PMUT Transducer

Abstract

PMUT Transducer This description relates to a PMUT transducer (100) 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) disposed 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), wherein the first and second electrodes (201A, 201B) are connected respectively to the fourth and third electrodes (401A, 401B). Figure for the abbreviation: Fig. 4B

Description

Title of the invention: PMUT transducer technical field

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

[0002] Conventionally, a PMUT transducer comprises a flexible membrane suspended above 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 piezoelectric material layer opposite the first electrode. When a suitable excitation voltage is applied between the transducer electrodes, 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 transducer electrodes.

[0003] A PMUT transducer is conventionally coupled to an electronic control circuit configured to, during an emission phase, apply 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, read 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 electrode arrays arranged on either side of the piezoelectric material layer have been proposed. Such transducers typically include a first electrode located below 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 voltage—for example, a voltage with the opposite sign to 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 manufacture and control.This stems in particular from the fact that these trans. PMUT inductors require the implementation of two separate power supplies to allow the application of two excitation voltages, for example opposite, 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] To this end, one embodiment provides a PMUT transducer comprising: - a flexible membrane suspended above a cavity; - a layer of a piezoelectric material located on one face of the flexible membrane opposite the cavity; - the first and second electrodes interposed between the flexible membrane and the layer of said piezoelectric material; and - the 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 initial 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 surround the first and third electrodes respectively.

[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 connected respectively to the fourth and third electrodes by first and second conductive vias.

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

[0014] According to one embodiment, the first and second conducting vias are offset out of the vertical line of 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 covers the first and second electrodes; and - the third and fourth electrodes are located on and in contact with one face of the layer of said piezoelectric material opposite to the flexible membrane.

[0016] According to one embodiment, the transducer further comprises: - the first and second coplanar conductive tracks to the first and second electrodes; and - of the 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 features and advantages, as well as others, will be described in detail in the following description of particular embodiments, given by way of non-limiting example, in relation to the accompanying figures, among which:

[0019] [Fig.1A] and [Fig.1B] are schematic and partial top and cross-sectional views along plane BB of [Fig.1A], respectively, illustrating a structure obtained at the end of a step in a manufacturing process of a PMUT transducer according to an embodiment;

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

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

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

[0023] [Fig.5A] and [Fig.5B] are schematic and partial top and cross-sectional views along plane BB of [Fig.5A], respectively, illustrating a structure obtained at the end of a step in another manufacturing process of a PMUT transducer according to an embodiment;

[0024] [Fig. 6A] and [Fig. 6B] are top and cross-sectional views respectively along the

[0025] [Fig. 6A] is a schematic and partial cross-sectional view, illustrating a structure obtained at the end of a subsequent step in the manufacturing process of the PMUT transducer; and

[0025] [Fig. 7] is a schematic and partial cross-sectional view, illustrating a structure obtained at the end of a manufacturing process of a PMUT transducer according to an embodiment. Description of the implementation methods

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

[0027] For the sake of clarity, only the steps and elements necessary 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, as the described embodiments are compatible with the usual applications of ultrasonic transducers, notably in ultrasonic imaging devices and / or biometric devices. Furthermore, the transducer control circuits have not been detailed, as the described embodiments are compatible with all or most known PMUT transducer control circuits, possibly with adaptations that are understandable to a person skilled in the art upon reading this description.

[0028] Unless otherwise specified, when referring to two elements connected together, this means directly connected without intermediate elements other than conductors, and when referring to two elements coupled together, this means that these two elements can be connected or linked through one or more other elements.

[0029] In the following description, when reference is made to absolute position qualifiers, such as the terms "front", "back", "top", "bottom", "left", "right", etc., or relative position qualifiers, such as the terms "above", "below", "superior", "inferior", 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 "approximately", "about", "substantially", and "in the order of" mean within 10%, preferably within 5%.

[0031] Fig.1A and Fig.1B are schematic and partial top and cross-sectional views respectively along plane BB of Fig.1A, illustrating a structure obtained at the end of a step in a manufacturing process of a PMUT 100 transducer according to an 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. Cavity 101 corresponds to a localized opening or recess formed in layer 103. In this example, cavity 101 extends vertically through the entire thickness of layer 103. Alternatively, cavity 101 may extend through only a portion of the thickness of layer 103. The lateral walls of cavity 101 are formed by an unrecessed peripheral region of layer 103.

[0033] In the example illustrated in [Fig. 1A], the cavity 101 has, in top view, a substantially circular shape. This example is not, however, limiting. As an alternative, 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 supported, by its lower surface, by the upper surface of the non-hollowed peripheral region of the layer 103. In the central part of the transducer, the lower surface of the flexible membrane 107 is separated from the upper surface of the substrate 105 by the cavity 101. The flexible membrane 107 is, for example, made of the same material as the layer 103. Alternatively, the membrane 107 may be made of a different material than that of the layer 103.

[0035] By way of example, the cavity 101 is formed in the layer 103 before the layer 103 is transferred to the substrate 105, for example by gluing to the side of the upper face of the substrate 105.

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

[0037] During this step, electrodes 201A and 201B are formed on the side of one face of the flexible membrane 107 opposite the cavity 101. The electrodes 201A and 201B are disjoint, i.e., electrically isolated from each other. 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, electrode 201A is located in the central part of the PMUT 100 transducer and, in top view, has a senile-shaped perimeter possibly circular. This example is not exhaustive, however; electrode 201A may, as an alternative, have a perimeter of any shape. Electrode 201A, for example, forms the lower central electrode of the PMUT 100 transducer.

[0039] Furthermore, in this example, electrode 201B has an annular shape surrounding electrode 201A. In the example shown, electrode 201B has, in top view, a substantially circular ring shape. This example is not limiting, however; electrode 201B may, alternatively, have any shape surrounding electrode 201A, for example, an annular shape other than a circular ring, for example, a substantially rectangular or square ring. Electrode 201B constitutes, for example, a lower peripheral electrode of the PMUT 100 transducer.

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

[0041] In the illustrated example, the electrodes 201A and 201B are respectively connected to conductive tracks 203A and 203B arranged on either side of the cavity 101, at the periphery of the transducer, directly above the non-hollowed 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 analogous or identical to the transducer 100.

[0042] By way of example, the electrodes 201A and 201B and the conductive tracks 203A and 203B are formed by a step of depositing a metallic layer coating the layer 103, followed by photolithography and then etching of the metallic 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 more specifically has a truncated annular shape, or open ring shape, allowing the central electrode 201A to be connected to the conductive track 203A without coming into contact with the peripheral electrode 201B. This example is not limiting, however, as the connection of the central electrode 201A to the conductive track 203A can, as an alternative, be made 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] Fig. 3A and Fig. 3B are schematic and partial top and cross-sectional views along plane BB of Fig. 3A, respectively, illustrating a structure obtained at the end of a later step in the manufacturing process of the PMUT 100 transducer.

[0045] During this step, a layer 301 of a piezoelectric material is deposited on the upper surface of the structure previously described in relation to Figures 2A and 2B. In the example shown, the piezoelectric material layer 301 covers 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 not detailed in Figures 3A and 3B, a dielectric filler layer can be deposited on the upper surface of the structure prior to the deposition of the piezoelectric material layer 301, for example, so as to fill all the gaps extending laterally between the electrodes 201A and 201B and the conductive tracks 203A and 203B. In this case, the dielectric filler layer is flush with the upper surface 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 surface prior to the deposition of the piezoelectric material layer 301, and avoids the presence of air or void areas 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.As an alternative, the dielectric filling layer is made of a piezoelectric material similar or identical to that of layer 301.

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

[0048] During this step, electrodes 401A and 401B are formed on the side of a face of the layer of piezoelectric material 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, electrodes 401A and 401B are disjoint, i.e., electrically isolated from each other. In the illustrated example, 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 layer 301, in the orientation of [Fig. 4B]).

[0050] In the example shown, electrode 401B is located in the central part of the PMUT 100 transducer and, viewed from above, has a substantially circular circumference. This example is not limiting, however; electrode 401B may, alternatively, have a circumference of any shape. Electrode 401B constitutes, for example, an upper central electrode of the PMUT transducer. 100. In the example shown, electrode 401B is located opposite electrode 201A, with electrodes 401B and 201A being, for example, substantially concentric. Furthermore, electrode 401B has, for example, a shape and dimensions that are substantially identical, within manufacturing variations, to those of electrode 201A.

[0051] Furthermore, in this example, electrode 401A has an annular shape surrounding electrode 401B. In the example shown, electrode 401A has, in top view, a substantially circular ring shape. This example is not limiting, however; electrode 401A may, alternatively, have any shape surrounding electrode 401B, for example, a rectangular, hexagonal, square, oval, etc. shape. Electrode 401A constitutes, for example, an upper peripheral electrode of the PMUT 100 transducer. In the example shown, electrode 401A is located opposite electrode 201B, electrodes 401A and 201B being, for example, substantially concentric. Moreover, electrode 401A has, for example, substantially identical dimensions and shape, within manufacturing variations, to those of electrode 201B.

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

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

[0054] By way of example, electrodes 401A and 401B and conductive tracks 403A and 403B are formed by a step of depositing a metallic layer coating the piezoelectric material layer 301, followed by photolithography and then etching of the metallic 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 more specifically has a truncated annular shape, or open ring shape, allowing the central electrode 401B to be connected to the conductive track 403B without coming into contact with the peripheral electrode 401A. This example is not limiting, however, as the connection of the central electrode 401B to the conductive track 403B can, as an alternative, be made in any way, for example by means of conductive vias and a conductive track located in a different level of metallization than that in which the electrodes 401A and 401B and the conductive tracks 403A and 403B are formed.

[0056] In the illustrated example, the PMUT 100 transducer further comprises conductive vias 405A and 405B extending vertically through the entire thickness of the piezoelectric material layer 301. In this example, conductive track 203A is connected to conductive track 403A by conductive via 405A, and conductive track 203B is connected to conductive track 403B by conductive via 405A. Electrode 201A is thus connected to 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 peripheral region of the layer 103, i.e., offset out of the vertical position of the cavity 101. This advantageously avoids or limits the influence of the vias 405A and 405B on the vibrations of the flexible membrane 107.

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

[0059] One advantage of the PMUT 100 transducer lies in the fact that the electrodes 201A, 201B, 401A and 401B allow greater deformations to be applied to the piezoelectric material layer 301 than would be obtained, for example, in a PMUT transducer similar to the PMUT 100 but comprising only two electrodes, for example electrodes 201A and 401B, are positioned on either side of layer 301. Electrodes 201A, 201B, 401A, and 401B allow, for example, the application of electric fields of opposite signs in a central region and a peripheral region of the piezoelectric material layer 301, respectively. This causes, during the emission phases of the PMUT 100 transducer, deformations of the flexible membrane 107 that are greater than those experienced by flexible membranes in existing PMUT transducers. Furthermore, another advantage of the PMUT 100 transducer is that a single excitation voltage is used to drive electrodes 201A, 201B, 401A, and 401B.Compared to existing PMUT transducers comprising electrode arrays arranged on either side of the piezoelectric material layer and controlled by at least two excitation voltages, this reduces the cost and complexity of implementation and control.

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

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

[0062] The structure of Figures 5A and 5B includes elements common to 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] Fig. 6A and Fig. 6B are schematic and partial top and cross-sectional views along plane BB of Fig. 6A, respectively, illustrating a structure obtained at the end of a later step in the manufacturing process of the PMUT 500 transducer.

[0064] During this step, the layer of piezoelectric material 301 is deposited on the upper face side of the structure of Figures 5A and 5B, in a manner analogous to what has been previously described in relation to Figures 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 layer 301, in the orientation of [Fig. 6B]). In the example shown, electrodes 401A and 401B are connected to electrodes 201A and 201B, respectively, by conductive vias 605A and 605B. In the illustrated example, conductive vias 605A and 605B extend vertically through the entire thickness of the piezoelectric material layer 301, directly above cavity 101. Alternatively, conductive tracks 403A and 403B, or conductive tracks 203A and 203B, may be omitted, for example, in a manner analogous to that described above for the PMUT 100 transducer.

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

[0067] The PMUT 500 transducer has advantages identical or similar to those of the PMUT 100 transducer.

[0068] Fig. 7 is a schematic and partial cross-sectional view illustrating a structure obtained at the end of a manufacturing process of a PMUT 700 transducer according to an embodiment.

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

[0070] The PMUT 700 transducer of [Fig. 7] differs from the PMUT 100 transducer of Figures 4A and 4B primarily in that the cavity 101 of the PMUT 700 transducer is formed within the support substrate 105. In the illustrated example, the cavity 101 extends vertically through the entire thickness of the support substrate 105. Furthermore, in the example shown, the PMUT 700 transducer lacks 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, disposed on and in contact with the upper surface of the support substrate 105. Although not detailed in [Fig. 7], the flexible membrane 107 may have a single-layer or multi-layer structure, for example, a bilayer structure comprising a silicon dioxide layer coated with a silicon layer.

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

[0072] By way of 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 then formed, for example, on the upper surface of the flexible membrane 107, for example, as previously described in relation to Figures 2A and 2B. Subsequent steps of depositing the piezoelectric material layer 301 and forming the electrodes 401A and 401B and the conductive tracks 403A and 403B can then be carried out, for example, as previously described in relation to Figures 3A, 3B, 4A, and 4B. Finally, the cavity 101 is formed, for example, in the support substrate 105.

[0073] The PMUT 700 transducer has advantages identical or similar to those of 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 become apparent to those skilled in the art. In particular, although examples in which electrodes 201A and 401B are substantially disc-shaped and in which electrodes 201B and 401A are substantially circular in 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 the first and second electrodes interposed between the flexible membrane 107 and the piezoelectric material layer 301; and - at least the third and fourth electrodes arranged on one side of 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 piezoelectric material layer 301, and exactly two electrodes 401A and 401B disposed on one side of the layer 301 opposite the flexible membrane 107, the electrodes 401A and 401B being located respectively in line with the electrodes 201B and 201A. More generally, the PMUT 100, 500, or 700 transducer can comprise an integer number N, greater than or equal to two, of electrode pairs, including, for example, first and second electrodes, the first and second electrodes of the same pair being located respectively on either side of layer 301, each first electrode of a pair being located directly above a second electrode belonging to another pair. In other words, the PMUT 100, 500, or 700 transducer can 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 arranged alternately on either side of the piezoelectric material layer 301. In a case where the number N is strictly greater than 2, this notably allows for an increase in the deformation of the flexible membrane 107 for resonance modes of a higher order than the excited resonance mode in a case where the number N is equal to 2.

[0076] Moreover, the embodiments described are not limited to the geometry shown in relation to figures IA and IB, 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 made simultaneously and integrated monolithically in and on the same chip.

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

[0079] Finally, the practical implementation of the described embodiments and variants is within the reach of a person skilled in the art, based on the functional specifications 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 not detailed above, conductive vias through the entire thickness of the substrate 105 can 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 re-establishment elements located for example on the side of a face of the substrate 105 opposite the cavity 101.

Claims

Demands

1. PMUT transducer (100; 500; 700) comprising: - a flexible membrane (107) suspended above a cavity (101); - a layer of a 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) disposed 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), wherein 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, wherein: - 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 (20IB, 401 A) surround respectively the first and third electrodes (201A, 401B).

4. Transducer (100; 500; 700) according to claim 3, wherein the second and fourth electrodes (20IB, 401 A) each have, in top view, an annular shape.

5. Transducer (100; 500; 700) according to claim 4, wherein the second and fourth electrodes (20IB, 401 A) each have, in top view, a substantially circular crown shape.

6. Transducer (100; 500; 700) according to claim 5, wherein 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, wherein the first and second conductive vias (605A, 605B) are located directly above the cavity (101).

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

10. Transducer (100; 500; 700) according to any one of claims 1 to 9, wherein: - 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 covers the first and second electrodes; and - the third and fourth electrodes (401A, 401B) are located on and in contact with a face of the layer of 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 to the first and second electrodes (201A, 201B); and - third and fourth conductive tracks (403B, 403A) coplanar to the third and fourth electrodes (401B, 401A).

12. Transducer (700) according to 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 over the entire thickness of the support substrate.

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