Imaging device having a piezoelectric transceiver with harmonic characteristics

Abstract

A micromachined ultrasonic transducer (MUT) including a first piezoelectric layer and a second piezoelectric layer. The first piezoelectric layer is disposed between a first electrode and a second electrode. The second piezoelectric layer is disposed between the second electrode and a third electrode. At least the first electrode has a first end and a second end along a first axis, one or more of which are defined by a radius of curvature R. A second axis perpendicular to the first axis passes through a midpoint of the first axis. A half-width of the first electrode is defined by a length L measured from the midpoint to the circumference of the first electrode in the direction of the second axis. A total width of the first electrode at its narrowest point along the first axis is at most 2L such that the first electrode has a concave shape. R / L is greater than 1.

Description

Technical Field

[0001] Cross-reference

[0001] This application claims the benefit of PCT Application No. PCT / US2021 / 025109, filed Mar. 31, 2021, and further claims the benefit of U.S. Patent Application No. 17 / 218,656, filed Mar. 31, 2021, the contents of which are hereby incorporated by reference in their entirety.

[0002]

[0003] The present invention relates to an imaging device, and more particularly to an imaging device having a microfabricated ultrasonic transducer (MUT) that exhibits improved pressure amplitude and frequency response behavior when driven at a fundamental frequency and a harmonic frequency.

Background Art

[0003]

[0005] A non-invasive imaging system for imaging internal organs of the human body and displaying an image of the internal organs transmits a signal into the human body and receives a signal reflected from the organ. Generally, a transducer such as a capacitive transducer (cMUT) or a piezoelectric transducer (pMUT) used in an imaging system is called a transceiver, and some of the transceivers are based on a photoacoustic effect or an ultrasonic effect.

[0004]

[0006] Generally, an MUT includes two or more electrodes, and the topology of the electrodes affects both the electrical performance and the acoustic performance of the MUT. For example, the amplitude of the sound pressure generated by a pMUT increases as the size of the electrode increases, thereby improving the acoustic performance of the pMUT. However, as the size of the electrode increases, the capacitance also increases, degrading the electrical performance of the pMUT. In another example, the amplitude of the sound pressure at the vibration resonance frequency of a pMUT is affected by the shape of the electrode. Therefore, there is a need for a method for designing electrodes to improve both the acoustic performance and the electrical performance of the transducer.

Summary of the Invention

Means for Solving the Problem

[0005]

[0007] In one aspect, a microfabricated ultrasonic transducer (MUT) is disclosed. The MUT includes at least a first piezoelectric layer and a second piezoelectric layer. The first piezoelectric layer is disposed between a first electrode and a second electrode. The second piezoelectric layer is disposed between the second electrode and a third electrode. At least the first electrode has a first end and a second end along a first axis. One or more of the first end or the second end is defined by a radius of curvature R. A second axis passes through the midpoint of the first axis, and the second axis is perpendicular to the first axis. The half-value width of the first electrode is defined by a length L measured from the midpoint in the direction of the second axis to the outer periphery of the first electrode. The full width of the first electrode at the narrowest point along the first axis is at most 2L such that the first electrode has a concave shape. R / L is greater than 1.

[0006]

[0008] In some embodiments, the first axis extends along the direction in which the first electrode has the longest dimension.

[0009] In some embodiments, the second axis extends along the direction in which the first electrode has the shortest dimension.

[0007]

[0010] In some embodiments, the piezoelectric layer is formed from at least one of PZT, KNN, PZT-N, PMN-Pt, AIN, Sc-AIN, ZnO, PVDF, and LiNiO3.

[0008]

[0011] In one aspect, a microfabricated ultrasonic transducer (MUT) is disclosed. The MUT includes a plurality of piezoelectric layers including M piezoelectric layers. The MUT further includes a plurality of electrodes including N electrodes. The piezoelectric layer having an index m among the plurality of piezoelectric layers is disposed between a first electrode having an index m and a second electrode having an index m+1. The index m is associated with the vertical distance of the piezoelectric layer. At least the first electrode has a first end and a second end along a first axis. One or more of the first end or the second end is defined by a radius of curvature R. A second axis passes through the midpoint of the first axis. The second axis is perpendicular to the first axis. The half-value width of the first electrode is defined by a length L measured from the midpoint to the outer periphery of the first electrode in the direction of the second axis. The total width of the first electrode at the narrowest point of the first electrode along the first axis is at most 2L such that the first electrode has a concave shape. R / L is greater than 1.

[0009]

[0012] In some embodiments, the first axis extends along the direction in which the first electrode has the longest dimension.

[0013] In some embodiments, the second axis extends along the direction in which the first electrode has the shortest dimension.

[0010]

[0014] In some embodiments, the MUT further includes a substrate and a membrane spanned from the substrate.

[0015] In some embodiments, the piezoelectric layer is formed from at least one of PZT, KNN, PZT-N, PMN-Pt, AIN, Sc-AIN, ZnO, PVDF, and LiNiO3.

[0011]

[0016] In some embodiments, N = M + 1.

[0017] In one aspect, a microfabricated ultrasonic transducer (MUT) is disclosed. The MUT includes at least a first piezoelectric layer and a second piezoelectric layer. The first piezoelectric layer is disposed between a first electrode and a second electrode. The second piezoelectric layer is disposed between the second electrode and a third electrode. At least the first electrode has a first end and a second end along a first axis. One or more of the first end or the second end is defined by a radius of curvature R. A second axis passes through the midpoint of the first axis, and the second axis is perpendicular to the first axis. The half-value width of the first electrode is defined by a length L measured from the midpoint to the outer periphery of the first electrode in the direction of the second axis. The overall width of the first electrode at the widest point along the first axis is at least twice L such that the first electrode has a convex shape. R / L is less than 1.

[0012]

[0018] In some embodiments, the first axis extends along the direction in which the first electrode has its longest dimension.

[0019] In some embodiments, the second axis extends along the direction in which the first electrode has its shortest dimension.

[0013]

[0020] In some embodiments, the MUT further includes a substrate and a membrane spanning from the substrate.

[0021] In some embodiments, the piezoelectric layer is formed from at least one of PZT, KNN, PZT-N, PMN-Pt, AIN, Sc-AIN, ZnO, PVDF, and LiNiO3.

[0014]

[0022] In one aspect, a microfabricated ultrasonic transducer (MUT) is disclosed. The MUT includes a plurality of piezoelectric layers including M piezoelectric layers. The MUT further includes a plurality of electrodes including N electrodes. The piezoelectric layer having index m among the plurality of piezoelectric layers is disposed between a first electrode having index m and a second electrode having index m+1. The index m is associated with the vertical distance of the piezoelectric layer. At least the first electrode has a first end and a second end along a first axis. One or more of the first end or the second end is defined by a radius of curvature R. A second axis passes through the midpoint of the first axis. The second axis is perpendicular to the first axis. The half-value width of the first electrode is defined by a length L measured from the midpoint to the outer periphery of the first electrode in the direction of the second axis. The full width of the first electrode at the widest point of the first electrode along the first axis is at least twice L such that the first electrode has a convex shape. R / L is less than 1.

[0015]

[0023] In some embodiments, the first axis extends along the direction in which the first electrode has its longest dimension.

[0024] In some embodiments, the second axis extends along the direction in which the first electrode has its shortest dimension.

[0016]

[0025] In some embodiments, the MUT further includes a substrate and a membrane spanned from the substrate.

[0026] In some embodiments, the piezoelectric layer is formed from at least one of PZT, KNN, PZT-N, PMN-Pt, AIN, Sc-AIN, ZnO, PVDF, and LiNiO3.

[0017]

[0027] In some embodiments, N = M + 1.

[0028] In an embodiment, the microfabricated ultrasonic transducer (MUT) includes a top electrode. The shape of the top electrode is defined by a major axis and a minor axis, and the major axis and the minor axis intersect at an origin. Both distal ends of the top electrode, i.e., the ends of the top electrode that are farthest from the origin in the direction of the major axis, are defined by a radius of curvature R. The intrinsic width L of the top electrode is measured from the origin in the direction of the minor axis (i.e., perpendicular to the major axis) to the outer edge or outer perimeter of the top electrode. When the ratio R / L of the radius of curvature to the intrinsic width is greater than 1, the top electrode is wider at the ends compared to the width of the central portion, and the electrode generally has a concave shape. When the ratio R / L of the radius of curvature to the intrinsic width is less than 1, the top electrode is narrower at the ends compared to the width of the central portion, and the electrode generally has a convex shape. As described in more detail herein, regardless of whether it is configured in a concave or convex shape, an electrode with a specific R / L value or an electrode within a specific range of values exhibits desirable pressure amplitude and frequency response behavior when driven at the fundamental frequency and harmonic frequencies compared to prior electrode shape designs. The surface density distribution of the concave or convex electrode along the axis has a plurality of maxima, and the locations of the plurality of maxima coincide with the locations where the plurality of antinodes at the vibration resonance frequency are positioned.

[0018]

[0029] In an embodiment, the microfabricated ultrasonic transducer (MUT) includes a symmetric convex top electrode. The surface density distribution of the symmetric convex electrode along the axis has a plurality of maxima, and the locations of the plurality of maxima coincide with the locations where the plurality of antinodes at the vibration resonance frequency are positioned.

[0019]

[0030] In an embodiment, the transducer array includes a plurality of microfabricated ultrasonic transducers (MUTs). Each of the plurality of MUTs includes a symmetric convex top electrode.

[0031] In an embodiment, the imaging device includes a transducer array having a plurality of microfabricated ultrasonic transducers (MUTs). Each of the plurality of MUTs includes a symmetric convex upper electrode. The surface density distribution of the symmetric convex electrode along the axis has a plurality of maxima, and the locations of the plurality of maxima coincide with the locations where a plurality of antinodes are positioned at the vibration resonance frequency.

[0020]

[0032] In an embodiment, the microfabricated ultrasonic transducer (MUT) includes a symmetric concave upper electrode. The surface density distribution of the symmetric concave electrode along the axis has a plurality of maxima, and the locations of the plurality of maxima coincide with the locations where a plurality of antinodes are positioned at the vibration resonance frequency.

[0021]

[0033] In an embodiment, the transducer array includes a plurality of microfabricated ultrasonic transducers (MUTs). Each of the plurality of MUTs includes a symmetric concave upper electrode.

[0034] In an embodiment, the imaging device includes a transducer array having a plurality of microfabricated ultrasonic transducers (MUTs). Each of the plurality of MUTs includes a symmetric concave upper electrode. The surface density distribution of the symmetric concave electrode along the axis has a plurality of maxima, and the locations of the plurality of maxima coincide with the locations where a plurality of antinodes are positioned at the vibration resonance frequency.

[0022]

[0035] In a first aspect, a microfabricated ultrasonic transducer (MUT) is provided. The MUT includes a first electrode having a first end and a second end along a first axis. One or more of the first end or the second end is defined by a radius of curvature R. A second axis passes through the midpoint of the first axis, and the second axis is perpendicular to the first axis. The half-value width of the first electrode is defined by a length L measured from the midpoint to the outer periphery of the first electrode in the direction of the second axis. The overall width of the first electrode at the widest point along the first axis is at least twice L such that the first electrode has a convex shape and R / L is less than 1.

[0023]

[0036] In an embodiment, the MUT is a capacitive micromachined ultrasonic transducer (cMUT).

[0037] In an embodiment, the MUT is a piezoelectric micromachined ultrasonic transducer (pMUT).

[0024]

[0038] In an embodiment, the first axis extends along the direction in which the first electrode has the longest dimension.

[0039] In an embodiment, the second axis extends along the direction in which the first electrode has the shortest dimension.

[0025]

[0040] In an embodiment, the MUT further includes a substrate, a membrane spanned from the substrate, a second electrode disposed on the membrane, and a piezoelectric layer disposed on one or more of the first electrode or the second electrode. In some embodiments, the piezoelectric layer includes a first piezoelectric layer disposed on the second electrode. In some embodiments, the MUT further includes a third electrode disposed on the first piezoelectric layer and a second piezoelectric layer disposed on the third electrode, and the first electrode is disposed on the second piezoelectric layer. In an embodiment, the piezoelectric layer is formed from at least one of PZT, KNN, PZT-N, PMN-Pt, AIN, Sc-AIN, ZnO, PVDF, and LiNiO3.

[0026]

[0041] In another aspect, an imaging device is provided. The imaging device includes a transducer array including a plurality of micromachined ultrasonic transducers (MUTs), and each of the plurality of MUTs includes a convex electrode.

[0027]

[0042] In another aspect, a MUT is provided. The MUT includes a first electrode having a first end and a second end along a first axis. One or more of the first end or the second end is defined by a radius of curvature R. A second axis passes through the midpoint of the first axis and is perpendicular to the first axis. The half-value width of the first electrode is defined by a length L measured from the midpoint in the direction of the second axis to the outer periphery of the first electrode. The overall width of the first electrode at the narrowest point along the first axis is less than 2L such that the first electrode has a concave shape and R / L is greater than 1.

[0028]

[0043] In an embodiment, the MUT is a capacitive microfabricated ultrasonic transducer (cMUT).

[0044] In an embodiment, the MUT is a piezoelectric microfabricated ultrasonic transducer (pMUT).

[0029]

[0045] In an embodiment, the first axis extends along the direction in which the first electrode has its longest dimension.

[0046] In an embodiment, the second axis extends along the direction in which the first electrode has its shortest dimension.

[0030]

[0047] In an embodiment, the MUT further includes a substrate, a membrane suspended from the substrate, a second electrode disposed on the membrane, and a piezoelectric layer disposed on one or more of the first electrode or the second electrode. In some embodiments, the piezoelectric layer includes a first piezoelectric layer disposed on the second electrode. In some embodiments, the MUT further includes a third electrode disposed on the first piezoelectric layer and a second piezoelectric layer disposed on the third electrode, and the first electrode is disposed on the second piezoelectric layer. In an embodiment, the piezoelectric layer is formed from at least one of PZT, KNN, PZT-N, PMN-Pt, AIN, Sc-AIN, ZnO, PVDF, and LiNiO3.

[0031]

[0048] In another aspect, an imaging device is provided. The imaging device includes a transducer array that includes a plurality of microfabricated ultrasonic transducers (MUTs), and each of the plurality of MUTs includes a concave electrode.

[0032] Incorporation by reference

[0049] All publications, patents, and patent applications mentioned in this specification are incorporated herein by reference to the same extent as if each individual publication, patent, or patent application was specifically and individually indicated to be incorporated by reference.

[0033]

[0050] Embodiments of the present invention are referred to, and examples thereof may be shown in the accompanying drawings. These drawings are intended to be illustrative and not limiting. It should be understood that the present invention is generally described in the context of these embodiments, but is not intended to limit the scope of the present invention to these particular embodiments.

Brief description of the drawings

[0034]

Figure 1

[0051] A diagram showing an imaging system according to an embodiment of the present disclosure.

Figure 2

[0052] A schematic diagram of an imager according to an embodiment of the present disclosure.

Figure 3A

[0053] A side view of a transceiver array according to an embodiment of the present disclosure.

Figure 3B

[0054] A top view of a transceiver tile according to an embodiment of the present disclosure.

Figure 4A

[0055] A cross-sectional view of a MUT applicable to a concave MUT or a convex MUT along direction 4-4 of FIGS. 4B and 4D according to an embodiment of the present disclosure.

Figure 4B

[0056] A top view of a concave MUT according to an embodiment of the present disclosure.

Figure 4C

[0057] An alternative top view of a concave MUT according to an embodiment of the present disclosure.

Figure 4D

[0058] It is a top view of a convex MUT according to an embodiment of the present disclosure.

Figure 4E

[0059] It is an alternative top view of a convex MUT according to an embodiment of the present disclosure.

Figure 4F

[0060] It is a cross-sectional view of another MUT applicable to a concave MUT or a convex MUT along the direction 4-4 of FIGS. 4B and 4D according to an embodiment of the present disclosure.

Figure 4G

[0061] It is a cross-sectional view of a pMUT having a plurality of piezoelectric layers.

Figure 4H

[0062] It is a diagram showing a sub-section of the cross-section of FIG. 4G in which the radius R and the characteristic half-width are displayed so as to be visible.

Figure 5A

[0063] It is a diagram showing a plot of the acoustic response of a MUT having a concave configuration according to an embodiment of the present disclosure.

Figure 5B

[0064] It is a diagram showing a plot of the acoustic response of a MUT having a convex configuration according to an embodiment of the present disclosure.

Figure 6A

[0065] It is a diagram showing the vibration mode shapes of a concave MUT and a convex MUT according to an embodiment of the present disclosure.

Figure 6B

Figure 6C

Figure 7A

[0066] It is a diagram showing a plot of the frequency response of a two-layer pMUT compared with the frequency response of a single-layer pMUT device.

Figure 7B

[0067] It is a diagram showing a plot of the frequency response of a two-layer pMUT having an electrode with a concave shape compared with the frequency response of a two-layer pMUT having an electrode with a convex shape.

Figure 7C

[0068] A diagram showing a plot of the frequency response of a two-layer pMUT having an electrode with a convex shape, compared to the frequency response of a two-layer pMUT having an electrode with a convex shape.

Best Mode for Carrying Out the Invention

[0035]

[0069] In the following description, for the purpose of explanation, specific details are set forth in order to provide an understanding of the present disclosure. However, it will be apparent to one of ordinary skill in the art that the present disclosure may be practiced without these specific details. Additionally, one of ordinary skill in the art will recognize that the embodiments of the present disclosure described hereinafter may be implemented in various ways, such as a process, apparatus, system, or device.

[0036]

[0070] The elements / components shown in the figures are examples of exemplary embodiments of the present disclosure and are intended to avoid obscuring the present disclosure. References herein to "one embodiment," "preferred embodiment," "an embodiment," or "embodiments" mean that a particular feature, structure, characteristic, or function described in connection with the embodiment is included in at least one embodiment of the present disclosure and may be present in two or more embodiments. The appearances of the phrases "in one embodiment," "in an embodiment," or "in embodiments" in various places in this specification are not necessarily all referring to the same embodiment or embodiments. The terms "include," "including," "comprise," and "comprising" are to be understood as open terms, meaning that the lists that follow are examples and are not meant to be limiting to the items listed. The headings used herein are for organizational purposes only and are not to be used to limit the scope of the description or claims. Further, the use of specific terms in various places in this specification is for illustrative purposes only and is not to be construed as limiting.

[0037] Overview

[0071] A multi-layer microfabricated ultrasonic transducer (MUT) is disclosed. The multi-layer MUT can include a number of alternating piezoelectric layers and electrodes (thus, a multi-layer pMUT) stacked on top of each other in such a way that the piezoelectric layers are "sandwiched" between sets of electrodes. Thus, a given electrode that is neither the top nor the bottom layer is shared by two piezoelectric layers and can be disposed on top of the first piezoelectric layer and under the second piezoelectric layer.

[0038]

[0072] The specific MUT device disclosed herein is a two-layer device that includes two piezoelectric layers and three conductive layers or electrodes, but MUT devices with additional layers may be designed. As the number of layers increases, the performance of the device can improve. However, if the number of layers is too large, the capacitance within the device may increase. As a result, the rise time of the signal input may slow down, which can degrade performance. Generally, a MUT device with M piezoelectric layers can have N conductive layers, where N is equal to M + 1.

[0039]

[0073] A piezoelectric transducer can transmit sound waves into a medium, receive sound waves from the medium, and convert the received waves into an electrical signal. A piezoelectric material accumulates electric charges when mechanically stressed. Piezoelectric materials also exhibit the inverse piezoelectric effect. When an electric field is applied to a piezoelectric material, the applied electric field causes mechanical strain. Thus, when a piezoelectric transducer is driven in the transmit (Tx) mode by applying an alternating current (AC) voltage, the oscillating voltage vibrates the piezoelectric layer, creating a sound wave. This wave resonates within the substrate layer disposed under the piezoelectric layer and can increase the output power of the sound wave before transmission. In the receive (Rx) mode, the reflected sound wave causes mechanical stress in the piezoelectric layer, accumulating electric charges in the piezoelectric layer. The accumulated charges generate an electrical signal, which can be read by an imaging device.

[0040]

[0074] By enhancing the MUT transducer with an additional piezoelectric layer, more vibrations can be created when stress is applied by an AC voltage, thereby increasing the power of the generated sound wave and accumulating more charges in response to the stress from the received sound wave. Thus, such a device can be more powerful and sensitive than a single-layer device.

[0041]

[0075] Thus, a device with multiple piezoelectric layers can generate sound waves with greater output power. When a voltage is applied to a multi-layer pMUT, more vibrations are created, so more powerful sound waves can be produced. Conversely, an incident wave can apply stress to multiple piezoelectric layers and generate a larger signal.

[0042]

[0076] In addition to the implementation of the additional piezoelectric layer, the disclosed MUT device can use convex or concave electrodes shaped to exhibit desirable pressure amplitudes and frequency responses when driven at the fundamental frequency and harmonics.

[0043]

[0077] The present disclosure defines the MUT aspect ratio, which is an engineering parameter that can provide information on the improvement of performance at high frequencies. The aspect ratio can be calculated by dividing the length of the long side of the electrode by twice the intrinsic half-width of the electrode (the width of the short side at the midpoint of the electrode). Thus, for electrodes of the same size, convex electrodes can have a smaller aspect ratio than concave electrodes.

[0044]

[0078] The present disclosure suggests that a multi-layer MUT with a specific aspect ratio can exhibit an increase in sound wave power and thus better performance at high frequencies. The multi-layer concave pMUT disclosed herein with an aspect ratio larger than that of another concave pMUT has been shown to have better performance at high frequencies. This result is consistent with the general relationship between the increase in R / L in concave pMUTs and the improvement of high-frequency performance.

[0045] Multi-layer MUT device

[0079] A micromachined ultrasonic transducer (MUT) that can be a piezoelectric MUT (pMUT device) is disclosed herein.

[0046]

[0080] The MUT device can include at least two piezoelectric layers. In some embodiments, the MUT device can include at least three layers, at least four layers, at least five layers, at least six layers, at least ten layers. The MUT device can include up to three layers, or up to four layers, or up to five layers, or up to six layers, or up to ten layers. The MUT device can include between three and six layers, or between four and seven layers, or between five and eight layers, or between six and nine layers, or between seven and ten layers. The piezoelectric layers can have a uniform thickness. The piezoelectric layers can have a non-uniform thickness. All of the piezoelectric layers can have different thicknesses. A subset of the piezoelectric layers can have the same thickness, but can have a different thickness from other subsets.

[0047]

[0081] The piezoelectric layer can be disposed between two electrodes, i.e., between an upper second electrode and a lower first electrode. Each piezoelectric layer of the device can be disposed between two electrodes in this way. Thus, the device can include one more electrode than the piezoelectric layers present, since the layers can share electrodes. In some embodiments, the MUT device can include at least three electrodes, at least four electrodes, at least five electrodes, at least six electrodes, at least ten electrodes. The MUT device can include up to three electrodes, or up to four electrodes, or up to five electrodes, or up to six electrodes, or up to ten electrodes. The MUT device can include between three and six electrodes, or between four and seven electrodes, or between five and eight electrodes, or between six and nine electrodes, or between seven and ten electrodes, or between eight and eleven electrodes.

[0048]

[0082] In some embodiments, at least the first electrode has a first end and a second end along a first axis. In some embodiments, all of the electrodes have a first end and a second end along a first axis. In other embodiments, less than half of the electrodes have a first end and a second end along a first axis. In other embodiments, more than half but less than all of the electrodes have a first end and a second end along a first axis.

[0049]

[0083] One or more of the first ends of the one or more electrodes or one or more of the second ends of the one or more electrodes may be defined by a radius of curvature R. The first end and the second end may be shaped like a part of a circle. The first end and the second end may or may not have the same radius of curvature R. The first end, and / or the second end may additionally be shaped like a part of an ellipse, triangle, square, or rectangle, provided that sharp edges that may degrade the performance of the MUT are not used. The first end and / or the second end may be shaped differently. All of the electrodes may have the same shape. The electrodes of a multi-electrode MUT may include some of the same shape and some of different shapes. Some or all of the electrodes may each have a different shape.

[0050]

[0084] The first axis and the second axis may be perpendicular or normal to each other. The second axis may pass through the midpoint of the first axis, and / or vice versa.

[0051]

[0085] The multi-layer MUT can include electrodes having a specific shape to improve performance. The MUT electrodes can be substantially oval or rectangular with long and short sides. The width of the electrode may vary along an axis bisecting the long side of the electrode. For example, near the midpoint, the electrode can be thinner than the long ends and create a concave shape. In other embodiments, the electrode can be thicker at the center than the long ends and create a convex shape.

[0052]

[0086] The half-width of the electrode can be defined by the length L measured from the midpoint to the outer periphery of the electrode in the direction of the second (or short) axis. All of the electrodes can have the same L. One set of electrodes can have the same L, while other electrodes can have different values for L. Additionally, some or all of the electrodes may have multiple different values for L.

[0053]

[0087] In some embodiments, the overall width of the electrode at the narrowest point along the first axis is less than 2L such that the electrode has a concave shape. This electrode can be one of the first, second, third, fourth, fifth, sixth, seventh, eighth, ninth, tenth, or eleventh electrodes. This electrode can be more than one of the first, second, third, fourth, fifth, sixth, seventh, eighth, ninth, tenth, or eleventh electrodes, but less than all. All of the electrodes may have the same concave shape, and the overall width at the narrowest point along the first axis is less than 2L.

[0054]

[0088] In some embodiments, the overall width of the electrode at the widest point along the first axis is at least twice L such that the electrode has a convex shape. This electrode can be one of the first, second, third, fourth, fifth, sixth, seventh, eighth, ninth, tenth, or eleventh electrodes. This electrode can be more than one of the first, second, third, fourth, fifth, sixth, seventh, eighth, ninth, tenth, or eleventh electrodes, but less than all. All of the electrodes may have the same convex shape, and the overall width at the widest point along the first axis is greater than twice L. In some embodiments, all of the electrodes can be symmetric. In some embodiments, one or more electrodes can be asymmetric with respect to the first axis and / or the second axis.

[0055]

[0089] In an embodiment where the electrode has a convex shape, the ratio of R to L can be less than 1. For example, this ratio can be less than 0.01, less than 0.1, less than 0.2, less than 0.3, less than 0.4, less than 0.5, less than 0.6, less than 0.7, less than 0.8, less than 0.9, less than 0.99, or less than 0.999. For example, this ratio can be greater than about 0.01, greater than 0.1, greater than 0.2, greater than 0.3, greater than 0.4, greater than 0.5, greater than 0.6, greater than 0.7, greater than 0.8, greater than 0.9, greater than 0.99, or greater than 0.999. This ratio can be between 0 and 0.1, between 0.1 and 0.2, between 0.2 and 0.3, between 0.3 and 0.4, between 0.4 and 0.5, between 0.5 and 0.6, between 0.6 and 0.7, between 0.7 and 0.8, between 0.8 and 0.9, and between 0.9 and 1.

[0056]

[0090] In an embodiment where the electrode has a concave shape, the ratio of R to L can be greater than 1. For example, this ratio can be less than 1.01, less than 1.1, less than 1.2, less than 1.3, less than 1.4, less than 1.5, less than 2, less than 5, less than 10, less than 25, less than 50, or less than 100. For example, this ratio can be greater than about 1.01, greater than 1.1, greater than 1.2, greater than 1.3, greater than 1.4, greater than 1.5, greater than 2, greater than 5, greater than 10, greater than 25, greater than 50, or greater than 100. This ratio can be between 1.0 and 1.1, between 1.1 and 1.2, between 1 and 2, between 2 and 5, between 5 and 10, between 10 and 25, between 25 and 50, or between 50 and 100.

[0057]

[0091] In some embodiments, the MUT further includes a substrate and a membrane spanned from the substrate. The substrate can include a semiconductor material or can include a number of alternating layers of semiconductor material and insulating material. For example, the substrate can include a silicon layer. The substrate can further include an alternating layer of silicon and silicon dioxide (i.e., a silicon-on-insulator (SOI) substrate). In other embodiments, the substrate can include a semiconductor material such as germanium, silicon germanium, carbon-doped silicon, carbon-doped silicon germanium, or another material. In some embodiments, the substrate can include a cavity disposed under the alternating piezoelectric layers and electrodes of the MUT.

[0058]

[0092] In some embodiments, the membrane can be a silicon layer configured to assist in the transmission and reception of sound waves. The membrane can vibrate in response to the movement from the piezoelectric element after an AC voltage is applied to the piezoelectric element, and as a result, can generate sound waves transmitted to the subject. When the sound waves are reflected, the sound waves disturb the membrane, and as a result, stress can be applied to the piezoelectric layer, causing the piezoelectric layer to generate an electrical signal. These electrical signals can be provided to an imaging device.

[0059]

[0093] In embodiments of the present disclosure, the first axis extends along the longest dimension of the electrode. In embodiments of the present disclosure, the second axis extends along the shortest dimension of the electrode.

[0094] In embodiments of the present disclosure, at least one piezoelectric layer can be formed from at least one of PZT, KNN, PZT-N, PMN-Pt, AIN, Sc-AIN, ZnO, PVDF, and LiNiO3. In some embodiments, all of the piezoelectric materials are formed from the same material. In some embodiments, at least one piezoelectric layer is a composite of one of the above materials. In some of the embodiments, the first plurality of piezoelectric layers may be formed from one material, and the second plurality of piezoelectric layers may be formed from another material. In some embodiments, all piezoelectric layers are heterogeneous. In some embodiments, the first plurality of piezoelectric layers are homogeneous and the second plurality of piezoelectric layers are heterogeneous.

[0060]

[0095] In embodiments of the present disclosure, the MUT device can have M piezoelectric layers. The MUT device can have N electrodes. Since the piezoelectric layer can be "sandwiched" between two electrodes, the number N can be made equal to M + 1. Generally, in an M-piezoelectric layer MUT device, the piezoelectric layers can be indexed from 1 to M, where 1 is the layer closest to the substrate and M is the layer farthest from the substrate. For piezoelectric layer m in this set, the adjacent electrodes can be indexed as m and m + 1, respectively, with respect to the electrode closer to the substrate and the electrode farther from the substrate. For example, the second piezoelectric layer can be given an index of 2, and the electrode below the second piezoelectric layer and the electrode above the second piezoelectric layer can be indexed as 2 and 3, respectively.

[0061] Description of the drawings

[0096] Figure 1 shows a schematic diagram of an imaging system 100 according to an embodiment of the present disclosure. As shown in the figure, in the transmission mode / process, the system 100 includes an imager 120 that generates a pressure wave 122, transmits it toward an internal organ 112 such as the heart, and receives the pressure wave reflected from the internal organ, and a device 102 that transmits and receives signals with the imager through a communication channel 130. In an embodiment, the internal organ 112 can reflect a part of the pressure wave 122 toward the imager 120, and the imager 120 can capture the reflected pressure wave and generate an electrical signal in the reception mode / process. The imager 120 can communicate the electrical signal to the device 102, and the device 102 can use the electrical signal to display an image of the organ or target on a display / screen 104.

[0062]

[0097] In an embodiment, the imager 120 can also be used to obtain an image of an animal's internal organ. The imager 120 can also determine the direction and speed of blood flow in arteries and veins, as in Doppler mode imaging, and can further be used to measure the hardness of tissue. In an embodiment, the pressure wave 122 can be a sound wave that travels through a human / animal body and can be reflected by internal organs, tissues, or arteries and veins.

[0063]

[0098] In an embodiment, the imager 120 can be a portable device and can communicate signals with the device 102 wirelessly (using a protocol such as the 802.11 protocol) or via a cable (such as USB2, USB3, USB3.1, USB-C, and USB Thunderbolt) through the communication channel 130. In an embodiment, the device 102 can be a mobile device such as a cell phone or iPad (registered trademark), or a stationary computing device that can display an image to the user.

[0064]

[0099] In an embodiment, two or more imagers may be used to create an image of a target organ. For example, a first imager may send a pressure wave towards the target organ, while a second imager may receive the pressure wave reflected from the target organ and create an electric charge in response to the received wave.

[0065]

[0100] FIG. 2 shows a schematic diagram of imager 120 according to an embodiment of the present disclosure. In an embodiment, imager 120 can be an ultrasonic imager. As shown in FIG. 2, imager 120 includes a transceiver tile 210 for transmitting and receiving pressure waves, a lens that operates as a lens for setting the propagation direction of the pressure wave and / or focusing the pressure wave, and also functions as an acoustic impedance interface between the transceiver tile and the human body 110. A coating layer 212, a control unit 202 such as an ASIC chip (or simply ASIC) coupled to the transducer tile 210 by bumps for controlling the transceiver tile 210, a field programmable gate array (FPGA) 214 for controlling the components of imager 120, a circuit 215 such as an analog front end (AFE) for processing / conditioning signals, an acoustic absorber layer 203 for absorbing waves generated by the transducer tile 210 and propagating towards the circuit 215, a communication unit 208 for communicating data with an external device such as device 102 through one or more ports 216, a memory 218 for storing data, a battery 206 for supplying power to the components of the imager, and optionally, a display 217 for displaying an image of the target organ.

[0066]

[0101] In an embodiment, device 102 can have a display / screen. In such a case, the display may not be included in imager 120. In an embodiment, imager 120 can receive power from device 102 through one of ports 216. In such a case, imager 120 may not include battery 206. It should be noted that one or more of the components of imager 120 may be combined into one integrated electrical element. Similarly, each component of imager 120 may be implemented in one or more electrical elements.

[0067]

[0102] In an embodiment, the user can apply a gel to the skin of human body 110 such that impedance matching at the interface between coating layer 212 and human body 110 can be improved before human body 110 comes into direct contact with coating layer 212, that is, the loss of pressure wave 122 at the interface is reduced and the loss of the reflected wave moving towards imager 120 is also reduced at the interface. In an embodiment, transceiver tile 210 can be mounted on a substrate and can be attached to an acoustic absorber layer. This layer absorbs the ultrasonic signals emitted in the reverse direction, which otherwise may be reflected and interfere with the image quality.

[0068]

[0103] As discussed below, coating layer 212 may simply be a flat matching layer to merely maximize the transmission of acoustic signals from the transducer to the body and vice versa. Beam focusing is not required in this case as it can be electronically implemented in control unit 202. Imager 120 can use the reflected signals to create an image of organ 112, and the results can be displayed on the screen in various formats such as graphs, plots, and statistical data, with or without an image of organ 112 being shown.

[0069]

[0104] In an embodiment, the control unit 202, e.g., an ASIC or the like, may be assembled as one unit together with the transceiver tile. In other embodiments, the control unit 202 may be disposed outside the imager 120 and electrically coupled to the transceiver tile 210 via a cable. In an embodiment, the imager 120 may include a housing that encloses the components 202-215 and a heat dissipation mechanism for dissipating the thermal energy generated by the components.

[0070]

[0105] FIG. 3A shows a side view of a transceiver array 200 according to an embodiment of the present disclosure. FIG. 3B shows a top view of a transceiver tile 210 according to an embodiment of the present disclosure. In an embodiment, the array 200 may include one or more transceiver tiles 210. As shown, the transceiver array 200 may include one or more transceiver tiles 210 arranged in a predetermined manner. For example, as shown in FIG. 3A, the transceiver tile (or simply tile) 210 may be physically bent to further form a curved transceiver array and disposed on the imager 120. The imager 120 may include any suitable number of tiles, the tiles may be arranged in any suitable manner, and it should be apparent to those skilled in the art that each tile 210 may include any suitable number of piezoelectric elements 302 having a concave or convex shape as described in more detail herein and disposed on a transceiver substrate 304. One or a plurality of temperature sensors 320 may be disposed on the substrate 304 to monitor the temperature of the operating transceiver tile 210. In an embodiment, the transceiver array 200 may be a micromachined array fabricated from a substrate.

[0071]

[0106] FIG. 4A shows a cross-sectional view of the MUT400 according to an embodiment of the present disclosure. The cross-sectional view of FIG. 4A is applicable to a concave MUT or a convex MUT according to an embodiment of the present disclosure. As shown, the concave or convex MUT can include a membrane layer 406 spanned from a substrate 402, a first (e.g., lower) electrode (O) 408 disposed on the membrane layer (or simply the membrane) 406, a piezoelectric layer 410 disposed on the lower electrode (O) 408, and a second (e.g., upper) electrode (X) 412 disposed on the piezoelectric layer 410.

[0072]

[0107] In an embodiment, the substrate 402 and the membrane 406 can be a single integral structure body, and the cavity 404 can be formed to define the membrane 406. In an embodiment, the cavity 404 may be filled with a gas at a predetermined pressure or an acoustic damping material to control the vibration of the membrane 406. In an embodiment, the geometric shape of the projection area of the upper electrode 412 can be configured in a generally concave shape or a convex shape having inherent geometric parameters to control the dynamic performance and the capacitance magnitude of the MUT400.

[0073]

[0108] In an embodiment, each MUT400 can be a pMUT and can include a piezoelectric layer formed from at least one of PZT, KNN, PZT-N, PMN-Pt, AIN, Si-AIN, ZnO, PVDF, and LiNiO3. In an alternative embodiment, each MUT400 can be a cMUT.

[0074]

[0109] In an embodiment, each MUT400 can include additional electrodes and / or PZE layers. For example, as shown in FIG. 4F, the MUT400 (whether concave, convex, or otherwise shaped as desired) can include a membrane layer 406 spanned from a substrate 402, a first electrode (O) 408 disposed on the membrane layer (or simply the membrane) 406, a first piezoelectric layer 410 disposed on the first electrode (O) 408, a second electrode 414 disposed on the first piezoelectric layer 410, a second piezoelectric layer 410 disposed on the second electrode 414, and a third electrode (X) 412 disposed on the second piezoelectric layer 410. Additional piezoelectric layers 410 and electrodes can be added as desired. In at least some cases, adding additional piezoelectric layers and / or electrodes (i.e., "sandwiching" electrodes and piezoelectric layers) increases the amplitude / dB output of the MUT400.

[0075]

[0110] In FIGS. 4B-4E and FIGS. 4G-4H, each MUT400 is shown as having either a concave or convex shape. In an embodiment, each concave MUT can include an upper electrode having a concave shape when viewed from the top surface of the MUT400. In an embodiment, each convex MUT can include an upper electrode having a convex shape when viewed from the top surface of the MUT400. Hereinafter, the term "shape of the upper electrode" refers to the two-dimensional shape of the upper electrode obtained by projecting the upper electrode onto the xy plane. Further, the shape of the upper electrode is called symmetric when the shape is symmetric with respect to two lines 450 and 452, and the lines 450 and 452 are parallel to the x-axis and y-axis, respectively, and pass through the midpoint of the upper electrode on the x-axis. Further, hereinafter, the x-axis, also referred to as the major axis in this specification, extends along the direction in which the upper electrode has the longest dimension. The y-axis, also referred to as the minor axis in this specification, extends along the direction in which the upper electrode has the shortest dimension in a direction perpendicular to the x-axis or the major axis in the xy plane.

[0076]

[0111] For the concave MUTs of FIGS. 4B - 4C and FIGS. 4G - 4H, and for the convex MUTs of FIGS. 4D - 4E, the shape of the upper electrode is defined by a major axis and a minor axis, which intersect at the origin. Both distal ends of the upper electrode, i.e., the ends of the upper electrode that are farthest from the origin in the direction of the major axis, are also referred to herein as the "head" of the electrode and are defined by a radius of curvature R. The intrinsic half-width of the upper electrode, also referred to herein as the "foot" of the electrode, is defined by a length L measured from the origin, in the direction of the minor axis (i.e., perpendicular to the major axis), to the outer edge or outer perimeter of the electrode. The overall width of the electrode at either the narrowest point (in the case of a concave MUT) or the widest point (in the case of a convex MUT) is twice L (i.e., 2L). The edge of the electrode between the head and the foot can be curved or straight.

[0077]

[0112] Alternatively, the head of the electrode may be straight or defined by some other curvature shape that is not perfectly circular. In at least some instances, it may be beneficial to avoid heads or other shapes that create local regions of concentrated mechanical stress that can enable local mechanical or material failure modes, such as those that might be created when the head (or for example the foot) is defined by two straight lines that converge at a sharp point.

[0078]

[0113] In some embodiments, the head need not be circular, but may further be defined by a non-circular curvature, such as a parabolic curvature, without limitation. A circular electrode head can be defined by a radius of curvature R, but the relevant parameter for a parabolic head can be the semi-latus rectum of the parabola, defined as twice the distance between the focus and the vertex of the parabola. Further, the perimeter between the head and the foot may be defined by either a straight line or a curvature and still be within the scope of the present invention.

[0079]

[0114] As shown in FIGS. 4B - 4C and FIGS. 4G - 4H, when the ratio R / L of the radius of curvature to the intrinsic width is greater than 1, the upper electrode is wider at the ends or the head compared to the width of the central or foot portions, and the electrode generally has a concave shape. As will be understood by those skilled in the art, as long as R / L is greater than 1, i.e., R > L, by changing the R / L ratio, this deformation of the concave MUT shape is possible and still within the scope of the present disclosure. For example, for an upper electrode having a head radius of curvature R of 43 micrometers, an appropriate foot width L of about 37 - 41 micrometers is within the scope of the present disclosure and exhibits improved pressure amplitude and frequency response behavior when driven at the fundamental and harmonic frequencies, as further described herein. On the other hand, if R / L is too large, such that the head radius or curvature R is much larger than the foot width L, the upper electrode may not exhibit the desired pressure amplitude and frequency response behavior when driven at the fundamental and harmonic frequencies and may even experience structural failures.

[0080]

[0115] As shown in FIGS. 4D - 4E, when the ratio R / L of the radius of curvature to the intrinsic width is less than 1, the upper electrode is narrower at the ends compared to the width of the central portion, and the electrode generally has a convex shape. As will be understood by those skilled in the art, as long as R / L is less than 1, i.e., R < L, by changing the R / L ratio, this deformation of the convex MUT shape is possible and still within the scope of the present disclosure. For example, for an upper electrode having a head radius of curvature R of 43 micrometers, an appropriate foot width L of about 43.1 - 500 micrometers is within the scope of the present disclosure and exhibits improved pressure amplitude and frequency response behavior when driven at the fundamental and harmonic frequencies, as further described herein. On the other hand, if R / L is too small, such that the head radius or curvature R is much smaller than the foot width L, the upper electrode is adversely affected by undesired pressure amplitude and frequency response behavior when driven at the fundamental and harmonic frequencies and may even experience structural failures.

[0081]

[0116] Regardless of whether it is configured in a concave or convex shape, electrodes with a specific R / L value or electrodes within a specific R / L value range exhibit desirable pressure amplitude and frequency response behavior when driven at the fundamental frequency and harmonic frequencies. The surface density distribution of concave or convex electrodes along the axis has multiple maxima, and the locations of the multiple maxima coincide with the locations where multiple antinodes at the vibration resonance frequencies are positioned. Generally, the sound pressure performance, which refers to the energy of the sound pressure wave generated by each MUT at a certain frequency, can increase as the peak amplitude of the MUT increases at that frequency.

[0082]

[0117] This ratio or R / L can be determined by the desired behavior of the MUT. Changing the R / L parameter of the electrode (and thus the shape of the electrode) changes the pressure amplitude and frequency response behavior of the electrode. The R / L can be as large or as small as desired, as long as the electrode exhibits the desired pressure amplitude and / or frequency response behavior. The design requirements of a specific transducer, which can be defined by factors such as the transducer's end-use case (e.g., industrial, medical diagnostic, etc.), power requirements, operating mode requirements, etc., indicate whether the pressure amplitude and frequency response exhibited by a specific R / L shape are acceptable or desirable. Additional considerations such as manufacturing and material performance may further limit the acceptable R / L range to a desirable or available range.

[0083]

[0118] Figure 4G shows a cross-sectional view of a MUT having a number of piezoelectric layers. This cross-sectional view shows the electrode that is furthest from the substrate of the MUT device (e.g., at the maximum vertical distance or z-distance). When viewed from above (e.g., above the MUT, where the MUT is in the negative z-direction from the observer), the topmost MUT electrode has a concave shape. In this embodiment, the layers of electrodes below the top electrode are hidden from view, but all of the electrodes can have the same shape. In this embodiment, at least the top electrode is symmetric with respect to the x-axis and y-axis. In other embodiments, the electrodes disposed below the top electrode may have different sizes. In other embodiments, the electrodes disposed below the top electrode may have different shapes.

[0084]

[0119] To evaluate whether electrode design can result in performance improvement at high frequencies, the present disclosure defines an electrode aspect ratio. The aspect ratio parameter is related to the ratio R / L and is defined as the ratio of the length of the electrode (from the tip of the upper head to the base of the lower head) to twice the intrinsic half-width (or twice L). For the embodiments disclosed herein, the concave embodiment of FIG. 4G has an aspect ratio of 7, the convex embodiment of FIG. 4D has an aspect ratio of 3, and the concave embodiment of FIG. 4B has an aspect ratio of 5. Generally, a larger aspect ratio may correlate with improved performance at high frequencies.

[0085]

[0120] If the electrode has an intrinsic half-width L equal to its radius, the electrode can be stadia-shaped rather than convex or concave. For a given length of electrode, it will have a higher aspect ratio as a concave electrode, an intermediate aspect ratio as a stadia-shaped electrode, and a lower aspect ratio as a convex electrode. The use of aspect ratio suggests that a longer convex electrode or set of electrodes may be able to achieve similar performance as a shorter concave electrode. Conversely, a smaller concave electrode may be used in place of a larger convex electrode.

[0086]

[0121] FIG. 4H shows a sub-section of the cross-section of FIG. 4G with the radius R and the intrinsic half-width shown visible. As in FIG. 4C, the value of R is larger than the value of L.

[0122] Figures 5A - 5B show exemplary idealized plots 500 and 510 of the acoustic responses of a MUT having a concave configuration and a MUT having a convex configuration, according to embodiments of the present disclosure. Figure 5A shows an idealized plot 500 of how acoustic power varies with frequency for a concave MUT 504 (e.g., R / L > 1) compared to a MUT 502 with R / L = 1. Figure 5B shows an idealized plot 510 of how acoustic power varies with frequency for a convex MUT 514 (e.g., R / L < 1) compared to a MUT 512 with R / L = 1. In the concave MUT 504, as indicated by arrow 506, as R / L increases, the power - frequency curve shifts to the right compared to MUT 502. In the convex MUT 514, as indicated by arrow 516, as R / L decreases, the power - frequency curve shifts upward compared to MUT 512.

[0087]

[0123] Further modifications to the concave or convex MUT shape, including changing the thickness of the membrane (e.g., a silicon membrane), or adding single or double notches around the membrane (such that the membrane behaves more like a pinned beam or spring rather than a cantilever beam), can provide further improved performance characteristics. Examples of such modifications can be found in U.S. Patent Application Nos. 17 / 018,304 and 15 / 820,319, which are incorporated herein by reference.

[0088]

[0124] Figures 6A - 6C show three vibration modes 600, 610, and 620 according to an embodiment of the present disclosure. In Figures 6A - 6C, each of MUTs 602, 612, and 622 is represented by a single line for illustrative purposes, whether concave or convex, and each single line indicates the curvature of the stack of layers in the MUT. During operation, the stack of layers having the membrane 406, the lower electrode 408, the piezoelectric layer 410, and the upper electrode 412 can move vertically as a single body and be deformed to have the curvature of a single line on the xz plane. Further, the lines 602, 612, and 622 corresponding to different vibration modes indicate the curvature of the stack in different vibration modes. Generally, the resonance characteristics of concave and convex MUTs are similar to each other, but the local gain may vary depending on whether the MUT is concave or convex. In some cases, the selection of a convex or concave shape can facilitate an improvement in the gain achieved at a specific frequency of interest.

[0089]

[0125] In an embodiment, the three vibration modes 600, 610, and 620 can be associated with three vibration resonance frequencies f1, f2, and f3, respectively. In Figures 6A - 6C, only three vibration modes are shown. However, it should be apparent to those skilled in the art that a concave or convex MUT can operate in four or more vibration resonance modes (or simply vibration modes).

[0090]

[0126] In Figure 6A, the concave or convex MUT 602 can operate in the first vibration mode 600, and the arrow 604 indicates that the MUT 602 (more specifically, the stack of layers) moves vertically in the first mode 600. In an embodiment, the first vibration mode 600 can be symmetric, i.e., the mode shape is symmetric with respect to the center line 606 of the MUT. In an embodiment, the shape of the upper electrode of the MUT 602 can be symmetric and can be either concave or convex as shown in Figures 4B - 4E.

[0091]

[0127] In FIG. 6B, MUT612 can operate in a second vibration mode 610. In an embodiment, the second vibration mode 610 can be symmetric, i.e., the mode shape is symmetric with respect to the center line 606. Hereinafter, the term symmetric vibration mode refers to a vibration mode in which the locations of antinodes (i.e., peak amplitudes) such as 615, 616, and 617 are arranged symmetrically with respect to the center line 606. The center line 606 is parallel to the z-axis and represents a line passing through the midpoint of the MUT on the x-axis.

[0092]

[0128] In the second vibration mode 610, MUT612 can have two nodes and three antinodes (or in other words, three peak amplitude points) 615, 616, and 617. In an embodiment, the shape of the upper electrode of MUT612 can be symmetric, as shown in FIGS. 4B to 4E, and can be either concave or convex.

[0093]

[0129] In FIG. 6C, MUT622 can operate in a third vibration mode 620. In an embodiment, the third vibration mode 620 can be symmetric, i.e., the mode shape is symmetric with respect to the center line 606. In the third vibration mode, MUT622 can have four nodes and five antinodes (i.e., five peak amplitude points) 624, 625, 626, 627, and 628. In an embodiment, the shape of the upper electrode of MUT622 can be symmetric, as shown in FIGS. 4B to 4E, and can be either concave or convex.

[0094]

[0130] Generally, the sound pressure performance, which refers to the energy of the sound pressure wave generated by each MUT at a certain frequency, can increase as the peak amplitude of the MUT increases at that frequency. However, compared with a convex MUT of the same or similar total area, a concave MUT has a larger local area distribution (i.e., R>L) at the distal end compared to the central part. As a result, compared with a convex MUT of the same or similar area, a concave MUT can output a higher sound pressure amplitude, especially at harmonic frequencies.

[0095]

[0131] It should be noted that each of the MUT302s in FIG. 3 can be a piezoelectric microfabricated ultrasonic transducer (pMUT). However, it should be apparent to those skilled in the art that the transceiver tile 210 can include an array of capacitive microfabricated ultrasonic transducers (cMUTs), that is, the piezoelectric element 302 may be replaced with a cMUT. In such a case, the top electrode of the CMUT can have a shape similar to one of the shapes of the top electrode 412, and as a result, the acoustic response of the cMUT is controlled at various vibration resonance frequencies based on the principles described in relation to FIGS. 4B to 6C.

[0096]

[0132] FIG. 7A shows a plot of the frequency response 710 of a two-layer pMUT compared to the frequency response 720 of a single-layer pMUT device. At high frequencies (between about 5 megahertz (MHz) and 10 megahertz (MHz)), the two-layer pMUT produces sound waves with greater acoustic power (in dB) than a single piezoelectric layer pMUT.

[0097]

[0133] FIG. 7B shows a plot of the frequency response 740 of a two-layer pMUT having a concave-shaped electrode compared to the frequency response 750 of a two-layer pMUT having a convex-shaped electrode. As can be seen from the plot, the pMUT with the concave electrode has better performance than the pMUT with the convex electrode and generates sound waves with more power in the target high-frequency region 760 between 6 MHz and 8 MHz.

[0098]

[0134] FIG. 7C shows a plot of the frequency response 770 of a two-layer pMUT having a convex-shaped electrode compared to the frequency response 760 of a two-layer pMUT having a convex-shaped electrode. As can be seen from the plot, the two-layer pMUT is superior in performance to the single-layer pMUT at most operating frequencies. Although the present invention is capable of accepting various modifications and alternative forms, specific examples thereof are shown in the drawings and are described in detail herein. However, it should be understood that the present invention should not be limited to the specific forms disclosed, but on the contrary, the present invention can include all modifications, equivalents, and alternatives falling within the scope of the appended claims.

Claims

1. A microfabricated ultrasonic transducer (MUT), comprising: at least a first piezoelectric layer and a second piezoelectric layer, wherein the first piezoelectric layer is disposed between a first electrode and a second electrode, and the second piezoelectric layer is disposed between the second electrode and a third electrode; comprising at least the first electrode having a first end and a second end along a first axis, i. one or more of the first end or the second end being defined by a radius of curvature R; ii. a second axis passing through a midpoint of the first axis and the second axis being perpendicular to the first axis; iii. the half-value width of the first electrode being defined by a length L measured from the midpoint in the direction of the second axis to the outer periphery of the first electrode; iv. the total width of the first electrode at the narrowest point along the first axis being at most 2L such that the first electrode has a concave shape; v. R / L being greater than 1; a microfabricated ultrasonic transducer (MUT).

2. The microfabricated ultrasonic transducer (MUT) according to claim 1, wherein the first axis extends along a direction in which the first electrode has the longest dimension.

3. The microfabricated ultrasonic transducer (MUT) according to claim 1 or 2, wherein the second axis extends along a direction in which the first electrode has the shortest dimension.

4. a substrate; a membrane spanned from the substrate; The microfabricated ultrasonic transducer (MUT) according to any one of claims 1 to 3, further comprising.

5. The piezoelectric layer is formed from at least one of PZT, KNN, PZT-N, PMN-Pt, AlN, Sc-AlN, ZnO, PVDF, and LiNiO ３ The microfabricated ultrasonic transducer (MUT) according to any one of claims 1 to 4, which is formed from at least one of the above

6. A microfabricated ultrasonic transducer (MUT), comprising: a plurality of piezoelectric layers including M piezoelectric layers; a plurality of electrodes including N electrodes; comprising a piezoelectric layer having an index m among the plurality of piezoelectric layers being disposed between a first electrode having the index m and a second electrode having the index m + 1, and the index m being associated with a vertical distance of the piezoelectric layer; at least the first electrode having a first end and a second end along a first axis, i. one or more of the first end or the second end being defined by a radius of curvature R; ii. a second axis passing through a midpoint of the first axis and the second axis being perpendicular to the first axis; iii. The half-value width of the first electrode is defined by a length L measured from the intermediate point to the outer periphery of the first electrode in the direction of the second axis. iv. The overall width of the first electrode at the narrowest point along the first axis is at most 2L such that the first electrode has a concave shape. v. R / L is greater than 1. Microfabricated ultrasonic transducer (MUT). **Claim 7** The microfabricated ultrasonic transducer (MUT) according to claim 6, wherein the first axis extends along the direction in which the first electrode has the longest dimension. **Claim 8** The microfabricated ultrasonic transducer (MUT) according to claim 6 or 7, wherein the second axis extends along the direction in which the first electrode has the shortest dimension. **Claim 9** A substrate, and a membrane spanned from the substrate. The microfabricated ultrasonic transducer (MUT) according to any one of claims 6 to 8, further comprising. **Claim 10** The piezoelectric layer is formed from at least one of PZT, KNN, PZT-N, PMN-Pt, AlN, Sc-AlN, ZnO, PVDF, and LiNiO ３ The microfabricated ultrasonic transducer (MUT) according to any one of claims 6 to 9, which is formed from at least one of these materials. **Claim 11** N = M + 1, the microfabricated ultrasonic transducer (MUT) according to any one of claims 6 to 10. **Claim 12** A microfabricated ultrasonic transducer (MUT), comprising at least a first piezoelectric layer and a second piezoelectric layer, the first piezoelectric layer being disposed between a first electrode and a second electrode, and the second piezoelectric layer being disposed between the second electrode and a third electrode. including when viewed from above, the first electrode has a first end and a second end along a longitudinal axis, has a transverse axis passing through the midpoint of the longitudinal axis and extending perpendicular to the longitudinal axis, the first end and the second end each have a semi-circular shape with a constant radius of curvature R, the first electrode is symmetric about both the longitudinal axis and the transverse axis, and has an outer periphery with a longitudinal edge that curves around the midpoint such that the shape has the widest width at the longitudinal position of the midpoint, the half-value width of the first electrode is defined by a length L from the midpoint along the transverse axis to the outer periphery of the first electrode, the widest transverse width is greater than 2R, and the longitudinal edges of the first electrode are curved convexly outward, R / L is less than 1. Microfabricated ultrasonic transducer (MUT). **Claim 13** The fine processing ultrasonic transducer (MUT) according to claim 12, wherein the longitudinal axis extends along the direction in which the first electrode has the longest dimension.

14. The fine processing ultrasonic transducer (MUT) according to claim 12 or 13, wherein the transverse axis extends along the direction in which the first electrode has the shortest dimension.

15. A fine processing ultrasonic transducer (MUT), including a plurality of piezoelectric layers including M piezoelectric layers, and a plurality of electrodes including N electrodes, wherein the piezoelectric layer having index m among the plurality of piezoelectric layers is disposed between a first electrode having index m and a second electrode having index m + 1, and the index m is associated with the vertical distance of the piezoelectric layer, when viewed from above, the first electrode has a first end and a second end along the longitudinal axis, a transverse axis that passes through the midpoint of the first electrode and extends perpendicular to the longitudinal axis, the midpoint having a longitudinal position along the longitudinal axis, the first end and the second end each having a semi-circular shape with a constant radius of curvature R, the first electrode is symmetric about both the longitudinal axis and the transverse axis, and has an outer periphery with a longitudinal edge that curves around the midpoint so that the shape has the widest transverse width at the longitudinal position of the midpoint, the half-value width of the first electrode is defined by the length L from the midpoint along the transverse axis to the outer periphery of the first electrode, the widest transverse width is greater than 2R, and the longitudinal edges of the first electrode curve convexly outward, R / L is less than 1, a fine processing ultrasonic transducer (MUT).

Images