PMUT transducer

Abstract

The present invention relates to a PMUT transducer (100) comprising: - a flexible membrane (107) suspended above a cavity (101); - a layer made of a piezoelectric material (301) located on a face of the flexible membrane opposite the cavity; - first and second electrodes (201A, 201B) inserted between the flexible membrane and the layer of piezoelectric material; and - third and fourth electrodes (401B, 401A) which are arranged on a side of the layer of piezoelectric material that is opposite the flexible membrane, and which are situated respectively opposite the first and second electrodes (201A, 201B), wherein the first and second electrodes (201A, 201B) are connected to the fourth and third electrodes (401A, 401B), respectively .

Description

DESCRIPTION PMUT transducer This application is based on, and claims priority from, French patent application 23 / 09581 filed on September 12, 2023 and entitled “PMUT Transducer”, which is considered to be an integral part of this description within the limits provided by law. Technical field

[0001] This description relates generally to the field of ultrasonic transducers, more particularly to piezoelectric membrane ultrasonic transducers, or PMUT transducers (from the English “Piezoelectric Micromachined Ultrasonic Transducer” - micro-machined piezoelectric ultrasonic transducer). Prior art

[0002] Typically, a PMUT transducer comprises a flexible membrane suspended over a cavity, a first electrode, located on one side of the flexible membrane opposite the cavity, a layer of piezoelectric material, located on one side of the first electrode opposite the flexible membrane, and a second electrode, located on one side of the layer of piezoelectric material opposite the first electrode. When an appropriate excitation voltage is applied between the electrodes of the transducer, the flexible membrane vibrates and emits an ultrasonic acoustic wave. Conversely, when the transducer receives an acoustic wave in a certain frequency range, the flexible membrane vibrates, leading to the appearance of a voltage between the electrodes of the transducer.

[0003] A PMUT transducer is conventionally coupled to an electronic control circuit configured to, during a transmission phase, applying an excitation voltage between the first and second electrodes of the transducer, so as to cause the emission of an ultrasonic wave by the transducer, and, during a reception phase, reading the voltage produced between the first and second electrodes of the transducer under the effect of the received acoustic wave.

[0004] In order to improve the performance of PMUT transducers, particularly in terms of vibration amplitude, structures comprising arrays of electrodes arranged on either side of the piezoelectric material layer have been proposed. Such transducers typically comprise a first electrode, located under the piezoelectric material layer, at least one second electrode, located on the piezoelectric material layer, and at least one third electrode, located on the piezoelectric material layer. A first excitation voltage is then applied between the second electrode and the first electrode and a second excitation voltage different from the first excitation, for example a voltage of opposite sign to that of the first excitation voltage, is applied between the third electrode and the first electrode. However, PMUT transducers of this type prove to be expensive and complex to produce and control.This is particularly due to the fact that these PMUT transducers require the implementation of two separate power sources to enable the application of two excitation voltages, for example opposite ones, referenced to the same potential. Summary of the invention

[0005] It would be desirable to have a PMUT transducer structure that overcomes all or part of the disadvantages of known structures.

[0006] For this, one embodiment provides a PMUT transducer comprising: - a flexible membrane suspended above a cavity; - a layer of piezoelectric material located on one side of the flexible membrane opposite the cavity; - first and second electrodes interposed between the flexible membrane and the layer of said piezoelectric material; and - third and fourth electrodes arranged on one side of the layer of said piezoelectric material opposite the flexible membrane, and located respectively opposite the first and second electrodes, in which the first and second electrodes are connected respectively to the fourth and third electrodes.

[0007] According to one embodiment: - the first and fourth electrodes are intended to be brought to the same first potential; and - the second and third electrodes are intended to be brought to the same second potential, different from the first potential.

[0008] According to one embodiment, the second and fourth electrodes respectively surround the first and third electrodes.

[0009] According to one embodiment, the second and fourth electrodes each have, in top view, an annular shape.

[0010] According to one embodiment, the second and fourth electrodes each have, in top view, a substantially circular crown shape.

[0011] According to one embodiment, the first and third electrodes each have, in top view, a disc shape.

[0012] According to one embodiment, the first and second electrodes are respectively connected to the fourth and third electrodes by first and second conductive vias.

[0013] According to one embodiment, the first and second conductive vias are located directly above the cavity.

[0014] According to one embodiment, the first and second conductive vias are offset out of line with the cavity.

[0015] According to one embodiment: - the first and second electrodes are located on and in contact with a face of the flexible membrane opposite the cavity; - the layer of said piezoelectric material coats the first and second electrodes; and - the third and fourth electrodes are located on and in contact with a face of the layer of said piezoelectric material opposite the flexible membrane.

[0016] According to one embodiment, the transducer further comprises: - first and second conductive tracks coplanar with the first and second electrodes; and - third and fourth coplanar conductive tracks to the third and fourth electrodes.

[0017] According to one embodiment, the transducer further comprises a support substrate in and on which the transducer is formed, the cavity extending over the entire thickness of the support substrate. Brief description of the drawings

[0018] These and other features and advantages will be set forth in detail in the following description of particular embodiments given without limitation in relation to the attached figures, among which:

[0019] Figure 1A and Figure 1B are respectively top and sectional views along plane BB of Figure 1A, schematic and partial, illustrating a structure obtained at the end of a step of a method of manufacturing a PMUT transducer according to one embodiment;

[0020] Figure 2A and Figure 2B are respectively top and sectional views along plane BB of Figure 2A, schematic and partial, illustrating a structure obtained at the end of a subsequent step of the manufacturing process of the PMUT transducer;

[0021] Figure 3A and Figure 3B are respectively top and sectional views along plane BB of Figure 3A, schematic and partial, illustrating a structure obtained at the end of a subsequent step of the manufacturing process of the PMUT transducer;

[0022] Figure 4A and Figure 4B are respectively top and sectional views along plane BB of Figure 4A, schematic and partial, illustrating a structure obtained at the end of a subsequent step of the manufacturing process of the PMUT transducer;

[0023] Figure 5A and Figure 5B are respectively top and sectional views along plane BB of Figure 5A, schematic and partial, illustrating a structure obtained at the end of a step of another method of manufacturing a PMUT transducer according to one embodiment;

[0024] Figure 6A and Figure 6B are respectively top and sectional views along plane BB of Figure 6A, schematic and partial, illustrating a structure obtained at the end of a subsequent step of the manufacturing process of the PMUT transducer; and

[0025] Figure 7 is a schematic and partial sectional view illustrating a structure obtained at the end of a method of manufacturing a PMUT transducer according to one embodiment. Description of the embodiments

[0026] The same elements have been designated by the same references in the different figures. In particular, the structural and / or functional elements common to the different embodiments may have the same references and may have identical structural, dimensional and material properties.

[0027] For the sake of clarity, only the steps and elements useful for understanding the described embodiments have been shown and are detailed. In particular, the various applications in which the described transducers can be implemented have not been detailed, the described embodiments being compatible with the usual applications of ultrasonic transducers, in particular in ultrasonic imaging devices and / or biometric devices. Furthermore, the transducer control circuits have not been detailed, the described embodiments being compatible with all or most of the known PMUT transducer control circuits, possibly subject to adaptations within the scope of the person skilled in the art upon reading this description.

[0028] Unless otherwise specified, when referring to two elements connected to each other, this means directly connected without intermediate elements other than conductors, and when referring to two elements connected (in English "coupled") to each other, this means that these two elements can be connected or be connected by means of one or more other elements.

[0029] In the following description, when referring to absolute position qualifiers, such as the terms "front", "back", "top", "bottom", "left", "right", etc., or relative, such as the terms "above", "below", "upper", "lower", etc., or to orientation qualifiers, such as the terms "horizontal", "vertical", etc., reference is made, unless otherwise specified, to the orientation of the figures.

[0030] Unless otherwise specified, the expressions “about”, “approximately”, “substantially”, and “in the order of” mean to within 10%, preferably to within 5%.

[0031] Figure 1A and Figure 1B are respectively top and sectional views along plane BB of Figure 1A, schematic and partial, illustrating a structure obtained at the end of a step of a method of manufacturing a PMUT 100 transducer according to one embodiment.

[0032] In this step, a cavity 101 is formed in a rigid support layer 103, for example a dielectric layer, for example a silicon oxide layer. In the example shown, the layer 103 rests, on its lower face, on the upper face of a support substrate 105. The support substrate 105 is, for example, a wafer or a piece of wafer made of a semiconductor material, for example silicon. Alternatively, the support substrate 105 may be made of a dielectric material, for example glass. The cavity 101 corresponds to a localized opening or recess formed in the layer 103. In this example, the cavity 101 extends vertically over the entire thickness of the layer 103. Alternatively, the cavity 101 may extend over only part of the thickness of the layer 103. The side walls of the cavity 101 are formed by a non-hollowed out peripheral region of layer 103.

[0033] In the example illustrated in Figure 1A, the cavity 101 has, in top view, a substantially circular shape. This example is not, however, limiting. As a variant, the cavity 101 may have, in top view, any shape, for example rectangular, hexagonal, square, oval, etc.

[0034] In the example shown, a flexible membrane 107 is suspended above the cavity 101. At the periphery of the cavity 101, the flexible membrane 107 is in contact or in support, by its lower face, with the upper face of the non-hollowed out peripheral region of the layer 103. In the central part of the transducer, the lower face of the flexible membrane 107 is separated from the upper face of the substrate 105 by the cavity 101. The flexible membrane 107 is for example made of the same material as the layer 103. As a variant, the membrane 107 may be made of a material different from that of the layer 103.

[0035] For example, the cavity 101 is formed in the layer 103 before the layer 103 is transferred onto the substrate 105, for example by bonding on the side of the upper face of the substrate 105.

[0036] Figure 2A and Figure 2B are respectively top and sectional views along plane BB of Figure 2A, schematic and partial, illustrating a structure obtained at the end of a subsequent step of the manufacturing process of the PMUT 100 transducer.

[0037] During this step, electrodes 201A and 201B are formed on the side of a face of the flexible membrane 107 opposite the cavity 101. The electrodes 201A and 201B are disjointed, that is to say electrically isolated from each other. In In the illustrated example, the electrodes 201A and 201B are located on and in contact with the face of the flexible membrane 107 opposite the cavity 101 (the upper face of the membrane 107, in the orientation of FIG. 2B).

[0038] In the example shown, the electrode 201A is located in the central part of the PMUT transducer 100 and has, in top view, a periphery of substantially circular shape. This example is however not limiting, the electrode 201A being able, as a variant, to have a periphery of any shape. The electrode 201A constitutes for example a lower central electrode of the PMUT transducer 100.

[0039] Furthermore, in this example, the electrode 201B has an annular shape surrounding the electrode 201A. In the example shown, the electrode 201B has, in top view, a substantially circular crown shape. This example is however not limiting, the electrode 201B being able, as a variant, to have any shape surrounding the electrode 201A, for example an annular shape other than a circular crown, for example a substantially rectangular or square crown. The electrode 201B constitutes for example a lower peripheral electrode of the PMUT transducer 100.

[0040] In the example shown, the electrodes 201A and 201B are substantially concentric and substantially centered relative to the cavity 101, the center of each electrode 201A, 201B being located substantially directly above the middle of the cavity 101.

[0041] In the example illustrated, the electrodes 201A and 201B are respectively connected to conductive tracks 203A and 203B arranged on either side of the cavity 101, on the periphery of the transducer, directly above the non-hollowed out peripheral region of the layer 103. The conductive tracks 203A and 203B are for example substantially parallel to each other and extend laterally along a direction orthogonal to the plane BB of FIG. 2A, for example along a column direction of a matrix of PMUT transducers similar or identical to the transducer 100.

[0042] For example, the electrodes 201A and 201B and the conductive tracks 203A and 203B are formed by a step of depositing a metal layer coating the layer 103, followed by steps of photolithography and then etching of the metal layer. In this case, the conductive tracks 203A and 203B and the electrodes 201A and 201B are coplanar.

[0043] In the example shown, the electrode 201B has more precisely a truncated annular shape, or an open ring, making it possible to connect the central electrode 201A to the conductive track 203A without coming into contact with the peripheral electrode 201B. This example is however not limiting, the connection of the central electrode 201A to the conductive track 203A being able, as a variant, to be carried out in any way, for example by means of conductive vias and a conductive track located in a metallization level different from that in which the electrodes 201A and 201B and the conductive tracks 203A and 203B are formed.

[0044] Figure 3A and Figure 3B are respectively top and sectional views along plane BB of Figure 3A, schematic and partial, illustrating a structure obtained at the end of a subsequent step of the manufacturing process of the PMUT 100 transducer.

[0045] During this step, a layer 301 of a piezoelectric material is deposited on the side of the upper face of the structure previously described in relation to FIGS. 2A and 2B. In the example shown, the layer 301 of piezoelectric material coats the electrodes 201A and 201B and the conductive tracks 203A and 203B. In this example, the electrodes 201A and 201B and the conductive tracks 203A and 203B are interposed between the flexible membrane 107 and the piezoelectric material layer 301. Alternatively, the piezoelectric material can be deposited locally around the cavity 101.

[0046] Although this has not been detailed in Figures 3A and 3B, a dielectric filling layer may be deposited on the side of the upper face of the structure prior to the deposition of the layer 301 of piezoelectric material, for example so as to fill all the free spaces extending laterally between the electrodes 201A and 201B and the conductive tracks 203A and 203B. In this case, the dielectric filling layer is exposed, for example, to the upper face of the electrodes 201A and 201B and the conductive tracks 203A and 203B. This allows, for example, the structure to have a substantially flat upper face prior to the deposition of the layer 301 of piezoelectric material, and to avoid the presence of air or vacuum zones between the electrodes 201A and 201B and the conductive tracks 203A and 203B. The dielectric filling layer is, for example, made of an electrically insulating material, for example an oxide.Alternatively, the dielectric filler layer is made of a piezoelectric material similar or identical to that of layer 301.

[0047] Figure 4A and Figure 4B are respectively top and sectional views along plane BB of Figure 4A, schematic and partial, illustrating a structure obtained at the end of a subsequent step of the manufacturing process of the PMUT 100 transducer.

[0048] In this step, electrodes 401A and 401B are formed on one side of the material layer. piezoelectric 301 opposite the cavity 101. The electrodes 401A and 401B are for example analogous, respectively, to the electrodes 201B and 201A.

[0049] In the example shown, the electrodes 401A and 401B are disjoint, that is to say electrically isolated from each other. In the example illustrated, the electrodes 401A and 401B are located on and in contact with the face of the piezoelectric material layer 301 opposite the cavity 101 (the upper face of the layer 301, in the orientation of FIG. 4B).

[0050] In the example shown, the electrode 401B is located in the central part of the PMUT transducer 100 and has, in top view, a periphery of substantially circular shape. This example is however not limiting, the electrode 401B being able, as a variant, to have a periphery of any shape. The electrode 401B constitutes for example an upper central electrode of the PMUT transducer 100. In the example shown, the electrode 401B is located opposite the electrode 201A, the electrodes 401B and 201A being for example substantially concentric. Furthermore, the electrode 401B has for example a shape and dimensions substantially identical, apart from manufacturing dispersions, to those of the electrode 201A.

[0051] Furthermore, in this example, the electrode 401A has an annular shape surrounding the electrode 401B. In the example shown, the electrode 401A has, in top view, a substantially circular crown shape. This example is however not limiting, the electrode 401A being able, as a variant, to have any shape surrounding the electrode 401B, for example a shape for example rectangular, hexagonal, square, oval, etc. The electrode 401A constitutes for example an upper peripheral electrode of the PMUT transducer 100. In the example shown, the electrode 401A is located opposite the electrode 201B, the electrodes 401A and 201B being for example substantially concentric. Furthermore, the electrode 401A has for example dimensions and a shape substantially identical, apart from manufacturing dispersions, to those of the electrode 201B.

[0052] In the example shown, the electrodes 401A and 401B are substantially concentric and substantially centered relative to the cavity 101, the center of each electrode 401A, 401B being located substantially directly above the middle of the cavity 101.

[0053] In the example illustrated, the electrodes 401A and 401B are respectively connected to conductive tracks 403A and 403B arranged on either side of the cavity 101, at the periphery of the PMUT transducer 100, directly above the non-hollowed out peripheral region of the layer 103. The conductive tracks 403A and 403B are for example substantially parallel to each other and extend laterally along a direction orthogonal to the plane BB of FIG. 4A, for example along a column direction of a transducer matrix. In the example shown, the conductive tracks 403A and 403B are located respectively opposite the conductive tracks 203A and 203B. Furthermore, the conductive tracks 403A and 403B have, for example, identical shapes and dimensions, apart from manufacturing variations, to those of the conductive tracks 203A and 203B, respectively.Alternatively, the conductive tracks 403A and 403B, or the conductive tracks 203A and 203B, may be omitted. In the case where the tracks 403A and 403B are omitted, the electrodes 401A and 401B are for example connected respectively to the conductive tracks 203A and 203B by conductive vias passing through the entire thickness of the layer 301 of piezoelectric material or of the layer. filling dielectric. Similarly, in the case where the conductive tracks 203A and 203B are omitted, the electrodes 201A and 201B are for example connected respectively to the conductive tracks 403A and 403B by conductive vias crossing the entire thickness of the layer 301 of piezoelectric material.

[0054] For example, the electrodes 401A and 401B and the conductive tracks 403A and 403B are formed by a step of depositing a metal layer coating the piezoelectric material layer 301, followed by steps of photolithography and then etching of the metal layer. In this case, the conductive tracks 403A and 403B and the electrodes 401A and 401B are coplanar.

[0055] In the example shown, the electrode 401A has more precisely a truncated annular shape, or an open ring, making it possible to connect the central electrode 401B to the conductive track 403B without coming into contact with the peripheral electrode 401A. This example is however not limiting, the connection of the central electrode 401B to the conductive track 403B being able, as a variant, to be carried out in any way, for example by means of conductive vias and a conductive track located in a metallization level different from that in which the electrodes 401A and 401B and the conductive tracks 403A and 403B are formed.

[0056] In the illustrated example, the PMUT transducer 100 further comprises conductive vias 405A and 405B extending vertically through the entire thickness of the piezoelectric material layer 301. In this example, the conductive track 203A is connected to the conductive track 403A by the conductive via 405A, and the conductive track 203B is connected to the conductive track 403B by the conductive via 405A. The electrode 201A is thus connected to the electrode 401A via conductive tracks 203A and 403A and conductive via 405A. Similarly, electrode 201B is connected to electrode 401B via conductive tracks 203B and 403B and conductive via 405B.

[0057] In the example shown, the vias 405A and 405B are located directly above the non-hollowed out peripheral region of the layer 103, i.e. offset from the vertical of the cavity 101. This advantageously makes it possible to avoid or limit the influence of the vias 405A and 405B on the vibrations of the flexible membrane 107.

[0058] For example, at least one of the electrodes 203A, 403A of the PMUT transducer 100, for example the electrode 203A, is intended to be brought to a first potential V A , for example a reference potential, for example ground. Similarly, at least one of the electrodes 203B, 403B, for example electrode 203B, is for example intended to be brought to a second potential V B, different from the first potential, for example an excitation potential. Thus, the electrode 401A is subjected to a potential different from that to which the electrode 201B located opposite is subjected, and the electrode 401B is subjected to a potential different from that to which the electrode 201A located opposite is subjected.

[0059] An advantage of the PMUT transducer 100 lies in the fact that the electrodes 201A, 201B, 401A and 401B make it possible to apply, to the layer of piezoelectric material 301, greater deformations than those which would be obtained, for example, in a PMUT transducer similar to the PMUT transducer 100 but comprising only two electrodes, for example the electrodes 201A and 401B, arranged on either side of the layer 301. The electrodes 201A, 201B, 401A and 401B make it possible, for example, more precisely to apply, in a central region and in a peripheral region of the layer 301 of piezoelectric material, respectively, fields electrical of opposite signs. This causes, during emission phases of the PMUT transducer 100, deformations of the flexible membrane 107 greater than the deformations to which flexible membranes of existing PMUT transducers are subjected. Furthermore, another advantage of the PMUT transducer 100 lies in the fact that a single excitation voltage is used to control the electrodes 201A, 201B, 401A and 401B. This makes it possible, compared to existing PMUT transducers comprising networks of electrodes arranged on either side of the layer of piezoelectric material and controlled by at least two excitation voltages, to reduce the cost and complexity of production and control.

[0060] Furthermore, an advantage of the PMUT 100 transducer lies in the fact that it allows, during reception phases, to produce, between the electrodes 203A and 203B or between the electrodes 403A and 403B, voltages higher than those produced by existing PMUT transducers. The PMUT 100 transducer thus has, for example, a sensitivity higher than that of existing PMUT transducers.

[0061] Figure 5A and Figure 5B are respectively top and sectional views along plane BB of Figure 5A, schematic and partial, illustrating a structure obtained at the end of a step of another method of manufacturing a PMUT 500 transducer according to one embodiment.

[0062] The structure of Figures 5A and 5B includes elements in common with the structure of Figures 2A and 2B. These common elements will not be detailed again below. The structure of Figures 5A and 5B differs from the structure of Figures 2A and 2B in that, in the structure of Figures 5A and 5B, the electrodes 201A and 201B are respectively connected to the conductive tracks 203A and 203B, located on either side of the cavity 101, by conductive tracks substantially orthogonal to the conductive tracks 203A and 203B.

[0063] Figure 6A and Figure 6B are respectively top and sectional views along plane BB of Figure 6A, schematic and partial, illustrating a structure obtained at the end of a subsequent step of the manufacturing process of the PMUT 500 transducer.

[0064] During this step, the layer of piezoelectric material 301 is deposited on the side of the upper face of the structure of FIGS. 5A and 5B, in a manner similar to that explained previously in relation to FIGS. 3A and 3B.

[0065] Furthermore, during this step, the electrodes 401A and 401B and the conductive tracks 403A and 403B are formed on and in contact with the face of the piezoelectric material layer 301 opposite the electrodes 201A and 201B and the conductive tracks 203A and 203B (the upper face of the layer 301, in the orientation of FIG. 6B). In the example shown, the electrodes 401A and 401B are respectively connected to the electrodes 201A and 201B by conductive vias 605A and 605B. In the illustrated example, the conductive vias 605A and 605B extend vertically through the entire thickness of the piezoelectric material layer 301, directly above the cavity 101. Alternatively, the conductive tracks 403A and 403B, or the conductive tracks 203A and 203B, may be omitted, for example in a manner analogous to what was described above for the PMUT transducer 100.

[0066] In the example shown, the electrodes 401A and 401B are respectively connected to the conductive tracks 403A and 403B, located on either side of the cavity 101, by conductive tracks substantially orthogonal to conductive tracks 403A and 403B.

[0067] The PMUT 500 transducer has the same or similar advantages as the PMUT 100 transducer.

[0068] Figure 7 is a schematic and partial sectional view illustrating a structure obtained at the end of a manufacturing method of a PMUT 700 transducer according to one embodiment.

[0069] The transducer 700 of FIG. 7 comprises elements in common with the transducer 100 of FIGS. 4A and 4B. These common elements will not be detailed again below. In top view, the PMUT transducer 700 has, for example, a structure similar or identical to that illustrated in FIG. 4A for the PMUT transducer 100.

[0070] The PMUT transducer 700 of Figure 7 differs from the PMUT transducer 100 of Figures 4A and 4B mainly in that the cavity 101 of the PMUT transducer 700 is formed in the support substrate 105. In the illustrated example, the cavity 101 extends vertically over the entire thickness of the support substrate 105. Furthermore, in the shown example, the PMUT transducer 700 is devoid of the rigid support layer 103, the flexible membrane 107 comprising a central region located directly above the cavity 101 and a peripheral region, surrounding the central region, arranged on and in contact with the upper face of the support substrate 105. Although this has not been detailed in Figure 7, the flexible membrane 107 may have a single-layer or multi-layer structure, for example a two-layer structure comprising a layer of silicon dioxide coated with a layer of silicon.

[0071] In the example shown, the cavity 101 opens onto the lower face of the support substrate 105, the cavity 101 not being, in the case of the PMUT 700 transducer, blocked unlike the cavities 101 of the PMUT transducers 100 and 500.

[0072] For example, the layer or stack of layers intended to form the flexible membrane 107 is first deposited on the upper face of the support substrate 105. The electrodes 201A and 201B and the conductive tracks 203A and 203B are for example then formed on the side of the upper face of the flexible membrane 107, for example as explained previously in relation to FIGS. 2A and 2B. Subsequent steps of depositing the layer 301 of piezoelectric material and of forming the electrodes 401A and 401B and the conductive tracks 403A and 403B can then be implemented, for example as explained previously in relation to FIGS. 3A, 3B, 4A and 4B. Finally, the cavity 101 is for example formed in the support substrate 105.

[0073] The PMUT 700 transducer has the same or similar advantages as the PMUT 100 and 500 transducers.

[0074] Various embodiments and variations have been described. Those skilled in the art will understand that certain features of these various embodiments and variations could be combined, and other variations will occur to those skilled in the art. In particular, although examples in which electrodes 201A and 401B have substantially a disc shape and in which electrodes 201B and 401A have substantially a circular crown shape surrounding the disc formed by electrode 201A or 401B, respectively, have been described above, the embodiments are not limited to this example but apply more generally to any type of structure comprising: - at least first and second interposed electrodes between the flexible membrane 107 and the piezoelectric material layer 301; and - at least third and fourth electrodes arranged on one side of the layer 301 opposite the flexible membrane 107, and located respectively opposite the first and second electrodes, the first and second electrodes being connected respectively to the fourth and third electrodes.

[0075] Thus, the embodiments are not limited to the case where the PMUT transducer 100, 500 or 700 comprises exactly two electrodes 201A and 201B interposed between the flexible membrane 107 and the layer of piezoelectric material 301, and exactly two electrodes 401A and 401B arranged on one side of the layer 301 opposite the flexible membrane 107, the electrodes 401A and 401B being located respectively directly above the electrodes 201B and 201A. More generally, the PMUT transducer 100, 500 or 700 may comprise an integer number N, greater than or equal to two, of pairs of electrodes comprising for example first and second electrodes, the first and second electrodes of the same pair being respectively located on either side of the layer 301, each first electrode of a pair being located directly above a second electrode forming part of another pair.In other words, the PMUT transducer 100, 500 or 700 may comprise a first group of N / 2 interconnected electrodes and a second group of N / 2 interconnected electrodes, isolated from the electrodes of the first group, the electrodes of the first and second groups being furthermore arranged, alternately, on either side of the layer 301 of piezoelectric material. In a case where the number N is strictly greater than 2, this makes it possible in particular to increase the deformation of the flexible membrane 107 for resonance modes of a higher order than the resonance mode excited in a case where the number N is equal to 2.

[0076] Furthermore, the embodiments described are not limited to the geometry set out in relation to figures 1A and 1B, but apply more generally to any type of PMUT cell structure, for example PMUT cells whose cavity 101 has, in top view, a hexagonal, oval, rectangular, square, etc. shape.

[0077] Furthermore, although a single PMUT 100, 500 or 700 transducer has been shown in the figures, a large number of identical or similar transducers, for example arranged in a matrix according to rows and columns, can in practice be produced simultaneously and integrated monolithically in and on the same chip.

[0078] Furthermore, the person skilled in the art is capable, from the indications of the present description, of providing a PMUT transducer comprising electrodes and conductive tracks similar or identical to those of the PMUT transducer 500 of FIGS. 6A and 6B and whose cavity 101 is located in the support substrate 105, for example in a manner similar to the PMUT transducer 700 of FIG. 7.

[0079] Finally, the practical implementation of the described embodiments and variants is within the reach of the person skilled in the art from the functional indications given above. In particular, the described embodiments are not limited to the examples of materials and / or dimensions mentioned in the description.

[0080] Furthermore, although this has not been detailed above, conductive vias passing through the entire thickness of the substrate 105 may in practice be provided to connect the conductive tracks 203A and 203B, or the electrodes 201A and 201B, for example in a case where the conductive tracks 203A and 203B are omitted, to contact recovery elements located for example on the side of a face of the substrate 105 opposite the cavity 101.

Claims

CLAIMS 1. PMUT transducer (100; 500; 700) comprising: - a flexible membrane (107) suspended above a cavity (101); - a layer of piezoelectric material (301) located on one face of the flexible membrane opposite the cavity; - first and second electrodes (201A, 201B) interposed between the flexible membrane and the layer of said piezoelectric material; and - third and fourth electrodes (401B, 401A) arranged on one side of the layer of said piezoelectric material opposite the flexible membrane, and located respectively opposite the first and second electrodes (201A, 201B), in which the first and second electrodes (201A, 201B) are connected respectively to the fourth and third electrodes (401A, 401B).

2. Transducer (100; 500; 700) according to claim 1, in which: - the first and fourth electrodes (201A, 401A) are intended to be brought to the same first potential; and - the second and third electrodes (201B, 401B) are intended to be brought to the same second potential, different from the first potential.

3. Transducer (100; 500; 700) according to claim 1 or 2, wherein the second and fourth electrodes (201B, 401A) respectively surround the first and third electrodes (201A, 401B).

4. Transducer (100; 500; 700) according to claim 3, wherein the second and fourth electrodes (201B, 401A) each have, in top view, an annular shape.

5. Transducer (100; 500; 700) according to claim 4, in which the second and fourth electrodes (201B, 401A) each have, in top view, a substantially circular crown shape.

6. Transducer (100; 500; 700) according to claim 5, in which the first and third electrodes (201A, 401B) each have, in top view, a disc shape.

7. Transducer (100; 500; 700) according to any one of claims 1 to 6, wherein the first and second electrodes (201A, 201B) are connected respectively to the fourth and third electrodes (401A, 401B) by first and second conductive vias (405A, 405B; 605A, 605B).

8. Transducer (500; 700) according to claim 7, in which the first and second conductive vias (605A, 605B) are located directly above the cavity (101).

9. Transducer (100; 700) according to claim 7, in which the first and second conductive vias (405A, 405B) are offset out of line with the cavity (101).

10. Transducer (100; 500; 700) according to any one of claims 1 to 9, in which: - the first and second electrodes (201A, 201B) are located on and in contact with a face of the flexible membrane (107) opposite the cavity (101); - the layer of said piezoelectric material coats the first and second electrodes; and - the third and fourth electrodes (401A, 401B) are located on and in contact with one face of the layer in said piezoelectric material opposite the flexible membrane.

11. Transducer (100; 500; 700) according to any one of claims 1 to 10, further comprising: - first and second conductive tracks (203A, 203B) coplanar with the first and second electrodes (201A, 201B); and - third and fourth conductive tracks (403B, 403A) coplanar with the third and fourth electrodes (401B, 401A).

12. The transducer (700) of any one of claims 1 to 11, further comprising a support substrate (105) in and on which the transducer is formed, the cavity (101) extending throughout the thickness of the support substrate.

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