Classifications

• • G—PHYSICS
  • G06—COMPUTING OR CALCULATING; COUNTING
  • G06F—ELECTRIC DIGITAL DATA PROCESSING
  • G06F3/00—Input arrangements for transferring data to be processed into a form capable of being handled by the computer; Output arrangements for transferring data from processing unit to output unit, e.g. interface arrangements
  • G06F3/01—Input arrangements or combined input and output arrangements for interaction between user and computer
  • G06F3/03—Arrangements for converting the position or the displacement of a member into a coded form
  • G06F3/041—Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means
  • G06F3/042—Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means by opto-electronic means
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J1/00—Photometry, e.g. photographic exposure meter
  • G01J1/02—Details
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J1/00—Photometry, e.g. photographic exposure meter
  • G01J1/58—Photometry, e.g. photographic exposure meter using luminescence generated by light
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
  • G01L1/00—Measuring force or stress, in general
  • G01L1/16—Measuring force or stress, in general using properties of piezoelectric devices
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03K—PULSE TECHNIQUE
  • H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
  • H03K17/94—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the way in which the control signals are generated
  • H03K17/96—Touch switches
  • H03K17/9627—Optical touch switches
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03K—PULSE TECHNIQUE
  • H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
  • H03K17/94—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the way in which the control signals are generated
  • H03K17/96—Touch switches
  • H03K17/964—Piezoelectric touch switches
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03K—PULSE TECHNIQUE
  • H03K2217/00—Indexing scheme related to electronic switching or gating, i.e. not by contact-making or -breaking covered by H03K17/00
  • H03K2217/94—Indexing scheme related to electronic switching or gating, i.e. not by contact-making or -breaking covered by H03K17/00 characterised by the way in which the control signal is generated
  • H03K2217/941—Indexing scheme related to electronic switching or gating, i.e. not by contact-making or -breaking covered by H03K17/00 characterised by the way in which the control signal is generated using an optical detector
  • H03K2217/94102—Indexing scheme related to electronic switching or gating, i.e. not by contact-making or -breaking covered by H03K17/00 characterised by the way in which the control signal is generated using an optical detector characterised by the type of activation
  • H03K2217/94106—Passive activation of light sensor, e.g. by ambient light

Definitions

• the invention relates to the field of tactile sensors, especially tactile sensors by pressure detection, and is particularly applicable in screens, keyboards, and touch pads.
• piezoelectric materials are usually sought which have both good mechanical properties and good piezoelectric qualities.
• piezoelectric materials have either good mechanical properties or good piezoelectric properties.
• piezoelectric materials commonly used for pressure sensors there are ceramics called “PZT” (acronym for lead titano-zirconate) and “PVDF” (acronym for polyvinylfluoride).
• PZT acronym for lead titano-zirconate
• PVDF acronym for polyvinylfluoride
• a PZT ceramic is certainly provided with a high piezoelectric constant, but nevertheless has a very high Young's modulus, and therefore insufficient mechanical properties.
• PVD has a low Young's modulus, and more generally good mechanical properties, but nevertheless has a low piezoelectric constant.
• piezoelectric materials having good mechanical strength, and therefore a low Young's modulus, are usually preferred.
• an electrical assembly called “capacity” is used to measure the amount of charges released.
• the layer of piezoelectric material is in contact with electrodes and forms with them a capacitive circuit, the capacity of which varies as a function of the electric charges released.
• a capacimeter connected to the electrodes, measures the capacitance of the capacitive circuit dynamically, in particular by imposing a variable voltage between the electrodes and / or by injecting into them a variable current of variable frequency.
• An electrical capacitance arrangement therefore requires complex measuring means.
• the object of the present invention is to provide a piezoresistive tactile sensor of increased sensitivity, not requiring the use of an electrical circuit in capacity to measure the presence of an object on its surface.
• the subject of the invention is a tactile sensor comprising:
• a piezoresistive layer whose electrical resistance varies as a function of mechanical stresses exerted thereon, the piezoresistive layer being at least partially transparent to light;
• the touch sensor according to the invention combines two different physical phenomena and concomitant to detect the presence of an object on its surface. Indeed, when an object, for example a finger, approaches the sensor, it hides the ambient brightness, and thus causes a variation in brightness detected by the sensor.
• a high variation of the electric resistance of the assembly is thus obtained when a finger presses the sensor and mask the light.
• Such a variation can in particular be measured statically, for example by applying a constant electric current of known value in the sensor and by measuring the resulting voltage across the latter. The variation of the voltage beyond a predetermined threshold then makes it possible to characterize the pressure exerted on the sensor.
• the piezoresistive layer and the photosensitive layer are separated by a more deformable medium than the piezoresistive layer, in particular by a fluid or viscous liquid, a gas such as air for example, a gas under a reduced pressure, vacuum, etc., which allows a large deformation of the piezoresistive layer, and therefore a large variation in its electrical resistance.
• the piezoresistive layer is arranged on one side of an electrically insulating protective layer, at least partially transparent to light and deformable, and in which the stack formed of the piezoresistive layer and the protective layer has openings arranged in line with the photosensitive layer. The sensitivity of the sensor to changes in ambient light is thus increased substantially by the presence of the openings.
• the piezoresistive layer is made in the form of a coil having a variable number of turns per unit area, and in particular a greater number of turns in a central zone of the sensor than the number of turns in peripheral areas of the sensor.
• a coil has a width much smaller than its length. A deformation of the coil thus induces a high variation of its electrical resistance.
• the number of turns per unit area provides a variable sensitivity of the sensor on its surface, including a greater sensitivity in a central area thereof.
• the coil travels between openings formed in the protective layer, in particular between rows of openings.
• the piezoresistive layer is made of PEDOT: PSS.
• PEDOT: PSS is a mixture of poly (3,4-ethylenedioxythiophene), or "PEDOT", and poly (styrene sulfonate).
• the PEDOT: PSS is a piezoresistive material, whose electrical resistance varies significantly depending on the constraints applied to it.
• the PEDOT: PSS also has the advantage of being transparent to visible and near infrared radiation.
• the photosensitive layer comprises a mixture of graphene and antimony-doped tin dioxide, or "ATO".
• ATO antimony-doped tin dioxide
• This material has the dual advantage of being sensitive to a broad spectrum of radiation, especially the red wavelength of the visible spectrum and the near-infrared spectrum, and of having an electrical resistance which decreases with the amount of radiation collected.
• a finger which emits a large amount of infrared radiation, is detected by the photosensitive layer even if the ambient visible light is very low.
• the piezoresistive materials generally exhibit an electrical resistance which increases when stressed. By connecting in parallel an electrical resistance which increases by the presence of an object and an electrical resistance which decreases due to this same presence, a strong variation of the electrical resistance of the assembly is obtained, and thus a very large sensor. sensitivity.
• the proportion by weight of the doped tin dioxide in the mixture is greater than 20%. It has thus been noted that this proportion allows optimal collection of radiation. For lower percentages, it is observed that the detection sensitivity decreases.
• the photosensitive layer is formed between the piezoresistive layer and a light reflecting layer.
• the reflective layer makes it possible to send back to the light-sensitive layer the radiation that has passed through it, for example because of a small thickness of this layer. In this way, the sensitivity of the sensor is increased.
• the reflective layer is able to reflect wavelengths in the visible and near-infrared range.
• the photosensitive layer is separated from the reflective layer ⁇
• the piezoresistive layer and the photosensitive layer are transferred to one another by means of metal balls connecting them electrically in parallel.
• the balls make it possible to adjust the distance separating them, in particular to focus the incident light on the photosensitive layer.
• the piezoresistive layer and the photosensitive layer are transferred to one another by means of stacks of at least two conductive balls secured to one another by an insert. In this way, it is possible to adjust the distance between the piezoresistive layer and the photosensitive layer by adjusting the number of stacked beads.
• FIG. 1 is a schematic sectional view of a sensor according to the invention.
• Figure 2 is a schematic top view of the Figure 1 sensor
• FIG. 3 is a schematic top view of a variant of the Figure 2 sensor
• FIG. 4 is an equivalent electrical diagram of the sensor according to the invention.
• FIGS. 5 to 16 are schematic views illustrating a manufacturing process of a sensor according to the invention.
• FIG. 17 is a schematic sectional view of a ball variant for hybridization of two parts of the sensor according to the invention.
• a touch sensor 10 for example intended to be incorporated in a screen, a keyboard, or a touchpad, comprises a pressure sensor 12 and a sensor 14. The latter is disposed under the pressure sensor 12 and the right thereof, the two sensors 12, 14 being electrically connected in parallel.
• the pressure sensor 12 comprises a piezoresistive layer 16, made of a piezoelectric material, whose electrical resistance varies as a function of the mechanical stresses that this material undergoes, sandwiched between protective layers, in particular a flexible substrate 18 defining a tactile surface, and an electrically insulating protective layer 20.
• the piezoresistive layer 16 is advantageously made of PEDOT: PSS, for example with a thickness of between 10 nm and 5 ⁇ m.
• the PEDOT: PSS is a piezoresistive material, that is to say a material whose electrical resistance varies greatly with the stresses it undergoes compared to other types of known piezoresistive materials.
• the PEDOT: PSS is also sensitive to temperature, and its electrical resistance decreases with increasing temperature. In addition, this material is substantially transparent to visible radiation and near infrared.
• the conductive elements 22 comprise two sets of metal tracks 24 in contact with the layer 16 and respectively connected to two metal areas 26.
• the flexible substrate 18 is chosen to be deformable under the pressure exerted by an object on its surface, for example by a finger 28 or a stylus.
• the flexible substrate 18 is for example made of a thin plastic layer with a thickness between 25 ⁇ and 200 ⁇ .
• the pressure sensor 12 is also designed at least partially transparent to the radiation detected by the light sensor 14. The transparency is obtained by the choice of the constituent materials of the sensor 12, and / or the thickness of the constituent layers of that and / or by arranging in the sensor preferred passages for the light, for example openings.
• the substrate 18 is made of a material at least partially transparent to visible light.
• the substrate 18 is made of polyethylene naphthalate (“PEN”) or poly (ethylene terephthalate) (“PET”), which has the triple advantage of being flexible, transparent to the visible spectrum and the near infrared, and to be inexpensive ..
• PEN polyethylene naphthalate
• PET poly (ethylene terephthalate)
• the protective layer 20 is preferably produced in a dielectric material which is at least partially transparent to the radiation detected by the sensor 14.
• the layer 20 is a CYTOP-type fluoropolymer layer, which is transparent and has a low permittivity, with a thickness of between 10 nanometers and 500 nanometers.
• Openings 30 are also made through the pressure sensor 12, and to the right of the light sensor 14, to increase the overall transparency of the sensor 12.
• a two-dimensional network, in particular a periodic network, of openings is made through the substrate 18, the piezoresistive layer 16, and the protective layer 20.
• the openings are, for example, of square and side cross-section between 50 nanometers and 5 micrometers.
• the piezoresistive layer 16 is made in the form of a solid rectangular layer traversed by the openings 30.
• the piezoresistive layer 20 alternatively takes the form of a serpentine running between rows of openings 30.
• a coil has a length much greater than its width, so that it is obtained an increased variation of its electrical resistance as a function of the pressure exerted on its surface.
• the coil has more turns in a central zone of the pressure sensor 12 than at the periphery thereof. In this way, the pressure sensor is more sensitive on this central zone than on its periphery due to the low resonance frequency which gives a maximum of stress to the center of the piezoresistive structure.
• the light sensor 14 comprises a substrate 32 on which a reflective layer 34 rests.
• the layer 34 is covered with a layer 36 of electrically insulating material and at least partially transparent to the radiation detected by the light sensor 14.
• the latter also comprises a photosensitive layer 38 formed on the insulating layer 36.
• Conductive elements 40 for example made of gold, platinum, nickel, copper, silver or aluminum , are furthermore made on the insulating layer 36 in contact with the photosensitive layer 38 in order to subject the latter to a voltage and / or to inject an electric current into it, as will be explained in more detail below.
• the conductive elements 40 comprise two sets of metal tracks 42 in contact with the layer 38 and connected to two metal plates 44.
• the assembly is optionally covered with an electrically insulating protective layer 48, except for the conductive pads 44 which remain open, and openings 50 are made in the layer 48 to the right of the openings 30 of the pressure sensor 12.
• the substrate 32 is advantageously a flexible and transparent substrate, for example a plastic substrate, such as PEN or PET, with a thickness of between 25 ⁇ m and 200 ⁇ m.
• the photosensitive layer 38 is advantageously constituted by a mixture of graphene and ATO (antimony doped tin dioxide (SnO2: Sb)), the proportion by weight of ATO in the mixture is advantageously greater than 20%.
• ATO antimony doped tin dioxide
• Such a material is capable of capturing in the visible spectrum (especially in the red) as well as in the near infrared and furthermore has an electrical resistance which decreases as a function of the amount of radiation captured.
• the photosensitive layer 38 thus captures the ambient light variations induced by the presence of the finger 28, as well as the heat variations induced by the presence of the finger 28, these heat variations resulting in variations of the near-infrared radiation emitted by the finger .
• the material of the insulating layer 36 as well as the distance separating the photosensitive layer 38 from the reflective layer 34 are chosen from ⁇ .
• the reflecting layer 34 is made of a material having a significant reflection of the radiation detected by the photosensitive layer 38.
• the reflective layer is a metallic layer of silver, aluminum or gold, these materials having a high reflectivity in the field visible and near infrared.
• the insulating layer 36 is made of a material transparent to the radiation detected by the photosensitive layer 38, for example an organic polymer type dielectric or an inorganic oxide such as Si0 2 , Zr0 2 , Ti0 2 , etc. . These materials have a high transparency in the visible and near infrared range.
• the pressure sensor 12 and the light sensor 14 are advantageously carried on one another by means of metal balls 52, each disposed between connection pads 26, 44 disposed facing the sensors 12, 14 respectively.
• the sensors 12 and 14 are therefore electrically connected in parallel.
• the balls 52 spacing them a distance di allowing the pressure sensor 12 to bend strongly under the pressure exerted on its surface, and therefore to undergo a large variation in its electrical resistance.
• the space separating the pressure sensor 12 and the light sensor 14 is for example filled by a gas, such as air, under reduced pressure or not, vacuum, a fluid or viscous liquid, etc. Of course. these two functions can be implemented by separate elements.
• FIG. 4 is an equivalent electrical diagram of the sensor according to the invention.
• the piezoresistive 16 and photosensitive layers 38 being electrically connected in parallel, the
• the sensor 10 is for example connected to an electric circuit 54 comprising a source of current or constant voltage making it possible to measure the resistance of the resistor or of an electrical quantity connected thereto, this measurement being analyzed by a circuit of analog or digital processing (not shown) to determine an event on the surface of the sensor, such as the presence of a finger for example.
• the sensor 10 according to the invention thus combines three different detection modes, namely a piezoresistive tactile detection mode, a light detection mode, and a detection mode combining the tactile and light detection mode.
• the piezoresistive detection mode the pressure exerted on the substrate 18 induces a piezoresistive effect, namely the variation of the electrical resistance of the piezoresistive layer 16 under the effect of the stress which it undergoes.
• the fact of pressing on the substrate 18 causes a local deformation of the piezoresistive layer 16, which causes a variation in its electrical resistance, a variation which results in a corresponding variation of an electrical quantity, in particular a current or a electric tension.
• the pressure exerted is then determined using, for example, a table of values of predetermined variations of the measured electrical quantity as a function of pressure values exerted.
• the light detection mode when a face, or both faces of the sensor 10 are illuminated, the electrical resistance of the photoresistor formed of the photosensitive layer 38 varies as a function of the light intensity, and the variation of this resistance is translated into an electrical magnitude, current or voltage, which is read by a read circuit in a manner similar to that described above.
• the light detection mode can also detect thermal waves in the near infrared, and thus allows the detection of a finger when the ambient light in the visible spectrum is of low intensity. It will also be noted that the materials and layers constituting the light sensor 14 allow detection of an incident light on the substrate 32, hence the possibility of detection only light if the application requires it.
• an object exerting a pressure on the surface of the pressure sensor 12 also masks the ambient luminosity and thus causes a light variation sensed by the light sensor 14.
• the object is a finger
• thermal waves in the near infrared can be further detected by the latter. The combination of these phenomena generates a large variation in the overall electrical resistance of the sensor, allowing a high sensitivity detection.
• the manufacture of the light sensor 14 begins with the production of a substrate 32 made of a flexible plastic bat cost of the PEN or PET type and with a thickness of between 25 and 200 micrometers, and continues with the deposition of a reflective metal layer. 34, for example silver, aluminum or gold, by means of a physical vapor deposition, a screen printing or an inkjet printing ( Figure 5).
• An electrically insulating and transparent layer 36 is then deposited, for example by means of a physical vapor deposition, a screen printing or an inkjet printing, on the assembly obtained.
• the thickness of the layer 36 is chosen so as to maximize the reflection of the light flux on the photosensitive element, which will subsequently be deposited (FIG. 6).
• the constituent material of the layer 36 is, for example, an organic polymer type dielectric or an inorganic passivation oxide such as SiO 2 , ZrO 2 , TiO 2 or the like.
• Two connection electrodes 40 are then made on the layer 36 by means of a physical vapor deposition, a screen printing or an inkjet printing (FIG. 7).
• the electrodes 40 are for example made of conductive graphene or a metal, especially gold, silver, aluminum, platinum, copper, or titanium.
• the process is continued by the deposition of the photosensitive layer 38 consisting of a mixture of graphene and ATO with a minimum of 20% by weight of ATO (FIG. 8).
• the deposition is carried out for example by means of a screen printing or an inkjet printing depositing a mixture of a conductive graphene ink and an ATO ink.
• the solvents of the graphene ink and the ATO ink advantageously have an evaporation temperature close to each other to form a very uniform deposited layer.
• the evaporation temperatures of the solvents are also advantageously chosen, compatible in terms of annealing, with a annealing temperature of the layers already formed during the deposition of the ink mixture, and in particular the evaporation temperatures below the glass transition temperature. of the plastic substrate 32.
• the evaporation temperatures are between 110 and 180 ° C.
• a dielectric layer 48 is then deposited on the assembly, for example by means of a physical vapor deposition, a screen printing or an inkjet printing, and openings 50 are made in the layer 48. to the photoresist layer 38 (FIGS. 9 and 10).
• the openings are for example made by means of screen printing or lithography.
• the manufacture of the pressure sensor 12 begins with the realization of a substrate 18 made of flexible plastic bat cost type PEN or PET, a thickness of between 25 and 200 micrometers, and continues with the realization of two electrodes 22, in particular by means of a full-plate deposit, for example a physical vapor deposition or by screen printing or by ink-jet printing, followed by a chemical, physical or laser etching, in order to define the electrodes 22 ( Figure 11).
• the electrodes 22 consist for example of conductive graphene or a metal, especially gold, silver, aluminum, platinum, copper, or titanium.
• the process continues with the deposition and definition of the geometry of the piezoresistive material.
• the geometric shape of the piezoresistive layer 16 is advantageously chosen to increase the sensitivity of the pressure sensor 12 in the center thereof by defining the serpentine pattern with tight turns in the center of the sensor (FIG. 12).
• the layer 20 is for example deposited by screen printing or by inkjet printing, and more generally by means of a low temperature deposition compatible with the plastic substrate 18.
• An annealing is then applied to stiffen the layer 20.
• Openings 30 are then produced in the substrate 18, for example by means of a laser etching, a plasma etching, or a chemical etching, through a lithography mask ( Figure 14).
• the dimensions of the openings 30 in the thickness of the substrate 18, and therefore through the pressure sensor 12, are advantageously optimized to have a maximum of light transfer to the light sensor 14. In particular, the dimensions of the openings are chosen to limit or avoid diffraction phenomena by the layers forming the pressure sensor 12 for the wavelengths detected by the light sensor 14.
• the pressure and light sensors 12 and 14 are preferably assembled using a conductive ink, for example based on silver.
• a conductive ink of the epoxy or other type comprising silver is deposited on each of the connection pads 44 of the light sensor 12, for example by screen printing or by means of a micro-syringe.
• the ink volume and the deposition conditions thereof make it possible to adjust the distance di separating the pressure sensor 12 from the light sensor 14 (FIG. 16).
• Light annealing is then performed to solidify the surface of the ink drops and then the pressure sensor 12 is then transferred to the conductive balls 52.
• a final annealing is then applied to solidify all the conductive balls.
• a first drop of conductive ink 52 is deposited on each connection pad 44, then a superficial annealing of the drops is applied to solidify their upper surfaces.
• a rigid metal insert 60, conductive, and having high adhesion properties with the conductive ink, is then inserted into each of the drops to mechanically support the structure of the final sensor and to prevent fatigue thereof following multiple tactile touch that it will undergo.
• the inserts 60 are rods of conductive carbon nanotubes, tungsten, nickel, titanium nitride, or tungsten nitride.
• a second drop 62 is then deposited on each of the first drops 52, and annealing is applied to stiffen the assembly.
• Other types of transfer are of course possible, the transfer by means of a conductive ink having the advantage of not requiring temperatures incompatible with the plastic materials present in the sensor.
• photosensitive layer consisting of a mixture of graphene and ATO has been described.
• Other photosensitive materials are also possible.

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• General Engineering & Computer Science (AREA)
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• Spectroscopy & Molecular Physics (AREA)
• Force Measurement Appropriate To Specific Purposes (AREA)

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• 2012
  • 2012-04-20 FR FR1253649A patent/FR2989829B1/fr not_active Expired - Fee Related
• 2013
  • 2013-03-28 US US14/388,536 patent/US9228908B2/en not_active Expired - Fee Related
  • 2013-03-28 KR KR1020147027051A patent/KR20140146594A/ko not_active Withdrawn
  • 2013-03-28 JP JP2015506279A patent/JP6125611B2/ja active Active
  • 2013-03-28 WO PCT/FR2013/050672 patent/WO2013156702A1/fr not_active Ceased
  • 2013-03-28 EP EP13719938.6A patent/EP2839361B1/fr not_active Not-in-force

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