11 This is a flow chart of the manufacturing process when the structure of the MEMS ultrasonic transducer belongs to case 2, the metal upper electrode is omitted, and the conformal electrode and the resonant plate or resonant membrane are integrated into one;

[0080] Figure 12 1 is a flow chart of the preparation process when the structure of the MEMS ultrasonic transducer belongs to case 2 and the bonding dielectric layer is omitted;

[0081] Figure 13 is a cross-sectional view of a capacitive MEMS ultrasonic transducer array (3×3 array);

[0082] Figure 14 A top view of a capacitive MEMS ultrasonic transducer array (3×3 array);

[0083] Figure 15 Schematic diagram of the sensitivity effect of the conformal curved electrode MEMS ultrasonic transducer (Example 2);

[0084] Figure 16 Schematic diagram of the receiving sensitivity effect of TGV glass substrate MEMS ultrasonic transducer;

[0085] Figure 17 Schematic diagram of the structure of a flat-plate electrode MEMS ultrasonic transducer based on a traditional silicon substrate;

[0086] Figures 1 to 14 as well as Figure 17 Middle: 1-TGV glass substrate, 2-metal lower electrode, 3-insulating layer, 4-first through-hole electrode, 5-second through-hole electrode, 6-first bump bottom UBM layer, 7-second bump bottom UBM layer, 8-first ball grid electrode, 9-second ball grid electrode, 10-conformal electrode, 11-resonance plate or resonant membrane, 12-metal upper electrode, 13-passivation layer, 14-micro-nano chamber, 15-integrated structure of conformal electrode and resonant plate, 16-bonding dielectric layer, 17-integrated structure of conformal electrode and resonant membrane when the material is metal or alloy, 18-SOI wafer device layer, 19-SOI wafer buried oxide layer, 20-SOI wafer substrate layer, 21-silicon nitride layer of composite mask layer, 22-silicon dioxide layer of composite mask layer, 23-silicon dioxide generated by thermal oxidation, 24-total through-hole electrode, 25-silicon substrate. DETAILED DESCRIPTION

[0087] The present invention provides a MEMS ultrasonic transducer, comprising a substrate unit and a structural unit;

[0088] The substrate unit includes a TGV glass substrate, a metal bottom electrode located on the upper surface of the TGV glass substrate, an insulating layer covering the upper surface of the metal bottom electrode, a first bump bottom UBM layer (referred to as the first UBM layer) and a second bump bottom UBM layer (referred to as the second UBM layer) located on the lower surface of the TGV glass substrate, a first ball grid electrode located on the lower surface of the first UBM layer, and a second ball grid electrode located on the lower surface of the second UBM layer;

[0089] The TGV glass substrate is provided with a first through-hole electrode and a second through-hole electrode that vertically penetrates the TGV glass substrate; the metal bottom electrode is in ohmic contact with the first through-hole electrode; the area of ​​the insulating layer is larger than the area of ​​the metal bottom electrode; the first UBM layer is in ohmic contact with the first through-hole electrode; the first ball grid electrode is in ohmic contact with the first UBM layer; the second UBM layer is in ohmic contact with the second through-hole electrode; and the second ball grid electrode is in ohmic contact with the second UBM layer.

[0090] The structural unit includes a resonant plate or a resonant membrane, a conformal electrode, and a metal upper electrode; the lower surface of the conformal electrode is a special-shaped surface, and the edge of the lower surface is bonded to the upper surface of the TGV glass substrate to form a micro-nano cavity; the metal lower electrode and the insulating layer are located in the micro-nano cavity, and the insulating layer and the conformal electrode do not contact each other;

[0091] A gap is provided at the edge of the conformal electrode at a position corresponding to the second through-hole electrode, and the metal top electrode is provided at the gap, located on the surface of the conformal electrode between the surface of the TGV glass substrate and the sidewall of the gap, the metal top electrode and the second through-hole electrode are in ohmic contact, and the edge of the metal top electrode contacts the edge of the conformal electrode, so that the conformal electrode and the second through-hole electrode are electrically connected;

[0092] The resonant plate or resonant film is arranged on the upper surface of the conformal electrode;

[0093] The metal lower electrode and the metal upper electrode form a pair of driving electrodes.

[0094] In the present invention, according to the material and shape of the conformal electrode, the MEMS ultrasonic transducer of the present invention is mainly divided into two cases, which are described in detail below.

[0095] In the present invention, the material of the conformal electrode is preferably silicon, and the silicon is preferably single crystal silicon or polycrystalline silicon. At this time, the upper surface of the conformal electrode is preferably flat, and the resonant plate or resonant film is preferably a flat resonant plate or a flat resonant film (recorded as case 1, the structural diagram is as shown in FIG. Figure 1 shown).

[0096] The following is a detailed introduction to the MEMS ultrasonic transducer in Case 1.

[0097] In the present invention, when the material of the conformal electrode is preferably single crystal silicon or polycrystalline silicon, the material of the resonant plate or resonant film may be the same as or different from the material of the conformal electrode. When the material of the resonant plate or resonant film is different from that of the conformal electrode, the material of the resonant plate or resonant film is preferably a non-metallic material or a metal material; the non-metallic material preferably includes silicon nitride, silicon oxide, silicon carbide or diamond; the metal material is preferably a metal element or alloy; the metal element includes but is not limited to gold (Au), silver (Ag), aluminum (Al), copper (Cu), tungsten (W), molybdenum (Mo), nickel (Ni), palladium (Pd), platinum (Pt), titanium (Ti), cobalt (Co), chromium (Cr), germanium (Ge), indium ( In), tantalum (Ta), iridium (Ir) and ruthenium (Ru); the alloy includes but is not limited to one or more of copper zinc, tin brass, phosphor bronze, aluminum bronze, silicon bronze, silicon brass, copper nickel, nickel silver, nickel molybdenum, nickel chromium, nickel chromium iron, nickel chromium molybdenum, nickel chromium cobalt, nickel titanium, gold copper, gold silver, gold platinum, gold zinc, gold palladium, gold nickel, gold cadmium, platinum iridium, platinum cobalt, platinum palladium, platinum ruthenium, platinum rhodium, platinum tungsten, platinum copper, aluminum copper, aluminum manganese, aluminum magnesium, aluminum magnesium silicon, aluminum zinc, aluminum tin, titanium copper, titanium aluminum, titanium nickel, titanium molybdenum, titanium palladium, tungsten rhenium and iridium rhenium metal alloys.

[0098] As a special case of the first case, the conformal electrode and the resonant plate or resonant membrane are made of the same material, either single crystal silicon or polycrystalline silicon. When the conformal electrode and the resonant plate or resonant membrane are made of single crystal silicon or polycrystalline silicon, the conformal electrode and the resonant plate or resonant membrane are an integral structure. In this case, the structural diagram of the MEMS ultrasonic transducer is as follows: Figure 2 shown.

[0099] As a special case of the first case, the MEMS ultrasonic transducer preferably further includes a bonding dielectric layer; the bonding dielectric layer is preferably arranged between the position where the substrate unit contacts the conformal electrode; the material of the bonding dielectric layer is preferably metal, polymer or semiconductor material; the metal includes but is not limited to one or more of gold (Au), silver (Ag), aluminum (Al), copper (Cu), titanium (Ti), tungsten (W), molybdenum (Mo), nickel (Ni), zirconium (Zr), palladium (Pd), platinum (Pt), chromium (Cr), indium (In), tantalum (Ta), iridium (Ir) and ruthenium (Ru); the polymer is preferably an insulating polymer, including but not limited to epoxy resin (Expoxies), UV epoxy resin (UV Expoxies), photoresist, SU-8 photoresist (SU-8), benzocyclobutene (BCB), polymethyl methacrylate (PMMA), polymethylsiloxane (PDMS), polyimide, parylene (Parylene), liquid crystal polymer (LCP), methylsilyl semisiloxane (MSSQ), polyether ketone (PEEK), thermosetting copolyester (ATSP), thermoplastic copolymer (PVDC), glass paste (Glass frit) and wax (Waxes); the semiconductor material includes but is not limited to one or more of single crystal silicon and polycrystalline silicon.

[0100] In the present invention, the material of the conformal electrode is preferably a non-silicon material (specifically, a non-single crystal silicon and non-polycrystalline silicon material). When the material of the conformal electrode is preferably a non-silicon material, the upper surface of the conformal electrode is preferably a special-shaped surface, and the resonant plate or resonant film is preferably a special-shaped resonant plate or special-shaped resonant film (recorded as case 2, the structural diagram is shown in FIG. Figure 3 As shown); in case 2, the shape of the upper surface of the conformal electrode is preferably consistent with the shape of the lower surface, and the shape of the special-shaped resonant plate or special-shaped resonant film matches the upper surface of the conformal electrode.

[0101] The following is a detailed introduction to the MEMS ultrasonic transducer in Case 2.

[0102] In the present invention, the material of the conformal electrode is preferably a non-silicon material, and the non-silicon material is preferably a metal; the metal preferably includes but is not limited to one or more of aluminum (Al), silver (Ag), gold (Au), cobalt (Co), chromium (Cr), copper (Cu), indium (In), molybdenum (Mo), nickel (Ni), palladium (Pd), platinum (Pt), titanium (Ti), tantalum (Ta) and tungsten (W), or an alloy of at least two of the above metals.

[0103] In case 2, the material of the resonant plate or resonant film is preferably a non-metallic material or a metal material; the non-metallic material preferably includes silicon nitride, silicon oxide, silicon carbide or diamond; the metal material is preferably a metal element or alloy; the metal element includes but is not limited to gold (Au), silver (Ag), aluminum (Al), copper (Cu), tungsten (W), molybdenum (Mo), nickel (Ni), palladium (Pd), platinum (Pt), titanium (Ti), cobalt (Co), chromium (Cr), germanium (Ge), indium (In), tantalum ( The alloy includes but is not limited to one or more of copper-zinc, tin-brass, phosphor bronze, aluminum-bronze, silicon-bronze, silicon-brass, copper-nickel, nickel-silver, nickel-molybdenum, nickel-chromium, nickel-chromium-iron, nickel-chromium-molybdenum, nickel-chromium-cobalt, nickel-titanium, gold-copper, gold-silver, gold-platinum, gold-zinc, gold-palladium, gold-nickel, gold-cadmium, platinum-iridium, platinum-cobalt, platinum-palladium, platinum-ruthenium, platinum-rhodium, platinum-tungsten, platinum-copper, aluminum-copper, aluminum-manganese, aluminum-magnesium, aluminum-magnesium-silicon, aluminum-zinc, aluminum-tin, titanium-copper, titanium-aluminum, titanium-nickel, titanium-molybdenum, titanium-palladium, tungsten-rhenium and iridium-rhenium alloy.

[0104] In the present invention, when the material of the conformal electrode is non-silicon material, the MEMS ultrasonic transducer preferably also includes a bonding dielectric layer; the bonding dielectric layer is preferably arranged between the contact position of the substrate unit and the conformal electrode; the material of the bonding dielectric layer is consistent with that in case 1 and will not be repeated here.

[0105] As a special case of the second case, when the material of the conformal electrode is metal and the material of the resonant plate or resonant membrane is also metal, the metal upper electrode is omitted, and the conformal electrode and the resonant plate or resonant membrane are integrated into one. More specifically, if the bonding dielectric layer is metal or has good conductivity and can simultaneously achieve ohmic contact with the conformal electrode and the second through-hole electrode, then the conformal electrode does not have a gap at the position corresponding to the second through-hole electrode. In this case, the structural diagram of the MEMS ultrasonic transducer is as follows: Figure 4 shown.

[0106] As a special case of the second situation, when the material of the conformal electrode is metal and the material of the conformal electrode has the function of a bonding dielectric layer, the bonding dielectric layer is omitted.

[0107] The basic parameters or performance of the MEMS ultrasonic transducer are described below, and the following description is applicable to Case 1 and Case 2.

[0108] In the present invention, the thickness of the conformal electrode is preferably 0.01 to 10 μm. In a specific embodiment of the present invention, when the thickness of each part of the conformal electrode is uniform, the thickness of the conformal electrode can be based on the thickness at any position. When the thickness of the conformal electrode is uneven, the thickness at the thickest point shall prevail. The lower surface of the conformal electrode is a special-shaped surface, and the special-shaped surface includes a curved surface, a step, a slope, or a composite special-shaped surface composed of multiple curved surfaces, multiple steps, or multiple slopes, and is more preferably a curved surface. In the present invention, the profiled surface is a profiled surface that is recessed toward the resonant plate or resonant membrane, and the depth of the recess is greatest at the center of the corresponding micro-nano chamber. After the edge of the conformal electrode is bonded to the TGV glass substrate (directly or through a bonding dielectric layer), a micro-nano chamber is formed between the recessed portion of the profiled surface and the upper surface of the TGV glass substrate. The micro-nano chamber is specifically located above the first through-hole electrode, and the second through-hole electrode is not within the micro-nano chamber. The present invention does not specifically limit the size of the micro-nano chamber, and any size familiar to those skilled in the art may be used. In a specific embodiment of the present invention, the lower surface of the conformal electrode is preferably a curved surface, and the radius of the curved surface is preferably 20 to 400 μm. The height of the micro-nano chamber is preferably 0.1 to 1.0 μm.

[0109] In the present invention, the interior of the micro-nano chamber is preferably vacuum or filled with gas; the gas includes but is not limited to one or more of filled air (Air), helium (He), argon (Ar) and high dielectric constant gas; the high dielectric constant gas includes but is not limited to one or more of nitrogen (N2), sulfur hexafluoride (SF6) and ammonia (NH3).

[0110] In the present invention, the thickness of the resonant plate or resonant film is preferably 0.3 to 300 μm, more preferably 1 to 100 μm; the thickness test standard of the resonant plate or resonant film is consistent with that of the conformal electrode and will not be repeated here. The resonant plate or resonant film is specifically arranged on the surface of the conformal electrode. When the resonant plate or resonant film is not made of metal or conductive material, the resonant plate or resonant film exposes a portion of the conformal electrode near the second through hole so that the metal upper electrode and the edge of the conformal electrode contact; when the resonant film is made of metal or conductive material and is integrated with the conformal electrode into an integrated structure, the resonant plate or resonant film completely covers the surface of the conformal electrode; the shape of the resonant plate or resonant film includes but is not limited to polygons such as circle, ellipse, positive direction, rectangle, pentagon, hexagon and octagon.

[0111] In the present invention, the diameters of the first and second through-hole electrodes are preferably independently 1 μm to 1 mm; the materials of the first and second through-hole electrodes independently include metal or non-metal; the metal is a metal element or an alloy, and the metal element includes but is not limited to one or more of gold (Au), silver (Ag), aluminum (Al), copper (Cu), tungsten (W), molybdenum (Mo), nickel (Ni), palladium (Pd), platinum (Pt), titanium (Ti), cobalt (Co), chromium (Cr), germanium (Ge), indium (In), tantalum (Ta), iridium (Ir) and ruthenium (Ru), or an alloy of at least two of the above metals; the non-metal preferably includes single crystal silicon or polycrystalline silicon; the single crystal silicon or polycrystalline silicon is specifically low-resistance single crystal silicon or low-resistance polycrystalline silicon; the resistance of the low-resistance single crystal silicon or low-resistance polycrystalline silicon is preferably ≤10Ω·cm. In the present invention, the radius of the first and second through-hole electrodes is preferably 10 μm to 10 mm, and the spacing between the first and second through-hole electrodes is preferably 20 μm to 20 mm.

[0112] In the present invention, the thickness of the metal bottom electrode is preferably 10 nm to 1 μm; the material of the metal bottom electrode is preferably a metal, including but not limited to one or more of gold (Au), silver (Ag), aluminum (Al), copper (Cu), tungsten (W), molybdenum (Mo), nickel (Ni), palladium (Pd), platinum (Pt), titanium (Ti), cobalt (Co), chromium (Cr), germanium (Ge), indium (In), tantalum (Ta), iridium (Ir), and ruthenium (Ru), or an alloy of at least two of the above metals. In a specific embodiment of the present invention, a Ti / Al composite layer is preferably used as the metal bottom electrode, wherein the Ti layer contacts the TGV glass substrate, the Al layer is located on the Ti layer, and the Ti layer serves as a bonding layer.

[0113] In the present invention, the thickness of the insulating layer is preferably 10 nm to 1 μm; the material of the insulating layer preferably includes, but is not limited to, one or more of silicon oxide (SiO2), silicon nitride (Si3N4), aluminum oxide (Al2O3), aluminum nitride (AlN), hafnium oxide (HfO2), zirconium oxide (ZrO2), and tantalum oxide (Ta2O5). The insulating layer can prevent short circuits during device operation.

[0114] In the present invention, the material of the metal upper electrode is preferably consistent with that of the metal lower electrode; in a specific embodiment of the present invention, Si-doped Al metal is preferably used as the metal upper electrode, and the Si doping amount in the Si-doped Al metal is preferably 2 wt%.

[0115] In the present invention, the surface of the structural unit is preferably coated with a passivation layer; the thickness of the passivation layer is preferably 0-1 μm (0 μm indicates no passivation layer), more preferably 0.1-1 μm; the material of the passivation layer includes, but is not limited to, one or more of silicon nitride, silicon oxide, aluminum oxide, phosphate glass, and polyimide. In the present invention, the passivation layer covers the exposed surfaces of the structural unit, specifically covering all exposed surfaces of the resonant plate or resonant membrane, the metal top electrode, and the conformal electrode, including the top surface and side surfaces. The present invention utilizes the passivation layer to insulate the device structure from the environment.

[0116] In the present invention, the thickness of the bonding dielectric layer is preferably 10 nm to 10 μm.

[0117] In a specific embodiment of the present invention, when the MEMS ultrasonic transducer is in use, a direct current bias voltage (DC) is applied through the metal upper electrode and the lower electrode to deform the resonant plate or the resonant membrane. When the ultrasonic signal hits the resonant plate or the resonant membrane, the resonant plate or the resonant membrane vibrates, causing a change in capacitance, generating current that is converted into an electrical signal through an amplification circuit; by applying an alternating current drive signal (AC) to the metal upper electrode and the lower electrode, the resonant plate or the resonant membrane can vibrate under the action of the alternating current electrostatic force with or without the action of the bias voltage DC, and hit the surrounding propagation medium to emit ultrasonic waves. Figure 5 is a schematic diagram of the principle when the MEMS ultrasonic transducer is used as a receiver; Figure 6 Schematic diagram of the principle when the MEMS ultrasonic transducer is used as a transmitter.

[0118] The present invention also provides a method for preparing the MEMS ultrasonic transducer described in the above solution, which is described in detail below.

[0119] When the structure of the MEMS ultrasonic transducer belongs to case 1, the method for preparing the MEMS ultrasonic transducer includes the following steps (referred to as method 1):

[0120] (1) providing a TGV glass substrate having a first through-hole electrode and a second through-hole electrode; sequentially preparing a metal bottom electrode and an insulating layer at a position on the surface of the TGV glass substrate corresponding to the first through-hole electrode to obtain a substrate to be bonded;

[0121] (2) Providing an SOI wafer; the SOI wafer includes a device layer, a buried oxide layer, and a substrate layer stacked in layers; preparing a mask layer on the surface of the device layer in an area corresponding to the bonding position with the TGV glass substrate, and then performing a thermal oxidation treatment on the SOI wafer, and then removing the mask layer and the silicon dioxide generated by the thermal oxidation to obtain a plate to be bonded; the mask layer is a silicon dioxide mask layer or a composite mask layer; the composite mask layer includes a silicon nitride layer and a silicon dioxide layer stacked in sequence from top to bottom;

[0122] (3) bonding the electrode plate to be bonded and the substrate to be bonded to form a micro-nano chamber, removing the substrate layer, the buried oxide layer and part of the device layer to obtain a conformal electrode;

[0123] (4) preparing a resonant plate or a resonant film on the upper surface of the conformal electrode, then etching the resonant plate or the resonant film to expose a portion of the conformal electrode, and then etching the conformal electrode to expose the second through-hole electrode of the TGV glass substrate;

[0124] (5) preparing a metal top electrode at a position on the TGV glass substrate corresponding to the second through-hole electrode, and making the edge of the metal top electrode contact the edge of the conformal electrode;

[0125] (6) sequentially preparing a first bump bottom UBM layer and a first ball grid electrode on the lower surface of the first through-hole electrode of the TGV glass substrate, and sequentially preparing a second bump bottom UBM layer and a second ball grid electrode on the lower surface of the second through-hole electrode to obtain the MEMS ultrasonic transducer;

[0126] There is no time sequence restriction for steps (1), (2) and (6).

[0127] Figure 7 This is a flow chart of the preparation process when the structure of the MEMS ultrasonic transducer belongs to situation one.

[0128] The present invention first provides a TGV glass substrate with a first through-hole electrode and a second through-hole electrode; a metal bottom electrode and an insulating layer are sequentially formed at positions on the TGV glass substrate corresponding to the first through-hole electrode to obtain a substrate to be bonded. In the present invention, the method for preparing the metal bottom electrode preferably includes sputtering, evaporation, or electroplating. The present invention does not specifically limit the preparation process of the metal bottom electrode; methods well known to those skilled in the art can be used. In specific embodiments of the present invention, sputtering, evaporation, or electroplating methods are preferably combined with patterning methods to prepare the metal bottom electrode. In the present invention, the method for preparing the insulating layer preferably includes atomic layer deposition (ALD), low-pressure chemical vapor deposition (LPCVD), or plasma-enhanced chemical vapor deposition (PECVD). The present invention does not specifically limit the preparation process of the insulating layer; methods well known to those skilled in the art can be used. In specific embodiments of the present invention, atomic layer deposition, low-pressure chemical vapor deposition, or plasma-enhanced chemical vapor deposition is preferably combined with patterning methods to prepare the insulating layer. The present invention does not specifically require the patterning method; methods commonly used in the art, such as photolithography plus etching or corrosion, can be used.

[0129] The present invention provides an SOI wafer; the SOI wafer includes a stacked device layer, a buried oxide layer, and a substrate layer; a mask layer is prepared on the surface of the device layer in an area corresponding to the bonding position with the TGV glass substrate, and then the SOI wafer is subjected to a thermal oxidation treatment, after which the mask layer and the silicon dioxide generated by the thermal oxidation treatment are removed to obtain a plate to be bonded. In the present invention, the thickness of the device layer is preferably 100nm to 300μm; the thickness of the buried oxide layer is preferably 100nm to 2μm; and the thickness of the substrate layer is preferably 300μm to 10mm. The device layer thickness of the SOI wafer is consistent, and the resonant plate or conformal electrode prepared using the same has low stress and good device consistency. The cross-sectional dimensions of the SOI wafer are preferably consistent with those of the TGV glass substrate.

[0130] In the present invention, the mask layer is a silicon dioxide mask layer or a composite mask layer; the composite mask layer includes a silicon nitride layer and a silicon dioxide layer stacked in sequence from top to bottom; when the mask layer is a silicon dioxide layer, the thickness of the silicon dioxide layer is preferably 100nm to 10μm; when the mask layer is a composite mask layer, the thickness of the silicon dioxide layer is preferably 100nm to 10μm; the thickness of the silicon nitride layer is preferably 10nm to 1μm. The present invention specifically prepares a mask layer on the surface of the SOI wafer device layer, corresponding to the area where the TGV glass substrate is bonded, i.e., the device edge of the transducer (see for details). Figure 7), preferably determined based on the position of the first through-hole electrode in the TGV glass substrate. Preferably, after the SOI wafer and the TGV glass substrate are aligned, the mask layer near the first through-hole electrode does not cover the first through-hole electrode, while the mask layer near the second through-hole electrode covers the second through-hole electrode. In the present invention, the silicon dioxide layer is preferably formed by a wet or dry thermal oxidation process. The temperature of the wet or dry thermal oxidation process is preferably 800-1200°C, more preferably 900-1100°C, and the time is preferably 1-2000 minutes, more preferably 10-1000 minutes. The present invention has no special requirements for the specific operating method of the wet or dry thermal oxidation process, and those familiar to those skilled in the art can be used. The silicon nitride layer is preferably prepared by LPCVD. In a specific embodiment of the present invention, the SOI wafer is preferably first subjected to a wet or dry thermal oxidation process to form a silicon dioxide layer on the surface of the device layer. A silicon nitride layer is then deposited on the surface of the silicon dioxide layer. The silicon nitride layer and the silicon dioxide layer are then patterned to obtain a composite mask layer. During the patterning process, the silicon nitride layer is preferably removed by reactive ion etching (RIE) or phosphoric acid wet etching, and then the silicon nitride layer is etched by BOE wet etching. The BOE wet etching process preferably uses a 6:1 etchant (i.e., a 6:1 volume ratio of 40 wt% NH4F aqueous solution to 49 wt% HF aqueous solution). If a silicon nitride layer is not required, the preparation of the silicon nitride layer is omitted, and the patterning process can be performed directly after the silicon dioxide layer is obtained.

[0131] After preparing the mask layer, the present invention performs a thermal oxidation treatment on the SOI wafer with the mask layer. In the present invention, the thermal oxidation treatment temperature is preferably 800-1200°C, and the treatment time is preferably 10-1000 minutes. During the thermal oxidation process, the thick silicon dioxide in the mask layer acts as an oxidation penetration layer, and the thin silicon nitride acts as a barrier layer. The silicon in the SOI wafer is thermally oxidized at high temperature, forming a silicon-silicon dioxide interface with a three-dimensional, non-uniform surface. The silicon dioxide in the mask layer acts as a mask penetration layer, and its thickness can adjust the curvature of the interface, while the oxidation time can control the depth of the interface. The mask layer and the silicon dioxide produced by the thermal oxidation are later removed to form a non-uniform surface structure, specifically a curved surface structure. The present invention does not specifically limit the removal method; methods familiar to those skilled in the art can be used. In the present invention, the silicon nitride removal method is preferably reactive ion etching (RIE) or phosphoric acid wet etching; the silicon dioxide removal method preferably includes reactive ion etching, BOE, or HF wet etching.

[0132] In the present invention, the special-shaped surface structure specifically includes a curved surface, a step, a slope, or a composite special-shaped surface composed of multiple curved surfaces, multiple steps, or multiple slopes.

[0133] After obtaining the electrode plate and substrate to be bonded, the present invention bonds the electrode plate and substrate to form a micro-nano chamber, then removes the substrate layer, buried oxide layer, and portions of the device layer to obtain a conformal electrode. In the present invention, the bonding method preferably includes anodic bonding or laser bonding. The present invention does not specifically limit the bonding process; methods familiar to those skilled in the art may be employed.

[0134] In the present invention, the method for removing the substrate layer preferably includes one or more of wet etching, dry etching, and mechanical polishing. In the present invention, the wet etching preferably includes wet etching with tetramethylammonium hydroxide (TMAH) or potassium hydroxide (KOH). In a specific embodiment of the present invention, the substrate removal process preferably includes first removing a portion of the substrate layer by mechanical polishing, preferably until the remaining thickness of the substrate layer is 50-200 μm, and then removing the remaining substrate layer by wet etching with tetramethylammonium hydroxide or potassium hydroxide. In the present invention, the concentration of the tetramethylammonium hydroxide solution used in the tetramethylammonium hydroxide (TMAH) etching is preferably 5-50 wt%; the silicon etching rate of the tetramethylammonium hydroxide etching is preferably 0.2-2 μm / min, and the etching temperature is preferably 25-100°C. In the present invention, the concentration of the potassium hydroxide solution used in the potassium hydroxide (KOH) wet etching is preferably 5-50 wt%; the silicon etching rate of the potassium hydroxide etching is preferably 0.2-5 μm / min, and the etching temperature is preferably 25-120°C. In the present invention, the buried oxide layer removal method preferably includes reactive ion etching (RIE), BOE, or HF wet etching. In the present invention, the device layer removal method preferably includes mechanical polishing, CMP, KOH, or TMAH wet etching. The present invention has no special requirements for the thickness of the device layer selected or removed, and can be set according to the thickness of the target conformal electrode.

[0135] After obtaining the conformal electrode, the present invention prepares a resonant plate or resonant film on the upper surface of the conformal electrode, then etches the resonant plate or resonant film to expose a portion of the conformal electrode. The conformal electrode is then etched to expose the second through-hole electrode of the TGV glass substrate. In the present invention, the preparation method of the resonant plate or resonant film preferably includes sputtering, evaporation, electroplating, low-pressure chemical vapor deposition (LPCVD), or plasma-enhanced chemical vapor deposition (PECVD). The present invention has no particular requirements for the etching method, and methods familiar to those skilled in the art can be used.

[0136] After the second via electrode is exposed, the present invention forms a metal top electrode at the location on the TGV glass substrate corresponding to the second via electrode, with the edge of the metal top electrode contacting the edge of the conformal electrode. In the present invention, a layer of metal electrode is preferably first sputtered on the surface of the device, and then the unwanted portion is removed through a patterning process, leaving the remaining portion as the metal top electrode; the patterning process is preferably performed by reactive ion etching (RIE) or wet etching.

[0137] In the present invention, when the MEMS ultrasonic transducer includes a passivation layer, before step (6), it is preferred that a passivation layer be prepared on the surface of the structural unit, specifically a passivation layer be prepared on the exposed surface of the resonant plate, the metal upper electrode, and the conformal electrode; in the present invention, the method for preparing the passivation layer preferably includes sputtering, atomic layer deposition (ALD), low pressure chemical vapor deposition (LPCVD), or plasma enhanced chemical vapor deposition (PECVD). The present invention does not specifically limit the specific preparation process of the passivation layer, and a method well known to those skilled in the art can be used.

[0138] After the above structure is prepared, the present invention sequentially forms a first under-bump UBM layer and a first ball grid electrode on the lower surface of the first through-hole electrode of the TGV glass substrate, and sequentially forms a second under-bump UBM layer and a second ball grid electrode on the lower surface of the second through-hole electrode, thereby obtaining the MEMS ultrasonic transducer. The present invention does not specifically limit the preparation process of the first under-bump UBM layer, the second under-bump UBM layer, the first ball grid electrode, and the second ball grid electrode; methods familiar to those skilled in the art can be used.

[0139] In the present invention, when the structure of the MEMS ultrasonic transducer belongs to case 1, and the conformal electrode and the resonant plate or the resonant membrane are integrated into one, the method for preparing the MEMS ultrasonic transducer includes the following steps (referred to as method 2):

[0140] (1) providing a TGV glass substrate having a first through-hole electrode and a second through-hole electrode; sequentially preparing a metal bottom electrode and an insulating layer at a position on the TGV glass substrate corresponding to the first through-hole electrode to obtain a substrate to be bonded;

[0141] (2) Providing an SOI wafer; the SOI wafer includes a device layer, a buried oxide layer, and a substrate layer stacked in layers; the thickness of the device layer is greater than the total thickness of the conformal electrode and the resonant plate; preparing a mask layer on the surface of the device layer in an area corresponding to the bonding position with the TGV glass substrate, and then performing a thermal oxidation treatment on the SOI wafer, and then removing the mask layer and the silicon dioxide generated by the thermal oxidation to obtain a plate to be bonded; the mask layer is a silicon dioxide mask layer or a composite mask layer; the composite mask layer includes a silicon nitride layer and a silicon dioxide layer stacked in sequence from top to bottom;

[0142] (3) bonding the electrode plate to be bonded and the substrate to be bonded to form a micro-nano chamber, removing the substrate layer and the buried oxide layer, and controlling the thickness of the remaining device layer to be the total thickness of the conformal electrode and the resonant plate to obtain an integrated structure of the conformal electrode and the resonant plate;

[0143] (4) etching the integrated structure of the conformal electrode and the resonant plate to expose the second through-hole electrode of the TGV glass substrate;

[0144] (5) preparing a metal top electrode at a position on the TGV glass substrate corresponding to the second through-hole electrode, and making the metal top electrode cover the conformal electrode and the integrated structure of the resonant plate;

[0145] (6) sequentially preparing a first bump bottom UBM layer and a first ball grid electrode on the lower surface of the first through-hole electrode of the TGV glass substrate, and sequentially preparing a second bump bottom UBM layer and a second ball grid electrode on the lower surface of the second through-hole electrode to obtain the MEMS ultrasonic transducer;

[0146] There is no time sequence restriction for steps (1), (2) and (6).

[0147] Figure 8 This is a flow chart of the preparation process when the structure of the MEMS ultrasonic transducer belongs to case 1 and the conformal electrode and the resonant plate are integrated into one.

[0148] In the present invention, when the structure of the MEMS ultrasonic transducer belongs to case 1, and the materials of the conformal electrode and the resonant plate are both single crystal silicon or both polycrystalline silicon, the preparation of the resonant plate or the resonant membrane is omitted, and in step (2), a SOI wafer with a thicker device layer is selected, and during the thermal oxidation treatment, the thickness of the remaining device layer is controlled by controlling the time of thermal oxidation, so that the thickness of the remaining device layer is equal to the total thickness of the conformal electrode and the resonant plate, thereby integrating the resonant plate and the conformal electrode. In addition, in step (4), the conformal electrode and the resonant plate integrated structure are directly etched, and when the metal upper electrode is prepared in step (5), the metal upper electrode is directly covered with the conformal electrode and the resonant plate integrated structure. The operating conditions of the remaining steps are consistent with those in method 1.

[0149] In the present invention, when the MEMS ultrasonic transducer includes a passivation layer, before step (6), it is preferably further included to prepare a passivation layer on the surface of the structural unit, specifically to prepare a passivation layer on the exposed surface of the conformal electrode and resonant plate integrated device; the preparation method of the passivation layer is consistent with the above-mentioned scheme and will not be repeated here.

[0150] In the present invention, when the structure of the MEMS ultrasonic transducer belongs to case 1 and is further provided with a bonding dielectric layer, the method for preparing the MEMS ultrasonic transducer includes the following steps (referred to as method 3):

[0151] Providing a TGV glass substrate with a first through-hole electrode and a second through-hole electrode; sequentially preparing a metal bottom electrode and an insulating layer at a position on the surface of the TGV glass substrate corresponding to the first through-hole electrode, and depositing a bonding dielectric layer at the device edge of the TGV glass substrate to obtain a substrate to be bonded;

[0152] Then, the MEMS ultrasonic transducer is prepared according to steps (2) to (6) of method 1, or according to steps (2) to (6) of method 2, to obtain the MEMS ultrasonic transducer. Moreover, when the MEMS ultrasonic transducer further includes a passivation layer, the passivation layer can be prepared according to the steps of method 1 or method 2.

[0153] Figure 9 This is a flow chart of the preparation process when the structure of the MEMS ultrasonic transducer belongs to case 1 and is also provided with a bonding medium layer.

[0154] The present invention has no special limitation on the preparation process of the bonding dielectric layer, and any method well known to those skilled in the art may be used.

[0155] In the present invention, when the structure of the MEMS ultrasonic transducer belongs to the second case, the method for preparing the MEMS ultrasonic transducer includes the following steps (referred to as method four):

[0156] (1) providing a TGV glass substrate with a first through-hole electrode and a second through-hole electrode; sequentially preparing a metal bottom electrode and an insulating layer at a position of the TGV glass substrate corresponding to the first through-hole electrode, and depositing a bonding dielectric layer at the device edge of the TGV glass substrate to obtain a substrate to be bonded;

[0157] (2) Providing an SOI wafer; the SOI wafer includes a device layer, a buried oxide layer, and a substrate layer stacked in layers; preparing a mask layer on the surface of the device layer in an area corresponding to the bonding position with the TGV glass substrate, then thermally oxidizing the SOI wafer, and then removing the mask layer and the silicon dioxide generated by the thermal oxidation to obtain a silicon-based mold with a special-shaped surface; the mask layer is a silicon dioxide mask layer or a composite mask layer; the composite mask layer includes a silicon nitride layer and a silicon dioxide layer stacked in sequence from top to bottom;

[0158] (3) sequentially preparing a barrier layer, a resonant film, and a conformal electrode on the surface of the silicon-based mold with the irregular surface to obtain a plate to be bonded;

[0159] (4) bonding the electrode plate to be bonded and the substrate to be bonded to form a micro-nano chamber, and removing the substrate layer, buried oxide layer, device layer and barrier layer; etching the resonant film to expose the conformal electrode; then etching the conformal electrode and the bonding dielectric layer to expose the second through-hole electrode of the TGV glass substrate;

[0160] (5) preparing a metal top electrode at a position on the TGV glass substrate corresponding to the second through-hole electrode, and making the edge of the metal top electrode contact the edge of the conformal electrode;

[0161] (6) sequentially preparing a first bump bottom UBM layer and a first ball grid electrode on the lower surface of the first through-hole electrode of the TGV glass substrate, and sequentially preparing a second bump bottom UBM layer and a second ball grid electrode on the lower surface of the second through-hole electrode to obtain the MEMS ultrasonic transducer;

[0162] There is no time sequence limitation for step (1), step (2) and step (6).

[0163] Figure 10 This is a flow chart of the preparation process when the structure of the MEMS ultrasonic transducer belongs to situation two.

[0164] The present invention provides a TGV glass substrate with a first through-hole electrode and a second through-hole electrode. A metal bottom electrode and an insulating layer are sequentially formed at locations corresponding to the first through-hole electrodes on the TGV glass substrate, and a bonding dielectric layer is deposited at the device edge of the TGV glass substrate to obtain a substrate to be bonded. The methods for preparing the metal bottom electrode, insulating layer, and bonding dielectric layer are the same as those described above and are not further described here.

[0165] The specific operation method of step (2) in method 4 is preferably the same as that in method 1 and will not be repeated here.

[0166] In the present invention, the special-shaped surface of the special-shaped silicon-based mold specifically includes a curved surface, a step, a slope, or a composite special-shaped surface consisting of multiple curved surfaces, multiple steps, or multiple slopes.

[0167] After obtaining the silicon-based mold with an irregular surface, the present invention sequentially prepares a barrier layer, a resonant film and a conformal electrode on the surface of the silicon-based mold with an irregular surface to obtain a plate to be bonded. In the present invention, the material of the barrier layer is preferably silicon oxide or silicon nitride, and the thickness of the barrier layer is preferably 0.1 μm to 10 μm. In the present invention, the method for preparing the barrier layer is preferably thermal oxidation, low-pressure chemical vapor deposition (LPCVD) or plasma-enhanced chemical vapor deposition (PECVD). In the present invention, the method for preparing the resonant film is preferably sputtering, evaporation or electroplating, low-pressure chemical vapor deposition (LPCVD) or plasma-enhanced chemical vapor deposition (PECVD). In the present invention, the method for preparing the conformal electrode is preferably sputtering, evaporation or electroplating.

[0168] After obtaining the electrode plate to be bonded and the substrate to be bonded, the present invention bonds the electrode plate to be bonded and the substrate to be bonded to form a micro-nano chamber, and removes the substrate layer, buried oxide layer, device layer and barrier layer; etches the resonant film to expose the conformal electrode; then etches the conformal electrode and the bonding dielectric layer to expose the second through-hole electrode of the TGV glass substrate. In the present invention, the bonding is intermediate dielectric bonding; the present invention has no special limitation on the process of the intermediate dielectric bonding, and it can be done by methods well known to those skilled in the art. In the invention, the method for removing the substrate layer, buried oxide layer and device layer is consistent with the above-mentioned technical solution and will not be repeated here. In the present invention, the method for removing the barrier layer is preferably RIE, DRIE etching or wet etching. The present invention has no special requirements for the specific operation method of the etching, and a method familiar to those skilled in the art can be used. In a specific embodiment of the present invention, it is preferred to first etch the resonant film to expose the conformal electrode and the bonding dielectric layer above the second through-hole electrode, and then etch the conformal electrode and the bonding dielectric layer in this area to expose the second through-hole electrode.

[0169] The preparation methods of the metal top electrode, the first bump bottom UBM layer, the second bump bottom UBM layer, the first ball grid electrode and the second ball grid electrode in the fourth method are the same as those in the first method and will not be repeated here.

[0170] In the present invention, when the MEMS ultrasonic transducer also includes a passivation layer, it also includes preparing a passivation layer on the surface of the obtained structural unit, specifically preparing a passivation layer on the exposed surface of the conformal electrode, the resonant membrane and the metal upper electrode; the specific preparation method is the same as the above-mentioned scheme and will not be repeated here.

[0171] In the present invention, when the structure of the MEMS ultrasonic transducer meets the second condition, the material of the resonant plate or resonant membrane is metal, and the material of the resonant plate or resonant membrane is the same as the material of the conformal electrode, the conformal electrode and the resonant plate or resonant membrane form an integral structure, and the metal upper electrode is omitted. In this case, the preparation method of the MEMS ultrasonic transducer includes the following steps (referred to as method five):

[0172] (1) providing a TGV glass substrate with a first through-hole electrode and a second through-hole electrode; sequentially preparing a metal bottom electrode and an insulating layer at a position corresponding to the first through-hole electrode on the surface of the TGV glass substrate, and depositing a bonding dielectric layer at the device edge of the TGV glass substrate to obtain a substrate to be bonded;

[0173] (2) Providing an SOI wafer; the SOI wafer includes a device layer, a buried oxide layer, and a substrate layer stacked in layers; preparing a mask layer on the surface of the device layer in an area corresponding to the bonding position with the TGV glass substrate, and then performing a thermal oxidation treatment on the SOI wafer, and then removing the mask layer and the silicon dioxide generated by the thermal oxidation to obtain a silicon-based mold with a special-shaped surface; the mask layer is a silicon dioxide mask layer or a composite mask layer; the composite mask layer includes a silicon nitride layer and a silicon dioxide layer stacked in sequence from top to bottom;

[0174] (3) sequentially preparing a barrier layer, a resonant film, and a conformal electrode integrated structure layer on the irregular surface of the irregular surface silicon-based mold to obtain a plate to be bonded;

[0175] (4) bonding the electrode plate to be bonded and the substrate to be bonded to form a micro-nano chamber, and contacting the resonant film and conformal electrode integrated structure layer with the second through-hole electrode of the TGV glass substrate; removing the substrate layer, buried oxide layer, device layer and barrier layer; etching the resonant film and conformal electrode integrated structure layer and the bonding dielectric layer to expose the TGV glass substrate at the edge of the device;

[0176] (5) sequentially preparing a first bump bottom UBM layer and a first ball grid electrode on the lower surface of the first through-hole electrode of the TGV glass substrate, and sequentially preparing a second bump bottom UBM layer and a second ball grid electrode on the lower surface of the second through-hole electrode to obtain the MEMS ultrasonic transducer;

[0177] There is no time sequence restriction for steps (1), (2) and (5).

[0178] In the present invention, steps (1) to (2) of the fifth method are preferably the same as those of the fourth method. The method for preparing the barrier layer in step (3) of the fifth method is the same as that of the fourth method. The method for preparing the integrated structure layer of the resonant film and the conformal electrode is the same as that of the resonant film in the fourth method, except that the thickness is increased to control the total thickness to be the sum of the thickness of the resonant film and the conformal electrode. The operation of step (4) of the fifth method is the same as that of the fourth method, except that the specific etching position during etching is different. When the integrated structure of the conformal electrode and the resonant film can have relatively good electrical contact with the bonding dielectric layer and the second through-hole electrode, it is not necessary to expose the second through-hole electrode before making the metal top electrode.

[0179] In addition, when the MEMS ultrasonic transducer further includes a passivation layer, the passivation layer can be prepared according to the steps in method four.

[0180] Figure 11 This is a flow chart of the preparation process when the structure of the MEMS ultrasonic transducer belongs to case 2, the metal upper electrode is omitted, and the conformal electrode and the resonant plate or resonant membrane are integrated into one.

[0181] In the present invention, when the structure of the MEMS ultrasonic transducer is case 2, and the material of the conformal electrode is metal, and the metal has the function of a bonding dielectric layer, the bonding dielectric layer is omitted. In this case, the method for preparing the MEMS ultrasonic transducer includes the following steps (referred to as method 6):

[0182] The preparation is carried out according to steps (1) to (6) in method 4, omitting only the bonding dielectric layer. Furthermore, when the MEMS ultrasonic transducer further includes a passivation layer, the passivation layer can be prepared according to the steps in method 4.

[0183] Figure 12 This is a flow chart of the preparation process when the structure of the MEMS ultrasonic transducer belongs to case 2 and the bonding dielectric layer is omitted.

[0184] The present invention also provides a capacitive MEMS ultrasonic transducer array, comprising a plurality of transducer units distributed in an array structure; the transducer unit is the MEMS ultrasonic transducer described in the above scheme or a MEMS ultrasonic transducer prepared by the preparation method described in the above scheme.

[0185] In the present invention, the transducer units in the capacitive MEMS ultrasonic transducer array can include various shapes, which are not specifically limited in the present invention, and can include polygons such as circles, squares, rectangles, ellipses, pentagons, hexagons, and octagons. The present invention has no special requirements for the number of the capacitive MEMS ultrasonic transducer array, and can be a large-scale array of N×M, and the specific number is not limited in the present invention.

[0186] In the present invention, a substrate unit of a plurality of transducer units distributed in an array structure forms an integral structure.

[0187] In the present invention, the passivation layers of multiple transducer units distributed in an array structure form a whole, that is, when preparing the transducer array, the device structure except the passivation layer is first prepared, and then the passivation layer is uniformly deposited and the surface of the device is completely covered with the passivation layer.

[0188] As a special case of the present invention, the second through-hole electrode and the second ball grid electrode in each transducer unit in the array are omitted, and a total through-hole electrode is provided at the edge of the capacitive MEMS ultrasonic transducer array, and a ball grid electrode is provided at the bottom of the total through-hole electrode; each transducer unit in the array is electrically connected to the total through-hole electrode through a metal top electrode; in this case, the cross-sectional view of the capacitive MEMS ultrasonic transducer array (3×3 array) is as follows Figure 13 As shown, the top view is Figure 14 shown.

[0189] In the present invention, the preparation method of the MEMS ultrasonic transducer refers to the preparation method of the ultrasonic transducer described in the above technical solution, and can be prepared according to the array structure.

[0190] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0191] Example 1

[0192] Taking a new CMUT with conformal electrodes made of single crystal silicon and a resonant membrane made of non-silicon as a specific example, a new CMUT manufacturing process based on local oxidation of silicon (LOCOS) and anodic bonding technology is demonstrated. Figure 7 As shown in the figure, the conformal electrode material is single-crystal silicon, and the resonant membrane is a non-silicon material. The operating frequency of the new CMUT is set to 1.0 MHz. The resonant membrane thickness is 2 μm. The CMUT radius is 65 μm, and the cavity height is 0.4 μm to achieve a reasonable driving voltage.

[0193] The specific process steps are as follows:

[0194] (a) A 500 μm thick TGV glass substrate was selected. The first and second through-hole electrodes had a through-hole radius of 20 μm and a spacing of 100 μm. Both the first and second through-hole electrodes were made of electroplated Cu.

[0195] (b) A Ti / Al electrode is sputtered onto a TGV glass substrate as the metal bottom electrode. The Ti layer is on the bottom, serving as an adhesion layer, and the Al layer is on the top. The Ti layer is 10 nm thick, and the Al layer is 300 nm thick. The sputtering power is 300 W, and the deposition rate is approximately 10 nm / min.

[0196] (c) PECVD is used to deposit a SiO2 insulating layer to obtain the substrate to be bonded. The insulating layer thickness is 250 nm, the deposition temperature is 250°C, the power is 200 W, and the rate is approximately 60 nm / min.

[0197] (d) Providing an SOI wafer having a device layer thickness of 2 μm, a buried oxide layer thickness of 0.5 μm, and a substrate layer thickness of 500 μm.

[0198] (e) The SOI wafer was thermally oxidized using a wet oxidation furnace (+H2O) process to form a 1μm-thick SiO2 mask layer at 1100°C for 135 minutes. A 100nm-thick SiN layer was deposited using LPCVD at 800°C for 35 minutes at a deposition rate of approximately 3nm / min. The mask was then patterned using photolithography. During the patterning process, the SiN layer was etched using RIE at an etch rate of approximately 25nm / min. The SiO2 layer was then etched using a wet 6:1 BOE at room temperature at an etch rate of approximately 90nm / min.

[0199] (f) The SOI wafer was subjected to a thermal oxidation treatment in an oxidation furnace with a wet method (+H2O) at a temperature of 1100°C and an oxidation time of 110 min, resulting in a silicon consumption of 397 nm.

[0200] (g) The SiN mask was removed using phosphoric acid (H3PO4) at a water bath temperature of 155°C at an etching rate of approximately 3.2 nm / min. The SiO2 mask and the thermally oxidized SiO2 were etched using a wet 6:1 BOE etching process at room temperature at a rate of approximately 90 nm / min. This resulted in the bonded plate.

[0201] (h) Anodically bonding the formed bonding plate to the substrate to be bonded to form a micro-nano cavity. The bonding temperature is 400°C, the voltage is 600V, and the height of the micro-nano cavity is 397nm.

[0202] (i) The substrate layer of the SOI wafer was removed by mechanical polishing to a thickness of 100 μm. The remaining substrate was then removed by wet etching with 20% TMAH at an 80°C water bath temperature and an etch rate of 0.6 μm / min. The buried oxide layer was then wet-etched with 6:1 BOE at room temperature at an etch rate of approximately 90 nm / min. This formed a conformal electrode.

[0203] (j) A 2 μm thick SiN resonant film was deposited by LPCVD at a temperature of 800°C and a pressure of 250 mtorr for approximately 200 min.

[0204] (k) RIE etching of the SiN resonant film reveals a portion of the single-crystal silicon conformal electrode. Etching power: 1600W, bias voltage: -530V, pressure: 40mtorr, etch rate: 50nm / min. DRIE etching of the single-crystal silicon conformal electrode reveals the second via electrode on the TGV glass substrate and the glass substrate at the device edge. Etching power: 500W, bias voltage: -530V, pressure: 40mtorr, etch rate: 50nm / min.

[0205] (l) After cleaning, a 300nm thick Al-2% Si electrode layer was sputtered. The sputtering power was 300W, and the deposition rate was approximately 10nm / min. The electrode was then patterned by photolithography to form a metal top electrode, which established an ohmic contact with the single-crystal silicon conformal electrode.

[0206] (m) PECVD deposition of a SiO2 passivation layer with a thickness of 100 nm at a temperature of 250°C, a power of 200 W, and a rate of approximately 60 nm / min.

[0207] (n) electroplating and patterning a UBM layer under the through-hole electrode to obtain a first UBM layer and a second UBM layer on the lower surface of the first through-hole electrode and the second through-hole electrode; and preparing a first ball grid electrode and a second ball grid electrode on the lower surface of the patterned UBM.

[0208] Example 2

[0209] Taking a new CMUT with conformal electrodes and a resonant plate made of single-crystal silicon as a specific example, a new CMUT manufacturing process based on local oxidation of silicon (LOCOS) and anodic bonding technology is demonstrated. Figure 8 As shown in the figure, both the conformal electrode and the resonant plate are made of single-crystal silicon. The operating frequency of the new CMUT is set to 1.0 MHz. To reduce geometric nonlinearity, a 20 μm thick resonant plate is selected. The CMUT has a radius of 220 μm and a cavity height of 0.4 μm.

[0210] The specific process steps are as follows:

[0211] (a) Following steps (a) to (c) in Example 1, a metal bottom electrode and an insulating layer were prepared on a TGV glass substrate. The spacing between the first through-hole electrode and the second through-hole electrode was 270 μm. The remaining steps were the same as in Example 1.

[0212] (b) Provide an SOI wafer. The device layer of the SOI wafer has a thickness of 20 μm, the buried oxide layer has a thickness of 1 μm, and the substrate layer has a thickness of 500 μm.

[0213] (c) According to steps (e) to (g) in Example 1, the integrated structure of the conformal electrode and the resonant plate is prepared to obtain the electrode plate to be bonded.

[0214] (d) According to steps (h)-(i) in Example 1, the anodic bonding of the electrode to be bonded and the substrate to be bonded is completed, and the SOI substrate layer and the buried oxide layer are removed to form an integrated structure of the conformal electrode and the resonant electrode.

[0215] (e) The integrated structure of the single-crystal silicon conformal electrode and the resonant plate is patterned by etching using the DRIE method at a power of 500 W and a rate of 0.5 μm / min, revealing the second through-hole electrode on the TGV glass substrate and the glass substrate at the edge of the device.

[0216] (f) According to steps (1) and (m) in Example 1, the metal top electrode and the passivation layer are prepared.

[0217] (g) According to step (n) in Example 1, the UBM layer and the ball grid array are prepared.

[0218] Example 3

[0219] Taking a new CMUT with conformal electrodes and conformal resonant membranes made of metal and non-metal as a specific example, a manufacturing process of a new CMUT based on silicon-based mold and dielectric layer bonding technology is demonstrated. Figure 10 As shown in Figure 2, the resonant membrane has a conformal structure consistent with that of the conformal electrode. Its material is non-metallic, while the conformal electrode is made of metal. The operating frequency of the new CMUT is set to 1.0 MHz. The resonant membrane has a thickness of 2 μm, a radius of 65 μm, and a cavity height of 0.4 μm.

[0220] The specific process steps are as follows:

[0221] (a) According to the steps in Example 1, the metal bottom electrode and the insulating layer on the TGV glass substrate are prepared.

[0222] (b) Ti, Pt, and Au were sequentially sputtered and patterned onto a TGV glass substrate to form a bonding dielectric layer. The Ti layer had a thickness of 10 nm, the Pt layer had a thickness of 30 nm, and the Au layer had a thickness of 200 nm. The sputtering power for Ti, Pt, and Au was 300 W, and the deposition rate was 10 nm / min. This yielded the substrate to be bonded.

[0223] (c) Following the steps in Example 1, the silicon-based mold is manufactured. Compared with the structure containing the silicon conformal electrode prepared in Example 1, the silicon-based mold here can be appropriately thinner.

[0224] (d) A 300nm-thick SiO2 barrier layer is formed on the silicon-based mold surface using thermal oxidation at 1050°C for 25 minutes. A 2μm-thick SiN resonant film is then deposited on the barrier layer surface using LPCVD at 800°C, a pressure of 250 mtorr, and a deposition time of approximately 200 minutes. A 200nm-thick Au electrode layer is then sputtered onto the SiN surface as a conformal electrode at a sputtering power of 300W and a deposition rate of approximately 10nm / min. This results in the bonded electrode.

[0225] (e) Bonding the substrate to be bonded and the electrode to be bonded using a gold-gold hot-compression bonding method at a bonding temperature of 300° C. and a pressure of 7 MPa.

[0226] (f) Mechanical polishing removes most of the backing silicon from the bond pad to a thickness of 100 μm. The remaining silicon is then removed using a 20% TMAH wet etch at an 80°C water bath temperature and an etch rate of approximately 0.6 μm / min. The buried oxide layer is then etched using a 6:1 BOE wet etchant at room temperature at an etch rate of approximately 90 nm / min. The silicon mold is then removed using a 20% TMAH wet etchant.

[0227] (g) The SiO2 barrier layer is etched using the RIE method with an etching power of 1600W, a bias voltage of -530V, a pressure of 40mtorr, and an etching rate of approximately 30nm / min.

[0228] (h) Patterning: RIE is used to etch the SiN resonant film to expose part of the conformal electrode. The etching power is 1600 W, the bias voltage is -530 V, the pressure is 40 mtorr, and the etching rate is 50 nm / min.

[0229] (i) RIE was used to etch the conformal electrode and bonding dielectric layer, revealing the second via electrode on the TGV glass substrate and the glass substrate at the device edge. Etching power was 600 W, chamber pressure was 100 mT, temperature was 60°C, and etch rate was 0.5 μm / min.

[0230] (j) After cleaning, a 300 nm thick Al-2% Si electrode layer was sputtered at a power of 300 W and a deposition rate of approximately 10 nm / min. The electrode layer was patterned by photolithography to obtain a metal top electrode.

[0231] (l) PECVD was used to deposit a SiO2 passivation layer with a thickness of 100 nm at a deposition temperature of 250 °C, a power of 200 W, and a rate of approximately 60 nm / min;

[0232] (m) electroplating a UBM layer under the through-hole electrode and patterning it to obtain a first UBM layer and a second UBM layer on the lower surfaces of the first through-hole electrode and the second through-hole electrode; and preparing a first ball grid electrode and a second ball grid electrode on the lower surface of the patterned UBM.

[0233] Example 4

[0234] Taking the new CMUT in which the resonant membrane and conformal electrode are both made of metal as a specific example, a manufacturing process of the new CMUT based on silicon mold and dielectric layer bonding technology is demonstrated. Figure 11 As shown in the figure, the resonant membrane and conformal electrodes are made of a special alloy with mechanical properties similar to silicon. The operating frequency of the new CMUT is set at 1.0 MHz. The resonant membrane thickness is 10 μm, the CMUT radius is 150 μm, and the cavity height is 0.4 μm.

[0235] The specific process steps are as follows:

[0236] (a) Following the steps in Example 3, a metal bottom electrode, an insulating layer, and a bonding dielectric layer were prepared on a TGV glass substrate. The spacing between the first and second via electrodes was 190 μm. All other conditions were the same as in Example 3, yielding a substrate to be bonded.

[0237] (b) Following the steps in Example 3, the silicon mold was fabricated and the SiO2 barrier layer was prepared;

[0238] (c) Electroplating a layer of titanium-nickel alloy (containing 1 wt% titanium, 52 wt% nickel, 20 wt% chromium, 0.7 wt% aluminum, 3.2 wt% molybdenum, 5.5 wt% niobium, 1 wt% cobalt, 0.3 wt% copper, 0.35 wt% manganese, 0.35 wt% silicon, 0.7 wt% aluminum, and 14.9 wt% iron) on the surface of the barrier layer to form an integrated structure of a resonant membrane and a conformal electrode. The thickness is 10 μm and the deposition rate is 0.2 μm / min. The electrode plate to be bonded is obtained.

[0239] (d) Bonding the substrate to be bonded and the electrode to be bonded using a gold-alloy hot-compression bonding method at a bonding temperature of 400° C. and a pressure of 10 MPa.

[0240] (e) Following the steps in Example 3, the SOI substrate layer, buried oxide layer, silicon mold, SiO2 barrier layer are removed, the passivation layer at the edge of the device is protected, and the UBM layer and ball gate electrode are prepared.

[0241] By establishing a multi-physics field simulation model of CMUT, the core performance of the CMUT prepared in Examples 1 to 4, such as the pull-down voltage, transmission and reception sensitivity, is obtained. Taking Example 2 as an example, the pull-down voltage of the CMUT with traditional planar electrodes is 97.1V, while the pull-down voltage of the CMUT with conformal curved electrodes is only 44.7V. Compared with the traditional planar electrodes, the conformal electrodes can reduce the pull-down voltage by at least 50%. The conformal curved electrode MEMS ultrasonic transducer prepared in Example 2 transmits sound pressure sensitivity in liquid propagation medium. Figure 15 As shown. Usually the driving voltage is a percentage voltage, that is, a percentage of the maximum pull-down voltage. When the driving voltage is 80%, the maximum sound pressure sensitivity of the CMUT with a traditional planar electrode is 4.52kPa / V, while the maximum sound pressure sensitivity of the CMUT with a conformal curved electrode is 8.70kPa / V. Compared with the traditional planar electrode, the sensitivity of the conformal curved electrode is improved by at least 90%. The receiving voltage sensitivity of the gas propagation medium of the conformal curved electrode MEMS ultrasonic transducer prepared in Example 2 is shown in FIG. Figure 16 As shown. Figure 16 The results show that the use of TGV glass substrate can almost eliminate the influence of parasitic capacitance, making the electromechanical coupling coefficient of the transducer reach above 0.8. Compared with the traditional silicon substrate, the receiving voltage sensitivity of the TGV glass substrate is significantly improved by more than 40%. Figures 15 and 16 In the example, a conventional silicon substrate flat electrode MEMS ultrasonic transducer is used as a comparison. The structure of the conventional silicon substrate flat electrode MEMS ultrasonic transducer is as follows: Figure 17 shown.

[0242] Although the above embodiment provides a detailed description of the present invention, it is only a part of the embodiments of the present invention, not all of the embodiments. Other embodiments can be obtained based on this embodiment without creativity, and these embodiments all fall within the scope of protection of the present invention.

Claims

1. A MEMS ultrasonic transducer, characterized in that: comprising a substrate unit and a structural unit; The substrate unit includes a TGV glass substrate, a metal bottom electrode located on the upper surface of the TGV glass substrate, an insulating layer covering the upper surface of the metal bottom electrode, a first bump bottom UBM layer and a second bump bottom UBM layer located on the lower surface of the TGV glass substrate, a first ball grid electrode located on the lower surface of the first bump bottom UBM layer, and a second ball grid electrode located on the lower surface of the second bump bottom UBM layer; The TGV glass substrate is provided with a first through-hole electrode and a second through-hole electrode that vertically penetrates the TGV glass substrate; the metal bottom electrode is in ohmic contact with the first through-hole electrode; the area of ​​the insulating layer is larger than the area of ​​the metal bottom electrode; the first bump bottom UBM layer is in ohmic contact with the first through-hole electrode; the first ball grid electrode is in ohmic contact with the first bump bottom UBM layer; The second bump bottom UBM layer is in ohmic contact with the second through-hole electrode; the second ball grid electrode is in ohmic contact with the second bump bottom UBM layer; The structural unit includes a resonant plate or a resonant membrane, a conformal electrode, and a metal upper electrode; the lower surface of the conformal electrode is a special-shaped surface, and the edge of the lower surface is bonded to the upper surface of the TGV glass substrate to form a micro-nano cavity; the metal lower electrode and the insulating layer are located in the micro-nano cavity, and the insulating layer and the conformal electrode do not contact each other; A gap is provided at the edge of the conformal electrode at a position corresponding to the second through-hole electrode, and the metal top electrode is provided in the gap, located on the surface of the conformal electrode between the surface of the TGV glass substrate and the sidewall of the gap; the metal top electrode and the second through-hole electrode are in ohmic contact, and the edge of the metal top electrode contacts the edge of the conformal electrode, so that the conformal electrode and the second through-hole electrode are electrically connected; The resonant plate or resonant film is arranged on the upper surface of the conformal electrode; The metal lower electrode and the metal upper electrode form a pair of driving electrodes.

2. The MEMS ultrasonic transducer according to claim 1, wherein: The conformal electrode is made of silicon, which is single crystal silicon or polycrystalline silicon; the resonant plate or resonant film is made of a material different from that of the conformal electrode.

3. The MEMS ultrasonic transducer according to claim 2, wherein: The resonant plate or the resonant membrane is made of a non-metallic material or a metal material; the non-metallic material includes silicon nitride, silicon oxide, silicon carbide or diamond; the metal material is a metal element or an alloy.

4. The MEMS ultrasonic transducer according to claim 1, wherein: The conformal electrode is made of silicon, which is single crystal silicon or polycrystalline silicon. The resonant plate or resonant film is made of the same material as the conformal electrode. The conformal electrode and the resonant plate or resonant film form an integral structure.

5. The MEMS ultrasonic transducer according to claim 2 or 4, characterized in that: The MEMS ultrasonic transducer further includes a bonding dielectric layer; the bonding dielectric layer is arranged between the contact positions of the substrate unit and the conformal electrode.

6. The MEMS ultrasonic transducer according to claim 2 or 4, characterized in that: The upper surface of the conformal electrode is flat, and the resonant plate or resonant film is a flat resonant plate or a flat resonant film.

7. The MEMS ultrasonic transducer according to claim 1, wherein: The conformal electrode is made of a non-silicon material, which is a metal or semiconductor material; the metal is a metal element or an alloy; and the MEMS ultrasonic transducer includes a bonding dielectric layer; the bonding dielectric layer is arranged between the contact position between the substrate unit and the conformal electrode.

8. The MEMS ultrasonic transducer according to claim 7, characterized in that: The material of the resonant plate or the resonant membrane is non-metal or metal, and the non-metal includes silicon nitride, silicon oxide, silicon carbide or diamond; the metal is a metal element or an alloy.

9. The MEMS ultrasonic transducer according to claim 7, characterized in that: The conformal electrode is made of metal, and the resonant plate or resonant film is made of the same material as the conformal electrode; the conformal electrode and the resonant plate or resonant film form an integral structure, and the metal upper electrode is omitted.

10. The MEMS ultrasonic transducer according to claim 7 or 9, characterized in that: The conformal electrode is made of metal, and the metal has the function of a bonding dielectric layer, so the bonding dielectric layer is omitted.

11. The MEMS ultrasonic transducer according to any one of claims 7 to 9, characterized in that: The upper surface of the conformal electrode is a special-shaped surface, and the resonant plate or the resonant film is a special-shaped resonant plate or a special-shaped resonant film.

12. The MEMS ultrasonic transducer according to claim 1, 2 or 7, characterized in that: The diameters of the first through-hole electrode and the second through-hole electrode are independently 1 μm to 1 mm; the materials of the first through-hole electrode and the second through-hole electrode independently include metal or non-metal; the metal is a metal element or an alloy; the non-metal includes single crystal silicon or polycrystalline silicon.

13. The MEMS ultrasonic transducer according to claim 1, 2 or 7, characterized in that: The thickness of the metal upper electrode and the metal lower electrode is 10 nm to 1 μm; the material of the metal upper electrode and the metal lower electrode is metal; The thickness of the insulating layer is 10 nm to 1 μm; the material of the insulating layer includes one or more of silicon oxide, silicon nitride, aluminum oxide, aluminum nitride, hafnium oxide, zirconium oxide and tantalum oxide.

14. The MEMS ultrasonic transducer according to claim 1, 2 or 7, characterized in that: The surface of the structural unit is coated with a passivation layer; the thickness of the passivation layer is 0 to 10 μm; the material of the passivation layer includes one or more of silicon nitride, silicon oxide, aluminum oxide, phosphate glass and polyimide.

15. The MEMS ultrasonic transducer according to claim 5 or 7, characterized in that: The thickness of the bonding dielectric layer is 10 nm to 10 μm; the material of the bonding dielectric layer is metal, polymer or semiconductor material.

16. The method for preparing the MEMS ultrasonic transducer according to claim 2, 3 or 6, characterized in that: The following steps are involved: (1) providing a TGV glass substrate having a first through-hole electrode and a second through-hole electrode; sequentially preparing a metal bottom electrode and an insulating layer at a position on the surface of the TGV glass substrate corresponding to the first through-hole electrode to obtain a substrate to be bonded; (2) Providing an SOI wafer; the SOI wafer includes a device layer, a buried oxide layer, and a substrate layer stacked in layers; preparing a mask layer on the surface of the device layer in an area corresponding to the bonding position with the TGV glass substrate, and then performing a thermal oxidation treatment on the SOI wafer, and then removing the mask layer and the silicon dioxide generated by the thermal oxidation to obtain a plate to be bonded; the mask layer is a silicon dioxide mask layer or a composite mask layer; the composite mask layer includes a silicon nitride layer and a silicon dioxide layer stacked in sequence from top to bottom; (3) bonding the electrode plate to be bonded and the substrate to be bonded to form a micro-nano chamber, removing the substrate layer, the buried oxide layer and part of the device layer to obtain a conformal electrode; (4) preparing a resonant plate or a resonant film on the upper surface of the conformal electrode, then etching the resonant plate or the resonant film to expose a portion of the conformal electrode, and then etching the conformal electrode to expose the second through-hole electrode of the TGV glass substrate; (5) preparing a metal top electrode at a position on the surface of the TGV glass substrate corresponding to the second through-hole electrode, and making the edge of the metal top electrode contact the edge of the conformal electrode; (6) sequentially preparing a first bump bottom UBM layer and a first ball grid electrode on the lower surface of the first through-hole electrode of the TGV glass substrate, and sequentially preparing a second bump bottom UBM layer and a second ball grid electrode on the lower surface of the second through-hole electrode to obtain the MEMS ultrasonic transducer; There is no time sequence restriction for steps (1), (2) and (6).

17. The method for preparing the MEMS ultrasonic transducer according to claim 4 or 6, characterized in that: The following steps are involved: (1) providing a TGV glass substrate having a first through-hole electrode and a second through-hole electrode; sequentially preparing a metal bottom electrode and an insulating layer at a position on the surface of the TGV glass substrate corresponding to the first through-hole electrode to obtain a substrate to be bonded; (2) Providing an SOI wafer; the SOI wafer includes a device layer, a buried oxide layer, and a substrate layer stacked in layers; the thickness of the device layer is greater than the total thickness of the conformal electrode and the resonant plate; preparing a mask layer on the surface of the device layer in an area corresponding to the bonding position with the TGV glass substrate, and then performing a thermal oxidation treatment on the SOI wafer, and then removing the mask layer and the silicon dioxide generated by the thermal oxidation to obtain a plate to be bonded; the mask layer is a silicon dioxide mask layer or a composite mask layer; the composite mask layer includes a silicon nitride layer and a silicon dioxide layer stacked in sequence from top to bottom; (3) bonding the electrode plate to be bonded and the substrate to be bonded to form a micro-nano chamber, removing the substrate layer and the buried oxide layer, and controlling the thickness of the remaining device layer to be the total thickness of the conformal electrode and the resonant plate to obtain an integrated structure of the conformal electrode and the resonant plate; (4) etching the integrated structure of the conformal electrode and the resonant plate to expose the second through-hole electrode of the TGV glass substrate; (5) preparing a metal top electrode at a position corresponding to the second through-hole electrode on the surface of the TGV glass substrate, and making the metal top electrode cover the conformal electrode and the integrated structure of the resonant plate; (6) sequentially preparing a first bump bottom UBM layer and a first ball grid electrode on the lower surface of the first through-hole electrode of the TGV glass substrate, and sequentially preparing a second bump bottom UBM layer and a second ball grid electrode on the lower surface of the second through-hole electrode to obtain the MEMS ultrasonic transducer; There is no time sequence restriction for steps (1), (2) and (6).

18. The method for preparing the MEMS ultrasonic transducer according to claim 5 or 6, characterized in that: The following steps are involved: Providing a TGV glass substrate with a first through-hole electrode and a second through-hole electrode; sequentially preparing a metal bottom electrode and an insulating layer at a position on the surface of the TGV glass substrate corresponding to the first through-hole electrode, and depositing a bonding dielectric layer at the device edge of the TGV glass substrate to obtain a substrate to be bonded; The MEMS ultrasonic transducer is prepared according to steps (2) to (6) of the preparation method according to claim 16, or prepared according to steps (2) to (6) of the preparation method according to claim 17 to obtain the MEMS ultrasonic transducer.

19. The method for preparing the MEMS ultrasonic transducer according to claim 7, 8 or 11, characterized in that: The following steps are involved: (1) providing a TGV glass substrate with a first through-hole electrode and a second through-hole electrode; sequentially preparing a metal bottom electrode and an insulating layer at a position corresponding to the first through-hole electrode on the surface of the TGV glass substrate, and depositing a bonding dielectric layer at the device edge of the TGV glass substrate to obtain a substrate to be bonded; (2) Providing an SOI wafer; the SOI wafer includes a device layer, a buried oxide layer, and a substrate layer stacked in layers; preparing a mask layer on the surface of the device layer in an area corresponding to the bonding position with the TGV glass substrate, and then performing a thermal oxidation treatment on the SOI wafer, and then removing the mask layer and the silicon dioxide generated by the thermal oxidation to obtain a silicon-based mold with a special-shaped surface; the mask layer is a silicon dioxide mask layer or a composite mask layer; the composite mask layer includes a silicon nitride layer and a silicon dioxide layer stacked in sequence from top to bottom; (3) sequentially preparing a barrier layer, a resonant film, and a conformal electrode on the irregular surface of the irregular surface silicon-based mold to obtain a plate to be bonded; (4) bonding the electrode plate to be bonded and the substrate to be bonded to form a micro-nano chamber, and removing the substrate layer, buried oxide layer, device layer and barrier layer; etching the resonant film to expose the conformal electrode; then etching the conformal electrode and the bonding dielectric layer to expose the second through-hole electrode of the TGV glass substrate; (5) preparing a metal top electrode at a position on the surface of the TGV glass substrate corresponding to the second through-hole electrode, and making the edge of the metal top electrode contact the edge of the conformal electrode; (6) sequentially preparing a first bump bottom UBM layer and a first ball grid electrode on the lower surface of the first through-hole electrode of the TGV glass substrate, and sequentially preparing a second bump bottom UBM layer and a second ball grid electrode on the lower surface of the second through-hole electrode to obtain the MEMS ultrasonic transducer; There is no time sequence restriction for steps (1), (2) and (6).

20. The method for preparing the MEMS ultrasonic transducer according to claim 9 or 11, characterized in that: The following steps are involved: (1) providing a TGV glass substrate with a first through-hole electrode and a second through-hole electrode; sequentially preparing a metal bottom electrode and an insulating layer at a position corresponding to the first through-hole electrode on the surface of the TGV glass substrate, and depositing a bonding dielectric layer at the device edge of the TGV glass substrate to obtain a substrate to be bonded; (2) Providing an SOI wafer; the SOI wafer includes a device layer, a buried oxide layer, and a substrate layer stacked in layers; preparing a mask layer on the surface of the device layer in an area corresponding to the bonding position with the TGV glass substrate, and then performing a thermal oxidation treatment on the SOI wafer, and then removing the mask layer and the silicon dioxide generated by the thermal oxidation to obtain a silicon-based mold with a special-shaped surface; the mask layer is a silicon dioxide mask layer or a composite mask layer; the composite mask layer includes a silicon nitride layer and a silicon dioxide layer stacked in sequence from top to bottom; (3) sequentially preparing a barrier layer, a resonant film, and a conformal electrode integrated structure layer on the irregular surface of the irregular surface silicon-based mold to obtain a plate to be bonded; (4) bonding the electrode plate to be bonded and the substrate to be bonded to form a micro-nano chamber, and contacting the resonant film and conformal electrode integrated structure layer with the second through-hole electrode of the TGV glass substrate; removing the substrate layer, buried oxide layer, device layer and barrier layer; etching the resonant film and conformal electrode integrated structure layer and the bonding dielectric layer to expose the TGV glass substrate at the edge of the device; (5) sequentially preparing a first bump bottom UBM layer and a first ball grid electrode on the lower surface of the first through-hole electrode of the TGV glass substrate, and sequentially preparing a second bump bottom UBM layer and a second ball grid electrode on the lower surface of the second through-hole electrode to obtain the MEMS ultrasonic transducer; There is no time sequence restriction for steps (1), (2) and (5).

21. The method for preparing the MEMS ultrasonic transducer according to claim 10 or 11, characterized in that: The method comprises the following steps: preparing according to steps (1) to (6) in the preparation method according to claim 19, omitting only the bonding medium layer.

22. The preparation method according to any one of claims 16 to 21, characterized in that: Before preparing the first bottom bump UBM layer, the first ball grid electrode, the second bottom bump UBM layer and the second ball grid electrode, the method further includes preparing a passivation layer on the surface of the obtained structural unit.

23. A capacitive MEMS ultrasonic transducer array, characterized in that: It comprises a plurality of transducer units distributed in an array structure; the transducer unit is the MEMS ultrasonic transducer according to any one of claims 1 to 15 or the MEMS ultrasonic transducer prepared by the preparation method according to any one of claims 16 to 22.

24. The capacitive MEMS ultrasonic transducer array according to claim 23, wherein: A substrate unit of a plurality of transducer units distributed in an array structure forms an integral structure; The second through-hole electrode and the second ball grid electrode in each transducer unit in the array are omitted, and a total through-hole electrode is provided at the edge of the capacitive MEMS ultrasonic transducer array, and a ball grid electrode is provided at the bottom of the total through-hole electrode; each transducer unit in the array is electrically connected to the total through-hole electrode through a metal top electrode.

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