Ultrasound imaging device with row and column addressing

Abstract

The present specification relates to an ultrasound imaging device comprising a plurality of ultrasound transducers (101) arranged in rows and in columns, each transducer (101) comprising a lower electrode (E1) and an upper electrode (E2), wherein: * - in each row, any two adjacent transducers (101) of this row are respectively connected to each other with their lower electrode (E1) and with their upper electrode (E2), or with their upper electrode (E2) and with their lower electrode (E1); and * - in each column, any two adjacent transducers (101) of this column are respectively connected to each other with their lower electrode (E1) and with their upper electrode (E2), or with their upper electrode (E2) and with their lower electrode (E1).

Description

[0001] This patent application claims priority from French patent application FR20 / 05636, which is incorporated herein by reference. TECHNICAL FIELD

[0002] The present disclosure relates to the field of ultrasonic imaging and more specifically aims to provide a device comprising an array of ultrasonic transducers with row and column addressing. BACKGROUND

[0003] An ultrasonic imaging device generally comprises a plurality of ultrasonic transducers and electronic control circuitry connected to the transducers. In operation, the transducer assembly is placed in front of the body whose image is desired to be acquired. The electronic device is configured to apply electrical excitation signals to the transducers to cause them to emit ultrasonic waves toward the body or object to be analyzed. The ultrasonic waves emitted by the transducers are reflected by the body to be analyzed (through its internal and / or surface structure) and then return to the transducers which convert them back into electrical signals. The electrical response signals are read by the electronic control circuitry and can be stored and analyzed to infer information about the body under study from them.

[0004] In the case of a two-dimensional image acquisition device, the ultrasonic transducers can be arranged in a linear array or, in the case of a three-dimensional image acquisition device, in an array. In the case of a two-dimensional image acquisition device, the acquired image represents a cross-section of the body under study in a plane defined on the one hand by the alignment axis of the transducers of the linear array and on the other hand by the direction of emission of the transducers. In the case of a three-dimensional image acquisition device, the acquired image represents a volume defined by the two alignment directions of the transducers of the array and by the direction of emission of the transducers.

[0005] In three-dimensional image acquisition devices, a distinction can be made between devices referred to as "fully populated", in which each transducer of the array is individually addressable, and devices referred to as row-column addressing or RCA, in which the transducers of the array are addressable by row and by column.

[0006] Fully populated devices offer greater flexibility in terms of ultrasonic beam shaping in transmission and reception modes. However, the control electronics of the array are complex, in the case of an array of M rows by N columns, the number of transmission / reception channels required is equal to M*N. In addition, the signal-to-noise ratio is generally relatively low because the surface area exposed to ultrasonic waves is small for each transducer.

[0007] RCA-type devices use algorithms to shape different ultrasonic beams. The beam shaping possibilities can be reduced relative to fully populated devices. However, the control electronics of the array are greatly simplified, in the case of an array of M rows and N columns, the number of transmission / reception channels required is reduced to M+N. In addition, the signal-to-noise ratio is improved thanks to the interconnection of the transducers in a row or a column during the transmission and reception phases.

[0008] Three-dimensional image acquisition devices with row-column addressing (RCA) are considered here in more detail. SUMMARY

[0009] It is an object of one embodiment to provide a three-dimensional ultrasound image acquisition device with row-column addressing that overcomes all or part of the drawbacks of known devices.

[0010] To this end, one embodiment provides an ultrasound imaging device comprising a plurality of ultrasound transducers arranged in rows and in columns, each transducer comprising a lower electrode and an upper electrode, wherein:

[0011] - in each row, any two adjacent transducers of the row have their lower electrodes and their upper electrodes connected to each other, respectively, or have their upper electrodes and their lower electrodes connected to each other, respectively; and

[0012] - in each column, any two adjacent transducers of the column have their lower electrodes and their upper electrodes connected to each other, respectively, or have their upper electrodes and their lower electrodes connected to each other, respectively.

[0013] According to one embodiment:

[0014] - in each row, any two adjacent transducers of the row have their respective lower electrodes electrically insulated from each other and have their respective upper electrodes electrically insulated from each other; and

[0015] - in each column, any two adjacent transducers of the column have their respective lower electrodes electrically insulated from each other and have their respective upper electrodes electrically insulated from each other.

[0016] According to one embodiment, each ultrasound transducer is a CMUT transducer comprising a flexible membrane suspended above a cavity, the lower electrode of the transducer being arranged on a side of the cavity opposite the flexible membrane, and the upper electrode of the transducer being arranged on a side of the flexible membrane opposite the cavity.

[0017] According to one embodiment, the cavities of the transducers are formed in a rigid support layer, and each transducer has its upper electrode electrically connected to the lower electrode of an adjacent transducer via an electrically conductive element passing through the rigid support layer.

[0018] According to one embodiment, the lower electrode of each transducer is made of a doped semiconductor material.

[0019] According to one embodiment, the metal layer extends under the lower electrode of each transducer, in contact with a lower surface of the lower electrode of the transducer.

[0020] According to one embodiment, in each transducer, the flexible membrane is made of a semiconductor material.

[0021] According to one embodiment, in each transducer, a dielectric layer is located on the upper surface of the lower electrode of the bottom transducer of the cavity.

[0022] According to one embodiment, each transducer is a PMUT transducer. Attached Figure Description

[0023] The foregoing features and advantages, as well as other features and advantages, will be described in detail with reference to the accompanying drawings in the remainder of the disclosure of specific embodiments given by way of illustration rather than limitation, wherein:

[0024] Figure 1 This is a top view schematically and partially illustrating an example of an array ultrasound imaging device with row and column addressing;

[0025] Figure 2A It is along Figure 1 Plane AA is shown in further detail. Figure 1 A cross-sectional view of an example embodiment of the device shown;

[0026] Figure 2B It is along Figure 1 The corresponding cross-sectional view of plane BB;

[0027] Figure 3 This is a top view schematically and partially illustrating an embodiment of an array ultrasound imaging device with row and column addressing;

[0028] Figure 4A It is along Figure 3 Plane AA is shown in further detail. Figure 3 A cross-sectional view of an example embodiment of the device shown;

[0029] Figure 4B It is along Figure 3 The corresponding cross-sectional view of plane BB;

[0030] Figure 5A It is along Figure 3 Plane BB is shown in further detail. Figure 3 A cross-sectional view of another example of an embodiment of the device;

[0031] Figure 5B It is along Figure 3 The corresponding cross-sectional view of plane BB;

[0032] Figures 6A to 6K It shows the manufacturing process. Figure 4A and Figure 4B A cross-sectional view of the steps of an example method for a device of the type shown; and

[0033] Figures 7A to 7Care cross-sectional views showing steps of an example of a method of manufacturing Figure 5A and Figure 5B are cross-sectional views showing steps of an example of a method of manufacturing DETAILED DESCRIPTION

[0034] In the various drawings, like features are designated by like reference numerals. In particular, structural and / or functional features common to the various embodiments can have the same reference numerals and can be provided with the same structural, dimensional and material properties.

[0035] For the sake of clarity, only the steps and elements useful for understanding the embodiments described herein have been shown and described in detail. In particular, the various possible applications of the imaging device described have not been described in detail, the described embodiments being compatible with the usual applications of ultrasonic imaging devices. In particular, the characteristics of the electrical excitation signal applied to the ultrasonic transducer (frequency, shape, amplitude, etc.) have not been described in detail, the described embodiments being compatible with the excitation signals currently used in ultrasonic imaging systems, which can be selected according to the application under consideration, and in particular according to the nature of the body to be analyzed and the type of information expected to be acquired. Similarly, the various processes applied to the electrical signals delivered by the ultrasonic transducer to extract useful information relating to the body to be analyzed have not been described in detail, the described embodiments being compatible with the processes currently implemented in ultrasonic imaging systems. Furthermore, the electrical circuits for controlling the ultrasonic transducers of the imaging device have not been described in detail, the described embodiments being compatible with all or most of the known electrical circuits for controlling the ultrasonic transducers of array ultrasonic imaging devices with row-column addressing. Moreover, the formation of the ultrasonic transducers of the imaging device has not been described in detail, the described embodiments being compatible with all or most of the known ultrasonic transducer structures.

[0036] Unless otherwise stated, when referring to two elements being connected together, this means a direct connection with no intervening elements other than conductors, and when referring to two elements being coupled together, this means that the two elements can be connected or they can be coupled via one or more other elements.

[0037] In the following disclosure, unless otherwise specified, when referring to absolute position qualifiers such as the terms "front", "back", "up", "top", "bottom", "right", and the like, or to relative position qualifiers such as the terms "above", "below", "upper" and "lower", and the like, or to directional qualifiers such as "horizontal", "vertical", and the like, reference is made to the directions shown in the figures.

[0038] Unless otherwise specified, the expressions "approximately", "about", "substantially" and "around" mean within 10%, preferably within 5%.

[0039] Figure 1This is a top view schematically and partially illustrating an example of an array ultrasound imaging device 100 with row and column addressing.

[0040] Figure 2A and Figure 2B They are Figure 1 Device 100 along Figure 1 Cross-sectional views of planes AA and BB.

[0041] The device 100 includes a plurality of ultrasonic transducers 101 arranged in M ​​rows L i And N columns C i An array of integers M and N, where M and N are integers greater than or equal to 2, i is an integer from 1 to M, and j is an integer from 1 to N.

[0042] exist Figure 1 The image shows four rows L1, L2, L3, L4 and four columns C1, C2, C3, C4. In reality, the number of rows M and columns N of device 100 can certainly be different from 4.

[0043] Each transducer 101 of the device 100 includes a lower electrode E1 and an upper electrode E2. Figure 2A and 2B When an appropriate excitation voltage is applied between its electrodes E1 and E2, the transducer emits ultrasonic waves. When the transducer receives ultrasonic waves within a given wavelength range, it delivers a voltage representing the received wave between its electrodes E1 and E2.

[0044] In this example, transducer 101 is a capacitive transducer with a membrane, also known as a CMUT transducer (“capacitive micromechanical ultrasonic transducer”).

[0045] In each column C of the transducer array j In this array, the transducers 101 in this column have their respective lower electrodes E1 interconnected. However, the lower electrodes E1 of transducers 101 in different columns are not interconnected. Furthermore, in each row L of the transducer array... i In this row, the transducers 101 connect their respective upper electrodes E2 to each other. However, the upper electrodes E2 of transducers 101 in different rows are not connected to each other.

[0046] In each column C of device 100 j In this column, the lower electrode E1 of the transducer 101 forms a continuous conductive or semiconductor strip 103 extending substantially along the entire length of the column. As a variation, each strip 103 of electrode E1 comprises a vertical stack of semiconductor and conductive strips, each strip extending substantially along the entire length of the column. Furthermore, each row L of the device 100... iIn this configuration, the upper electrode E2 of the transducer 101 in the row forms a continuous conductive or semiconductor strip 105 extending substantially along the entire length of the row. As a variation, each strip 105 of electrode E2 comprises a vertical stack of semiconductor and conductive strips, each strip extending substantially along the entire length of the row. For simplicity, Figure 1 Only the lower electrode strip 103 and the upper electrode strip 105 are shown in the image.

[0047] In the example shown, the strips 103 forming the column electrodes are made of a doped semiconductor material, such as a silicon-doped semiconductor material. Furthermore, in this example, the strips 105 forming the row electrodes are made of metal. For example, in the top view, the lower strips 103 are parallel to each other, and the upper strips 105 are parallel to each other and perpendicular to the strips 103.

[0048] exist Figure 1 In one example, device 100 includes a support substrate 110 made of, for example, a semiconductor material (e.g., silicon). An array of ultrasonic transducers 101 is disposed on the upper surface of the substrate 110. More specifically, in this example, a dielectric layer 112 (e.g., a silicon oxide layer) forms the interface between the substrate 110 and the array of ultrasonic transducers 101. The dielectric layer 112 extends continuously, for example, over the entire upper surface of the support substrate 110. For example, layer 112 contacts the upper surface of the substrate 110 through its lower surface, substantially spanning the entire upper surface of the substrate 110.

[0049] The lower electrode strip 103 is disposed on the upper surface of the dielectric layer 112, for example, in contact with the upper surface of the dielectric layer 112. The strips 103 can be laterally separated from each other by dielectric strips 121, which are made of silicon oxide, for example, extend parallel to the strips 103 and have substantially the same thickness as the strips 103.

[0050] Each transducer 101 includes a cavity 125 formed in a rigid support layer 127 and a flexible membrane 123 suspended above the cavity 125. Layer 127 is, for example, a silicon oxide layer. Layer 127 is disposed on the upper surface (e.g., substantially planar) of an assembly formed by alternating strips 103 and 121. In each transducer 101, the cavity 125 is located in front of the lower electrode E1 of the transducer.

[0051] In the example shown, each transducer 101 includes a single cavity 125 in front of its lower electrode E1. As a variation, in each transducer 101, the cavity 125 may be divided into a plurality of basic cavities, for example, arranged as an array of rows and columns in a top view, laterally separated from each other by sidewalls formed by portions of layer 127.

[0052] In the illustrated example, at the bottom of each cavity 125, a dielectric layer 129, for example made of silicon oxide, covers the lower electrode E1 of the transducer, to prevent any electrical contact between the flexible membrane 123 and the lower electrode E1 of the transducer. As a variant, to ensure this electrical insulation function, a dielectric layer (not shown) can be covered on the lower surface of the membrane 123. In this case, the layer 129 can be omitted.

[0053] In each transducer 101, the flexible membrane 123 covering the transducer cavity 125 is for example made of a doped or undoped semiconductor material, for example silicon.

[0054] In each transducer 101, the upper electrode E2 of the transducer is arranged on and in contact with the upper surface of the flexible membrane 123 of the transducer, in vertical alignment with the cavity 125 and the lower electrode E1 of the transducer. As a variant, in the case of a semiconductor membrane, the upper electrode E2 of each transducer 101 can be formed by the actual membrane, in which case the layer 105 can be omitted.

[0055] For example, in each row L of the device 100, i the flexible membranes 123 of the transducers 101 of the row form a continuous strip of membranes extending substantially along the entire length of the row, laterally separated from the strip of membranes of the adjacent row by a dielectric region. In each row L i the strip of membranes 123 of the row coincides with the strip of upper electrodes 105 of the row, for example in plan view.

[0056] For each row L i of the array of transducers 101, the device 100 can comprise a transmission circuit, a reception circuit and a switch controllable to connect, in a first configuration, the electrodes E2 of the transducers of the row to the output terminal of the transmission circuit of the row, and, in a second configuration, the electrodes E2 of the transducers of the row to the input terminal of the reception circuit of the row.

[0057] Furthermore, for each column C j of the array of transducers 101, the device 100 can comprise a transmission circuit, a reception circuit and a switch controllable to connect, in a first configuration, the electrodes E1 of the transducers of the column to the output terminal of the transmission circuit of the column, and, in a second configuration, the electrodes E1 of the transducers of the column to the input terminal of the reception circuit of the column.

[0058] For simplicity, the transmitting and receiving circuits of the device 100 and the switches are not shown in the figures. Moreover, the formation of these elements is not detailed, the described embodiments being compatible with usual embodiments of the transmitting / receiving circuits of an array ultrasound imaging device with row-column addressing. As non-limitative examples, the transmitting / receiving circuits can be identical or similar to those described in the French patent application No. 19 / 06515 filed by the Applicant on June 18, 2019.

[0059] Figure 1 The limitations of the device of the prior art are related to the fact that the capacitive coupling between the lower electrode strips 103 and the substrate 110 is much higher than the capacitive coupling between the upper electrode strips 105 and the substrate 110. This leads to a difference of behavior between the rows L i and the columns C j of the device. More specifically, this leads to a difference of sensitivity of the reception mode between the rows L i and the columns C j of the device. In particular, it can be observed that, for the same received acoustic power, the voltage generated on the upper electrode strips 105 of the rows L i during the phase of reading from the rows L i is much higher than the voltage generated on the lower electrode strips 103 of the columns C j during the phase of reading from the columns C j . This can lead to the appearance of unwanted artifacts in the acquired images.

[0060] Figure 3 is a top view schematically and partially illustrating an example of an embodiment of an array ultrasound imaging device 300 with row-column addressing.

[0061] Figure 4A and Figure 4B are respectively Figure 3 cross-sectional views of the device 300 of Figure 3 along the planes A-A and B-B.

[0062] The device 300 has elements in common with the previously described device 100. These common elements will not be detailed again hereinafter. In the rest of the description, only the differences with respect to the device 100 will be emphasized.

[0063] As with the device 100, the device 300 comprises a plurality of ultrasound transducers 101 arranged in an array of M rows L i and N columns C j .

[0064] As in the device 100, each transducer 101 of the device 300 comprises a lower electrode E1 and an upper electrode E2. For simplicity, Figure 3 only the upper electrode E2 is shown in .

[0065] The main difference between device 300 and device 100 lies in the interconnection scheme of the lower electrode E1 and upper electrode E2 of transducer 101 in device 300.

[0066] In device 300, in each row L of transducer 101 i In the middle, any two adjacent transducers 101 in this row ij and 101 ij+1 (101 here) ij and 101 ij+1 These represent the rows L of the array. i and column C j The transducer 101, and the array of rows L i and column C j+1 The transducers 101 are configured such that their lower electrodes E1 and their upper electrodes E2 are connected to each other, or their upper electrodes E2 and their lower electrodes E1 are connected to each other. However, the transducers 101 ij and 101 ij+1 The upper electrodes E2 are electrically insulated from each other. Similarly, transducer 101 ij and 101 ij+1 The lower electrodes E1 are electrically insulated from each other.

[0067] Similarly, in each column C of transducer 101 j In this column, any two adjacent transducers 101 ij and 101 i+1j (101 here) i+1j Indicates line L i+1 and column C j The transducers 101 respectively connect their lower electrodes E1 and their upper electrodes E2 to each other, or connect their upper electrodes E2 and their lower electrodes E1 to each other. However, the transducers 101 ij and 101 i+1j The upper electrodes E2 are electrically insulated from each other. Similarly, transducer 101 ij and 101 i+1j The lower electrodes E1 are electrically insulated from each other.

[0068] Therefore, in each column C of device 300 j In this column, the column conductor 303, shared by all transducers 101 in the column, is vertically wound between the transducers in the column, alternately passing through the lower electrode E1 and upper electrode E2 of the transducers in the column. Similarly, in each row L of the device 300... i In the middle, the row conductor 305, which is shared by all transducers 101 in the row, is wound vertically between the transducers in the row and alternately passes through the lower electrode E1 and the upper electrode E2 of the transducers in the row.

[0069] In this example, the electrical connection between the upper electrode E2 and the lower electrode E1 of adjacent transducers is formed by a connecting element 311, for example made of metal, which vertically crosses a portion of the dielectric layer 127 separating the cavities 125 of the transducers laterally. Figure 4A and Figure 4B In the example of Figs. 3 and 4, each connecting element 311 extends vertically from the lower surface of the upper electrode E2 of a transducer 101 to the upper surface of the lower electrode of an adjacent transducer.

[0070] In the device 300, in a top view, the dielectric region 121 forms a continuous gate which completely surrounds each electrode E1 and laterally separates each electrode E1 from the electrode E1 of an adjacent transducer. Similarly, in a top view, each electrode E2 is completely surrounded by a dielectric region, possibly air or vacuum, and laterally separated from the electrode E2 of an adjacent transducer.

[0071] For example, in a top view, each flexible membrane 123 is completely surrounded by a dielectric region and laterally separated from the membrane 123 of an adjacent transducer. As a variant, the flexible membrane 123 can be made of a dielectric material, for example silicon oxide. In this case, the membrane of an adjacent transducer can form a continuous layer.

[0072] The operation of the device 300 is substantially the same as that of the aforementioned device 100, by replacing the column conductor 103 and the row conductor 105 of the device 100 respectively arranged on the lower surface side and on the upper surface side of the transducers 101 by the column conductor 303 and the row conductor 305, and by alternating the lower electrode E1 and the upper electrode E2 of the transducers of the row or of the column.

[0073] Thus, for each row L i of the array of transducers 101, the device 300 can comprise a transmission circuit, a reception circuit and a switch controllable to connect, in a first configuration, the row conductor 305 of the row L i to the output terminal of the transmission circuit of the row and, in a second configuration, to connect the row conductor 305 of the row L i to the input terminal of the reception circuit of the row.

[0074] Furthermore, for each column C j of the array of transducers 101, the device 300 can comprise a transmission circuit, a reception circuit and a switch controllable to connect, in a first configuration, the column conductor 303 of the column C j to the output terminal of the transmission circuit of the column and, in a second configuration, to connect the column conductor 303 of the column C j to the input terminal of the reception circuit of the column.

[0075] The advantage of device 300 is that the capacitive coupling between row conductor 305 and substrate 110 is substantially the same as the capacitive coupling between column conductor 303 and substrate 110. This allows for the symmetry of the row L of the device. i and column C j The behavior of the device is as follows: Specifically, the sensitivity in the receiving mode is substantially the same in both rows and columns, which enables improved image quality. This further results in substantially the same electrical characteristics in both rows and columns, and in particular, substantially the same impedance.

[0076] Figure 5A and Figure 5B They are along Figure 3 The cross-sectional views of planes AA and BB show another embodiment of device 300.

[0077] Figure 5A and 5B The variant and the previous ones about Figure 3 , Figure 4A and Figure 4B The main difference in the described variant is that, in this variant, a metal layer portion 501 extends beneath each electrode E1 of the device, for example, made of the same metal as the upper electrode E2 of the device. Layer 501 contacts the lower surface of electrode E1 through its upper surface. For example, layer 501 contacts the upper surface of dielectric layer 112 through its lower surface. In this example, each connecting element 311 extends vertically from the lower surface of the upper electrode E2 of transducer 101 to the upper surface of the metal layer portion 501 of the adjacent transducer 101.

[0078] The advantage of this alternative embodiment is that, when the lower electrode E1 of the transducer is made of a semiconductor material, it can improve the conductivity of the conductive row elements and conductive column elements 305 and 303 at the level of the lower electrode E1 of the transducer.

[0079] Figures 6A to 6K It shows the manufacturing process. Figure 4A and Figure 4B A cross-sectional view of the steps of an example method for a device of the type shown.

[0080] Figure 6A The oxidation steps of a portion of the semiconductor layer in an SOI ("semiconductor-on-insulator") structure are shown.

[0081] The initial structure comprises a support substrate 10 (for example made of a semiconductor material, for example of silicon), a dielectric layer 12 (for example made of silicon oxide) covering the upper face of the substrate 10, and a semiconductor layer 14 (for example a layer of monocrystalline silicon) covering the upper face of the dielectric layer 12. The dielectric layer 12 and the upper semiconductor layer 14 each extend continuously over the entire upper face of the substrate 10, for example with a substantially constant thickness. In this example, the dielectric film 12 is in contact with the upper face of the substrate 10 by its lower face, and the semiconductor layer 14 is in contact with the upper face of the dielectric layer 12 by its lower face.

[0082] Figure 6A The step of oxidation of the upper part of the semiconductor layer 14 is illustrated more particularly. In this step, the upper part of the layer 14 is transformed into a layer 14a of dielectric material, for example of silicon oxide (in the case where the initial layer 14 is made of silicon). The nature of the lower part 14b of the layer 14 is not modified.

[0083] The oxidation of the upper part of the layer 14 is performed, for example, by a dry thermal oxidation method. The initial thickness of the semiconductor layer 14 is for example in the range 50 nm to 3 μιη. The thickness of the insulating layer 14a after oxidation is for example in the range 10 to 500 nm, for example approximately 50 nm.

[0084] Figure 6B The step of forming local cavities in the insulating layer 14a, corresponding to the cavities 125 of the CMUT transducers, is illustrated.

[0085] The cavities 125 extend perpendicularly from the upper face of the insulating layer 14a towards the layer 14b. In the illustrated example, the cavities 125 are through, i.e. they appear on the upper face of the semiconductor layer 14b.

[0086] The cavities 125 can be formed by etching, for example by plasma etching. An etching mask can be used to define the position of the cavities 125.

[0087] Figure 6C The step of oxidation of the upper face of a second semiconductor substrate 20, for example made of silicon, is illustrated. In this step, a dielectric layer 22, for example made of silicon oxide, is formed on the upper face of the substrate 20. The oxidation can be performed by a dry thermal oxidation method. The thickness of the dielectric layer 22 formed during this step is for example in the range 50 nm to 1 μιη, for example approximately 100 nm.

[0088] Figure 6D The step of transferring the assembly comprising the substrate 20 and the dielectric layer 22 to the structure obtained at the end of the previous step is illustrated. Figure 6A and Figure 6B The step of turning over the structure obtained at the end of the previous step is illustrated. More particularly, in the illustrated example, the substrate 20 is turned over relative to the direction Figure 6C and is transferred to the structure obtained at the end of the previous step. Figure 6BThe structure of the layer 22 is such that its lower surface is in contact with the upper surface of the layer 14a. The two structures are bonded to each other by direct bonding or molecular bonding of the lower surface of the layer 22 with the upper surface of the layer 14a. The dielectric layer 22 thus encloses the cavity 125 from its upper surface.

[0089] Figure 6E A step of thinning the substrate 20 is shown from its upper surface, i.e. from the opposite surface to the dielectric layer 22, in the direction of Figure 6E The thinning is performed for example by lapping. The initial thickness of the substrate 20 before thinning is for example about 700 pm. After thinning, the thickness of the substrate can be in the range 300 nm to 100 pm.

[0090] Figure 6F A step of forming an insulating trench 121 filled with a dielectric material (for example silicon oxide) from the upper surface of the thinned substrate 20 is shown. The trench 121 (in black in the figure) Figure 6F corresponds to the dielectric region 121 of Figure 4A and Figure 4B The trench 121 passes completely through the substrate 20, through its entire thickness, and appears on the upper surface of the insulating layer 22. The trench 121 is formed for example by deep reactive ion etching of the substrate 20, and is then filled with a dielectric material. The portion of the substrate 20 delimited by the trench corresponds to the electrode El of the transducer.

[0091] Figure 6G A step of oxidation of the upper surface of a third semiconductor substrate 30, for example made of silicon, is shown. During this step, a dielectric layer 32, for example made of silicon oxide, is formed on the side of the upper surface of the substrate 30. This oxidation can be performed by a dry thermal oxidation method. The thickness of the dielectric layer 32 formed during this step is for example in the range 100 nm to 10 pm, for example about 2 pm, for example in the range 2 to 10 pm. As a variant, the layer 32 can be formed by depositing an insulating material (for example silicon oxide) on the upper surface of the substrate 30. Furthermore, as a variant, the substrate 30 can be a substrate made of a dielectric material (for example glass), or a high-resistivity semiconductor substrate, for example an undoped or lightly doped silicon substrate.

[0092] Figure 6H A step of transferring the structure of Figure 6F onto the structure of Figure 6G In the example shown, the structure in Figure 6F is flipped over with respect to the direction of Figure 6F and is transferred onto Figure 6GStructurally, the lower surface of electrode E1 and the lower surface of dielectric region 121 are in contact with the upper surface of dielectric layer 32. These two structures are bonded to each other through direct bonding of the lower surface of electrode E1 and the dielectric region 121 on the upper surface of dielectric layer 32.

[0093] Figure 6I The subsequent steps for removing the substrate 10 and the dielectric layer 12 of the initial structure are shown. Thus, only the semiconductor layer 14b is held above the cavity to form the transducer film 123.

[0094] Figure 6J The structure obtained at the end of one or more subsequent structuring steps of semiconductor layer 14b and dielectric layers 14a and 22 is shown, on the one hand defining a flexible film 123 of the transducer in semiconductor layer 14, and on the other hand forming an opening 41 in dielectric layers 14a and 22 leading to the upper surface of the electrode E1 of the transducer.

[0095] Figure 6K Shown in Figure 6I The subsequent step is to deposit a metal layer 43 on the entire upper surface of the structure, and then structure the metal layer 43, for example by photolithography and etching, to define the upper electrode E2 of the transducer.

[0096] In this example, Figure 4A and Figure 4B The connecting element 311 of the structure corresponds to a portion of layer 43 that covers the side of opening 41 and contacts the upper surface of electrode E1 at the bottom of opening 41. Figure 4A and Figure 4B The substrate 110 and dielectric layer 112 of the structure correspond to the substrate 30 and dielectric layer 32, respectively. The sidewalls and bottom of the cavity 125 are formed. Figure 4A and Figure 4B The dielectric regions 127 and 129 of the structure correspond to layers 14a and 22.

[0097] Figures 7A to 7C It shows the manufacturing process. Figure 5A and Figure 5B A cross-sectional view of the steps of an example method for a device of the type shown.

[0098] The initial steps of this method are the same as those mentioned earlier. Figures 6A to 6G The steps described are the same.

[0099] Figure 7A Showing from Figure 6F The structure begins with the following structure and ends with the following consecutive additional steps:

[0100] - A laterally insulating conductive via 51 is formed, which extends vertically through the entire thickness of the semiconductor layer 20 and appears on the upper surface of the dielectric layer 22.

[0101] - A metal layer 53 is deposited on the upper surface of the structure, and the metal layer 53 contacts the upper surface of the electrode E1 and the upper surface of the conductive via 51 through its lower surface; and

[0102] - Partially remove the metal layer 53, for example, in front of the dielectric region 121, to make the electrodes E1 electrically insulated from each other.

[0103] Figure 7B Showing from Figure 6G The structure begins with the following structure and ends with the following consecutive additional steps:

[0104] - A metal layer 61 is deposited on the upper surface of the structure, and the metal layer 61 contacts the upper surface of the dielectric layer 32 through its lower surface; and

[0105] -Partially remove metal layer 61 to define a plurality of metal portions that are insulated from each other, the metal portions being in contact with... Figure 7A The metal portions defined in the metal layer 53 of the structure are arranged in the same or similar manner.

[0106] The rest of the method is similar to the previous section on... Figures 6H to 6K As described.

[0107] Figure 7C The structure obtained at the end of this method is shown. It should be noted that in this variation, Figure 7A Structure and Figure 7B The bonding of the structure is the surface of the metal layer 53 opposite to the semiconductor layer 20 (i.e., it is on the surface of the metal layer 53). Figure 7C The lower surface in the direction of the metal layer 61 opposite to the substrate 30 (i.e., its lower surface in the direction of the substrate 30) and the surface of the metal layer 61 opposite to the substrate 30 (i.e., its lower surface in the direction of the substrate 30) Figure 7B Direct metal-to-metal bonding between the upper surfaces in the direction of the metal.

[0108] The stacking of the metal layers 61 and 53 in front of the lower electrode E1 corresponds to Figure 5A and Figure 5B The metal layer portion 501 of the structure. The insulating conductive via 51 corresponds to Figure 5A and Figure 5B The connecting element 311 of the structure.

[0109] Various embodiments and variations have been described. Those skilled in the art will understand that certain features of these different embodiments and variations can be combined, and other variations will occur to those skilled in the art. In particular, the embodiments are not limited to the specific examples of materials and dimensions mentioned in this disclosure.

[0110] Moreover, the described embodiments are not limited to the specific examples of the structure of the CMUT transducer described above, nor to the specific examples of the manufacturing method of the CMUT transducer described above. In particular, it should be noted that the provided solution can be applied to CMUT transducers formed by surface micromachining.

[0111] It should also be noted that the described embodiments are not limited to the examples shown in the figures, in which the rows and columns of transducers of the device are straight, and in which the rows are orthogonal to the columns. As a variant, the rows and / or columns of transducers of the device are non-straight. Moreover, the rows and columns of transducers can not be respectively parallel to each other. Moreover, the rows of transducers can not be orthogonal to the columns.

[0112] More generally, the described embodiments are applicable to any type of ultrasonic transducer having a lower electrode and an upper electrode, and to control according to row-column addressing, for example, piezoelectric transducers (for example, transducers of the PMUT ("Piezoelectric Micromachined Ultrasonic Transducer") type.

Claims

1. An ultrasound imaging device (300) comprising a row-by-row (L i ) and by column (C j Multiple ultrasonic transducers (101) are arranged in a manner that includes a lower electrode (E1) and an upper electrode (E2), wherein: - In each row (L) i In the above, any two adjacent transducers (101) in the row are configured to connect the lower electrode (E1) of one ultrasonic transducer to the upper electrode (E2) of another ultrasonic transducer, or to connect the upper electrode (E2) of one ultrasonic transducer to the lower electrode (E1) of another ultrasonic transducer; and - In each column (C j In the column, any two adjacent transducers (101) are configured to connect the lower electrode (E1) of one ultrasonic transducer to the upper electrode (E2) of another ultrasonic transducer, or to connect the upper electrode (E2) of one ultrasonic transducer to the lower electrode (E1) of another ultrasonic transducer.

2. The device according to claim 1, wherein: - In each row (L) i In the above, any two adjacent transducers (101) in the row are configured to electrically insulate the lower electrode (E1) of one ultrasonic transducer from the lower electrode of another ultrasonic transducer from each other and to electrically insulate the upper electrode (E2) of one ultrasonic transducer from the upper electrode of another ultrasonic transducer from each other; and - In each column (C j In the column, any two adjacent transducers (101) are configured to electrically insulate the lower electrode (E1) of one ultrasonic transducer from the lower electrode of another ultrasonic transducer from each other and to electrically insulate the upper electrode (E2) of one ultrasonic transducer from the upper electrode of another ultrasonic transducer from each other.

3. The device according to claim 1 or 2, wherein, Each ultrasonic transducer (101) is a CMUT transducer comprising a flexible membrane (123) suspended above a cavity (125), wherein the lower electrode (E1) of the transducer is disposed on the side of the cavity (125) opposite to the flexible membrane (123), and the upper electrode (E2) of the transducer is disposed on the side of the flexible membrane (123) opposite to the cavity (125).

4. The device according to claim 3, wherein, The cavity (125) of the transducer (101) is formed in a rigid support layer (127), and each transducer (101) electrically connects its upper electrode (E2) to the lower electrode (E1) of the adjacent transducer (101) via a conductive element (311) passing through the rigid support layer (127).

5. The device according to claim 3 or 4, wherein, The lower electrode (E1) of each transducer (101) is made of doped semiconductor material.

6. The device according to claim 5, wherein, The metal layer portion (501) extends below the lower electrode (E1) of each transducer (101) and contacts the lower surface of the lower electrode (E1) of the transducer.

7. The device according to any one of claims 3 to 6, wherein, In each transducer (101), the flexible membrane (123) is made of semiconductor material.

8. The device according to any one of claims 3 to 7, wherein, In each transducer (101), a dielectric layer (129) covers the upper surface of the lower electrode (E1) of the transducer at the bottom of the cavity (125).

9. The device according to claim 1 or 2, wherein, Each transducer (101) is a PMUT transducer.

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