Micromachined ultrasonic transducer device with high quality factor

Abstract

Embodiments of the present disclosure relate to a micromachined ultrasonic transducer device with a high quality factor. A micromachined ultrasonic transducer is disclosed in which a die comprising a semiconductor material accommodates at least one ultrasonic unit. Each ultrasound unit includes a piezoelectric structure, a cavity, and a membrane region that are vertically aligned with each other. The cavity extends inside the die and defines a membrane region downward. A piezoelectric structure is disposed on the membrane region and has at least one annular piezoelectric region. The micromachining ultrasonic transducer is configured to operate about a second axisymmetric vibration mode.

Description

Technical Field

[0001] The present disclosure relates to micromachined ultrasonic transducer devices having a high quality factor. Background Art

[0002] As is known, an ultrasonic transducer is a device capable of transmitting and receiving sound waves (particularly ultrasound with a frequency comprised between 20 kHz and 100 MHz) in a fluid (liquid or gas) and / or solid propagation medium by converting electromechanical energy, acoustic energy or optical energy.

[0003] In particular, silicon micromachined ultrasonic transducers (MUTs) have very small dimensions and are manufactured using silicon bulk micromachining and / or surface micromachining processes.

[0004] MUT devices include a membrane that can vibrate both when electrically excited for generating acoustic waves that are transmitted to an external medium and when the membrane receives the acoustic waves and generates corresponding electrical signals. Thus, they can form a transmitter-receiver system.

[0005] In particular, in the MUT device, the vibration operation of the membrane utilizes the piezoelectric effect (piezoelectric MUT, PMUT) or the electrostatic effect (capacitive MUT, CMUT).

[0006] The electro-acoustic conversion efficiency of transmitted / received energy, the frequency response gain and the bandwidth are the characteristic parameters of the MUT. They depend on both factors specific to the MUT (such as the geometry and material of the transducer, which determine the mechanical impedance of the MUT) and factors specific to the acoustic wave propagation medium (such as the density of the propagation medium and the speed of sound transmitted thereby, which determine its acoustic impedance).

[0007] Micromachined ultrasonic transducers have been proposed for different applications, such as distance measurement and imaging of objects and the environment, based on pulse-echo detection, i.e. on the transmission of sound waves (e.g. ultrasound pulses) and on the reception of ultrasound echoes generated by reflection and propagation of the sound waves in the environment.

[0008] Recently, the use of MUT transducers has been proposed to wirelessly transfer energy to microsystems operating in non-direct contact environments, such as implantable biomedical devices, or other devices that are arranged in air (or in inaccessible liquid media) and cannot be powered by batteries with large size.

[0009] In particular, implantable biomedical devices use batteries that have small dimensions and therefore have a limited duration and need to be replaced or recharged regularly, which presents difficulties in implanted systems or in any case in non-direct contact systems.

[0010] To overcome this problem, due to the small size of MUT devices, it has been proposed to use micromachined ultrasound systems to transfer power from an external transducer element (thus operating as a transmitter) to an internal transducer element associated with the implanted device (thus operating as a receiver).

[0011] For example, in the case of a PMUT, both the implantable transducer element and the transmitter include a piezoelectric structure covering a vibrating membrane, thereby forming a PMUT cell, or a pair of electrodes, one of which is in contact with the membrane, spaced apart from each other, thereby forming a CMUT cell.

[0012] These cells may be arranged side by side, forming a matrix of PMUT or CMUT cells.

[0013] When used in a device implantable in the human body, the ultrasound transducer may be coated with a biocompatible material.

[0014] For example, Figure 1 The structure of a PMUT device 1 that can be used as a transmitter in an energy transfer system is shown. However, the same structure can be used in case the PMUT device 1 operates as a receiver.

[0015] The PMUT device 1 comprises a substrate, e.g. an insulating material such as FR4, carrying a die 2 and a printed circuit 3. Here, the printed circuit 3 has a through opening 4, and the die 2 is arranged inside the through opening 4, at a distance from the printed circuit 3, and connected to the printed circuit 3 by a wire 5, which is covered by an insulating region 6 of e.g. a resin such as a globtop, and the wire 5 also fills the through opening 4 between the die 2 and the printed circuit 3.

[0016] The die 2 comprising a semiconductor material (typically silicon) has a plurality of cavities 10, typically cylindrical, extending thereover a corresponding plurality of membranes 11, formed by the die 2 and thus typically of silicon (non-piezoelectric silicon) or a dielectric material used in the semiconductor industry.

[0017] Above each membrane 11, a piezoelectric structure 12 is formed, shown schematically, and typically formed of pairs of electrodes separated by a piezoelectric layer. The piezoelectric layer can be any suitable material, such as lead zirconate titanate PZT, aluminum nitride (AlN) and scandium-doped aluminum nitride (AlScN) deposited via PVD (physical vapor deposition) or as a sol-gel.

[0018] An elastic region 13 , for example silicone or polyurethane, covers the upper surface of the die 2 at the piezoelectric structure 12 , as well as the insulating region 6 and the printed circuit 3 .

[0019] The elastic region 13 embeds the electrical structures (the piezoelectric structure 12 as well as the contacts on the die and the contacts on the printed circuit 3, not shown), protecting them. Furthermore, it has an impedance similar to that of water and human tissue, ensuring good coupling.

[0020] In use, an alternating current signal is applied to the piezoelectric structure 12 at a suitable frequency, causing the membrane 11 to vibrate at that frequency and ultrasonic waves (at Figure 1 The ultrasonic wave is generated by Figure 1 The signal is transmitted through a medium (such as water or human tissue) indicated by 17.

[0021] Generally speaking, micromachining ultrasonic systems vibrate in bending modes and in broadband (see Figure 2 ) operate at frequencies in the range of 1 MHz to 5 MHz, where they resonate in air with a high mechanical quality factor (Q).

[0022] However, when operating in a liquid propagation medium or a solid medium with an impedance similar to water (e.g., human tissue or biocompatible soft materials such as silicone or polyurethane), Figure 1 Micromachined ultrasonic systems of the type shown have a low mechanical impedance; therefore, under these conditions, the mechanical quality factor Q is significantly reduced due to the damping effect of the acoustic loading of the medium.

[0023] Furthermore, since the electromechanical coupling factor of the MUT transducer (i.e., the ratio between the energy actually converted into mechanical energy and the electrical energy obtained) is relatively low, and most of the energy is used to charge and discharge the transducer capacitance and is not transferred, the electrical impedance is mainly capacitive; therefore, the phase angle is large and close to -90°, reducing efficiency.

[0024] Therefore, in order to maximize power transfer and improve both transmit (TX) and receive (RX) conversion efficiency, electrical matching networks using inductors are typically used.

[0025] However, there are several problems with using inductors for electrical matching:

[0026] Inductors are large and heavy, reducing the possibility of miniaturizing the system.

[0027] The efficiency is limited by the inductor of the MUT and / or the equivalent series resistance of the electrical interconnects. Summary of the invention

[0028] The present disclosure is directed to overcoming the problems of the prior art as discussed above.

[0029] According to the present disclosure, a micro-machined ultrasonic transducer device and a manufacturing process thereof are provided.

[0030] For example, at least one embodiment of the micromachined ultrasonic transducer device of the present disclosure is summarized as including: a tube core including a semiconductor material, and the tube core includes one or more ultrasonic units, wherein each of the one or more ultrasonic units includes a cavity and a vibration structure, the cavity is within the tube core, the vibration structure covers the cavity, is aligned with the cavity, and overlaps with the cavity, wherein the vibration structure includes a ring-shaped vibration element. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] For a better understanding of the present disclosure, some embodiments of the present disclosure will now be described by way of non-limiting examples only, with reference to the accompanying drawings, in which:

[0032] Figure 1 is a cross section of a known micromachined transducer;

[0033] Figure 2 Shows Figure 1 TX sensitivity of micromachined transducers;

[0034] Figure 3 is a simplified cross-section of one embodiment of a piezoelectric micromachined transducer;

[0035] Figure 4 yes Figure 3 A top view of a portion of a micromachined transducer;

[0036] Figure 5 is a simplified cross-section of another embodiment of the present piezoelectric micromachined transducer;

[0037] Figure 6 yes Figure 5 A top view of a portion of a micromachined transducer;

[0038] Figure 7 yes Figure 5 and Figure 6 A simplified perspective view, partially cut away, of a cell of a micromachined transducer during operation;

[0039] Figure 8 is a simplified perspective view, partially cut away, of a unit cell of various embodiments of a micromachined transducer during operation;

[0040] Fig. 9 is a simplified cross-section of another embodiment of the present micromachined transducer;

[0041] Fig.10 yes Fig. 9 A top view of a portion of a micromachined transducer;

[0042] Fig.11 It is available for Figures 3 to 10 Cross section of a multilayer piezoelectric structure of a micromachined transducer;

[0043] Fig.12 Is has Fig.11 The multilayer piezoelectric structure is suitable for Figures 5 to 10 Cross section of a micromachined transducer of the solution;

[0044] Fig.13A are simplified cross-sections of various embodiments of the present micromachined transducer;

[0045] Fig. 13B are simplified cross-sections of various embodiments of the present micromachined transducer;

[0046] FIG. 14A to FIG. 14C It is shown Figure 1 Trends in electrical quantities of micromachined transducers and Figure 3 and Figure 4 Comparison diagram of the trends of electrical quantities of micro-machined transducers;

[0047] FIG. 15A to FIG. 15C It is shown Figure 1 Trends in electrical quantities of micromachined transducers and Figure 5 and Figure 6 Comparison diagram of the trends of electrical quantities of micro-machined transducers;

[0048] FIG. 16A to FIG. 16C It is shown Figure 1 Trends in electrical quantities of micromachined transducers and Fig. 9 and Fig.10 Comparative graph of trends of electrical quantities of a transducer in which the piezoelectric region is formed using the sol-gel technique;

[0049] FIG. 17A to FIG. 17C It is shown Figure 1 Trends in electrical quantities of micromachined transducers and Fig. 9 and Fig.10 Comparative diagram of trends of electrical quantities of a transducer in which the piezoelectric region is formed by PVD deposition;

[0050] 18A to 18E shows a cross section of a wafer for micromachining a piezoelectric ultrasonic transducer in successive manufacturing steps; and

[0051] FIG. 19A to FIG. 19F A cross section of a wafer for micromachining a capacitive ultrasound transducer is shown in successive manufacturing steps. DETAILED DESCRIPTION

[0052] The following description relates to the arrangement shown; therefore, expressions such as "above", "below", "upper", "lower", "right", "left" and the like relate to the drawings and should not be interpreted in a limiting manner. Furthermore, the vertically aligned indications used refer to common practice in the semiconductor field.

[0053] Figure 3 and Figure 4 A PMUT device 20 is shown which may be used as both a transmitter as well as a receiver of an energy transfer system.

[0054] The PMUT device 20 includes a die 21 and a support structure 22 .

[0055] The support structure 22 includes a support element 23 , a printed circuit board 26 and a soft layer 28 .

[0056] The printed circuit board 26 is formed of an insulating material such as FR4 and is provided with a through opening 24 accommodating the die 21 at a distance from the printed circuit board 26. The through opening 24 is defined by at least one through opening side wall of the printed circuit board 26. The at least one through opening side wall is spaced apart from a corresponding side wall of the die 21.

[0057] The printed circuit board 26 may form electrical connections (not shown) that are accessible externally (for the PMUT device 20 formed as a transmitter).

[0058] Alternatively, the printed circuit board 26 may house or carry power supply components.

[0059] Furthermore, for a PMUT device 20 formed as a receiver, the printed circuit board 26 may carry an electronic medical device (not shown) intended to be implanted and / or electrical connections for coupling the die 21 to the electronic medical device.

[0060] The printed circuit board 26 and the die 21 are electrically connected via conductive lines 25 and contact pads (not shown).

[0061] The die 21, typically made of silicon, has a first main surface 21A and a second main surface 21B, which is opposite to the first main surface 21A. The first main surface 21A and the second main surface 21B extend parallel to the main extension plane of the PMUT device 20, which is parallel to the plane XY of the Cartesian reference system XYZ.

[0062] A plurality of cavities 29 extend from the second main surface 21B towards the first main surface 21A and delimit downwardly a respective membrane 30 formed by the same die 21. The cavities 29 typically have a cylindrical shape, the axis of which is parallel to the vertical axis Z of the Cartesian reference system XYZ.

[0063] A respective piezoelectric structure 31 extends above each membrane 30. Each membrane 30 forms a vibration structure 27 with the respective piezoelectric structure 31.

[0064] The piezoelectric structure 31 is shown in Figure 3 In the enlarged detail of , and is formed by a stack comprising pairs of electrodes (lower electrode 34 and upper electrode 35), the pairs of electrodes being separated by a piezoelectric region 36.

[0065] Each corresponding cavity of the plurality of cavities 29 overlaps with a corresponding piezoelectric structure 31 of the plurality of piezoelectric structures 31. Each corresponding cavity of the plurality of cavities 29 is defined by a corresponding cavity sidewall of the die 21.

[0066] For example, electrodes 34 and 35 are made of platinum, and piezoelectric region 36 is made of any suitable material such as lead zirconate titanate PZT, aluminum nitride (AlN), and scandium-doped aluminum nitride (AlScN) deposited via PVD (physical vapor deposition) or sol-gel.

[0067] The piezoelectric structure 31 is covered by a passivation layer 37 which is interrupted to connect the electrodes 34, 35 to metal connection lines (a connection line, connection line 38, can be seen, coupled to the upper electrode 35).

[0068] Each membrane 30 has an associated piezoelectric structure 31 and a cavity 29, defining an ultrasound unit or ultrasound pixel 45 of the PMUT device 20; in particular, the PMUT device 20 includes a plurality of ultrasound units 45, such as Figure 4 , a portion of the main surface 21A of the die 21 is shown, and the matrix arrangement of the ultrasound units 45 is highlighted.

[0069] As mentioned before, here the piezoelectric structure 31 , and in particular the piezoelectric region 36 , has a disc shape.

[0070] The piezoelectric region 36 may have a thickness comprised between 1 and 50 μm (eg, 2 μm), and a diameter comprised between 30 and 800 μm (eg, 300 μm).

[0071] The diameter of the cavity 29 (and therefore the membrane 30 ) is larger than the piezoelectric structure 31 , for example 40-50% larger.

[0072] exist Figure 3 In the embodiment, the support element 23 has an upper surface 23A facing the die 21 which is not planar but has a recess 33 facing the same die 21, thereby defining a gap (indicated by the same reference numeral 33) allowing the die 21 to vibrate freely.

[0073] In practice, the support element 23 here forms a lower wall 23B spaced apart from the die 21 and closes the gap 33 with respect to the outside.

[0074] The recess 33 has an area greater than the die 21 (in top view), for example approximately equal to the area of ​​the through opening 24 here, so as to avoid clamping of the die 21 on its second main surface 21B (die unclamped downward).

[0075] Alternatively, the recess 33 may be a through recess.

[0076] The recess 33 may be filled with a soft material, for example the same silicone as the soft layer 28 (see below) or a different, softer silicone, for example a sealing silicone commonly found on the market.

[0077] The support element 23 is made of single crystal silicon, for example, but can be made of any material compatible with the application (in particular, when it operates as a receiver intended to be implanted in human tissue, made of a biocompatible material), thereby having suitable mechanical strength and providing stability for the PMUT device 20.

[0078] A soft layer 28 (electrically insulating layer) covers the first major surface 21B of the die 21 , and the upper surface of the printed circuit board 26 incorporates the wires 25 by adhering to the soft layer 28 and keeps the die 21 suspended above the recess 33 .

[0079] To this end, the soft layer 28 is made of a material that has adhesive properties, such as to hold the die 21 securely over time, flexibility, so as to allow for the unclamped vibration of the membrane 30 during use, and has a good fit with the medium in which it operates (in Figure 3 A specific acoustic impedance (the product of the density and velocity of longitudinal elastic waves (here ultrasound)) that is similar to the acoustic impedance of the layer 40 (schematically represented by layer 40 in FIG. 1 ).

[0080] Possibly, an adhesion promoting layer may be arranged between the soft layer 28 and the die 21 , for example based on silanes such as 3-aminopropyltriethoxysilane (APTES) and 3-glycidoxypropyltrimethoxysilane (GPTMS).

[0081] For example, the soft layer 28 may be an elastic material, such as silicone or polyurethane, having an acoustic impedance close to that of human tissue, thereby ensuring good coupling in the case of applications for implantable medical devices. For example, the soft layer 28 may have a specific acoustic impedance comprised between 1 and 2 MRayl, a specific acoustic impedance comprised between 0.8 and 2 g / cm 3 and an ultrasonic velocity comprised between 1000 and 2000 m / s.

[0082] In use, according to the first axisymmetric vibration mode, the supply of voltage between the electrodes 34, 35 of the piezoelectric structure 31 or the reception of sound waves by the membrane 30 determines the vibration of the membrane 30 by means of a simple alternating movement upwards (towards the soft layer 28) and downwards (towards the inside of the cavity 29), as Figure 3 As shown by the double arrow 50.

[0083] Suspending the die 21 by the soft layer 28 rather than by attaching to the substrate of the die down on the second major surface 21B and / or sides of the die, and eliminating the top package area allows the die to vibrate more freely with greater displacement, thereby improving the quality factor Q.

[0084] Soft layer 28 extends from the through opening sidewalls of printed circuit board 26 to the corresponding sidewalls of die 21. Soft layer 28 extends from printed circuit board 26 to layer 40. Soft layer 28 extends through main surface 21A of die 21. Soft layer 28 embeds conductive line 25. Soft layer 28 extends over recess 33.

[0085] In addition, the presence of air on the back side of the die 21 enables the quality factor Q of the PMUT device 20 to be further improved, achieving better and more efficient energy transfer.

[0086] The die 21 may be formed with a very small thickness, such as 100-200 μm or even as low as 40-50 μm in thickness, to avoid damage and reduce the overall thickness of the PMUT device 20 when used in non-critical environments.

[0087] Figure 5 and Figure 6 A PMUT device 120 is shown that may be used as both a transmitter and a receiver of an energy transfer system.

[0088] Figure 5 and Figure 6 The PMUT device 120 has Figure 3 and Figure 4 The PMUT device 20 of FIG. 1 is similar in overall structure to the PMUT device 20 of FIG. 1 ; therefore, only a brief description of the common parts is given. Figure 3 and Figure 4 Portions corresponding to similar portions of the PMUT device 20 are indicated with reference numerals increased by 100.

[0089] In particular, Figure 5 and Figure 6 The PMUT device 120 includes a die 121 and a support structure 122 .

[0090] The support structure 122 here includes a support element 123 , a printed circuit board 126 and a soft layer 128 .

[0091] The die 121 has a first major surface 121A and a second major surface 121B, the second major surface 121B being opposite to the first major surface 121A.

[0092] The die 121 also has a plurality of cavities 129 extending from the second major surface 121B to the interior of the die 121 and delimiting corresponding films 130 downwardly.

[0093] The support element 123 here has an upper surface 123A arranged facing the die 121 , which is planar and is bonded (eg glued) to the second main surface 121B of the die 121 , closing the cavity 129 downwardly.

[0094] Here, the printed circuit board 126 also has a through opening 124 in which the die 121 is arranged.

[0095] The die 121 is electrically coupled to the printed circuit board 126 via conductive lines 125 embedded in an insulating region 141 , for example made of a resin such as a top encapsulation, which also fills the through opening 124 between the die 121 and the printed circuit board 126 and is otherwise covered by a soft layer 128 .

[0096] Soft layer 128 (electrically insulating layer) covers and adheres to upper side 121B of die 121 and printed circuit board 126 , including insulating region 141 , as described above.

[0097] The piezoelectric structure 131 extends on the respective membrane 130 and forms a respective vibration structure 127 therewith.

[0098] Here, the piezoelectric structure 131 is also formed by a stack including a pair of electrodes 34, 35 and a piezoelectric region 36, which is not shown in detail and is similar to Figure 3 The stackup is shown in an enlarged detail of FIG.

[0099] exist Figure 5 and Figure 6 In the embodiment, the piezoelectric structure 131 has a ring shape, especially in Figure 6 It can be seen in the top view of that it is associated with a portion of the first main surface 121A of the tube core 121.

[0100] The cavities 129 have a vertical central axis S extending parallel to the vertical axis Z; in particular, they have a cylindrical shape, and the piezoelectric structures 131 are each concentric with a respective cavity 129 .

[0101] The piezoelectric structure 131 may have a thickness comprised between 1 and 50 μm, for example 2 μm, an outer diameter comprised between 30 and 800 μm, for example 350 μm, and an inner diameter comprised between 10 and 780 μm, for example 150 μm.

[0102] Forming the piezoelectric structure 131 to have a ring shape allows the PMUT device 120 to operate in a second axisymmetric vibration mode different from the first axisymmetric vibration mode.

[0103] In particular, here, the annular shape of the piezoelectric structure 131 causes the membrane 130 to Figure 7 Move as shown.

[0104] In particular, if Figure 7 As shown, in each membrane 130, the portion of the membrane surface located beneath the respective piezoelectric structure 131 (indicated as annular portion 131A) surrounds a central portion 131B which moves in use in a sinusoidal motion opposite to that of the annular portion 231A.

[0105] According to various embodiments, each piezoelectric structure may be made of a plurality of ring structures, causing the micromachined transducer to operate in an even larger vibration mode (eg, the third mode or the fourth mode), thereby increasing the natural frequency of the micromachined transducer.

[0106] For example, Figure 8 A PMUT device 220 is shown having an ultrasound unit 245 formed in a die 221 having a cavity 229 defining a membrane 230 in the die 221 .

[0107] exist Figure 8 In the embodiment, the piezoelectric structure (indicated here by 231 and forming the vibration structure 227 together with the membrane 230) includes two concentric rings 231A and 231B, which, in use, cause the lower layer part of the membrane 230 to vibrate in a phase-opposite manner relative to the adjacent part.

[0108] In one embodiment, the PMUT device 220 has a natural frequency of approximately 3 MHz.

[0109] In general, by modifying the position and number of rings of the piezoelectric structure, a PMUT device can be designed so that it has a resonant frequency of a desired value.

[0110] Fig. 9 and Fig.10 A PMUT device 320 is shown, which may be used as both a transmitter and a receiver in an energy transfer system.

[0111] Fig. 9 and Fig.10 The PMUT device 320 has Figure 3 and Figure 4 The PMUT device 320 has a similar overall structure to the PMUT device 20 of FIG. 1 ; therefore, only a brief description of the common parts is given below. Figure 3 and Figure 4 Portions corresponding to similar portions of the PMUT device 20 are indicated with reference numerals increased by 300.

[0112] In particular, Fig. 9 and Fig.10 The PMUT device 320 includes a die 321 and a support structure 322 .

[0113] The support structure 322 here includes a support element 323 , a printed circuit board 326 and a soft layer 328 .

[0114] The die 321 has a first main surface 321A and a second main surface 321B, the second main surface 321B being opposite to the first main surface 121A.

[0115] The die 321 also has a plurality of cavities 329 extending from the second main surface 321B into the interior of the die 321 and delimiting the respective films 330 downwards.

[0116] Here, the support member 323 has an upper surface 323A arranged facing the tube core 321, which is not a plane and has a recess 333 arranged facing the tube core 321, similar to Figure 3 PMUT device 20.

[0117] Thus, the cavity 329 of each ultrasound unit 345 covers the recess 333 and is directly connected to the recess 333, as in Figure 3 As in the PMUT device 20 in FIG. 1 , the recess may contain air or soft gel.

[0118] exist Fig. 9 In the embodiment, the die 321 is inserted into the through opening 324 of the printed circuit board 326 and is suspended above the recess 333 by the soft layer 328, which covers and adheres to the first main surface of the die 321 and the upper surface of the printed circuit board 326, including the wire 325.

[0119] The soft layer 328 may be made of Figure 3 The soft layer 28 is made of the same material.

[0120] exist Fig. 9 and Fig.10 In the PMUT device 320, a piezoelectric structure (indicated here by 331) forms a vibration structure 327 with the corresponding membrane 230, and the piezoelectric structure has a ring shape (see also Fig.10) and is arranged concentrically with the corresponding membrane 330, similar to Figure 5 PMUT device 120.

[0121] In practice, the PMUT device 320 combines Figure 3 The characteristics of the PMUT device 20 in Figure 5 The characteristics of the PMUT device 120 in the embodiment of the present invention achieve a synergistic effect and significantly improve the quality factor and the impedance phase under resonance, as shown in the following reference FIG. 17A to FIG. 17C Further discussion.

[0122] Fig.11 One vibrating structure 427 is shown. The piezoelectric structure 431 is of a multi-layer type and can be used in any embodiment of a PMUT device.

[0123] In detail, the piezoelectric structure 431 includes a stack of layers, including lower electrodes 434 (two here), upper electrodes 435 (two here), and piezoelectric regions 436 (three here). The lower electrodes 434 and the upper electrodes 435 alternate with each other, and each piezoelectric region 436 is arranged between the lower electrodes 434 and the upper electrodes 435.

[0124] The upper electrodes 435 are electrically connected to each other and to the voltage generator 460 ; the lower electrodes 434 are electrically connected to each other and to the ground ( 461 ).

[0125] For example, the electrodes 434 and 435 are made of platinum, and the piezoelectric region 436 is made of one of the materials indicated above for the electrodes 34 and 35 .

[0126] In the case of a piezoelectric region 436 of ScAlN, the piezoelectric region 436 may have a thickness of 1 μm.

[0127] An insulating layer 462 extends between the piezoelectric structure 431 and the membrane, here indicated by 430; a passivation layer 463 covers the piezoelectric structure 431 and is open at the contacts.

[0128] The piezoelectric structure 431 may have a disc-like shape (in top view) and may be used to Figure 3 In the PMUT device 21 , the piezoelectric structure 31 is replaced.

[0129] Alternatively, it may have an annular shape (in top view), wherein Fig.11 shows a cross section of the part and can be used Figure 5 PMUT device 120, Figure 8 PMUT device 220 or Fig. 9 In the PMUT device 320, the piezoelectric structures 131, 231, and 331 are replaced. For example, Fig.12A PMUT device 120, 220, 320 having a piezoelectric structure 431 of a multi-layer type is shown.

[0130] Fig.13A It is shown that a capacitive ultrasound device, CMUT device 520, can be used as both a transmitter and a receiver of an energy transfer system.

[0131] The CMUT device 520 includes a die 521 and a support structure 522 .

[0132] The support structure 522 here includes a printed circuit board 526 and a soft layer 528 .

[0133] The printed circuit board 526 and the soft layer 528 may be formed as described above for the PMUT device 20 .

[0134] In particular, the die 521 is inserted into the through opening 524 of the printed circuit board 326 , and the printed circuit board 526 may be electrically connected to the die 521 through the wire 525 .

[0135] The die 521 including a silicon substrate and an insulating layer (not shown) has a first main surface 521A and a second main surface 521B, which is opposite to the first main surface 521A.

[0136] The tube core 521 forms a plurality of ultrasound units 545 , each of which includes a cavity 529 , a membrane 530 , a first electrode 590 , and a second electrode 591 .

[0137] The membrane 530 and the electrodes 590 , 591 of each ultrasound unit 545 form a corresponding vibrating structure 527 .

[0138] Each cavity 529 typically has a cylindrical shape, extends below the first main surface 521A of the die 521 and delimits downwardly a corresponding membrane 530 formed by the same die 521 .

[0139] Here, each first electrode 590 extends over a corresponding membrane 530 .

[0140] Each second electrode 591 is arranged in the cavity 529, on the side of the corresponding cavity 529 opposite to the membrane 530 (arranged facing the second major surface 521B of the tube core 521). Each second electrode 591 is vertically aligned with the corresponding first electrode 590 and capacitively coupled to the corresponding first electrode 590, wherein the air in the corresponding cavity 529 and any dielectric passivation layer (not shown) operate as a dielectric.

[0141] The electrodes 590, 591 may be formed from a deposited and patterned metal layer or from other conductive materials such as doped single crystal silicon or polycrystalline silicon.

[0142] Here, the soft layer 528 is also an electrically insulating layer, covers the first main surface 521A of the tube core 521 and the upper surface of the printed circuit board 526, contains the conductive line 525 and supports the tube core 521, and the tube core 521 is suspended below the soft layer 528.

[0143] The soft layer 528 can be formed as already indicated for the PMUT devices 20, 120 and 320; specifically, it is made of a material having an acoustic impedance and acoustic transmission characteristics (propagation velocity) similar to those of the medium in which the CMUT device 520 is expected to operate, adhesion such as for securely holding the tube core 521 over time, and flexibility such as for allowing unclamped vibration of the membrane 530 during use.

[0144] Suspending the die 521 by the soft layer 528 rather than by being attached down to the substrate of the die 521 can significantly improve the quality factor.

[0145] Fig. 13B A capacitive ultrasound device 520' is shown that is similar to the CMUT device 520, but has an annular shaped electrode 590'.

[0146] Fig.14A , Fig. 14B and Fig. 14C The piezoelectric structure for sol-gel is shown respectively. Figure 1 PMUT device 1 (curve A) and Figure 3 Simulation of the electrical impedance phase, open-circuit RX sensitivity magnitude, and TX sensitivity magnitude of the PMUT device 20 (curve B).

[0147] In particular, Figure 1 The PMUT device 1 and Figure 3 A transducer 20 is simulated. The PMUT device 1 has a tube core 2 with a thickness of 400 μm, a piezoelectric structure 12 with a diameter of 140 μm and a thickness of 2 μm. The transducer 20 has a tube core 21 with a thickness of 200 μm, a disc-shaped piezoelectric structure 12 with a diameter of 140 μm and a thickness of 2 μm.

[0148] As described above, eliminating the clamping of the die 21 and forming the support for the die 21 by the soft layer 28 (eliminating the insulating region 6 of the top package of the PMUT device 1) allows Figure 3 The tube core 21 has a greater degree of freedom of displacement; therefore, the mechanical quality factor Q is increased and the reactance to resonance is reduced (reducing the impedance phase angle).

[0149] In the simulation shown, where the die 21 also has a small thickness, the phase angle is increased by more than 8° and RX( Fig. 14B) and TX( Fig. 14C ) Both have a peak sensitivity of about 900kHz, thus achieving higher efficiency. In particular, Fig. 14B Curve B shows an 8dB improvement over Curve A, and Fig. 14C Curve B shows a 3dB fractional bandwidth (FBW) that is one fifth lower than that of Curve A. -3dB ).

[0150] Fig.15A , Fig. 15B and Fig. 15C shows the piezoelectric structure for sol-gel, Figure 1 PMUT device 1 (curve A) and Figure 5 Similar simulations of the electrical impedance phase, open circuit RX sensitivity magnitude, and TX sensitivity magnitude of the PMUT device 120 (curve C) are shown in FIG.

[0151] In particular, Fig.15A , Fig. 15B and Fig. 15C Curve C of FIG. 1 refers to a PMUT device 120 having a ring-shaped piezoelectric structure 131 with an outer diameter of 350 μm and an inner diameter of 150 μm.

[0152] As described above, forming the piezoelectric structure 131 with a ring shape allows the PMUT device 120 to improve the phase angle by more than 12° (with less loss), and RX ( Fig. 15B ) and TX( Fig. 15C ) have a peak sensitivity of about 800kHz. In particular, Fig. 14B Curve B shows an 11 dB improvement over Curve A, and Fig. 14C Curve B shows a 3dB fractional bandwidth (FBW) that is less than one tenth of Curve A. -3dB ).

[0153] Fig.16A , Fig. 16B and Fig. 16C shows the piezoelectric structure for sol-gel, Figure 1 PMUT device 1 (curve A) and Fig. 9 Similar simulations of the electrical impedance phase, open circuit RX sensitivity magnitude, and TX sensitivity magnitude of the PMUT device 320 (curve D) are shown in FIG.

[0154] In particular, Fig.16A , Fig. 16B and Fig. 16C Curve D of 2 refers to a PMUT device 220 having an unclamped die 321 and a ring-shaped piezoelectric structure 331 with an outer diameter of 350 μm and an inner diameter of 150 μm.

[0155] As described above, the soft suspension of the die 321 combined with the formation of the annular shaped piezoelectric structure 331 allows the PMUT device 320 to achieve a phase angle improvement of more than 39°, and RX( Fig. 16B ) and TX( Fig. 16C ) have a peak sensitivity of about 880kHz. In particular, Fig. 16B Curve D shows a 13 dB improvement over Curve A, and Fig. 14C Curve D shows a 3dB fractional bandwidth (FBW) that is almost two orders of magnitude lower than Curve A. -3dB ).

[0156] Fig.17A , Fig. 17B and Fig. 17C shows the piezoelectric structure for plasma deposited PZT (PVD PZT), Figure 1 PMUT device 1 (curve A) and Fig. 9 Similar simulations of the electrical impedance phase, open circuit RX sensitivity magnitude, and TX sensitivity magnitude of the PMUT device 320 (curve E) are shown in FIG.

[0157] In particular, Fig.17A , Fig. 17B and Fig. 17C Curve E of refers to a PMUT device 320 having an unclamped die 321 and a ring-shaped piezoelectric structure 331 with an outer diameter of 350 μm and an inner diameter of 150 μm.

[0158] As described above, forming the piezoelectric region by PVD rather than sol-gel allows the PMUT device 320 to achieve a very large improvement in phase angle, which becomes equal to about 0°, and a sensitivity peak above Fig. 16B and Fig. 16C The peak sensitivity in .

[0159] In this way, FIG. 16A to FIG. 16C In the PMUT device 320 simulated in FIG. 1 , the electrical impedance is purely resistive, allowing for a perfect theoretical match with a resistive medium / load.

[0160] Fig. 9 The PMUT device 320 can be pressed FIG. 18A to FIG. 18E The formation is shown, wherein, for simplicity, undefined layers and structures (where helpful for understanding) are utilized with Fig. 9 and Fig.10 The same reference numerals are used to indicate the same.

[0161] In detail, Fig.18AA wafer 380 is shown including a substrate 381. The substrate 381 may be a semiconductor material, such as single crystal silicon, and have a thickness of 500 μm.

[0162] Above the substrate 381, a first dielectric layer 382 has been formed, for example by depositing TEOS (tetraethyl orthosilicate) with a thickness of 1 μm; a structural layer 383, for example an epitaxially grown silicon layer, with a thickness of 4 μm; and a second dielectric layer 384, for example by depositing TEOS with a thickness of 5 μm.

[0163] A piezoelectric structure 331 in the shape of a ring has been formed on the second dielectric layer 384. For example, the piezoelectric structure 331 is formed by sequentially depositing a first platinum electrode layer, a PZT piezoelectric layer (as sol-gel or by PVD), a second electrode layer such as TiW, and a passivation layer such as undoped silicate-based glass (USG) with a thickness of 0.5 um; patterning the deposited layers; depositing and patterning a metal layer to form a lower electrode 334, a piezoelectric region 336, an upper electrode 335, a passivation layer 337, and metal connection lines (connection line 338 is visible here).

[0164] exist Fig.18B In the process, the wafer 380 is thinned, flipped, an insulating layer such as TEOS is deposited and patterned to form a hard mask 387, and using the hard mask 387, the substrate 381 is etched, such as by dry etching, stopping on the first dielectric layer 382 and forming the cavity 329.

[0165] exist Fig.18C , the wafer 380 is cut to obtain a plurality of slices 321 (one slice is visible); and each die 321 is inserted into a corresponding through opening 324 of a printed circuit board 326 .

[0166] In particular, in this step, the printed circuit board 326 is attached to a tape 388 of, for example, a PVC (polyvinyl chloride), polyolefin or polyethylene-based coating material through a portion of the hard mask 387. In particular, a portion of the hard mask 387 is bonded to the tape 388 by ultraviolet or heat treatment.

[0167] exist Fig.18D In FIG. 3 , the wire 325 is bonded between a contact pad (not shown) arranged on the first main surface 321A of the die 321 and a similar contact pad (not shown) on the upper surface of the printed circuit board 326 .

[0168] Furthermore, a soft layer 328 is formed, for example by dispense deposition.

[0169] The printed circuit board 326 may be cut and the tape 388 may then be removed by UV treatment to obtain Fig.18E structure.

[0170] The CMUT device 520 of FIG. 13 may be FIG. 19A to FIG. 19F The formation is shown, wherein for simplicity, layers and undefined structures that are helpful for understanding are used in conjunction with Fig. 9 and Fig.10 The same reference numerals are indicated in FIG.

[0171] In detail, Fig.19A A wafer 580 is shown including a substrate 581. The substrate 581 may be a semiconductor material, such as single crystal silicon, and have a thickness of 500 μm.

[0172] A first dielectric layer 582 of, for example, thermally grown or deposited silicon oxide and having a thickness of 2 μm extends over the substrate 581 ; a second electrode 591 extends over the first dielectric layer 582 , which is formed, for example, by depositing and defining a metal layer, such as an aluminum-based alloy.

[0173] exist Fig.19B In the embodiment, a second dielectric layer 584 of silicon oxide, for example with a thickness of 0.2 μm, is deposited on the second electrode 591 and the first dielectric layer 582 , exposed there, and together with the first dielectric layer 582 forms an overall dielectric layer 585 .

[0174] A sacrificial region 587 of metal such as aluminum-based alloy is formed on the second dielectric layer 584 vertically covering the second electrode 591. The sacrificial region 587, formed by depositing and defining a metal layer such as aluminum-based alloy, has a thickness equal to the depth of the cavity 529 of FIG.

[0175] exist Fig.19C In the embodiment of the present invention, a third dielectric layer 588 of silicon oxide, for example with a thickness of 0.2 μm, is deposited on the sacrificial area 587 and the overall dielectric layer 585 (not covered), thereby increasing its thickness. For simplicity, the resulting layer is again referred to as the overall dielectric layer 585.

[0176] Then, a first electrode 590 is formed on the third dielectric layer 588, vertically covering the sacrificial region 587. The first electrode 590 has a smaller size (area) than the sacrificial region 587, typically equal to the second electrode 591. For example, the first electrode 590 is formed by depositing and defining a metal layer such as an aluminum-based alloy.

[0177] Subsequently, a membrane layer 589 is formed over the uncovered first electrode 590 and the overall dielectric layer 585 .

[0178] The film layer 589 is, for example, silicon nitride (Si3N4) with a thickness of 2 μm.

[0179] exist Fig.19DIn the process, the film layer 589 and the dielectric layer 588 above the sacrificial region 587 are etched and selectively removed to form an opening 595 reaching the same sacrificial region 587; then, the sacrificial region 587 is removed through the opening 595, for example, by wet etching. Thus, the cavity 529 is formed.

[0180] exist Fig.19E In the embodiment, a film layer 588 is added by material deposition. For example, Fig.19C The same material used in the step of , here silicon nitride, closes the opening 595 and forms the film 530 of FIG. 13 over the first electrode 590 .

[0181] Then, follow the same FIG. 18C to FIG. 18E The steps described are similar to the steps to obtain Fig.19F device 520 ; in particular, the wafer 580 may be thinned (eg, down to 200 μm); cut (to obtain a plurality of slices 521 , one visible); and each die 521 is inserted into a respective printed circuit board 526 .

[0182] Here again, the printed circuit board 526 may be attached to the temporary tape; the wires 525 are bonded; and the soft layer 528 is formed.

[0183] After possible removal of the tape (not shown), the Fig.19F CMUT device 520.

[0184] Thus, the MUT devices described herein allow for a significant improvement in the quality factor and thus the achievable energy transfer efficiency, using common process steps in the fabrication of micro-machined semiconductor devices, and therefore at a lower cost.

[0185] Finally, it is obvious that modifications and variations may be made to the MUT device and its manufacturing process described and illustrated herein without departing from the scope of the present disclosure, as defined by the appended claims.For example, the different embodiments described may be combined to provide further solutions.

[0186] For example, Fig. 13B As shown, the electrodes 591, 592 may have a ring shape. In this case, the capacitive CMUT device 520' is biased by direct current (DC) so that it can generate a received electrical signal. In the specific case of an implanted device, where an external bias applied, for example, by a DC voltage generator is impractical, the CMUT device 520 may be pre-biased by applying a voltage, such as to inject and trap charge within a dielectric passivation layer surrounding the electrode.

[0187] In addition, if Fig.11 , Fig.12As shown, the multilayer structure of piezoelectric regions can be used for all PMUT devices 20 , 120 , 220 , 320 .

[0188] The piezoelectric structure 131, 231, 331 of the PMUT device 20, 120, 220, 320 may include one or more rings, similar to Figure 8 The loop shown allows setting the resonant frequency and thus the desired optimum operating frequency also based on the desired application.

[0189] The support elements 23, 123, and 323 may be absent and / or replaced by examples of biocompatible materials, such as polyetheretherketone (PEEK) or titanium, that completely surround the PMUT or CMUT device.

[0190] The micromachined ultrasonic transducers described herein may also be used for communication and information exchange between transmitting elements and receiving elements.

[0191] In summary, exemplary embodiments of the present acoustic transducer can be summarized as follows:

[0192] Example 1. A micromachined ultrasonic transducer (120; 220; 320; 520; 520′) comprising a die (121; 221; 321; 521), the die (121; 221; 321; 521) comprising a semiconductor material, wherein:

[0193] The tube core (121; 221; 321; 521) accommodates at least one ultrasound unit (145; 245; 345; 545),

[0194] Each ultrasonic unit (145; 245; 345; 545) comprises a cavity (129; 229; 329; 529) extending inside the tube core (121; 221; 321) and a vibrating structure (127; 227; 327; 427; 527) covering the cavity and vertically aligned with the cavity,

[0195] wherein the vibration structure (127; 227; 327; 427; 527) comprises an annular element (131; 231; 331; 431; 590),

[0196] The micromachined ultrasonic transducer is configured to operate in a symmetric vibration mode about a second axis.

[0197] Example 2. A micromachined ultrasonic transducer according to the preceding example, wherein the vibrating structure (127; 227; 327; 427; 527) comprises a membrane region (130; 230; 330; 530) and at least one electrode carried by the membrane region.

[0198] Example 2-2. A micromachined ultrasonic transducer according to the preceding example, wherein the cavity (129; 229; 329; 529) has a vertical central axis (S) and the vibrating structure (127; 227; 327; 427; 527) is concentric with the cavity.

[0199] Example 3. A micromachined ultrasonic transducer according to Example 1 or 2, wherein the annular element includes at least one piezoelectric region (36) of a piezoelectric structure (131; 231; 331; 431), the piezoelectric structure including at least one electrode and a second electrode, and the at least one piezoelectric region is inserted between the at least one electrode and the second electrode.

[0200] Example 4. A micromachined ultrasonic transducer according to the preceding example, wherein the piezoelectric structure (431) comprises at least one additional piezoelectric annular region (231B) having an annular shape, the at least one additional piezoelectric region being concentric with the at least one piezoelectric region (231A).

[0201] Example 5. A micromachined ultrasonic transducer according to Example 3 or 4, wherein the piezoelectric structure (131; 231; 331; 431) is formed by a stack (131; 231; 331) comprising a plurality of piezoelectric regions (436), each piezoelectric region (436) being interposed between a corresponding first electrode (434) and a corresponding second electrode (435), wherein the first electrodes are electrically coupled to each other and the second electrodes are electrically coupled to each other.

[0202] Example 6. A micromachined ultrasonic transducer according to any of the preceding examples, comprising a support structure (122; 322) mechanically and electrically coupled to a die (121; 321; 521), wherein:

[0203] The support structure (122; 322) includes an electrical connection plate (126; 326) and a soft area (128; 328);

[0204] The electrical connection plate (126; 326) has an opening (124; 324) for receiving the die; and

[0205] The soft region extends over and adheres to the electrical connection plate (126; 326) and the die (121; 321; 521), the soft region covering the main surface (121A; 321A) of the die, the main surface (121A; 321A) of the die delimiting the membrane region (130; 230; 330; 530) upwardly.

[0206] Example 7. A micromachined ultrasonic transducer according to the previous example, wherein the soft region (128; 328) has an acoustic impedance comprised between 1 and 2 MRayl, a 3and a speed of sound comprised between 1000 and 2000 m / s.

[0207] In Example 7, the ranges can include the upper and lower ends of the ranges as set forth in Example 7 above.

[0208] Example 8. A micromachined ultrasonic transducer according to Example 6 or 7, wherein the electrical connection board (126; 326) is a printed circuit board, which is wire-bonded to the die (121; 321; 521) using wires (125; 325) enclosed in the soft area (128; 328).

[0209] Example 9. A micromachined ultrasonic transducer according to any one of Examples 6-8, wherein the opening (124; 324) of the electrical connection plate (126; 326) is a through opening, and the die (21; 321; 521) is suspended on a gap open to the outside.

[0210] Example 9-2. A micromachined ultrasonic transducer according to any one of Examples 6-8, wherein the support structure (122; 322) includes a support element (123; 323) that is attached downwardly to the electrical connection plate (126; 326) and forms a support wall spaced apart from the tube core and closes downwardly a gap (133) filled with air or a soft material such as silicone.

[0211] Example 10. A micromachined ultrasonic transducer according to any of Examples 6-8, wherein the support structure (122; 322) includes a support element (123; 323) attached downwardly to the tube core (121; 321; 521) and closing the cavity (129; 329; 529) downwardly.

[0212] Example 11. The micromachined ultrasonic transducer comprises a die (21; 221; 321; 521) comprising a semiconductor material and a support structure (22; 322; 522) mechanically and electrically coupled to the die, wherein:

[0213] The tube core (21; 221; 321; 521) accommodates at least one ultrasound unit (45; 345; 545),

[0214] The support structure (22; 322; 522) comprises an electrical connection plate (26; 326; 526) and a soft area (28; 328; 528), and

[0215] The electrical connection plate (26; 326; 526) has an opening (24; 324; 524) for accommodating the tube die,

[0216] The soft region (28; 328; 528) extends over and adheres to the electrical connection board (26; 326; 526) and the die (21; 221; 321; 521) so that the die (21; 221; 321; 521) is suspended below the soft region (28; 328; 528).

[0217] Example 12. A micromachined ultrasonic transducer according to the previous example, the micromachined ultrasonic transducer is a piezoelectric type, wherein:

[0218] Each ultrasound unit comprises a cavity (29; 229; 329), a membrane region (30; 230; 330) and a piezoelectric structure (31; 231; 331), the cavity, the membrane region and the piezoelectric structure being vertically aligned with each other, the cavity (29; 229; 329) extending in the tube core (21; 221; 321), the membrane region (30; 230; 330) being formed by the tube core and bounded on one side by the cavity (29; 229; 329), and the piezoelectric structure (31; 231; 331) covering the membrane region (30; 230; 330),

[0219] The piezoelectric structure (31; 231; 331) comprises a stack including a lower electrode (34; 434), a piezoelectric region (36; 436) above the lower electrode, and an upper electrode (35; 435) covering the piezoelectric region and having a disk or ring shape.

[0220] Example 13. The micromachined ultrasonic transducer of Example 11, wherein the micromachined ultrasonic transducer is a capacitive type, wherein:

[0221] Each ultrasound unit (545) comprises a first electrode (590; 590'), a second electrode (591), a cavity (529) and a membrane region (530), the first electrode, the second electrode, the cavity and the membrane region being vertically aligned with each other,

[0222] A cavity (529) extends in the tube core (521),

[0223] The membrane region (530) extends over the cavity (529),

[0224] A first electrode (590; 590') is carried by the membrane region (530), and

[0225] The second electrode (591) is arranged inside the cavity (529) and is capacitively coupled to the first electrode (590; 590').

[0226] Example 14. A system for wirelessly transferring energy, comprising an energy transmitting element and an energy receiving element, wherein the energy transmitting element is configured to generate ultrasonic waves and the energy receiving element is configured to receive ultrasonic waves generated by a transmitting micromachined ultrasonic transducer during use, wherein at least one of the energy transmitting element and the energy receiving element comprises a micromachined ultrasonic transducer according to any of the preceding examples.

[0227] Example 15. A method of manufacturing a micromachined ultrasonic transducer, comprising:

[0228] forming a tube core (21; 221; 321; 521) comprising a semiconductor material, having a main surface (21A; 221A; 321A; 521A) and accommodating an ultrasound unit (45; 345; 545);

[0229] Introducing the tube core (21; 221; 321; 521) into the opening (24; 324; 524) of the electrical connection plate (26; 326; 526);

[0230] electrically coupling the die (21; 221; 321; 521) to an electrical connection board (26; 326; 526); and

[0231] A soft area (28; 328; 528) is formed on the main surface (21A; 221A; 321A; 521A) which adheres to the electrical connection plate (26; 326; 526) and the tube core (21; 221; 321; 521) and suspends the tube core.

[0232] The various embodiments described above can be combined to provide further embodiments. Aspects of the embodiments can be modified, if necessary to employ concepts of the various patents, applications and publications to provide further embodiments.

[0233] These and other changes can be made to the embodiments in light of the above detailed description. In general, in the appended claims, the terms used should not be interpreted as limiting the claims to the specific embodiments disclosed in the specification and claims, but should be interpreted to include all possible embodiments and the full range of equivalents to which these claims are entitled. Therefore, the claims are not limited by this disclosure.

Claims

1. A micro-machined ultrasonic transducer, comprising: a tube core, the tube core comprising a semiconductor material, and the tube core comprising one or more ultrasound units, wherein each of the one or more ultrasound units comprises a cavity and a vibrating structure, the cavity being within the tube core, the vibrating structure covering the cavity, being aligned with the cavity, and overlapping the cavity, The vibration structure includes a ring-shaped vibration element. 2 . The micromachined ultrasonic transducer according to claim 1 , wherein the vibrating structure comprises a membrane region and at least one electrode, the at least one electrode being carried by the membrane region.

3. The micromachined ultrasonic transducer according to claim 1, wherein the annular vibration element includes at least one piezoelectric region of a piezoelectric structure, the piezoelectric structure includes at least one electrode and a second electrode, and the at least one piezoelectric region is inserted between the at least one electrode and the second electrode.

4. The micromachined ultrasonic transducer of claim 3, wherein the piezoelectric structure comprises at least one additional piezoelectric region, the at least one additional piezoelectric region having an annular shape, and the at least one additional piezoelectric region is concentric with the at least one piezoelectric region.

5. The micromachined ultrasonic transducer according to claim 3, wherein the piezoelectric structure is formed by a stack, the stack comprising a plurality of piezoelectric regions, each of the plurality of piezoelectric regions being interposed between a corresponding first electrode and a corresponding second electrode, and the first electrodes of the stack are electrically coupled to each other, and the second electrodes of the stack are electrically coupled to each other.

6. The micromachined ultrasonic transducer of claim 1 further comprising a support structure mechanically and electrically coupled to the die, wherein: The support structure includes an electrical connection plate and a soft area; The electrical connection plate has an opening, the opening accommodating the die; and The soft area extends over the electrical connection plate and the die and is adhered thereto, the soft area covering a main surface of the die which delimits the membrane area upwards.

7. The micromachined ultrasonic transducer of claim 6, wherein the soft region has a specific acoustic impedance between 1 and 2 MRayl, a specific acoustic impedance between 0.8 and 2 g / cm 3 density between 0.8 and 2 g / cm2, and a sound velocity between 1000 and 2000 m / s, the specific acoustic impedance is comprised between 1 and 2 Mrayl, the density is comprised between 0.8 and 2 g / cm2 3 , the sound speed includes 1000 and 2000m / s.

8. The micromachined ultrasonic transducer of claim 6, wherein the electrical connection board is a printed circuit board that is wire-bonded to the die using wires enclosed in the soft region.

9. The micromachined ultrasonic transducer of claim 6, wherein the opening of the electrical connection plate is a through-opening extending completely through the electrical connection plate, and the die is suspended over a gap between the die and the support element by the soft area.

10. The micromachined ultrasonic transducer of claim 6, wherein the support structure further comprises a support element, the support element being attached to the electrical connection board and defining a support wall and a gap, the support wall being spaced apart from the tube core, the gap being filled with air or a soft material, such as silicone.

11. The micromachined ultrasonic transducer of claim 6, wherein the support structure further comprises a support element attached to the die and defining the cavity.

12. A method for manufacturing a micro-machined ultrasonic transducer, comprising: forming a die comprising a semiconductor material, having a major surface, and having one or more ultrasound units; introducing the die into the opening of the electrical connection plate; electrically coupling the die to the electrical connection board; as well as A soft area is formed over the major surface of the die, the soft area being adhered to the electrical connection plate and the die.

13. The method of claim 12, wherein forming the die having the one or more ultrasound units further comprises: The one or more ultrasound units are formed by: forming one or more piezoelectric structures on one or more dielectric layers stacked on a first surface of a substrate of a wafer; as well as One or more cavities are formed, the one or more cavities extending into the second surface of the substrate, and the one or more cavities extend through the substrate to the one or more dielectric layers, the second surface of the substrate is opposite to the first surface of the substrate, the one or more cavities are formed to define one or more side walls of the substrate, and the one or more side walls of the substrate define the one or more cavities.

14. The method according to claim 13, further comprising: coupling the electrical connection plate to a ribbon, and wherein electrically coupling the die to the electrical connection plate further comprises: coupling the die to a ribbon, closing the one or more cavities with the ribbon, and inserting the die into an opening of the electrical connection board; and One or more conductive lines are formed that electrically couple the electrical connection pad to the die.

15. The method of claim 14, wherein the soft region formed over the major surface of the die further comprises: covering the one or more piezoelectric structures with the soft region; as well as The die is physically coupled to the electrical connection pad.

16. The method according to claim 15, further comprising: The tape is removed from the die, and the die is suspended from the electrical connection board using the soft area to physically couple the die to the electrical connection board.

17. A micro-machined ultrasonic transducer, comprising: an electrical connection plate comprising a through-opening extending completely through the electrical connection plate and bounded by one or more through-opening sidewalls of the electrical connection plate; a tube die, the tube die being present in the through opening, the tube die comprising a third surface and a fourth surface, the fourth surface being opposite to the third surface, the tube die being electrically coupled to the electrical connection board; as well as A soft area extends from the electrical connection plate through the through-opening to the fourth surface of the die, the soft area being on the fourth surface of the die and physically coupling the electrical connection plate to the die.

18. The micromachined ultrasonic transducer of claim 17, wherein the die further comprises: one or more vibrating structures, the one or more vibrating structures being on the fourth surface of the die, the one or more vibrating structures being covered by the soft area; as well as One or more cavities extending into the third surface of the die and terminating within the die before reaching the fourth surface of the die, each respective one of the one or more cavities being aligned with and overlapping a corresponding one of the one or more vibrating structures.

19. The micromachined ultrasonic transducer of claim 18, wherein each respective one of the one or more vibrating structures and each respective one of the one or more cavities define a corresponding one of the one or more unit cells of the die.

20. The micromachined ultrasonic transducer of claim 17, wherein the soft region suspends the die from the electrical connection pad, thereby spacing the die from the electrical connection pad.

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