WO2016027028A1

WO2016027028A1 - Device for obtaining fingerprints

Info

Publication number: WO2016027028A1
Application number: PCT/FR2015/052204
Authority: WO
Inventors: Jean-François Mainguet
Original assignee: Commissariat A L'energie Atomique Et Aux Energies Alternatives; Safran
Priority date: 2014-08-22
Filing date: 2015-08-13
Publication date: 2016-02-25
Also published as: FR3025042A1; FR3025042B1

Abstract

The invention relates to a device (100) for obtaining finger or palm prints, comprising: a print sensor (110) provided with, on a supporting substrate (112), a plurality of cells (114) for obtaining prints, each cell (114) comprising a photoelectric, pyroelectric, capacitive or piezoelectric conversion element (201), and at least one TFT transistor; and a false finger detector comprising at least one conductive winding (130) and a circuit (132) for measuring a variable representing the inductance of said winding (130).

Description

DEVICE FOR ACQUIRING DIGITAL IMPRESSIONS

The present patent application claims the priority of the French patent application FR14 / 57928 which will be considered as an integral part of the present description.

Field

The present application relates to the field of electronic devices in general, and more particularly relates to the field of fingerprint acquisition devices. Presentation of the prior art

Various devices and methods have been proposed for performing an electronic acquisition of a fingerprint, that is to say to provide an image of the pattern formed by the crests and troughs of the skin of a finger, of several fingers, or from the palm of the hand. In particular, optical sensors, capacitive sensors, thermal sensors, ultrasonic sensors, and electric field sensors have been proposed.

We are more particularly interested in optical, thermal, capacitive or pressure fingerprint sensors, made in TFT (Thin Film Transistor) technology, that is to say comprising, on a support substrate, one or more elementary acquisition cells, each cell comprising a photoelectric, pyroelectric, capacitive conversion element, or piezoelectric, and one or more TFT transistors for controlling this element. By transistor TFT is meant here transistors formed by successive deposition of conductive, insulating and semiconductive layers on the support substrate. In particular, in a TFT transistor, the semiconductor channel-forming region of the transistor is produced by depositing a layer of a semiconductor material, for example hydrogenated amorphous silicon or polycrystalline silicon (polycrystalline rendering after annealing, for example). or a type of material IGZO (of the "Indium Gallium Zinc Oxide" - indium gallium zinc oxide), this deposit may be preceded by a deposit of a conductive layer for forming a gate electrode, source or drain of the transistor. The optical, thermal and capacitive impression sensors made in TFT technology have the advantage of being relatively inexpensive, in particular by virtue of the use of a support substrate made of a low-cost material such as glass (instead of a monocrystalline silicon substrate generally used to make transistors), and to be easily integrable in many types of electronic devices, and in particular in devices already using TFT technology to perform other functions, for example to make screens.

In addition to the fingerprint sensor itself, a fingerprint acquisition device may include one or more fraud protection devices. A relatively common method of fraud is to affix on the sensor an artificial reproduction of the fingerprint, for example a fake finger made by molding in a material such as clay, modeling clay, gelatin or gelatin. silicone.

False finger detectors have been proposed in which the electrical conductivity of the finger is measured by means of electrodes arranged in contact with the finger. This method has the disadvantage of requiring contact between the user's finger and at least one electrode of the false detector fingers. This can pose practical design problems, and in the long run, reliability problems of the fingerprint acquisition device. In addition, this method of detection, widespread, has already been bypassed by some fraudsters who use false fingers in materials with electrical conductivities substantially identical to those of human skin.

It has also been proposed in WO2014 / 015095, a magnetic field fingerprint acquisition device comprising a plurality of pixels each comprising a coil and means for measuring the inductance of this coil. This document indicates that inductance measurements can be used to detect fraud attempts, but does not explain how to perform such detections. A disadvantage of this fingerprint acquisition device lies in its very great complexity of implementation, if it is desired to acquire images at a resolution usable by the usual fingerprint recognition devices. For example, if it is desired to acquire images at a resolution of 500 pixels per inch or more, is not a inter pixel ^¬ 50.8 microns or less, each reel must fit into a lower zone of width equal to or 50.8 μm. As a result, the coils inevitably have a low number of turns, and therefore a low sensitivity. In addition, because of their small size, the coils generate a magnetic field on a shallow depth.

In particular, such coils do not allow to create a penetrating magnetic field in the inner layers of the skin. In practice, such a sensor only makes it possible to obtain images at resolutions very much lower than those which can typically be obtained with optical, thermal or capacitive sensors made using TFT technology.

summary

Thus, an embodiment provides a device for acquiring fingerprints or palmar, comprising: a fingerprint sensor comprising, on a support substrate, a plurality of finger acquisition cells, each cell comprising a photoelectric, pyroelectric, capacitive or piezoelectric conversion element, and at least one TFT transistor; and a false finger detector having at least one conductive winding and a measuring circuit of a magnitude representative of the inductance of this winding, wherein the winding is disposed above the substrate.

According to one embodiment, the winding and the sensor are superimposed.

According to one embodiment, the device comprises several windings superimposed on acquisition zones that are distinct from the sensor.

According to one embodiment, the winding and the sensor are not superimposed.

According to one embodiment, the sensor is a scroll sensor, having an acquisition surface smaller than the surface of the impression to be acquired.

According to one embodiment, the assembly formed by the sensor and the winding is coated with an insulating protective layer.

According to one embodiment, the thickness of the protective insulating layer above the winding is less than 50 μm and preferably less than 10 μm.

According to one embodiment, the winding is made of a transparent conductive material.

According to one embodiment, each cell comprises a photoelectric conversion element, and the winding is in an opaque conductive material.

According to one embodiment, the inner end of the winding is connected to an application node of a reference potential of a subacute cell.

According to one embodiment, the acquisition cells are arranged in a matrix.

According to one embodiment, the substrate is transparent. According to one embodiment, the inductance measurement operations carried out by the measurement circuit and the fingerprint acquisition operations by the sensor are not implemented simultaneously.

According to one embodiment, the acquisition of a fingerprint by the sensor comprises several successive phases of acquisition of portions of the cavity, these successive phases being separated in pairs by a phase of measuring the inductance of the sensor. 'winding.

Brief description of the drawings

These and other features and advantages will be set forth in detail in the following description of particular embodiments in a non-limiting manner with reference to the accompanying drawings in which:

Figure 1 is a schematic top view of an example of an embodiment of a fingerprint acquisition device;

Figure 2 is an enlarged schematic sectional view of a portion of the fingerprint acquisition device of Figure 1;

Figure 3 is a schematic top view of an alternative embodiment of a fingerprint acquisition device;

Figure 4 is a schematic top view of another alternative embodiment of a fingerprint acquisition device; and

FIG. 5 is a diagram illustrating, in block form, an example of a control method of a fingerprint acquisition device of the type described in relation to FIGS. 1 to 4.

detailed description

For the sake of clarity, the same elements have been designated by the same references in the various figures and, moreover, as is customary in the representation of the integrated circuits, the various figures are not drawn to scale. By elsewhere, in the remainder of the description, unless otherwise indicated, the terms "approximately", "substantially", "about", and "of the order of", etc., mean "to within 20%", and references such as "upper", "lower", "overlying", "over", etc., apply to devices oriented in the manner illustrated in the corresponding views, it being understood that, in practice, such devices can be oriented differently.

Figure 1 is a schematic top view of an example of an embodiment of a device 100 for acquiring fingerprints.

The device 100 comprises an optical impression sensor 110, thermal, capacitive or pressure, made in TFT technology. The impression sensor 110 comprises, on a support substrate 112, for example an insulating substrate, a plurality of elementary acquisition cells 114 each comprising at least one photoelectric conversion element, pyroelectric, capacitive or piezoelectric, and a TFT transistor. control of this element. The cells are for example regularly distributed on the substrate with a pitch between

10 and 100 μm. In the example shown, the sensor 110 comprises a plurality of cells 114 arranged in rows and columns. The embodiments described are not limited to the schematic example of FIG. 1 in which the sensor 110 comprises six rows and five columns. By way of non-limiting example, the sensor 110 comprises 200 to 400 lines and 300 to 500 columns. Such a sensor is for example suitable for static acquisition, that is to say to acquire an image of the impression without the user's finger moving relative to the sensor. Alternatively, the sensor 110 may comprise a single row of cells 114, or a small number of lines, for example 2 to 10 lines. Such a sensor is for example adapted to a scrolling acquisition, that is to say to acquire an image of the fingerprint in several sections when the finger of the user scrolls with respect to the sensor. In this example, the device 100 further comprises a circuit 116 (CTRL) for controlling the elementary cells 114 of the sensor 110, and a circuit 118 (RD) for reading the output values of the cells 114. As a nonlimiting example , the control circuit 116 and the read circuit 118 are adapted to simultaneously simultaneously control and read the cells 114 of the same line of the sensor 110, the different lines of the sensor 110 can be read successively.

According to one aspect of an embodiment, the device 100 further comprises a conductive winding 130 disposed above the sensor 110, the ends of which are connected to a circuit 132 for measuring the inductance of this winding, or a magnitude representative of the inductance of this winding. For example, the circuit 132 is adapted to apply a voltage or a current across the winding 130, and to measure a current / voltage phase shift to deduce the value of the inductance of the winding 130. winding 130 is preferably a planar winding, that is to say that the different turns of the winding are disposed substantially in the same plane, in the same conductive level of the device, an additional conductive level can be provided, for connect the inner end of the winding to the circuit 132. In the example shown, seen from above, the outer dimensions of the winding 130 are substantially identical to the dimensions of the sensor 110. However, the described embodiments are not limited to to this particular case. Alternatively, in top view, the winding may be smaller than the sensor and be disposed opposite a central portion of the sensor. The winding 130 preferably comprises a high number of turns, for example greater than 4 and preferably greater than 10, or even greater than 100, in order to increase its own value of inductance and thus the sensitivity of the system. Note that the number of turns of the winding 130 can be conditioned by the minimum track width that can be formed in the considered technology. For example, a winding in A planar spiral consisting of 100 turns, having a conductive track width of 3 μm and an inter-turn spacing of 3 μm wide, has a bulk equivalent to that of a disk of 1.2 mm diameter. If several conductive levels are available to carry out the winding, the number of turns may be increased, or the surface space decreased. Alternatively, a magnetic material may be added around the winding and / or in the center of the winding, to increase the detection sensitivity.

The inventors have found that the presence of a real finger above winding 130 modifies the value of its inductance, whereas the presence of a false finger does not modify or modify it in different proportions. The winding 130 and the circuit 132 thus form elements of a false finger detector. By way of nonlimiting example, the inventors have found that a winding having a vacuum inductance of 19.4 μΗ sees its inductance rise to 20.540 μΗ in the presence of a real finger placed above the winding, then that the presence of a false finger made of a printed paper or silicone material above the winding, reduces the inductance to a value of 19.8 μΗ. The detector may further comprise a unit (not shown) for processing the measurements provided by the circuit 132, adapted to determine, from these measurements, whether a real finger is placed above the winding 130. The winding 130 is preferably disposed in an area of the device 100 above which the user poses or inevitably passes his finger during a fingerprint acquisition. This avoids fraudulent use in which a user would place a real finger on the false finger detector, and a false finger on the fingerprint sensor, to deceive the security device. Alternatively, the winding 130 may be replaced by a plurality of smaller surface windings distributed over the surface of the sensor so as to ensure that under normal conditions of use the user's finger covers at least one winding. In addition, to increase robustness to fraud, it can be provided to check the consistency between the detection carried out via the conductive winding (s), and the image of the impression.

An advantage of such a false finger detector is that the finger does not need to be in contact with the conductive winding 130 to enable its authentication. Thus, the conductive winding 130 may be coated with an insulating passivation layer (not visible in FIG. 1), for example a protective lacquer or a layer of nitride or silicon oxide, providing the device 100 with a high degree of robustness. Preferably, to allow reliable detection, the distance between the winding 130 and the user's finger, that is to say the distance between the average plane of the winding 130 and the upper face of the device 100 is relatively low, for example less than 50 μm and preferably less than 10 μm.

FIG. 2 is an enlarged schematic sectional view of an exemplary embodiment of the fingerprint acquisition device 100 of FIG. 1. More particularly, FIG. 2 is a schematic view of an elementary cell 114 and FIG. a portion of the winding 130, according to the sectional plane F2 of FIG.

In this example, the sensor 110 is an optical sensor made of TFT technology. The substrate 114 is a transparent substrate, for example made of glass. Each cell 114 of the sensor 110 comprises a photoelectric conversion element 201 and at least one access transistor or transistor 203 for controlling this element. The element 201 comprises a phototransistor 205 and a capacity 207 for storing the photogenerated charges by the phototransistor 205. The phototransistor 205 comprises a stack comprising, in order from the surface of the substrate 112, a conductive grid 209, an insulator gate 211, and a semiconductor region 213 for channel formation. At its ends, the channel forming region 213 is respectively connected to a source conductive electrode 215 and a drain conductor electrode 217. The capacitor 207 includes a stack comprising, in order from the surface of the substrate 112, a first conductive electrode 219 connected to the gate 209 of the phototransistor 205, an insulating region 221 formed in the same insulating level as the gate insulator 211 of the phototransistor 205 and a second conductive electrode 223 connected to the drain electrode 217 of the phototransistor 205. The access transistor 203 comprises a stack comprising, in order from the surface of the substrate, a conductive grid 225 formed in the same direction. conductive level as the gate 209, a gate insulator 227 formed in the same insulating level as the regions 211 and 221, and a semiconductor region 229 channel forming, formed in the same semiconductor level as the region 213. At its ends, the channel forming region 229 is respectively connected to a source conductive electrode 231 and a drain conductor electrode 233. In this example, the the gate electrodes 209 and 225 of the transistors 205 and 203 are formed in a first non-transparent conductive level, for example aluminum or molybdenum, the lower electrode 219 of the capacitor 207 is formed in a first transparent conductive level by example of the ITO (of the English "Indium Tin Oxide" - indium tin oxide), the source and drain electrodes 231 and 233 of the transistor 203 are formed in the same second non-transparent conductive level, for example aluminum or molybdenum, and the electrodes 215, 217 and 223 are formed in the same second transparent conductive level, for example ITO.

In the example shown, the assembly of the cell 114 comprising the phototransistor 205, the capacitor 207 and the access transistor 203 is covered by an insulating layer 235, this layer being surmounted, facing the transistor 203, by a screen opaque 237, for example aluminum or molybdenum.

In this example, the conductive winding 130 is formed above the insulating layer 235, in a third transparent conductive level, for example in ITO. A fourth conductive level (not visible in FIG. 2), for example a transparent conductive level, can be provided for connecting the end Inside the winding 130 to the impedance measuring circuit 132. As an advantageous variant, the inner end of the winding 130 can be connected to an available reference potential in a pixel or elementary acquisition cell. acente, for example the mass, which avoids the realization of an additional layer specifically to connect this inner end to the circuit 132.

A transparent passivation layer 239 covers the entire structure comprising the sensor 110 and the winding 130.

The operation of the fingerprint acquisition device 100 of FIG. 2 is as follows. The user places a finger on or above the upper surface of the passivation layer 239. A backlight light source, not shown, disposed on the underside side of the substrate 112, illuminates the finger through the device 100 In the example of FIG. 2, the backlighting light passes in particular through the device 100 at the level of the capacitor 207, which consists solely of transparent layers and which is not surmounted by an opaque layer. The conductive winding 130 is made in a transparent conductive level, it does not prevent the passage of light from the backlight source. The light is then reflected by the finger towards the phototransistor 205, with more or less attenuation depending on whether the finger portion above the cell 114 corresponds to a peak or a hollow of the skin of the finger. The light reflected by the finger is converted into electric charges by the phototransistor 205. These charges are stored in the capacitor 207 and can be read by an external circuit, for example the circuit 118 of Figure 1, via the transistor. 203.

Note that in the case of an optical impression sensor, of the type described in relation to FIG. 2, the provision of a transparent conductive winding 130 advantageously makes it possible to arrange the winding 130 as close as possible the fingerprint acquisition area, and preferably facing the fingerprint acquisition area, without disturbing the operation of the fingerprint sensor.

Alternatively, the phototransistor 205 and the capacitor 207 may be replaced by a pyroelectric element (not shown) to provide a thermal sensor. In this case, the sensor 110 does not require a backlight light source for its operation, and the device 100 may be opaque. The conductive winding 130 can then be formed in a non-transparent conductive level, for example aluminum or molybdenum, preferably near the elementary cells acquisition of imprint, for example in the central position.

Furthermore, it will be noted that in the case of an optical sensor, if the winding 130 is arranged so that a sufficient quantity of light is received by each cell 114, the winding 130 may be of a non-transparent material, for example aluminum or molybdenum. By way of example, it is possible to make the winding 130 of an opaque material, and to size and arrange the winding 130 so that the surface of each cell 114 coated by the winding is less than or equal to half of the total surface of the cell. The winding 130 can then advantageously be formed in the same level as the opaque screen 237 of FIG. 2. In a particularly advantageous embodiment, the winding 130 and the opaque screen 237 of FIG. 2 (coating the transistor 203) are combined, that is to say that, in each cell, the winding 130 covers the transistor 203 and serves as an opaque mask to prevent the photo-generation of electric charges by the transistor 203.

The embodiment of the winding 130 in an opaque material advantageously makes it possible to obtain a winding having a better electrical conductivity than can typically be obtained with transparent conductive materials. FIG. 3 is a view from above schematically illustrating an alternative embodiment of the fingerprint acquisition device of FIGS. 1 and 2. In the example of FIG. 3, the fingerprint acquisition device 300 comprises a scrolling fingerprint sensor 310, that is to say to say a sensor having an acquisition area smaller than the impression area to be acquired. During an acquisition, the user scrolls in front of the sensor (or the sensor scrolls in front of the finger of the user) so that the sensor can acquire a complete image of the fingerprint. The sensor 310 may be an optical sensor, thermal, capacitive or pressure, made in TFT technology, for example a sensor of the type described in connection with Figures 1 and 2.

The device 300 further comprises a false finger detector of the type described in relation with FIGS. 1 and 2, that is to say based on an inductance measurement. In the example of FIG. 3, the false finger detector comprises two conductive windings 330 and 330 'disposed respectively upstream and downstream of the sensor 310 with respect to the direction of movement of the finger in front of the sensor 310. The windings 330 and 330 'may be the same or similar. The dimensions and the position of the windings 330 and 330 'are preferably chosen so that the user can not scroll his finger in front of the sensor 310 without also passing in front of the windings 330 and 330'. By way of example, the area occupied by the sensor 310 and the windings 330 and 330 'is smaller than the surface of a fingerprint, for example less than 1 cm 2. By way of nonlimiting example, each of the windings 330 and 330 'has external dimensions of the same order as those of the sensor

310. The windings 330 and 330 'are not arranged opposite the sensor 310, they can be made of a non-transparent conductive material, for example copper or aluminum, even if the sensor 310 is an optical sensor. The prediction of two conductive windings increases the reliability detection. However, alternatively, the device 300 may comprise a single conductive winding placed upstream or downstream of the sensor 310 relative to the direction of travel of the finger, or comprise a number of conductive windings greater than two. Furthermore, the windings 330 and 330 'may have dimensions, and therefore different inductance values.

FIG. 4 is a view from above schematically illustrating another variant embodiment of the fingerprint acquisition device 100 of FIGS. 1 and 2. The fingerprint acquisition device 400 of FIG. 4 comprises elements that are common with FIG. the device 100 of Figure 1. In the following, only the differences between the devices of Figures 1 and 4 will be detailed.

The device 400 comprises an optical, thermal, capacitive or pressure fingerprint sensor 110, made of TFT technology, similar or identical to that of FIG. 1. In the example of FIG. 4, the matrix of elementary cells 114 is divided into several sub-matrices each comprising several cells 114, corresponding to several acquisition zones distinct from the sensor, four zones 412a, 412b, 412c and 412d in the example of FIG. 4, each acquisition zone being adapted to perform a static acquisition of a part of the fingerprint or the palm of the user.

The device 400 further comprises a circuit 116

(CTRL) for controlling the elementary cells 114, and a circuit 118 (RD) for reading the output values of the cells 114. The circuits 116 and 118 are for example identical or similar to those of the device 100 of FIG.

The device 400 further comprises a conductive winding 430 disposed above each of the acquisition zones of the sensor 110, ie four conductive windings 430 in the example of FIG. 4. Each conductive winding 430 of the device 400 is for example identical or similar to the winding 130 of the device 100 of FIG. non-limiting example, each winding 430 has outer dimensions substantially identical to those of the acquisition area above which it is located. Each winding 430 has its ends connected to a circuit 132 for measuring the inductance of this winding. The windings 430 and the circuit 132 form elements of a false finger detector.

When an object, for example a finger, is placed on the sensor 110, it may or may not cover an acquisition zone. By way of illustrative example, the finger can cover most of the area 412a, and not cover or cover only a small portion of the areas 412b, 412c and 412d. In this case, if the finger is authentic, the detection of real finger will be positive in the zone 412a and negative in the other zones. The device can then check the coherence between the image acquired by the sensor 110 and the inductance measurements made by the circuit 132. By way of example, the decision of authenticity of the finger (or the palm) can be taken independently for each area covered by the finger. If all the areas that provided part of the fingerprint image are considered valid, the acquired fingerprint can be considered authentic. If, on the other hand, zones having provided a part of the image of the impression are considered as invalid, an alarm can be triggered. This makes it possible to detect, in the same acquisition phase, the presence on a part of the surface of the sensor, of an authentic finger, and, on another part of the surface of the sensor, of a false. A number of false detections may possibly be tolerated. Spatial and temporal consolidations can be planned to improve the robustness of the system.

By way of example, the area of each zone of the sensor may be between 2 and 100 mm 2. The area and the number of zones can be adapted according to the intended use. By way of example, a sensor intended for the acquisition of a fingerprint may have a size of approximately 13 × 20 mm, and may be divided into 6 to 12 zones each surmounted by a conductive winding. Alternatively, a sensor for acquisition of the fingerprint of four fingers simultaneously can have a size of about 80x80 mm, and be divided into 64 to 256 zones each surmounted by a conductive winding.

In practice, the inventors have determined that, in fingerprint acquisition devices of the type described with reference to FIGS. 1 to 4, it is preferable not to make an inductance measurement of the conductive winding (s) of the detector. false fingers at the same time as one acquires a fingerprint via the fingerprint sensor. The application of a voltage or a current across the conductor winding to measure its inductance may indeed cause, at the level of the TFT transistors of the fingerprint sensor, electromagnetic interferences or disturbances likely to cause malfunctions of the sensor.

To avoid such malfunctions, it is possible to perform the fingerprint detection and fingerprint acquisition operations successively. Preferably, provision is then made for a relatively short time, for example less than 50 ms and preferably less than 10 ms between the end of a false finger detection phase and the start of a fingerprint acquisition phase, to prevent fraudulent use in which a malicious user would substitute a false finger for a real finger between the false finger detection operation and the fingerprint acquisition operation. For added security, a second false finger detection operation can also be implemented just after the acquisition of the fingerprint. Alternatively, to further enhance the security of the device, an alternation of false finger detection operations and fingerprint acquisition operations can be provided, preferably at a relatively high frequency, for example greater than or equal to 10 Hz.

In certain optical, thermal, capacitive, or pressure sensors, made in TFT technology, the acquisition of an image of a fingerprint may comprise several successive phases of acquisition of portions of the fingerprint. By way of example, in the sensor of FIG. 3, slices or lines of the image of the finger are successively acquired by the sensor 310. Moreover, in the sensor of FIG. 1, lines of the image of the Finger can be acquired and read successively by the sensor 110. In this case, it is possible to provide a control method for the device in which, between two successive phases of acquisition of a portion of the image of the finger, a phase is provided. false finger detection, which provides a particularly high level of security to the device.

FIG. 5 is a diagram illustrating, in the form of blocks, a nonlimiting example of such a method of controlling a fingerprint acquisition device comprising an inductance-type false-finger detector of the type described in FIG. relationship with Figure 3.

During a step 501 (FINGER DETECTED?), The device is for example in a standby mode, and monitors the possible arrival of a finger above the sensor. This detection can be performed by measuring the inductance of a conductive winding of the device, or by any other suitable means.

If an object, for example a finger, is detected on the sensor, a step 503 (SENSE L) for detecting a false finger, comprising measuring the inductance of a conductive winding of the device, is implemented.

In a step 505 (SPOOF?) Subsequent to step 503, the device determines whether the inductance value measured in step 503 is likely to correspond to the presence of a false finger on the sensor. This determination can be made by checking whether the inductance value is lower than a low threshold, corresponding to the presence, above the winding, of a material insufficiently conductive compared to a real finger, for example a false latex finger, or greater than a high threshold, corresponding to the presence, above the winding, of a material too conductive compared to a real finger, for example a false metal finger.

If a false finger is detected, a false finger detection counter may be incremented in a step 507 (CPT). Alternatively, an alarm can be triggered at this stage. The process can then proceed to step 509.

During a step 509 (READ) subsequent to step 505, an image viewed by the fingerprint sensor of the device, corresponding to a portion of the image of the fingerprint, is acquired and stored.

During a step 511 (FINGER STILL PRESENT?), The device checks whether a finger is still present above the sensor. If a finger is still present, steps 503 to 511 are repeated. If the finger is no longer present, the acquisition process ends. The image of the impression can then be reconstructed during a step 513, from the image portions acquired during the successive iterations of the step 509. In the step 513, the device can also, in taking into account the value of the false finger detection counter (step 507), decide whether or not to trigger an alarm. By way of example, a false detection error rate of less than or equal to 1% may be acceptable.

Particular embodiments have been described. Various variations and modifications will be apparent to those skilled in the art.

In particular, the embodiments described are not limited to the particular examples of TFT structures described with reference to FIG. 2. Other types of TFT structures may be provided, for example TFT structures in which the gate electrodes of the transistors are disposed on the side of the semiconductor layer opposite to the support substrate.

Moreover, the described embodiments are not limited to the particular examples described above of arrangement of the conductive winding (s) of the false finger detector with respect to the fingerprint sensor.

In addition, the described embodiments are not limited to the aforementioned examples of control methods of the fingerprint acquisition device. In particular, although it has been indicated above that it is preferable to temporally separate the inductance measurement phases by the false finger detector, and the image acquisition phases by the fingerprint sensor, the modes described embodiments are not limited to this particular case. Depending on the circumstances, it will be possible to simultaneously perform the false finger detection by inductance measurement and the acquisition of an image of the fingerprint.

In addition, although embodiments of devices adapted to the acquisition of a fingerprint of a single finger of a user have been described above, the embodiments described can be adapted to adapted devices. to simultaneously acquire the fingerprints of several fingers of a user, or to acquire the imprint of the palm of a user. By way of illustrative and non-limiting example, in the example of FIG. 1, to produce a device adapted to acquire in parallel the fingerprints of a user's fingers, the sensor 110 may comprise 1400 to 1600 lines and 1500 to 1700 columns of elementary cells, and, to achieve a device for acquiring a palm footprint (fingerprint of the palm or the entire hand), the sensor 110 may comprise 2600 to 2800 lines and 3900 to 4100 columns.

Claims

A fingerprint or palmar acquisition device (100; 300; 400) comprising:

a fingerprint sensor (110; 310; 410) having, on a support substrate (112), a plurality of finger acquisition cells (114), each cell (114) having a conversion element (201). photoelectric, pyroelectric, capacitive or piezoelectric, and at least one TFT transistor (203); and

a false finger detector having at least one conductive winding (130; 330,330 '; 430) and a circuit (132) for measuring a magnitude representative of the inductance of said winding (130; 330,330; )

wherein said at least one winding (130; 330, 330 '; 430) is disposed above the substrate.

The device (100; 400) according to claim 1, wherein the winding (130; 430) and the sensor (110; 410) are superimposed.

3. Device (400) according to claim 2, comprising a plurality of windings (430) superimposed on acquisition areas (412a, 412b, 412c, 412d) separate from the sensor (410).

4. Device (300) according to claim 1, wherein the winding (330, 330 ') and the sensor (310) are not superimposed.

5. Device (300) according to any one of claims 1 to 4, wherein the sensor (310) is a scroll sensor having an acquisition surface smaller than the surface of the impression to be acquired.

The device (100; 300; 400) according to any one of claims 1 to 5, wherein the assembly formed by the sensor (110; 310; 410) and the winding (130; 330,330; ) is coated with an insulating protective layer (239).

The device (100; 300; 400) according to claim 6, wherein the thickness of the protective insulating layer. (239) above the winding (130; 330,330 '; 430) is less than 50 μm and preferably less than 10 μm.

The device (100; 300; 400) according to any one of claims 1 to 7, wherein the winding (130; 330,330 '; 430) is of a transparent conductive material.

The device (100; 300; 400) according to any one of claims 1 to 7, wherein each cell (114) comprises a photoelectric conversion element, and the winding (130; 330,330 '; 430) is in an opaque conductive material.

The device (100; 400) according to any one of claims 1 to 9, wherein the inner end of the winding (130; 430) is connected to an application node of a reference potential of an underlying cell (114).

11. Device (100; 300; 400) according to any one of claims 1 to 10, wherein the acquisition cells (114) are arranged in a matrix.

The device (100; 300; 400) according to any one of claims 1 to 11, wherein the substrate (112) is transparent.

A method of controlling a device (100; 300; 400) according to any one of claims 1 to 12, wherein the inductance measuring operations performed by the measuring circuit (132) and the operations of fingerprint acquisition by the sensor (110; 310; 410) are not performed simultaneously.

14. The method of claim 13, wherein the acquisition of a fingerprint by the sensor (110; 310; 410) comprises several successive phases (509) of acquisition portions of the footprint, these successive phases being separated two by two by a phase (503) for measuring the inductance of the winding (130; 330, 330 '; 430).