CN109909140B - Piezoelectric micromechanical ultrasonic transducer and preparation method thereof - Google Patents
Piezoelectric micromechanical ultrasonic transducer and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a piezoelectric micro-mechanical ultrasonic transducer and a preparation method thereof, wherein the transducer sequentially comprises the following components from bottom to top: the piezoelectric film comprises a substrate layer, a lower electrode layer, a piezoelectric film layer and an upper electrode layer; the upper electrode layer comprises a first upper electrode and a second upper electrode, the first upper electrode and the second upper electrode are arranged in an annular cross mode to form a pair of prong electrodes, when the transducer is used, a detected component is placed on the upper portion of the upper electrode layer, a first alternating current signal is applied between the first upper electrode and the lower electrode layer, a second alternating current signal is applied between the second upper electrode and the lower electrode layer, the vibration state of the piezoelectric film layer can be adjusted by adjusting the phase difference of the first alternating current signal and the second alternating current signal, the direction characteristic and the vibration mode of sound waves in the detected component are further adjusted, and the direction characteristic and the vibration mode of sound waves emitted by the transducer are adjusted and controlled simply and efficiently.
Description
Technical Field
The invention relates to the field of ultrasonic transducers, in particular to a piezoelectric micromechanical ultrasonic transducer and a preparation method thereof.
Background
An ultrasonic transducer is an energy conversion device that converts alternating electrical signals into acoustic signals or external acoustic signals into electrical signals in the ultrasonic frequency range. Among the ultrasonic transducer types, the piezoelectric ultrasonic transducer is most widely used because of its characteristics of good high-frequency characteristics, simple structure, easy excitation, easy molding and processing, and the like.
Piezoelectric Micromachined Ultrasonic Transducers (PMUTs), which are alternatives to conventional Piezoelectric Ultrasonic Transducers, have been widely studied. Compared with the traditional ultrasonic transducer, the PMUT has the characteristics of small volume, light weight, low cost, low power consumption, high reliability, flexible frequency control, wide frequency band, high sensitivity, easy integration with a circuit, realization of intellectualization and the like. Is one of the important research directions of the piezoelectric ultrasonic transducer.
Ultrasonic transducers, whether used for transmission or reception, have a directional characteristic and a vibration mode of acoustic transmission itself. Generally, an elastic wave generated by the piezoelectric effect is classified into a longitudinal wave and a transverse wave according to a relationship between a propagation direction and a vibration direction. When the vibration direction of the mass point is consistent with the propagation direction of the elastic wave, the vibration direction is called longitudinal wave; when the vibration direction of the mass point is perpendicular to the propagation direction of the elastic wave, it is called a transverse wave. The transducers for different applications have different requirements on the acoustic wave directional characteristics and vibration modes. For example, ultrasonic level gauges, anemometry transducers, underwater ranging transducers, etc. measure up and down, typically using longitudinal waves; in the measurement of a wide range of terrain, topography, rail, etc., the measurement of transverse waves is generally selected. How to adjust and control the direction characteristic and the vibration mode of the transducer for transmitting the sound wave has important practical significance in meeting the diversified requirements of practical application (the material structure and the position and the orientation where the discontinuity can exist determine the direction of the selected wave beam and the mode of vibration).
For conventional or larger-sized piezoelectric ultrasonic transducers, a wedge material is usually introduced between the transducer and the measured member, and the directional characteristic and vibration mode of the sound wave are adjusted by changing the angle of the wedge. The propagation angle (measured from the normal to the inspected surface) and vibration mode of the ultrasonic wave in the material will depend on the wedge angle, the ultrasonic sound velocity in the wedge and the ultrasonic sound velocity in the inspected material. The adoption of the wedge to the PMUT piezoelectric ultrasonic transducer based on the micromachining technology has the disadvantages of complex machining process, relatively high machining difficulty and machining cost, and easy deformation or abrasion of the wedge structure caused by mechanical vibration or thermal stress and the like of a device, so that the adjustment capability of the sound wave direction and the vibration mode is reduced and even fails.
Another method for effectively controlling the direction and vibration mode of sound waves is a phased technology based on ultrasonic arrays. The technology generally excites a group of transducer wafers according to certain rules and timing, and controls the shape, the axis deflection angle, the focal position and the like of an acoustic wave beam by adjusting the sequence, the number and the timing of the excited wafers. However, the ultrasonic phased technology usually requires a precise and complex phased device layout and a powerful software system for support, the manufacturing process is complex, the requirement on the excitation capability of a phased array instrument is high, and the equipment is expensive.
How to simply and efficiently adjust and control the directional characteristic and the vibration mode of the sound wave emitted by the transducer becomes a technical problem to be solved urgently.
Disclosure of Invention
The invention aims to provide a piezoelectric micromechanical ultrasonic transducer and a preparation method thereof, so as to realize simple and efficient adjustment and control of the directional characteristic and the vibration mode of the sound wave emitted by the transducer.
In order to achieve the purpose, the invention provides the following scheme:
a piezoelectric micromachined ultrasonic transducer, the transducer comprising: the piezoelectric film comprises a substrate layer, a lower electrode layer, a piezoelectric film layer and an upper electrode layer;
the lower electrode layer is arranged on the upper part of the substrate layer, the piezoelectric film layer is arranged on the upper part of the lower electrode layer, and the upper electrode layer is arranged on the upper part of the piezoelectric film layer; a member to be measured is placed on the upper portion of the upper electrode layer;
the upper electrode layer comprises a first upper electrode and a second upper electrode, the first upper electrode and the second upper electrode are arranged in an annular crossed mode to form a pair of prong electrodes, a first alternating current signal is applied between the first upper electrode and the lower electrode layer, a second alternating current signal is applied between the second upper electrode and the lower electrode layer, the vibration state of the piezoelectric film layer is adjusted by adjusting the phase difference of the first alternating current signal and the second alternating current signal, and then the direction characteristic and the vibration mode of the acoustic wave in the measured component are adjusted.
Optionally, the transducer further includes a mechanical support layer disposed between the substrate layer and the lower electrode layer, and the mechanical support layer is configured to limit lateral vibration of the piezoelectric thin film layer.
Optionally, an acoustic coupling layer is further disposed on an upper portion of the upper electrode layer, and the measured member is placed on the acoustic coupling layer.
Optionally, the substrate layer is a cylinder with a cavity.
Optionally, the tine electrodes are circular in shape.
Optionally, the substrate layer is a cuboid with a cavity.
Optionally, the tine electrodes are square in shape.
Optionally, the spontaneous polarization direction of the internal electric domain of the piezoelectric thin film layer is perpendicular to the upper surface of the piezoelectric thin film layer.
A method for manufacturing a piezoelectric micromechanical ultrasonic transducer, the method comprising the steps of:
selecting an SOI (silicon on insulator) sheet as a substrate layer;
sequentially growing a lower electrode layer, a piezoelectric film layer and an upper electrode layer from bottom to top on the upper surface of the SOI sheet in a magnetron sputtering mode;
and etching a prong pattern on the upper electrode layer to form a prong electrode.
Optionally, etching a tine pattern on the upper electrode layer to form a tine electrode, and then:
etching a cavity on the SOI wafer by adopting a deep reactive ion etching method;
depositing an isolation layer on the upper electrode layer; the isolating layer is a silicon dioxide layer or a silicon nitride layer;
and growing a layer of metal on the isolation layer to serve as a signal line.
According to the specific embodiment provided by the invention, the invention discloses the following technical effects:
the invention discloses a piezoelectric micro-mechanical ultrasonic transducer and a preparation method thereof, wherein the transducer sequentially comprises the following components from bottom to top: the piezoelectric film comprises a substrate layer, a lower electrode layer, a piezoelectric film layer and an upper electrode layer; the upper electrode layer comprises a first upper electrode and a second upper electrode, the first upper electrode and the second upper electrode are arranged in an annular crossed mode to form a pair of prong electrodes, when the transducer is used, a detected component is placed on the upper portion of the upper electrode layer, a first alternating current signal is applied between the first upper electrode and the lower electrode layer, a second alternating current signal is applied between the second upper electrode and the lower electrode layer, the vibration state of the piezoelectric film layer can be adjusted by adjusting the phase difference of the first alternating current signal and the second alternating current signal, the direction characteristic and the vibration mode of sound waves in the detected component are further adjusted, and the simple and efficient adjustment and control of the direction characteristic and the vibration mode of sound waves emitted by the transducer are achieved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.
FIG. 1 is a schematic diagram of adjusting the directional characteristic and vibration mode of sound waves by changing the angle of a wedge;
FIG. 2 is a schematic diagram of an ultrasonic phase-controlled scan;
FIG. 3 is a schematic diagram of a structure of a piezoelectric micromachined ultrasonic transducer provided by the present invention;
FIG. 4 is a schematic diagram of the structure of a circular tine electrode provided by the present invention;
FIG. 5 is a schematic diagram of the structure of a square tine electrode provided by the present invention;
FIG. 6 is a schematic diagram of the mechanical support layer provided by the present invention limiting lateral vibration of the piezoelectric thin film layers;
FIG. 7 is a flow chart of a method of fabricating a piezoelectric micromachined ultrasonic transducer according to the present invention;
fig. 8 is a schematic diagram of the directional characteristic and vibration mode of the acoustic wave when the phase difference between the first ac electrical signal and the second ac electrical signal provided by the present invention is 0 °;
fig. 9 is a schematic diagram of the directional characteristic and the vibration mode of the acoustic wave when the phase difference between the first ac electrical signal and the second ac electrical signal provided by the present invention is 180 °.
Detailed Description
For the adjustment method of adjusting the directional characteristic and the vibration mode of the acoustic wave by changing the angle of the wedge, as shown in fig. 1, the wedge makes the ultrasonic transducer wafer and the surface of the workpiece to be inspected form a strict included angle to ensure that the ultrasonic wave emitted by the wafer is obliquely incident on the interface according to the incident angle, so that waveform conversion is generated at the interface, and the acoustic beam with a specific form and angle is obtained in the workpiece. According to Snell's theorem, the angle of the wedge determines the type and refraction angle of the converted acoustic wave for a given material. As shown in FIG. 1, the included angle between the wedge plane of the transducer and the interface is α, the ultrasonic longitudinal wave emitted from the wafer is incident on the interface obliquely at an incident angle α, and for a small-angle longitudinal wave probe, the incident angle α is small and generally smaller than a first critical angle, waveform conversion occurs at the interface to generate a refracted longitudinal wave and a refracted transverse wave, the angle of refraction of the longitudinal wave is β l, the angle of refraction of the transverse wave is β s, and the sound velocity of the longitudinal wave is greater than that of the transverse wave in a solid medium, so that β l > β s. In the case of oblique incidence of ultrasonic waves, the sound field in the workpiece consists of two parts, a refracted transverse wave sound field and a refracted longitudinal wave sound field. By taking the angle of a probe wedge block in organic glass as an example, when the angle of the wedge block is 0-30 degrees, a refracted transverse wave sound field and a refracted longitudinal wave sound field exist at the same time, and mainly refract longitudinal waves. As the wedge angle is further increased, the refracted longitudinal wave becomes weaker until it disappears, while the coexisting refracted transverse wave increases. And the longitudinal wave refraction angle beta l and the transverse wave refraction angle beta s both increase along with the increase of the wedge angle alpha. However, the PMUT piezoelectric ultrasonic transducer based on the micromachining technology has the disadvantages of complex machining process, relatively high machining difficulty and machining cost, and easy deformation or abrasion of the wedge structure due to mechanical vibration or thermal stress and the like, which leads to the reduction and even failure of the adjustment capability of the sound wave direction and the vibration mode. And the conversion between the transverse wave and the longitudinal wave needs to be carried out by replacing the wedges with different inclination angles, so that the application is limited.
The principle of ultrasonic phased array scanning is shown in fig. 2, M piezoelectric elements in an xOy plane are uniformly arranged into a linear array along a Z axis at equal intervals, the interval between each piezoelectric element is d, and a point P (rho, theta) is any point in a monitoring far field region. When a coordinate system is established with the central position of the piezoelectric array as the origin, the coordinate of the piezoelectric element No. i is (x)i,0). When the array element transmits signals, the signals received by the P point of the far field region are the accumulation of the signals after each excitation signal propagates in the board for a certain distance. Corresponding time delay is added to each array element excitation, so that excitation signals generated by each array element can reach a point P at the same time, phase control focusing is realized, the energy of signals received by the point P is the maximum, and the maximum value of wave beams is pointed to theta at the moment. However, the ultrasonic phased technology usually requires a precise and complex phased device layout and a powerful software system for support, the manufacturing process is complex, the requirement for the excitation capability of the phased array instrument is high, and the equipment is expensive.
The invention aims to provide a piezoelectric micro-mechanical ultrasonic transducer and a preparation method thereof, so as to realize simple and efficient adjustment and control of the directional characteristic and the vibration mode of the sound wave emitted by the transducer.
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.
Example 1
As shown in fig. 3, the transducer includes: the structure comprises a substrate layer 1, a lower electrode layer 3, a piezoelectric film layer 4 and an upper electrode layer 5; the lower electrode layer 3 is arranged on the upper part of the substrate layer 1, the piezoelectric film layer 4 is arranged on the upper part of the lower electrode layer 3, and the upper electrode layer 5 is arranged on the upper part of the piezoelectric film layer 4; a member to be measured is placed on the upper portion of the upper electrode layer 5; the upper electrode layer 5 comprises a first upper electrode and a second upper electrode, the first upper electrode and the second upper electrode are arranged in an annular cross manner to form a pair of prong electrodes, a first alternating current signal is applied between the first upper electrode and the lower electrode layer 3, a second alternating current signal is applied between the second upper electrode and the lower electrode layer 3, and the vibration state of the piezoelectric thin film layer 4 is adjusted by adjusting the phase difference between the first alternating current signal and the second alternating current signal, so that the direction characteristic and the vibration mode of the acoustic wave in the detected component are adjusted.
Example 2
As shown in fig. 3, the transducer further comprises a mechanical support layer 2, the mechanical support layer 2 being arranged between the substrate layer 1 and the lower electrode layer 3, as shown in fig. 6, the mechanical support layer 2 being adapted to limit lateral vibrations of the piezoelectric thin film layer. In order to better adjust the resonant frequency and protect the piezoelectric film layer, a mechanical support layer is arranged below the piezoelectric film layer, the mechanical support layer prevents the piezoelectric film layer from changing in displacement in the X direction and the Y direction (wherein the Z axis is perpendicular to the piezoelectric film layer, and the X direction and the Y direction are perpendicular to each other and perpendicular to the Z axis), and drives the piezoelectric film layer to generate bending deformation instead, and finally the vibration direction of the piezoelectric film layer mainly adopts Z-direction vibration.
An acoustic coupling layer 6 is further arranged on the upper part of the upper electrode layer 5, and the tested component is placed on the upper part of the acoustic coupling layer 6; the acoustic coupling layer 6 is usually made of a material having a relatively low acoustic attenuation coefficient and an acoustic resistivity between the piezoelectric thin film layer 3 and the measured member, so as to ensure close adhesion between the measured member and the piezoelectric thin film layer and promote smooth transmission of mechanical vibration of the piezoelectric thin film layer to the measured member.
The substrate layer is a cylinder with a cavity. The backing layer provides mechanical support for the entire diaphragm. The substrate layer is provided with the cavity structure, so that the excitation of a d31 mode is ensured. d31 mode: dmn is an important piezoelectric strain constant for characterizing the piezoelectric effect of piezoelectric thin film materials, and the physical meaning refers to the ratio of electric polarization generated by applying unit mechanical stress. By index, the piezoelectric strain constant dmn represents the strain along the n-axis that a piezoelectric material experiences when subjected to a unit electric field along the m-axis, under all external stress conditions held constant. For example, d31 represents the strain in direction 1 of the piezoelectric film in the absence of a stress field when a unit electric field is applied in direction 3. In the present invention, the direction 3 is the Z direction, and the direction 1 is the X or Y direction. The direction of the electric field received by the piezoelectric thin film layer operating in the d31 mode is perpendicular to the vibration direction of the piezoelectric thin film layer. After the mechanical supporting layer is added, the displacement change of the piezoelectric film in the X direction and the Y direction is limited, the piezoelectric film is driven to generate bending deformation, and finally the vibration direction of the piezoelectric film layer mainly vibrates in the Z direction.
At this time, as shown in fig. 4, the tine electrodes are circular in shape. The number of pairs N of teeth, the width W and the distance g of the fork teeth of the fork tooth electrodes are adjustable according to actual test requirements so as to change the amplitude, the phase, the spatial distribution and the like of the transmitted sound waves.
The spontaneous polarization direction of the internal electric domain of the piezoelectric thin film layer is vertical to the upper surface of the piezoelectric thin film layer. The piezoelectric thin film layer is a core functional layer, the spontaneous polarization direction of the electric domain in the piezoelectric thin film layer is along the Z direction (vertical to the upper surface of the piezoelectric thin film layer), and the electric domain is a small area with the consistent spontaneous polarization direction. When the direction of the external electric field is also the Z direction, that is, the direction is the same as the polarization direction of the piezoelectric thin film material, if the device operates mainly in the d13 mode, the vibration direction of the piezoelectric thin film layer is perpendicular to the direction of the electric field, and each mass point in the piezoelectric thin film layer vibrates in the X/Y direction.
Example 3
Example 3 of the present invention provides another preferred embodiment of a piezoelectric micromachined ultrasonic transducer, but the practice of the present invention is not limited to the embodiment defined in example 3 of the present invention.
The difference from example 2 is that the substrate layer is a rectangular parallelepiped with a cavity. At this time, as shown in fig. 5, the tine electrodes are square in shape.
Example 4
The preparation method comprises the following steps:
selecting an SOI (silicon on insulator) sheet as a substrate layer; sequentially growing a lower electrode layer, a piezoelectric film layer and an upper electrode layer from bottom to top on the upper surface of the SOI sheet in a magnetron sputtering mode; and etching a prong pattern on the upper electrode layer to form a prong electrode. Etching a cavity on the SOI wafer by adopting a deep reactive ion etching method; depositing an isolation layer on the upper electrode layer; the isolating layer is a silicon dioxide layer or a silicon nitride layer; and growing a layer of metal on the isolation layer to serve as a signal line.
Specifically, as shown in fig. 7, an SOI wafer with a top layer of silicon is selected, a piezoelectric thin film layer of PZT piezoelectric ceramic (lead zirconate titanate piezoelectric ceramic, where P is an abbreviation of lead element Pb, Z is an abbreviation of zirconium element Zr, and T is an abbreviation of titanium element Ti) is grown on the upper surface by magnetron sputtering, and a lower electrode and an upper electrode of the PZT piezoelectric ceramic use metal Pt. The upper electrode of the PZT piezoceramic is then patterned into a pattern of tines. The PZT is partially etched by wet etching to expose the lower electrode (ground). Subsequently, a layer of silicon dioxide or silicon nitride is deposited as an isolation layer covering all but the electrode pad (electrode pad). And growing a layer of metal above the isolation layer as a top electrode to lead a signal wire. Therefore, silicon dioxide is used to isolate the lower upper electrode from the upper signal line. Then DRIE Etching (Deep Reactive Ion Etching) is carried out on the SOI bottom layer silicon to form a cavity structure.
Example 5
When the piezoelectric micromechanical ultrasonic transducer is used as an ultrasonic transmitter, a grounding signal is applied to the lower electrode 3, and a certain phase difference is applied to the first upper electrode 501 and the second upper electrode 502
The alternating current signal of (1). The corresponding deformation, namely mechanical vibration, is generated through the inverse piezoelectric effect of the piezoelectric film layer. The mechanical vibration of the piezoelectric film layer can drive the medium of the tested component to vibrate and convert the medium into sound waves to be emitted out, so that the piezoelectric film layer is practicalThe conversion from the electric signal to the mechanical wave is realized, and the transmission of the ultrasonic wave is realized. The detected component can be metal, welding seam, bridge, human tissue, etc., and the detected physical quantity can be human tumor, crack of bridge, impurity in metal piece, etc. The basic principle is as follows: when meeting the interface with difference of acoustic impedance at two sides, part of the sound wave is reflected, and the detection equipment evaluates whether the defect exists or the size and the position of the defect and the like by receiving, displaying and analyzing the information such as the amplitude, the position and the like of the sound wave sent by the detected component, wherein the difference of the acoustic impedance is usually caused by certain discontinuity in materials, such as cracks, air holes, slag inclusion and the like. The working mode of the device adopts a d31 mode, as shown in fig. 6, namely, the direction of the electric field is the same as the polarization direction of the piezoelectric film material, and the electric field is parallel to the Z direction, while the vibration direction of the piezoelectric film is perpendicular to the electric field direction, and the vibration is generated in the X/Y direction. Generally, in order to better adjust the resonant frequency and protect the piezoelectric diaphragm, a mechanical support layer is arranged below the piezoelectric film layer, the existence of the support layer hinders the piezoelectric film from changing in the displacement in the X direction and the Y direction, and drives the piezoelectric film to generate bending deformation, and finally the vibration direction of the piezoelectric film layer mainly vibrates in the Z direction.
In order to effectively adjust the directional characteristic and vibration mode of acoustic waves emitted from the PMUT into the member under test, it is possible to simply set different phase differences
To be implemented. As exemplified in the two extreme cases, the case,
when in use
When the alternating current signals with the same amplitude, the same frequency and the same phase are applied to the first upper electrode 501 and the second upper electrode 502, the vibration direction of each mass point on the piezoelectric film layer is towards the + Z direction or the-Z direction simultaneouslyAnd vibrated as shown in fig. 8. And then can drive the mass point of the measured component to produce the flexible vibration taking Z direction as the main, vibration direction and vibration propagation direction of each point in the measured component body all take Z direction as the main, therefore under this power-up mode, convert into a sound wave that longitudinal wave is the main and launch, the transmission direction of sound wave is mainly along Z direction. (the shape of the diaphragm can be designed to change the directional characteristics and vibration mode of the sound wave, because the shape of the diaphragm is changed, and the shape and size of the corresponding upper and lower electrodes are changed accordingly, as for the arrangement of the polarization direction, the invention ensures the excitation of the d31 mode, and finally, the polarization is fixed in the Z direction)
When in use
When the alternating current signals with the same frequency and opposite phases are applied to the first upper electrode 501 and the second upper electrode 502, the vibration direction of each mass point on the piezoelectric thin film layer is controlled by the direction of the electric field, although the vibration directions of the mass points of the piezoelectric thin film layer covered by the electric fields of the first upper electrode 501 and the second upper electrode 502 are all along the Z axis, the vibration directions are just opposite, and the mass points corresponding to adjacent electrode fork teeth generate shear vibration, as shown in fig. 9. The mass point of the tested component is driven to generate shearing vibration mainly in the Z direction, but the vibration propagation direction is mainly in the X/Y direction, so that in the power-up mode, the vibration is converted into sound wave mainly in the transverse wave and is emitted, and the transmission direction of the sound wave is mainly in the X/Y direction. With other values of θ, the directional characteristic and vibration mode of the acoustic wave are between the two extremes.
The invention discloses a piezoelectric micro-mechanical ultrasonic transducer and a preparation method thereof, wherein the transducer sequentially comprises the following components from bottom to top: the piezoelectric film comprises a substrate layer, a lower electrode layer, a piezoelectric film layer and an upper electrode layer; the upper electrode layer comprises a first upper electrode and a second upper electrode, the first upper electrode and the second upper electrode are arranged in an annular cross mode to form a pair of prong electrodes, when the transducer is used, a detected component is placed on the upper portion of the upper electrode layer, a first alternating current signal is applied between the first upper electrode and the lower electrode layer, a second alternating current signal is applied between the second upper electrode and the lower electrode layer, the vibration state of the piezoelectric film layer can be adjusted by adjusting the phase difference of the first alternating current signal and the second alternating current signal, the direction characteristic and the vibration mode of sound waves in the detected component are further adjusted, and the direction characteristic and the vibration mode of sound waves emitted by the transducer are adjusted and controlled simply and efficiently.
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other.
The principle and the implementation manner of the present invention are explained by applying specific examples, the above description of the embodiments is only used to help understanding the method of the present invention and the core idea thereof, the described embodiments are only a part of the embodiments of the present invention, not all embodiments, and all other embodiments obtained by a person of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the protection scope of the present invention.
Claims (9)
1. A piezoelectric micromachined ultrasonic transducer, comprising: the piezoelectric film comprises a substrate layer, a lower electrode layer, a piezoelectric film layer and an upper electrode layer;
the lower electrode layer is arranged on the upper part of the substrate layer, the piezoelectric film layer is arranged on the upper part of the lower electrode layer, and the upper electrode layer is arranged on the upper part of the piezoelectric film layer; a member to be measured is placed on the upper portion of the upper electrode layer;
the upper electrode layer comprises a first upper electrode and a second upper electrode, the first upper electrode and the second upper electrode are annularly and crossly arranged to form a pair of prong electrodes, a first alternating current signal is applied between the first upper electrode and the lower electrode layer, a second alternating current signal is applied between the second upper electrode and the lower electrode layer, and the vibration state of the piezoelectric film layer is adjusted by adjusting the phase difference between the first alternating current signal and the second alternating current signal, so that the direction characteristic and the vibration mode of the acoustic wave in the measured component are adjusted;
specifically, when phi is 0 °, the same-amplitude, same-frequency, and same-phase alternating current signals are applied to the first upper electrode and the second upper electrode, the vibration direction of each mass point on the piezoelectric film layer vibrates in the + Z direction or the-Z direction at the same time, and then the mass points of the detected member are driven to generate telescopic vibration mainly in the Z direction, and the vibration direction and the vibration propagation direction of each point in the detected member are mainly in the Z direction, so that the vibration direction and the vibration propagation direction of each point in the detected member are mainly in the Z direction, and the vibration is converted into a sound wave mainly in a longitudinal wave and transmitted out, wherein the transmission direction of the sound wave is mainly in the Z direction;
when phi is 180 degrees, the same amplitude of alternating current signals with the same frequency and opposite phases are applied to the first upper electrode and the second upper electrode, the vibration direction of each mass point on the piezoelectric film layer is controlled by the direction of an electric field, although the mass points of the piezoelectric film layer covered by the electric fields of the first upper electrode 501 and the second upper electrode 502 vibrate along the Z axis, the vibration directions are just opposite, the mass points corresponding to adjacent electrode fork teeth generate shear vibration, and then the mass points of the tested component can be driven to generate shear vibration mainly in the Z direction, but the vibration propagation direction is mainly in the X/Y direction, so that in the power-up mode, the sound waves converted into transverse waves are emitted, and the transmission direction of the sound waves is mainly in the X/Y direction;
when θ takes values other than 0 ° and 180 °, the directional characteristic and vibration mode of the acoustic wave are between the two extreme cases;
an acoustic coupling layer is further arranged on the upper portion of the upper electrode layer, and the measured component is placed on the upper portion of the acoustic coupling layer.
2. A piezoelectric micromachined ultrasonic transducer according to claim 1, further comprising a mechanical support layer disposed between the substrate layer and the lower electrode layer.
3. A piezoelectric micromachined ultrasonic transducer according to claim 1, wherein the substrate layer is a cylinder with a cavity.
4. A piezoelectric micromachined ultrasonic transducer according to claim 3, wherein the tine electrodes are circular in shape.
5. A piezoelectric micromachined ultrasonic transducer according to claim 1, wherein the substrate layer is a cuboid with a cavity.
6. A piezoelectric micromachined ultrasonic transducer according to claim 5, wherein the tine electrodes are square in shape.
7. A piezoelectric micromachined ultrasonic transducer according to claim 1, wherein a direction of spontaneous polarization of the inner electric domain of the piezoelectric thin film layer is perpendicular to the upper surface of the piezoelectric thin film layer.
8. A method for manufacturing a piezoelectric micromechanical ultrasonic transducer is characterized by comprising the following steps:
selecting an SOI (silicon on insulator) sheet as a substrate layer;
sequentially growing a lower electrode layer, a piezoelectric film layer and an upper electrode layer on the upper surface of the SOI sheet in a magnetron sputtering mode;
etching a fork tooth pattern on the upper electrode layer to form a fork tooth electrode, so as to obtain an upper electrode layer comprising a first upper electrode and a second upper electrode, wherein the first upper electrode and the second upper electrode are annularly and crossly arranged to form a pair of fork tooth electrodes, a first alternating current signal is applied between the first upper electrode and the lower electrode layer, a second alternating current signal is applied between the second upper electrode and the lower electrode layer, and the vibration state of the piezoelectric film layer is adjusted by adjusting the phase difference of the first alternating current signal and the second alternating current signal, so that the direction characteristic and the vibration mode of the acoustic wave in the measured component are adjusted;
specifically, when phi is 0 °, the same-amplitude, same-frequency, and same-phase alternating current signals are applied to the first upper electrode and the second upper electrode, the vibration direction of each mass point on the piezoelectric film layer vibrates in the + Z direction or the-Z direction at the same time, and then the mass points of the detected member are driven to generate telescopic vibration mainly in the Z direction, and the vibration direction and the vibration propagation direction of each point in the detected member are mainly in the Z direction, so that the vibration direction and the vibration propagation direction of each point in the detected member are mainly in the Z direction, and the vibration is converted into a sound wave mainly in a longitudinal wave and transmitted out, wherein the transmission direction of the sound wave is mainly in the Z direction;
when phi is 180 degrees, the same amplitude of alternating current signals with the same frequency and opposite phases are applied to the first upper electrode and the second upper electrode, the vibration direction of each mass point on the piezoelectric film layer is controlled by the direction of an electric field, although the mass points of the piezoelectric film layer covered by the electric fields of the first upper electrode 501 and the second upper electrode 502 vibrate along the Z axis, the vibration directions are just opposite, the mass points corresponding to adjacent electrode fork teeth generate shear vibration, and then the mass points of the tested component can be driven to generate shear vibration mainly in the Z direction, but the vibration propagation direction is mainly in the X/Y direction, so that in the power-up mode, the sound waves converted into transverse waves are emitted, and the transmission direction of the sound waves is mainly in the X/Y direction;
when θ takes values other than 0 ° and 180 °, the directional characteristic and vibration mode of the acoustic wave are between the two extreme cases.
9. The method as claimed in claim 8, wherein the etching of the tine pattern on the top electrode layer to form the tine electrode further comprises:
etching a cavity on the SOI wafer by adopting a deep reactive ion etching method;
depositing an isolation layer on the upper electrode layer; the isolating layer is a silicon dioxide layer or a silicon nitride layer;
and growing a layer of metal on the isolation layer to serve as a signal line.
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| CN111430412B (en) * | 2020-03-30 | 2022-11-04 | 京东方科技集团股份有限公司 | Display substrate, manufacturing method and display panel |
| CN111515111B (en) * | 2020-04-17 | 2022-02-11 | 上海师范大学 | Piezoelectric micro-mechanical ultrasonic transducer based on relaxor ferroelectric single crystal film and preparation thereof |
| CN114157966B (en) * | 2021-11-23 | 2023-09-26 | 苏州清听声学科技有限公司 | Sound transmitting, receiving and transmitting device based on piezoelectric film |
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