A large bandwidth arrayed ultrasonic transducer device

Abstract

The application belongs to the technical field of ultrasonic transducer, and discloses a large-bandwidth array ultrasonic transducer device, which comprises a substrate, an array of PMUT units, a plurality of PMUT units arranged on the substrate around an axis to form an array, and a plurality of back cavities opened on the side of the substrate away from the PMUT units, wherein the center point distance between two adjacent PMUT units is configured as a first distance to enhance mutual impedance, and each back cavity has a PMUT unit, and the plurality of back cavities are configured as a first length to enhance impedance. The application can realize the arrangement of a plurality of PMUT units in an array on the substrate, so that the mutual impedance is generated through the acoustic path interaction between the PMUT units, the mutual impedance can provide additional acoustic damping, the mutual impedance value between the PMUT units is increased, and the bandwidth is significantly increased.

Description

Technical Field

[0001] This invention belongs to the field of ultrasonic transducer technology, and particularly relates to a large-bandwidth array-type ultrasonic transducer device. Background Technology

[0002] Based on the piezoelectric effect and the principle of mechanical vibration, piezoelectric ultrasonic transducers achieve electroacoustic signal conversion through an energy conversion path of electrical energy-mechanical energy-acoustic energy. Piezoelectric micromachined ultrasonic transducers (PMUTs) fabricated using MEMS technology have the advantages of small size, low power consumption, high sensitivity, flexible design, and mass production capability, and are widely used in the field of ultrasonic sensing.

[0003] To achieve higher detection accuracy and a wider operating bandwidth, expanding bandwidth is a consistent pursuit for acoustic devices. Acoustic detection devices require a wider bandwidth to obtain narrower time-domain pulses, thereby improving time resolution; MEMS loudspeakers, microphones, and other devices require a wider bandwidth to maintain high sensitivity over a larger frequency range; similarly, energy conversion devices also require a larger operating bandwidth to achieve higher energy efficiency.

[0004] However, air-coupled PMUTs often have narrow bandwidths and low coupling efficiency between mechanical and acoustic energy, mainly due to impedance mismatch between the PMUT diaphragm and air.

[0005] To increase the bandwidth of PMUTs and improve acoustic-energy coupling efficiency, many methods have been proposed. These methods include: aliasing multiple adjacent resonant frequencies, increasing the acoustic radiation area through diaphragm design, and introducing additional damping, etc. However, these methods have limited bandwidth improvement and introduce problems such as increased complexity of device structure and back-end circuitry, and decreased energy coupling efficiency. Therefore, a high-bandwidth array-type ultrasonic transducer device is proposed to solve the above problems. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention proposes a high-bandwidth array-type ultrasonic transducer device, which enables the arrangement of multiple PMUT units in an array on a substrate. This allows the PMUT units to interact with each other through acoustic paths, generating mutual impedance. The mutual impedance provides additional acoustic damping, increasing the mutual damping value between the PMUT units and thus significantly increasing the bandwidth.

[0007] To achieve the above objectives, the present invention provides a high-bandwidth array-type ultrasonic transducer device, comprising:

[0008] Substrate;

[0009] A PMUT cell array having at least two PMUT cells, wherein a plurality of said PMUT cells are arranged around an axis on said substrate to form an array, and the center-to-center spacing between two adjacent said PMUT cells is configured as a first spacing to enhance mutual impedance, and,

[0010] Multiple back cavities are formed on the side of the substrate away from the PMUT unit, each back cavity having one PMUT unit, and the multiple back cavities are configured with a first length to enhance impedance.

[0011] Furthermore, it also includes an additional substrate, which is fixed to the end face of the substrate away from the PMUT unit.

[0012] Furthermore, the acoustic positions of the multiple PMUT units are identical.

[0013] Furthermore, the PMUT unit array includes two first PMUT units, which are arranged symmetrically about the axis, the substrate is a first substrate structure, and the back cavity is a first back cavity.

[0014] Furthermore, when the PMUT unit array includes two first PMUT units, d / λ = 0.5 to 1, where d is the first spacing and λ is the wavelength.

[0015] Furthermore, the PMUT unit array includes four second PMUT units, which are distributed circumferentially along the axis, the substrate is a second substrate structure, and the back cavity is a second back cavity.

[0016] Furthermore, the additional substrate fixed on the end face of the second substrate structure is the first additional substrate.

[0017] Furthermore, when the PMUT unit array includes four second PMUT units, d / λ = 0.35 to 1, where d is the first spacing and λ is the wavelength.

[0018] Furthermore, the PMUT unit array includes six third PMUT units, which are distributed circumferentially along the axis, the substrate is a third substrate structure, and the back cavity is a third back cavity.

[0019] Furthermore, the additional substrate fixed on the end face of the third substrate structure is a second additional substrate.

[0020] Furthermore, when the PMUT unit array includes six third PMUT units, d / λ = 0.3 to 1, where d is the first spacing and λ is the wavelength.

[0021] Further, the Hsub satisfies H - 100μm < Hsub < H + 100μm, where H = 9.305E4 * f -1.094 + λ / 2 * n, with the unit of μm, f is the resonance frequency with the unit of kHz, λ is the wavelength, and n is an integer greater than or equal to 0.

[0022] Compared with the prior art, the present invention has the following advantages and technical effects:

[0023] By arranging multiple PMUT units in an array on the substrate, the PMUT units interact with each other through an acoustic path to generate mutual impedance. The mutual impedance can provide additional acoustic damping, increasing the mutual damping value between the PMUT units, and thus significantly increasing the bandwidth. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The drawings constituting a part of this application are used to provide a further understanding of this application. The schematic embodiments and descriptions thereof of this application are used to explain this application and do not constitute an improper limitation to this application. In the drawings:

[0025] Figure 1 It is a schematic structural diagram of Embodiment 1;

[0026] Figure 2 It is Figure 1 a cross-sectional view taken along A - A in

[0027] Figure 3 It is a schematic structural diagram of Embodiment 2;

[0028] Figure 4 It is Figure 3 a cross-sectional view taken along B - B in

[0029] Figure 5 It is a schematic structural diagram of Embodiment 3;

[0030] Figure 6 It is Figure 5 a cross-sectional view taken along C - C in

[0031] Figure 7 It is a diagram showing the relationship between the bandwidth and the thickness of the first substrate structure and the distance between two adjacent first PMUT units in Embodiment 1;

[0032] Figure 8 It is a diagram showing the relationship between the bandwidth and the thickness of the second substrate structure and the distance between two adjacent second PMUT units in Embodiment 2;

[0033] Figure 9 It is a diagram showing the relationship between the bandwidth and the thickness of the third substrate structure and the distance between two adjacent third PMUT units in Embodiment 3;

[0034] Wherein, 101-first substrate structure; 102-first PMUT unit; 103-first back cavity; 201-second substrate structure; 202-second PMUT unit; 203-second back cavity; 204-first additional substrate; 301-third substrate structure; 302-third PMUT unit; 303-third back cavity; 304-second additional substrate. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0037] Reference Figures 1-9 The present invention provides a high-bandwidth array-type ultrasonic transducer device, comprising: a substrate.

[0038] Specifically, the substrate is used to support the PMUT unit.

[0039] In one specific embodiment of the present invention, the substrate includes a base silicon layer, a buried oxide layer, and a structural silicon layer, and the substrate is an SOI substrate.

[0040] The PMUT cell array has at least two PMUT cells, and multiple PMUT cells are arranged around an axis on a substrate to form an array. The center point spacing between two adjacent PMUT cells is configured as a first spacing to enhance mutual impedance. Additionally, multiple back cavities are formed on the side of the substrate away from the PMUT cells, each back cavity containing one PMUT cell. The multiple back cavities are configured as a first length to enhance impedance.

[0041] Specifically, at least two PMUT units are set on the substrate. Multiple PMUT units are identical and have an axis on the substrate. Multiple PMUT units are arranged around this axis. Each PMUT unit can rotate a certain angle around the axis to coincide with other PMUT units, thereby realizing that all PMUT units in the PMUT unit array have the same acoustic position and will not produce asynchronous vibration due to acoustic crosstalk during operation.

[0042] The PMUT cell is thinner than the substrate. The substrate extends below the PMUT cell to form a back cavity, so that each PMUT cell has a corresponding back cavity. The back cavity has an opening at the end for communication with the outside atmosphere.

[0043] The back cavity is a cavity surrounded by a substrate and formed during the etching process on the back side of the wafer.

[0044] The number of PMUT units can be two, three, four, five, six or more.

[0045] The depth of the back cavity can be adjusted by thinning or thickening the substrate.

[0046] The PMUT unit comprises a multi-layered material stack structure. Its structural design is not limited; during vibration, any PMUT structure can be equivalent to a translational piston with a certain area, thus possessing the same acoustic coupling mechanism. Under specific acoustic configurations, the bandwidth of the PMUT unit array can generate a gain effect.

[0047] Existing air-coupled PMUTs often have narrow bandwidths and low coupling efficiency between mechanical and acoustic energy, primarily due to impedance mismatch between the PMUT unit's diaphragm and air. The fractional bandwidth of a PMUT unit can be expressed by the following formula:

[0048]

[0049] Where FBW is the fractional bandwidth of the PMUT element, R is the air radiation damping, S is the acoustic radiation area of ​​the PMUT element, ω0 is the resonant frequency of the PMUT element, and M is the modal mass of the PMUT element. Generally, the radiation damping of a PMUT in air is relatively small, with a bandwidth of only 1% to 10%. This greatly limits the application of air-coupled PMUTs.

[0050] In this technical solution, when the array-type PMUT units are in operation, the PMUT units interact with each other through acoustic paths, generating mutual impedance. This mutual impedance provides additional acoustic damping, and its value is related to the acoustic configuration. Under a preferred acoustic configuration of array spacing and back cavity depth, the mutual damping between PMUT units reaches its maximum, resulting in a significantly increased bandwidth.

[0051] Further optimizations include an additional substrate, fixed to the end face of the substrate away from the PMUT cell.

[0052] Specifically, the additional substrate is used to thicken the substrate so as to increase the back cavity depth. The additional substrate can work with the substrate to adjust the back cavity depth of the PMUT cell.

[0053] The size, number, geometry, and arrangement of the back cavities are all adapted to the back cavities of the PMUT unit.

[0054] The design was further optimized so that the acoustic positions of multiple PMUT units are the same.

[0055] Specifically, the acoustic positions of multiple PMUT units are the same, which can avoid asynchronous vibration caused by acoustic crosstalk during operation.

[0056] Example 1

[0057] Reference Figure 1 , Figure 2 The PMUT cell array includes two first PMUT cells 102, which are arranged symmetrically around an axis. The substrate is a first substrate structure 101, and the back cavity is a first back cavity 103.

[0058] Specifically, when the PMUT unit array has two PMUT units, the two PMUT units are the first PMUT units 102, the substrate for mounting the first PMUT units 102 is the first substrate structure 101, and a first back cavity 103 is formed on the first substrate structure 101. Under this structure, the two first PMUT units 102 are arranged on both sides of the axis and symmetrically arranged with the axis as the center line.

[0059] The distance between the centers of the two first PMUT units 102 is d, and the thickness of the first substrate structure 101 is Hsub.

[0060] Reference Figure 7 The bandwidth of Example 1 is calculated using theoretical formulas, relating it to the center-to-center spacing of the first PMUT units 102 and the depth of the first back cavity 103. Adjusting the spacing between the two first PMUT units 102 and the depth of the first back cavity 103 improves the bandwidth of the PMUT. An optimal bandwidth exists for the PMUT array at a specific center-to-center spacing of the first PMUT units 102 and the depth of the first back cavity 103. In Example 1, the spacing between the two first PMUT units 102 is determined by the design layout, and the depth of the first back cavity 103 of the PMUT is achieved by adjusting the thickness of the first substrate structure 101.

[0061] In this embodiment, the thickness of the first substrate structure 101 is adjusted by wafer thinning.

[0062] The PMUT unit array includes two first PMUT units 102, with d / λ = 0.5 to 1, where d is the first spacing and λ is the wavelength.

[0063] Preferably, d / λ = 0.7 to 0.8.

[0064] Example 2

[0065] Reference Figure 3 , Figure 4The PMUT cell array includes four second PMUT cells 202, which are distributed circumferentially along the axis. The substrate is a second substrate structure 201, and the back cavity is a second back cavity 203.

[0066] Specifically, when the PMUT unit array has four PMUT units, the four PMUT units are the second PMUT units 202, the substrate for mounting the second PMUT units 202 is the second substrate structure 201, and a second back cavity 203 is formed on the second substrate structure 201. Under this structure, the four second PMUT units 202 are arranged circumferentially with the axis as the center.

[0067] Reference Figure 8 The bandwidth of Example 2 is calculated using theoretical formulas, relating it to the center-to-center spacing between two adjacent second PMUT units 202 and the depth of the second back cavity 203. Adjusting the spacing between adjacent second PMUT units 202 and the depth of the second back cavity 203 improves the bandwidth of the PMUT. An optimal bandwidth exists for the PMUT array at specific center-to-center spacing and second back cavity 203 depths. In Example 2, the spacing between adjacent second PMUT units 202 is determined by the design layout, and the depth of the second back cavity 203 of the second PMUT unit 202 is achieved by adjusting the thickness of the second substrate structure 201 and the first additional substrate 204.

[0068] In a further optimized design, the additional substrate fixed on the end face of the second substrate structure 201 is the first additional substrate 204.

[0069] In this embodiment, the thickness of the second substrate structure 201 is adjusted by fixing the first additional substrate 204.

[0070] When the PMUT unit array includes four second PMUT units 202, d / λ = 0.35~1, where d is the first spacing and λ is the wavelength.

[0071] Preferably, d / λ = 0.6 to 0.7.

[0072] Example 3

[0073] Reference Figure 5 , Figure 6 The PMUT cell array includes six third PMUT cells 302, which are distributed circumferentially along the axis. The substrate is a third substrate structure 301, and the back cavity is a third back cavity 303.

[0074] Specifically, when the PMUT unit array has six PMUT units, the six PMUT units are the third PMUT units 302, the substrate for mounting the third PMUT units 302 is the third substrate structure 301, and at the same time, a third back cavity 303 is formed on the third substrate structure 301. Under this structure setting, the six third PMUT units 302 are circumferentially and equally spaced with the axis as the center.

[0075] Refer to Figure 9 , the relationship between the bandwidth of Embodiment 3 obtained by theoretical formula calculation and the center-to-center spacing of adjacent two third PMUT units 302 and the depth of the third back cavity 303; by adjusting the center-to-center spacing between adjacent two third PMUT units 302 and the depth of the third back cavity 303, the bandwidth of the PMUT can be improved; at a specific center-to-center spacing between adjacent two third PMUT units 302 and the depth of the third back cavity 303, there is an optimal value for the bandwidth of the PMUT array. In Embodiment 3, the spacing between adjacent two third PMUT units 302 is determined by the design layout, and the depth of the third back cavity 303 of the third PMUT unit 302 is achieved by adjusting the thicknesses of the third substrate structure 301 and the second additional substrate 304.

[0076] For a further optimized solution, the additional substrate fixed on the end face of the third substrate structure 301 is the second additional substrate 304.

[0077] Among them, in this embodiment, the thickness of the third substrate structure 301 is adjusted by fixing the second additional substrate 304.

[0078] In a preferred embodiment of the present invention, the additional substrate is fixedly bonded or silicon-silicon bonded to the PMUT unit. Or other fixing methods are adopted.

[0079] Among them, when the PMUT unit array includes six third PMUT units 302, d / λ = 0.3 to 1, where d is the first spacing and λ is the wavelength.

[0080] Preferably, d / λ = 0.45 to 0.55, or d / λ = 0.85 to 0.95.

[0081] Further, the first length Hsub satisfies H - 100μm < Hsub < H + 100μm, where H = 9.305E4 * f -1.094 + λ / 2 * n, with the unit of μm, f is the resonance frequency with the unit of kHz, λ is the wavelength, and n is an integer greater than or equal to 0.

[0082] Among them, n is the value range of Hsub.

[0083] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A high-bandwidth array-type ultrasonic transducer device, characterized in that: include: Substrate; A PMUT cell array, comprising multiple PMUT cells, is circumferentially arranged on the substrate around a central axis to form an array. The center-to-center spacing between adjacent PMUT cells is configured as a first spacing to enhance mutual impedance. Multiple back cavities are formed on the side of the substrate away from the PMUT unit, each back cavity has one PMUT unit, and the multiple back cavities are configured with a first length to enhance impedance; It also includes an additional substrate, which is fixed to the end face of the substrate away from the PMUT unit; The acoustic positions of multiple PMUT units are the same; When the PMUT unit array includes four PMUT units (202), the four PMUT units (202) are distributed circumferentially along the axis, with d / λ = 0.35~1, where d is the first spacing and λ is the wavelength; The first length Hsub satisfies H-100μm < Hsub < H+100μm, where, The unit is μm, f is the resonant frequency in kHz, λ is the wavelength, and n is an integer greater than or equal to 0.

2. The large bandwidth array-type ultrasonic transducer device according to claim 1, characterized in that: The PMUT unit array includes six PMUT units (302), which are distributed circumferentially along the axis.

3. The large bandwidth array-type ultrasonic transducer device according to claim 2, characterized in that: When the PMUT unit array includes six PMUT units (302), d / λ = 0.3 to 1, where d is the first spacing and λ is the wavelength.

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