WO2024027730A1 - Structure de transducteur ultrasonore micro-usinée ayant des doubles pmut disposés sur le même côté que le substrat, et son procédé de fabrication - Google Patents

Structure de transducteur ultrasonore micro-usinée ayant des doubles pmut disposés sur le même côté que le substrat, et son procédé de fabrication Download PDF

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WO2024027730A1
WO2024027730A1 PCT/CN2023/110644 CN2023110644W WO2024027730A1 WO 2024027730 A1 WO2024027730 A1 WO 2024027730A1 CN 2023110644 W CN2023110644 W CN 2023110644W WO 2024027730 A1 WO2024027730 A1 WO 2024027730A1
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pmut
layer
transistor
unit
piezoelectric
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PCT/CN2023/110644
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English (en)
Chinese (zh)
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庞慰
牛鹏飞
张孟伦
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天津大学
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B06—GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS IN GENERAL
    • B06B—METHODS OR APPARATUS FOR GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS OF INFRASONIC, SONIC, OR ULTRASONIC FREQUENCY, e.g. FOR PERFORMING MECHANICAL WORK IN GENERAL
    • B06B1/00—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency
    • B06B1/02—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy
    • B06B1/06—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction
    • B06B1/0607—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction using multiple elements
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B06—GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS IN GENERAL
    • B06B—METHODS OR APPARATUS FOR GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS OF INFRASONIC, SONIC, OR ULTRASONIC FREQUENCY, e.g. FOR PERFORMING MECHANICAL WORK IN GENERAL
    • B06B1/00—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency
    • B06B1/02—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy
    • B06B1/06—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B06—GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS IN GENERAL
    • B06B—METHODS OR APPARATUS FOR GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS OF INFRASONIC, SONIC, OR ULTRASONIC FREQUENCY, e.g. FOR PERFORMING MECHANICAL WORK IN GENERAL
    • B06B3/00—Methods or apparatus specially adapted for transmitting mechanical vibrations of infrasonic, sonic, or ultrasonic frequency
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B81—MICROSTRUCTURAL TECHNOLOGY
    • B81B—MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES
    • B81B7/00—Microstructural systems; Auxiliary parts of microstructural devices or systems
    • B81B7/02—Microstructural systems; Auxiliary parts of microstructural devices or systems containing distinct electrical or optical devices of particular relevance for their function, e.g. microelectro-mechanical systems [MEMS]
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B81—MICROSTRUCTURAL TECHNOLOGY
    • B81C—PROCESSES OR APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OR TREATMENT OF MICROSTRUCTURAL DEVICES OR SYSTEMS
    • B81C3/00—Assembling of devices or systems from individually processed components
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B06—GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS IN GENERAL
    • B06B—METHODS OR APPARATUS FOR GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS OF INFRASONIC, SONIC, OR ULTRASONIC FREQUENCY, e.g. FOR PERFORMING MECHANICAL WORK IN GENERAL
    • B06B2201/00—Indexing scheme associated with B06B1/0207 for details covered by B06B1/0207 but not provided for in any of its subgroups
    • B06B2201/50—Application to a particular transducer type
    • B06B2201/55—Piezoelectric transducer

Definitions

  • 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.
  • PMUT Pielectric Micromachined Ultrasonic Transducer
  • ultrasonic transducer 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.
  • 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.
  • CMUT capacitive micromachined ultrasonic transducer
  • PMUT piezoelectric micromachined ultrasonic transducer
  • the CMUT needs to apply a large bias voltage when working, resulting in high power consumption and certain limitations in application.
  • PMUT is a promising solution.
  • the effective integration of PMUT and CMOS is a crucial factor in realizing the above-mentioned ultrasonic transducer.
  • 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.
  • the PMUT usually exhibits bending vibration mode.
  • 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.
  • the ultrasonic emission sensitivity S T of the flexural vibration PMUT is proportional to the piezoelectric coefficient réelle 31f of the piezoelectric film: S T ⁇ e 31f (1)
  • the receiving sensitivity S R is proportional to the ratio of the piezoelectric coefficient réelle 31f and the dielectric constant ⁇ 33 ; S R ⁇ e 31f / ⁇ 33 (2)
  • the ultrasonic transducer probe 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 réelle 31 to the dielectric constant ⁇ 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.
  • 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.
  • the sensitivity of the pulse-echo (transmit-receive) signal of the PMUT developed is equivalent.
  • 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.
  • 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.
  • 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,
  • 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 including a transistor substrate and first and second transistors arranged spaced apart in a lateral direction;
  • a PMUT unit bonded to a surface of one side of the transistor 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,
  • 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;
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • films such as piezoelectric films, electrode films, etc.
  • 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. .
  • the piezoelectric properties of the piezoelectric film are a crucial determinant of PMUT performance.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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).
  • 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.
  • CMOS unit or transistor unit 1000: CMOS unit or transistor unit.
  • CMOS substrate or transistor substrate optional materials are single crystal silicon, gallium nitride, gallium arsenide, sapphire, quartz, silicon carbide, diamond, etc.
  • Circuit protection layer which is an insulating material layer, which can be silicon dioxide, silicon nitride, etc.
  • 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.
  • PMUT preliminary substrate optional materials are single crystal silicon, gallium nitride, gallium arsenide, sapphire, quartz, silicon carbide, diamond, etc.
  • 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.
  • 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.
  • 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.
  • 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).
  • AlScN scandium Doped aluminum nitride
  • Structural protective layer usually dielectric material, such as silicon dioxide, aluminum nitride, silicon nitride, etc.
  • Conductive layer or electrical connection layer the material of which can be selected from the materials used to form the electrode layer.
  • Conductive layer or electrical connection layer the material of which can be selected from the materials used to form the electrode layer.
  • Device protective layer usually dielectric material, such as silicon dioxide, aluminum nitride, silicon nitride, etc.
  • Auxiliary substrate, optional materials are single crystal silicon, gallium nitride, gallium arsenide, sapphire, quartz, silicon carbide, diamond, etc.
  • 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.
  • 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.
  • Micromachined ultrasound transducer structure or PMUT structure see Figure 1 and Figure 14).
  • 1-4 are schematic structural diagrams of a micromachined ultrasound transducer structure 3000 according to different exemplary embodiments of the present invention.
  • 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).
  • 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.
  • 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.
  • 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
  • 110 is a circuit protection layer.
  • 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.
  • piezoelectric layer 230 is PZT or doped PZT
  • piezoelectric layer 270 is ALN or AlScN.
  • 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.
  • 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.
  • 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).
  • 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.
  • the piezoelectric layer 230 of the first PMUT is PZT and the piezoelectric layer 270 of the second PMUT is AlN.
  • 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.
  • 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.
  • the first PMUT of the PMUT unit is used to transmit ultrasonic waves
  • the second PMUT is used to receive ultrasonic waves.
  • FIG. 5-13 are exemplary illustrations of the microcomputer shown in FIG. 2 according to an exemplary embodiment of the present invention.
  • 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
  • 112 and 114 are the electrical connection layers between the CMOS layers.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • an AlN-based PMUT is constructed on a wafer or initial substrate 200' provided with a PZT-based PMUT.
  • the AlN-based PMUT includes a piezoelectric film layer or an ALN piezoelectric layer 270 and top and bottom electrode layers 280 and 260.
  • the structural protection layer 250 of the PZT-based PMUT is removed to obtain the PMUT unit 2000 .
  • the PMUT preliminary unit 2000' does not include an electrical connection structure that connects the PMUT electrodes and the CMOS electrodes together.
  • 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.
  • 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 .
  • 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 .
  • the auxiliary substrate 300 is provided for subsequent PMUT initial substrate thinning.
  • 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 ⁇ m, or even less than 5 ⁇ m, 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.
  • 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.
  • 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.
  • 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.
  • 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). .
  • 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.
  • the electrical connection layers 235 and 275 of PMUT and CMOS are provided, Realize the electrical connection between PMUT and CMOS.
  • a protective layer or device protection layer 290 is deposited over the entire device surface.
  • 235 and 275 are electrical connection layers.
  • Various conductive materials can be used, such as materials to form electrode layers.
  • 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.
  • 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. .
  • 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.
  • 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.
  • 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.
  • AlN aluminum nitride
  • PZT lead zirconate titanate
  • LiNbO 3 lithium niobate
  • LiTaO 3 lithium tantalate
  • KNbO 3 potassium niobate
  • 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.
  • a bonding material layer 500 which may be a metal bonding layer, is provided between the PMUT substrate and the circuit protection layer.
  • connection between the PMUT substrate and the circuit protection layer is taken as an example for illustration.
  • 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.
  • 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 .
  • the PMUT unit can also be bonded to the CMOS substrate 100, which is also within the protection scope of 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.
  • 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.
  • 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.
  • 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.
  • cavity 201 may extend through PMUT substrate 200 .
  • the PMUT substrate 200 is provided with a cavity 201 for the PMUT.
  • the cavity 201 may not be provided in the PMUT substrate 200.
  • 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
  • the integration process of CMOS and PMUT adversely affects the cavity size.
  • 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.
  • 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.
  • the PMUT unit 2000 includes a support layer 210, and the support layer 210 is used to realize the bending vibration of the PMUT.
  • 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.
  • the first conductive hole 400A and the second conductive hole 400B Through the support layer 210.
  • 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.
  • the first conductive holes 400A and the second conductive holes 400B need to penetrate the PMUT unit to reach the underlying electrical connection layer.
  • 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.
  • 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.
  • the reliability and long-term stability of the final imaging system can be improved.
  • FIG 14 is a schematic diagram of a PMUT structure array according to an exemplary embodiment of the present invention.
  • the above-mentioned PMUT structure 3000 may be only one array element in the array 4000.
  • 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.
  • the electrodes of the PMUT structures 3000 on the same column are interconnected to form a one-dimensional line array.
  • 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.
  • 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,
  • 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.
  • the piezoelectric layer of the first PMUT is PZT or doped PZT, and the piezoelectric layer of the second PMUT is ALN or AlScN.
  • the first PMUT is used to transmit ultrasonic waves
  • the second PMUT is used to receive ultrasonic waves.
  • 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.
  • 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.
  • 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.
  • 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.
  • the cavity penetrates the PMUT substrate
  • 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.
  • 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;
  • 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.
  • 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 first conductive layer is electrically connected to the first electrical connection layer through the first conductive hole
  • the second conductive layer is electrically connected to the second electrical connection layer through the second conductive hole.
  • micromechanical ultrasonic transducer structure according to 4, wherein:
  • the transistor unit includes a circuit protection layer covering the transistor
  • the surface on one side of the circuit protection layer is the joint surface.
  • micromechanical ultrasonic transducer structure according to 4, wherein:
  • the transistor unit includes one of a CMOS unit, a BiMOS unit, and a BCD unit.
  • the absolute value of the piezoelectric coefficient of the piezoelectric layer of the first PMUT is greater than 1C/m 2 ;
  • the dielectric constant of the piezoelectric layer of the second PMUT is less than 1200.
  • 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 ;
  • the dielectric constant of the piezoelectric layer of the second PMUT is less than 100.
  • a method for manufacturing a micromechanical ultrasonic transducer structure including the steps:
  • a transistor unit including a transistor substrate and first and second transistors arranged spaced apart in a lateral direction;
  • a PMUT unit bonded to a surface of one side of the transistor 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,
  • 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;
  • 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.
  • step of providing the PMUT unit includes:
  • step of providing the PMUT unit includes:
  • the method further includes the step of removing the temporary adhesive layer and the auxiliary substrate.
  • 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.
  • the transistor unit 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.
  • 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;
  • the first conductive layer is electrically connected to the first electrical connection layer through the first conductive hole
  • 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.
  • 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.
  • the piezoelectric layer of the first PMUT is PZT or doped PZT, and the piezoelectric layer of the second PMUT is AlN or AlScN.
  • the first PMUT is used to transmit ultrasonic waves
  • the second PMUT is used to receive ultrasonic waves.
  • the transistor unit includes one of a CMOS unit, a BiMOS unit, and a BCD unit.
  • the absolute value of the piezoelectric coefficient of the piezoelectric layer of the first PMUT is greater than 1C/m 2 ;
  • the dielectric constant of the piezoelectric layer of the second PMUT is less than 1200.
  • the absolute value of the piezoelectric coefficient of the piezoelectric layer of the first PMUT is greater than 5C/m 2 ;
  • the dielectric constant of the piezoelectric layer of the second PMUT is less than 100.
  • 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 .
  • 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.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Computer Hardware Design (AREA)
  • Transducers For Ultrasonic Waves (AREA)

Abstract

La présente invention concerne une structure de transducteur ultrasonore micro-usinée et son procédé de fabrication. La structure de transducteur ultrasonore micro-usinée comprend une unité PMUT ; l'unité PMUT comprend un substrat PMUT, un premier PMUT et un second PMUT ; chaque PMUT comprend une première couche d'électrode, une seconde couche d'électrode et une couche piézoélectrique, le premier PMUT et le second PMUT étant agencés comme espacés latéralement sur un côté du substrat PMUT ; le coefficient piézoélectrique de la couche piézoélectrique du premier PMUT étant supérieur au coefficient piézoélectrique de la couche piézoélectrique du second PMUT ; et la permittivité de la couche piézoélectrique du premier PMUT étant inférieure à la permittivité de la couche piézoélectrique du second PMUT. La présente invention concerne en outre un dispositif électronique comprenant la présente structure de transducteur ultrasonore micro-usinée.
PCT/CN2023/110644 2022-08-05 2023-08-02 Structure de transducteur ultrasonore micro-usinée ayant des doubles pmut disposés sur le même côté que le substrat, et son procédé de fabrication WO2024027730A1 (fr)

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CN202210959236.2A CN117548320A (zh) 2022-08-05 2022-08-05 基底同侧设置有双pmut的微机械超声换能器结构及其制造方法
CN202210959236.2 2022-08-05

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20170194934A1 (en) * 2014-05-09 2017-07-06 Chirp Microsystems, Inc. Micromachined ultrasound transducer using multiple piezoelectric materials
CN110575946A (zh) * 2019-09-26 2019-12-17 索夫纳特私人有限公司 一种压电微机械超声换能器
CN111182429A (zh) * 2020-01-03 2020-05-19 武汉大学 高填充率mems换能器
TW202139493A (zh) * 2020-04-06 2021-10-16 日商住友化學股份有限公司 壓電積層體、壓電積層體的製造方法及壓電元件
CN114682472A (zh) * 2022-03-25 2022-07-01 深圳市汇顶科技股份有限公司 超声换能器及其制造方法

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20170194934A1 (en) * 2014-05-09 2017-07-06 Chirp Microsystems, Inc. Micromachined ultrasound transducer using multiple piezoelectric materials
CN110575946A (zh) * 2019-09-26 2019-12-17 索夫纳特私人有限公司 一种压电微机械超声换能器
CN111182429A (zh) * 2020-01-03 2020-05-19 武汉大学 高填充率mems换能器
TW202139493A (zh) * 2020-04-06 2021-10-16 日商住友化學股份有限公司 壓電積層體、壓電積層體的製造方法及壓電元件
CN114682472A (zh) * 2022-03-25 2022-07-01 深圳市汇顶科技股份有限公司 超声换能器及其制造方法

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