Grooves for Reducing Crosstalk in MUT Arrays

Abstract

DETAILED DESCRIPTION A micromachined ultrasound transducer (MUT) array with grooves that reduce crosstalk between the MUTs to mitigate unwanted artifacts in ultrasound images, as well as a method of operating the same, are described.

Description

Technical Field

[0001] Cross-reference The subject matter of this application is related to the subject matter of International Patent Application PCT / US2020 / 050374, filed on September 11, 2020, the entire content of which is incorporated herein by reference.

Background Art

[0002] Micro-machine ultrasonic transducers (MUTs) present great potential in many fields including, but not limited to, medical imaging, air-coupled imaging, distance monitoring, fingerprint monitoring, non-destructive defect monitoring, and diagnosis. In many of these applications, there are more than one MUT operating in concert. In many of these applications, multiple MUTs operate simultaneously. For example, in the case of high-end medical ultrasonic imaging, it is reasonable to find systems with 1024, 2048, or 4096 MUTs.

Summary of the Invention

[0003] MUTs are designed to transfer energy to the attached acoustic medium for proper operation. Please refer to the generalized example of the MUT array in Figure 1A. In this case, the MTUs are represented by the movable diaphragms (101a), (101b), (101c) formed in or on the substrate (100) by the cavities (120a), (120b), and (120c). The diaphragms (101a), (101b), (101c) are acoustically coupled to the semi-infinite acoustic medium (200) at the interface (110). The acoustic medium (200) can be any substance or substances; common media include air, water, fibers, electrolytic gels, metals, silicone rubber used as a matching layer to the body, etc.

[0004] During operation, diaphragms (101a)-(101c) are excited to move mainly in the z-direction. The excitation is usually caused by the piezoelectric effect (in the case of piezoelectric MUT (pMUT)) or the capacitive effect (in the case of capacitive MUT (cMUT)). In both cases, the movement of the diaphragm generates a pressure wave that is transmitted to the acoustic medium (200). However, the movement of the diaphragm further generates unwanted waves outside the acoustic medium (200). The most common unwanted waves are elastic compression waves that travel within and through the substrate (100), and interface waves that travel along the interface (110) between the substrate (100) and the acoustic medium (200), as well as other interfaces attached to the substrate (100).

[0005] All the energy radiated outside the acoustic medium (200) is unwanted. It not only wastes power but also has the potential to interfere with the function of the MUT. For example, in medical imaging, elastic compression waves bounce off other surfaces, causing artifacts such as stationary images on medically relevant images formed from the reflected energy from the acoustic medium (200). As another example, interface waves traveling along the interface (110) cause crosstalk in medical imaging, resulting in spot illumination effects and unwanted ghost images.

[0006] A generalized example of the MUT array (210) is shown in FIG. 1B. The MUT array (210) includes a substrate (100) and a plurality of MUTs (101). The plurality of MUTs (101) are fixed to the surface of the substrate. Each MUT includes a movable diaphragm as shown in FIG. 1A. In some embodiments, each MUT (101) is a pMUT. In some embodiments, each MUT (101) is a cMUT. The MUTs (101) can be arranged in a two-dimensional array (210) arranged in orthogonal directions. That is, the MUTs (101) are formed in a two-dimensional MxN array (210) having N columns and M rows of MUTs (101). The number of columns (N) and the number of rows (M) may be the same or different. In some examples, the array (210) can be curved, for example, to provide a wider angle of the object to be imaged. In some examples, the array may provide a different packing, such as hexagonal packing, rather than the standard square packing shown in FIG. 1B. In some examples, the array can be asymmetric, as described, for example, in U.S. Patent No. 10,656,007, the entire contents of which are incorporated herein by reference.

[0007] The present disclosure provides a new solution to address the problems of compression waves and interface waves in a MUT array and the crosstalk they generate. FIG. 2 provides an example of this crosstalk in a MUT array formed from a silicon substrate (100) coupled to a hydroacoustic medium ((200). The diagonal ripple (220) represents the propagating pressure wave. The two dashed-dotted lines (230) represent the speed of sound in the hydroacoustic medium (about 1,480 m / s). The ripples and high-amplitude data (240) below these lines (230) typically represent good acoustic data. The data (250) above the two dashed-dotted lines (230) represents various forms of crosstalk.

[0008] When performing the spatial and temporal Fourier transform of the data in FIG. 2, the f-k plot of FIG. 3 is obtained. In FIG. 3, it can be seen that the crosstalk acoustic energy surrounded by the dashed-dotted line (300) is distributed at approximately 2,000 to 6,000 m / s. While the longitudinal wave velocity in silicon is approximately 8,800 m / s, the interfacial wave velocities of Rayleigh waves and shear waves are 5,000 to 5,500 m / s. This suggests that the crosstalk energy may be due to a combination of interfacial waves and bulk waves.

[0009] To image the phantom, using a MUT array as used to generate the outputs shown in FIGS. 2 and 3 produces results such as those in FIG. 4. Two artifacts are clearly visible: (1) a "spotlight" effect (420) where the central portion of the image is brighter than the edges, and (2) a "ghost" image (430) of the highly reflective target, which is seen at the edges of the image.

[0010] Such artifacts of crosstalk energy are undesirable. This specification discloses a general approach for destroying compression waves and interfacial waves and significantly reducing crosstalk between MUTs.

[0011] In one aspect, this specification shows a MUT array including a substrate and a plurality of MUTs. The plurality of MUTs are fixed to the surface of the substrate. Each MUT includes a movable diaphragm. The substrate includes a groove at least partially around the outer periphery of the diaphragm of one or more of the plurality of MUTs. In some embodiments, each MUT of the plurality of MUTs is a pMUT. In some embodiments, each MUT of the plurality of MUTs is a cMUT.

[0012] In some embodiments, the groove extends from the surface of the substrate to at least 10%, at least 50%, or at least 90% of the thickness of the substrate. In some embodiments, the groove extends throughout the thickness of the substrate.

[0013] In some embodiments, the groove extends from below the surface of the substrate to at least 10%, at least 50%, or at least 90% of the thickness of the substrate.

[0014] In some embodiments, the groove extends from the opposite surface (110) of the substrate through the substrate to at least 10%, at least 50%, or at least 90% of its thickness.

[0015] In some embodiments, the groove has a constant width of 1 μm to 40 μm. In some embodiments, the groove has a variable width of 1 μm to 40 μm.

[0016] In some embodiments, the groove has a constant distance of 1 μm to 40 μm from the outer periphery of the diaphragm. In some embodiments, the groove has a variable distance of 1 μm to 40 μm from the outer periphery of the diaphragm.

[0017] In some embodiments, the groove extends to at least 50%, 60%, 70%, 80%, or 90% of the outer periphery of the diaphragm. In some embodiments, the groove extends to the entire outer periphery of the diaphragm.

[0018] In some embodiments, the groove extends at least partially to at least 10%, at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, or at least 90% of the outer periphery of the diaphragms of a plurality of MUTs. In some embodiments, the groove extends at least partially to the outer periphery of the diaphragm of each MUT of a plurality of MUTs.

[0019] In some embodiments, the groove is at least partially filled with an acoustic damping material.

[0020] In some embodiments, the plurality of MUTs are arranged in a plurality of columns and a plurality of rows. In some embodiments, the trenches extend along the rows of the MUTs. In some embodiments, each row of the MUTs has a trench extending along it. In some embodiments, the trenches extend along the columns of the MUTs. In some embodiments, each column of the MUTs has a trench extending along it. In some embodiments, each row of the MUTs has a first trench extending along it, and each column of the MUTs has a second trench extending along it.

[0021] In some embodiments, the trenches at least partially extend to the outer periphery of the diaphragm of one of the plurality of MUTs.

[0022] In some embodiments, each of the plurality of MUTs is at least partially surrounded by the trenches.

[0023] In some embodiments, the MUT array further includes at least a second trench that at least partially extends to the outer periphery of the diaphragm of one or more of the plurality of MUTs. In some embodiments, the second trench at least partially extends to the outer periphery of the diaphragm of one of the plurality of MUTs. In some embodiments, each of the plurality of MUTs is at least partially surrounded by the first trench and the second trench.

[0024] In some embodiments, the trenches are disposed between an adjacent pair of MUTs.

[0025] In some embodiments, the substrate includes a plurality of grooves that at least partially extend to the outer periphery of the diaphragm of one or more of the plurality of MUTs. In some embodiments, the substrate includes one groove per one of the plurality of MUTs. In some embodiments, the substrate includes one groove per pair of adjacent MUTs of the plurality of MUTs. In some embodiments, the substrate includes less than one groove per one of the plurality of MUTs. In some embodiments, the substrate includes less than one groove per pair of adjacent MUTs of the plurality of MUTs. In some embodiments, the substrate includes more than one groove per one of the plurality of MUTs. In some embodiments, the substrate includes more than one groove per pair of adjacent MUTs of the plurality of MUTs.

[0026] In some forms, the MUT array is configured for medical imaging.

[0027] In another aspect, a method of manufacturing a MUT array is disclosed herein.

[0028] Incorporation by reference All publications, patents, and patent applications cited herein are hereby incorporated by reference in the same manner as if each individual publication, patent, or patent application was specifically and individually indicated to be incorporated by reference. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] A better understanding of the features and advantages of particular aspects of the present invention will be obtained from the following detailed description, which illustrates exemplary embodiments, and from the accompanying drawings.

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[0030] This specification describes, in certain embodiments, a micromachine ultrasonic transducer (MUT) array.

[0031] In one aspect, this specification discloses a MUT array including a substrate and a plurality of MUTs. The plurality of MUTs are fixed to the surface of the substrate. Each MUT includes a movable diaphragm. The substrate includes grooves that are at least partially around the diaphragm of one or more of the plurality of MUTs. In some embodiments, each MUT of the plurality of MUTs is a pMUT. In some embodiments, each MUT of the plurality of MUTs is a cMUT.

[0032] In some embodiments, the groove extends from the surface of the substrate to at least 10%, at least 50%, or at least 90% of the thickness of the substrate. In some embodiments, the groove extends through the entire thickness of the substrate.

[0033] In some embodiments, the groove extends from the opposite surface of the substrate to at least 10%, at least 50%, or at least 90% of the thickness of the substrate.

[0034] In some embodiments, the groove extends from below the surface of the substrate to at least 10%, at least 50%, or at least 90% of the thickness of the substrate.

[0035] In some embodiments, the groove has a constant width of 1 μm to 40 μm. In some embodiments, the groove has a variable width of 1 μm to 40 μm.

[0036] In some embodiments, the groove has a constant distance of 1 μm to 40 μm from the outer periphery of the diaphragm. In some embodiments, the groove has a variable distance of 1 μm to 40 μm from the outer periphery of the diaphragm.

[0037] In some embodiments, the groove extends to at least 50%, 70%, or 90% of the outer periphery of the diaphragm. In some embodiments, the groove extends through the entire outer periphery of the diaphragm.

[0038] In some embodiments, the groove extends at least partially to at least 10%, at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, or at least 90% of the outer periphery of the diaphragms of a plurality of MUTs. In some embodiments, the groove extends at least partially to the outer periphery of the diaphragm of each MUT of a plurality of MUTs.

[0039] In some embodiments, the groove is at least partially filled with an acoustic damping material.

[0040] In some forms, the MUT array is configured for medical imaging.

[0041] This specification describes, in certain embodiments, a method of manufacturing a micromachine ultrasonic transducer (MUT) array. Specific definitions

[0042] Unless defined otherwise, all technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field of the present invention. As used in this specification and the appended claims, the singular forms "a", "an", and "the" also include plural references unless the context clearly dictates otherwise. Any reference to "or" is intended to encompass "and / or" unless otherwise specified.

[0043] MUT The present disclosure may be utilized in the context of an imaging device that utilizes micromachine ultrasonic transducer (MUT) technology, including either piezoelectric micromachine ultrasonic transducer (pMUT) or capacitive micromachine ultrasonic transducer (cMUT) technology.

[0044] Figure 1C is a block diagram of an imaging device (105) having selectively changeable channels (106), (108), controlled by a controller (109), and having imaging calculations executed on a computing device (110) in accordance with the principles described herein. The imaging device (105) can be used to generate images of internal tissues, bones, blood flow, or organs of a human or animal body. Thus, the imaging device (105) transmits signals to the body and receives reflected signals from the body part being imaged. Such an imaging device may include either a pMUT or a cMUT, which may be referred to as a transceiver or imager that may be based on a photoacoustic effect or an ultrasonic effect. The imaging device (105) can also be used to image other objects. For example, the imaging device (105) can be used for medical imaging; flow measurement of pipes, speakers, microphone arrays; lithotripsy; local tissue heating for treatment; high-intensity focused ultrasound (HIFU) surgery.

[0045] In addition to use in human patients, the imaging device (105) can also be used to acquire images of animal internal organs. Further, in addition to internal organ imaging, the imaging device (105) can also be used to determine the direction and velocity of blood flow in arteries and veins, such as in Doppler mode imaging, and can also be used to measure tissue stiffness.

[0046] The imaging device (105) can be used to perform different types of imaging. For example, the imaging device (105) can be used to perform one-dimensional imaging, also known as A-scan, two-dimensional imaging, also known as B-scan, three-dimensional imaging, also known as C-scan, and Doppler imaging. The imaging device (105) can be switched between different imaging modes and electronically configured under program control.

[0047] To facilitate such imaging, the imaging device (105) includes an array of pMUT or cMUT transducers (210), and each transducer (210) includes an array of transducer elements (i.e., MUTs) (101). The MUTs (101) are operative to 1) generate pressure waves that pass through a body or other mass, and 2) receive reflected waves from objects within the body or other mass being imaged. In some examples, the imaging device (105) may be configured to simultaneously transmit and receive ultrasonic waveforms. For example, certain MUTs (101) transmit pressure waves toward a target object being imaged, and other MUTs (101) receive the pressure waves reflected from the target object and generate an electric charge in response to the received waves.

[0048] FIG. 1D shows a top view of an exemplary MUT (400) (a pMUT in this example). FIG. 1E shows a cross-sectional view of the MUT (400) taken along line 4-4 in FIG. 1D, according to an embodiment of the present disclosure. The MUT (400) may be substantially similar to the MUT (101) described herein. As depicted, the MUT is suspended from a substrate (402) and includes a membrane layer (406) disposed over a cavity (404), a lower electrode (O) (408) disposed over the membrane layer (or, in short, the membrane) (406), a piezoelectric layer (410) disposed over the lower electrode (O) (408), and an upper electrode (X) (412) disposed over the piezoelectric layer (410).

[0049] Any MUT, whether MUT or pMUT, can be efficiently formed on a substrate by leveraging various semiconductor wafer manufacturing operations. The semiconductor wafers may be provided in sizes of 6 inches, 8 inches, and 12 inches and can accommodate hundreds of transducer arrays. These semiconductor wafers begin as silicon substrates on which various processing steps are performed. An example of such an operation is the formation of a SiO2 layer, also known as an insulating oxide film. Various other steps are performed, such as the addition of metal layers that function as interconnects and bond pads to enable connection to other electronic devices. Yet another example of a mechanical operation is the etching of cavities (e.g., cavity (404) in FIG. 1E) within the substrate.

[0050] According to the present disclosure, in order to significantly reduce crosstalk, during the wafer manufacturing process, a groove (103) that generally surrounds each MUT (101) is formed within the substrate (100). This example is depicted in FIGS. 5A and 5B. FIG. 5A shows an exemplary schematic diagram showing a generalized MUT array (101a)-(101c) with diaphragm-side crosstalk grooves (103). FIG. 5B shows a cross-sectional view of the MUT array of FIG. 5A taken along line A-A'. The MUT array may be substantially similar to the array shown in FIGS. 1A-1C with one or more grooves (103) added. The MUT array (210) includes a substrate (100) and a plurality of MUTs (101a)-(101c). The plurality of MUTs (101a)-(101c) are fixed to the surface of the substrate (100). Each MUT (101a)-(101c) includes a movable diaphragm. The substrate (100) includes grooves (103) that are at least partially on the outer periphery of the diaphragms of the plurality of MUTs (101a)-(101c). The grooves (103) introduce an impedance mismatch between the substrate (100) and any material within the crosstalk grooves (103). This impedance mismatch disturbs the crosstalk waves by attenuation, reflection, and scattering.

[0051] The position of the crosstalk groove (103) will affect the amount of attenuation provided by the groove. The velocity data from FIG. 3 suggests that the surface waves at the interface (110) account for a portion of the crosstalk energy. Surface waves, such as Rayleigh waves, typically affect the surface region and materials within a certain distance of the interface, which is characterized by the wavelength of the traveling wave. In this case, the groove (103) attached to the surface of the substrate (100) and intersecting the interface (110) is optimal compared to the embedded crosstalk groove (104) that is not near the interface (110) as shown in FIGS. 6A and 6B.

[0052] FIGS. 7A and 7B are exemplary schematic diagrams showing (a) the layout and (b) the cross-sectional views of a generalized MUT array (101a)-(101c) with cavity-side crosstalk grooves (105). In some embodiments, the substrate (100) includes cavity-side grooves (105) that are at least partially around the cavities (120a)-(120c) of the plurality of MUTs. The grooves (105) introduce an impedance mismatch between the substrate (100) and any material within the crosstalk grooves (105). This impedance mismatch disrupts the crosstalk waves by attenuation, reflection, and scattering. The cavity-side grooves (105) are effective in reducing the crosstalk velocity by increasing the path length of the elastic waves.

[0053] FIGS. 8A and 8B are exemplary schematic diagrams showing (a) the layout and (b) the cross-sectional views of a generalized MUT array (101a)-(101c) with crosstalk grooves on both the diaphragm side (103) and the cavity side (105). In some embodiments, the substrate (100) includes both diaphragm-side grooves (103) and cavity-side grooves (105). In at least some examples, the combination of the diaphragm-side grooves (103) and the cavity-side grooves (105) can reduce the crosstalk effect (e.g., by reducing the velocity and / or amplitude of the crosstalk effect) compared to the case of only one type of either groove.

[0054] In some embodiments, the substrate (100) includes a diaphragm-side groove (103), an embedded groove (104), and a cavity-side groove (105).

[0055] Figs. 9A - 9D are cross-sectional views of a capacitive MUT with an embedded cavity having (a) a diaphragm-side crosstalk trench (103), (b) an embedded crosstalk trench (104), (c) a cavity-side crosstalk trench (105), and (d) crosstalk trenches on both the cavity side (105) and the diaphragm side (103). The MUT array (210) includes a substrate (100) and a plurality of MUTs (101a)-(101c). The plurality of MUTs (101a)-(101c) are fixed to the surface of the substrate (100). Each MUT (101a)-(101c) includes a movable diaphragm formed in or on the substrate (100) by embedded cavities (130a), (130b), and (130c). The substrate (100) includes grooves (103), (104), and / or (105) at least partially on the outer periphery of the diaphragms (101a)-(101c) of the plurality of MUTs. The grooves (103), (104), and / or (105) introduce an impedance mismatch between the substrate (100) and any material within the crosstalk trenches (103), (104), and / or (105). This impedance mismatch disturbs the crosstalk wave by attenuation, reflection, and scattering.

[0056] In some embodiments, the groove (103), (104), or (105) is formed via deep reactive ion etching (DRIE), plasma etching, wet etching, or other etching techniques that would be apparent to one of ordinary skill in the art based on the teachings herein.

[0057] In some embodiments, the grooves (103), (104), or (105) have a constant distance of 1 μm to 40 μm (e.g., 10 μm to 40 μm) from the outer periphery of the diaphragm or cavity. Alternatively, or in combination therewith, in some embodiments, the grooves (103), (104), or (105) have a variable distance of 1 μm to 40 μm (e.g., 10 μm to 40 μm) from the outer periphery of the diaphragm or cavity. The distance of the grooves (103), (104), or (105) from the outer periphery of the diaphragm or cavity can be made as close (e.g., atomically close) or as far as necessary.

[0058] In some embodiments, the grooves (103), (104), or (105) extend to at least 50%, 70%, or 90% of the outer periphery of the diaphragm or cavity. In some embodiments, the grooves (103), (104), or (105) extend to the entire outer periphery of the diaphragm or cavity.

[0059] In some embodiments, the grooves (103), (104), or (105) extend at least partially to at least 10%, at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, or at least 90% of the outer periphery of the diaphragms or cavities of a plurality of MUTs. In some embodiments, the grooves (103), (104), or (105) extend at least partially to the outer periphery of the diaphragm or cavity of each MUT of a plurality of MUTs.

[0060] In some embodiments, the grooves (103), (104), or (105) extend at least partially around the perimeter of the diaphragm or cavity on the first side of the MUT. Optionally, the second groove (103), (104), or (105) extends at least partially around the perimeter of the diaphragm or cavity on the second side of the MUT. In some embodiments, the MUT has grooves (103), (104), or (105) on both of its sides. In some embodiments, the grooves (103), (104), or (105) are symmetrically arranged around the perimeter of the diaphragm or cavity. In some embodiments, the grooves (103), (104), or (105) are asymmetrically arranged around the perimeter of the diaphragm or cavity. In some embodiments, the MUT has grooves (103), (104), or (105) on one of its sides.

[0061] As shown in FIG. 10, the depth of the crosstalk grooves (103), (104), or (105) will affect the attenuation. FIG. 10 is a graph showing the simulated attenuation of the crosstalk groove (103) versus the groove depth (in the range of 0 to 55 μm) according to the thickness (75 μm or 150 μm) of a plurality of substrates. The y-axis is the ratio of the maximum velocity of the element adjacent to the actuated element to the maximum velocity (dB) of the actuated element. In this case, the simulation shows that deeper crosstalk grooves (103) are more effective than shallower grooves. This is because both the surface wave and the longitudinal wave have a spatial range in the vertical direction. Grooves with a greater depth result in a greater proportion of the crosstalk wave being blocked by the grooves.

[0062] In some embodiments, the grooves (103), (104), or (105) extend from the surface of the substrate (diaphragm side or cavity side) to at least 10%, at least 50%, or at least 90% of the thickness of the substrate. In some embodiments, the groove extends through the entire thickness of the substrate (e.g., 100%). In some embodiments, the groove extends from the surface of the substrate (diaphragm side or cavity side) to about 1% of the thickness of the substrate.

[0063] In some embodiments, the grooves (103), (104), or (105) extend from below the surface of the substrate (diaphragm side or cavity side) to at least 10%, at least 50%, or at least 90% of the thickness of the substrate.

[0064] Finally, the width of the sidewalls of the grooves also affects the attenuation characteristics of the crosstalk grooves (103), (104), or (105), especially when the grooves are filled with a high attenuation material. Larger sidewall dimensions and / or a greater number of grooves produce better crosstalk attenuation. In the most common MUT arrays, the width of the sidewalls of the crosstalk grooves (103) and (104) is limited by the fill density of the MUTs.

[0065] In some embodiments, the grooves (103), (104), or (105) have a constant distance of 1 μm to 40 μm. In some embodiments, the grooves (103), (104), or (105) have a constant distance of 1 μm to 100 μm. In some embodiments, the grooves (103), (104), or (105) have a constant distance of 5 μm to 10 μm. The width of the grooves (103), (104), or (105) can be made thin (e.g., atomically thin) or large as needed.

[0066] In some embodiments, the grooves (103), (104), or (105) have a variable distance of 1 μm to 40 μm. In some embodiments, the grooves (103), (104), or (105) have a variable distance of 1 μm to 100 μm. In some embodiments, the grooves (103), (104), or (105) have a variable distance of 5 μm to 10 μm. The width of the grooves (103), (104), or (105) can be made thin (e.g., atomically thin) or large as needed.

[0067] In some embodiments, the grooves (103), (104), or (105) are at least partially filled with an acoustic damping material. Alternatively, or in combination therewith, in some embodiments, the grooves (103), (104), or (105) are at least partially filled with an acoustic damping material.

[0068] In some embodiments, there is one groove (103), (104), or (105) per MUT. In some embodiments, there is one groove (103), (104), or (105) per pair of adjacent MUTs. In some embodiments, the grooves (103), (104), or (105) can cross and extend between MUTs as one continuous groove. In some embodiments, there are fewer than one groove (103), (104), or (105) per pair of MUTs. In some embodiments, there is more than one groove (103), (104), or (105) per MUT.

[0069] In some embodiments, there are more than one groove (103), (104), or (105) per MUT. For example, each MUT has a first proximal groove on a first side of the MUT and a second proximal groove on a second side of the MUT, such that each pair of adjacent MUTs has at least two grooves therebetween. The proximal groove on the first side of the first MUT and the proximal groove on the second side of the second MUT can be disposed in the substrate between the first MUT and the second MUT. In some embodiments, a central groove can be disposed between the proximal grooves, and a total of at least three grooves can be disposed between adjacent first and second MUTs. In some embodiments, the proximal grooves and the central groove are formed within the same surface of the substrate (diaphragm side or cavity side). In some embodiments, the proximal grooves and the central groove are formed within different surfaces of the substrate. For example, as shown in FIGS. 8B and 9D, the proximal groove (103) can be formed on the diaphragm side and the central groove (105) can be formed on the cavity side. In at least some examples, a combination of a diaphragm side proximal groove (103) and a cavity side central groove (105) can reduce crosstalk effects (e.g., by reducing the speed and / or amplitude of crosstalk effects) more than either groove type alone.

[0070] In some embodiments, all of the grooves (103), (104), or (105) of the MUT array have the same dimensions. In some embodiments, one or more of the grooves (103), (104), or (105) have different dimensions. For example, the central groove (105) shown in FIGS. 8B and 9D can be wider than the proximal groove (103).

[0071] In some embodiments, for each MUT, there is one groove (103), (104), or (105) that surrounds at least 80% of the MUT. Alternatively, or in combination therewith, there is one groove (103), (104), or (105) under each row of the MUT. Alternatively, or in combination therewith, there is one groove (103), (104), or (105) under each column of the MUT. Alternatively, or in combination therewith, there is one groove (103), (104), or (105) under each row of the MUT and one groove (103), (104), or (105) under each column of the MUT. Alternatively, or in combination therewith, there are multiple grooves (103), (104), or (105) around each MUT.

[0072] The effectiveness of such grooves has been demonstrated in a silicon MUT array with a 150 μm substrate. FIG. 11A shows the f-k and images of a MUT array (101a)-(101c) without crosstalk grooves. FIG. 11B shows the f-k and images of a MUT array (101a)-(101c) with crosstalk grooves (103) (75 μm deep in a 150 μm silicon substrate). As shown in FIGS. 11A and 11B, the crosstalk grooves (103) effectively reduce crosstalk energy and remove artifacts of the "spotlight" (420) and ghosting (430) associated with crosstalk.

[0073] Method for manufacturing a pMUT with grooves

[0074] Next, an exemplary manufacturing method of a pMUT with grooves, such as the pMUT shown in FIGS. 5A to 8B, will be described.

[0075] (a) First, a substrate (e.g., substrate (402) or (100)), typically single-crystalline silicon, is provided.

[0076] (b) Optionally, the embedded crosstalk grooves (104) can be patterned and etched into the substrate to create a "handle" wafer. Another silicon "device" wafer can be thermally oxidized and then fused to the "handle", forming the embedded grooves (104) therebetween (e.g., as shown in FIGS. 6A and 6B). The "device" wafer can be ground and polished to the desired diaphragm thickness.

[0077] (c) Thereafter, an insulating layer can be deposited on the substrate. The insulating layer is typically some form of SiO2 with a thickness of about 0.1 μm to 3 μm. It is usually deposited by thermal oxidation, PECVD deposition, or other techniques.

[0078] (d) Thereafter, a first metal layer (408) (also called M1 or metal 1) can be deposited. Typically, this is a combination of films that adhere to the substrate, prevent diffusion of the piezoelectric element, assist in the structured deposition / growth of the piezoelectric element, and are conductive. SRO (SrRuO3) may be used on top of Pt for diffusion barrier and conduction, on top of Ti as an adhesion layer (from Pt to SiO2), and for the growth of structured films. Usually, these layers are thin, less than 200 nm, and some films are 10 - 40 nm. Due to pressure, manufacturing, and cost issues, typically this stack is limited to less than 1 μm. The conductor (Pt) is typically thicker than the structured layer (SRO) and the adhesion layer (Ti). Other common structured layers that are not SRO include (La0.5Sr0.5)CoO3, (La0.5Sr0.5)MnO3, LaNiO3, RuO2, IrO2, BaPbO3, etc. Pt can be replaced with other conductor materials such as Cu, Cr, Ni, Ag, Al, Mo, W, and NiCr. These other materials usually have drawbacks such as poor diffusion barrier, brittleness, and poor adhesion, and Pt is the most commonly used conductor. The adhesion layer Ti can be replaced with any common adhesion layer such as TiW, TiN, Cr, Ni, Cr, etc.

[0079] (e) Subsequently, the piezoelectric material (410) can be deposited. Some common examples of suitable piezoelectric materials include PZT, KNN, PZT-N, PMN-Pt, AlN, Sc-AlN, ZnO, PVDF, and LiNiO3. The thickness of the piezoelectric layer can vary between 100 nm to 5 μm, or in some cases even more.

[0080] (f) Subsequently, the second metal layer (412) (also referred to as M2 or metal 2) can be deposited. This second metal layer (412) can be similar to the first metal layer (408) and can serve a similar purpose. In the case of M2, it can be the same stack as M1 but used in reverse: there is Ti for adhesion on top of Pt to prevent diffusion on top of the structural SRO.

[0081] (g) Subsequently, the second metal layer or M2 (412) can be stopped on the piezoelectric layer and patterned and etched. The etching can be done in many ways herein, for example, via RIE (reactive ion etching), ion milling, wet chemical etching, isotropic gas etching, etc. After patterning and etching, the photoresist used to pattern M2 can be removed via wet and / or dry etching. In many embodiments for manufacturing cMUT and pMUT described herein, any number of etching methods can be used, and the photoresist is typically removed after most patterning and etching steps.

[0082] (h) Subsequently, the piezoelectric layer can similarly be stopped on the first metal layer or M1 (408) and patterned and etched. Typically, wet, RIE, and / or ion milling etching are used.

[0083] (i) Subsequently, the first metal layer or M2 (408) can similarly be stopped on the dielectric insulating layer and similarly patterned and etched.

[0084] (j) Optionally, either or both of the following can be added: (1) H2 Barrier. Diffusion of H2 into the piezoelectric layer can limit its lifespan. To prevent this, an H2 barrier can be used. To achieve this, 40 nm of ALD (Atomic Layer Deposition) aluminum oxide (Al2O3) can be used. Other suitable materials may include SiC, diamond-like carbon, etc. (2) Redistribution Layer (RDL). This layer can provide connections between M1 and M2 and other connections (such as wire bonding, bump bonding, etc.). The RDL can be formed by first adding a dielectric such as oxide, etching vias in the dielectric, depositing a conductor (typically Al), and finally patterning the conductor. Additionally, a passivation layer (usually oxide + nitride) may be added to prevent physical scratches, accidental short circuits, and / or moisture ingress.

[0085] (k) The groove (103) on the diaphragm side may be patterned and etched (as shown, for example, in FIGS. 5A, 5B, 8A, and 8B). The dielectric layer may be etched by RIE or wet etching. The substrate (100) is typically silicon and can typically be etched via DRIE (Deep Reactive Ion Etching).

[0086] (l) Often, a silicon-on-insulator (SOI) substrate is used. In this case, there is an embedded insulator layer or an embedded oxide (BOX) layer directly below the diaphragm (101). Subsequently, the diaphragm is composed of a "device" layer (the layer above the BOX) and a "handle" layer below the BOX layer. The cavity in the device layer stops at the BOX and can be etched from the handle layer. In this case, trench etching may include two additional steps: (1) after the device layer is etched via DRIE, the BOX is etched (usually via dry RIE etching or, in some cases, via wet etching), and (2) the handle layer is etched to the desired depth via DRIE. Most SOI wafers are silicon, that is, the device layer and the handle layer are typically single-crystalline silicon. In this case, the insulator BOX is typically thermally grown silicon dioxide, called an "embedded oxide film", which is the origin of the term "BOX". Typically, a silicon SOI wafer with a single-crystalline silicon handle and device layer together with the oxide film BOX can be used. The device layer can be 5 μm, but typically varies from 100 nm to 100 μm, while the thickness of the handle layer typically varies from 100 μm to 1000 μm. The BOX is typically 100 nm to 5 μm, but often 1 μm can be used.

[0087] (m) Optionally, the back side of the wafer or the handle can be thinned by grinding and optionally polished at this point. In many embodiments, the handle layer is thinned to a thickness of 500 μm to 300 μm. The typical thickness generally varies from 50 μm to 1000 μm.

[0088] (n) The trench (105) on the cavity side may be patterned and etched (as shown, for example, in FIGS. 7A - 8B). The back side of the substrate (100) can typically be etched via DRIE (deep reactive ion etching).

[0089] (o) The cavity can be patterned on the back side of the wafer or the handle, and the cavity can be etched. Typically, the wafer / handle is composed of silicon, and the etching is performed by DRIE. The timing of the etching can be adjusted. The cavity may be etched simultaneously with the grooves (105) on the cavity side. The etching may be selectively stopped on the BOX. The cavity can be etched by other techniques such as KOH, TMAH, HNA, and RIE. The wafer can be considered complete after the photoresist is removed.

[0090] Those skilled in the art will understand, based on the teachings herein, that other processes can be used to achieve similar final results.

[0091] Manufacturing method of cMUT with grooves

[0092] Next, an exemplary manufacturing method of a cMUT with grooves, such as the cMUT shown in FIGS. 9A - 9D, will be described.

[0093] (a) First, a substrate (e.g., substrate (402) or (100)), typically single - crystal silicon, is provided.

[0094] (b) Thereafter, the substrate may be thermally oxidized.

[0095] (c) Cavities (130a), (130b), (130c) can be patterned and etched in the oxide film to create a "handle" wafer. This is typically accomplished by plasma etching or wet etching (e.g., HF) of the oxide film.

[0096] (d) Optionally, the embedded crosstalk grooves (104) can be patterned and etched in the oxide film of the "handle" wafer. This is typically accomplished by plasma etching or wet etching (e.g., HF) of the oxide film.

[0097] (e) Thereafter, the silicon "device" wafer may be fused to the patterned oxide "handle" wafer. Optionally, the "device" wafer may be patterned and etched (e.g., via DRIE) prior to fusion to correspond to the embedded grooves (104) of the "handle" wafer so as to form grooves (104) in which the fusion of the "handle" wafer and the "device" wafer is embedded (as shown, for example, in FIG. 9B).

[0098] (f) The "device" wafer may be ground and polished to the desired diaphragm thickness.

[0099] (g) The grooves (103) on the diaphragm side may be patterned and etched on the diaphragm side of the ground and polished wafer (as shown, for example, in FIGS. 9A and 9D).

[0100] (h) The grooves (105) on the cavity side may be patterned and etched on the cavity side of the ground and polished wafer (as shown, for example, in FIGS. 9C and 9D).

[0101] Those skilled in the art will understand that other processes can be used to achieve similar end results based on the teachings herein.

Examples

[0102] The following examples represent embodiments of the software applications, systems, and methods described herein and are not intended to be limiting in any way.

[0103] Example 1 - Azimuth Response of Cavity-Side Grooves Test pMUT wafers were fabricated with variable depths of the grooves from the cavity (25 μm, 37.5 μm, and 50 μm for 75-μm-thick pMUTs) and stand-off distances (10 μm, 15 μm, 20 μm, and 25 μm), and groove widths (5 μm and 10 μm). The azimuthal response of the pMUT was measured at various frequencies. FIGS. 12A and 12B show the azimuthal responses at the 3-dB shift of the cavity-side grooves with depths of 50 μm and 25 μm, respectively, for various stand-offs and widths. The naming convention “XX-YYW” is such that XX = stand-off distance and YY = width. Thus, 20-05W is a groove with a stand-off of 20 μm from the cavity and a width of 5 μm. As shown in FIG. 12A, the spotlight angle of the cavity-side groove with a depth of 50 μm appears to be further pushed out as the stand-off distance of the groove increases. As shown in FIG. 12B, the spotlight angle of the cavity-side groove with a depth of 25 μm has no linear correlation with the stand-off distance of the groove, but as a general trend, the spotlight angle becomes narrower as the stand-off distance increases. The crosstalk dip occurs at 3.5 MHz, specifically at 20-10W (20-μm stand-off, 10-μm width), with a depth of 25 μm, at approximately + / -28 degrees.

[0104] Preferred embodiments of the invention have been shown and described herein, but it will be apparent to those skilled in the art that such embodiments are provided by way of example only. Many variations, changes, and substitutions will occur to those skilled in the art without departing from the invention. It should be understood that various alternatives to the embodiments of the invention described herein may be utilized in practicing the invention.

Claims

1. A micromachine ultrasonic transducer (MUT) array, comprising a substrate and a plurality of micromachine ultrasonic transducers (MUTs), wherein the plurality of micromachine ultrasonic transducers (MUTs) are fixed on the surface of the substrate, and each micromachine ultrasonic transducer (MUT) includes a movable diaphragm, the substrate includes a groove that is at least partially around the outer periphery of the diaphragm of one or more of the plurality of micromachine ultrasonic transducers (MUTs), in the micromachine ultrasonic transducer (MUT) array, the groove includes a diaphragm-side groove extending from the diaphragm side of the substrate into the substrate and a cavity-side groove extending from the cavity side of the substrate into the substrate, and a micromachine ultrasonic transducer (MUT) array.

2. Each micromachine ultrasonic transducer (MUT) of the plurality of micromachine ultrasonic transducers (MUTs) is a pMUT or a cMUT, the micromachine ultrasonic transducer (MUT) array according to Claim 1.

3. (i) The groove extends from the surface of the substrate to at least 10%, at least 50%, or at least 90% of the thickness of the substrate, (ii) The groove extends through the entire thickness of the substrate, (iii) The groove extends from the opposite surface of the substrate to at least 10%, at least 50%, or at least 90% of the thickness of the substrate, or (iv) The groove extends from below the surface of the substrate to at least 10%, at least 50%, or at least 90% of the thickness of the substrate, the micromachine ultrasonic transducer (MUT) array according to Claim 1.

4. The groove has a constant width of 1 μm to 40 μm or a variable width of 1 μm to 40 μm, the micromachine ultrasonic transducer (MUT) array according to Claim 1.

5. (i) The groove has a constant distance of 1 μm to 40 μm from the outer periphery of the diaphragm, (ii) The groove has a variable distance of 1 μm to 40 μm from the outer periphery of the diaphragm, (iii) The groove extends to at least 50%, 60%, 70%, 80%, or 90% of the outer periphery of the diaphragm, (iv) The groove extends through the entire outer periphery of the diaphragm, (v) The groove extends at least partially to the outer periphery of the diaphragm of at least 10%, at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, or at least 90% of the plurality of micromachine ultrasonic transducers (MUTs), or (vi) The groove extends at least partially to the outer periphery of the diaphragm of each micromachine ultrasonic transducer (MUT) of the plurality of micromachine ultrasonic transducers (MUTs). The micromachine ultrasonic transducer (MUT) array according to claim 1. **Claim 6** The micromachine ultrasonic transducer (MUT) array according to claim 1, wherein the groove is at least partially filled with an acoustic attenuation material. **Claim 7** The micromachine ultrasonic transducer (MUT) array according to claim 1, wherein the plurality of micromachine ultrasonic transducers (MUTs) are arranged in a plurality of rows and a plurality of columns. **Claim 8** (i) The groove extends along a row of the micromachine ultrasonic transducer (MUT). (ii) Each row of the micromachine ultrasonic transducer (MUT) has a groove extending along it. (iii) The groove extends along a column of the micromachine ultrasonic transducer (MUT), or (iv) Each column of the micromachine ultrasonic transducer (MUT) has a groove extending along it. The micromachine ultrasonic transducer (MUT) array according to claim 7. **Claim 9** The groove extends at least partially to the outer periphery of the diaphragm of one micromachine ultrasonic transducer (MUT) of the plurality of micromachine ultrasonic transducers (MUTs), or Each micromachine ultrasonic transducer (MUT) of the plurality of micromachine ultrasonic transducers (MUTs) is at least partially surrounded by a groove. The micromachine ultrasonic transducer (MUT) array according to claim 1. **Claim 10** It further includes at least one second groove that extends at least partially to the outer periphery of the diaphragm of one or more micromachine ultrasonic transducers (MUTs) of the plurality of micromachine ultrasonic transducers (MUTs). The second groove at least partially extends to the outer periphery of the diaphragm of one of the plurality of micromachine ultrasonic transducers (MUTs), or each of the plurality of micromachine ultrasonic transducers (MUTs) is at least partially surrounded by the first groove and the second groove, The micromachine ultrasonic transducer (MUT) array according to claim 1. **Claim 11** The micromachine ultrasonic transducer (MUT) array according to claim 1, wherein the groove is disposed between a pair of adjacent micromachine ultrasonic transducers (MUTs). **Claim 12** The substrate includes a plurality of grooves that at least partially extend to the outer periphery of the diaphragm of one or more of the plurality of micromachine ultrasonic transducers (MUTs), (i) each of the plurality of micromachine ultrasonic transducers (MUTs) is at least partially surrounded by one of the plurality of grooves, (ii) each of the adjacent pairs of the plurality of micromachine ultrasonic transducers (MUTs) is at least partially surrounded by one of the plurality of grooves, (iii) some of the plurality of micromachine ultrasonic transducers (MUTs) are surrounded by one of the plurality of grooves, or (iv) each of the adjacent pairs of the plurality of micromachine ultrasonic transducers (MUTs) is surrounded by one of the plurality of grooves, The micromachine ultrasonic transducer (MUT) array according to claim 1. **Claim 13** The micromachine ultrasonic transducer (MUT) array according to claim 1, configured for medical imaging. **Claim 14** The micromachine ultrasonic transducer (MUT) array according to claim 1, wherein the groove includes a diaphragm-side groove extending into the substrate from the diaphragm side of the substrate and a cavity-side groove extending into the substrate from the cavity side of the substrate.

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