JP2009244206A - Pressure sensitive sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pressure sensitive sensor for facilitating pressure detection by preventing excessive reduction in resistivity between a pair of electrodes by a tunnel barrier between the electrodes and a pressure sensitive conductive layer. <P>SOLUTION: This pressure sensitive sensor comprises a substrate 7 having a pair of electrodes 5 and 6, and the pressure sensitive conducting layer 8 where the pair of electrodes 5 and 6 in the substrate 7 and the gap between the pair of electrodes 5 and 6 are covered and tunnel current flows between conductive particles, included inside following the application of the pressure to change the insulation state to the current-carrying state. The insulation layer 9 with a thickness that allows the tunnel current flow to be interposed in between the electrodes 5 and 6 and the pressure sensitive conducting layer 8. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a pressure sensor used to detect pressure.

Such a pressure-sensitive sensor is provided on, for example, a touch panel or a pen tablet, and can detect a finger pressure, a pen writing pressure, or the like.
Conventionally, this type of pressure-sensitive sensor uses a pressure-sensitive conductive rubber in which the conductive particles contained therein are brought into contact with each other as pressure is applied to form a conduction path and the resistivity changes. (For example, see Patent Document 1). Then, an electrode is attached to the pressure-sensitive conductive rubber, and the pressure is detected by performing signal processing on the resistance change of the pressure-sensitive conductive rubber.

  However, as the pressure-sensitive conductive rubber is repeatedly pressed, the pressure-sensitive conductive rubber undergoes plastic deformation over time due to fatigue, so that the conductive particles do not come back apart and remain in contact with each other. Even if the pressure is applied, the pressure-sensitive conductive rubber hardly changes in resistance, and it may be difficult to detect pressure. In addition, it is difficult to make pressure-sensitive conductive rubber into ink, and it is difficult to print pressure-sensitive conductive rubber. In addition to being troublesome, such as the conductive rubber must be placed between the pair of electrodes and the pair of electrodes on the base material, there is a possibility that the thickness of the pressure-sensitive conductive rubber may increase. It was.

  Therefore, as a material that changes to pressure-sensitive conductive rubber, a pressure-sensitive conductive composition that changes from an insulating state to an energized state due to the tunnel current flowing between the conductive particles contained in the interior with the application of pressure recently. It has been proposed and applied to pressure-sensitive conductive inks.

  Thus, the pressure-sensitive conductive ink was printed and dried by directly printing the pressure-sensitive conductive ink between the pair of electrodes and the pair of electrodes on the base material to form the pressure-sensitive conductive layer. After that, since there is almost no change in shape, it is possible to prevent the pressure from becoming difficult to detect over time even if it is repeatedly pressed. It will be possible. By the way, when the conductive particles are not in contact but are very close in nanometer order, the existence probability density of electrons between the conductive particles is not zero, so that the electrons ooze out. Tunnel current flows, and this phenomenon is essentially explained by quantum mechanics.

  As such a pressure-sensitive sensor using pressure-sensitive conductive ink, an FPC (flexible substrate) as a base material on which a pair of electrodes are formed, a pair of electrodes in the FPC, and the pair of electrodes It is conceivable to form a pressure-sensitive conductive layer by directly printing a pressure-sensitive conductive ink.

JP 2005-135876 A

  In the conventional pressure-sensitive sensor, the electrode and the pressure-sensitive conductive layer are directly bonded, and the resistivity between the pair of electrodes becomes too low, so that it is difficult to detect the pressure.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a pressure-sensitive sensor that can easily detect pressure.

  The first characteristic configuration of the pressure-sensitive sensor according to the present invention includes a base material on which a pair of electrodes are formed, the pair of electrodes on the base material, and a space between the pair of electrodes and the inside of the pair with the application of pressure. A pressure-sensitive conductive layer in which a tunnel current flows between contained conductive particles and changes from an insulating state to an energized state, and an insulating layer having a thickness through which the tunnel current flows between the electrode and the pressure-sensitive conductive layer The point is that there is intervening.

  That is, since an insulating layer having a thickness through which a tunnel current flows is interposed between the electrode and the pressure-sensitive conductive layer, the resistivity between the pair of electrodes is caused by the tunnel barrier between the electrode and the pressure-sensitive conductive layer. Is prevented from becoming too low, and the pressure is easily detected.

  The second characteristic configuration of the present invention is characterized in that, in addition to the first characteristic configuration, the pressure-sensitive conductive layer is formed of ink.

  That is, in addition to being easy to mass-produce by forming a pressure-sensitive conductive layer by directly printing a pressure-sensitive conductive ink between the pair of electrodes and the pair of electrodes in the base material, The thickness can be reduced.

  The third characteristic configuration of the present invention is characterized in that, in addition to the first or second characteristic configuration, the insulating layer is made of an inorganic oxide.

  That is, since the insulating layer is made of an inorganic oxide, it is difficult to change in quality, and it is easy to suitably form the insulating layer. In addition, the thickness control is easy and the reproducibility is excellent.

  According to a fourth characteristic configuration of the present invention, in addition to the first or second characteristic configuration, the insulating layer is made of an organic material.

  That is, since the insulating layer is made of an organic material, it is easy to form the insulating layer suitably. In addition, a printing method such as screen printing can be used, which is advantageous in terms of cost.

  A fifth characteristic configuration of the present invention is characterized in that, in addition to the first or second characteristic configuration, the insulating layer is made of an inorganic material.

  That is, since the insulating layer is made of an inorganic material, it is easy to form the insulating layer suitably. In addition, it is easy to secure the insulating layer, and the reliability is excellent.

[First embodiment]
Hereinafter, a touch panel provided with a pressure-sensitive sensor according to the present invention will be described.
As shown in FIGS. 1 to 3, a design film 2 is attached to the lower surface of a hard coat film 1 made of synthetic resin such as PET or PE, and a touch panel portion 3 is attached to the lower surface of the design film 2. To constitute the touch panel unit 3, a transparent insulating film 3b having a transparent electrode 3a on the lower surface and a glass plate 3c having a transparent electrode 3a on the upper surface are opposed to each other through a large number of dot spacers 3d. A substrate 4 is attached to the lower surface of the touch panel portion 3. Thereby, the hard coat film 1, the design film 2, the touch panel part 3, and the substrate 4 constitute the touch panel A.

A pressure sensor B is attached to the lower surface of the touch panel A. The pressure-sensitive sensor B covers the pressure between the pair of electrodes 5 and 6 and the pair of electrodes 5 and 6 in the FPC 7 as a base material on which the pair of electrodes 5 and 6 is formed. Between the electrodes 5 and 6 and the pressure-sensitive conductive layer 8. The pressure-sensitive conductive layer 8 changes from an insulating state to an energized state due to a tunneling current flowing between the conductive particles contained therein. An insulating layer 9 of silicon dioxide (SiO ₂ ) having a thickness through which a tunnel current flows, that is, a thickness of approximately 20 nanometers is interposed. Incidentally, the thicknesses of the electrodes 5 and 6, the pressure-sensitive conductive layer 8, and the FPC 7 are 18 μm, 20 μm, and 35 μm, respectively. In addition, a composition constituting the pressure-sensitive conductive layer 8 in which a tunnel current flows between conductive particles contained therein with application of pressure and changes from an insulating state to an energized state is a composition of Darlington, England. It is a quantum tunneling composite material (Quantum Tuning Composite) available from PERATECH LTD under the trade name “QTC”.

  If it demonstrates, as shown in FIG. 1, the protective film 10 will be affixed on the lower surface of the touchscreen A, and FPC7 will be affixed on the lower surface of the protective film 10 via the adhesive agent 11 which can be elastically deformed. Electrodes 5 and 6 and a pressure-sensitive conductive layer 8 are formed on the upper surface of the FPC 7. A pair of electrodes 5 and 6 are formed on the FPC 7 by silver printing. As shown in FIG. 2, the pair of electrodes 5 and 6 includes comb teeth 5a and 6a, respectively, and the comb teeth 5a and 6a are inserted at a predetermined interval. Then, as shown in FIG. 3, a silicon dioxide insulating layer 9 is formed so as to cover the pair of electrodes 5 and 6 and the pair of electrodes 5 and 6 in the FPC 7 by sputtering. The FPC 7 is printed so as to cover the pair of electrodes 5 and 6 and between the pair of electrodes 5 and 6, and the pressure-sensitive conductive ink is heated to volatilize the solvent and the thermosetting resin is cured to pressure-sensitive. A conductive layer 8 is formed.

  Accordingly, since the insulating layer 9 having a thickness through which a tunnel current flows is interposed between the electrodes 5 and 6 and the pressure-sensitive conductive layer 8, the tunnel barrier between the electrodes 5 and 6 and the pressure-sensitive conductive layer 8 is interposed. Therefore, the resistivity between the pair of electrodes 5 and 6 is prevented from becoming too low, and the pressure is easily detected. Moreover, in addition to being easily mass-produced by printing the pressure-sensitive conductive ink, the thickness of the pressure-sensitive sensor can be reduced.

Hereinafter, the experimental result measured about the pressure change of the resistance of pressure-sensitive conductive ink is demonstrated.
(experimental method)
A pair of electrodes having a width of 100 μm are arranged on the FPC board with an interval of 130 μm, a resistance meter is connected to each end of the pair of electrodes, and a pair of electrodes and a pair of silicon dioxide are formed by sputtering. An insulating layer having a thickness of 20 nanometers is formed by vapor deposition so as to cover between the electrodes, and a pressure sensitive conductive ink is directly printed between the pair of electrodes and the pair of electrodes to obtain a thickness of 20 μm. The pressure-sensitive conductive layer was formed, and a pressure change of the resistance of the pressure-sensitive conductive ink was measured by pressing the hemispherical silicone rubber with a predetermined pressure so as to cover the pair of electrodes.

(Experimental result)
FIG. 7 shows the relationship between pressure and resistance of pressure-sensitive conductive ink when an insulating layer is not formed, and FIG. 8 shows pressure-sensitive conductivity when an insulating layer having a thickness of 20 nanometers is formed. This shows the relationship between the resistance and pressure of the reactive ink. The resistance value is about an order of magnitude higher when the insulating layer having a thickness of 20 nanometers is formed than when the insulating layer is not formed. Thereby, the resistance value between the pair of electrodes is prevented from becoming too low, and the pressure is easily detected. Moreover, since the pressure change in resistance value is larger when the insulating layer having a thickness of 20 nanometers is formed than when the insulating layer is not formed, it is easier to detect the pressure change.

[Another embodiment]
(1) In the above embodiment, the protective film 10 is attached to the lower surface of the touch panel A, and the FPC 7 is attached to the lower surface of the protective film 10 via the elastically deformable adhesive 11. The configuration in which the electrodes 5 and 6 and the pressure-sensitive conductive layer 8 are formed on the upper surface of the FPC 7 is illustrated, but is not limited to such a configuration. For example, as illustrated in FIG. Are formed on the lower surface of the touch panel A via an elastically deformable adhesive, as shown in the first embodiment. It is good also as a structure stuck. Further, as shown in FIG. 5, a pressure-sensitive layer in which the electrodes 5 and 6 and the pressure-sensitive conductive layer 8 are formed is formed on the lower surface of the FPC 7, and the pressure-sensitive layer is adhered to the lower surface of the touch panel A. As shown in the embodiment, the protective film 10 may be attached to the lower surface of the FPC 7 via an elastically deformable adhesive. In addition, as shown in FIG. 6, a pressure-sensitive layer in which the electrodes 5 and 6 and the pressure-sensitive conductive layer 8 are formed is formed on the lower surface of the FPC 7, and the pressure-sensitive layer is simply attached to the lower surface of the touch panel A. It is good also as a structure.

(2) In the above embodiment, the configuration in which the thickness of the insulating layer 9 is approximately 20 nanometers has been exemplified, but the present invention is not limited to this.

(3) In the above embodiment, the configuration in which the electrode is formed by silver printing is illustrated, but the configuration is not limited to such a configuration, and metallic printing other than silver, for example, by a material such as carbon or carbon nanotube The electrode may be formed, or the electrode may be formed by laminating a metal foil such as copper or gold-plated copper, or an electrode pattern is formed with a resist on a copper-plated FPC and protected by the resist. A configuration in which an electrode is formed by etching a portion of copper that is not formed may be employed.

(4) In the above embodiment, the configuration in which the insulating layer 9 is formed by the sputtering method is exemplified, but the configuration is not limited to such a configuration, and the CVD method, the EB vapor deposition method, the sol-gel method, the roll coater, the spin coater, You may form by various methods, such as angstrom, gravure, and screen printing.

(5) In the above embodiment, the configuration in which the insulating layer 9 is silicon dioxide has been exemplified, but aluminum oxide (Al ₂ O ₃ ), zirconium oxide (ZrO ₂ ), bismuth oxide (Bi ₂ O ₃ ), chromium oxide (Cr ₂ O ₃ ), iron oxide (FeO, Fe ₂ O ₃ , Fe ₃ O ₄ ), cobalt oxide (Co ₃ O ₄ ), nickel oxide (NiO), niobium oxide (Nb ₂ O ₅ ), molybdenum oxide ( MoO ₃ ), calcium oxide (CaO), strontium oxide (SrO), barium oxide (BaO), lanthanum oxide (La ₂ O ₃ ), silica (SiO ₂ ), calcium silicate (CaSiO ₃ ), aluminum borate (Al Inorganic oxides such as ₁₈ B ₄ O ₃₃ ), nitrides such as silicon nitride (Si ₃ N ₄ ) and aluminum nitride (ALN), oxynitrides such as silicon oxynitride (SiO _X N _1-X ), carbonization Carbides such as silicon (SiC), hydroxides such as aluminum hydroxide (Al (OH) ₃ ), magnesium hydroxide (Mg (OH) ₂ ), calcium carbonate (CaCO ₃ ), potassium carbonate (K ₂ CO ₃ ) , Carbonates such as barium carbonate (BaCO ₃ ), phosphates such as calcium phosphate (CaH 2 (PO) ₄ ), sulfates such as barium sulfate (BaSO ₄ ), viscosity minerals such as talc, halosite, celite, clay, Sol gel using inorganic materials such as clay, zeolite, inorganic balloon, and chelates such as alkoxides (alcolate), acylate, β-diketone, ketoester, hydroxyamate, geolate, hydroxyacylate made of insulating metal An insulating oxide obtained by a method may be used. In addition, an insulating material partially containing an organic material, for example, an organic material such as polyorganosiloxane, or a hybrid of these inorganic material and organic material may be used.

Cross section of touch panel with pressure sensor The perspective view which shows the state in which the electrode and the pressure-sensitive conductive layer were formed in FPC Cross section of pressure sensor Sectional drawing of the pressure-sensitive sensor in another embodiment Sectional drawing of the pressure-sensitive sensor in another embodiment Sectional drawing of the pressure-sensitive sensor in another embodiment Diagram showing the relationship between resistance and pressure of pressure-sensitive conductive ink Diagram showing the relationship between resistance and pressure of pressure-sensitive conductive ink

Explanation of symbols

5, 6 Electrode 7 Base material 8 Pressure sensitive conductive layer 9 Insulating layer

Claims (5)

  A tunnel current flows between a base material on which a pair of electrodes are formed, the pair of electrodes on the base material, and the pair of electrodes, and the conductive particles contained therein as a result of application of pressure. A pressure-sensitive sensor comprising a pressure-sensitive conductive layer that changes from an insulating state to an energized state, and an insulating layer having a thickness through which a tunnel current flows between the electrode and the pressure-sensitive conductive layer.   The pressure-sensitive sensor according to claim 1, wherein the pressure-sensitive conductive layer is formed of ink.   The pressure-sensitive sensor according to claim 1, wherein the insulating layer is made of an inorganic oxide.   The pressure-sensitive sensor according to claim 1, wherein the insulating layer is made of an organic material.   The pressure-sensitive sensor according to claim 1, wherein the insulating layer is made of an inorganic material.

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