Biometric sensor

Abstract

The present invention relates to a biometric sensor (200) comprising: - a support substrate (101); - an ultrasonic transduction device (103) comprising a plurality of elementary ultrasonic transducers, located on an upper face (101T) of the support substrate; and - an acoustic coupling structure (105) coating an upper face (103T), opposite the support substrate, of the ultrasonic transduction device, wherein the acoustic coupling structure comprises an upper face (105T), which is opposite the upper face of the support substrate and intended to receive at least one finger (111) of a user, and which is inclined with respect to the upper face of the ultrasonic transduction device.

Description

DESCRIPTION Biometric sensor This application is based on, and claims priority from, French patent application 23 / 09571 filed on September 12, 2023 and entitled “Biometric Sensor”, which is considered to be an integral part of this description within the limits provided by law. Technical field

[0001] This description relates generally to electronic devices, more particularly to biometric sensors. Prior art

[0002] Biometric sensors capable of identifying a user's physical characteristics have been proposed. These sensors are used, for example, for recognition, authentication, or identification purposes. Among existing biometric sensors, microvascular imaging biometric sensors, or microvascular biometric sensors, capable of acquiring images of blood vessels in a user's finger, have been proposed in particular.

[0003] Existing biometric sensors, particularly microvascular biometric sensors, however, suffer from various drawbacks. Summary of the invention

[0004] It would be desirable to overcome all or part of the disadvantages of existing biometric sensors. In particular, there is a need to overcome all or part of the disadvantages of existing microvascular biometric sensors.

[0005] For this, one embodiment provides a biometric sensor comprising: - a support substrate; - an ultrasonic transduction device comprising a plurality of elementary ultrasonic transducers, located on the side of an upper face of the support substrate; and - an acoustic coupling structure covering an upper face, opposite the support substrate, of the ultrasonic transduction device, in which the acoustic coupling structure comprises an upper face, opposite the upper face of the support substrate and intended to receive at least one finger of a user, inclined relative to the upper face of the ultrasonic transduction device, the biometric sensor further comprising a device for modifying the inclination, relative to the upper face of the support substrate: A) the upper face of the ultrasonic transduction device, the upper face of the acoustic coupling structure being substantially parallel to the upper face of the support substrate; or B) of the upper face of the acoustic coupling structure, the upper face of the ultrasonic transduction device being substantially parallel to the upper face of the support substrate.

[0006] According to one embodiment, the upper face of the acoustic coupling structure is inclined, relative to the upper face of the ultrasonic transduction device, by an angle of between 5° and 45°, preferably between 5° and 20°, more preferably equal to approximately 10°.

[0007] According to one embodiment, in option A), the sensor further comprises an interposed tilting wedge between the upper face of the support substrate and the ultrasonic transduction device.

[0008] According to one embodiment, in option A), the tilt modification device comprises a microelectromechanical system.

[0009] According to one embodiment, the acoustic coupling structure comprises a shell containing an acoustic coupling material having a mechanical stiffness lower than that of the shell.

[0010] According to one embodiment, the elementary ultrasonic transducers are PMUT transducers.

[0011] According to one embodiment, the elementary ultrasonic transducers are CMUT transducers.

[0012] According to one embodiment, the elementary ultrasonic transducers are piezoelectric transducers. Brief description of the drawings

[0013] These and other features and advantages will be set forth in detail in the following description of particular embodiments given without limitation in relation to the attached figures, among which:

[0014] Figure 1 is a schematic and partial side and sectional view of an example of a biometric sensor;

[0015] Figure 2 is a schematic and partial side and sectional view of an example biometric sensor according to one embodiment; and

[0016] Figure 3 is a schematic and partial side and sectional view of an example biometric sensor according to one embodiment. Description of the embodiments

[0017] 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.

[0018] For the sake of clarity, only the steps and elements useful for understanding the described embodiments have been shown and are detailed. In particular, the various applications in which the described biometric sensors can be implemented have not been detailed, the described embodiments being compatible with the usual applications of these sensors. Furthermore, the control and processing circuits of the biometric sensors have not been detailed, the described embodiments being compatible with all or most of the known biometric sensor control and processing circuits, possibly subject to adaptations within the scope of the person skilled in the art upon reading this description.

[0019] 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.

[0020] In the following description, when referring to absolute position qualifiers, such as the terms "front", "back", "top", "bottom", "left", "right", etc., or relative, such as the terms "above", "below", "upper", "lower", etc., or to orientation qualifiers, such as the terms "horizontal", "vertical", etc., reference is made, unless otherwise specified, to the orientation of the figures.

[0021] Unless otherwise specified, the expressions “about”, “approximately”, “substantially”, and “in the order of” mean to within 10%, preferably to within 5%.

[0022] Figure 1 is a schematic and partial side and sectional view of an exemplary biometric sensor 100.

[0023] In the example shown, the biometric sensor 100 comprises a support substrate 101. The support substrate 101 is, for example, a wafer or a piece of wafer made of a semiconductor material, for example silicon, or a printed circuit board (PCB). Alternatively, the support substrate 101 may be made of a dielectric material, for example glass.

[0024] In the illustrated example, the biometric sensor 100 further comprises an ultrasonic transduction device 103. The ultrasonic transduction device 103 comprises a plurality of elementary ultrasonic transducers, for example arranged in a matrix according to rows and columns. The elementary ultrasonic transducers of the ultrasonic transduction device 103 are for example of the PMUT type (from the English “Piezoelectric Micromachined Ultrasonic Transducer” - micro-machined piezoelectric ultrasonic transducer), of the CMUT type (from the English “Capacitive Micromachined Ultrasonic Transducer” - micro-machined capacitive ultrasonic transducer) or of the piezoelectric type

[0025] In the case of PMUT transducers, each elementary ultrasonic transducer of the ultrasonic transduction device 103 comprises for example a flexible membrane suspended above a cavity, a first electrode, located on one side of the flexible membrane opposite the cavity, a layer of piezoelectric material, located on one side of the first electrode opposite the flexible membrane, and a second electrode, located on one side of the layer of piezoelectric material opposite the first electrode.

[0026] In the case of CMUT transducers, each elementary ultrasonic transducer of the ultrasonic transduction device 103 comprises for example a flexible membrane suspended above a cavity, a first electrode, called the lower electrode, located on the side of the cavity opposite the membrane, and a second electrode, called the upper electrode, located on the side of the cavity opposite the lower electrode and mechanically secured to the flexible membrane.

[0027] In the case of piezoelectric transducers, each elementary ultrasonic transducer of the ultrasonic transduction device 103 comprises, for example, a region, or pellet, made of a piezoelectric material interposed between two electrodes. In this case, each elementary ultrasonic transducer is in particular devoid of a flexible membrane suspended above a cavity. The electrodes are, for example, respectively located on either side of the pellet made of piezoelectric material, for example on and in contact with two opposite faces of the pellet made of piezoelectric material. The piezoelectric material is, for example, chosen from a piezoelectric ceramic (for example, a lead zirconate titano, PZT), a piezoelectric composite, or piezocomposite, comprising, for example, a piezoelectric ceramic and an epoxy resin, a polyvinylidene fluoride (PVDF), etc.

[0028] In the case of PMUT transducers as in the case of CMUT transducers, when an appropriate excitation voltage is applied between the electrodes of the transducer In elementary ultrasound, the flexible membrane vibrates and emits an ultrasonic acoustic wave. Conversely, when the elementary ultrasonic transducer receives an acoustic wave in a certain frequency range, the flexible membrane vibrates, leading to the appearance of a voltage between the electrodes of the elementary ultrasonic transducer.

[0029] Similarly, in the case of piezoelectric transducers, when a suitable excitation voltage is applied between the electrodes of the elementary ultrasonic transducer, the piezoelectric material pellet vibrates and emits an ultrasonic acoustic wave. Conversely, when the elementary ultrasonic transducer receives an acoustic wave in a certain frequency range, the piezoelectric material pellet vibrates, leading to the appearance of a voltage between the electrodes of the elementary ultrasonic transducer.

[0030] Although this has not been detailed in figure 1, the elementary ultrasonic transducers of the ultrasonic transduction device 103 are for example coupled to an electronic control circuit configured to, during a transmission phase, apply an excitation voltage between the electrodes of the transducers, so as to cause the emission of an ultrasonic wave by the transducers, and, during a reception phase, read the voltage produced between the electrodes of the transducers under the effect of the received acoustic wave.

[0031] The ultrasonic transduction device 103 has, for example, in top view, a periphery of substantially rectangular or square shape. The ultrasonic transduction device 103 has, for example, lateral dimensions of the order of a centimeter, for example a side equal to approximately 1 cm in the case where the device ultrasonic transduction 103 has a substantially square-shaped perimeter.

[0032] In the example illustrated in Figure 1, the ultrasonic transduction device 103 is located on the side of a face 101T of the support substrate 101 (the upper face of the support substrate 101, in the orientation of Figure 1). More precisely, in the example shown, the ultrasonic transduction device 103 is arranged on and in contact with the upper face 101T of the support substrate 101. This example is however not limiting, the biometric sensor 100 being able, as a variant, to comprise one or more layers interposed between the upper face 101T of the support substrate 101 and the ultrasonic transduction device 103.

[0033] The ultrasonic transduction device 103 comprises a face 103T opposite the support substrate 101 (the upper face of the ultrasonic transduction device 103, in the orientation of FIG. 1) which is substantially planar and substantially parallel to the upper face 101T of the support substrate 101. The upper face 103T of the ultrasonic transduction device 103 corresponds, for example, to, or is substantially parallel to: - on one face of an encapsulation housing of the elementary ultrasonic transducers of the ultrasonic transduction device 103 opposite the upper face 101T of the support substrate 101; - to faces of the flexible membranes of the elementary ultrasonic transducers of the ultrasonic transduction device 103 opposite the upper face 101T of the support substrate 101, for example in a case where the elementary ultrasonic transducers are of the PMUT type or of the CMUT type; and / or - has a plane orthogonal to a direction of emission of each elementary ultrasonic transducer of the ultrasonic transduction device 103.

[0034] In the example illustrated, the emission direction of each of the elementary ultrasonic transducers of the ultrasonic transduction device 103 is orthogonal to the upper face 101T of the support substrate 101.

[0035] In the example shown, the biometric sensor 100 further comprises an acoustic coupling structure 105 covering the upper face 103T and the sides of the ultrasonic transduction device 103, as well as parts of the upper face 101T of the support substrate 101 not covered by the ultrasonic transduction device 103. The acoustic coupling structure 105 comprises, for example, as illustrated in FIG. 1, an envelope 107 containing an acoustic coupling material 109. The envelope 107 comprises, for example, side walls or walls, symbolized by hatched rectangles in FIG. 1, making it possible to ensure the mechanical strength of the acoustic coupling material 109 around the ultrasonic transduction device 103 and / or to prevent any lateral movement of the acoustic coupling material 109 relative to the upper face 101T of the support substrate 101.The acoustic coupling material 109 has, for example, a mechanical rigidity, or a viscosity, lower than that of the side walls of the casing 107. For example, the acoustic coupling material 109 is a gel or a liquid. In this case, although this has not been detailed in FIG. 1, the casing 107 may further comprise a membrane closing a cavity delimited by the side walls of the casing 107 and the parts of the upper face of the support substrate 101 not coated by the ultrasonic transduction device 103, and filled at least partially with the acoustic coupling material 109. Alternatively, the casing 107 may be omitted, for example. in a case where the acoustic coupling material 109 is a solid having a mechanical rigidity, or a viscosity, sufficient to remain mechanically secured to the upper face 101T of the support substrate 101 and not undergo displacements likely to damage the ultrasonic transduction device 103.

[0036] The acoustic coupling structure 105 makes it possible to perform an impedance matching function between the ultrasonic transduction device 103 and a finger 111 of a user placed on the side of a face 105T of the acoustic coupling structure 105 opposite the upper face 101T of the support substrate 101 (the upper face of the acoustic coupling structure 105, in the orientation of FIG. 1). In the example shown, the upper face 105T of the acoustic coupling structure 105 is substantially planar, and substantially parallel to the upper face 101T of the support substrate 101. Furthermore, in this example, the upper face 105T of the acoustic coupling structure 105 is substantially parallel to the upper face 103T of the ultrasonic transduction device 103.

[0037] The biometric sensor 100 is for example adapted to produce, by means of the ultrasound transduction device 103, microvascular images of the finger 111 in contact with the upper face 105T of the coupling structure 105. The ultrasound transduction device 103 is for example more precisely capable of capturing, by Doppler imaging, images of blood vessels (not illustrated in FIG. 1) of the finger 111 located opposite its upper face 103T, by detecting a non-zero speed of movement of the blood inside these vessels. In this case, the elementary ultrasound transducers of the ultrasound transduction device 103 are for example controlled to emit an incident ultrasound beam USW in the direction of the finger 111, and to receive an ultrasound beam reflected by the blood circulating inside the blood vessels of the finger 111. The incident ultrasound beam USW symbolized, in figure 1, by a series of lines parallel to each other, corresponds for example to a pulse signal, for example plane waves propagating along a direction substantially orthogonal to the upper face 103T of the ultrasound transduction device 103, of frequency f^ and the reflected ultrasound beam corresponds for example to a pulse signal of frequency f r . By measuring a frequency shift between the incident and reflected signals, that is, by measuring a difference between the frequencies f r and f T , it is possible to go back to a speed v of movement of the blood inside the blood vessels of the finger 111.

[0038] A disadvantage of the biometric sensor 100 is that the images of the finger 111 that it is capable of acquiring have so-called “blind” zones, i.e. partially or totally devoid of information relating to the vascularization of the finger 111, corresponding for example to locations of blood vessels of the finger 111 within which the ultrasound transduction device 103 is unable to detect blood circulation. The inventors have realized that this comes from the fact that the majority of the blood vessels present in the vicinity of the end of the finger 111 are oriented in a direction substantially parallel to the axis of the finger, and that the biometric sensor 100 does not make it possible to detect blood flows running through blood vessels oriented parallel to the upper face 103T of the ultrasound transduction device 103.

[0039] To try to overcome this problem, it is possible to control the ultrasonic transduction device 103 so as to emit the incident ultrasonic beam USW, by example in the form of plane waves, with a non-zero angle relative to the upper face 103T of the ultrasonic transduction device 103, for example by introducing phase shifts between the signals emitted by the different elementary ultrasonic transducers of the ultrasonic transduction device 103. However, this does not make it possible to achieve emission angles of the incident ultrasonic beam USW, relative to the upper face 103T of the ultrasonic transduction device 103, having values ​​high enough to solve the aforementioned problem, and numerous blind zones remain in the microvascular images of the finger 111 acquired by the biometric sensor 100.

[0040] Embodiments of biometric sensors making it possible to overcome all or part of the drawbacks of the biometric sensor 100 previously described in relation to FIG. 1 are set out below in relation to FIGS. 2 and 3.

[0041] Figure 2 is a schematic and partial side and sectional view of an example of a biometric sensor 200 according to one embodiment. The biometric sensor 200 of Figure 2 includes elements in common with the biometric sensor 100 of Figure 1. These common elements will not be detailed again below.

[0042] The biometric sensor 200 of Figure 2 differs from the biometric sensor 100 of Figure 1 in that the upper face 105T of the acoustic coupling structure 105 is, in the case of the biometric sensor 200 of Figure 2, inclined relative to the upper face 103T of the ultrasonic transduction device 103.

[0043] In the example shown, the upper face 103T of the ultrasonic transduction device 103 is inclined, relative to the upper face 101T of the support substrate 101, of a non-zero angle α. Furthermore, in this example, the upper face 105T of the acoustic coupling structure 105 is substantially parallel to the upper face 101T of the support substrate 101. In this case, the upper face 105T of the acoustic coupling structure 105 is inclined by the angle α relative to the upper face 103T of the ultrasonic transduction device 103. For example, the angle α is between 5° and 45°, for example between 5° and 20°. The angle α is for example equal to approximately 10°.

[0044] For example, in the case where the ultrasonic transduction device 103 has, in top view, a periphery of substantially rectangular or square shape, only one side or one edge of the ultrasonic transduction device 103 is for example in contact with the upper face 101T of the support substrate 101. As a variant, the ultrasonic transduction device 103 can be inclined so that only one of its corners is in contact with the upper face 101T of the support substrate 101.

[0045] In the example illustrated in Figure 2, the biometric sensor 200 comprises a tilting wedge 201 interposed between the upper face 101T of the support substrate 101 and a face of the ultrasonic transduction device 103 opposite its upper face 103T (the lower face of the ultrasonic transduction device 103, in the orientation of Figure 2). In this example, the tilting wedge 201 is fixed, the angle a then being substantially invariable during the lifetime of the biometric sensor 200.

[0046] This example is however not limiting, the biometric sensor 200 being able to comprise, as a variant or in a complementary manner, a device for modifying the inclination of the upper face 103T of the ultrasonic transduction device 103 relative to the upper face 101T of the support substrate 101. In this case, the angle a is for example adjustable several times during the lifetime of the biometric sensor 200. Such a tilt modification device comprises for example a microelectromechanical system, or MEMS (from the English “MicroElectroMechanical System”). For example, the angle a is modified several times during the same phase of acquisition of microvascular images of the finger 111.

[0047] An advantage of the biometric sensor 200 lies in the fact that it makes it possible, in particular compared to the biometric sensor 100, to emit the USW ultrasound beam at a non-orthogonal incidence to the vessels substantially parallel to the axis of the finger 111. This makes it possible to detect blood circulation in a greater number of blood vessels of the finger 111 than in the case of the biometric sensor 100, and therefore to acquire microvascular images of the finger 111 comprising more information than that produced by the biometric sensor 100.

[0048] Figure 3 is a schematic and partial side and sectional view of an example of a biometric sensor 300 according to one embodiment. The biometric sensor 300 of Figure 3 comprises elements in common with the biometric sensor 100 of Figure 1. These common elements will not be detailed again below.

[0049] Similar to the biometric sensor 200 described previously in relation to FIG. 2, the biometric sensor 300 of FIG. 3 differs from the biometric sensor 100 of FIG. 1 in that the upper face 105T of the acoustic coupling structure 105 is inclined relative to the upper face 103T of the ultrasonic transduction device 103.

[0050] In the example shown, the upper face 105T of the acoustic coupling structure 105 is inclined, relative to the upper face 101T of the support substrate 101, of a non-zero angle [3. Furthermore, in this example, the upper face 103T of the ultrasonic transduction device 103 is substantially parallel to the upper face 101T of the support substrate 101. In this case, the upper face 105T of the acoustic coupling structure 105 is inclined by the angle p relative to the upper face 103T of the ultrasonic transduction device 103. For example, the angle 3 is between 5° and 45°, for example between 5° and 20°. The angle p is for example equal to approximately 10°.

[0051] In the example shown, the lower face of the ultrasonic transduction device 103 is located on and in contact with the upper face 101T of the support substrate 101.

[0052] The angle β is for example substantially invariable during the lifetime of the biometric sensor 300. This example is however not limiting, the biometric sensor 300 being able to comprise, as a variant, a device for modifying the inclination of the upper face 105T of the acoustic coupling structure relative to the upper face 101T of the support substrate 101. In this case, the angle β is for example adjusted several times during the lifetime of the biometric sensor 300. Such an inclination modification device comprises for example a rotation mechanism making it possible to rotate the walls of the casing 107 around a central axis of rotation substantially orthogonal to the upper face 101T of the support substrate 101.More specifically, in a case where the acoustic coupling material 109 is a liquid or a gel, a mechanism may be provided for modifying, at constant volume, the inclination of the upper face 105T of the coupling structure 105 relative to the upper face 101T of the support substrate 101. The design and production of such a mechanism are within the capabilities of the individual. of the trade upon reading this description. For example, the angle p is modified several times during the same phase of acquisition of microvascular images of the finger 111.

[0053] The biometric sensor 300 has, in particular compared to the biometric sensor 100, advantages similar or identical to those of the biometric sensor 200.

[0054] Various embodiments and variations have been described. Those skilled in the art will understand that certain features of these various embodiments and variations could be combined, and other variations will occur to those skilled in the art. In particular, the embodiments of the biometric sensors 200 and 300 may be combined to obtain a biometric sensor in which the upper face 103T of the ultrasonic transduction device 103 and the upper face 105T of the acoustic coupling structure 105 are each inclined relative to the upper face 101T of the support substrate 101. The production of such a biometric sensor is within the ability of those skilled in the art upon reading the present description.

[0055] Finally, the practical implementation of the described embodiments and variants is within the reach of the person skilled in the art from the functional indications given above. In particular, the described embodiments are not limited to the examples of materials and / or dimensions mentioned in the description.

Claims

CLAIMS 1. Biometric sensor (200; 300) comprising: - a support substrate (101); - an ultrasonic transduction device (103) comprising a plurality of elementary ultrasonic transducers, located on the side of an upper face (101T) of the support substrate; and - an acoustic coupling structure (105) covering an upper face (103T), opposite the support substrate, of the ultrasonic transduction device, in which the acoustic coupling structure comprises an upper face (105T), opposite the upper face of the support substrate and intended to receive at least one finger (111) of a user, inclined relative to the upper face of the ultrasonic transduction device, the biometric sensor (200; 300) further comprising a device for modifying the inclination, relative to the upper face (101T) of the support substrate (101): A) of the upper face (103T) of the ultrasonic transduction device (103), the upper face (105T) of the acoustic coupling structure (105) being substantially parallel to the upper face (101T) of the support substrate (101); or B) of the upper face (105T) of the acoustic coupling structure (105), the upper face (103T) of the ultrasonic transduction device (103) being substantially parallel to the upper face (101T) of the support substrate (101).

2. Sensor (200; 300) according to claim 1, in which the upper face (105T) of the acoustic coupling structure (105) is inclined, relative to the upper face (103T) of the ultrasonic transduction device (103), by an angle (a; p) of between 5° and 45°, preferably between 5° and 20°, more preferably equal to approximately 10°.

3. Sensor (200) according to claim 1 or 2, in its option A), further comprising a tilting wedge (201) interposed between the upper face (101T) of the support substrate (101) and the ultrasonic transduction device (103).

4. Sensor (200) according to claim 1, 2 or 3, in its option A), in which the tilt modification device comprises a microelectromechanical system.

5. Sensor (200; 300) according to any one of claims 1 to 4, wherein the acoustic coupling structure (105) comprises an envelope (107) containing an acoustic coupling material (109) having a mechanical rigidity lower than that of the envelope.

6. Sensor (200; 300) according to any one of claims 1 to 5, in which the elementary ultrasonic transducers are PMUT transducers.

7. Sensor (200; 300) according to any one of claims 1 to 5, in which the elementary ultrasonic transducers are CMUT transducers.

8. Sensor (200; 300) according to any one of claims 1 to 5, in which the elementary ultrasonic transducers are piezoelectric transducers.

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