MEMS ultrasonic transducer, preparation method thereof and ultrasonic transducer array

Abstract

The invention belongs to the technical field of MEMS ultrasonic transducers and three-dimensional micro-nano manufacturing, and particularly relates to an MEMS ultrasonic transducer, a preparation method of the MEMS ultrasonic transducer and an ultrasonic transducer array. According to the invention, the conformal electrode can significantly enhance the electric field intensity outside the central area of the chamber, so that the sensitivity is significantly improved and the driving voltage is reduced; the TGV glass substrate can significantly reduce parasitic capacitance and improve sensitivity. Furthermore, the conformal electrode and the resonant plate or the resonant membrane can be made of metal or alloy, and compared with traditional monocrystalline silicon or silicon nitride and other materials, the mechanical life of the device can be remarkably prolonged, and the reliability of the device can be remarkably improved. The invention also provides a preparation method of the MEMS ultrasonic transducer. The preparation method provided by the invention can realize high-precision 3D processing of the conformal electrode, is good in consistency and low in cost, is suitable for large-scale array wafer-level manufacturing, can be compatible with an ASIC (Application Specific Integrated Circuit) process, and is easy to realize 3D integration with an ASIC.

Description

Technical Field

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

[0002] Capacitive MEMS ultrasonic transducer (CMUT) is an electrostatic conversion type ultrasonic sensor, which uses micro-electromechanical technology and capacitive sensing principle, and can achieve high-precision ultrasonic detection and high-sound pressure ultrasonic output. CMUT has the significant advantages of high sensitivity, high output sound pressure, large bandwidth, easy large-scale array manufacturing, and easy integration with ASIC. It has been widely used in medical imaging diagnosis and treatment, high-intensity focused ultrasound (HIFU), handheld personal medical ultrasound equipment, chemical sensing, and applications with gas as the transmission medium, becoming a powerful substitute for piezoelectric transducers.

[0003] The 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, thereby generating an electrical signal; when an AC signal is applied, the resonant plate or membrane vibrates under the action of electrostatic force and emits ultrasound. However, the performance of the traditional CMUT is limited by the planar electrode structure. Only the central area with the largest vibration amplitude and a size accounting for about 20% 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 purpose of the present invention is to provide a MEMS ultrasonic transducer and a preparation method thereof and an ultrasonic transducer array. The present invention proposes a new CMUT including a new structure and a new material, and proposes a corresponding preparation method, aiming to improve the receiving sensitivity of the CMUT, reduce the driving voltage, improve the imaging quality, reliability and other performance, and improve the processing accuracy and consistency of the device, and reduce the manufacturing cost.

[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 which penetrate the TGV glass substrate vertically; 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;

[0009] The structural unit includes a resonant plate or a resonant film, 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 chamber; the metal lower electrode and the insulating layer are located in the micro-nano chamber, and the insulating layer and the conformal electrode are not in contact;

[0010] The edge of the conformal electrode is provided with a gap at a position corresponding to the second through-hole electrode, and the metal upper electrode is provided at the gap, located on the surface of the TGV glass substrate and the conformal electrode surface of the gap sidewall; the metal upper electrode and the second through-hole electrode are in ohmic contact, and the edge of the metal upper electrode is in contact with 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; the resonance plate or resonance 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 metallic material; the non-metallic material includes silicon nitride, silicon oxide, silicon carbide or diamond; the metallic 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 resonance plate or resonance film is made of the same material as the conformal electrode; the conformal electrode and the resonance plate or resonance film form an integral structure.

[0016] Preferably, the MEMS ultrasonic transducer further comprises a bonding dielectric layer; the bonding dielectric layer is arranged between the positions where the substrate unit contacts the conformal electrode.

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

[0018] Preferably, the conformal electrode is made of non-silicon material, the non-silicon material is metal or semiconductor material; the metal is a metal element or 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.

[0019] Preferably, the material of the resonance plate or the resonance film 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 resonance plate or resonance film is made of the same material as the conformal electrode; the conformal electrode and the resonance plate or resonance film form an integral structure, and the metal upper electrode is omitted.

[0021] Preferably, the conformal electrode is made of metal, and the metal has a bonding dielectric layer function, 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 0-10 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 one), comprising the following steps:

[0029] (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 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 comprises a device layer, a buried oxide layer and a substrate layer which are stacked; 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 subjecting the SOI wafer to a thermal oxidation treatment, 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 comprises a silicon nitride layer and a silicon dioxide layer which are 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 an edge of the metal top electrode contact an 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 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 to obtain a substrate to be bonded;

[0038] (2) Providing an SOI wafer; the SOI wafer comprises a device layer, a buried oxide layer and a substrate layer which are stacked; 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 subjecting the SOI wafer to a thermal oxidation treatment, 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 comprises a silicon nitride layer and a silicon dioxide layer which are 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 upper electrode at a position on the surface of the TGV glass substrate corresponding to the second through-hole electrode, and making the metal upper 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 a MEMS ultrasonic transducer.

[0047] The present invention also provides a method for preparing the MEMS ultrasonic transducer described in the above scheme (method 4), 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 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;

[0049] (2) providing an SOI wafer; the SOI wafer comprises a device layer, a buried oxide layer and a substrate layer which are stacked; 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 subjecting the SOI wafer to a thermal oxidation treatment, 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 comprises a silicon nitride layer and a silicon dioxide layer which are 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 an edge of the metal top electrode contact an 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 five), 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 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;

[0057] (2) providing an SOI wafer; the SOI wafer comprises a device layer, a buried oxide layer and a substrate layer which are stacked; 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 subjecting the SOI wafer to a thermal oxidation treatment, 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 comprises a silicon nitride layer and a silicon dioxide layer which are stacked in sequence from top to bottom;

[0058] (3) sequentially preparing a barrier layer, a resonance film and a conformal electrode integrated structure layer on the profiled surface of the profiled 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 making the resonant film and conformal electrode integrated structure layer contact 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, characterized in that it includes 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 bump bottom UBM layer, the first ball grid electrode, the second bump bottom 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, 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 upper 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 chamber height, and the chamber height gradually decreases outside the 20% central area with the largest vibration amplitude. Therefore, the electric field strength outside the central area is significantly enhanced, and thus the sensitivity can be significantly improved and the driving voltage can be reduced compared with the traditional planar electrode. At the same time, after the resonance plate or resonance membrane is deformed under the drive of an AC signal, a relatively uniform chamber height can be obtained to maintain 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 the traditional silicon-based substrate that requires 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, which can eliminate the influence of parasitic capacitance and significantly improve the receiving sensitivity. Furthermore, the material of the conformal electrode and the resonance plate or resonance 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 through 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 profiled surface structure on 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 profiled surface can be directly used to prepare the conformal electrode. When the conformal electrode is made of other materials, the SOI wafer with a profiled 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 realize 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 easy to achieve 3D integration with ASIC. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0070] Figure 2 It is a schematic structural diagram of a MEMS ultrasonic transducer when the upper surface of the conformal electrode is a plane and the resonant plate or the resonant membrane is integrated with the conformal electrode;

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

[0072] Figure 4 The schematic diagram of the structure of the MEMS ultrasonic transducer is that the upper surface of the conformal electrode is a curved surface, the resonant plate or the resonant membrane is a curved resonant plate or a curved resonant membrane, the metal upper electrode is omitted, and the resonant plate or the resonant membrane is integrated with the conformal electrode;

[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 of the principle when the MEMS ultrasonic transducer is used as a transmitter;

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

[0076] Figure 8 It 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 resonance plate or the resonance membrane are integrated into one.

[0077] Fig. 9 is a preparation process flow chart when the structure of the MEMS ultrasonic transducer belongs to case 1 and a bonding medium layer is also provided;

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

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

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

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

[0082] Fig.14 is a top view of a capacitive MEMS ultrasonic transducer array (3×3 array);

[0083] Fig.15 This is a schematic diagram of the sensitivity effect of a conformal curved electrode MEMS ultrasonic transducer (Example 2);

[0084] Fig.16 This is a schematic diagram of the receiving sensitivity effect of the TGV glass substrate MEMS ultrasonic transducer;

[0085] Fig.17 It is a schematic diagram of the structure of a flat electrode MEMS ultrasonic transducer with a traditional silicon substrate;

[0086] Figures 1 to 14 as well as Fig.17 In the figure: 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 film, 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 film 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 treatment, 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 which vertically penetrate 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; 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 film, 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 chamber; the metal lower electrode and the insulating layer are located in the micro-nano chamber, and the insulating layer and the conformal electrode are not in contact;

[0091] The edge of the conformal electrode is provided with a gap at a position corresponding to the second through-hole electrode, and the metal upper electrode is provided at the gap, located on the surface of the TGV glass substrate and the conformal electrode surface of the gap sidewall, the metal upper electrode and the second through-hole electrode are in ohmic contact, and the edge of the metal upper electrode is in contact with 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 schematic diagram is as shown in Figure 1 shown).

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

[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 ( The alloys include, but are 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 the resonant film are made of the same material, which is single crystal silicon or polycrystalline silicon. When the conformal electrode and the resonant plate or the resonant film are made of single crystal silicon or polycrystalline silicon, the conformal electrode and the resonant plate or the resonant film are an integral structure. In this case, the structural schematic diagram of the MEMS ultrasonic transducer is as follows: Figure 2 shown.

[0099] As a special case of situation one, 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, polyparaxylene (Parylene), liquid crystal polymer (LCP), methylsilyl semi-siloxane (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 profiled surface, and the resonant plate or resonant film is preferably a profiled resonant plate or a profiled resonant film (recorded as case 2, the structural schematic 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 lower surface, and the shape of the special-shaped resonance plate or special-shaped resonance 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 an 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 alloys.

[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 between 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 the resonant film is also metal, the metal upper electrode is omitted, and the conformal electrode and the resonant plate or the resonant film 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 schematic diagram of the MEMS ultrasonic transducer is as follows: Figure 4 shown.

[0106] As a special case of the second case, 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 profiled surface, and the profiled surface includes a composite profiled surface consisting of a curved surface, a step, a slope, or 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 concave in the direction of the resonant plate or the resonant membrane, and the depth of the concave corresponding to the center of the micro-nano chamber is the largest; after the edge of the conformal electrode is bonded to the TGV glass substrate (directly bonded or bonded through a bonding dielectric layer), a micro-nano chamber is formed between the concave part of the profiled surface and the upper surface of the TGV glass substrate, and the micro-nano chamber is specifically located above the first through-hole electrode, and the second through-hole electrode is not inside the micro-nano chamber; the present invention has no special limitation on the size of the micro-nano chamber, and it can be used as those familiar to those skilled in the art. 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, and 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, which 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 are in 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 diameter of the first through-hole electrode and the second through-hole electrode is preferably 1 μm to 1 mm independently; the material of the first through-hole electrode and the second through-hole electrode independently includes metal or non-metal; the metal is a metal single substance or alloy, and the metal single substance 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 through-hole electrode and the second through-hole electrode is preferably 10 μm to 10 mm, and the spacing between the first through-hole electrode and the second through-hole electrode is preferably 20 μm to 20 mm.

[0112] In the present invention, the thickness of the metal bottom electrode is preferably 10nm to 1μm; the material of the metal bottom electrode is preferably metal, and the metal 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. 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 is in contact with 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 10nm to 1μm; 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 the device from short-circuiting when it is driven.

[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 2wt%.

[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 means 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 is covered on the exposed surface of the structural unit, specifically on the resonant plate or resonant film, the metal upper electrode and all exposed surfaces of the conformal electrode, including the upper surface and the side surface. The present invention uses 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 amplifying 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 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 It is a 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 situation 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 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 to obtain a substrate to be bonded;

[0121] (2) providing an SOI wafer; the SOI wafer comprises a device layer, a buried oxide layer and a substrate layer which are stacked; 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 subjecting the SOI wafer to a thermal oxidation treatment, 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 comprises a silicon nitride layer and a silicon dioxide layer which are 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 of the TGV glass substrate corresponding to the second through-hole electrode, and making an edge of the metal top electrode contact an 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 lower electrode and an insulating layer are sequentially prepared at the position of 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 lower electrode preferably includes sputtering, evaporation or electroplating. The present invention has no special restrictions on the preparation process of the metal lower electrode, and those familiar to those skilled in the art can be used. In a specific embodiment of the present invention, it is preferred to combine the sputtering, evaporation or electroplating method with a graphic method to prepare the metal lower 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 has no special restrictions on the preparation process of the insulating layer, and those familiar to those skilled in the art can be used. In a specific embodiment of the present invention, it is preferred to combine atomic layer deposition, low pressure chemical vapor deposition or plasma enhanced chemical vapor deposition with a graphic method to prepare the insulating layer. The present invention has no special requirements on the method used for the graphic method, and the photolithography plus etching or corrosion method commonly used in the art 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 and in the area corresponding to the bonding position with the TGV glass substrate, and then the SOI wafer is subjected to a thermal oxidation treatment, and then 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 thickness consistency of the device layer of the SOI wafer is good, and the resonant plate or conformal electrode prepared using the same has low stress and good device consistency. The cross-sectional size of the SOI wafer is preferably consistent with that 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 specifically Figure 7), preferably determined according to 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 close to the first through-hole electrode does not cover the first through-hole electrode, and the mask layer close to the second through-hole electrode covers the second through-hole electrode. In the present invention, the silicon dioxide layer is preferably formed by wet or dry thermal oxidation treatment, the temperature of the wet or dry thermal oxidation treatment is preferably 800-1200°C, more preferably 900-1100°C, and the time is preferably 1-2000min, more preferably 10-1000min; the present invention has no special requirements for the specific operation method of the wet or dry thermal oxidation treatment, and it can be used by those skilled in the art; the silicon nitride layer is preferably prepared by LPCVD. In a specific embodiment of the present invention, it is preferred to first perform a wet or dry thermal oxidation treatment on the SOI wafer to form a silicon dioxide layer on the surface of the device layer, and then deposit a silicon nitride layer on the surface of the silicon dioxide layer, and then perform a patterning treatment on the silicon nitride layer and the silicon dioxide layer to obtain a composite mask layer; during the patterning treatment, it is preferred to use a reactive ion etching method (RIE) or a phosphoric acid wet etching method to remove the silicon nitride layer, and then use a BOE wet etching method to etch the silicon nitride layer; the etchant used in the BOE wet etching method is preferably a 6:1 BOE etchant (i.e., the volume ratio of 40wt% NH4F aqueous solution and 49wt% HF aqueous solution is 6:1). When a silicon nitride layer is not needed, the preparation of the silicon nitride layer is omitted, and the patterning treatment can be directly performed after the silicon dioxide layer is obtained.

[0131] After preparing the mask layer, the present invention performs thermal oxidation treatment on the SOI wafer with the mask layer; in the present invention, the temperature of the thermal oxidation treatment is preferably 800-1200°C, and the treatment time is preferably 10min-1000min. During the thermal oxidation treatment, the thick film of silicon dioxide in the mask layer serves as an oxidation penetration layer, and the thin film of silicon nitride serves as a barrier layer. The silicon in the SOI wafer is thermally oxidized at high temperature to form a silicon-silicon dioxide interface with a three-dimensional profiled surface; the silicon dioxide in the mask layer serves as a mask penetration layer, and its thickness can adjust the curvature of the interface, and the oxidation time can control the depth of the interface. After the mask layer and the silicon dioxide generated by thermal oxidation are removed later, a profiled surface structure, specifically a curved surface structure, can be formed. The present invention does not specifically limit the removal method, and it can be used by those skilled in the art. In the present invention, the removal method of silicon nitride is preferably reactive ion etching (RIE) or phosphoric acid wet etching removal; the removal method of silicon dioxide 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 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, removes the substrate layer, the buried oxide layer and part of the device layer, and obtains a conformal electrode. In the present invention, the bonding method preferably includes anodic bonding or laser bonding. The present invention has no special limitation on the bonding process, and the bonding process known to those skilled in the art can be used.

[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 tetramethylammonium hydroxide (TMAH) or potassium hydroxide (KOH) wet etching. In a specific embodiment of the present invention, the substrate removal process is preferably: first remove part of the substrate layer by mechanical polishing, preferably remove until the remaining thickness of the substrate layer is 50-200μm, and then use tetramethylammonium hydroxide or potassium hydroxide wet etching to remove the remaining substrate layer. In the present invention, the concentration of the tetramethylammonium hydroxide solution used in the tetramethylammonium hydroxide (TMAH) etching is preferably 5-50wt%; the silicon etching rate of the tetramethylammonium hydroxide etching is preferably 0.2-2μm / min, and the etching temperature is preferably 25-100℃. In the present invention, the concentration of the potassium hydroxide solution used in the potassium hydroxide (KOH) wet etching is preferably 5-50wt%; the silicon etching rate of the potassium hydroxide etching is preferably 0.2-5μm / min, and the etching temperature is preferably 25-120℃. In the present invention, the method for removing the buried oxide layer preferably includes reactive ion etching (RIE), BOE or HF wet etching. In the present invention, the method for removing the partial device layer is preferably mechanical polishing, CMP, KOH or TMAH wet etching; the present invention has no special requirements for the selection or removal of the thickness of the device layer, which 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 a resonant film on the upper surface of the conformal electrode, then etches the resonant plate or the resonant film to expose part of the conformal electrode, and then etches the conformal electrode to expose the second through-hole electrode of the TGV glass substrate. In the present invention, the preparation method of the resonant plate or the 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 special requirements for the etching method, and a method well known to those skilled in the art can be used.

[0136] After the second through-hole electrode is exposed, the present invention prepares a metal upper electrode at the position of the TGV glass substrate corresponding to the second through-hole electrode, and makes the edge of the metal upper electrode contact the edge of the conformal electrode. In the present invention, it is preferred to first sputter a layer of metal electrode on the surface of the device, and then remove the unnecessary part by patterning, and the remaining part is the metal upper electrode; the patterning method is preferably 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 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 resonant plate, the metal upper electrode and the conformal electrode; in the present invention, the preparation method of 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 has no special limitation on the specific preparation process of the passivation layer, and it can be adopted by those skilled in the art.

[0138] After the above structure is prepared, the present invention sequentially prepares 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 prepares 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. The present invention has no special limitation on the preparation process of the first bump bottom UBM layer, the second bump bottom UBM layer, the first ball grid electrode and the second ball grid electrode, and those 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 of 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 comprises a device layer, a buried oxide layer and a substrate layer which are stacked; 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 subjecting the SOI wafer to a thermal oxidation treatment, 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 comprises a silicon nitride layer and a silicon dioxide layer which are 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 upper electrode at a position of the TGV glass substrate corresponding to the second through-hole electrode, and making the metal upper 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 film is omitted, and an SOI wafer with a thicker device layer is selected in step (2), 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 one.

[0149] In the present invention, when the MEMS ultrasonic transducer includes a passivation layer, before step (6), it preferably also includes preparing a passivation layer on the surface of the structural unit, specifically preparing 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 a bonding medium layer is also provided, 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) in method 1, or according to steps (2) to (6) in method 2, to obtain the MEMS ultrasonic transducer. Furthermore, when the MEMS ultrasonic transducer further includes a passivation layer, the passivation layer can be prepared according to the steps in method 1 or method 2.

[0153] Fig. 9 The figure is a flow chart of the preparation process when the structure of the MEMS ultrasonic transducer belongs to the first case and a bonding medium layer is also provided.

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

[0155] In the present invention, when the structure of the MEMS ultrasonic transducer belongs to situation 2, the method for preparing the MEMS ultrasonic transducer includes the following steps (referred to as method 4):

[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 a device edge of the TGV glass substrate to obtain a substrate to be bonded;

[0157] (2) providing an SOI wafer; the SOI wafer comprises a device layer, a buried oxide layer and a substrate layer which are stacked; 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 subjecting the SOI wafer to a thermal oxidation treatment, 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 comprises a silicon nitride layer and a silicon dioxide layer which are 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 an 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 of the TGV glass substrate corresponding to the second through-hole electrode, and making an edge of the metal top electrode contact an 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] Fig.10 It 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 prepared at the position of the TGV glass substrate corresponding to the first through-hole electrode, and a bonding dielectric layer is deposited at the device edge of the TGV glass substrate to obtain a substrate to be bonded. The preparation method of the metal bottom electrode, the insulating layer and the bonding dielectric layer is the same as the above scheme, and will not be repeated 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 profiled surface of the profiled surface silicon-based mold specifically includes a curved surface, a step, a slope, or a composite profiled 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 intermediate dielectric bonding, and the method familiar to those skilled in the art can be adopted. 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 may 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 upper 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 consistent with 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 the resonant membrane is metal, and the material of the resonant plate or the resonant membrane is the same as the material of the conformal electrode, the conformal electrode and the resonant plate or the resonant membrane form an integral structure, and the metal upper electrode is omitted. At this time, 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 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;

[0173] (2) providing an SOI wafer; the SOI wafer comprises a device layer, a buried oxide layer and a substrate layer which are stacked; 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 subjecting the SOI wafer to a thermal oxidation treatment, 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 comprises a silicon nitride layer and a silicon dioxide layer which are stacked in sequence from top to bottom;

[0174] (3) sequentially preparing a barrier layer, a resonance film and a conformal electrode integrated structure layer on the profiled surface of the profiled 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 making the resonant film and conformal electrode integrated structure layer contact 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, the steps (1) to (2) in the method 5 are preferably the same as those in the method 4, the preparation method of the barrier layer in the step (3) in the method 5 is the same as that in the method 4, the preparation method of the integrated structure layer of the resonance film and the conformal electrode is the same as that of the resonance film in the method 4, only the thickness is increased, and the total thickness is controlled to be the sum of the thickness of the resonance film and the conformal electrode; the operation mode of the step (4) in the method 5 is the same as that of the method 4, and only the specific etching position is different during etching. When the conformal electrode and the resonance film integrated structure can have a 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 upper 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] Fig.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 resonance plate or the resonance 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. At this time, 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, and only the bonding medium layer is omitted. 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] Fig.12 This is a flow chart of the preparation process when the structure of the MEMS ultrasonic transducer belongs to situation 2 and the bonding medium 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 may include a variety of shapes, which are not specifically limited in the present invention, such as circular, square, rectangular, elliptical, pentagonal, hexagonal, octagonal and other polygons. The present invention has no special requirements on the number of the capacitive MEMS ultrasonic transducer array, which 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 finally the passivation layer is uniformly deposited to completely cover the device surface.

[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 upper electrode; at this time, the cross-sectional view of the capacitive MEMS ultrasonic transducer array (3×3 array) is as follows: Fig.13 As shown, the top view is Fig.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 described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[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 embodiment, a new CMUT manufacturing process based on local oxidation of silicon (LOCOS) and anodic bonding technology is demonstrated. Figure 7 As shown. The conformal electrode material is selected as single crystal silicon, and the resonant film is selected as non-silicon material. The operating frequency of the new CMUT is set to 1.0MHz. A 2μm thick resonant film is selected. The radius of the CMUT is 65μm, and the cavity height is 0.4μm to obtain a reasonable driving voltage.

[0193] The specific process steps are as follows:

[0194] (a) A 500 μm thick TGV glass substrate is selected. The through hole radius of the first through hole electrode and the second through hole electrode is 20 μm, and the spacing is 100 μm. The materials of the first through hole electrode and the second through hole electrode are both electroplated Cu.

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

[0196] (c) The SiO2 insulating layer is deposited by PECVD to obtain a substrate to be bonded. The thickness of the insulating layer is 250nm, the deposition temperature is 250℃, the power is 200W, and the rate is about 60nm / min.

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

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

[0199] (f) The SOI wafer is 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, with a silicon consumption of 397 nm.

[0200] (g) Phosphoric acid (H3PO4) was used to remove the SiN mask, the water bath temperature was 155°C, and the etching rate was about 3.2nm / min. The SiO2 mask and the SiO2 generated by thermal oxidation were etched at room temperature using wet 6:1 BOE, and the etching rate was about 90nm / min. The electrode to be bonded was obtained.

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

[0202] (i) Remove most of the substrate layer of the SOI wafer by mechanical polishing to a thickness of 100 μm, and then remove the remaining substrate by 20% TMAH wet etching, the water bath temperature is 80°C, and the etching rate is 0.6 μm / min. Wet 6:1 BOE is used to etch the buried oxide layer at room temperature, and the etching rate is about 90 nm / min. A conformal electrode is formed.

[0203] (j) A layer of SiN is deposited as a resonance film by LPCVD with a thickness of 2 μm at a temperature of 800°C and a pressure of 250 mtorr for about 200 min.

[0204] (k) The SiN resonant film was etched by RIE, exposing part of the single-crystal silicon conformal electrode, with an etching power of 1600W, a bias voltage of -530V, a pressure of 40mtorr, and an etching rate of 50nm / min. The single-crystal silicon conformal electrode was etched by DRIE, with an etching power of 500W and a rate of 0.5μm / min, exposing the second through-hole electrode on the TGV glass substrate and the glass substrate at the edge of the device.

[0205] (l) After cleaning, an Al-2% Si electrode layer is sputtered with a thickness of 300 nm. The sputtering power is 300 W and the deposition rate is about 10 nm / min. The electrode is then patterned by photolithography to obtain a metal upper electrode and achieve ohmic contact with the single crystal silicon conformal electrode.

[0206] (m) PECVD deposition of SiO2 passivation layer with a thickness of 100 nm, deposition temperature of 250°C, power of 200 W, and rate of about 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 novel CMUT with conformal electrodes and a resonant plate made of single-crystal silicon as a specific embodiment, a novel CMUT manufacturing process based on local oxidation of silicon (LOCOS) and anodic bonding technology is demonstrated. Figure 8 As shown. The conformal electrode and the resonant plate are both selected to be single crystal silicon. The operating frequency of the new CMUT is set to 1.0MHz. In order to reduce geometric nonlinearity, a 20μm thick resonant plate is selected. The radius of the CMUT is 220μm and the cavity height is 0.4μm.

[0210] The specific process steps are as follows:

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

[0212] (b) A SOI wafer is provided, wherein the device layer of the SOI wafer is 20 μm thick, the buried oxide layer is 1 μm thick, and the substrate layer is 500 μm thick.

[0213] (c) According to steps (e)-(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 plate 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 a conformal electrode and a resonant electrode plate.

[0215] (e) The integrated structure of the single-crystal silicon conformal electrode and the resonant plate is etched by DRIE to pattern the integrated structure, with a power of 500 W and a rate of 0.5 μm / min, exposing 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 (l) 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 having conformal electrodes and conformal resonant membranes, made of metal and non-metal respectively, as a specific example, a manufacturing process of a new CMUT based on silicon-based mold and dielectric layer bonding technology is demonstrated. Fig.10 As shown. The resonant film has a conformal structure consistent with the conformal electrode, and its material is selected as non-metal, and the material of the conformal electrode is metal. The operating frequency of the new CMUT is set to 1.0MHz. The thickness of the resonant film is 2μm, the radius is 65μm, and the cavity height is 0.4μm.

[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 sputtered sequentially on a TGV glass substrate and patterned to obtain a bonding dielectric layer. The thickness of the Ti layer was 10 nm, the thickness of the Pt layer was 30 nm, and the thickness of the Au layer was 200 nm. The sputtering power of Ti, Pt and Au was 300 W, and the deposition rate was 10 nm / min. The substrate to be bonded was obtained.

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

[0224] (d) A SiO2 barrier layer with a thickness of 300nm is formed on the surface of the silicon-based mold by thermal oxidation. The thermal oxidation temperature is 1050℃ and the oxidation time is 25min. Then, a layer of SiN is deposited on the surface of the barrier layer by LPCVD as a resonant film with a thickness of 2μm, a deposition temperature of 800℃, a pressure of 250mtorr and a time of about 200min. Then, an Au electrode layer is sputtered on the SiN surface as a conformal electrode with a thickness of 200nm, a sputtering power of 300W and a deposition rate of about 10nm / min. The electrode to be bonded is obtained.

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

[0226] (f) Mechanically polish and remove most of the substrate silicon on the back of the bonding plate to a thickness of 100 μm, and then remove the remaining substrate silicon by 20% TMAH wet etching, the water bath temperature is 80°C, and the etching rate is about 0.6 μm / min. Then, wet 6:1 BOE is used to etch the buried oxide layer at room temperature, and the etching rate is about 90 nm / min. Then, 20% TMAH wet etching is used to remove the silicon-based mold.

[0227] (g) The SiO2 barrier layer is etched by RIE with an etching power of 1600 W, a bias voltage of -530 V, a pressure of 40 mtorr, and an etching rate of about 30 nm / 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 the bonding dielectric layer, exposing the second through-hole electrode on the TGV glass substrate and the glass substrate at the edge of the device. The etching power was 600 W, the chamber pressure was 100 mT, the temperature was 60°C, and the etching rate was 0.5 μm / min.

[0230] (j) Cleaning, sputtering Al-2% Si electrode layer with a thickness of 300 nm, sputtering power of 300 W, and deposition rate of about 10 nm / min. Photolithography, patterning the electrode layer to obtain a metal upper electrode.

[0231] (l) The SiO2 passivation layer was deposited by PECVD with a thickness of 100 nm, a deposition temperature of 250 °C, a power of 200 W, and a rate of about 60 nm / min;

[0232] (m) 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.

[0233] Example 4

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

[0235] The specific process steps are as follows:

[0236] (a) According to the steps in Example 3, the metal bottom electrode, the insulating layer and the bonding dielectric layer on the TGV glass substrate are prepared. The distance between the first through-hole electrode and the second through-hole electrode is 190 μm. The other conditions are the same as those in Example 3 to obtain a substrate to be bonded.

[0237] (b) According to the steps in Example 3, the silicon mold is manufactured and the SiO2 barrier layer is prepared;

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

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

[0240] (e) According to the steps in Example 3, the removal of the SOI substrate layer, the buried oxide layer, the silicon mold, the SiO2 barrier layer, the passivation layer protection of the device edge, and the preparation of the UBM layer and the ball gate electrode are completed in sequence.

[0241] By establishing a multi-physics field simulation model of CMUT, the core performances of the CMUT prepared in Examples 1 to 4, such as the pull-down voltage, transmission and reception sensitivity, are 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. Fig.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 transmission sound pressure sensitivity of the CMUT with a traditional planar electrode is 4.52 kPa / V, while the maximum sound pressure transmission sensitivity of the CMUT with a conformal curved electrode is 8.70 kPa / 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. Fig.16 As shown. Fig.16 It can be seen from the results that the use of TGV glass substrate can almost eliminate the influence of parasitic capacitance and make 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%. Figure 15-16 In the present invention, 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: Fig.17 shown.

[0242] Although the above embodiment describes the present invention in detail, 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 protection scope 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 which vertically penetrate 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 film, 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 chamber; the metal lower electrode and the insulating layer are located in the micro-nano chamber, and the insulating layer and the conformal electrode are not in contact; The edge of the conformal electrode is provided with a gap at a position corresponding to the second through-hole electrode, and the metal upper electrode is provided at the gap, located on the surface of the TGV glass substrate and the conformal electrode surface of the gap sidewall; the metal upper electrode and the second through-hole electrode are in ohmic contact, and the edge of the metal upper electrode is in contact with 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, characterized in that: The conformal electrode is made of silicon, which is single crystal silicon or polycrystalline silicon; the resonance plate or resonance film is made of a material different from that of the conformal electrode.

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

4. The MEMS ultrasonic transducer according to claim 1, characterized in that: The conformal electrode is made of silicon, which is single crystal silicon or polycrystalline silicon. The resonance plate or resonance film is made of the same material as the conformal electrode. The conformal electrode and the resonance plate or resonance 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 medium layer; the bonding medium layer is arranged between the positions where the substrate unit contacts 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, characterized in that: The conformal electrode is made of non-silicon material, which is metal or semiconductor material; the metal is a metal element or 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 resonance plate or the resonance film 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.

9. The MEMS ultrasonic transducer according to claim 7, characterized in that: The conformal electrode is made of metal, and the resonance plate or resonance film is made of the same material as the conformal electrode; the conformal electrode and the resonance plate or resonance 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 10nm-1μm; 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 0-10 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 medium layer is 10 nm to 10 μm; the material of the bonding medium 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 comprises a device layer, a buried oxide layer and a substrate layer which are stacked; 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 subjecting the SOI wafer to a thermal oxidation treatment, 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 comprises a silicon nitride layer and a silicon dioxide layer which are 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 an edge of the metal top electrode contact an 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 comprises a device layer, a buried oxide layer and a substrate layer which are stacked; 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 subjecting the SOI wafer to a thermal oxidation treatment, 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 comprises a silicon nitride layer and a silicon dioxide layer which are 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 upper electrode at a position on the surface of the TGV glass substrate corresponding to the second through-hole electrode, and making the metal upper 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 obtained by preparing according to steps (2) to (6) of the preparation method according to claim 16, or preparing according to steps (2) to (6) of the preparation method according to claim 17.

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 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; (2) providing an SOI wafer; the SOI wafer comprises a device layer, a buried oxide layer and a substrate layer which are stacked; 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 subjecting the SOI wafer to a thermal oxidation treatment, 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 comprises a silicon nitride layer and a silicon dioxide layer which are 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 an edge of the metal top electrode contact an 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 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; (2) providing an SOI wafer; the SOI wafer comprises a device layer, a buried oxide layer and a substrate layer which are stacked; 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 subjecting the SOI wafer to a thermal oxidation treatment, 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 comprises a silicon nitride layer and a silicon dioxide layer which are stacked in sequence from top to bottom; (3) sequentially preparing a barrier layer, a resonance film and a conformal electrode integrated structure layer on the profiled surface of the profiled 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 making the resonant film and conformal electrode integrated structure layer contact 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, except that the bonding medium layer is omitted.

22. The preparation method according to any one of claims 16 to 21, characterized in that: Before preparing the first bump bottom UBM layer, the first ball grid electrode, the second bump bottom 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 a MEMS ultrasonic transducer as claimed in any one of claims 1 to 15 or a MEMS ultrasonic transducer prepared by the preparation method as claimed in any one of claims 16 to 22.

24. The capacitive MEMS ultrasonic transducer array according to claim 23, characterized in that: 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, 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 upper electrode.

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