Ultrasonic probe with MUT transducers and method of manufacturing such a probe

Abstract

Ultrasonic probe with MUT transducers and method for manufacturing such a probe The present description relates to an ultrasonic probe (100) comprising: - an electronic chip (110) having a front face (110A) and comprising a substrate (111) and at least one ultrasonic transducer (210) micro-machined in and on the substrate on the front face; - an electrically insulating protective layer (130) covering the at least one transducer; and - a metal shielding layer (140) on the protective layer, the shielding layer forming an electromagnetic shielding of said at least one transducer. Figure for abstract: Fig. 2

Description

Title of the invention: Ultrasonic probe with MUT transducers and method of manufacturing such a probe Technical field

[0001] The present description relates generally to the field of ultrasonic probes comprising ultrasonic transducers and, more particularly, micro-machined ultrasonic transducers, also called MUT type transducers.

[0002] An example of application of such an ultrasound probe concerns intravascular ultrasound diagnosis or treatment, the ultrasound probe being for example integrated into a catheter or in an external housing. Prior art

[0003] A MUT transducer typically comprises a membrane and two electrodes, for example an upper electrode and a lower electrode, for example on either side of the membrane. The lower and upper electrodes are generally adapted to apply an electrical excitation signal to the transducer and / or to recover a signal from the transducer to be transformed into an electrical signal. One of the lower and upper electrodes may be connected to ground, and the other may be dedicated to the electrical signal.

[0004] A MUT transducer is for example a micromachined capacitive ultrasonic transducer, also called a CMUT transducer, from the English "capacitive micromachined ultrasonic transducer", or a micromachined piezoelectric ultrasonic transducer, also called a PMUT transducer, from the English "piezoelectric micromachined ultrasonic transducer".

[0005] A CMUT transducer generally has a structure close to that of a planar capacitor, with two lower and upper electrodes arranged opposite each other, one of the electrodes being secured to a membrane which is suspended above a cavity.

[0006] A PMUT transducer generally comprises a membrane suspended above a cavity, the membrane comprising a piezoelectric layer covered on either side by a lower electrode and an upper electrode.

[0007] An ultrasonic probe may comprise several elements that can be electrically controlled independently and arranged in a bar (in a line, on a single column), or in a matrix (on several lines and columns). Each element of the ultrasonic probe comprises one or more MUT transducers. In operation, all of the transducers of the probe are arranged opposite a body to be analyzed. The face of the probe facing the body to be analyzed can be called the front face. Ultrasonic waves emitted by the transducers are reflected by the body to be analyzed, then return to the transducers which convert them back into electrical signals.

[0008] MUT transducers can be manufactured, like microelectromechanical systems (MEMS), using microelectronics processes that allow batch manufacturing of MUT transducers. Among the manufacturing processes, mention may be made of the surface micromachining technique, i.e. on the surface of a wafer, or the wafer bonding technique, which consists of preparing the lower electrode and the transducer cavities on a first wafer, then bonding a second wafer incorporating the transducer membranes on the surface of this second wafer as well as the upper electrode.

[0009] Once manufactured, the MUT transducers can be integrated in subsequent steps to form the ultrasound probe. However, there is a risk that the MUT transducers may be damaged during these steps.

[0010] It would be desirable to have an ultrasonic probe with MUT transducers, as well as a method of manufacturing an ultrasonic probe with MUT transducers, at least partially overcoming some of the disadvantages of ultrasonic probes, and known methods of manufacturing ultrasonic probes, in particular making it possible to protect the MUT transducers during the manufacturing of the ultrasonic probe and in operation. Summary of the invention

[0011] One embodiment overcomes all or part of the drawbacks of known MUT transducer ultrasonic probes, and of known manufacturing methods of such ultrasonic probes.

[0012] One embodiment provides an ultrasonic probe comprising: - an electronic chip having a front face and comprising a substrate and at least one ultrasonic transducer micro-machined in and on the substrate on the front face; - an electrically insulating protective layer covering the at least one transducer; and - a metal screen layer on the protective layer, the screen layer forming an electromagnetic shield for said at least one transducer.

[0013] According to one embodiment, the ultrasonic probe further comprises an interconnection substrate assembled to a rear face of the electronic chip opposite the front face, the interconnection substrate being adapted to connect the screen layer to the ground, by example by ground connection pads dedicated to grounding the screen layer.

[0014] According to one embodiment, the ultrasonic probe further comprises a layer of an acoustically transparent material to ultrasound on the screen layer, said layer of the acoustically transparent material being for example molded above said screen layer.

[0015] One embodiment provides a method of manufacturing an ultrasonic probe, the method comprising depositing, on an electronic chip having a front face and comprising a substrate and at least one micromachined ultrasonic transducer formed in and on the front face substrate: - a protective layer covering the at least one transducer; then - a metal screen layer on the protective layer, the screen layer forming an electromagnetic shield for said at least one transducer.

[0016] According to one embodiment, the method further comprises assembling an interconnection substrate to a rear face of the electronic chip opposite the front face, the interconnection substrate being adapted to connect the screen layer to ground.

[0017] According to one embodiment, the method further comprises forming a layer of an acoustically transparent material to ultrasound on the screen layer, said formation being carried out for example by molding the acoustically transparent material above said screen layer.

[0018] The following embodiments may be applied to the probe and / or method.

[0019] According to embodiments: - the acoustically transparent material is an elastomer and / or is biocompatible; and / or - the thickness of the layer of acoustically transparent material is between 300 micrometers and 1 millimeter; and / or - the layer of acoustically transparent material is an acoustic lens.

[0020] According to embodiments: - the protective layer is made of a material that is acoustically transparent to ultrasound, for example an elastomer, such as a silicone, a thermoplastic polyurethane, a polyether block amide, a fluorocarbon elastomer, a polybutadiene, or a combination of several of these materials; and / or - the protective layer is made of a biocompatible material; and / or - the thickness of the protective layer is between 10 micrometers and 1 millimeter, for example between 10 and 500 micrometers or between 10 and 100 micrometers.

[0021] According to embodiments: - the shielding layer is made of gold, silver, aluminum, copper, or a combination of several of these materials; and / or - the screen layer is made of a biocompatible material; and / or - the thickness of the screen layer is adapted to the propagation of ultrasonic waves in said screen layer; and / or - the thickness of the screen layer is less than 10 micrometers, for example less than 5 micrometers.

[0022] According to one embodiment, the electrical connection of the at least one transducer is on the rear face of the electronic chip, for example by means of conductive vias crossing the substrate.

[0023] According to one embodiment, the electrical connection of the at least one transducer is on the front face of the electronic chip, for example via conductive wires.

[0024] According to one embodiment, the electrical connection of the at least one transducer is made by means of conductive wires, said conductive wires being electrically insulated by sealing drops, and the screen layer extending over the sealing drops.

[0025] According to embodiments, the interconnection substrate is: - a flexible interconnect substrate; and / or - a printed circuit; and / or - an integrated circuit specific to an application.

[0026] According to one embodiment, the ultrasonic probe comprises an integrated circuit suitable for an application between the interconnection substrate and the electronic chip.

[0027] According to embodiments: - each micromachined ultrasonic transducer is a micromachined capacitive ultrasonic transducer or a micromachined piezoelectric ultrasonic transducer; and / or - the electronic chip comprises several micro-machined ultrasonic transducers covered by the protective layer and the shielding layer; and / or - the ultrasonic probe comprises several electronic chips each comprising one or more micro-machined ultrasonic transducers covered by the protective layer and the screen layer, the electronic chips being arranged in line or according to a matrix network, for example the different electronic chips, in particular the ultrasonic transducers of the different electronic chips, being individually connectable to an electrical signal.

[0028] According to one embodiment, the ultrasonic probe is arranged in a housing.

[0029] According to one embodiment, the ultrasonic probe is adapted to be inserted into a catheter. Brief description of the drawings

[0030] These characteristics and advantages, as well as others, will be explained in detail in the following description of particular embodiments given without limitation in relation to the attached figures among which:

[0031] [Fig.lA], [Fig.lB], [Fig.lC] and [Fig.lD] are sectional views illustrating successive steps of a method of manufacturing an ultrasonic probe according to one embodiment;

[0032] [Fig.2] is a sectional view showing details of the ultrasonic probe of [Fig.1C];

[0033] [Fig.3A], [Fig.3B], [Fig.3C] and [Fig.3D] are sectional views illustrating successive steps of a method of manufacturing an ultrasonic probe according to another embodiment;

[0034] [Fig.4] is a sectional view showing details of the ultrasonic probe of [Fig.3C];

[0035] [Fig.5] is a sectional view showing an ultrasonic probe according to another embodiment; and

[0036] [Fig.6A], [Fig.6B] and [Fig.6C] are top views showing several modes of connecting the ultrasonic probe of [Fig.5] to ground. Description of the embodiments

[0037] The same elements have been designated by the same references in the different figures. In particular, the structural and / or functional elements common to the different embodiments may have the same references and may have identical structural, dimensional and material properties.

[0038] For the sake of clarity, only the steps and elements useful for understanding the described embodiments have been shown and are detailed. In particular, the production of the MUT transducers of the described ultrasonic probes has not been detailed, the described embodiments being compatible with all or most of the known structures of MUT transducers, and the manufacture of the MUT transducers being within the capabilities of the person skilled in the art. Furthermore, the production of the control circuits of the MUT transducers has not been detailed, the described embodiments being compatible with the usual control circuits of MUT transducers, and the production of the control circuits being within the capabilities of the person skilled in the art.

[0039] Unless otherwise specified, when referring to two elements connected to each other, this means directly connected without intermediate elements other than conductors, and when referring to two elements connected (in English "coupled") to each other, this means that these two elements can be connected or be connected by means of one or more other elements.

[0040] 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", "upper", "lower", etc., or to orientation qualifiers, such as the terms "horizontal", "vertical", etc., reference is made unless otherwise specified to the orientation of the figures.

[0041] In the following description, when reference is made to a probe, unless otherwise specified, it is referred to an ultrasonic probe with micromachined ultrasonic transducers, or MUT transducers. Furthermore, when reference is made to a transducer, it is referred to a micromachined ultrasonic transducer, or MUT transducer, unless otherwise specified.

[0042] In the following description, when reference is made to a conductive element, it is meant, unless otherwise specified, to an electrically conductive element.

[0043] In the following description, when reference is made to a connection pad, or track, it is referred to, unless otherwise specified, to an electrical connection pad, or track. In addition, when reference is made to a ground pad, or track, it is referred to, unless otherwise specified, to a ground (or mass) connection pad, or track.

[0044] Unless otherwise specified, the expressions "about", "approximately", "substantially", and "of the order of" mean to within 10%, preferably to within 5%.

[0045] The following description relates to ultrasonic probes with micromachined ultrasonic transducers, or MUT transducers. As indicated above, once manufactured, the MUT transducers are integrated in subsequent steps to form an ultrasonic probe.

[0046] In operation, all of the transducers of the probe are arranged facing a body to be analyzed. This face of the ultrasound probe facing the body to be analyzed can be designated the front face.

[0047] Generally, several MUT transducers are manufactured in batches, on the same support, for example the same wafer, and this support is then cut either to separate the MUT transducers from each other, or to divide the support into several elements, for example into several electronic chips, each electronic chip comprising several MUT transducers. In addition, once manufactured and separated, the MUT transducers are generally assembled to an interconnection substrate, for example a rigid or flexible printed circuit, or an interposer, in order to electrically connect the transducers of the ultrasonic probe. The interconnection substrate is generally arranged on the rear face of the probe, opposite the front face.

[0048] More generally, in the manufacture of an ultrasonic probe with MUT transducers, the MUT transducers once manufactured on the same support can still be integrated into later stages of ultrasound probe manufacturing, which may include the cutting step described above. It may be necessary to protect these MUT transducers during these later stages of probe manufacturing.

[0049] One solution to protect these MUT transducers is to deposit a layer, called a passivation layer, or protective layer, covering the MUT transducers, on the front side of the future ultrasonic probe.

[0050] The thickness of this protective layer can be between ten and one hundred micrometers, or even between ten and several hundred micrometers.

[0051] The protective layer can be deposited on the MUT transducers not yet divided into electronic chips, or on the MUT transducers already divided into electronic chips.

[0052] Different techniques can be used to deposit the protective layer, and in particular one or more of the following techniques: - spin coating, which is preferred for full-plate, non-localized deposition; - stencil printing, or screen printing, which can be used for full plate deposition or for localized deposition; - sol-gel inkjet deposition, which can be used for full-plate deposition or for localized deposition; - spray coating, which can be used for full-plate deposition or for localized deposits; - a photolithography technique; - the deposition of a photopolymerizable resin.

[0053] The protective layer may be retained once the ultrasonic probe has been manufactured, for example instead of removing it and replacing it with an encapsulation layer. In this case, the material of the protective layer is preferably chosen to allow the propagation of ultrasonic waves, for example similar to a liquid. The protective layer may be a polymer layer, for example an elastomer, for example silicone.

[0054] However, the protective layer generally does not protect MUT transducers from electromagnetic interference (EMI).

[0055] There is therefore a need to protect the MUT transducers of an ultrasonic probe from electromagnetic interference.

[0056] [Fig.lA], [Fig.lB], [Fig.lC] and [Fig.lD] are sectional views illustrating successive steps of a method of manufacturing an ultrasonic probe according to one embodiment.

[0057] [Fig. 1 A] illustrates a starting structure comprising an electronic chip 110 comprising a set 112 of ultrasonic transducers on a substrate 111, which may be made of silicon (Si).

[0058] The electronic chip 110 may come from the cutting of a wafer on which several MUT transducers are formed.

[0059] The electronic chip 110 is for example an ultrasonic wave emission / reception chip, also called an "ultrasonic array", or "array". Each array may comprise several MUT transducers. Alternatively to a array, it may be a matrix of MUT transducers. The starting structure may also comprise several electronic chips.

[0060] The transducers (not detailed in Figures 1A to 1D) are MUT transducers. They are more detailed in [Fig.2] described later.

[0061] The electronic chip 110 comprises a front face 110A corresponding to the face for transmitting / receiving the ultrasonic waves, and a rear face 110B opposite its front face. The set 112 of MUT transducers of the ultrasonic probe is arranged on the front face 110A side.

[0062] A protective layer 130 is disposed on the front face 110A of the electronic chip 110, so as to protect the MUT transducers. The protective layer is preferably electrically insulating.

[0063] The protective layer 130 is made of a material allowing the propagation of ultrasonic waves, for example similar to a liquid.

[0064] The protective layer 130 may be a polymer layer, preferably flexible, for example an elastomer, for example a silicone, a thermoplastic polyurethane, a polyether block amide (PEBA), a fluorocarbon elastomer (FKM), a polybutadiene.

[0065] The material of the protective layer 130 is for example chosen to be compatible with medical applications (biocompatible).

[0066] The thickness of the protective layer 130 may be between ten and one hundred micrometers, or even between ten and several hundred micrometers.

[0067] The positioning precision of the protective layer 130 on the electronic chip 110 is for example of the order of 10 pm.

[0068] The protective layer 130 may be formed by one or more of the techniques described above.

[0069] In the example shown, the electrical connection of the ultrasonic transducers is provided on the rear face 110B of the electronic chip 110. The set 112 of ultrasonic transducers is electrically connected to the rear face 110B of the electronic chip 110 by conductive vias 102 commonly called "TSV" (of English: "Through-Silicon Vias"), the conductive vias being able to be connected to connection pads 104 positioned on the rear face 110B of the electronic chip 110.

[0070] [Fig. 1B] illustrates a structure obtained after assembly of the electronic chip 110, on the side of its rear face 110B, on a connection face of an interconnection substrate 120.

[0071] The interconnect substrate 120 is, for example, a rigid or flexible printed circuit, an application-specific integrated circuit (ASIC), or an interposer.

[0072] The interconnect substrate 120 may be connected to electronic circuits external to the ultrasonic probe, for example to control the transducers.

[0073] Although this does not appear in Figures 1B to 1D, the lateral dimensions of the interconnect substrate 120 may be larger than those of the electronic chip 110. This is for example shown in the example of [Fig.2].

[0074] The interconnection substrate 120 can be assembled to the electronic chip 110 using an adhesive film 101. The adhesive film can be insulating or conductive, for example an anisotropic conductive film. If the adhesive film is insulating, the electrical connection can be made by solder ball 106 (in English "solder bail") between the connection pads 104 of the electronic chip 110 and the interconnection substrate 120, or by a bonding technique by forming conductive protrusions (in English "stud-bump bonding").

[0075] [Fig.lC] illustrates a structure obtained after the deposition of a metallic screening layer 140 on the structure of [Fig.lB], and more precisely on the protective layer 130.

[0076] The screen layer 140 is adapted to form a screen for protecting the MUT transducers against electromagnetic interference (EMI), more generally an electromagnetic protection screen.

[0077] The shielding layer 140 may be adapted to block light beams, for example laser beams which may propagate in a medium, such as human tissue, in the direction of the ultrasound probe and may disrupt the operation of the MUT transducers by photoacoustic effect.

[0078] The shielding layer 140 may also be adapted to form a chemical barrier layer.

[0079] The material of the screen layer 140 is for example chosen to be compatible with medical applications (biocompatible).

[0080] The shielding layer 140 may be made of gold. Alternatively, the shielding layer may be made of copper, silver, aluminum, or a mixture of gold, copper, silver, and / or aluminum.

[0081] Furthermore, the shielding layer 140 must not block the propagation of ultrasonic waves. The thickness of the shielding layer is therefore preferably less than 10 μm, or even less than 5 pm. The thickness of the screening layer is for example between 100 nm and 10 pm, or even between 100 nm and 5 pm, for example equal to approximately 1 pm.

[0082] The screen layer 140 is shown deposited after the assembly of the electronic chip 110 with the interconnection substrate 120. Alternatively, the screen layer can be deposited before the assembly of the electronic chip with the interconnection substrate, or even before the cutting of the wafer to form the electronic chip.

[0083] The screen layer 140 is for example deposited using a physical vapor deposition (PVD) technique. Alternatively, the screen layer may be deposited using an atomic layer deposition (ALD) technique, or an inkjet deposition technique.

[0084] Preferably, the shielding layer 140 is connected to ground.

[0085] The structure of [Fig.1C] forms all or part of the ultrasonic probe 100, which may include other components, such as those described later.

[0086] [Fig. 1D] illustrates a structure obtained after assembling an encapsulation layer 150 on the screen layer 140, and placing the ultrasonic probe in a housing 160.

[0087] It can be considered in this case that the encapsulation layer 150 and the housing 160 are part of the ultrasonic probe 100.

[0088] The encapsulation layer 150 forms with the housing 160 a waterproof barrier to possible pollution and / or fluids external to the probe. The external surface of the encapsulation layer 150 may be curved, for example concave or convex in shape so as to form an acoustic lens for the acoustic waves which pass through it.

[0089] Alternatively, the ultrasound probe 100 is not disposed in a housing, for example if the ultrasound probe is intended to be used in a catheter.

[0090] The assembly of the encapsulation layer 150 can be carried out by molding the material of the encapsulation layer on the screen layer, or even around the electronic chip and the interconnection substrate.

[0091] The encapsulation layer is preferably acoustically transparent. The material of the encapsulation layer allows the propagation of acoustic waves, and is for example an elastomeric material, for example a polymer containing fillers, for example silicone.

[0092] The average thickness of the encapsulation layer 150 is for example a few hundred micrometers, for example between 100 and 800 μm, and can be a few millimeters.

[0093] The encapsulation layer may advantageously be biocompatible.

[0094] If the ultrasound probe is intended to be used in a catheter, the encapsulation layer can be replaced by the catheter sheath which is then preferably acoustically transparent.

[0095] [Fig.2] is a sectional view showing details of the ultrasonic probe 100 shown in [Fig.1C].

[0096] The ultrasound probe 100 shown comprises at least one electronic chip 110, the electronic chip comprising several MUT transducers 210 formed in and on a substrate 111, for example a silicon substrate. The plurality of MUT transducers 210 corresponds for example to the set 112 of MUT transducers described in connection with [Fig.lA].

[0097] This is not limiting and an electronic chip could only comprise one transducer.

[0098] The electronic chip 110 is assembled on its rear face 110B side on a connection face of an interconnection substrate 120.

[0099] The MUT transducers shown in [Fig. 2] are CMUT type transducers. Each CMUT transducer 210 comprises a membrane cavity 211, a first electrode 212, or upper electrode, surmounting the cavity 211, and a second electrode 213, or lower electrode, arranged under the cavity 211. An insulating layer 214, for example made of silicon dioxide SiO2, forming the membrane of the transducers 210, is positioned between the cavities 211 and the upper electrodes 212. The upper electrodes 212 of the transducers of the electronic chip 110 are connected to each other by a conductive track 201.

[0100] In the example shown, the upper electrodes 212 are dedicated to the electrical signal, and the lower electrode 213 is connected to ground.

[0101] Each upper electrode 212 is connected, via the conductive track 201, to a connection track 222 of the interconnection substrate 120 by a conductive via 202 passing through the insulating layer 214 and the substrate 111 to the interconnection substrate 120.

[0102] In the example shown, the lower electrode 213 is formed by metallization of a portion of the substrate 111 located under the cavities 211 of the electronic chip 110. The lower electrode 213 is connected to a ground track 223 of the interconnection substrate 120 by a conductive via 203 passing through the substrate 111 from the lower electrode 213 to the interconnection substrate 120. This example can be applied for a substrate made of undoped silicon, i.e., little or no conductive. This example is not limiting and other variants will appear to those skilled in the art. According to a variant, when the substrate is conductive, for example when it is made of doped silicon, the metallization can be omitted, and the electrode lower may be formed by a portion of the conductive substrate, the contact recovery of the lower electrode with the ground track being ensured by a conductive via crossing the substrate to the interconnection substrate.

[0103] The connection tracks 222 and ground tracks 223 of the interconnection substrate 120 are located at the connection face of the interconnection substrate.

[0104] When there are several electronic chips of MUT transducers to be connected to the interconnection substrate, for example in a strip or a matrix, the interconnection substrate may comprise several connection tracks insulated from each other, or even several ground tracks insulated or not from each other. The different MUT transducers of the same element, for example of the same electronic chip, in the strip or the matrix are generally connected to each other. In the strip or the matrix, there may be as many conductive vias as there are elements connected to upper electrodes, for the electrical signals (individual addressing for each element). On the other hand, the lower electrodes, connected to ground, of the different elements may all be connected to each other with a single conductive via. However, several conductive vias for ground connection may be provided for better conductivity.

[0105] In [Fig.1C], the protective layer 130 and the screen layer 140 completely cover the substrate 111. [Fig.2] shows a variant where the protective layer 130 and the screen layer 140 cover the transducers 210 but do not necessarily cover the entire surface of the substrate 111. In other variants, such as those described later, the screen layer may extend beyond the protective layer on either side, for example surrounding the protective layer, or even extending beyond portions of the substrate.

[0106] In the embodiments described in relation to Figures 1A to 1D and 2, the electrical connection has been described via the rear face of the electronic chip, the latter comprising conductive vias passing through the substrate, but this connection method is not limiting. The electrical connection can for example be made via the front face of the electronic chip as described in relation to Figures 3A to 3D and 4, the electronic chip then not necessarily comprising conductive vias. It is also conceivable to make electrical connections both via the front face and via the rear face, for example the connection of the earth via the front face and the connection of the signal via the rear face, or even conversely the connection of the earth via the rear face and the connection of the signal via the front face.

[0107] [Fig.3A], [Fig.3B], [Fig.3C] and [Fig.3D] are sectional views illustrating successive steps of a method of manufacturing an ultrasonic probe 300 according to another embodiment.

[0108] [Fig.3A] illustrates a starting structure comprising an electronic chip 310 comprising a set 312 of ultrasonic transducers on a substrate 311, which may be made of silicon (Si).

[0109] The electronic chip 310 may come from the cutting of a wafer on which several MUT transducers are formed.

[0110] The electronic chip 310 is for example an ultrasonic wave emission / reception chip, also called an "ultrasonic array", or "array". Each array may comprise several MUT transducers. Alternatively to a array, it may be a matrix of MUT transducers. The starting structure may also comprise several electronic chips.

[0111] The transducers (not detailed in Figures 3A to 3D) are MUT transducers. They are more detailed in [Fig.4] described later.

[0112] The electronic chip 310 comprises a front face 310A corresponding to the face for transmitting / receiving ultrasonic waves, and a rear face 310B opposite its front face. All of the transducers of the probe are arranged on the front face side.

[0113] A protective layer 330 is arranged on the front face 310A of the electronic chip 310, so as to protect the transducers.

[0114] The characteristics and variants of the protective layer of [Fig. 1 A] can be applied to the protective layer of [Fig. 3A], except that the protective layer 330 does not cover the entire surface of the substrate 311. On uncovered portions of the substrate 311, the electronic chip 310 comprises connection pads 302.

[0115] [Fig.3B] illustrates a structure obtained after assembling the electronic chip 310, on its rear face 310B side, on a connection face of an interconnection substrate 320, using a glue or an adhesive film 301.

[0116] The characteristics and variants of the interconnect substrate of [Fig.lB] can be applied to the interconnect substrate of [Fig.3B].

[0117] Furthermore, a connection by conductive wire 304, by the technique known as "wire-bonding" in English, is made between each connection pad 302 of the electronic chip 310 and a connection track 322 of the interconnection substrate 320. A sealing drop 306 (in English "glob-top") of electrically insulating resin encapsulates each conductive wire 304, as well as the connection pads 302 and the connection tracks 322, in order to avoid short circuits.

[0118] The diameter of the conductive wires 304 is for example equal to approximately 15 μm, 20 μm or 25 μm. The length of the conductive wires is for example equal to a few millimeters, depending on the connection distance to be achieved.

[0119] [Fig.3C] illustrates a structure obtained after the deposition of a metallic screen layer 340 on the structure of [Fig.3B], more precisely on the protective layer 330, the screen layer 340 extending over portions of the substrate 311 not covered by the protective layer 330 to cover the glob-top 306.

[0120] The characteristics, manufacturing methods and variants of the screen layer of [Fig. 1C] can be applied to the screen layer of [Fig. 3C], except that, in this embodiment, the deposition of the screen layer 340 is preferably carried out after the assembly of the electronic chip 310 with the interconnection substrate 320, and after the bonding by conductive wire and the encapsulation by the glop-top 306, in order to avoid a short circuit between the screen layer 340 and the conductive wires 304.

[0121] Preferably, the shielding layer 340 is connected to ground. Embodiments of grounding the shielding layer are described later.

[0122] For example, a space is maintained on the substrate 311 between the protective layer 330, and therefore the screen layer 340, and the sealing drops 306 encapsulating the conductive wires 304, so as to provide a connection pad to the ground of the screen layer on the substrate 311.

[0123] The structure of [Fig.3C] forms all or part of the ultrasonic probe 300, which may include other components, such as those described later.

[0124] [Fig.3D] illustrates a structure obtained after assembling an encapsulation layer 350, for example a lens, on the screen layer 340, and placing the ultrasonic probe 300 in a housing 360. It can be considered in this case that the encapsulation layer 350 and the housing 360 are part of the ultrasonic probe 300. The encapsulation layer 350 is preferably an acoustically transparent layer.

[0125] The features, embodiments and variants of the lens or transparent layer described in connection with [Fig. 1D] may be applied to the structure of [Fig. 3D]. The same applies to the housing.

[0126] [Fig.4] is a sectional view showing details of the ultrasonic probe 300 of [Fig.3C].

[0127] The ultrasound probe 300 shown comprises at least one electronic chip 310, the electronic chip comprising several MUT transducers 410 formed in and on a substrate 311. The plurality of MUT transducers 410 corresponds for example to the set 312 of MUT transducers described in connection with [Fig.3A].

[0128] This is not limiting and an electronic chip could only comprise one transducer.

[0129] The electrical chip 310 is assembled on its rear face 310B side on a connection face of an interconnection substrate 320.

[0130] The MUT transducers shown in [Fig.4] are CMUT type transducers. Each CMUT transducer 410 comprises a membrane cavity 411, a first electrode 412, or upper electrode, surmounting the cavity 411, and a second electrode 413, or lower electrode, arranged under the cavity 411. A layer of insulation 414, for example silicon dioxide SiO2, forming the membrane of the transducers 410, is positioned between the cavities 411 and the upper electrodes 412. The upper electrodes 412 of the transducers of the electronic chip 310 are connected to each other by a conductive track 401. In the example shown, the upper electrodes 412 are dedicated to the electrical signal, and the lower electrode 413 is connected to ground.

[0131] The electronic chip 310 further comprises a connection pad 402 connected to the conductive track 401. The connection pad 402 can be connected to a connection track 422 of the interconnect substrate 320 by a first conductive wire 404. A glob-top 306 similar to that of [Fig.3C] covers the connection pad 402, the connection track 422, and the first conductive wire 404.

[0132] The electronic chip 310 further comprises a ground pad 403 connected to the lower electrode 413 by a conductive via 406 passing through the insulating layer 414, as well as the substrate 311 over a partial thickness.

[0133] In the example shown, the lower electrode 413 is formed by metallization of a portion of the substrate 311 located under the cavities 411 of the electronic chip 310. The lower electrode 413 is connected to a ground track 423 of the interconnection substrate 320 by a second conductive wire 405, via the ground pad 403 of the electronic chip and the conductive via 406. A glob-top 306 similar to that of [Fig. 3C] covers the ground pad 403, the ground track 423, and the second conductive wire 405. This example can be applied for an undoped silicon substrate, i.e. a low or non-conductive one. This example is not limiting and other variants will appear to those skilled in the art.According to a variant, when the substrate is conductive, for example when it is made of doped silicon, the metallization can be omitted, and the lower electrode can be formed by a portion of the conductive substrate, the resumption of contact of the lower electrode with the ground pad of the electronic chip can be ensured by a conductive via crossing the insulating layer and the substrate over a partial thickness.

[0134] The transducers of Figures 1A to 1D, 2, 3A to 3D and 4 may be adapted by a person skilled in the art for PMUT transducers, instead of CMUT transducers.

[0135] The shield layer of Figures 1A to 1D, 2, 3A to 3D and 4 may be connected to ground via a grounding track of the interconnect substrate which is preferably different from the ground tracks provided for connecting the lower electrodes of the electronic chip to ground.

[0136] [Fig. 5] is a sectional view showing an ultrasonic probe 500 according to another embodiment. The ultrasonic probe 500 is a variation of the ultrasonic probe 300 of [Fig. 3C] which differs therefrom mainly in that the glob-top 506 extend over portions of the protective layer 330, and that the shielding layer 540 extends over the glob-top 506 without descending onto the substrate 311 of the electronic chip 310, and covers the glob-top up to the interconnect substrate 320.

[0137] [Fig.6A], [Fig.6B] and [Fig.6C] are top views showing several ways of connecting the ultrasonic probe 500 of [Fig.5] to ground. The shielding layer is made transparent in Figures 6A to 6C to better visualize the connections.

[0138] The sectional view of [Fig.5] corresponds to a section taken in the plane AA identified in figures 6A to 6C.

[0139] In the connection mode of [Fig.6A], ground connection pads 601 (ground pads) of the shield layer 540 are positioned on edges of the interconnect substrate 320 not covered by the glob-tops 506. The shield layer 540 is connected to these ground pads 601, for example by wire-bonding.

[0140] In the connection mode of [Fig.6B], ground connection pads 602 (ground pads) of the shield layer 540 are positioned on edges of the chip 310 not covered by the glob-tops 506. These ground pads 602 are connected to the interconnect substrate 320 by vias in the chip. The shield layer 540 is connected to these ground pads 602, for example by wire-bonding.

[0141] In the connection mode of [Fig.6C], ground connection pads 603 (earth pads) of the screen layer 540 are also positioned on edges of the chip 310, which are not entirely covered by the glob-tops 606. But the ground pads 603 each comprise a first part 603A not covered by the glob-tops 606 and adapted to be connected to the screen layer 540, for example by wire-bonding, as well as a second part 603B covered by the glob-tops 606 and connected by wire-bonding to another ground connection pad 604 of the interconnection substrate 320, different from the ground tracks 322 provided for connecting the electronic chip to the ground. These other ground connection pads are covered by the glob-tops 606 which have a shape that is significantly different from the glob-tops 506 of Figures 5, 6A and 6B.

[0142] As an alternative to the connection method of [Fig.6C], instead of two-part ground pads 603, it may be pairs of pads, the two pads of each pair being insulated from each other but connected for example by wire-bonding, a first pad of each pair being adapted to be connected to the screen layer, and a second pad of the pair being covered by one of the glob-tops and connected by wire-bonding to a ground connection pad of the interconnection substrate.

[0143] In the embodiments described with reference to FIGS. 6A, 6B and 6C, the glob-top protection 506 is located at the place where the wires 304 of wire-bonding to protect them. As a variant, the glob-top protection can advantageously extend over the entire perimeter of the electronic chip 310 and the protective layer 330 to prevent the side faces of the electronic chip 310 from being in contact with the screen layer 540.

[0144] The ultrasound probes previously described, more generally the ultrasound probes according to the embodiments, may be intended for diagnostic or ultrasound treatment applications using ultrasound probes external to the body, or internal probes which can be inserted into the body, into cavities or blood vessels, for example integrated into a catheter.

[0145] Various embodiments and variations have been described. Those skilled in the art will understand that certain features of these various embodiments and variations could be combined, and other variations will occur to those skilled in the art. For example, those skilled in the art will understand that an application-specific integrated circuit (ASIC) may be interposed between the electronic chip and the interconnect substrate, or as a replacement for the latter.

[0146] Finally, the practical implementation of the embodiments and variants described is within the reach of those skilled in the art from the functional indications given above.

Claims

Claims

1. An ultrasonic probe (100; 300; 500) comprising: - an electronic chip (110; 310) having a front face (110A; 310A) and comprising a substrate (111; 311) and at least one ultrasonic transducer (210; 410) micro-machined in and on the substrate on the front face and comprising a first electrode (212; 412), for example dedicated to an electrical signal, and a second electrode (213; 413), for example dedicated to grounding; - an electrically insulating protective layer (130; 330) covering the at least one transducer; and - a metal shielding layer (140; 340; 540) on the protective layer, the shielding layer forming an electromagnetic shielding of said at least one transducer.

2. An ultrasonic probe (100; 300; 500) according to claim 1, further comprising an interconnection substrate (120; 320) assembled to a rear face (110B; 310B) of the electronic chip opposite the front face, the interconnection substrate being adapted to connect the screen layer (140; 340; 540) to ground, for example by ground connection pads (601, 602, 603) dedicated to grounding the screen layer.

3. An ultrasonic probe (100; 300) according to claim 1 or 2, further comprising a layer (150; 350) of an acoustically transparent material to ultrasound on the shield layer (140; 340), said layer of the acoustically transparent material being for example molded above said shield layer.

4. A method of manufacturing an ultrasonic probe (100; 300; 500), the method comprising, on an electronic chip (110; 310) having a front face (110A; 310A) and comprising a substrate (111; 311) and at least one micromachined ultrasonic transducer (210; 410) formed in and on the substrate on the front face and comprising a first electrode (212; 412), for example dedicated to an electrical signal, and a second electrode (213; 413), for example dedicated to grounding, the deposition of: - a protective layer (130; 330) covering the at least one transducer; then - a metallic screen layer (140; 340; 540) on the protective layer, the screen layer forming an electromagnetic shield for said at least one transducer.

5. Method according to claim 4, further comprising assembling an interconnect substrate (120; 320) to a rear face (110B; 310B) of the electronic chip opposite the front face, the interconnect substrate being adapted to connect the screen layer (140; 340; 540) to ground.

6. A method according to claim 4 or 5, further comprising forming a layer (150; 350) of an acoustically transparent material to ultrasound on the shielding layer (140; 340), said formation being carried out for example by molding the acoustically transparent material above said shielding layer.

7. An ultrasonic probe according to claim 3, or a method according to claim 6, wherein: - the acoustically transparent material is an elastomer and / or is biocompatible; and / or - the thickness of the layer of the acoustically transparent material is between 300 micrometers and 1 millimeter; and / or - the layer of the acoustically transparent material is an acoustic lens.

8. An ultrasound probe according to any one of claims 1 to 3 and 7, or a method according to any one of claims 4 to 7, wherein: - the protective layer is made of a material acoustically transparent to ultrasound, for example an elastomer, such as a silicone, a thermoplastic polyurethane, a polyether block amide, a fluorocarbon elastomer, a polybutadiene, or a combination of several of these materials; and / or - the protective layer is made of a biocompatible material; and / or - the thickness of the protective layer is between 10 micrometers and 1 millimeter, for example between 10 and 500 micrometers or between 10 and 100 micrometers.

9. An ultrasonic probe according to any one of claims 1 to 3, 7 and 8, or a method according to any one of claims 4 to 8, wherein: - the shielding layer is made of gold, silver, aluminum, copper, or a combination of several of these materials; and / or - the screen layer is made of a biocompatible material; and / or - the thickness of the screen layer is adapted to the propagation of ultrasonic waves in said screen layer; and / or - the thickness of the screen layer is less than 10 micrometers, for example less than 5 micrometers.

10. An ultrasonic probe (100) according to any one of claims 1 to 3, 7 to 9, or a method according to any one of claims 4 to 9, wherein the electrical connection of the at least one transducer (210) is on the rear face (110B) of the electronic chip (110), for example via conductive vias (102; 202, 203) passing through the substrate (111).

11. Ultrasonic probe (300; 500) according to any one of claims 1 to 3, 7 to 9, or method according to any one of claims 4 to 9, in which the electrical connection of the at least one transducer (410) is on the front face (310A) of the electronic chip (310), for example via conductive wires (304; 404, 405).

12. An ultrasonic probe (300; 500) according to claim 11, or a method according to claim 11, wherein the electrical connection of the at least one transducer (410) is made via conductive wires (304; 404, 405), said conductive wires being electrically insulated by sealing drops (306; 506; 606), and the shielding layer (340; 540) extending over the sealing drops.

13. An ultrasonic probe according to any one of claims 1 to 3, 7 to 12 in combination with claim 2, or a method according to any one of claims 4 to 12 in combination with claim 5, wherein the interconnect substrate is: - a flexible interconnect substrate; and / or - a printed circuit; and / or - an application-specific integrated circuit.

14. An ultrasonic probe according to any one of claims 1 to 3, 7 to 13 in combination with claim 2, or a method according to any one of claims 4 to 13 in combination with claim 5, comprising an application-specific integrated circuit between the interconnect substrate and the electronic chip.

15. An ultrasonic probe according to any one of claims 1 to 3, 7 to 14, or a method according to any one of claims 4 to 14, wherein: - each micromachined ultrasonic transducer is a micromachined capacitive ultrasonic transducer or a micromachined piezoelectric ultrasonic transducer; and / or - the electronic chip comprises several micro-machined ultrasonic transducers covered by the protective layer and the shielding layer; and / or - the ultrasonic probe comprises several electronic chips each comprising one or more micro-machined ultrasonic transducers covered by the protective layer and the screen layer, the electronic chips being arranged in line or according to a matrix network, for example the different electronic chips, in particular the ultrasonic transducers of the different electronic chips, being individually connectable to an electrical signal.

16. An ultrasonic probe (100; 300) according to any one of claims 1 to 3, 7 to 15, or a method according to any one of claims 4 to 15, the ultrasonic probe being disposed in a housing (160; 360).

17. An ultrasound probe according to any one of claims 1 to 3, 7 to 15, or a method according to any one of claims 4 to 15, the ultrasound probe being adapted to be inserted into a catheter.

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