Preparation method of piezoelectric type and capacitive type compatible micro-mechanical ultrasonic transducer

Abstract

The invention belongs to the technical field of micromachinery, and particularly relates to a preparation method of a piezoelectric type and capacitive type compatible micromechanical ultrasonic transducer. The preparation method of the micromechanical ultrasonic transducer comprises a silicon-silicon bonding process and an anodic bonding process. The micro-mechanical ultrasonic transducer is divided into a capacitance type, a piezoelectric type and a piezoelectric-capacitance mixed type; each piezoelectric unit structure comprises a substrate layer, a cavity layer, an elastic layer, a middle electrode layer, a piezoelectric layer, a top electrode layer, a passivation layer and a bonding pad; the capacitive unit structure comprises a substrate layer, a bottom electrode layer, a cavity layer, an elastic layer, a middle electrode layer and a bonding pad; the piezoelectric-capacitance hybrid unit structure comprises a substrate layer, a bottom electrode layer, a cavity layer, an elastic layer, a middle electrode layer, a piezoelectric layer, a top electrode layer, a passivation layer and a bonding pad. According to the invention, processing of the three devices can be realized, and the three devices can be compatible on the same wafer. Wherein the piezoelectric-capacitance hybrid type breaks through the loop sensitivity bottleneck of the traditional piezoelectric type and capacitance type micromechanical ultrasonic transducers.

Description

Technical Field

[0001] The invention belongs to the field of micro-mechanical technology, and in particular relates to a method for preparing a micro-mechanical ultrasonic transducer. Background Art

[0002] In recent years, micro-electro-mechanical systems (MEMS) technology has been widely used in medical imaging, non-destructive testing, fingerprint recognition and other fields. According to the structure and working principle, MEMS ultrasonic transducers can be divided into two main types: piezoelectric micromachined ultrasonic transducer (PMUT) and capacitive micromachined ultrasonic transducer (CMUT). Piezoelectric transducers drive the film to vibrate through the inverse piezoelectric effect in piezoelectric materials, and receive ultrasonic signals through the charge generated by the piezoelectric effect. Capacitive transducers, on the other hand, receive and transmit ultrasonic signals based on the change in the amount of charge of the electrostatic force and the flat capacitor structure.

[0003] The existing PMUT and CMUT each have certain advantages and limitations. PMUT has high transmission efficiency and stability, but its receiving sensitivity is limited due to the characteristics of piezoelectric materials. In contrast, CMUT performs well in frequency regulation and bandwidth, but its transmission efficiency is relatively low. In order to give full play to the advantages of these two types of devices to break through the bottleneck of loop sensitivity, some studies have attempted to combine the characteristics of the two and proposed a piezoelectric-capacitive hybrid micromachined ultrasonic transducer (Piezoelectric-Capacitive Hybird Micromachined Ultrasonic Transducer, HMUT). However, the existing preparation process is difficult to be compatible with the structural requirements of PMUT and CMUT at the same time, especially when processing multiple types of devices on the same wafer. The process flow is complicated, the compatibility is insufficient, and the manufacturing cost is high.

[0004] Therefore, there is an urgent need for a new preparation method that is compatible with PMUT, CMUT and their hybrid structures, simplifies the manufacturing process, and improves the performance of the device. Summary of the invention

[0005] The purpose of the present invention is to provide a preparation method for compatible piezoelectric and capacitive micromechanical ultrasonic transducers, which is used to process piezoelectric, capacitive and piezoelectric-capacitive hybrid micromechanical ultrasonic transducers, and realize the compatible preparation of piezoelectric and capacitive devices on the same wafer, which not only reduces the manufacturing cost, but also overcomes the bottleneck of the prior art in sensitivity and device structure complexity.

[0006] The method for preparing a micromechanical ultrasonic transducer provided by the present invention adopts a silicon-silicon bonding process or an anodic bonding process; wherein the micromechanical ultrasonic transducer includes a capacitive micromechanical ultrasonic transducer, a piezoelectric micromechanical ultrasonic transducer, and a piezoelectric-capacitive hybrid micromechanical ultrasonic transducer; wherein:

[0007] The capacitive micromechanical ultrasonic transducer has a unit structure comprising: a substrate layer 1, a bottom electrode layer 2, a cavity layer 5, an elastic layer 6, an intermediate electrode layer 7 and a pad 11 arranged from bottom to top; specifically, a capacitive micromechanical ultrasonic transducer formed by a silicon-silicon bonding process, such as Figure 1 As shown in FIG. 1 , a capacitive micromachined ultrasonic transducer formed by an anodic bonding process is Figure 6 As shown; among which:

[0008] The cavity layer 5 is a hollow structure including a cavity 3 and a support layer 4, and the cavity 3 is surrounded by the bottom electrode layer 2, the support layer 4 and the elastic layer 6;

[0009] The elastic layer 6 and the intermediate electrode layer 7 stacked in sequence constitute a vibration layer 12;

[0010] The pad 11 includes pins of the bottom electrode layer 2 and the middle electrode layer 7;

[0011] The vibration layer 8 is located on the top of the cavity 3 and the support layer 4, wherein the vibration layer 12 located on the top of the cavity 3 can perform film-type bending vibration, that is, the cavity 3 provides a vibration space for the vibration layer 12;

[0012] The bottom electrode layer 2 and the middle electrode layer 7 constitute the upper and lower electrodes of the capacitive structure; the two are subjected to mutually attractive electrostatic forces; when a DC bias voltage is pre-applied, the structural layer 12 is subjected to a downward electrostatic force and bends.

[0013] The piezoelectric micromechanical ultrasonic transducer has a unit structure comprising: a substrate layer 1, a cavity layer 5, an elastic layer 6, an intermediate electrode layer 7, a piezoelectric layer 8, a top electrode layer 9, a passivation layer 10 and a pad 11 arranged from top to bottom; specifically, it is divided into a piezoelectric micromechanical ultrasonic transducer formed by a silicon-silicon bonding process, such as Figure 2 As shown in FIG. 1 , a piezoelectric micromechanical ultrasonic transducer formed by an anodic bonding process is shown in FIG. Figure 7 As shown; among which:

[0014] The cavity layer 5 is a hollow structure including a cavity 3 and a support layer 4, and the cavity 3 is surrounded by the substrate layer 1, the support layer 4 and the elastic layer 6;

[0015] The elastic layer 6, the middle electrode layer 7, the piezoelectric layer 8, the top electrode layer 9 and the passivation layer 10 stacked in sequence constitute a vibration layer 12;

[0016] The pad 11 includes pins of the middle electrode layer 7 and the top electrode layer 9;

[0017] The vibration layer 8 is located on the top of the cavity 3 and the support layer 4, wherein the vibration layer 12 located on the top of the cavity 3 can perform film-type bending vibration, that is, the cavity 3 provides a vibration space for the vibration layer 12;

[0018] The middle electrode layer 7 and the top electrode layer 9 constitute the upper and lower electrodes of the piezoelectric layer 8; when a voltage is applied between them, the inverse piezoelectric effect of the piezoelectric material is excited, thereby generating a bending moment that causes the vibration layer 12 to bend.

[0019] The piezoelectric-capacitive hybrid micromechanical ultrasonic transducer has a unit structure comprising a substrate layer 1, a bottom electrode layer 2, a cavity layer 5, an elastic layer 6, an intermediate electrode layer 7, a piezoelectric layer 9, a top electrode layer 9, a passivation layer 10 and a pad 11 arranged from bottom to top; specifically, it is divided into a piezoelectric-capacitive hybrid micromechanical ultrasonic transducer formed by a silicon-silicon bonding process, such as Figure 3 As shown in FIG. 1 , a piezoelectric-capacitive hybrid micromechanical ultrasonic transducer formed by an anodic bonding process is shown in FIG. Figure 8 As shown; among which:

[0020] The cavity layer 5 is a hollow structure including a cavity 3 and a support layer 4, and the cavity 3 is surrounded by the bottom electrode layer 2, the support layer 4 and the elastic layer 6;

[0021] The elastic layer 6, the middle electrode layer 7, the piezoelectric layer 8, the top electrode layer 9 and the passivation layer 10 stacked in sequence constitute a vibration layer 12;

[0022] The pad 11 includes pins of the bottom electrode layer 2, the middle electrode layer 7 and the top electrode layer 9;

[0023] The vibration layer 8 is located on the top of the cavity 3 and the support layer 4, wherein the vibration layer 12 located on the top of the cavity 3 can perform film-type bending vibration, that is, the cavity 3 provides a vibration space for the vibration layer 12;

[0024] The middle electrode layer 7 and the top electrode layer 9 constitute the upper and lower electrodes of the piezoelectric layer 8; when a voltage is applied between them, the inverse piezoelectric effect of the piezoelectric material is excited, thereby generating a bending moment acting on the vibration layer 12; the bottom electrode layer 2 and the middle electrode layer 7 constitute the upper and lower electrodes of the capacitive structure; the two are subject to mutually attractive electrostatic forces; when a DC bias voltage is pre-applied, the structural layer 12 is subjected to a downward electrostatic force; the piezoelectric bending moment and the electrostatic force act together on the vibration layer 12, causing it to bend and vibrate.

[0025] Further, in the present invention:

[0026] The substrate layer 1 is conductively doped silicon or an insulating glass wafer, and preferably has a thickness of 100 to 1000 microns.

[0027] The bottom electrode layer 2 is conductively doped silicon or metal, and the middle electrode layer 7, the top electrode layer 9 and the pad 11 are thin metal layers, preferably with a thickness of 0.1 to 1 micrometer.

[0028] The cavity 3 is a vacuum cavity, and its shape is circular, square or hexagonal, preferably with a radius of 10 to 100 microns and a thickness of 0.1 to 1 micron.

[0029] The elastic layer 6 is usually made of silicon, and preferably has a thickness of 0.5 to 5 microns.

[0030] The piezoelectric layer 8 is usually a piezoelectric film such as aluminum nitride or PZT, and preferably has a thickness of 0.1 to 2 microns.

[0031] The passivation layer 10 is generally made of silicon oxide or silicon nitride, and preferably has a thickness of 0.1 to 1 micrometer.

[0032] The method for preparing a compatible piezoelectric and capacitive micromechanical ultrasonic transducer provided by the present invention is divided into a process based on silicon-silicon bonding and a process based on anodic bonding; wherein:

[0033] The process based on silicon-silicon bonding is described in Figure 5 As shown, the specific steps are:

[0034] Step 1, etching the front and back overlay marks 2 on the silicon wafer 1;

[0035] Step 2, thermally oxidizing the silicon wafer 1 to form an oxide layer 3;

[0036] Step 3, etching the front oxide layer to form a cavity 4, and further etching the silicon layer to form a deeper cavity 4';

[0037] Step 4, performing silicon-silicon bonding between the front side of the silicon wafer 1 and the surface of the device layer 6 of the SOI wafer 5;

[0038] Step 5, removing the substrate silicon layer 7 and the buried oxide layer 8 of the SOI wafer 5;

[0039] Step 6, depositing a metal layer 9, a piezoelectric material layer 10 and a metal layer 11 in sequence;

[0040] Step 7, etching the metal layer 11, the piezoelectric material layer 10 and the metal layer 9 in sequence to form a patterned structure;

[0041] Step 8: depositing and etching the dielectric material layer 12 to form a passivation layer;

[0042] Step 9: deposit and etch the metal layer 13 to form a pad.

[0043] The process based on anodic bonding, see Fig. 9 As shown, the specific steps are:

[0044] Step 1, etching a cavity 2 on the front side of a glass sheet 1;

[0045] Step 2, depositing a metal layer 3, and removing the metal layer outside the cavity 2 area;

[0046] Step 3, performing silicon-silicon bonding between the front surface of the glass sheet 1 and the surface of the device layer 5 of the SOI sheet 4;

[0047] Step 4, removing the substrate silicon layer 6 and the buried oxide layer 7 of the SOI wafer 4;

[0048] Step 5, etching the device layer 5;

[0049] Step 6, depositing a metal layer 8, a piezoelectric material layer 9 and a metal layer 10 in sequence;

[0050] Step 7, etching the metal layer 10, the piezoelectric material layer 9 and the metal layer 8 in sequence to form a patterned structure;

[0051] Step 8: depositing and etching the dielectric material layer 11 to form a passivation layer;

[0052] Step 9: deposit and etch the metal layer 12 to form a pad.

[0053] The preparation method provided by the present invention is applicable to different types of piezoelectric materials (such as aluminum nitride, barium titanate, lithium niobate, etc.), conductive materials (such as gold, silver, aluminum, molybdenum, etc.) and different substrate materials (such as conductive doped silicon, insulating glass, polymer substrate, etc.), and the method is compatible with a variety of manufacturing processes, including but not limited to chemical vapor deposition, physical vapor deposition, sputtering process, etching process, wafer bonding process, etc.

[0054] Compared with the prior art, the present invention has at least the following beneficial technical effects:

[0055] (1) Strong compatibility: Based on the wafer bonding process, the present invention can realize compatible processing of piezoelectric micromachined ultrasonic transducers (PMUT), capacitive micromachined ultrasonic transducers (CMUT) and piezoelectric-capacitive hybrid micromachined ultrasonic transducers on the same wafer; this compatibility solves the problem that different types of devices need to adopt different preparation processes in the prior art, greatly simplifies the production process and improves production efficiency;

[0056] (2) Sensitivity improvement: Through the piezoelectric-capacitive hybrid structure design, the present invention breaks through the limitations of existing piezoelectric transducers and capacitive transducers in loop sensitivity; this structure utilizes the synergistic effect of the piezoelectric layer and the capacitive layer to significantly improve the transmission and receiving sensitivity of the ultrasonic transducer, especially in high-frequency applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 It is a structural schematic diagram (vertical section view) of a capacitive micromechanical ultrasonic transducer unit based on a silicon-silicon bonding process of the present invention.

[0058] Figure 2 It is a structural schematic diagram (vertical section view) of the piezoelectric micromechanical ultrasonic transducer unit based on the silicon-silicon bonding process of the present invention.

[0059] Figure 3 It is a structural schematic diagram (vertical section view) of the piezoelectric-capacitive hybrid micromechanical ultrasonic transducer unit based on the silicon-silicon bonding process of the present invention.

[0060] Figure 4 The micromechanical ultrasonic transducer structure processed by the preparation method of the present invention (vertical section view); the micromechanical ultrasonic transducer structure includes a capacitive micromechanical ultrasonic transducer unit, a piezoelectric micromechanical ultrasonic transducer unit and a piezoelectric-capacitive hybrid micromechanical ultrasonic transducer unit arranged in a planar manner (from left to right).

[0061] Figure 5 The present invention is a schematic diagram of the preparation process of a compatible piezoelectric and capacitive micromechanical ultrasonic transducer based on a silicon-silicon bonding process.

[0062] Figure 6 It is a structural schematic diagram (vertical section view) of a capacitive micromechanical ultrasonic transducer unit based on an anodic bonding process of the present invention.

[0063] Figure 7 It is a structural schematic diagram (vertical section view) of the piezoelectric micromechanical ultrasonic transducer unit based on the anodic bonding process of the present invention.

[0064] Figure 8It is a structural schematic diagram (vertical section view) of the piezoelectric-capacitive hybrid micromechanical ultrasonic transducer unit based on the anodic bonding process of the present invention.

[0065] Fig. 9 The present invention is a schematic diagram of the preparation process of a compatible piezoelectric and capacitive micromechanical ultrasonic transducer based on a silicon-silicon bonding process.

[0066] The numbers in the figure are: 1 is the substrate layer, 2 is the bottom electrode layer, 3 is the cavity, 4 is the support layer, 5 is the cavity layer, 6 is the elastic layer, 7 is the middle electrode layer, 8 is the piezoelectric layer, 9 is the top electrode layer, 10 is the passivation layer, 11 is the pad, and 12 is the vibration layer. DETAILED DESCRIPTION

[0067] The present invention will be described in more detail below with reference to the accompanying drawings. In each of the accompanying drawings, the same elements are represented by similar reference numerals. For the sake of clarity, the various parts in the accompanying drawings are not drawn to scale. In addition, some well-known parts may not be shown.

[0068] Many specific details of the present invention are described below, such as device structure, material size processing technology and technology, so as to more clearly understand the present invention. However, as can be understood by those skilled in the art, the present invention can be implemented without being limited to these specific details.

[0069] Figure 1 FIG. 1 is a structural schematic diagram (vertical section view) of a capacitive micromechanical ultrasonic transducer unit based on silicon-silicon bonding technology of the present invention. Figure 1 As shown, the structure of the capacitive micromechanical ultrasonic transducer includes: a substrate layer 1, a bottom electrode layer 2, a cavity 3, a support layer 4, an elastic layer 6, an intermediate electrode layer 7 and a pad 11 arranged from top to bottom. Among them, the bottom electrode layer 2 and the intermediate electrode layer 7 constitute the upper and lower electrodes of the parallel plate capacitor; the elastic layer 6 and the intermediate electrode layer 7 are combined to form a vibration layer 12; the cavity layer 5 is a hollow structure, and the bottom electrode layer 2, the support layer 4 and the elastic layer 6 are surrounded to form a cavity 3; the cavity 3 provides a deformation space for the vibration layer 12.

[0070] The substrate layer 1 is conductively doped silicon with a thickness of 100 to 1000 microns; the bottom electrode layer 2 is a thin layer on the upper surface of the substrate layer 1; the cavity 3 is a vacuum structure with a radius of 10 to 100 microns; the support layer 4 is silicon oxide with a thickness of 0.1 to 1 micron; the elastic layer is silicon with a thickness of 0.5-5 microns; the intermediate electrode layer 7 and the pad 11 are metals, such as gold or aluminum, with a thickness of 0.1 to 0.5 microns.

[0071] Figure 2 Schematic diagram (vertical section view) of the structure of the piezoelectric micromechanical ultrasonic transducer unit based on the silicon-silicon bonding process of the present invention. Figure 2As shown, the structure of the piezoelectric micromechanical ultrasonic transducer includes: a substrate layer 1, a cavity 3, a support layer 4, an elastic layer 6, an intermediate electrode layer 7, a piezoelectric layer 8, a top electrode layer 9, a passivation layer 10 and a pad 11 arranged from top to bottom. Among them, the intermediate electrode layer 7 and the top electrode layer 9 constitute the upper and lower electrodes of the piezoelectric layer 8; the elastic layer 6, the intermediate electrode layer 7, the piezoelectric layer 8, the top electrode layer 9 and the passivation layer 10 are combined into a vibration layer 12; the cavity layer 5 is a hollow structure, and the substrate layer 1, the support layer 4 and the elastic layer 6 are enclosed to form a cavity 3; the cavity 3 provides a deformation space for the vibration layer 12.

[0072] The substrate layer 1 is silicon, preferably with a thickness of 100 to 1000 microns; the support layer 4 is silicon oxide, preferably with a thickness of 0.1 to 1 micron; the cavity 3 is a vacuum structure, preferably with a radius of 10 to 100 microns; the elastic layer is silicon, preferably with a thickness of 0.5 to 5 microns; the intermediate electrode layer 7, the top electrode layer 9 and the pad 11 are metals, such as gold or aluminum, preferably with a thickness of 0.1 to 0.5 microns; the piezoelectric layer 8 is PZT or aluminum nitride, preferably with a thickness of 0.5 to 2 microns; the passivation layer 10 is silicon oxide or silicon nitride, preferably with a thickness of 0.1 to 1 micron.

[0073] Figure 3 Schematic diagram (vertical section view) of the structure of the piezoelectric-capacitive hybrid micromechanical ultrasonic transducer unit based on silicon-silicon bonding process of the present invention. Figure 3 As shown, the structure of the piezoelectric-capacitive hybrid micromechanical ultrasonic transducer includes: a substrate layer 1, a bottom electrode layer 2, a cavity 3, a support layer 4, an elastic layer 6, an intermediate electrode layer 7, a piezoelectric layer 8, a top electrode layer 9, a passivation layer 10 and a pad 11 arranged from top to bottom. Among them, the bottom electrode layer 2 and the intermediate electrode layer 7 constitute the upper and lower electrodes of the parallel plate capacitor; the intermediate electrode layer 7 and the top electrode layer 9 constitute the upper and lower electrodes of the piezoelectric layer 8; the elastic layer 6, the intermediate electrode layer 7, the piezoelectric layer 8, the top electrode layer 9 and the passivation layer 10 are combined into a vibration layer 12; the cavity layer 5 is a hollow structure, and the substrate layer 1, the support layer 4 and the elastic layer 6 are enclosed to form a cavity 3; the cavity 3 provides a deformation space for the vibration layer 12.

[0074] The substrate layer 1 is silicon with a thickness of 100 to 1000 microns; the support layer 4 is silicon oxide with a thickness of 0.1 to 1 micron; the bottom electrode layer 2 is a thin surface layer of the substrate layer 1; the cavity 3 is a vacuum structure with a radius of 10 to 100 microns; the elastic layer is silicon with a thickness of 0.5-5 microns; the intermediate electrode layer 7, the top electrode layer 9 and the pad 11 are metals, such as gold or aluminum, with a thickness of 0.1 to 0.5 microns; the piezoelectric layer 8 is PZT or aluminum nitride with a thickness of 0.5 to 2 microns; the passivation layer 10 is silicon oxide or silicon nitride with a thickness of 0.1 to 1 micron.

[0075] Figure 5 The figure is a schematic diagram of the process of preparing a compatible piezoelectric and capacitive micromechanical ultrasonic transducer based on the silicon-silicon bonding process of the present invention. Figure 5 As shown, the preparation steps include:

[0076] Step 1, etching the front and back overlay marks 2 on the silicon wafer 1;

[0077] Step 2, thermally oxidizing the silicon wafer 1 to form an oxide layer 3;

[0078] Step 3, etching the front oxide layer to form a cavity 4, and further etching the silicon layer to form a deeper cavity 4';

[0079] Step 4, performing silicon-silicon bonding between the front side of the silicon wafer 1 and the surface of the device layer 6 of the SOI wafer 5;

[0080] Step 5, removing the substrate silicon layer 7 and the buried oxide layer 8 of the SOI wafer 5;

[0081] Step 6, depositing a metal layer 9, a piezoelectric material layer 10 and a metal layer 11 in sequence;

[0082] Step 7, etching the metal layer 11, the piezoelectric material layer 10 and the metal layer 9 in sequence to form a patterned structure;

[0083] Step 8: depositing and etching the dielectric material layer 12 to form a passivation layer;

[0084] Step 9: deposit and etch the metal layer 13 to form a pad.

[0085] Figure 6 FIG. 1 is a structural schematic diagram (vertical section view) of a capacitive micromechanical ultrasonic transducer unit based on an anodic bonding process of the present invention. Figure 6 As shown, the structure of the capacitive micromechanical ultrasonic transducer includes: a substrate layer 1, a bottom electrode layer 2, a cavity 3, a support layer 4, an elastic layer 6, an intermediate electrode layer 7 and a pad 11 arranged from top to bottom. Among them, the bottom electrode layer 2 and the intermediate electrode layer 7 constitute the upper and lower electrodes of the parallel plate capacitor; the elastic layer 6 and the intermediate electrode layer 7 are combined to form a vibration layer 12; the cavity layer 5 is a hollow structure, and the bottom electrode layer 2, the support layer 4 and the elastic layer 6 are surrounded to form a cavity 3; the cavity 3 provides a deformation space for the vibration layer 12.

[0086] The substrate layer 1 is insulating glass, preferably with a thickness of 100 to 1000 microns; the bottom electrode layer 2 is a metal layer, preferably with a thickness of 0.1 to 0.5 microns; the cavity 3 is a vacuum structure, preferably with a radius of 10 to 100 microns; the support layer 4 is silicon oxide, preferably with a thickness of 0.1 to 1 micron; the elastic layer is silicon, preferably with a thickness of 0.5 to 5 microns; the intermediate electrode layer 7 and the pad 11 are metals, such as gold or aluminum, preferably with a thickness of 0.1 to 0.5 microns.

[0087] Figure 7 FIG. 1 is a schematic structural diagram (vertical section view) of a piezoelectric micromechanical ultrasonic transducer unit based on an anodic bonding process of the present invention. Figure 7 As shown, the structure of the piezoelectric micromechanical ultrasonic transducer includes: a substrate layer 1, a cavity 3, a support layer 4, an elastic layer 6, an intermediate electrode layer 7, a piezoelectric layer 8, a top electrode layer 9, a passivation layer 10 and a pad 11 arranged from top to bottom. Among them, the intermediate electrode layer 7 and the top electrode layer 9 constitute the upper and lower electrodes of the piezoelectric layer 8; the elastic layer 6, the intermediate electrode layer 7, the piezoelectric layer 8, the top electrode layer 9 and the passivation layer 10 are combined to form a vibration layer 12; the cavity layer 5 is a hollow structure, and the substrate layer 1, the support layer 4 and the elastic layer 6 are enclosed to form a cavity 3; the cavity 3 provides a deformation space for the vibration layer 12.

[0088] The substrate layer 1 is glass, preferably with a thickness of 100 to 1000 microns; the support layer 4 is glass, preferably with a thickness of 0.1 to 1 micron; the elastic layer is silicon, preferably with a thickness of 0.5 to 5 microns; the cavity 3 is a vacuum structure, preferably with a radius of 10 to 100 microns; the intermediate electrode layer 7, the top electrode layer 9 and the pad 11 are metals, such as gold or aluminum, preferably with a thickness of 0.1 to 0.5 microns; the piezoelectric layer 8 is PZT or aluminum nitride, typically with a thickness of 0.5 to 2 microns; the passivation layer 10 is silicon oxide or silicon nitride, preferably with a thickness of 0.1 to 1 micron.

[0089] Figure 8 Schematic diagram (vertical section view) of the structure of the piezoelectric-capacitive hybrid micromechanical ultrasonic transducer unit based on the anodic bonding process of the present invention. Figure 8 As shown, the structure of the piezoelectric-capacitive hybrid micromechanical ultrasonic transducer includes: a substrate layer 1, a bottom electrode layer 2, a cavity 3, a support layer 4, an elastic layer 6, an intermediate electrode layer 7, a piezoelectric layer 8, a top electrode layer 9, a passivation layer 10 and a pad 11 arranged from top to bottom. Among them, the bottom electrode layer 2 and the intermediate electrode layer 7 constitute the upper and lower electrodes of the parallel plate capacitor; the intermediate electrode layer 7 and the top electrode layer 9 constitute the upper and lower electrodes of the piezoelectric layer 8; the elastic layer 6, the intermediate electrode layer 7, the piezoelectric layer 8, the top electrode layer 9 and the passivation layer 10 are combined to form a vibration layer 12. The cavity layer 5 is a hollow structure, and the substrate layer 1, the support layer 4 and the elastic layer 6 are enclosed to form a cavity 3; the cavity 3 provides a deformation space for the vibration layer 12.

[0090] The substrate layer 1 is silicon, and its thickness is usually 100 to 1000 microns; the support layer 4 is silicon oxide, and its total thickness is about 0.1-1 microns; the bottom electrode layer 2 is a metal layer, and its thickness is usually 0.1 to 0.5 microns; the cavity 3 is a vacuum structure, and its radius is usually 10 to 100 microns; the elastic layer is silicon, and its thickness is usually 0.5 to 5 microns; the intermediate electrode layer 7, the top electrode layer 9 and the pad 11 are metals, such as gold or aluminum, and their thickness is usually 0.1 to 0.5 microns; the piezoelectric layer 8 is PZT or aluminum nitride, and its thickness is usually 0.5 to 2 microns; the passivation layer 10 is silicon oxide or silicon nitride, and its thickness is 0.1 to 1 micron.

[0091] Fig. 9 The present invention is a schematic diagram of the preparation process of a compatible piezoelectric and capacitive micromechanical ultrasonic transducer based on an anodic bonding process.

[0092] like Fig. 9 As shown, the preparation steps include:

[0093] Step 1, etching a cavity 2 on the front side of a glass sheet 1;

[0094] Step 2, depositing a metal layer 3, and removing the metal layer outside the cavity 2 area;

[0095] Step 3, performing silicon-silicon bonding between the front surface of the glass sheet 1 and the surface of the device layer 5 of the SOI sheet 4;

[0096] Step 4, removing the substrate silicon layer 6 and the buried oxide layer 7 of the SOI wafer 4;

[0097] Step 5, etching the device layer 5;

[0098] Step 6, depositing a metal layer 8, a piezoelectric material layer 9 and a metal layer 10 in sequence;

[0099] Step 7, etching the metal layer 10, the piezoelectric material layer 9 and the metal layer 8 in sequence to form a patterned structure;

[0100] Step 8: depositing and etching the dielectric material layer 11 to form a passivation layer;

[0101] Step 9: deposit and etch the metal layer 12 to form a pad.

[0102] Without departing from the spirit and scope of the present invention, any ordinary technician in the field can make many variations and modifications based on the contents disclosed by the present invention, which should also be considered as the protection scope of the present invention.

Claims

1. A method for preparing a compatible piezoelectric and capacitive micromechanical ultrasonic transducer, characterized in that: A silicon-silicon bonding process or an anodic bonding process is used; the micromechanical ultrasonic transducer is divided into a capacitive micromechanical ultrasonic transducer, a piezoelectric micromechanical ultrasonic transducer, and a piezoelectric-capacitive hybrid micromechanical ultrasonic transducer; wherein: The piezoelectric micromechanical ultrasonic transducer comprises a substrate layer (1), a cavity layer (5), an elastic layer (6), an intermediate electrode layer (7), a piezoelectric layer (8), a top electrode layer (9), a passivation layer (10) and a pad (11) arranged from bottom to top, and is specifically divided into a capacitive micromechanical ultrasonic transducer formed by a silicon-silicon bonding process and a capacitive micromechanical ultrasonic transducer formed by an anodic bonding process, wherein: The cavity layer (5) is a hollow structure comprising a cavity (3) and a support layer (4), and the cavity (3) is surrounded by the substrate layer (1), the support layer (4) and the elastic layer (6); The elastic layer (6), the middle electrode layer (7), the piezoelectric layer (8), the top electrode layer (9) and the passivation layer (10) stacked in sequence form a vibration layer (12); The pad (11) includes pins of the middle electrode layer (7) and the top electrode layer (9); The vibration layer (8) is located on the top of the cavity (3) and the support layer (4), wherein the vibration layer (12) located on the top of the cavity (3) performs a thin film bending vibration, that is, the cavity (3) provides a vibration space for the vibration of the vibration layer (12); The intermediate electrode layer (7) and the top electrode layer (9) constitute the upper and lower electrodes of the piezoelectric layer (8); when a voltage is applied between them, a bending moment acting on the vibration layer (12) is generated through the inverse piezoelectric effect; The capacitive micromechanical ultrasonic transducer has a structure comprising a substrate layer (1), a bottom electrode layer (2), a cavity layer (5), an elastic layer (6), an intermediate electrode layer (7) and a pad (11) arranged from bottom to top; specifically, it is divided into a piezoelectric micromechanical ultrasonic transducer formed by a silicon-silicon bonding process and a piezoelectric micromechanical ultrasonic transducer formed by an anode bonding process; wherein: The cavity layer (5) is a hollow structure comprising a cavity (3) and a support layer (4), and the cavity (3) is surrounded by the bottom electrode layer (2), the support layer (4) and the elastic layer (6); The elastic layer (6) and the intermediate electrode layer (7) stacked in sequence form a vibration layer (12); The pad (11) includes pins of the bottom electrode layer (2) and the middle electrode layer (7); The vibration layer (8) is located on the top of the cavity (3) and the support layer (4), wherein the vibration layer (12) located on the top of the cavity (3) performs a thin film bending vibration, that is, the cavity (3) provides a vibration space for the vibration of the vibration layer (12); The bottom electrode layer (2) and the middle electrode layer (7) constitute the upper and lower electrodes of the capacitive structure; the two are subjected to mutually attractive electrostatic forces; when a DC bias voltage is pre-applied, the structural layer (12) is subjected to the downward electrostatic force and bends; The piezoelectric-capacitive hybrid micromechanical ultrasonic transducer has a structure comprising a substrate layer (1), a bottom electrode layer (2), a cavity layer (5), an elastic layer (6), an intermediate electrode layer (7), a piezoelectric layer (8), a top electrode layer (9), a passivation layer (10) and a pad (11) arranged from bottom to top; specifically, it is divided into a piezoelectric-capacitive hybrid micromechanical ultrasonic transducer formed by a silicon-silicon bonding process and a piezoelectric-capacitive hybrid micromechanical ultrasonic transducer formed by an anode bonding process; wherein: The cavity layer (5) is a hollow structure comprising a cavity (3) and a support layer (4), and the cavity (3) is surrounded by the bottom electrode layer (2), the support layer (4) and the elastic layer (6); The elastic layer (6), the middle electrode layer (7), the piezoelectric layer (8), the top electrode layer (9) and the passivation layer (10) stacked in sequence form a vibration layer (12); The pad (11) includes pins of a bottom electrode layer (2), a middle electrode layer (7) and a top electrode layer (9); The vibration layer (8) is located on the top of the cavity (3) and the support layer (4), wherein the vibration layer (12) located on the top of the cavity (3) performs a thin film bending vibration, that is, the cavity (3) provides a vibration space for the vibration of the vibration layer (12); The middle electrode layer (7) and the top electrode layer (9) constitute the upper and lower electrodes of the piezoelectric layer (8); when a voltage is applied between them, the inverse piezoelectric effect of the piezoelectric material is excited, thereby generating a bending moment acting on the vibration layer (12); the bottom electrode layer (2) and the middle electrode layer (7) constitute the upper and lower electrodes of the capacitive structure; the two are acted upon by mutually attractive electrostatic forces; when a DC bias voltage is pre-applied, the structural layer (12) is subjected to a downward electrostatic force; the piezoelectric bending moment and the electrostatic force act together on the vibration layer (12), causing it to bend and vibrate.

2. The method for preparing a micromechanical ultrasonic transducer according to claim 1, characterized in that: The substrate layer (1) is conductively doped silicon or an insulating glass wafer, and has a thickness of 100 to 1000 micrometers.

3. The method for preparing a micromechanical ultrasonic transducer according to claim 1, characterized in that: The bottom electrode layer (2) is conductively doped silicon or metal, and the middle electrode layer (7), the top electrode layer (9) and the pad (11) are thin metal layers with a thickness of 0.1 to 1 micrometer.

4. The method for preparing a micromechanical ultrasonic transducer according to claim 1, characterized in that: The cavity (3) is a vacuum cavity, which is circular, square or hexagonal in shape, with a maximum size of 10 to 100 micrometers and a thickness of 0.1 to 1 micrometer.

5. The method for preparing a micromechanical ultrasonic transducer according to claim 1, characterized in that: The elastic layer (6) is made of silicon and has a thickness of 0.5 to 5 micrometers.

6. The method for preparing a micromechanical ultrasonic transducer according to claim 1, characterized in that: The piezoelectric layer (8) is aluminum nitride or a PZT piezoelectric film with a thickness of 0.1 to 2 micrometers.

7. The method for preparing a micromechanical ultrasonic transducer according to claim 1, characterized in that: The passivation layer (10) is silicon oxide or silicon nitride; the substrate layer (1) is conductively doped silicon or an insulating glass wafer, with a thickness of 300 to 1000 micrometers.

8. A method for preparing a micromechanical ultrasonic transducer according to any one of claims 1 to 7, characterized in that: The specific steps based on the silicon-silicon bonding process are: Step 1, etching front and back overlay marks (2) on the silicon wafer (1); Step 2, thermally oxidizing the silicon wafer (1) to form an oxide layer (3); Step 3, etching the front oxide layer to form a cavity (4), and further etching the silicon layer to form a deeper cavity (4'); Step 4, performing silicon-silicon bonding on the front side of the silicon wafer (1) and the surface of the device layer (6) of the SOI wafer (5); Step 5, removing the substrate silicon layer (7) and the buried oxide layer (8) of the SOI wafer (5); Step 6: depositing a metal layer (9), a piezoelectric material layer (10) and a metal layer (11) in sequence; Step 7: etching the metal layer (11), the piezoelectric material layer (10) and the metal layer (9) in sequence to form a patterned structure; Step 8: depositing and etching a dielectric material layer (12) to form a passivation layer; Step 9: depositing and etching a metal layer (13) to form a pad; The specific steps of the anodic bonding process are: Step 1, etching a cavity (2) on the front side of the glass sheet (1); Step 2, depositing a metal layer (3), and removing the metal layer outside the cavity (2); Step 3, performing silicon-silicon bonding between the front surface of the glass sheet (1) and the surface of the device layer (5) of the SOI sheet (4); Step 4, removing the substrate silicon layer (6) and the buried oxide layer (7) of the SOI wafer (4); Step 5, etching the device layer (5); Step 6: depositing a metal layer (8), a piezoelectric material layer (9) and a metal layer (10) in sequence; Step 7: etching the metal layer (10), the piezoelectric material layer (9) and the metal layer (8) in sequence to form a patterned structure; Step 8: depositing and etching a dielectric material layer (11) to form a passivation layer; Step 9: deposit and etch the metal layer (12) to form a pad.

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