Ultrasonic capture device with encapsulated acoustic propagation layer

Abstract

Ultrasonic capture device with encapsulated acoustic propagation layer The present description relates to an ultrasonic capture device (100) comprising at least: - an ultrasonic transducer circuit (106) arranged on and / or in a substrate (102); - an acoustic propagation material (114) arranged in a cavity (110) in which the ultrasonic transducer circuit (106) is located; - a sealing layer (118) closing the cavity (110) on the side of a capture surface (102) of the ultrasonic capture device (100) configured so that at least one element is arranged thereon during a capture by the ultrasonic capture device. Figure for abstract: Fig. 1

Description

Title of the invention: Ultrasonic capture device with encapsulated acoustic propagation layer Technical field

[0001] The present description relates generally to the field of devices for capturing information by ultrasonic transduction, finding for example applications in the fields of biometric identification, medicine, non-destructive testing, or even in other general public fields. Prior art

[0002] A biometric identification device is used to verify or determine the identity of a user of the device based on a measurement of at least one biometric characteristic of the user such as a fingerprint, face shape, iris pattern, retina pattern, etc. The different techniques for measuring one or other of these characteristics each have advantages and disadvantages depending on different criteria, including in particular: more or less significant error rate, ease or not of stealing the template with which the measurements are compared, possibility of detecting an imitation or not, proof or not of life, ease and comfort of use, size of the sensor required, energy consumption required, etc.

[0003] In the case of a biometric identification device by ultrasonic transduction in which the measurement of biometric characteristics involves propagation between the device and the user, it may be advisable to optimize the acoustic coupling between the part of the user's body on which the measurement is intended to be carried out (corresponding for example to one or more fingers of the user) and the capture surface of the device with which this part of the user's body is intended to be in contact. This is particularly the case for identification devices measuring biometric characteristics present under the user's skin, for example devices performing recognition of the microvasculature of the user's finger(s), i.e. performing image capture of the micro-blood vessels of this or these fingers of the user of the device.Optimizing this acoustic coupling generally involves depositing a lubricant such as water-based gel, or a pad, or block, of semi-solid hydrogel, on the capture surface of the device. The lubricant can be deposited, directly or via a container such as a vial or bottle, on the capture surface by the user.

[0004] However, this intervention on the part of the user to deposit the lubricant on the capture surface has several disadvantages. For example, this dispensation can be poorly performed (uncontrolled quantity of lubricant, dispersion of the lubricant outside the capture surface, etc.). In addition, this implies that the user must have such a lubricant. Then, cleaning of the coated surfaces must be carried out after use. Finally, this solution offers no sustainability given that the lubricant evaporates or flows very quickly, and the lubricant must be dispensed just before each measurement.

[0005] As an alternative to dispensing lubricant onto the capture surface, it is possible to use, at the capture surface of the device, a permanent coupling layer. Such a coupling layer comprises, for example, an elastomeric material. The acoustic coupling obtained with such a coupling layer is, however, less good than that obtained by dispensing a lubricant onto the capture surface, due in particular to the much higher attenuation, the poorer mechanical conformability to surface asperities (due to the solid nature of the coupling layer, compared to the liquid nature of the lubricant) and the parasitic reflections linked to the impedance mismatch generally generated by this layer.

[0006] These problems are also found for capture devices other than biometric identification devices, for example in the medical field, non-destructive testing, or even in other consumer fields. Summary of the invention

[0007] There is a need to propose an ultrasound capture device, or ultrasound transduction capture device, which does not have at least some of the drawbacks of existing solutions.

[0008] One embodiment overcomes all or part of the drawbacks of the known solutions and proposes an ultrasonic capture device comprising at least:

[0009] - an ultrasonic transducer circuit arranged on and / or in a substrate;

[0010] - an acoustic propagation material arranged in a cavity in which find the ultrasonic transducer circuit;

[0011] - a sealing layer closing the cavity on the side of a capture surface of the ultrasonic capture device configured so that at least one element is disposed thereon during capture by the ultrasonic capture device.

[0012] According to a particular embodiment, the acoustic propagation material is a gel or a viscous liquid, preferably hydrogel and / or silicone oil and / or silicone gel.

[0013] According to a particular embodiment, the acoustic propagation material forms a layer with a thickness of between 1 mm and 5 mm.

[0014] According to a particular embodiment, the acoustic propagation material has a Shore 00 hardness of between 10 and 60.

[0015] According to a particular embodiment, the sealing layer has a thickness of between 8 μm and 250 μm and / or less than an ultrasound wavelength intended to be emitted by the ultrasound transducer circuit.

[0016] According to a particular embodiment, the sealing layer comprises polyester.

[0017] According to a particular embodiment, the ultrasonic capture device further comprises a passivation and acoustic impedance matching layer arranged at least between the ultrasonic transducer circuit and the acoustic propagation material.

[0018] According to a particular embodiment, the ultrasonic capture device further comprises a barrier layer closing, with the sealing layer, the cavity on the side of the capture surface, the barrier layer being arranged between the sealing layer and the acoustic propagation material.

[0019] According to a particular embodiment, the barrier layer comprises a metal oxide or an organic compound.

[0020] According to a particular embodiment, the barrier layer and the sealing layer together form a stack whose modulus of elasticity is between 1 GPa and 4 GPa.

[0021] According to a particular embodiment, the ultrasonic capture device further comprises a contact layer such that the sealing layer is arranged between the contact layer and the acoustic propagation material, the contact layer forming the capture surface.

[0022] According to a particular embodiment, the contact layer comprises elastomer and / or a thermoplastic.

[0023] According to a particular embodiment, the contact layer has a thickness of between 10 μm and 100 μm and / or less than an ultrasound wavelength intended to be emitted by the ultrasound transducer circuit.

[0024] According to a particular embodiment, the ultrasonic capture device further comprises a frame arranged on the substrate and forming side walls of the cavity.

[0025] According to a particular embodiment, the ultrasonic capture device corresponds to a biometric identification device configured to implement biometric identification from a part of a user's body intended to be placed on the capture surface. Brief description of the drawings

[0026] 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:

[0027] [Fig.l] schematically represents an ultrasonic capture device according to a particular embodiment. Description of the embodiments

[0028] 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.

[0029] For the sake of clarity, only the elements useful for understanding the described embodiments have been shown and are detailed. In particular, various elements of the capture device such as the ultrasonic transducer circuit, the control circuit, the data processing circuit, etc. are not detailed. Those skilled in the art will be able to produce these elements in detail from the functional description given here.

[0030] 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 in a normal position of use.

[0031] Unless otherwise specified, the expressions "about", "approximately", "substantially", and "of the order of" mean to within 10%, preferably to within 5%.

[0032] An ultrasonic capture device 100 according to a particular embodiment is described below in connection with [Fig.l].

[0033] In the example described, the device 100 is configured to implement biometric identification by performing measurements of biometric characteristics of a part of the body of the user of the device 100. This part of the user's body may correspond to one or more fingers of the user. Alternatively, other parts of the user's body may be used to perform the biometric identification by the device 100. Furthermore, in the example described here, the part of the user's body used to perform the biometric identification corresponds to a single finger of the user.

[0034] The device 100 comprises a capture surface 102 on which the finger of the user of the device 100 is intended to be placed during biometric identification.

[0035] The device 100 further comprises a substrate 104 serving, in the embodiment described, as a support for the various elements of the device 100. For example, the substrate 104 may correspond to a printed circuit of the PCB type (“Printed Circuit Board" in English). Other types of substrate can be used to produce the substrate 104.

[0036] The device 100 also comprises an ultrasonic transducer circuit 106 configured to transmit and receive ultrasonic signals during the measurements used for the biometric identification of the user of the device 100. According to an exemplary embodiment, the circuit 106 may comprise a plurality of ultrasonic transducers configured to carry out the image acquisitions required for the biometric identification. The ultrasonic transducers are for example arranged in a matrix manner or in another manner adapted to the captures to be carried out. The number of ultrasonic transducers of the circuit 106 may depend on the dimensions of the capture surface 102, the dimensions of each ultrasonic transducer, the resolution of the measurements intended to be carried out by the device 100, etc.The circuit 106 may for example comprise transducers of the CMUT type (“Capacitive Micromachined Ultrasonic Transducer” in English, or capacitive micromachined ultrasonic transducer) or of the PMUT type (“Piezoelectric Micromachined Ultrasonic Transducer” in English, or piezoelectric micromachined ultrasonic transducer) or of another type.

[0037] In the described embodiment, the device 100 can be configured to perform an acquisition of at least one surface image of the user's finger placed on the capture surface 102 and in contact therewith, that is to say an acquisition of at least one image of a fingerprint of the finger, formed of ridges and valleys present on the surface of the skin of the finger placed on the capture surface 102. In the device 100, the acquisition of a surface image of the user's finger placed on the capture surface 102 and in contact therewith is possible because the ultrasound emitted by the circuit 106 is reflected more significantly against the air present in the valleys of the finger than against the ridges.The difference between the signals received by the circuit 106 which are reflected on the valleys and those which are reflected on the peaks can be used to reconstruct the image of the fingerprint of the user's finger present on the capture surface 102.

[0038] In addition, the device 100 may also be configured to carry out acquisitions of volume or depth information of the finger placed on the capture surface 102 of the device 100 and in contact with it, and from which it is for example possible to determine, by processing this volume information, global information on the microvasculature of the finger and the consequences of its activity, for example a global volume image of the microvasculature of this finger, that is to say a capture of images of the blood vessels of the finger of the user of the device 100, or even information relating to the proof of life or which can serve as an identification element. According to a particular example, the acquired volume information may correspond to volume or depth images of the finger placed on the capture surface 102. The overall volume information obtained can be deduced from several pieces of volume information captured successively at non-zero depths (dimension parallel to the Z axis visible in [Fig.l] and which is for example substantially perpendicular to the capture surface 102) of the finger present on the capture surface 102.

[0039] Alternatively, it is possible for the device 100 to be configured to perform only one of the two types of acquisition described above.

[0040] In the embodiment described, the device 100 comprises a frame 108 arranged on the substrate 104 and forming side walls of a cavity 110 in which the circuit 106 is located. In the example of [Fig.l], the bottom wall of the cavity 110 is formed by the substrate 104. In the example of [Fig.l], in a plane parallel to the plane (X,Y), that is to say parallel to the face of the substrate 104 on which the frame 108 is arranged, the frame 108 has a square-shaped section. Other shapes are possible, in particular depending on the general shape desired for the device 100.

[0041] The frame 108 can ensure the cohesion and durability of the multi-layer assembly formed by the device 100. The frame 108 can in particular have the following advantages:

[0042] - provision of mechanical robustness, allowing in particular the device 100 to resist to shocks and stresses experienced during its manufacture and use;

[0043] - contribution of environmental and thermomechanical robustness, allowing in particular to the device 100 to resist the effects of temperature and differential expansions of its constituent elements;

[0044] - function of encapsulating the elements present in the cavity 110, forming in particular a barrier blocking the diffusion or permeation of chemical species from and / or towards these elements, i.e. blocking the entry of contaminants coming from outside the cavity 110, and / or limiting the leakage of species contained in the materials present in the cavity 110 (for example the leakage of water when hydrogel is present in the cavity 110).

[0045] The material(s) and dimensions of the frame 108 may in particular be chosen such that the frame 108 has the above advantages. The height of the frame 108 (corresponding to the dimension parallel to the Z axis shown in [Fig.l]) may be chosen as a function of the thickness of the materials intended to be present in the cavity 110, and may for example be between 1 mm and 5 mm. The thickness of the walls of the frame 108 (i.e. the dimension perpendicular to the side walls of the frame 108) may be between 150 μm and a few millimeters.

[0046] According to a first example, the frame 108 can be produced in the form of a peripheral bead as produced during the encapsulation of electronic components by a technique called “Dam-and-Fill”. In this first example, the frame 108 can comprise at least one epoxy resin and / or polyurethane and / or an encapsulating silicone.

[0047] According to a second example, the frame 108 can be made in the form of a machined metal part, comprising for example aluminum and / or stainless steel, which can be manufactured and then bonded to the substrate 104. In this second example, the form factor between the height of the frame 108 and the thickness of the walls of the frame 108 can be maximized.

[0048] According to a third example, the frame 108 may comprise a ceramic-polymer composite material.

[0049] Other configurations of the cavity 110 are conceivable.

[0050] In the embodiment described, the device 100 further comprises a passivation and acoustic impedance matching layer 112. In the example of [Fig.l], this layer 112 is arranged in the cavity 110 and covers the circuit 106 as well as regions of the substrate 104 located in the cavity 110 and not covered by the circuit 106. The characteristics of the layer 112 may be such that this layer 112 forms electrical insulation and mechanical and environmental protection of the circuit 106.

[0051] According to an exemplary embodiment, the thickness of the layer 112 can be minimized in order to reduce the acoustic attenuation generated by this layer 112, while avoiding interference phenomena (case where the thickness is a multiple of X / 4, with X corresponding to the length of the ultrasound transmitted from or to the circuit 106. The layer 112 can also be produced such that its flatness is as good as possible. Thus, depending on the method implemented for its production (for example dispensing in the liquid state), a compromise between thickness (on which the attenuation depends) and flatness may be necessary.

[0052] The device 100 further comprises an acoustic propagation material 114 arranged, in the example of [Fig.l], on the passivation and impedance matching layer 112. This acoustic propagation material 114 is chosen such that it minimizes the acoustic attenuation of the ultrasounds passing through it. Furthermore, the acoustic propagation material 114 can be chosen such that its acoustic impedance is matched with that of the other materials located in the propagation path of the ultrasounds emitted and received by the circuit 106. More particularly, this impedance matching can be carried out as a function of the target medium intended to be analyzed, for example biological tissues when the device 100 is a biometric identification device (the acoustic speed in such tissues is of the order of 1540 m / s).It is also possible to achieve matching with the material of the passivation and acoustic impedance matching layer 112 as well as the materials of the layers covering the material 114 (described later). The material of . the layer 112 can in particular be chosen such that it achieves an impedance matching between the circuit 106 and the acoustic propagation material 114.

[0053] The acoustic propagation material 114 is also chosen such that its mechanical characteristics are adapted to the use of the device 100. For example, when the device 100 corresponds to a fingerprint sensor, the acoustic propagation material 114 can be chosen such that its modulus of elasticity is adapted to present a reaction force adapted to the pressing of the finger on the capture surface 102. By way of example, the acoustic propagation material 114 can be chosen such that it has a Shore 00 hardness of between 10 and 60 (for example measured in accordance with the ASTM D2240 standard).

[0054] In the described embodiment, the acoustic propagation material 114 may correspond to a layer of gel or a viscous liquid, for example, the viscosity of which is between 1000 and 50000 centipoise, or mPa.s. According to a particular embodiment, the acoustic propagation material 114 may comprise a hydrogel. This hydrogel may be based on polymers such as polyethylene glycol (PEG), polyethylene glycol diacrylate (PEGDA), polyvinyl alcohol (PVA), polyacrylamide, polyacrylic acid (PAA), agar-agar, agarose, etc. It is also possible for the acoustic propagation material 114 to comprise silicone oil and / or silicone gel, as well as other non-aqueous gels.

[0055] Furthermore, the acoustic propagation material 114 can form, in the cavity 110, a layer with a thickness of, for example, between 1 mm and 5 mm.

[0056] In the example of [Fig. 1], the acoustic propagation material 114 corresponds to hydrogel, and the remainder of the space of the cavity 110 not occupied by the circuit 106, the layer 112 and the acoustic propagation material 114 is occupied by a liquid corresponding for example to a “swelling” agent or solvent of the hydrogel, such as water which may comprise one or more miscible organic compounds. This liquid forms for example a reserve intended to compensate for the risks of possible loss by leakage and by permeation, and / or to guarantee stability of the composition of the hydrogel over a long lifetime. Such a reserve can operate passively because the natural diffusion of the liquid towards the acoustic propagation material 114, tending towards a uniformization of the species concentration, can guarantee the homogeneity of the liquid content of the acoustic propagation material 114.

[0057] In the exemplary embodiment described, the device 100 further comprises a barrier layer 116 and a sealing layer 118 closing the cavity 110 on the side of the capture surface 102. In this exemplary embodiment, the barrier layer 116 is arranged between the sealing layer 118 and the acoustic propagation material 114.

[0058] In the embodiment described, the barrier layer 116 and the layer of sealing 118 cooperate to seal the cavity 110 and ensure the physical integrity and durability of the acoustic propagation material 114. Furthermore, the barrier layer 116 and the sealing layer 118 can be made such that together they form a stack whose modulus of elasticity is between 1 GPa and 4 GPa, thus offering a good compromise between mechanical strength, durability and deflection when pressed on the capture surface 102. In addition, the materials of these layers 116 and 118 can be chosen such that they are easily usable when producing the device 100, i.e. such that they can be easily cut, laminated, glued, etc.

[0059] According to a particular example, the sealing layer 118 may have a thickness of between 8 μm and 250 μm. In such a case, the sealing layer 118 may be called a “sealing film” given its small thickness. Furthermore, the total thickness of the barrier layer 116 and the sealing layer 118, or the thickness of the sealing layer 118 or the barrier layer 116 (preferably the layer generating the highest attenuation and / or the least well-matched in impedance) may be less than an ultrasound wavelength intended to be emitted by the circuit 106.

[0060] For example, the sealing layer 118 may comprise polyester such as PE (polyethylene) or PET (polyethylene terephthalate). The barrier layer 116 may comprise a metal oxide or a specific organic compound, for example SiO2 or BOPP (biaxially oriented polypropylene). It is also possible that the material of the barrier layer 116 corresponds to a metallic material deposited on the sealing layer 118 before the cavity 110 is closed.

[0061] Alternatively, it is possible that the barrier layer 116 is not present and that the sealing layer 118 also fulfills the functions of barrier layer.

[0062] In the described embodiment, the device 100 also comprises a contact layer 120 such that the sealing layer 118 is arranged between the contact layer 120 and the acoustic propagation material 114. Furthermore, in this example, one of the main faces of the contact layer 120 forms the capture surface 102.

[0063] The contact layer 120 may be made such that it ensures optimal contact with the target element (the skin of a finger in the example described) intended to come into contact with the capture surface 102, in particular in terms of acoustic coupling with this element. The contact layer 120 may also be made so as to contribute to a high durability of the sealing of the acoustic propagation material 114 in the cavity 110, obtaining good resistance to external aggressions (thermal, chemical, UV, etc.), and such that it is easily cleanable. Furthermore, when the contact layer 120 is intended to be in contact with skin, the material of the contact layer 120 may be chosen such that it is biocompatible.

[0064] The geometric characteristics of the contact layer 120 and its material(s) may be such that the contact layer 120 is deformable and flexible. These properties of the contact layer 120 may in particular be such that the layer 120 has excellent conformability to the finger, in particular at the submillimeter scale, intended to be positioned on the capture surface 102, even when this finger applies moderate pressure to the capture surface 102 (for example less than approximately 50 gf, i.e. less than approximately 0.5 N). Thus, the layer 120 can deform so as to at least partially match the microtopography of the finger applying pressure to the layer 120.For example, in order to obtain the desired effects, the material of the contact layer 120 may have a Shore 00 hardness of between 10 and 60 (for example measured in accordance with the ASTM D2240 standard), this hardness value corresponding substantially to that of the surface layers of a finger (as described for example in the document by Dzidek Brygida M. et al., “Contact mechanics of the human finger pad under compressive loads”, JR Soc. Interface. 2017 Feb, 14(127):20160935).

[0065] For example, the contact layer 120 may correspond to a wet layer (coating) or vacuum (evaporation, for example by chemical vapor deposition) elastomer deposition. It is also possible for the contact layer 120 to comprise an elastomer from the silicone family, or a thermoplastic (for example based on polyurethane or other block copolymers). The thickness of the contact layer 120 is for example between 10 μm and 100 μm. Furthermore, the thickness of the contact layer 120 may be less than an ultrasound wavelength intended to be emitted by the circuit 106, the value of this wavelength being defined here as equal to the ratio of the propagation speed in the contact layer 120 to the ultrasound frequency set by the circuit 106.

[0066] In the device 100, the characteristics of the layers 116, 118, 120 and of the acoustic propagation material 114 may be such that they give it good acoustic propagation properties in order to ensure good acoustic coupling (i.e. low attenuation in the transmission of the acoustic waves) between the capture surface 102 and the circuit 106. Such acoustic coupling may be obtained by ensuring good acoustic impedance matching between the circuit 106 and the target of the ultrasonic waves (the target corresponding to the user's finger in the example described).

[0067] Alternatively, it is possible for the device 100 to comprise layers of materials additional to the layers 116, 118, 120.

[0068] The device 100 comprises other elements which are not described in detail in the present description, such as for example a control circuit intended to control the circuit 106, a data processing circuit, etc.

[0069] The device 100 can implement additional functions to those previously described, such as for example a contribution to the detection of living things from the captured information.

[0070] In the various embodiments described above, the ultrasound capture device 100 corresponds to a biometric identification device. Alternatively, these various examples may apply to a device 100 performing an ultrasound capture not corresponding to a biometric identification, such as for example a capture performed for medical purposes or to perform a non-destructive test, for example, of an object. In this case, the element intended to be placed on the capture surface 102 of the device 100 may correspond to something other than a part of the body of the user of the device 100, for example a surface to be checked by ultrasound measurement.

[0071] 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.

[0072] 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 capture device (100) comprising at least: - an ultrasonic transducer circuit (106) arranged on and / or in a substrate (102); - an acoustic propagation material (114) arranged in a cavity (110) in which the ultrasonic transducer circuit (106) is located; - a sealing layer (118) closing the cavity (110) on the side of a capture surface (102) of the ultrasonic capture device (100) configured so that at least one element is arranged thereon during a capture by the ultrasonic capture device (100).

2. An ultrasonic capture device (100) according to claim 1, wherein the acoustic propagation material (114) is a gel or a viscous liquid, preferably hydrogel and / or silicone oil and / or silicone gel.

3. An ultrasonic capture device (100) according to one of the preceding claims, wherein the acoustic propagation material (114) forms a layer with a thickness of between 1 mm and 5 mm.

4. An ultrasonic capture device (100) according to one of the preceding claims, wherein the acoustic propagation material (114) has a Shore 00 hardness of between 10 and 60.

5. An ultrasonic capture device (100) according to one of the preceding claims, wherein the sealing layer (118) has a thickness of between 8 pm and 250 pm and / or less than an ultrasound wavelength intended to be emitted by the ultrasonic transducer circuit (106).

6. An ultrasonic capture device (100) according to one of the preceding claims, wherein the sealing layer (118) comprises polyester.

7. An ultrasonic capture device (100) according to one of the preceding claims, further comprising an acoustic impedance matching and passivation layer (112) disposed at least between the ultrasonic transducer circuit (106) and the acoustic propagation material (114).

8. An ultrasonic capture device (100) according to one of the preceding claims, further comprising a barrier layer (116) closing, with the sealing layer (118), the cavity (110) on the side of the capture surface (102), the barrier layer (116) being disposed between the layer sealing (118) and the acoustic propagation material (114).

9. An ultrasonic capture device (100) according to one of the preceding claims, wherein the barrier layer (116) comprises a metal oxide or an organic compound.

10. An ultrasonic capture device (100) according to one of claims 8 or 9, wherein the barrier layer (116) and the sealing layer (118) together form a stack whose modulus of elasticity is between 1 GPa and 4 GPa.

11. An ultrasonic capture device (100) according to one of the preceding claims, further comprising a contact layer (120) such that the sealing layer (118) is disposed between the contact layer (120) and the acoustic propagation material (114), the contact layer (120) forming the capture surface (102).

12. An ultrasonic capture device (100) according to claim 11, wherein the contact layer (120) comprises elastomer and / or thermoplastic.

13. An ultrasonic capture device (100) according to one of claims 11 or 12, wherein the contact layer (120) has a thickness of between 10 pm and 100 pm and / or less than an ultrasound wavelength intended to be emitted by the ultrasonic transducer circuit (106).

14. An ultrasonic capture device (100) according to one of the preceding claims, further comprising a frame (108) disposed on the substrate (102) and forming side walls of the cavity (110).

15. Ultrasonic capture device (100) according to one of the preceding claims, corresponding to a biometric identification device configured to implement a biometric identification from a part of the body of a user intended to be arranged on the capture surface (102).

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