BIOMETRIC SENSOR CARD

Description

[0001] The invention relates to a card with a biometric sensor.

[0002] It relates more specifically to a biometric sensor card in which a coating is deposited at least on the sensor.

[0003] The invention applies, in particular, to technical fields such as a payment card or any secure access card.

[0004] A biometric sensor card typically consists of a body and a fingerprint sensor embedded in the body.

[0005] To achieve this, the body is machined to form a cavity in which the sensor is then placed.

[0006] For many reasons, it may be advantageous for at least part of the sensor to be coated.

[0007] For example, a sensor typically has a black surface. However, the card's body, called the inlay, is white. This results in a visible gap between the sensor's edge and the edge of the cavity. Such a gap is unsightly. Furthermore, this gap can expose the fingerprint sensor's edge to potential external damage, which could, for example, lead to the sensor being detached or otherwise damaged.

[0008] According to another example, it is interesting to be able to produce a unified aspect map, in which the sensor blends into a surface of the map body.

[0009] As another example, it can also be beneficial to make it easier for a user to identify the sensor's location. While fingerprint sensors typically have a smooth external surface, it can be helpful for the user to be able to identify the sensor by touch.

[0010] However, it is desirable not to degrade or alter the quality of an image acquired (i.e., a fingerprint of a user) by the sensor when it is coated at least in part.

[0011] Indeed, an alteration, or degradation, of the image acquired by the sensor has a direct impact on a false acceptance ratio (False Acceptance Ratio: FAR) and a false rejection ratio (False Reject Ratio: FRR), which then prevents effective finger recognition.

[0012] US8787631B2 discloses a capacitive sensor comprising a plurality of electrodes, each emitting an electrical signal corresponding to a capacitance determined by the distance between a surface of the capacitive sensor and an electrical conductor. The plurality of electrodes includes electrodes exhibiting a first parasitic capacitance and electrodes exhibiting a second parasitic capacitance different from the first parasitic capacitance, and they are arranged in a prescribed pattern different from a pattern of biometric information of a body part to be read by the capacitive sensor.

[0013] US2006 / 119369A1 discloses an electrostatic capacitance detection sensor that includes first electrodes extending from row wiring lines, second electrodes extending from row wiring lines and formed on a different layer from the first electrodes, a third electrode that is electrically independent of the first and second electrodes by an insulating film, a first electrostatic capacitance region C1 formed between the first and third electrodes, and a second electrostatic capacitance region C2 formed between the second and third electrodes.

[0014] US2018 / 300521A1 discloses a fingerprint detection device comprising a plurality of fingerprint detection elements, and each fingerprint detection element comprises: a detection electrode for forming a detection capacitance from a relationship with a subject; an amplifier having a first input terminal connected to the detection electrode and a second input terminal into which a bias signal, the potential of which is changed from a high level to a low level or from a low level to a high level during a fingerprint detection operation, is injected; and a gain controller comprising a plurality of feedback subcapacitors, the gain controller being selectively connected between the first input terminal and an output terminal of the amplifier.

[0015] The present invention aims to overcome at least some of these drawbacks, possibly leading to other advantages.

[0016] To this end, a biometric sensor card is proposed, according to a first aspect, comprising a body and a capacitive fingerprint sensor embedded in said body, said capacitive sensor being configured to acquire a fingerprint of a finger of a user of said card, said capacitive sensor comprising a sensitive film and a dielectric film, said dielectric film covering the sensitive film and defining an external surface of said capacitive sensor, said sensitive film being configured to form a capacitor with the user's finger, said card being characterized in that it comprises a coating covering at least the external surface of the capacitive sensor, said coating comprising at least a first part made of a first material having a first dielectric value and a first thickness,said sensitive film coated with said at least a first part being configured to form a capacitor of a first capacitance with the user's finger applied to this at least a first part, said coating comprising at least a second part made of a second material of a second dielectric value and having a second thickness, said sensitive film coated with said at least a second part being configured to form a capacitor of a second capacitance with the user's finger applied to this at least a second part, said second capacitance having a value between 0.9 and 1.1 times that of the first capacitance.

[0017] Such a coating helps to limit alteration or degradation of the quality of the fingerprint acquired by the capacitive sensor compared to the uncoated sensor.

[0018] Indeed, with such a coating, the capacitance perceived by the sensor is homogenized, which limits the impact of the coating on the sensor's ability to capture the fingerprint.

[0019] Applying such a coating at least to the external surface of the capacitive sensor also helps to protect the capacitive sensor.

[0020] Applying such a coating at least to the external surface of the capacitive sensor allows the tactile appearance of the external surface of the capacitive sensor to be modified.

[0021] Depositing such a coating at least on the external surface of the capacitive sensor allows for a surface heterogeneity between at least a first part and at least a second part.

[0022] For example, the coating is deposited on the external surface of the capacitive sensor and at least partially on the body of the card, in particular on the periphery of a cavity in the card housing the capacitive sensor.

[0023] This type of coating visually reduces the demarcation between the capacitive sensor and the card body, effectively filling or concealing any gaps between them. It also protects the sensor's edges from external damage.

[0024] For example, the coating is applied to the entire external surface of the capacitive sensor and the board body. Such a coating completely masks the capacitive sensor from the board body.

[0025] For example, the first material of at least one first part is a paint. For example, the material of at least one first part is a varnish, in particular a transparent or opaque varnish, or one colored by pigments.

[0026] For example, the first thickness of at least one first part is between 20 and 120 µm.

[0027] For example, the second material of at least one second part is a paint.

[0028] For example, the second material of at least one second part is a varnish, in particular a transparent or opaque varnish, or one colored by color pigments.

[0029] For example, the second thickness of at least one second part is between 20 and 120 µm.

[0030] In one embodiment, said at least a first part forms a first pattern on the external surface of the capacitive sensor and said at least a second part forms a second pattern on the external surface of the capacitive sensor.

[0031] The coating includes, for example, an external surface on which a user applies their finger.

[0032] The surface can be configured to have a smooth or rough appearance.

[0033] In one embodiment, at least a first part and a second part form a rough external surface of the coating.

[0034] Applying such a coating, at least on the external surface of the capacitive sensor, results in a rough surface. This rough texture makes it easier to identify the capacitive sensor by touch.

[0035] In one embodiment, said coating comprises at least a third part deposited on said at least a first part and at least a second part, said at least a third part being made of a third material of a third dielectric value, said at least a third part having a third thickness on said at least a first part and a fourth thickness on said at least a second part, the sensitive film coated with the at least a third part being configured to form a capacitor having a third capacitance with the user's finger applied to the at least a third part coating the at least a first part and a capacitor having a fourth capacitance with the user's finger applied to the at least a third part coating the at least a second part, said fourth capacitance having a value between 0.9 and 1.1 times that of the third capacitance.

[0036] At least one third part helps to protect at least one first and second parts of the coating.

[0037] For example, the third material of at least one third part is a varnish, in particular a varnish that is transparent or opaque to light, or one that is colored by color pigments.

[0038] For example, the third and fourth thicknesses of at least one third part are between 20 and 120 µm.

[0039] In one embodiment, in which the third part forms a smooth external surface of the coating.

[0040] In one embodiment, said capacitive sensor includes at least a first indentation cut into a thickness of the dielectric film of said sensor, said at least a first indentation being configured to accommodate at least partially said first thickness of the at least a first part.

[0041] At least one first indentation cut into a thickness of the dielectric film of the capacitive sensor allows at least partially to accommodate the first thickness of at least one first part.

[0042] At least one initial impression thus allows a reduction in the thickness of the assembly formed by the sensor and coating at the level of at least one initial part.

[0043] For example, at least one initial impression is made by removing material directly from the dielectric film of the capacitive sensor.

[0044] For example, at least one initial impression is made by milling.

[0045] For example, at least one initial imprint includes an extension into the body of the card.

[0046] In one embodiment, said capacitive sensor includes at least one second indentation cut into a thickness of the dielectric film of said sensor, said at least one second indentation being configured to accommodate at least partially said second thickness of the at least one second part.

[0047] At least one second indentation cut into a thickness of the dielectric film of the capacitive sensor allows at least partially to accommodate the second thickness of at least one second part.

[0048] The at least second imprint thus allows a reduction in the thickness of the assembly formed by the sensor and the coating at the level of at least a second part.

[0049] For example, at least a second imprint is made by removing material directly from the dielectric film of the capacitive sensor.

[0050] For example, at least a second impression is made by milling.

[0051] For example, at least one second imprint has an extension into the body of the card.

[0052] For example, a biometric sensor card is a bank card, a security card, or a smart card.

[0053] The invention will be better understood and its advantages will become more apparent upon reading the following detailed description, given by way of example only and not as a limitation, with reference to the accompanying drawings in which: there figure 1 schematically illustrates a cross-sectional view of a biometric sensor card according to a first embodiment of the invention; figure 2 illustrates a partial cross-sectional view of a biometric sensor according to a second embodiment of the invention; the figure 3illustrates a partial cross-sectional view of a biometric sensor according to a third embodiment of the invention; and the figure 4 illustrates a partial cross-sectional view of a biometric sensor according to a fourth embodiment of the invention.

[0054] Identical elements represented in the aforementioned figures are identified by identical numerical references.

[0055] There figure 1 presents a biometric sensor card 10 according to a first embodiment of the invention.

[0056] The biometric sensor card 10 comprises a body 20 and a capacitive sensor 30.

[0057] Body 20 typically has a rectangular shape outline.

[0058] The body 20 has an upper face and a lower face, generally parallel to each other, and defining between them a thickness of the body.

[0059] The body 20 further includes here a cavity 25, hollowed out in part of the thickness of the body from the upper surface, and opening onto the upper surface.

[0060] Cavity 25 is configured here to accommodate capacitive sensor 30.

[0061] The capacitive sensor 30 here refers to a sensor configured to acquire a fingerprint of a user's finger.

[0062] The capacitive sensor 30 is here embedded in the body 20, that is to say, arranged in the cavity 25.

[0063] The capacitive sensor 30 here comprises a sensitive film 35 and a dielectric film 36.

[0064] The dielectric film 36 covers the sensitive film 35.

[0065] A dielectric film here refers to a layer of a material that becomes polarized when subjected to an electric field.

[0066] In this case, the dielectric film 36 has a free surface which forms an external surface 31 of the capacitive sensor 30.

[0067] The dielectric film 36 also includes a contact surface with the sensitive film. The dielectric film 36 here has a thickness d0.

[0068] The contact surface and the free surface define the thickness d0 of the dielectric film 36.

[0069] The dielectric film 36 is here in a dielectric material M0 of dielectric constant ε c.

[0070] The dielectric film 36 helps in particular to protect the sensitive film 35.

[0071] The sensitive film 35 is configured here to form a condenser with a user's finger.

[0072] When a user's finger is in contact with the external surface 31 of the capacitive sensor 30, the sensitive film 35 is configured to form a capacitor of capacitance C0.

[0073] In other words, the sensitive film 35 and a user's finger in contact with the external surface 31 of the capacitive sensor 30 here form two "conducting plates" of the capacitor.

[0074] These two "conducting plates" are separated here by a dielectric, which includes at least the dielectric film 36.

[0075] The capacitance C of the capacitor can be calculated, for example, using the following relationship: C = ε r ∗ ε 0 ∗ A d With : ε 0 corresponding to the dielectric constant of vacuum; A corresponding to an area of ​​a contact surface between a user's finger and the external surface 31 of the capacitive sensor 30; ε r corresponding to a dielectric constant of the dielectric film 36 arranged between the sensitive film 35 and a user's finger; and d corresponding to a thickness of the dielectric film 36 between the sensitive film 35 and the user's finger in contact on the surface.

[0076] The capacitive sensor 30 finally includes, in a traditional manner, a functional base 32, the sensitive film 35 being disposed between the functional base 32 and the dielectric film 36.

[0077] The functional base 32 here refers to a whole part of the capacitive sensor 30 comprising electronic components and electrical tracks configured to operate the capacitive sensor 30.

[0078] In this example, the biometric sensor card 10 also has a coating 40.

[0079] The coating 40 is deposited at least on the external surface 31 of the capacitive sensor 30.

[0080] The coating 40 has an external surface 41.

[0081] Surface 41 can be configured to have a smooth or rough appearance.

[0082] Coating 40 comprises at least a first part X1.

[0083] The first part X1 here draws a first pattern at least on the external surface 31 of the capacitive sensor 30.

[0084] At least a first part X1 is composed here of a first material M1 of a first dielectric value ε1.

[0085] The at least first part X1 has here a first thickness d1.

[0086] The sensitive film 35 coated with at least a first part X1 is configured to form a capacitor having a first capacitance C1 with a user's finger applied to the first part X1.

[0087] The first capacitance C1 is therefore here a function in particular of the first thickness d1 and of the first dielectric value ε1 of at least a first part X1.

[0088] Coating 40 includes at least a second part X2.

[0089] The second part X2 here draws at least a second pattern on the external surface 31 of the capacitive sensor 30.

[0090] The at least second part X2 is composed here of a second material M2 of a second dielectric value ε2.

[0091] The at least second part X2 here has a second thickness d2.

[0092] The sensitive film 35 covered with at least a second part X2 being configured to form a capacitor having a second capacitance C2 with a user's finger applied to the second part X2.

[0093] The second capacitance C2 is thus a function of the second thickness d2 and the second dielectric value ε2 of at least a second part X2.

[0094] The second capacitance C2 here has a value very close to that of the capacitance C1. That is to say, the ratio between the second capacitance C2 and the first capacitance C1 has a value between 0.9 and 1.1.

[0095] In other words, the ratio between the first dielectric value ε1 and the first thickness d1 of at least one first part X1, and the ratio between the second dielectric value ε2 and the second thickness d2 of at least one second part X2, tend to respect the following mathematical relationship: ε 1 d 1 = ε 2 d 2 .

[0096] This helps to limit the degradation of the quality of the fingerprint acquired by the capacitive sensor 30.

[0097] In this case, the first thickness d1 of at least one first part X1 and the second thickness d2 of at least one second part X2 are specifically chosen so that the coating 40 has a rough external surface 41. The roughness of the external surface 41 of the coating 40 facilitates the identification of the sensor by touch.

[0098] There figure 2presents a coated biometric sensor according to a second embodiment of the invention.

[0099] In the second example described, the coating 40 differs in that it also includes at least a third part X3.

[0100] At least one third part X3 is here in a third material M3 of third dielectric value ε3.

[0101] At least one third part X3 is deposited here at least on at least one first part X1 and on at least one second part X2.

[0102] In other words, at least one third part X3 covers at least one first part X1 and at least one second part X2.

[0103] The at least third part X3 has here a third thickness d3 on the at least first part X1.

[0104] The at least third part X3 has here a fourth thickness d3' on the at least second part X2.

[0105] The sensitive film 35 covered with at least one third part X3 and at least one first part X1, here forms a capacitor having a third capacitance C3 with the finger of a user applied to the at least one third part X3 covering the at least one first part X1.

[0106] The sensitive film 35 covered with at least one third part X3 and at least one second part X2, here forms a capacitor having a fourth capacitance C3' with the finger of a user applied to the at least one third part X3 covering the at least one second part X2.

[0107] The fourth capacitance C3' here has a value very close to that of the third capacitance C3. That is to say, the ratio between the fourth capacitance C3' and the third capacitance C3 has a value between 0.9 and 1.1.

[0108] In other words, the third thickness d3 on at least one first part X1 and the fourth thickness d3' on at least one second part X2, of at least one third part X3, tend to respect the following mathematical relationship: e 1 * d1 + ε3 * d3 = e 2 * d2 + e 3 * d3'.

[0109] Thus, the third thickness d3 on the at least one first part X1 and the fourth thickness d3' on the at least one second part X2, of the at least one third part X3, are chosen according to the dielectric value and the respective thickness of the at least one first part X1 and the at least one second part X2.

[0110] The third and fourth thicknesses d3 and d3' of at least one third part X3 are specifically chosen here so that the coating 40 has a smooth external surface 41. In other words, the thicknesses of the different layers X1, X2, and X3 here follow the following relationship: d 1 + d 3 = d 2 + d 3 '.

[0111] There figure 3 presents a coated biometric sensor according to a third embodiment of the invention.

[0112] In the third example described, the capacitive sensor 30 differs from that of the first example in that it includes at least one first Y1 imprint.

[0113] At least one first Y1 imprint is here etched into a thickness of the dielectric film 36 of the capacitive sensor 30.

[0114] The at least first footprint Y1 is configured here to accommodate at least partially the first thickness d1 of the at least first part X1.

[0115] At least one first impression Y1 is notably made here by removing material directly from the dielectric film 36 of the capacitive sensor 30.

[0116] In this case, the material removal is achieved by milling.

[0117] There figure 4 presents a coated biometric sensor according to a fourth embodiment of the invention.

[0118] In the fourth example described, the capacitive sensor 30 differs from that of the third example in that it has at least a second Y2 imprint.

[0119] At least one second Y2 indentation is here etched into a thickness of the dielectric film 36 of the capacitive sensor 30.

[0120] The at least second Y2 footprint is configured here to accommodate at least partially the second thickness d2 of the at least second part X2.

[0121] At least one second Y2 imprint is notably made here by removing material directly from the dielectric film 36 of the capacitive sensor 30.

[0122] In this case, the material removal is achieved by milling.

Claims

1. Biometric sensor card (10) comprising an inlay (20) and a capacitive fingerprint sensor (30) embedded in said inlay (20), said capacitive sensor (30) being configured to acquire a fingerprint of a finger of a user of said card (10), said capacitive sensor (30) comprising a sensing film (35) and a dielectric film (36), said dielectric film (36) covering the sensing film (35) and defining an external surface (31) of said capacitive sensor (30), said sensing film (35) being configured to form a capacitor with the finger of the user, said card (10) being characterized in that it comprises a coating (40) covering at least the external surface (31) of the capacitive sensor (30), said coating (40) comprising at least one first portion (X1) made of a first material (M1) of a first dielectric constant (ε1) and having a first thickness (d1), said sensing film (35) covered with said at least one first portion (X1) being configured to form a capacitor of a first capacitance (C1) with the finger of the user applied to this at least one first portion (X1), said coating (40) comprising at least one second portion (X2) made of a second material (M2) of a second dielectric constant (ε2) and having a second thickness (d2), said sensing film (35) covered with said at least one second portion (X2) being configured to form a capacitor of a second capacitance (C2) with the finger of the user applied to this at least one second portion (X2), said second capacitance (C2) having a value between 0.9 and 1.1 times the value of the first capacitance (C1).

2. Card according to Claim 1, wherein said at least one first portion (X1) forms a first pattern on the external surface (31) of the capacitive sensor (30) and said at least one second portion (X2) forms a second pattern on the external surface (31) of the capacitive sensor (30).

3. Card according to Claims 1 to 2, wherein the first portion (X1) and the second portion (X2) form a roughened external surface (41) of the coating (40).

4. Card according to any of Claims 1 to 3, wherein said coating (40) comprises at least one third portion (X3) deposited on said at least one first portion (X1) and at least one second portion (X2), said at least one third portion (X3) being made of a third material (M3) of a third dielectric constant (ε3), said at least one third portion (X3) having a third thickness (d3) on said at least one first portion (X1) and a fourth thickness (d3') on said at least one second portion (X2), the sensing film (35) covered with the at least one third portion (X3) being configured to form a capacitor having a third capacitance (C3) with the finger of the user applied to the at least one third portion (X3) coating the at least one first portion (X1) and a capacitor having a fourth capacitance (C3') with the finger of the user applied to the at least one third portion (X3) coating the at least one second portion (X2), said fourth capacitance (C3') having a value between 0.9 and 1.1 times the value of the third capacitance (C3).

5. Card according to Claim 4, wherein the third portion (X3) forms a smooth external surface (41) of the coating (40).

6. Card according to any of Claims 1 to 5, wherein said capacitive sensor (30) comprises at least one first indentation (Y1) hollowed out in a thickness of the dielectric film (36) of said capacitive sensor (30), said at least one first indentation (Y1) being configured to at least partially accommodate said first thickness (d1) of the at least one first portion (X1).

7. Card according to any of Claims 1 to 6, wherein said capacitive sensor (30) comprises at least one second indentation (Y2) hollowed out in a thickness of the dielectric film (36) of said capacitive sensor (30), said at least one second indentation (Y2) being configured to at least partially accommodate said second thickness (d2) of the at least one second portion (X2).