WO2024027730A1 - Micromachined ultrasonic transducer structure having having dual pmuts provided at same side as substrate, and manufacturing method therefor - Google Patents

Abstract

The present invention relates to a micromachined ultrasonic transducer structure and a manufacturing method therefor. The micromachined ultrasonic transducer structure comprises a PMUT unit; the PMUT unit comprises a PMUT substrate, a first PMUT, and a second PMUT; each PMUT comprises a first electrode layer, a second electrode layer, and a piezoelectric layer, wherein the first PMUT and the second PMUT are arranged as laterally spaced apart at one side of the PMUT substrate; the piezoelectric coefficient of the piezoelectric layer of the first PMUT is higher than the piezoelectric coefficient of the piezoelectric layer of the second PMUT; and the permittivity of the piezoelectric layer of the first PMUT is lower than the permittivity of the piezoelectric layer of the second PMUT. The present invention further relates to an electronic device comprising the present micromachined ultrasonic transducer structure.

Description

Micromechanical ultrasonic transducer structure with dual PMUTs on the same side of the base and manufacturing method thereof Technical field

Embodiments of the present invention relate to the field of semiconductors, and in particular to a micromachined ultrasonic transducer structure with dual PMUTs (Piezoelectric Micromachined Ultrasonic Transducer, PMUT) disposed on the same side of the base and a manufacturing method thereof, and a micromachined ultrasonic transducer having the same electronic equipment.

Background technique

As an electroacoustic component, ultrasonic transducer is widely used in production and life. The ultrasonic transducer emits ultrasonic waves to the external environment, and receives the reflected ultrasonic waves through the ultrasonic transducer and converts them into electrical signals for sensing, imaging, and acting on the external environment. Typical applications of ultrasonic transducers include fingerprint recognition, ultrasonic imaging, ultrasonic radar and ranging, non-destructive testing, flow measurement, force feedback, etc., in human body imaging, car reversing radar, underwater sonar detection, sweeping robots, ultrasonic smoke It will be used in scenes such as alarms. The above applications all involve the transmission of ultrasonic signals and the reception of ultrasonic signal echoes by the ultrasonic transducer. Therefore, the transmitting sensitivity and receiving sensitivity of the ultrasonic transducer determine the quality of the ultrasonic transducer to a large extent. The above-mentioned Key indicators in application scenarios.

The use of traditional mechanical cutting solutions to manufacture ultrasonic transducers is limited in terms of miniaturization of the size of the vibration unit, production cost, efficiency, product consistency and yield, etc., and cannot satisfy the further development of ultrasonic imagers, especially in low-cost, Portability, high resolution, etc.

MEMS manufacturing technology based on the semiconductor industry is a very effective way to produce small-size devices with high efficiency, low cost, and mass production. Ultrasonic transducers developed using MEMS technology are mainly based on two principles: capacitive and piezoelectric, corresponding to capacitive micromachined ultrasonic transducer (CMUT) and piezoelectric micromachined ultrasonic transducer (PMUT) respectively. ), they can be integrated with complementary metal oxide semiconductor (Complementary Metal Oxide Semiconductor, CMOS) circuits to achieve low-cost, consistent and large-scale manufacturing of micro-ultrasound transducers with high integration and strong computing capabilities. Among these two transducers, the CMUT needs to apply a large bias voltage when working, resulting in high power consumption and certain limitations in application. In comparison, PMUT is a promising solution. The effective integration of PMUT and CMOS is a crucial factor in realizing the above-mentioned ultrasonic transducer.

As key performance indicators, the transmitting sensitivity and receiving sensitivity of the piezoelectric micromachined ultrasonic transducer PMUT play a vital role in the application of PMUT in the above-mentioned scenarios. If the transmitting sensitivity and receiving sensitivity are too low, the signal signal-to-noise ratio will be affected. Eventually the system becomes inoperable or performs poorly.

PMUT usually exhibits bending vibration mode. When used as an ultrasonic transmitter, an alternating electric field is applied to the electrodes on both sides of the piezoelectric film. Due to the inverse piezoelectric effect, transverse stress is generated in the piezoelectric layer, which in turn generates a bending moment, forcing the film to deviate from the plane and emit into the surrounding medium. Sound pressure wave. As shown in formula (1), the ultrasonic emission sensitivity S _T of the flexural vibration PMUT is proportional to the piezoelectric coefficient е _31f of the piezoelectric film:
S _T ∝e _31f (1)

When the PMUT is used as an ultrasonic receiver, the incident ultrasonic wave deflects the piezoelectric film to generate lateral stress. Due to the positive piezoelectric effect, charges are accumulated on the electrodes on both sides of the piezoelectric film to form a voltage signal, as shown in formula (2). The receiving sensitivity S _R is proportional to the ratio of the piezoelectric coefficient е _31f and the dielectric constant ε ₃₃ ;
S _R ∝e _31f /ε ₃₃ (2)

In ultrasonic imaging, the ultrasonic transducer probe not only serves as a transmitter to emit ultrasonic waves, but also as a receiver to receive ultrasonic waves reflected back from the object to be imaged. The working mode is usually pulse-echo mode, as shown in formula (3). shows that the PMUT pulse-echo sensitivity S _T · S _R is proportional to the ratio of the square of the piezoelectric coefficient е ₃₁ to the dielectric constant ε ₃₃ .

Piezoelectric coefficient and dielectric constant are the basic properties of piezoelectric materials. Table 1 lists the piezoelectric coefficient and dielectric constant properties of PZT and AlN among common piezoelectric materials.

Table 1. Properties of PZT and AlN in common piezoelectric materials

Comparing the two piezoelectric materials PZT and AlN, it can be seen that when used only as a transmitting ultrasonic probe, the piezoelectric constant of PZT is 10 times higher than that of AlN. Based on formula (1), the emission sensitivity of PZT-based PMUT will be that of AlN-based PMUT. 10 times.

However, when used only as a probe for receiving ultrasonic waves, the dielectric constant of PZT is about 110 times that of AlN. times, so the receiving sensitivity of PZT-based PMUT will be about one-twelfth that of AlN-based PMUT. When using an ultrasonic probe in both transmitting and receiving modes, using PZT or AlN as a single piezoelectric material, as shown in Table 1, the sensitivity of the pulse-echo (transmit-receive) signal of the PMUT developed is equivalent.

Therefore, it is difficult for a single piezoelectric material to meet the characteristics of both high voltage coefficient and low dielectric constant. Devices such as PMUT-on-CMOS based on a single piezoelectric material cannot achieve ultra-high ultrasonic emission intensity and ultra-high ultrasonic receiving sensitivity at the same time. application requirements.

In addition, the PMUT manufacturing process includes the deposition of various films (such as piezoelectric films, electrode films, etc.) at different temperatures and the etching of corresponding films in different atmospheres and liquid environments. These processing processes may cause damage to CMOS circuits. In addition, the thinning and patterning processes of different piezoelectric materials and the electrode materials deposited on both sides of the film are also very different. Therefore, there is a process incompatibility problem when processing PMUTs of two materials on the same substrate. This leads to great risks and difficulties in fabricating PMUTs based on different piezoelectric films layer by layer on the same wafer. It is necessary to develop a PMUT-on-CMOS integration with strong process compatibility and convenience that contains different types of piezoelectric materials. plan.

Contents of the invention

In order to alleviate or solve at least one aspect of the above-mentioned problems in the prior art, the present invention is proposed.

Embodiments of the present invention relate to a micromechanical ultrasonic transducer structure, including:

The PMUT unit includes a PMUT substrate, a first PMUT and a second PMUT. Each PMUT includes a first electrode layer, a second electrode layer and a piezoelectric layer,

in:

The first PMUT and the second PMUT are laterally spaced apart from each other and arranged on one side of the PMUT substrate;

The piezoelectric coefficient of the piezoelectric layer of the first PMUT is higher than the piezoelectric coefficient of the piezoelectric layer of the second PMUT, and the dielectric constant of the piezoelectric layer of the first PMUT is lower than the dielectric constant of the piezoelectric layer of the second PMUT. .

Embodiments of the present invention also relate to a method for manufacturing a micromechanical ultrasonic transducer structure, which includes the steps:

A transistor unit is provided, the transistor unit including a transistor substrate and first and second transistors arranged spaced apart in a lateral direction; and

A PMUT unit bonded to a surface of one side of the transistor unit is provided. The PMUT unit includes a PMUT substrate, a first PMUT and a second PMUT. The PMUT base is bonded to the surface of one side of the transistor unit in a surface bonding manner. Each PMUT includes a third PMUT. an electrode layer, a second electrode layer and a piezoelectric layer,

in:

The first PMUT and the second PMUT are laterally spaced apart from each other and arranged on one side of the PMUT substrate, and respectively correspond to the first transistor and the second transistor in the thickness direction of the micromachined ultrasound transducer structure; and

The piezoelectric coefficient of the piezoelectric layer of the first PMUT is higher than the piezoelectric coefficient of the piezoelectric layer of the second PMUT, and the dielectric constant of the piezoelectric layer of the first PMUT is lower than the dielectric constant of the piezoelectric layer of the second PMUT.

Embodiments of the present invention also relate to an electronic device, including the above-mentioned micro-machined ultrasonic transducer structure, or the micro-machined ultrasonic transducer structure manufactured by the above-mentioned manufacturing method.

Description of drawings

These and other features and advantages of various disclosed embodiments of the present invention may be better aided in understanding by the following description and accompanying drawings, in which like reference numerals refer to like parts throughout, wherein:

1-4 are schematic structural diagrams of micromachined ultrasound transducer structures according to different exemplary embodiments of the present invention;

5-13 are schematic cross-sectional views illustrating a manufacturing method of the micromachined ultrasonic transducer structure shown in FIG. 2 according to an exemplary embodiment of the present invention;

Figure 14 is a schematic diagram of a PMUT structure array according to an exemplary embodiment of the present invention.

Detailed ways

The technical solution of the present invention will be further described in detail below through examples and in conjunction with the accompanying drawings. In the specification, the same or similar reference numbers indicate the same or similar components. The following description of the embodiments of the present invention with reference to the accompanying drawings is intended to explain the general inventive concept of the present invention and should not be understood as a limitation of the present invention. Some, but not all, embodiments of the invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art fall within the scope of protection of the present invention.

The inventor found that if a piezoelectric material-based PMUT with a high voltage coefficient is used as an ultrasonic transmitter and a piezoelectric material-based PMUT with a low dielectric constant is used as an ultrasonic receiver, for example, they can be integrated on a set of ultrasonic transducers as shown in the table below. For the PZT-based PMUT and AlN-based PMUT shown in 1, where the PZT-based PMUT is used as the ultrasonic transmitter and the AlN-based PMUT is used as the ultrasonic receiver, its pulse-echo sensitivity will be 100 times higher than that of a single material-based PMUT.

In addition, the existing integration of PMUT and CMOS is mainly achieved through the following two solutions:

Plan 1. Use the CMOS wafer as the substrate, perform various thin film deposition and etching processes on it, and then The PMUT manufacturing process includes the deposition of various films (such as piezoelectric films, electrode films, etc.) at different temperatures and the etching of corresponding films in different atmospheres and liquid environments. This requires that the processing process does not cause damage to the CMOS circuit. Among known piezoelectric materials, only a few piezoelectric films such as AlN-based piezoelectric materials have MEMS manufacturing processes that are compatible with CMOS. Therefore, this solution is mainly used for the development of integrated ultrasonic transducers based on corresponding piezoelectric materials. . However, the piezoelectric properties of the piezoelectric film are a crucial determinant of PMUT performance. For example, piezoelectric materials with very excellent piezoelectric properties such as PZT and LiNbO ₃ have more demanding processing techniques than AlN and poor compatibility with CMOS. Therefore, the development of CMOS integrated PMUT based on the above process flow is very limited and difficult to achieve.

Option 2. Process PMUT wafers and CMOS wafers separately, set the side of the PMUT wafer with the piezoelectric film and the side of the CMOS wafer with the transistor as the front side of the corresponding wafer, connect the front side of the PMUT wafer and CMOS front-side bonding to build a CMOS integrated PMUT. Compared with the above scheme 1, this scheme has fewer limitations on piezoelectric materials. However, the effective vibration of the PMUT mechanical vibration unit is the key to efficiently transmitting and receiving ultrasonic waves, which requires a cavity structure below the vibration unit to provide space For the vibration unit to vibrate effectively, this requires a corresponding cavity on the CMOS. However, the cavity size is the core factor that determines the PMUT ultrasonic frequency, and changes in the cavity size will lead to changes in the PMUT ultrasonic frequency. When two wafers of PMUT and CMOS are bonded, alignment deviations inevitably occur, resulting in random deviations between the vibration unit area and its own design, resulting in frequency fluctuations of the developed CMOS integrated PMUT. It is worth pointing out that the diameter of PMUT transducers used in the field of ultrasound imaging is very small, usually tens of microns or even smaller. Even an alignment deviation of 1 micron will cause great adverse effects.

Therefore, there is still a need in the existing technology to develop a CMOS and PMUT integration solution that is highly adaptable to the piezoelectric material itself, and/or the integration process of the CMOS unit and the PMUT unit does not affect the cavity size.

Based on the above, the present invention proposes to separately integrate piezoelectric material-based PMUTs with high voltage electrical coefficients (for example, the absolute value is higher than 1C/m ² , and further higher than 5C/m ² ) and low voltage electrical coefficients on the same CMOS wafer. Two types of ultrasonic transducers are piezoelectric material-based PMUTs with a dielectric constant (for example, lower than 1200 and further lower than 100). Among them, piezoelectric material-based PMUTs with high dielectric coefficient are dedicated to emitting ultrasonic waves, while those with low dielectric coefficients are The constant piezoelectric material-based PMUT is used to receive the reflected ultrasonic waves. The above-mentioned PMUT and CMOS integration solution is the key to developing MEMS ultrasound transducers with excellent performance and low cost.

The present invention also proposes a solution to simultaneously integrate the above two types of piezoelectric material-based PMUTs on the same CMOS wafer.

First, the reference numbers in the drawings of the present invention are explained as follows:

1000: CMOS unit or transistor unit.

100: CMOS substrate or transistor substrate, optional materials are single crystal silicon, gallium nitride, gallium arsenide, sapphire, quartz, silicon carbide, diamond, etc.

101: Source and drain of the transistor.

110: Circuit protection layer, which is an insulating material layer, which can be silicon dioxide, silicon nitride, etc.

111: Gate of transistor.

113A: The electrical connection layer within the transistor unit layer, corresponding to the first electrical connection layer, the material can be molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper, titanium, iridium, osmium, chromium or a composite of the above metals or their alloys etc., the above materials are also suitable for other electrical connection layers.

113B: Electrical connection layer within the transistor unit layer, corresponding to the second electrical connection layer.

113, 115: Electrical connection layers within other transistor unit layers.

112 and 114: electrical connection layers between transistor unit layers.

2000’: PMUT preliminary unit, see Figure 9 for example.

2000: PMUT unit, see Figure 11.

200’: PMUT preliminary substrate, optional materials are single crystal silicon, gallium nitride, gallium arsenide, sapphire, quartz, silicon carbide, diamond, etc.

200: PMUT substrate, the material is consistent with the PMUT preliminary substrate.

201 and 202: Cavities for PMUT.

210: The material of the support layer may be the same as or different from the material of the electrode layer. The support layer can be provided at the lower part of the PMUT as shown in Figure 6, that is, between the PMUT and the PMUT substrate. In this case, the support layer is an insulating layer, and its material can be non-conductive materials such as silicon, silicon dioxide, and silicon nitride. The support layer can also be provided on the upper part of the PMUT. It should be pointed out that the support layer does not need to be provided.

220, 240: Electrode layer, the material can be molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper, titanium, iridium, osmium, chromium or composites of the above metals or their alloys, etc. The materials of the two electrode layers can be the same or different.

230, 270: Piezoelectric layer. Materials available include polycrystalline aluminum nitride (AlN), polycrystalline zinc oxide, polycrystalline lead zirconate titanate (PZT), polycrystalline lithium niobate (LiNbO ₃ ), polycrystalline lithium tantalate (LiTaO ₃ ), polycrystalline niobium Materials such as potassium nitrate (KNbO ₃ ), or single crystal aluminum nitride, single crystal gallium nitride, single crystal lithium niobate, single crystal lead zirconate titanate, single crystal potassium niobate, single crystal quartz film, or single crystal tantalum Lithium oxide and other materials, the above-mentioned single crystal or polycrystalline materials can also include rare earth element doped materials with a certain atomic ratio, all of which belong to the piezoelectric layer that can be used in the present invention, such as scandium Doped aluminum nitride (AlScN).

250: Structural protective layer, usually dielectric material, such as silicon dioxide, aluminum nitride, silicon nitride, etc.

235: Conductive layer or electrical connection layer, the material of which can be selected from the materials used to form the electrode layer.

275: Conductive layer or electrical connection layer, the material of which can be selected from the materials used to form the electrode layer.

290: Device protective layer, usually dielectric material, such as silicon dioxide, aluminum nitride, silicon nitride, etc.

300: Auxiliary substrate, optional materials are single crystal silicon, gallium nitride, gallium arsenide, sapphire, quartz, silicon carbide, diamond, etc.

310: Temporary adhesive layer, which can be made of any material that can temporarily join the PMUT unit and the auxiliary substrate 300, such as photoresist.

400A: First conductive hole.

400B: Second conductive hole.

500: Bonding material layer, see Figure 4, which can be a metal bonding layer, such as gold-gold bonding, aluminum-germanium bonding, etc., or other material layers that bond two layers together.

3000: Micromachined ultrasound transducer structure or PMUT structure (see Figure 1 and Figure 14).

4000: PMUT structure array (see Figure 14).

1-4 are schematic structural diagrams of a micromachined ultrasound transducer structure 3000 according to different exemplary embodiments of the present invention.

In the illustrated embodiment, a single PMUT generally includes a support layer 210, a piezoelectric layer 230, and a top electrode layer 240 and a bottom electrode layer 220 on both sides of the piezoelectric layer 230 (see, for example, Figures 6 to 9). When the PMUT vibrates Cavities 201 and 202 are provided on the side of the unit facing the CMOS, so that the PMUT vibration unit can generate effective bending vibration to generate ultrasonic waves. In the present invention, two types of ultrasonic transducers, a piezoelectric material-based PMUT with a high voltage coefficient and a piezoelectric material-based PMUT with a low dielectric constant, are simultaneously integrated on a CMOS wafer or the transistor unit 1000 as shown in the figure.

As shown in Figure 1, 230 and 270 respectively represent the high-voltage coefficient-based piezoelectric film and the low-dielectric constant-based piezoelectric film. 201 and 202 are respectively the cavity areas where the PMUT composed of two types of piezoelectric films undergoes effective bending vibration. 200 is a substrate for building a PMUT or a PMUT base, 100 is a substrate for building a CMOS circuit or a transistor base, and 110 is a circuit protection layer.

As mentioned before, in more specific embodiments, the absolute value of the piezoelectric coefficient of the piezoelectric layer 230 is greater than 1 C/m ² , and/or the dielectric constant of the piezoelectric layer 270 is less than 1200. Further, the absolute value of the piezoelectric coefficient of the piezoelectric layer 230 is greater than 5C/m ² , and/or the dielectric constant of the piezoelectric layer 270 is less than 100.

In a more specific embodiment, piezoelectric layer 230 is PZT or doped PZT, and piezoelectric layer 270 is ALN or AlScN. In terms of PMUT-on-CMOS integration, the present invention produces CMOS wafers and PMUT wafers respectively, in which two types of piezoelectric film-based PMUTs are produced on the PMUT wafer, and then the substrate side of the PMUT wafer is thinned and combined with the CMOS The front side of the wafer is bonded, and finally the PMUT wafer electrodes are interconnected with the corresponding electrodes on the CMOS wafer to achieve electrical connection. If necessary, the surface of the device is protected (for details, please refer to the examples in Figures 5 to 13). gender description). In this integrated solution, when processing different types of piezoelectric film-based PMUTs, even if there are relatively harsh processing conditions, the CMOS wafer will not be damaged, and the process compatibility is good.

In terms of the formation method of the cavities 201 and 202 required for PMUT vibration, as shown in Figure 1, the cavities can be formed by presetting the cavities, filling them with sacrificial layer materials, and releasing them in the final stage. Figure 2 shows the cavity formed by back-engraving. Figure 3 shows a piezoelectric film-based PMUT that uses a back-engraving method, and another piezoelectric film-based PMUT that uses a sacrificial layer to form a cavity.

In the bonding of PMUT wafers and CMOS wafers, the PMUT wafer substrate layer can be directly bonded to the circuit protection layer of the CMOS wafer (for example, see Figure 1-Figure 3), or through an intermediate bonding layer material (such as Metal bonding, etc., corresponding to the bonding material layer 500) realizes the integration of the PMUT unit and the CMOS unit (see, for example, Figure 4).

In the embodiment shown in FIGS. 1 to 4 , the PMUT unit includes two PMUTs spaced apart in the lateral direction, namely a first PMUT and a second PMUT. The piezoelectric coefficient of the piezoelectric layer 230 of the first PMUT is high. The piezoelectric coefficient of the piezoelectric layer 270 of the second PMUT, and the dielectric constant of the piezoelectric layer 230 of the first PMUT is lower than the dielectric constant of the piezoelectric layer 270 of the second PMUT. In a further embodiment, the piezoelectric layer 230 of the first PMUT is PZT and the piezoelectric layer 270 of the second PMUT is AlN.

In the present invention, for the independent claims, the PMUT substrate can be a substrate such as single crystal silicon, gallium nitride, gallium arsenide, sapphire, quartz, silicon carbide, diamond, etc., as shown in Figures 1 to 4, Other support structures for generating PMUT may also be used, which are all within the protection scope of the present invention.

In the embodiments shown in FIGS. 1 to 4 , a PMUT-on-CMOS structure is adopted, but the present invention is not limited thereto. The above-mentioned PMUT unit can also be arranged on other structures, and PMUT-on-CMOS is an advantageous embodiment of the present invention.

In the embodiment shown in FIGS. 1 to 4 , the first PMUT of the PMUT unit is used to transmit ultrasonic waves, and the second PMUT is used to receive ultrasonic waves.

5-13 are exemplary illustrations of the microcomputer shown in FIG. 2 according to an exemplary embodiment of the present invention. Schematic cross-sectional view of the manufacturing method of the mechanical ultrasonic transducer structure. More specifically, Figures 5 to 13 illustrate the formation of the cavity required for PMUT vibration in the form of back-engraving, taking the direct bonding of the PMUT substrate 200 and the CMOS circuit protection layer 110 as an example, in which the high-voltage electrical coefficient material 230 or the first PMUT The piezoelectric layer 230 is made of PZT, and the low dielectric constant material 270 or the piezoelectric layer 270 of the second PMUT is made of AlN to construct a PMUT-on-CMOS ultrasonic transducer with ultra-high pulse-echo sensitivity.

Transistor unit 1000 is provided first. Figure 5 is a schematic diagram of the CMOS structure, in which 100 is the CMOS substrate, that is, the transistor substrate (which can be silicon, etc.), and 110 is the circuit protection layer (which can be silicon oxide, silicon nitride, etc.). 101 is the source and drain of the transistor, 111 is the gate of the transistor, 113A, 113B, 113 and 115 are the electrical connection layers within the CMOS layer, and 112 and 114 are the electrical connection layers between the CMOS layers. As shown in FIG. 5 , the transistor unit includes a transistor substrate 100 and first and second transistors spaced apart in the lateral direction. It should be noted that the structure shown in Figure 2 is exemplary. For the present invention, the CMOS unit 1000 may include a CMOS transistor and a circuit protection layer 110, and may optionally include a first electrical connection layer 113A, a second electrical connection layer 113A, and a second electrical connection layer 113A. Connection layer 113B.

Next, a PMUT preliminary unit 2000' is provided, see Figure 9. The PMUT preliminary unit 2000' includes a PMUT preliminary base 200', a first PMUT and a second PMUT. Each PMUT includes a bottom electrode layer 220, a top electrode layer 240, and a piezoelectric layer 230. The following describes how to provide the PMUT preliminary unit 2000' with specific reference to Figures 6-9.

In Figure 6, a PZT-based PMUT is first formed on the support layer 210, where 200' is the PMUT substrate, that is, the PMUT initial substrate (which can be silicon), 210 is the support layer (can be silicon oxide, etc.), and 230 is PZT Piezoelectric film layer or piezoelectric layer, 220 and 240 are the bottom and top electrode layers on both sides of the piezoelectric film layer. MEMS technology can be used to form PZT-based PMUT. The initial substrate 200' here is relative to the substrate 200 in Figure 11. The initial substrate 200' becomes the substrate 200 after being thinned.

As shown in Figure 7, after the piezoelectric layer 230 and the top and bottom electrode structures of the PZT-based PMUT are patterned, a structural protective layer 250 is deposited on the surface of the PZT-based PMUT to protect the PZT-based PMUT during the subsequent processing of the AlN-based PMUT. .

As shown in Figure 8, on a wafer or initial substrate 200' provided with a PZT-based PMUT, an AlN-based PMUT is constructed. The AlN-based PMUT includes a piezoelectric film layer or an ALN piezoelectric layer 270 and top and bottom electrode layers 280 and 260.

As shown in FIG. 9 , after the PZT-based PMUT and the AlN-based PMUT are formed on the wafer or initial substrate 200 ′, the structural protection layer 250 of the PZT-based PMUT is removed to obtain the PMUT unit 2000 . As shown in Figure 9 It includes two PMUTs, PZT-based PMUT and AlN-based PMUT.

As shown in Figure 9, the PMUT preliminary unit 2000' does not include an electrical connection structure that connects the PMUT electrodes and the CMOS electrodes together. In Figure 9, the thickness of the PMUT preliminary substrate 200' in Figure 9 is too large and needs to be thinned in subsequent steps based on the subsequent thinning process to make the electrical connection part between the PMUT and CMOS as short as possible and requires bonding The thickness of the PMUT substrate on the CMOS wafer should be as thin as possible, preferably below 10 microns, or even below 5 microns. However, if the thickness of the PMUT substrate already meets the requirements, the subsequent substrate thinning step may not be performed, or if the length of the electrical connection part between the PMUT and CMOS can be tolerated, the subsequent substrate thinning step may not be performed. Thinning steps, these are all within the protection scope of the present invention.

The following exemplifies how to bond the PMUT unit 2000 to the transistor unit 1000 with reference to FIGS. 10 and 11 .

As shown in FIG. 10 , the PZT-based PMUT and the AlN-based PMUT are covered with a temporary adhesive layer 310 and an auxiliary substrate 300 is provided. The auxiliary substrate 300 is bonded to the temporary adhesive layer 310 . In wafer-level fabrication, the auxiliary substrate 300 is provided for subsequent PMUT initial substrate thinning.

As shown in FIG. 11, a thinning process is performed on the other side of the initial substrate 200' to form the PMUT substrate 200. The auxiliary substrate 200' in Figure 10 can be thinned to a required size, for example, less than 10 μm, or even less than 5 μm, and can be surface polished if required by the bonding process. Then the cavities 201 and 202 required for PMUT vibration are etched through a back etching process, as shown in Figure 11.

Then, the PMUT substrate 200 is bonded to the surface of the transistor unit or the CMOS circuit protection layer 110, and the temporary adhesive layer 310 and the auxiliary substrate 300 are removed, as shown in FIG. 11 . Various bonding solutions can be selected, including silicon-silicon bonding, silicon-silicon oxide bonding, and metal bonding.

As shown in FIG. 12 , the PMUT substrate 200 and the CMOS circuit protection layer 110 are etched through an etching process to form conductive holes, exposing the electrical connection terminals or the electrical connection layer of the CMOS. As shown in FIG. 12 , for each PMUT, a first conductive hole 400A and a second conductive hole 400B are etched to expose the intra-transistor unit layer electrical connection layer 113A and the transistor unit layer intra-electrical connection layer 113B respectively. Optionally, the first electrical connection layer 113A is electrically connected to one of the electrodes of the CMOS transistor (for example, the source), and the second electrical connection layer 113B is electrically connected to another one of the electrodes of the CMOS transistor (for example, the gate). . However, when there are other electrical connection structures in the CMOS unit, based on needs and requirements, the first electrical connection layer 113A and/or the second electrical connection layer 113B can also be electrically connected thereto, which is also within the scope of the present invention. within the range.

As shown in Figure 13, for example, using a deposition process, the electrical connection layers 235 and 275 of PMUT and CMOS are provided, Realize the electrical connection between PMUT and CMOS. Finally, if desired, a protective layer or device protection layer 290 is deposited over the entire device surface. Among them, 235 and 275 are electrical connection layers. Various conductive materials can be used, such as materials to form electrode layers. In addition, the conductive channel or electrical connection layer 235 used to connect the PZT-based PMUT and the CMOS circuit is similar to the material used to realize AlN. The conductive channel or electrical connection layer 275 that electrically connects the base PMUT to the CMOS may be of the same type of material or may be of different types of conductive materials. As can be understood, it is obvious that the electrical connection layers 235 and 275 are electrically insulated from each other, and both the electrical connection layers 235 and 275 are electrically connected to the transistor unit intra-layer electrical connection layer 113A and the intra-layer electrical connection layer 113B respectively through conductive holes. .

As can be understood, in the above method, if the bonding between the PMUT unit and the transistor unit is achieved by providing the bonding material layer 500, then the PMUT unit, the transistor unit and the bonding material layer jointly define a cavity, and the bonding material layer 500 The thickness defines the height of the cavity.

In addition, in the above technical solution, the PMUT substrate 200 is bonded to the circuit protection layer 110, as shown in Figure 1, that is, the base side (or back side) of the PMUT unit 2000 is bonded to the wafer side (or front side) of the CMOS unit 1000. , thus: (1) When PMUT needs to be prepared on the PMUT substrate 200 in subsequent steps, the PMUT substrate 200 can protect the CMOS unit 1000, or (2) the PMUT unit 2000 can be directly connected to the CMOS unit 1000 without considering the preparation of PMUT. impact on the CMOS unit 1000. This can make the above-mentioned micromechanical ultrasonic transducer structure highly adaptable to piezoelectric materials, which can be aluminum nitride (AlN), lead zirconate titanate (PZT), or lithium niobate (LiNbO ₃ ) , lithium tantalate (LiTaO ₃ ), potassium niobate (KNbO ₃ ) and other materials.

It should be pointed out that the "bonding of the PMUT substrate and the circuit protection layer" in the present invention not only includes the direct bonding of the two as shown in Figure 1, but also includes other bonding layers or film layers provided between the two. For example, in Figure 4, a bonding material layer 500, which may be a metal bonding layer, is provided between the PMUT substrate and the circuit protection layer.

It should be noted that in the specific embodiment of the present invention, the connection between the PMUT substrate and the circuit protection layer is taken as an example for illustration. However, the connection between the PMUT substrate and the CMOS unit 1000 may be to define the surface of the CMOS unit. The circuit protection layer, which may also be other layers defining the surface of the CMOS unit, is within the scope of the present invention.

In the embodiment shown in FIGS. 1 to 4 , the CMOS unit 1000 further includes a CMOS substrate 100 , one side of the circuit protection layer 110 is bonded to the PMUT substrate 200 , and the other side of the circuit protection layer 110 is bonded to the CMOS substrate 100 . Optionally, in some cases, the PMUT unit can also be bonded to the CMOS substrate 100, which is also within the protection scope of the present invention.

It should also be specifically pointed out that in the present invention, CMOS is used as an example of a transistor, and thus a CMOS unit is used as an example of a transistor unit. However, the invention is not limited thereto. The transistor can also be a BiMOS unit or BCD, etc., so that a transistor The unit can also be a BiMOS unit or a BCD unit, etc.

Similar to the explanation and description of "the PMUT substrate is bonded to the circuit protective layer", the "surface bonding of the PMUT unit and the transistor unit" in the present invention may be the case where the PMUT unit is directly bonded to the surface of the transistor unit, and may also include The situation where other bonding layers or film layers are provided between the surface of the unit and the transistor unit are within the scope of protection of the present invention.

As shown in Figures 1-4, the PMUT substrate 200 is provided with a cavity 201 for the PMUT. That is, in the case where the PMUT unit 2000 is used to bond with the CMOS unit 1000, the cavity 201 has been set in the PMUT unit 2000. In other words, in wafer-level manufacturing, the cavity structure required for PMUT vibration is set on the side of the PMUT wafer, and there is no need to form a cavity on the CMOS wafer. Therefore, there is no alignment problem during the integration process between the CMOS wafer and the PMUT wafer. The change in the vibration area caused by the deviation, and the resulting change in the frequency of the ultrasonic transducer, overcome the technical problem in the existing technology that the integration process of CMOS and PMUT has a negative impact on the cavity size. Although not shown, in alternative embodiments, cavity 201 may extend through PMUT substrate 200 .

In the structure shown in FIGS. 1-4 above, the PMUT substrate 200 is provided with a cavity 201 for the PMUT. However, the present invention is not limited to this. The cavity 201 may not be provided in the PMUT substrate 200. More specifically, a bonding material layer 500 is provided between the PMUT unit 2000 and the transistor unit. The PMUT unit 2000, the transistor unit 1000 and the bonding material layer 500 jointly define the cavity 201. The thickness of the bonding material layer 500 defines the height of the cavity 201 . In this way, in wafer-level manufacturing, the cavity 201 required for PMUT vibration does not need to be formed on the CMOS wafer, and the bonding material layer 500 based on, for example, a metal bonding layer can define the sides of the cavity 201 in the lateral direction. The area of the cavity 201 is larger, which can reduce the changes in the vibration area caused by the alignment deviation during the integration process of the CMOS wafer and the PMUT wafer, and the resulting changes in the frequency of the ultrasonic transducer, overcoming or reducing In the prior art, there is a technical problem that the integration process of CMOS and PMUT adversely affects the cavity size. In the above solution, the cavity 201 is located on the side of the joint surface where the PMUT unit is installed. The formation of the cavity 201 will not cause additional changes to the structure of the transistor unit. There is no need to set a cavity in the transistor unit before integrating the two. , reducing or avoiding the technical problem in the prior art that the integration process of the CMOS unit and the PMUT unit has an adverse impact on the cavity size.

As shown in Figures 1-4, in an optional embodiment, for each PMUT, the micromachined ultrasonic transducer structure is provided with a first conductive hole 400A and a second conductive hole 400B. The first conductive hole 400A through The second conductive hole 400B penetrates the PMUT substrate 200 and/or the support layer 210 and reaches the first electrical connection layer 113A in the circuit protection layer 110. Two electrical connection layers 113B, wherein: the first conductive layer 235 is electrically connected to the first electrical connection layer 113A through the first conductive hole 400A, and the second conductive layer 275 is electrically connected to the second electrical connection layer 113B through the second conductive hole 400B. connect.

As shown in Figures 1-4, in an optional embodiment, the PMUT unit 2000 includes a support layer 210, and the support layer 210 is used to realize the bending vibration of the PMUT. As shown in Figures 1 to 4, the support layer 210 is provided between the PMUT (including the electrode layers 220, 240 and the piezoelectric layer 230) and the PMUT substrate 200. At this time, the first conductive hole 400A and the second conductive hole 400B Through the support layer 210. As can be understood, the support layer 210 may not be provided, or the support layer 210 may be provided above the top electrode or the first electrode layer 240. In this case, the first conductive hole 400A and the second conductive hole 400B do not use or have no through support. layer situation. These solutions are all within the protection scope of the present invention.

However, regardless of whether the support layer 210 and/or the PMUT substrate 200 is provided, the first conductive holes 400A and the second conductive holes 400B need to penetrate the PMUT unit to reach the underlying electrical connection layer.

Although not shown, the first conductive layer 235 and the second conductive layer 275 may be electrically connected to the first electrical connection layer 113A and the second electrical connection layer 113B exposed on the side of the micromachined ultrasonic transducer structure, respectively. It is also within the protection scope of the present invention.

In addition, when the PMUT is placed in the cavity, the cavity plays a protective role in isolating the PMUT (especially the piezoelectric layer) from the external environment, which can improve the reliability and long-term stability of the PMUT, and then be used in the above-mentioned PMUT structure. When used, for example, in an imager, the reliability and long-term stability of the final imaging system can be improved.

Figure 14 is a schematic diagram of a PMUT structure array according to an exemplary embodiment of the present invention. As shown in Figure 14, the above-mentioned PMUT structure 3000 may be only one array element in the array 4000. In Figure 14, the hollow circle represents the PMUT vibration area of the PMUT structure 3000. In addition to the circle, it can be any desired shape such as an ellipse, a polygon, and a combination thereof. The solid black circle represents the electrical connection between the PMUT unit and the CMOS unit, as shown in Figure 5 at the first electrical connection layer 113A and the second electrical connection layer 113B, which can also be in any desired shape. The PMUT structures 3000 are combined to form a PMUT structure array 4000.

Each PMUT unit can be individually controlled through a matching CMOS circuit to form a two-dimensional PMUT structure array 4000.

Multiple PMUT structures 3000 can also be connected together. For example, the electrodes of the PMUT structures 3000 on the same column are interconnected to form a one-dimensional line array. At this time, the circuit of the CMOS unit and the electrical connection point of the PMUT unit Reduce, the electrical connection points of a pair of CMOS units and PMUT units control multiple PMUT units simultaneously.

An ultrasonic transducer can be formed based on a PMUT structure or a PMUT structure array. The ultrasonic transducer can be used in an ultrasonic imager. The PMUT structure or PMUT structure array can also be used in other electronic devices, such as ultrasonic rangefinders, Ultrasonic fingerprint sensors, non-destructive flaw detectors used in industrial fields, etc.

Based on the above, the present invention proposes the following technical solutions:

1. A micromechanical ultrasonic transducer structure, including:

The PMUT unit includes a PMUT substrate, a first PMUT and a second PMUT. Each PMUT includes a first electrode layer, a second electrode layer and a piezoelectric layer,

in:

The first PMUT and the second PMUT are laterally spaced apart from each other and arranged on one side of the PMUT substrate;

The piezoelectric coefficient of the piezoelectric layer of the first PMUT is higher than the piezoelectric coefficient of the piezoelectric layer of the second PMUT, and the dielectric constant of the piezoelectric layer of the first PMUT is lower than the dielectric constant of the piezoelectric layer of the second PMUT. .

2. The micromechanical ultrasonic transducer structure according to 1, wherein:

The piezoelectric layer of the first PMUT is PZT or doped PZT, and the piezoelectric layer of the second PMUT is ALN or AlScN.

3. The micromechanical ultrasonic transducer structure according to 1, wherein:

The first PMUT is used to transmit ultrasonic waves, and the second PMUT is used to receive ultrasonic waves.

4. The micromechanical ultrasonic transducer structure according to any one of 1-3, also includes:

A transistor unit, including a transistor substrate and a first transistor and a second transistor arranged spaced apart in a lateral direction, the first PMUT and the second PMUT being respectively aligned with the first transistor and the second transistor in the thickness direction of the micromachined ultrasonic transducer structure corresponding;

The PMUT unit is bonded to a surface on one side of the transistor unit, and the surface on one side of the transistor unit is the bonding surface of the transistor unit.

5. The micromechanical ultrasonic transducer structure according to 4, wherein:

The cavities for the first PMUT and the second PMUT are on the side of the joint surface on which the PMUT units are disposed.

6. The micromechanical ultrasonic transducer structure according to 5, wherein:

The PMUT substrate is bonded to the surface of one side of the transistor cell, the PMUT substrate being provided with the cavity.

7. The micromechanical ultrasonic transducer structure according to 6, wherein:

The PMUT unit also includes a support layer for supporting the PMUT, and the support layer is disposed between the two PMUTs and the PMUT substrate.

8. The micromechanical ultrasonic transducer structure according to 6, wherein:

The cavity penetrates the PMUT substrate; or

A bonding material layer is provided between the PMUT unit and the transistor unit. The PMUT unit, the transistor unit and the bonding material layer jointly define the cavity. The thickness of the bonding material layer defines the cavity. high.

9. The micromechanical ultrasonic transducer structure according to 4, wherein:

Each transistor unit includes the transistor, a first electrical connection layer and a second electrical connection layer electrically insulated from each other; and

For each PMUT and corresponding transistor: the micromachined ultrasonic transducer structure further includes a first conductive layer and a second conductive layer that are electrically insulated from each other, and the first electrode layer is electrically connected to the first electrical connection layer through the first conductive layer. connection, the second electrode layer is electrically connected to the second electrical connection layer via the second conductive layer.

10. According to the micromachined ultrasonic transducer structure described in 9, for each PMUT and corresponding transistor, it also includes:

A first conductive hole and a second conductive hole. The first conductive hole penetrates the PMUT unit and reaches the first electrical connection layer in the transistor unit. The second conductive hole penetrates the PMUT unit and reaches the second electrical connection layer in the transistor unit. ,

in:

The first conductive layer is electrically connected to the first electrical connection layer through the first conductive hole, and the second conductive layer is electrically connected to the second electrical connection layer through the second conductive hole.

11. The micromechanical ultrasonic transducer structure according to 4, wherein:

The transistor unit includes a circuit protection layer covering the transistor; and

The surface on one side of the circuit protection layer is the joint surface.

12. The micromechanical ultrasonic transducer structure according to 4, wherein:

The transistor unit includes one of a CMOS unit, a BiMOS unit, and a BCD unit.

13. The micromechanical ultrasonic transducer structure according to 1, wherein:

The absolute value of the piezoelectric coefficient of the piezoelectric layer of the first PMUT is greater than 1C/m ² ; and/or

The dielectric constant of the piezoelectric layer of the second PMUT is less than 1200.

14. The micromechanical ultrasonic transducer structure according to 13, wherein:

The absolute value of the piezoelectric coefficient of the piezoelectric layer of the first PMUT is greater than 5C/m ² ; and/or

The dielectric constant of the piezoelectric layer of the second PMUT is less than 100.

15. A method for manufacturing a micromechanical ultrasonic transducer structure, including the steps:

A transistor unit is provided, the transistor unit including a transistor substrate and first and second transistors arranged spaced apart in a lateral direction; and

A PMUT unit bonded to a surface of one side of the transistor unit is provided. The PMUT unit includes a PMUT substrate, a first PMUT and a second PMUT. The PMUT base is bonded to the surface of one side of the transistor unit in a surface bonding manner. Each PMUT includes a third PMUT. an electrode layer, a second electrode layer and a piezoelectric layer,

in:

The first PMUT and the second PMUT are laterally spaced apart from each other and arranged on one side of the PMUT substrate, and respectively correspond to the first transistor and the second transistor in the thickness direction of the micromachined ultrasound transducer structure; and

The piezoelectric coefficient of the piezoelectric layer of the first PMUT is higher than the piezoelectric coefficient of the piezoelectric layer of the second PMUT, and the dielectric constant of the piezoelectric layer of the first PMUT is lower than the dielectric constant of the piezoelectric layer of the second PMUT.

16. The method according to 15, wherein the step of providing the PMUT unit includes:

After forming a PMUT, set a protective layer covering it;

disposing another PMUT laterally spaced apart from the one PMUT;

Remove the protective layer.

17. The method according to 15 or 16, wherein the step of providing the PMUT unit includes:

providing a PMUT initial base and laterally spaced first and second PMUTs disposed on one side of the initial base;

covering the first PMUT and the second PMUT with a temporary adhesive layer and providing an auxiliary substrate, the auxiliary substrate being bonded to the temporary adhesive layer;

Perform a thinning process on the other side of the initial substrate to form the PMUT substrate, and

After the step of bonding the PMUT substrate to the surface of the transistor unit, the method further includes the step of removing the temporary adhesive layer and the auxiliary substrate.

18. The method according to 15, wherein:

The PMUT substrate is bonded to the surface of one side of the transistor unit using a bonding material layer. The PMUT unit, the transistor unit and the bonding material layer jointly define the cavity. The thickness of the bonding material layer defines the cavity. cavity height.

19. The method according to 15, wherein:

For each transistor, the transistor unit includes a first electrical connection layer and a second electrical connection layer that are electrically insulated from each other;

The method further includes the steps of: for each PMUT and the corresponding transistor, providing a first conductive layer and a second conductive layer that are electrically insulated from each other, the first electrode layer is electrically connected to the first electrical connection layer via the first conductive layer, and The two electrode layers are electrically connected to the second electrical connection layer through the second conductive layer.

20. According to the method described in 19, for each PMUT and corresponding transistor, where:

Before the step of providing the first conductive layer and the second conductive layer that are electrically insulated from each other, the method further includes the step of forming a first conductive hole and a second conductive hole, and the first conductive hole penetrates the PMUT unit and reaches to expose the inside of the transistor unit. The first electrical connection layer, the second conductive hole penetrates the PMUT unit and reaches to expose the second electrical connection layer in the transistor unit;

In the step of providing the first conductive layer and the second conductive layer that are electrically insulated from each other, the first conductive layer is electrically connected to the first electrical connection layer through the first conductive hole, and the second conductive layer is electrically connected to the first conductive layer through the second conductive hole. The two electrical connection layers are electrically connected.

21. The method according to any one of 15-20, wherein:

Providing a transistor unit includes providing a transistor wafer based on a MEMS process, the transistor wafer being formed with a plurality of transistor units, each transistor unit including a first transistor and a second transistor arranged spaced apart in a lateral direction;

Providing a PMUT unit bonded to the surface of one side of the transistor unit includes: providing a PMUT wafer based on the MEMS process, the PMUT wafer is formed with a plurality of PMUT units respectively corresponding to the plurality of transistor units, each PMUT unit including a first PMUT and a second PMUT arranged laterally spaced apart from each other, the first PMUT and the second PMUT respectively corresponding to the first transistor and the second transistor in the thickness direction of the micromechanical ultrasonic transducer structure;

The method also includes the step of performing cutting to form a micromachined ultrasound transducer structure including a single PMUT unit and a single transistor unit.

22. The method according to any one of 15-21, wherein:

The piezoelectric layer of the first PMUT is PZT or doped PZT, and the piezoelectric layer of the second PMUT is AlN or AlScN.

23. The method according to any one of 15-22, wherein:

The first PMUT is used to transmit ultrasonic waves, and the second PMUT is used to receive ultrasonic waves.

24. The method according to any one of 15-23, wherein:

The transistor unit includes one of a CMOS unit, a BiMOS unit, and a BCD unit.

25. The method according to 15, wherein:

The absolute value of the piezoelectric coefficient of the piezoelectric layer of the first PMUT is greater than 1C/m ² ; and/or

The dielectric constant of the piezoelectric layer of the second PMUT is less than 1200.

26. The method according to 25, wherein:

The absolute value of the piezoelectric coefficient of the piezoelectric layer of the first PMUT is greater than 5C/m ² ; and/or

The dielectric constant of the piezoelectric layer of the second PMUT is less than 100.

27. An electronic device, including the micromachined ultrasonic transducer structure according to any one of 1-14, or the micromachined ultrasonic transducer structure manufactured according to the manufacturing method according to any one of 15-26 .

28. The electronic device according to 27, wherein:

The electronic device includes at least one of the following: an ultrasonic imager, an ultrasonic range finder, an ultrasonic fingerprint sensor, a non-destructive flaw detector, a flow meter, a force feedback device, and a smoke alarm.

Although embodiments of the invention have been shown and described, it will be understood by those of ordinary skill in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention. The scope of the invention is determined by are defined in the appended claims and their equivalents.

Claims (28)

1. A micromachined ultrasonic transducer structure, including:

   The PMUT unit includes a PMUT substrate, a first PMUT and a second PMUT. Each PMUT includes a first electrode layer, a second electrode layer and a piezoelectric layer,

   in:

   The first PMUT and the second PMUT are laterally spaced apart from each other and arranged on one side of the PMUT substrate;

   The piezoelectric coefficient of the piezoelectric layer of the first PMUT is higher than the piezoelectric coefficient of the piezoelectric layer of the second PMUT, and the dielectric constant of the piezoelectric layer of the first PMUT is lower than the dielectric constant of the piezoelectric layer of the second PMUT. .
2. The micromachined ultrasonic transducer structure according to claim 1, wherein:

   The piezoelectric layer of the first PMUT is PZT or doped PZT, and the piezoelectric layer of the second PMUT is ALN or AlScN.
3. The micromachined ultrasonic transducer structure according to claim 1, wherein:

   The first PMUT is used to transmit ultrasonic waves, and the second PMUT is used to receive ultrasonic waves.
4. The micromechanical ultrasonic transducer structure according to any one of claims 1-3, further comprising:

   A transistor unit, including a transistor substrate and a first transistor and a second transistor arranged spaced apart in a lateral direction, the first PMUT and the second PMUT being respectively aligned with the first transistor and the second transistor in the thickness direction of the micromachined ultrasonic transducer structure corresponding;

   The PMUT unit is bonded to a surface on one side of the transistor unit, and the surface on one side of the transistor unit is the bonding surface of the transistor unit.
5. The micromachined ultrasound transducer structure according to claim 4, wherein:

   The cavities for the first PMUT and the second PMUT are on the side of the joint surface on which the PMUT units are disposed.
6. The micromachined ultrasonic transducer structure according to claim 5, wherein:

   The PMUT substrate is bonded to the surface of one side of the transistor cell, the PMUT substrate being provided with the cavity.
7. The micromachined ultrasound transducer structure according to claim 6, wherein:

   The PMUT unit also includes a support layer for supporting the PMUT. The support layer is provided on the two PMUTs. and PMUT substrate.
8. The micromachined ultrasound transducer structure according to claim 6, wherein:

   The cavity penetrates the PMUT substrate; or

   A bonding material layer is provided between the PMUT unit and the transistor unit. The PMUT unit, the transistor unit and the bonding material layer jointly define the cavity. The thickness of the bonding material layer defines the cavity. high.
9. The micromachined ultrasound transducer structure according to claim 4, wherein:

   Each transistor unit includes the transistor, a first electrical connection layer and a second electrical connection layer electrically insulated from each other; and

   For each PMUT and corresponding transistor: the micromachined ultrasonic transducer structure further includes a first conductive layer and a second conductive layer that are electrically insulated from each other, and the first electrode layer is electrically connected to the first electrical connection layer through the first conductive layer. connection, the second electrode layer is electrically connected to the second electrical connection layer via the second conductive layer.
10. The micromachined ultrasonic transducer structure according to claim 9, for each PMUT and corresponding transistor, further comprising:

    A first conductive hole and a second conductive hole. The first conductive hole penetrates the PMUT unit and reaches the first electrical connection layer in the transistor unit. The second conductive hole penetrates the PMUT unit and reaches the second electrical connection layer in the transistor unit. ,

    in:

    The first conductive layer is electrically connected to the first electrical connection layer through the first conductive hole, and the second conductive layer is electrically connected to the second electrical connection layer through the second conductive hole.
11. The micromachined ultrasound transducer structure according to claim 4, wherein:

    The transistor unit includes a circuit protection layer covering the transistor; and

    The surface on one side of the circuit protection layer is the joint surface.
12. The micromachined ultrasound transducer structure according to claim 4, wherein:

    The transistor unit includes one of a CMOS unit, a BiMOS unit, and a BCD unit.
13. The micromachined ultrasonic transducer structure according to claim 1, wherein:

    The absolute value of the piezoelectric coefficient of the piezoelectric layer of the first PMUT is greater than 1C/m ² ; and/or

    The dielectric constant of the piezoelectric layer of the second PMUT is less than 1200.
14. The micromachined ultrasound transducer structure according to claim 13, wherein:

    The absolute value of the piezoelectric coefficient of the piezoelectric layer of the first PMUT is greater than 5C/m ² ; and/or

    The dielectric constant of the piezoelectric layer of the second PMUT is less than 100.
15. A method for manufacturing a micromechanical ultrasonic transducer structure, including the steps:

    A transistor unit is provided, the transistor unit including a transistor substrate and first and second transistors arranged spaced apart in a lateral direction; and

    A PMUT unit bonded to a surface of one side of the transistor unit is provided. The PMUT unit includes a PMUT substrate, a first PMUT and a second PMUT. The PMUT base is bonded to the surface of one side of the transistor unit in a surface bonding manner. Each PMUT includes a third PMUT. an electrode layer, a second electrode layer and a piezoelectric layer,

    in:

    The first PMUT and the second PMUT are laterally spaced apart from each other and arranged on one side of the PMUT substrate, and respectively correspond to the first transistor and the second transistor in the thickness direction of the micromachined ultrasound transducer structure; and

    The piezoelectric coefficient of the piezoelectric layer of the first PMUT is higher than the piezoelectric coefficient of the piezoelectric layer of the second PMUT, and the dielectric constant of the piezoelectric layer of the first PMUT is lower than the dielectric constant of the piezoelectric layer of the second PMUT.
16. The method of claim 15, wherein the step of providing a PMUT unit includes:

    After forming a PMUT, set a protective layer covering it;

    disposing another PMUT laterally spaced apart from the one PMUT;

    Remove the protective layer.
17. The method according to claim 15 or 16, wherein the step of providing a PMUT unit includes:

    providing a PMUT initial base and laterally spaced first and second PMUTs disposed on one side of the initial base;

    covering the first PMUT and the second PMUT with a temporary adhesive layer and providing an auxiliary substrate, the auxiliary substrate being bonded to the temporary adhesive layer;

    Perform a thinning process on the other side of the initial substrate to form the PMUT substrate, and

    After the step of bonding the PMUT substrate to the surface of the transistor unit, the method further includes the step of removing the temporary adhesive layer and the auxiliary substrate.
18. The method of claim 15, wherein:

    The PMUT substrate is bonded to the surface of one side of the transistor unit using a layer of bonding material, the The PMUT unit, the transistor unit and the bonding material layer together define the cavity, and the thickness of the bonding material layer defines the height of the cavity.
19. The method of claim 15, wherein:

    For each transistor, the transistor unit includes a first electrical connection layer and a second electrical connection layer that are electrically insulated from each other;

    The method further includes the steps of: for each PMUT and the corresponding transistor, providing a first conductive layer and a second conductive layer that are electrically insulated from each other, the first electrode layer is electrically connected to the first electrical connection layer via the first conductive layer, and The two electrode layers are electrically connected to the second electrical connection layer through the second conductive layer.
20. The method of claim 19, for each PMUT and corresponding transistor, wherein:

    Before the step of providing the first conductive layer and the second conductive layer that are electrically insulated from each other, the method further includes the step of forming a first conductive hole and a second conductive hole, and the first conductive hole penetrates the PMUT unit and reaches to expose the inside of the transistor unit. The first electrical connection layer, the second conductive hole penetrates the PMUT unit and reaches to expose the second electrical connection layer in the transistor unit;

    In the step of providing the first conductive layer and the second conductive layer that are electrically insulated from each other, the first conductive layer is electrically connected to the first electrical connection layer through the first conductive hole, and the second conductive layer is electrically connected to the first conductive layer through the second conductive hole. The two electrical connection layers are electrically connected.
21. The method according to any one of claims 15-20, wherein:

    Providing a transistor unit includes providing a transistor wafer based on a MEMS process, the transistor wafer being formed with a plurality of transistor units, each transistor unit including a first transistor and a second transistor arranged spaced apart in a lateral direction;

    Providing a PMUT unit bonded to the surface of one side of the transistor unit includes: providing a PMUT wafer based on the MEMS process, the PMUT wafer is formed with a plurality of PMUT units respectively corresponding to the plurality of transistor units, each PMUT unit including a first PMUT and a second PMUT arranged laterally spaced apart from each other, the first PMUT and the second PMUT respectively corresponding to the first transistor and the second transistor in the thickness direction of the micromechanical ultrasonic transducer structure;

    The method also includes the step of performing cutting to form a micromachined ultrasound transducer structure including a single PMUT unit and a single transistor unit.
22. The method according to any one of claims 15-21, wherein:

    The piezoelectric layer of the first PMUT is PZT or doped PZT, and the piezoelectric layer of the second PMUT is AlN or AlScN.
23. The method according to any one of claims 15-22, wherein:

    The first PMUT is used to transmit ultrasonic waves, and the second PMUT is used to receive ultrasonic waves.
24. The method according to any one of claims 15-23, wherein:

    The transistor unit includes one of a CMOS unit, a BiMOS unit, and a BCD unit.
25. The method of claim 15, wherein:

    The absolute value of the piezoelectric coefficient of the piezoelectric layer of the first PMUT is greater than 1C/m ² ; and/or

    The dielectric constant of the piezoelectric layer of the second PMUT is less than 1200.
26. The method of claim 25, wherein:

    The absolute value of the piezoelectric coefficient of the piezoelectric layer of the first PMUT is greater than 5C/m ² ; and/or

    The dielectric constant of the piezoelectric layer of the second PMUT is less than 100.
27. An electronic device, comprising a micromachined ultrasonic transducer structure according to any one of claims 1-14, or a micromachined ultrasonic transducer manufactured according to the manufacturing method according to any one of claims 15-26 device structure.
28. The electronic device of claim 27, wherein:

    The electronic device includes at least one of the following: an ultrasonic imager, an ultrasonic range finder, an ultrasonic fingerprint sensor, a non-destructive flaw detector, a flow meter, a force feedback device, and a smoke alarm.