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    • 专利摘要:
    A thermal pattern sensor (100) having a plurality of pixels (102) disposed on a front face (112) of a substrate (104), each pixel (102) comprising at least one pyroelectric capacitance formed by at least one portion of pyroelectric material ( 106) disposed between two electrically conductive electrodes (108, 110) and such that the electrically conductive electrodes (108, 110) are disposed in a same plane substantially parallel to the front face (112) of the substrate (104).
    公开号:FR3044408A1
    申请号:FR1561580
    申请日:2015-11-30
    公开日:2017-06-02
    发明作者:Abdelkader Aliane；Jean-Francois Mainguet
    申请人:Commissariat a lEnergie Atomique CEA；Safran SA；Commissariat a lEnergie Atomique et aux Energies Alternatives CEA；
    IPC主号:
    专利说明:

    THERMAL PATTERN SENSOR WITH HORIZONTAL PYROELECTRIC CAPABILITY
    DESCRIPTION
    TECHNICAL FIELD AND PRIOR ART The invention relates to a thermal pattern sensor, or temporal temperature variation transducer in a difference of electrical potentials, comprising pyroelectric capacitors, advantageously used to perform a fingerprint capture. The invention applies to the field of sensors of the active type, that is to say comprising one or more heating elements intended to heat the pixels, but also to the field of passive type sensors which do not include such heating elements .
    It is known to produce a fingerprint sensor comprising thermal detection means. These thermal detection means may correspond to pyroelectric elements, diodes, thermistors or any other temperature-sensitive element making it possible to convert a temperature variation into a variation of potential or electrical current.
    Fingerprint detection can be carried out by so-called "passive" sensors exploiting a temperature difference between that of the finger and that of the sensor, as described in US Pat. No. 4,394,773, US Pat. No. 4,429,413 and US Pat. No. 6,289,114. These sensors, however, have the disadvantage of making a measurement that depends solely on the difference between the temperature of the finger and the temperature of the sensor. It may therefore happen that the level of the signal obtained is zero when the finger and the sensor are at the same temperature, or that the contrast of the captured images varies, which then poses problems during the subsequent processing of the images obtained (for example, a reversal of the temperatures causes a reversal of the image obtained).
    To eliminate the problems raised by passive heat sensors, and especially in the case of a static acquisition where the finger does not move, so-called "active" fingerprint sensors have been proposed, such as those described in the US documents In such a sensor, each pixel comprises a pyroelectric capacitance formed of two conductive electrodes superimposed one above the other and between which a portion of pyroelectric material is disposed, and a heating element. This heating element dissipates a certain amount of heat in the pixel, and heating of the pixel is measured after a certain acquisition time in the presence of the finger on the sensor. This makes it possible to distinguish, at the level of each pixel, the presence of a peak or a valley of the detected imprint according to whether the heat is absorbed by the skin (pixel in the presence of a crest of the impression) or preserved in the pixel (pixel in the presence of a valley of the footprint). This leads to a lower final temperature in the case of a pixel in the presence of a peak of the footprint, where the heat is absorbed by the skin, compared to a pixel in the presence of a valley of the footprint .
    In the first order, such a sensor can measure the heat capacity, also called specific heat or specific heat capacity, of an element in contact with the sensor. The measurements obtained also depend on the thermal conductivity between the sensor and the part of the element (peak or valley in the case of a fingerprint) in the presence on the sensor.
    At the physical level, it is the heat exchange by contact between the sensor and the skin that make the operation of the sensor possible. Indeed, air, or any gas, can not transport heat as efficiently as dense material such as skin, which results in significant thermal conductivity differences between a pixel in contact with air and a pixel in contact with the skin. In addition, the depth of the valleys increases the thermal resistance towards the thermal capacity of the skin. Radiation is very secondary in the transport of energy compared to heat transmission by contact.
    In order to obtain a good sensitivity to detection, reflecting a strong temperature difference between a pixel in contact with a peak of the cavity and a pixel in contact with a valley of the cavity, the electric powers injected into the element heating can range from 0.5 mW / pixel to 5 mW / pixel in the case of pixels having sides of dimension equal to about 50 μm (as is the case for a standard fingerprint sensor of resolution equal to 500 dpi).
    There are several ways to measure the temperature variation due to the presence of the thermal pattern. FIG. 1 represents a sectional view of a pixel 10 of a thermal pattern sensor making it possible to carry out such a measurement.
    The sensor is made from a substrate 12, for example glass. The pixel 10 comprises a lower electrode 14 and an upper electrode 16 between which a portion of pyroelectric material 18 is disposed, forming a pyroelectric capacitance. The pyroelectric material may be for example a poly (vinylidene fluoride-trifluoroethylene) or P (VDF-TrFE) or PVDF (polyvinylidene fluoride), a ceramic such as PZT (titanium lead zirconate, or "Lead Zirconate Titanate"). In English), AIN, BaTiC> 3 or ZnO. Other pyroelectric materials are possible, namely all those that produce electric charges according to a pyro-piezoelectric parameter. The upper electrode 16 is covered with a protective layer 20 on which the element whose thermal pattern is measured, for example a finger, is intended to be disposed during the measurement.
    When the pyroelectric material portion 18 is subjected to a temperature variation ΔΤ, this temperature variation ΔΤ causes the appearance of an additional electric field within the pyroelectric capacitance, generating AQ charges between the electrodes 14, 16 such that : AQ = SYAT (1)
    The parameter S corresponds to the surface of the portion of pyroelectric material 18 facing each of the electrodes 14, 16. The parameter y corresponds to the pyroelectric coefficient of the pyroelectric material of the portion 18. For example, the pyroelectric coefficient y of the PVDF is equal to approximately 29 pC / m 2 / K.
    The portion of pyroelectric material 18 and the electrodes 14, 16 forming a capacity of value C, the charges ΔΟ. generated induce a difference of electric potentials AV between the electrodes 14,16 such that: C.AV = AQ = Ξ.γ.ΑΤ (2)
    However, in addition to the charges generated by the capacitance C, other charges are also generated by the parasitic capacitances present at the pixel, for example those related to the gate of the read transistor when the sensor comprises a read circuit. in tension.
    In the case of an active thermal sensor, the sensor is also provided with a heating element generally made from the same electrically conductive layer as that used to produce the upper electrode 16. This heating element is for example produced under the a serpentine shape partially surrounding the upper electrodes 16 and for laterally heating the pyroelectric capacitors, at the upper electrodes 16. This provision of the heating element is however not ideal because to heat the pixels laterally is not very performance due to the high thermal resistance formed by the pyroelectric material. In addition, by making the upper electrode and the heating element from the same electrically conductive layer, it is necessary to make a compromise between the surface occupied by the upper electrode and that occupied by the heating element. Finally, the heating element thus produced can also greatly disturb the operation of the sensor.
    A problem common to active sensors and passive sensors is their cost of implementation, particularly related to the realization of the electrodes.
    STATEMENT OF THE INVENTION
    An object of the present invention is to propose a thermal pattern sensor whose structure is compatible with the production of a sensor of passive or active type, and whose production cost is lower than that of the sensors of the prior art.
    For this, the present invention proposes a thermal pattern sensor comprising a plurality of pixels arranged on a front face of a substrate, each pixel comprising at least one pyroelectric capacitor formed by, or comprising, at least one portion of pyroelectric material disposed between two electrodes. electrically conductive and such that the electrically conductive electrodes are disposed in the same plane substantially parallel to the front face of the substrate.
    Thus, instead of producing a "vertical" pyroelectric capacitance with respect to the front face of the substrate on which the pixels are made, the sensor according to the invention proposes to carry out the pyroelectric capacitance "horizontally" by arranging the two electrodes of each pixel in the same horizontal plane parallel to the front face of the substrate. Such a configuration makes it possible to produce the electrodes of the pixels using a single level of metal and not two as is usually done, which results in a lowering of the cost related to their production (a mask of less to achieve, and an operation). deposit / engraving in less to implement).
    The pyroelectric material corresponds to a material capable of generating electrical charges when it is subjected to a temperature variation.
    The electrically conductive electrodes of a pixel are disposed in the same plane substantially parallel to the front face of the substrate, that is to say that a part of each of the electrodes is part of a plane parallel to the front face of the substrate.
    It is also described a thermal pattern sensor comprising at least one pixel disposed on a front face of a substrate and comprising at least one pyroelectric capacitor formed by, or comprising, at least one portion of pyroelectric material disposed between two electrically conductive electrodes and such that the electrically conductive electrodes are disposed in the same plane substantially parallel to the front face of the substrate.
    Advantageously, a spacing "e" between the electrically conductive electrodes of each pixel may be less than or equal to about 2 μm. With such spacing, the pixels can be made with a small pitch. In addition, when the pyroelectric material must initially be polarized by applying a DC voltage at these terminals, via the electrodes, this small spacing between the electrodes makes it possible to achieve this polarization of the pyroelectric material with a lower bias voltage than in the case of a "vertical" pyroelectric capacitance which requires having a greater spacing between the electrodes because this spacing corresponds to the thickness of the deposited pyroelectric material, and therefore a higher level of polarization voltage of the pyroelectric material. The spacing "e" between the electrodes is at least partially, and advantageously completely, filled by the portion of pyroelectric material.
    According to an advantageous embodiment, the pyroelectric material may comprise PVDF and / or P (VDF-TrFE) and / or P (VDF-TrFE-CFE) and / or P (VDF-TrFE-CTFE) and / or AIN. The AIN is advantageously used for producing a scanning sensor on a CMOS substrate.
    Advantageously, the electrically conductive electrodes of each pixel can form interdigitated combs. Such electrodes make it possible to obtain, for a given surface on the substrate, a large electrode surface facing the pyroelectric material. In this case, the electrodes comprise straight portions substantially parallel to one another (corresponding to the "teeth" of the combs), each of the rectilinear portions of one of the two electrodes being interposed between two rectilinear portions of the other of the two. electrodes.
    Each of the electrically conductive electrodes may have a thickness greater than or equal to about 100 nm, or even greater than or equal to about 1 μm. This thickness makes it possible to obtain a large electrode surface facing the pyroelectric material.
    The sensor may further comprise, in each pixel, a layer of pyroelectric material (advantageously the same as that of the dielectric material portions disposed between the electrodes) covering the portion of pyroelectric material and the electrically conductive electrodes such as the portion of pyroelectric material. and the electrically conductive electrodes are disposed between the pyroelectric material layer and the substrate. The presence of such a layer of pyroelectric material facilitates the production of pyroelectric material portions since these portions can be made via a deposit of pyroelectric material of greater thickness than electrically conductive electrodes. One of the electrically conductive electrodes of each pixel can be electrically connected to a fixed electrical potential, for example to the mass of the sensor. The other electrically conductive electrodes of each pixel can in this case serve as read electrode of the pixel, that is to say form the electrode on which the electrical charges generated in the pyroelectric capacitance are intended to be read.
    With the sensor according to the invention, it is no longer necessary to deposit an additional metal to form the upper electrode of the pixel, which represents a gain for the manufacture of the sensors, and in particular the passive sensors.
    For active sensors, it is possible to realize the heating element from the level of metal used for producing the electrodes. In this case, the heating element is arranged next to the electrodes, and thus performs lateral heating of the pixel. However, advantageously, the sensor may further comprise at least one electrically insulated heating element electrically conductive electrodes and disposed facing at least a portion of the portion of pyroelectric material, and advantageously facing the entire portion of pyroelectric material, such as the portion of pyroelectric material is disposed between the heating element and the substrate. This configuration corresponds to an active type sensor which has the advantage over the active sensors of the prior art of not having to compromise between the surface occupied by the upper electrode and that occupied by the heating element. while having a sensor pixel heating more efficient than side heating pixels. This horizontal configuration of the electrodes makes it possible to free up space for the heating element which can cover, in each pixel, the entire surface of the portion of pyroelectric material. No problem of space or arrangement between the heating element and the electrodes does not arise in this configuration. The heating element may comprise at least one continuous portion of electrically conductive material extending facing portions of pyroelectric material of several pixels.
    The continuous portion of electrically conductive material may be disposed facing the entire surface of the pyroelectric material portions of said plurality of pixels. Thus, the heating of the pixels by the heating element is optimal and maximized.
    The pixels can be arranged on the substrate by forming a matrix of several lines and several columns, and the sensor can comprise several heating elements each associated with one of the rows of pixels. The same heating element can therefore be used to heat all the pixels of the same line.
    When the sensor comprises the layer of pyroelectric material covering the portion of pyroelectric material and the electrically conductive electrodes, the layer of pyroelectric material may be disposed, at each pixel, between the heating element and the portion of pyroelectric material and between heating element and the electrically conductive electrodes. Thus, the layer of pyroelectric material can provide electrical insulation between the conductive electrodes and the heating element which is for example formed of a portion of electrically conductive material.
    Advantageously, the sensor may be a fingerprint sensor. The invention also relates to a method for producing a thermal pattern sensor, comprising the production of several pixels on a front face of a substrate, each pixel comprising at least one pyroelectric capacitor formed by at least one portion of pyroelectric material. disposed between two electrically conductive electrodes and such that the electrically conductive electrodes are disposed in the same plane substantially parallel to the front face of the substrate.
    The pixels may be produced at least by the following steps: depositing at least a first electrically conductive layer on the front face of the substrate; etching the first electrically conductive layer, forming the electrically conductive electrodes of each pixel; depositing the pyroelectric material, forming at least the portion of pyroelectric material between the electrically conductive electrodes of each pixel.
    If the pyroelectric material is mechanically strong enough to form a surface protection against external aggression, such as for example when the pyroelectric material is ΓΑΙΝ, the pyroelectric material can then itself provide the mechanical protection of the pyroelectric capacitance. Otherwise, an additional layer of protection can be added.
    The embodiment of the pixels may further comprise, after the step forming the portion of pyroelectric material of each pixel, the implementation of a deposit and an etching of at least a second electrically conductive layer, forming at least one heating element arranged facing at least a portion of the portion of pyroelectric material. This second electrically conductive layer may also serve as protection against electrostatic discharges, when at least one of the ends of this second layer is connected to ground.
    In addition, the deposited pyroelectric material may furthermore form, in each pixel, a layer of pyroelectric material covering the pyroelectric material portion and the electrically conductive electrodes, the heating element then being formed at least on the layer of pyroelectric material.
    BRIEF DESCRIPTION OF THE DRAWINGS
    The present invention will be better understood on reading the description of exemplary embodiments given purely by way of indication and in no way limiting, with reference to the appended drawings in which: FIG. 1 represents a sectional view of a pixel of a thermal pattern sensor of the prior art; - Figure 2 shows a sectional view of a portion of a pixel of a thermal pattern sensor object of the present invention, according to a first embodiment; FIG. 3 represents a top view of several pixels of a thermal pattern sensor, object of the present invention, according to the first embodiment; FIG. 4 represents a sectional view of a portion of a pixel of a thermal pattern sensor, object of the present invention, according to a second embodiment; FIG. 5 represents a top view of several pixels of a thermal pattern sensor, object of the present invention, according to the second embodiment; FIG. 6 represents a top view of several pixels of a thermal pattern sensor, object of the present invention, according to a variant of the second embodiment; FIG. 7 represents a view from above of a portion of the pixel matrix of a thermal pattern sensor, object of the present invention, according to the second embodiment; FIGS. 8A to 81 represent steps of a method for producing a thermal pattern sensor, object of the present invention, according to a particular embodiment; - Figure 9 shows a top view of a heating element made in the form of a coil.
    Identical, similar or equivalent parts of the different figures described below bear the same numerical references so as to facilitate the passage from one figure to another.
    The different parts shown in the figures are not necessarily in a uniform scale, to make the figures more readable.
    The different possibilities (variants and embodiments) must be understood as not being exclusive of each other and can be combined with one another.
    DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS
    Referring first to FIG. 2, which represents a sectional view of a portion of a pixel 102 of a thermal pattern sensor 100 according to a first embodiment, showing in particular a pyroelectric capacitance of the pixel 102 which form the thermal detecting element of the pixel 102. In this first embodiment, the sensor 100 corresponds to a fingerprint sensor. In addition, in this first embodiment, the sensor 100 is able to carry out passive detection of a thermal pattern, that is to say without using means for heating the pixels 102.
    The sensor 100 comprises a substrate 104 corresponding for example to a glass substrate or a semiconductor substrate such as silicon. A substrate 104 of glass may advantageously be used when the sensor 100 comprises a read circuit made from thin film transistor (TFT) transistors, while a semiconductor substrate 104 (FIG. The conductor can be used when the reading circuit of the sensor 100 comprises transistors made in MOS technology. The substrate 104 may also be a flexible substrate, comprising, for example, polyimide and / or PEN (polyethylene naphthalate) and / or PET (polyethylene terephthalate)), on which the electronic components of the 100 sensors are made by printed electronic technology (for example via an embodiment with inkjet type writing heads, or by lithography on plastic, or in TFT technology on flexible plastic or metal substrate).
    The pixels 102 of the sensor 100 are arranged forming a matrix of several rows and several columns of pixels 102. The pitch of the pixels 102 in the (X, Y) plane (i.e., the main plane of the substrate 104 ), is for example between about 25 μιτι and 100 μιτι. In the case of a 100 resolution sensor equal to 500 dpi, the pitch of the pixels 102 is equal to 50.8 μιτι.
    Each of the pixels 102 of the sensor 100 comprises measurement means, or thermal detection means corresponding to a pyroelectric capacitance. Each pyroelectric capacitor comprises a portion 106 of pyroelectric material disposed between a first electrically conductive electrode 108 and a second electrically conductive electrode 110. The pyroelectric material of the portion 106 is advantageously PVDF (polyvinylidene fluoride) and / or at least one copolymer of the PVDF such as P (VDF-TrFE) or poly (vinylidene fluoride-trifluoroethylene), and / or P (VDF-TrFE-CFE) or poly (vinylidene fluoride-trifluoroethylene-chlorofluoroethylene), and / or P ( VDF-TrFe-CTFE) or poly (vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene). As a variant, the pyroelectric material of the portion 106 may be AIN or PZT or BaTiCh or else ZnO, or any other pyroelectric material adapted to form a pyroelectric capacitor and whose pyroelectric coefficient is at least equal to that from ΓΑΙΝ. The electrodes 108, 110 each comprise at least one electrically conductive material, for example a metallic material such as Ti and / or Pt and / or Ni and / or Au and / or ΙΆΙ and / or Ag and / or AISi and / or AICu. In an advantageous embodiment, the electrodes 108, 110 are each formed of one or more superimposed Ti / TiN stacks, with a Ti thickness between about 50 nm and 500 nm and a TiN thickness between about 10 nm. and 500 nm.
    Unlike the sensors of the prior art in which the electrodes of the pyroelectric capacitor are arranged one above the other, the electrodes 108, 110 are here formed by electrically conductive portions arranged in the same horizontal plane which is parallel to a front face 112 of the substrate 104 on which the pyroelectric capacitance is made (parallel to the plane (X, Y) in Figure 2).
    When the portion 106 is made, the thickness of deposited pyroelectric material (dimension along the Z axis shown in FIG. 2) is greater here than that of the electrodes 108, 110, thus forming, in addition to the portion 106, a layer of pyroelectric material 114 covering the portion 106 and the electrodes 108, 110. The total thickness of deposited pyroelectric material (thickness of the portion 106 + thickness of the layer 114) is for example between about 1 pm and 5 pm.
    The layer 114 may be covered by a protective layer 115 whose upper face 116 corresponds to the surface on which is located the thermal pattern to be detected, for example a finger whose fingerprint is intended to be detected. This layer 115 may preferably comprise ZnO and / or ΓAIN and / or IGZO ("Indium Galium Zinc Oxide") and / or ΓΙΖΟ ("Indium Zinc Oxide") and / or ΓΑΤΟ ("Antimony Tin Oxide"). And / or ΙΆΙ2Ο3 and / or SiN weakly constrained at low temperature. Other materials are also conceivable for this layer 115, such as for example polyimide, PVDF and / or its copolymers, PMMA, etc. The material or materials used as well as the thickness of the layer 115 are chosen to obtain good heat transfer from the front face 116 to the pyroelectric capacitance. Thus, the protective layer 115 is made such that it is neither too thermally resistive (because the heat would not cross it), nor too thermally conductive (because the heat would leave in this case on the sides, towards the other pixels, causing diathermy within the sensor), neither too thick (to have a heat transfer from the front face 116 to the pyroelectric capacitor), nor too thin (the thickness of the layer 115 must still be sufficient for its protective role to be fulfilled). The thickness of the layer 115 may be between about 30 nm and 500 nm.
    FIG. 3 represents a top view of three pixels 102.1, 102.2 and 102.3 belonging to the same line of the pixel array 102 of the sensor 100, each delimited by dotted lines. For reasons of readability, the optional protection layer 115 is not shown in this FIG. 3. In each of the pixels 102.1, 102.2 and 102.3, the electrodes 108 and 110 are made in the form of interdigitated combs, which makes it possible to to confer, for a given pixel size, a large area of pyroelectric material facing the electrodes 108, 110 (this area corresponding to the parameter S in the preceding equations (1) and (2)). Moreover, in this example, the second electrodes 110 of the pixels 102.1, 102.2 and 102.3 are electrically connected to each other because all the second electrodes 110 of the pixel matrix are intended to be connected to a common electrical potential, advantageously to the mass. The first electrodes 108 correspond to the reading electrodes of the pixels 102, that is to say the electrodes on which the electrical charges generated by the pyroelectric capacitances of the pixels are recovered. The thickness of the pyroelectric capacitor thus formed, which corresponds to the spacing "e" between the electrodes 108, 110 in which the portion 106 is located, is preferably less than about 2 μm in order to favor the polarization of the pyroelectric material of this capacitance. , the level of the electric voltage applied between the electrodes 108, 110 to achieve the initial polarization of the pyroelectric material (when the pyroelectric material must initially be polarized as is the case of PVDF) being in this case lower than that encountered in the case of the sensors of the prior art with vertical pyroelectric capabilities. In general, this spacing "e" between the electrodes 108, 110 of the same pixel 102 is between about 100 nm and 5 μm, preferably less than about 2 μm and for example equal to about 1 μm.
    In a pyroelectric capacitor of the prior art in which the upper and lower electrodes are superimposed on each other with the pyroelectric material arranged between them, the thickness of deposited pyroelectric material is precisely controlled because this thickness corresponds to the thickness of the pyroelectric capacitance (distance between the electrodes) and directly intervenes in the value obtained C of the pyroelectric capacitance. In the pyroelectric capacitance shown in FIG. 2, the thickness of the deposited pyroelectric material does not require such precise control because this thickness is preferably greater than that of the electrodes 108, 110, and these are the thicknesses of the electrodes 108, 110 which define the thickness, or height, of pyroelectric material lying opposite the electrodes 108, 110. The electrically conductive layer used for producing the electrodes 108, 110 is therefore produced with the greatest thickness, or height, possible to maximize the surface of pyroelectric material facing the electrodes 108, 110, and therefore maximize the measurement signal that will be delivered by the pixel 102. This thickness of the electrodes 108, 110 is for example between about 100 nm and 2 pm, and for example equal to about 1 μm.
    In the case of a voltage reading of the measurement made by each pixel 102 (via a transistor mounted as a voltage follower and whose gate is electrically connected to the reading electrode of the pyroelectric capacitor), a spacing "e" low between the electrodes 108, 110 however leads to a higher capacitance C, which reduces the measurement sensitivity. In this case, a compromise is found for the value of this spacing "e". In the case of a reading current (current from the pyroelectric capacitance sent directly to the input of a sense amplifier), only the pyroelectric material surface facing the electrodes 108, 110 is involved, and a spacing "e" more low allows to reduce the necessary bias voltage when the pyroelectric material must be initially polarized, as in the case of PVDF. When the spacing "e" is not constant throughout the pixel 102, the capacitances formed within the pixel 102 for each of the different values of this spacing "e" can be considered individually and then summed to obtain the resulting capacitance. throughout the pixel 102.
    With respect to a pyroelectric capacitance formed of two superimposed electrodes between which the pyroelectric material is disposed, the pyroelectric capacitance as described with reference to FIGS. 2 and 3 makes it possible to reduce the costs of producing the sensor 100 because only one level of electrically conductive material is necessary for the production of the two electrodes between which the pyroelectric material is located, which makes it possible to economize an etching mask and a photolithography / etching step.
    FIG. 4 represents a sectional view of a portion of a pixel 102 of the thermal pattern sensor 100 according to a second embodiment. FIG. 5 represents a view from above of three pixels 102.1, 102.2 and 102.3 of the sensor 100 according to this second embodiment.
    In this second embodiment, the sensor 100 is able to perform an active thermal detection. Thus, in addition to the elements previously described for the sensor 100 according to the first embodiment, the sensor 100 according to the second embodiment comprises a level of additional electrically conductive material disposed above the layer 114 of pyroelectric material and from of which a heating element 118 is made. This heating element 118 is here produced in the form of a rectangular metal line disposed above the pixels 102, of width "W" for example between about 25 μm and 500 μm and of length "L" between about 50 pm and 500 pm. The protective layer 115 is formed on this heating element 118.
    With such a configuration, no problem of size or arrangement between this heating element 118 and the electrodes 108, 110 does not arise since the heating element 118 is not made from the same level of electrically conductive material as that used for the realization of the electrodes 108, 110.
    In this configuration, the heating element 118 is therefore in direct contact with the whole of the pyroelectric material of the pyroelectric capacitors, and covers in particular the entire surface of the pixels 102, and more particularly the entire surface occupied by the pyroelectric material of the portions 106. located between the electrodes 108, 110 of the pixels 102. The heating of the pixels 102 made by this heating element 118 is therefore optimal and maximized because all the pyroelectric material of the portion 106 is opposite the heating element 118. The heat generated by the heating element 118 is thus diffused vertically and sent directly into the pyroelectric material of the portions 106.
    In operation of the sensor 100, a heating control (voltage or constant current) is applied to a first end 120 of the heating element 118, and a second end 122 of the heating element 118 is connected to a common potential, by example the mass. A current thus flows in the heating element 118, which causes its heating as well as that of the pyroelectric material of the portions 106.
    The fact that the second end 122 is connected to the ground also gives the sensor 100 protection against possible electrostatic discharges, the currents related to its discharges can flow in this case to the ground via the heating element 118.
    In the example described above, the heating element 118 is made in the form of a rectangular line covering the entire surface of the pixels 102. Other forms are however possible for the embodiment of the heating element 118. for example, Figure 6 shows a view of another configuration in which the heating element 118 is formed in the form of a coil whose segments only cover the portions 106 of pyroelectric material. In the example of FIG. 6, the segments of the heating element 118 each have a width "K" of between approximately 1 μιτι and 20 μm, a length "M" at the level of the pixels 102 of between approximately 50 μm. and 500 μm, and are arranged on a width "N", for each pixel 102, between about 25 pm and 500 pm. The length "M" and the width "N" of the heating element 118 may or may not be adapted to the dimensions of the pixels 102. This heating element 118 is shown in FIG. 9 without the other elements of the sensor 100.
    In general, the shape of the heating element 118 (for example the coil shape or the line shape) will be chosen according to the desired value of the electrical resistance of the heating element 118 so that the heating power obtained corresponds to that desired.
    Whatever the shape of the heating element 118, the dimensions thereof and the voltage or current levels applied to effect heating of the pyroelectric material are adjusted according to the desired heating power. In order to obtain a good detection sensitivity (which corresponds to a large temperature difference when reading the pixels of the sensor), the electric power injected into the heating element 118 may be between approximately 0.5 mW / pixel. and 5 mW / pixel.
    FIG. 7 is a view from above of a portion of the pixel array 102 of the sensor 100 as previously described in connection with FIG. 5. This FIG. 7 represents in particular the fact that all the second electrodes 110 are electrically connected to a electrically conductive portion 124 itself connected to the mass of the sensor 100. The portion 124 is for example made from the same electrically conductive layer or layers used for the realization of the heating elements 118. The electrical access to the first electrodes 108 are independent from each other and formed by contact pads 126 made from the same electrically conductive layer or layers for producing the electrodes 108, 110. The heating elements 118 are formed by conductive portions each common to all the pixels of the same line. In the example of FIG. 7, each of these portions forms a continuous line of conductive material arranged facing the entire surface of the portions of pyroelectric material 106 of the same line. The second ends 122 of the conductive portions forming the heating elements 118 are electrically connected to another conductive portion 128 itself connected to the ground of the sensor 100.
    As a variant of the configuration shown in FIG. 7, the pixels of two adjacent columns may be made symmetrically so that the conductive line to which the second electrodes of the pixels of these two columns are connected may be shared and common to the pixels of these two columns. two columns. Such a variant can be applied in the case of pixels of large dimensions, for example made with a pitch of 200 μm, the area of the pyroelectric capacitance being in this case of the order of 500 pm 2.
    The heating of the pixels may also be performed in a manner other than that shown in FIG. 7, for example pixel by pixel.
    A method of realizing the pyroelectric capacitances of the sensor 100 similar to that of FIG. 6 is described with reference to FIGS. 8A to 81.
    The sensor 100 is made from the substrate 104. The material of the substrate 104 (glass, semiconductor, plastic, etc.) is chosen according to the technology with which the various electronic elements of the sensor 100 are made. The substrate 104 is first cleaned to remove organic residues present thereon. The type of cleaning used will be a function of the material of the substrate 104.
    The second step is to deposit on the front face 112 of the substrate 104 a first electrically conductive layer 150, for example metal, from which the electrodes 108 and 110 are intended to be made (Figure 8A). The material of the layer 150 may comprise at least one of the following materials: Ti, Pt, Ni, Au, Al, Ag, AlSi, AlCu. This layer 150 is preferably formed of one or more Ti / TiN type stacks with a Ti thickness of between about 50 nm and 500 nm and a TiN thickness between about 10 nm and 500 nm. The layer 150 may be PVD vapor deposited by evaporation ("sputtering" in English), screen printing, spray ("spray" in English) or even by inkjet, depending on the materials and thicknesses to be deposited. When the layer 150 is formed by PVD deposition, the thickness of the layer 150 may be between about 100 nm and 2 μm. In general, the thickness of the layer 150 is greater than about 100 nm. Other types of deposition may allow the production of a layer 150 with a thickness greater than about 2 μm.
    As represented in FIG. 8B, the structure of the electrodes 108, 110 is defined by implementing a step of photolithography and etching of the layer 150. In the example described here, this structure corresponds to those previously described in connection with the first and second embodiments, that is to say in the form of interdigitated combs made throughout the thickness of the layer 150. The electrical access to the electrodes 108, 110 are not visible in FIGS. 8B to 81
    This structuring step of the layer 150 defines the spacing "e" between the electrodes 108, 110. The spacing "e" between two adjacent fingers, or adjacent teeth, interdigitated combs formed by the electrodes 108, 110 is for example between about 100 nm and 5 μιτι, and preferably less than about 2 pm, for example equal to about 1 pm. The width "I" of these fingers is for example between about 1 pm and 20 pm, preferably between about 1 pm and 10 pm.
    The pyroelectric material is then deposited on the entire structure previously made (FIG. 8C). The portions of the pyroelectric material deposited between the electrodes 108, 110 form the portions 106 and those covering the portions 106 and the electrodes 108, 110 form the layer 114. When the pyroelectric material is PVDF or one of its copolymers, it can be deposited by "spin coating" on a thickness between about 1 pm and 5 pm. Other types of localized deposits can be used such as screen printing or spraying, or even ink jet deposition. Various compositions in TrFe in P (VDF-TrFe) can be envisaged, in order to obtain high pyroelectric coefficient values. These compositions may correspond to a mole percentage of between about 10% and 50% for TrFe and from about 90% to 50% of VDF. Preferably, the mole percentage is about 30% for TrFe and about 70% for VDF, which makes it possible to obtain better characteristics in crystallization of the pyroelectric material (crystallization carried out in the next step).
    When the previously deposited pyroelectric material is a semi-crystalline polymer such as PVDF or one of the PVDF copolymers, a step of irradiation of this material can then be implemented in order to optimize the crystallization of the pyroelectric material at the a front face 152 of the deposited layer, in order to obtain good pyroelectric performance. This irradiation is for example implemented with a UV flash light, with a duration of the flash, or pulse, of between about 500 ps to 2 ms, a fluence (energy delivered per unit of area) of between about 15 J / cm 2 and 25 J / cm 2, and with light of wavelength between about 200 nm and 380 nm. The number of flashes, or pulses, of UV light produced during this irradiation varies according to the thickness on which the pyroelectric material is to be crystallized. For example, for a thickness of P (VDF-TrFe) equal to about 2 μιτι, the irradiation can be implemented with a fluence equal to about 17 J / cm 2, a pulse duration equal to about 2 ms and a number of pulses equal to 5.
    As shown in FIG. 8D, portions 154 of the pyroelectric material are then defined by the implementation of photolithography and etching of the pyroelectric material. When the etching used corresponds to a plasma etching, an O2 plasma can be used alone or in combination with SF6 (sulfur hexafluoride). The portions 154 of pyroelectric material conserved after the implementation of this etching correspond to the portions of the pyroelectric material located at the level of the pixels 102 of the sensor 100.
    As a variant, the portions 154 can be made directly, without an etching step, by a localized deposit corresponding, for example, to an ultrasonic spray deposition, or an ink jet or screen printing.
    The pyroelectric material having optionally undergone previous crystallization of its front face is then subjected to annealing, for example carried out at about 130 ° C. for about 60 minutes, to finalize the total crystallization of the pyroelectric material.
    The crystallization of the pyroelectric material is therefore carried out in two stages: first of all irradiation by UV light pulse to crystallize well the front face 152 of the pyroelectric material in order to increase its thermal conductivity at the level of at least a part of the layer 114, then a thermal anneal completing the crystallization for the remainder of pyroelectric material not crystallized by the previous irradiation.
    One or more second electrically conductive layers for forming the heating elements 118 are then deposited on the structure obtained at this stage of the process, in particular on the portions 154 of pyroelectric material. The material or materials used for producing the heating element 118 may be selected from among my materials: Ti, Pt, Ni, Au, Al, Ag, AlSi, AlCu. In the exemplary embodiment shown in FIG. 8E, the heating element 118 is intended to be formed from an electrically conductive layer 156 of Ti having a thickness of between approximately 30 nm and 100 nm and another layer. electrically conductive 158 having AISi or AICu and thickness between about 100 nm and 700 nm. In such a configuration, the AISi or AICu layer passivates the titanium layer, thus protecting the titanium against oxidation.
    Parts of the layer or layers 156, 158 deposited beside the portions 154 of pyroelectric material, on the substrate 104, are intended to form electrical contact pads corresponding to the ends 120 and 122 at the terminals of which the heating voltage is intended to to be applied. The heating element 118 is then formed by etching the electrically conductive layer or layers previously deposited according to the pattern of the heating element 118, for example in the form of a coil as previously described in connection with FIG. 6 or in the form of a rectangular line as previously described in connection with Figure 5. A photolithography step followed by a plasma etching step or wet are for example implemented for the formation of the heating element 118.
    In the example described here, this etching of the second electrically conductive layers is carried out in two stages. At first, photolithography and wet etching or plasma etching are used to etch the layer 158 comprising AISi or AICu stopping on the layer 156 (Figure 8F). The layer 156 will then protect the pyroelectric material during removal of the resin having served as a mask for the photolithography of the layer 158.
    The layer 156 is then etched, for example by the implementation of a plasma etching, according to the pattern previously etched through the layer 158 which serves as a hard mask during this etching (Figure 8G). The pattern of the heating element 118 is thus obtained and formed through the second electrically conductive layer or layers previously deposited.
    As shown in FIG. 8H, the material or materials 162 intended to form the protective layer 115 is or are then deposited on the whole of the structure previously produced. Depending on the deposited material (s) 162, the deposit (s) can be physically (for example PVD) at low temperature or by liquid means (for example by centrifugation, spraying or inkjet).
    When this or these protective materials 162 are deposited in a localized manner, for example by spraying or by ink jet, the layer 115 is formed as soon as the deposition is localized on the heating element 118 and any parts of pyroelectric material. not covered by the heating element 118 (as is the case when the heating element 118 forms a coil located only above the portions 106), and it is not necessary to use an etching of the deposited materials to form the layer 115. In the opposite case, as is the case in Figure 8H where the material or materials 162 are also deposited next to the portions 154 of pyroelectric material, etching, for example by plasma, is then implemented in order to remove the portions of the material or materials 162 deposited next to the portions 154, thus allowing access to the ends 120,122 (Figure 81).
    When the pyroelectric material is a P-based copolymer (VDF-TrFe), it is necessary to implement, before the first use of the sensor 100 to detect a thermal pattern, an initial polarization step of the pyroelectric material by applying a voltage continuous electrical terminals, via the electrodes 108, 110, to improve the pyroelectric coefficient of this material. This polarization is performed only once for the entire lifetime of the pyroelectric material. This DC bias can be at room temperature or hot (up to about 100 ° C). When the polarization is performed at a room temperature, it is possible to apply a DC voltage up to about 120 V / pm interdigital spacing (corresponding to the spacing "e") for a duration for example between a few seconds and a few minutes. When the polarization is carried out hot, for example at a temperature of about 90 ° C., a DC voltage for example between about 50 V and 80 V per micron interdigital spacing may be applied for a duration for example between about 1 min and 5 min. The temperature is then lowered until the ambient temperature is reached, then the electric field applied to the pyroelectric material, via the applied DC voltage, is stopped. Such polarizations allow the PVDF to reach pyroelectric coefficients of between approximately 30 and 45 pC / (m2.K). The fact that the electrodes 108, 110 are in the form of interdigitated combs with a spacing "e" of less than or equal to approximately 2 μm, with the pyroelectric material of the portions 106 placed between the fingers of these combs, has the advantage of lowering the level the bias voltage of the pyroelectric material necessary to obtain a given level of pyroelectric coefficient, thanks to this small distance between the electrodes 108, 110.
    The pixel array 102 of the sensor 100 is read line by line by means of selection transistors integrated in each pixel 102 and via an electronic reading circuit arranged in columns (not shown in the figures) making it possible to carry out a direct reading. charges generated by each pixel (current reading), or to perform a voltage reading of the pixels 102 via the use of a transistor mounted voltage follower.
    Various calibration methods, for example using a reference pixel having a known heat capacity, can be implemented. Such methods are described for example in the document FR 2 959 814.
    In the various examples described above, the sensor 100 is used as a fingerprint detector. However, the sensor 100 can be used to perform a thermal pattern detection other than fingerprints, because each pixel 102 of the sensor 100 reads the heat capacity placed above it and this whatever the nature of the thermal pattern .
    In addition, the sensor 100 can also be used for producing a non-cooled infrared imager. The pixels 102 of the sensor 100, for example as described above in connection with FIGS. 2 and 3, are in this case integrated on a CCD or CMOS-type integrated circuit collecting the electrical charges generated by the sensor 100. Such an imager comprises furthermore, an infrared lens filtering the light arriving on the sensor 100. In order for the sensor 100 to be subjected to a difference in temperature (necessary taking into account the measurement made by the pyroelectric capacitors), the imager comprises a device that successively block the infrared light arriving on the sensor 100 and then let this light. Such a device may correspond to a "chopper", that is to say a wheel provided with a hole and rotating in front of the sensor 100. An absorber element may be added to the pyroelectric material in order to improve the absorption of the received infrared radiation, especially when the pyroelectric material is PVDF which is not good conductor of heat.
    权利要求:
    Claims (14)
    [1" id="c-fr-0001]
    A thermal pattern sensor (100) having a plurality of pixels (102) disposed on a front face (112) of a substrate (104), each pixel (102) comprising at least one pyroelectric capacitance formed by at least a portion of material pyroelectric (106) disposed between two electrically conductive electrodes (108, 110) and such that the electrically conductive electrodes (108, 110) are disposed in the same plane substantially parallel to the front face (112) of the substrate (104).
    [2" id="c-fr-0002]
    2. Sensor (100) according to claim 1, wherein the spacing "e" between the electrically conductive electrodes (108, 110) of each pixel (102) is less than or equal to about 2 μιτι.
    [3" id="c-fr-0003]
    3. Sensor (100) according to one of the preceding claims, wherein the pyroelectric material comprises PVDF and / or P (VDF-TrFe) and / or P (VDF-TrFE-CFE) and / or P ( VDF-TrFE-CTFE) and / or AIN.
    [4" id="c-fr-0004]
    4. Sensor (100) according to one of the preceding claims, wherein the electrically conductive electrodes (108, 110) of each pixel (102) form interdigitated combs.
    [5" id="c-fr-0005]
    5. Sensor (100) according to one of the preceding claims, wherein each of the electrically conductive electrodes (108, 110) has a thickness greater than or equal to about 100 nm.
    [6" id="c-fr-0006]
    6. Sensor (100) according to one of the preceding claims, further comprising, in each pixel (102), a layer of pyroelectric material (114) covering the portion of pyroelectric material (106) and the electrically conductive electrodes (108, 110) such that the pyroelectric material portion (106) and the electrically conductive electrodes (108, 110) are disposed between the pyroelectric material layer (114) and the substrate (104).
    [7" id="c-fr-0007]
    7. Sensor (100) according to one of the preceding claims, wherein one of the electrically conductive electrodes (108, 110) of each pixel (102) is electrically connected to a fixed electrical potential.
    [8" id="c-fr-0008]
    8. Sensor (100) according to one of the preceding claims, further comprising at least one heating element (118) electrically insulated electrically conductive electrodes (108, 110) and disposed opposite at least a portion of the portion of a pyroelectric material (106) such that the portion of pyroelectric material (106) is disposed between the heating element (118) and the substrate (104).
    [9" id="c-fr-0009]
    9. Sensor (100) according to claim 8, wherein the heating element (118) comprises at least one continuous portion of electrically conductive material extending opposite portions of pyroelectric material (106) of several pixels (102).
    [10" id="c-fr-0010]
    The sensor (100) of claim 9, wherein the continuous portion of electrically conductive material is disposed opposite the entire surface of the pyroelectric material portions (106) of said plurality of pixels (102).
    [11" id="c-fr-0011]
    The sensor (100) according to one of claims 9 or 10, wherein the pixels (102) are arranged on the substrate (104) forming a matrix of plural rows and columns, and wherein the sensor (100) has a plurality of heating elements (118) each associated with one of the pixel lines (102).
    [12" id="c-fr-0012]
    12. Sensor (100) according to one of claims 8 to 11, wherein, when the sensor comprises the layer of pyroelectric material (114) covering the portion of pyroelectric material (106) and the electrically conductive electrodes (108, 110), the a pyroelectric material layer (114) is disposed at each pixel (102) between the heating element (118) and the pyroelectric material portion (106) and between the heating element (118) and the electrically conductive electrodes (108,110).
    [13" id="c-fr-0013]
    13. Sensor (100) according to one of the preceding claims, wherein the sensor (100) is a fingerprint sensor.
    [14" id="c-fr-0014]
    14. A method for producing a thermal pattern sensor (100), comprising the production of several pixels (102) on a front face (112) of a substrate (104), each pixel (102) comprising at least one capacitor pyroelectric formed by at least one portion of pyroelectric material (106) disposed between two electrically conductive electrodes (108, 110) and such that the electrically conductive electrodes (108, 110) are disposed in a same plane substantially parallel to the front face (112 ) of the substrate (104).
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    同族专利:
    公开号 | 公开日
    FR3044408B1|2019-06-14|
    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    US5008541A|1988-11-29|1991-04-16|Commissariat A L'energie Atomique|Monolithic detection or infrared imaging structure and its production process|
    EP2385486A1|2010-05-06|2011-11-09|Commissariat à l'Énergie Atomique et aux Énergies Alternatives|Transducer for temporal variation of temperature, electronic chip including transducteur and method for manufacturing chip|FR3069354A1|2017-07-24|2019-01-25|Commissariat A L'energie Atomique Et Aux Energies Alternatives|THERMAL SENSOR WITH TWO OVERLAY PYROELECTRIC PORTIONS FOR MEASURING A DIFFERENTIAL LOAD|
    EP3492893A1|2017-12-04|2019-06-05|Commissariat à l'énergie atomique et aux énergies alternatives|Thermal pattern sensor with pyroelectric capacity and hard protective layer|
    EP3640615A1|2018-10-19|2020-04-22|Commissariat à l'énergie atomique et aux énergies alternatives|Pyroelectric sensor with improved coating for abrasion resistance|
    FR3093658A1|2019-03-15|2020-09-18|Commissariat A L'energie Atomique Et Aux Energies Alternatives|PROCESS FOR DEPOSITING A LAYER OF PVDF OR ONE OF ITS COPOLYMERS ON A GLASS OR POLYMER SUBSTRATE|
    EP3767261A1|2019-07-18|2021-01-20|Idemia Identity & Security France|Pixel matrix of a thermal pattern sensor, associated sensor with heating lines in coil|
    US10949638B2|2018-08-16|2021-03-16|Idemia Identity & Security France|Manufacturing process of a pixel array of a thermal pattern sensor and associated sensor|
    法律状态:
    2016-11-30| PLFP| Fee payment|Year of fee payment: 2 |
    2017-06-02| PLSC| Publication of the preliminary search report|Effective date: 20170602 |
    2017-11-30| PLFP| Fee payment|Year of fee payment: 3 |
    2019-11-29| PLFP| Fee payment|Year of fee payment: 5 |
    2020-11-30| PLFP| Fee payment|Year of fee payment: 6 |
    优先权:
    申请号 | 申请日 | 专利标题
    FR1561580|2015-11-30|
    FR1561580A|FR3044408B1|2015-11-30|2015-11-30|THERMAL PATTERN SENSOR WITH HORIZONTAL PYROELECTRIC CAPABILITY|FR1561580A| FR3044408B1|2015-11-30|2015-11-30|THERMAL PATTERN SENSOR WITH HORIZONTAL PYROELECTRIC CAPABILITY|
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