Capacitive sensor

Abstract

[The technical problem to be solved] A capacitive sensor with improved sensitivity is provided. Technical means to solve the problem The capacitive sensor 1A includes a sensor section 20, which includes a sensor electrode 22 that forms a capacitance with the object being detected 100; and a molding section 11 disposed between the object being detected 100 and the sensor electrode 22. Furthermore, the molding section 11 includes an insulator 12 made of an electrically insulating material; and a filler 13, which includes a conductive filler or a dielectric filler dispersed in the insulator 12.

Description

[Technical Field]

[0001] This invention relates to capacitive sensors. [Previous Technology]

[0002] A known capacitive sensing module includes a housing with an operating surface; a capacitive sensor chip stacked on the opposite side of the operating surface of the housing and having multiple electrodes formed thereon; and a circuit board spaced apart on the opposite side of the operating surface of the capacitive sensor chip and connected to the multiple electrodes (for example, see Patent Document 1). In this capacitive sensing module, when an input device approaches an electrode through the operating surface of the housing, the capacitive sensor chip detects the capacitance change between the input device and the electrode. [Prior Art Documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2023-112268 [Summary of the Invention]

[0004] [Problem to be solved by the invention] In the capacitive sensing module described in the above-mentioned conventional technology, if the thickness of the outer shell increases, the distance between the input body and the electrode will increase, resulting in a decrease in sensing sensitivity.

[0005] The problem to be solved by the present invention is to provide a capacitive sensor capable of improving sensing sensitivity. [Means for solving the problem]

[0006] [1] The capacitive sensor of the present invention includes: a sensor portion including a sensor electrode that forms a capacitance with a detected object; and an insulating portion disposed between the detected object and the sensor electrode; wherein the insulating portion includes: an insulator made of an electrically insulating material; and a conductive filler or a dielectric filler dispersed in the insulator.

[0007] [2] In the present invention, in the capacitive sensor of the present invention, the aforementioned insulating part includes the aforementioned conductive filler; and the resistivity of the aforementioned conductive filler is lower than the resistivity of the aforementioned electrical insulating material.

[0008] [3] In the present invention, the state sample 3 is in the capacitive sensor of the state sample 2, wherein the aforementioned conductive filler is made of carbon or metal material.

[0009] [4] In the present invention, in the capacitive sensor of the present invention, the aforementioned insulating part includes the aforementioned dielectric filler; the relative permittivity of the aforementioned dielectric filler is higher than the relative permittivity of the aforementioned electrical insulating material.

[0010] [5] In the present invention, the state 5 is in the capacitive sensor of the state 4, where the relative permittivity of the aforementioned dielectric filler is equal to or greater than 100.

[0011] [6] In the present invention, the state sample 6 is a capacitive sensor of state sample 4 or 5, wherein the aforementioned dielectric filler is made of metal oxide.

[0012] [7] In the present invention, in any of the capacitive sensors in the present invention, the aforementioned insulating portion is directly stacked on the aforementioned sensor portion.

[0013] [8] In any of the capacitive sensors in the present invention, the capacitive sensor further includes an adhesive layer disposed between the insulating portion and the sensor portion.

[0014] [9] In the capacitive sensor of the present invention, the aforementioned insulating portion includes a molded portion formed by three-dimensionally molding at least a portion of the insulating portion in the capacitive sensor of the present invention 7 or 8; and the aforementioned sensor portion may be stacked on the aforementioned molded portion.

[0015]

[10] In the present invention, in the capacitive sensor of the present invention, the aforementioned insulating part may include the housing of the aforementioned molded part, and the aforementioned sensor part may be stacked on the inner surface of the aforementioned housing.

[0016]

[11] In the present invention, in any of the capacitive sensors of embodiments 1 to 10, the aforementioned insulating portion may be provided on the side opposite to the aforementioned sensor portion, and may include a contact surface that contacts the object being detected. [Effects of the Invention]

[0017] In this invention, the insulating portion between the object being detected and the sensing electrode includes conductive filler or dielectric filler dispersed in the insulator. This increases the effective dielectric constant of the insulating portion, thereby suppressing the decrease in sensing sensitivity caused by the increased distance between the object being detected and the sensing electrode.

Implementation Method

[0019] [Forms for Implementing the Invention] Embodiments of the present invention will now be described with reference to the accompanying drawings.

[0020] FIG1 is a cross-sectional view of the capacitive sensor 1A in this embodiment, FIG2 is an enlarged cross-sectional view of part II in FIG1, and FIG3 is a plan view of the sensor part 20 in this embodiment.

[0021] The capacitive sensor 1A of this embodiment detects the contact or proximity of the detected object 100 by detecting the change in capacitance caused by the detected object 100. The detected object 100 is not particularly limited as long as it can form a capacitance with the sensor electrode 22 described below (refer to Figures 2 and 3), and can be, for example, a human body, a stylus, etc. The potential of the detected object 100 is not particularly limited, but can be considered as grounded.

[0022] The capacitive sensor 1A of this embodiment can be applied to touch screens of smartphones and tablets, touchpads of PC operating units, switch parts of home appliances, car control panels, steering wheel grip detection sensors, etc., but is not limited thereto.

[0023] As shown in FIG1, the capacitive sensor 1A of this embodiment includes a housing 10 and a sensor section 20. The housing 10 corresponds to an example of the "insulating section" in the present invention.

[0024] In this embodiment, the housing 10 is a high-rigidity component used to house the sensor section 20. This housing 10 includes a molded portion 11 pre-formed into a three-dimensional shape. In this embodiment, the molded portion 11 is molded into a three-dimensional shape with a generally U-shaped cross-section, but it is not limited to this and can be molded into any three-dimensional shape suitable for the use of the capacitive sensor 1A. Furthermore, the housing 10 may also have flexible components. Materials constituting such components include, but are not limited to, resins such as polyurethane.

[0025] The molding section 11 includes a contact surface 11a that contacts the object being tested 100. When the object being tested 100 approaches or contacts this contact surface 11a, the capacitance between the object being tested 100 and the sensor electrode 22 described below (see Figures 2 and 3) changes. Based on the change in capacitance, the capacitance sensor 1A can detect the contact or approach of the object being tested 100.

[0026] Furthermore, the molding portion 11 does not need to be in direct contact with the object being detected 100. For example, a cover layer made of glass, resin, fiber, or leather can be laminated on this molding portion 11. Even if the object being detected 100 is in contact with this cover layer, the capacitive sensor 1A can still detect the approach of the object being detected 100.

[0027] As shown in FIG. 2, the molding section 11 includes an insulator 12 and a plurality of fillers 13. The insulator 12 is made of an insulating material with insulating properties and electrically insulates the object to be detected 100 from the sensor section 20. While there are no particular limitations on such insulating materials, they may be, for example, a photoresist material formed by curing a photoresist ink containing components such as polycarbonate, polypropylene, polyurethane, or polyurethane acrylate resin, or a two-component mixed resin. Furthermore, while there are no particular limitations on the relative permittivity of the insulating material constituting the insulator 12, it is approximately 3 to 10.

[0028] Multiple fillers 13 are dispersed in the insulator 12. Furthermore, although FIG2 shows an elliptical filler 13 in this embodiment, it is not limited to this. The shape of the filler 13 can also be spherical, polyhedral, scaly, or needle-like, etc.

[0029] The filler 13 is a conductive filler or a dielectric filler. There are no particular restrictions on the constituent materials of the conductive filler, such as carbon and metals. Furthermore, there are no particular restrictions on metals, such as copper, silver, and nickel.

[0030] On the other hand, the material constituting the dielectric filler is a dielectric material with a relative permittivity higher than that of the insulating material constituting the insulator 12. There are no particular limitations on such dielectric materials; for example, inorganic dielectrics are included. Furthermore, ferroelectric materials are preferred as dielectric materials, and it is particularly preferred that the dielectric constant of this ferroelectric material is 100 or higher. Such ferroelectric materials include, but are not limited to, metal oxides such as titanium dioxide, barium titanate, and zinc zirconate.

[0031] Furthermore, the particle size D of the filler 13 is preferably from 5 nm to 100 μm (5 nm ≤ D ≤ 100 μm). If the particle size D is 100 μm or smaller, the dispersibility of the filler 13 in the insulating material during molding will increase. Furthermore, since the particle size of the filler 13 is not too large, the viscosity of the mixture of liquid insulating material and filler 13 during molding will not be too high. In addition, cracks caused by the filler 13 are less likely to occur during the curing of the insulating material. In other words, if the particle size D is 100 μm or smaller, the occurrence of molding defects can be suppressed, and the moldability can be improved. Furthermore, in this embodiment, the particle size of the filler 13 is the median particle size D50. This median particle size D50 is not particularly limited and can be calculated using methods such as laser diffraction scattering.

[0032] Furthermore, the volume ratio Pv of the filler 13 in the molding section 11 is preferably 5 vol% to 40 vol% (5 vol% ≤ Pv ≤ 40 vol%). If this volume ratio Pv is equal to or greater than 5 vol%, the effective dielectric constant of the molding section 11 can be further improved. If this volume ratio Pv is equal to or less than 40 vol%, similar to the above, the occurrence of molding defects can be suppressed and the moldability can be improved. In addition, if this volume ratio Pv is equal to or less than 40 vol%, the decrease in the insulation performance of the molding section 11 can also be suppressed.

[0033] As shown in Figures 1 and 2, in this embodiment, the sensor unit 20 is stacked on the inner surface 11b of the housing 10. The sensor unit 20 is located on the inner surface 11b at a position corresponding to the contact surface 11a. When the object to be detected 100 contacts the contact surface 11a, the sensor unit 20 faces the object to be detected 100 through the molding portion 11. As shown in Figure 3, the sensor unit 20 includes a substrate 21, a plurality of sensor electrodes 22, and a plurality of leads 23. Furthermore, the number of sensor electrodes 22 can be one, and similarly, the number of leads 23 can also be one.

[0034] The substrate 21 is not particularly limited and may be a thin film resin material. Examples of resin materials used to form this substrate 21 include polyimide, liquid crystal polymer, polyethylene terephthalate, polyethylene naphthalate, polyether ketone, polyether ether ketone, and aramid.

[0035] A plurality of sensor electrodes 22 are disposed on the main surface of the substrate 21 and located between the substrate 21 and the molding part 11. Each sensor electrode 22 is a self-capacitive capacitive sensor and forms a capacitance between itself and the object being detected 100.

[0036] Leads 23 are electrically connected to sensor electrodes 22. These leads 23 are electrically connected to a circuit device (not shown) that can apply voltage to the sensor electrodes 22, and the voltage is applied from the circuit device (not shown) to the sensor electrodes 22 through the leads 23. In addition, the circuit device (not shown) may be housed together with the sensor part 20 in the housing 10, or it may be disposed outside the housing 10.

[0037] The sensor electrode 22 and the lead 23 can be formed by printing conductive paste on the substrate 21 and then curing (hardening) it. Methods for printing conductive paste include, for example, screen printing, gravure printing, flexographic printing, and inkjet printing. In addition, the conductive paste is composed of conductive particles, binder resin, water or solvent, and various additives.

[0038] Specific examples of conductive particles include silver, copper, nickel, tin, bismuth, zinc, indium, palladium, and alloys thereof, metal salts thereof, carbon, and conductive polymers such as PEDOT / PSS. Specific examples of adhesive resins include acrylic resins, polyester resins, epoxy resins, vinyl resins, polyurethane resins, phenolic resins, polyimide resins, silicone resins, and fluoropolymers. Examples of solvents contained in the conductive paste include α-terpineol, butylcarbital acetate, butylcarbital, 1-decyl alcohol, butyl cellosolve, diethylene glycol monoethyl ether acetate, and tetradecane. Furthermore, the adhesive resin may be omitted from the conductive paste. Additionally, conductive ink may be used instead of the aforementioned conductive paste.

[0039] Alternatively, the sensor electrode 22 and the lead 23 may also be formed on the substrate 21 by methods such as subtraction or addition (either full addition or semi addition). In this case, examples of materials for the sensor electrode 22 and the lead 23 include metallic materials such as copper and aluminum.

[0040] Furthermore, the sensor electrode 22 can be a mutual capacitance type capacitive sensor. Specifically, the sensor electrode 22 consists of a transmitting electrode (Tx) and a receiving electrode (Rx) adjacent to and spaced apart from the transmitting electrode. In this mutual capacitance type capacitive sensor, a capacitance is formed between the detected object 100 and the transmitting electrode, causing a change in the capacitance between the transmitting electrode and the receiving electrode. The mutual capacitance type capacitive sensor detects the contact or proximity of the detected object 100 by detecting this capacitance change.

[0041] Furthermore, in a mutual capacitance type capacitive sensor, the transmitting electrode and the receiving electrode can be formed on different layers, and the two can present a grid-like structure when viewed in a plan view. For example, although there are no particular limitations, the transmitting electrode can be disposed on the surface of the substrate 21 and extend along the X direction, and the receiving electrode can be disposed on the back side of the substrate 21 and extend along the Y direction.

[0042] The capacitive sensor 1A described above is not particularly limited, but it can be manufactured, for example, by injection molding such as insert molding. Specifically, insert molding first requires placing the sensor part 20, which serves as an insert, into a mold. Next, particles made of the aforementioned insulating material are loaded into a molding machine and conveyed to the mold via the screw of the molding machine, while the particles are heated and melted. At the same time, filler 13 is loaded into the molding machine, causing the filler 13 to diffuse into the molten insulating material, forming a mixed paste of insulating material and filler 13. This mixed paste is injected into the mold and allowed to solidify, thereby manufacturing the capacitive sensor 1A including the housing 10 and the sensor part 20. Furthermore, the capacitive sensor 1A of this embodiment can also be manufactured using other molding methods.

[0043] As described above, the capacitive sensor 1A of this embodiment has the following effects. First, the effects obtained when the filler 13 is a conductive filler will be explained. FIG4(a) is an enlarged cross-sectional view for explaining the capacitive sensor 1C of the comparative example, and FIG4(b) is an enlarged cross-sectional view for explaining the function of the conductive filler in the molding section 11 of the capacitive sensor 1A of this embodiment.

[0044] As shown in FIG4(a), the comparative example capacitive sensor 1C has a sensor portion 20C including a sensor electrode 22C, and an insulating molded portion 11C stacked on the sensor electrode 22C. In the comparative example molded portion 11C, the conductive filler is not dispersed in the insulator 12C.

[0045] When the object to be detected 100 comes into contact with the molded portion 11C, an electric field EC is generated between the object to be detected 100 and the sensor electrode 22C. The path length of this electric field EC is substantially equal to the thickness T0 of the molded portion 11C. Since the capacitance formed between the object to be detected 100 and the sensor electrode 22C is inversely proportional to the path length of the electric field EC, if the thickness T0 of the molded portion 11C increases, the capacitance formed between the object to be detected 100 and the sensor electrode 22C will decrease. Therefore, the amount of capacitance change caused by the proximity or contact of the object to be detected 100 will also decrease, and the sensitivity of the capacitive sensor 1C will also decrease.

[0046] As shown in Figure 4(a), the conductive filler 13a dispersed in the insulator 12 can be regarded as a virtual parallel plate capacitor 30 formed in the insulator 12. For convenience, Figure 4(a) shows an example of the parallel plate capacitor 30 having two parallel plates (a first virtual parallel plate 31 and a second virtual parallel plate 32).

[0047] As shown in FIG4(b), in the capacitive sensor 1A of this embodiment, when the detected object 100 approaches the molding part 11, an electric field E is generated between the detected object 100 and the sensor electrode 22. At this time, since the first virtual parallel plates 31 and 32 are conductors, the free electrons inside the first virtual parallel plates 31 and 32 move under the action of the electric field E, generating dielectric polarization (electrostatic induction).

[0048] For example, in the structure shown in FIG4(a), in the first virtual parallel plate 31, the negative charge (free electron) moves along the +Z direction as if attracted by the positive charge of the detected object 100, while the positive charge moves along the -Z direction opposite to the negative charge. Similarly, in the second virtual parallel plate 32, the negative charge (free electron) moves along the +Z direction, while the positive charge moves along the -Z direction opposite to the negative charge.

[0049] Thus, it can be considered that three capacitors connected in series are formed between the object being detected 100 and the first virtual parallel plate 31, between the first virtual parallel plate 31 and the second virtual parallel plate 32, and between the second virtual parallel plate 32 and the sensor electrode 22. Inside the first and second virtual parallel plates 31 and 32, the electric field generated by electrostatic induction cancels out the aforementioned electric field E, resulting in an equipotential formation inside the first virtual parallel plates 31 and 32. Therefore, the thickness of the first and second virtual parallel plates 31 and 32 can be subtracted from the path length of the electric field E.

[0050] Therefore, the path length of the electric field E can be considered as the thickness of the insulator 12 between the object under test 100 and the sensor electrode 22. Thus, the path length of the electric field E can be considered as the sum (d1+d2+d3) of the distances d1 between the object under test 100 and the first virtual parallel plate 31, d2 between the first virtual parallel plate 31 and the second virtual parallel plate 32, and d3 between the second virtual parallel plate 32 and the sensor electrode 22. This sum (d1+d2+d3) is less than the thickness T0 of the molding portion 11 (d1+d2+d3<T0), thereby increasing the capacitance formed between the object under test 100 and the sensor electrode 22. As described above, since the effective dielectric constant of the molding portion 11 can be increased, the decrease in sensitivity caused by the increase in the distance between the object under test 100 and the sensor electrode 22 (in this example, the thickness T0 of the molding portion 11) can be suppressed. Furthermore, when the thicknesses of the molding portions 11 and 11C are the same, this embodiment can improve sensitivity compared to the comparative example.

[0051] Furthermore, if the filler 13 is a dielectric filler, the electric field E between the test object 100 and the sensor electrode 22 will polarize the dielectric filler and weaken the electric field E, causing the voltage between the test object 100 and the sensor electrode 22 to be less than a predetermined voltage. In order to raise this voltage to the predetermined voltage (that is, to generate an electric field that can reach the predetermined voltage), the circuit device (not shown) will send more charge to the sensor electrode 22, thereby increasing the capacitance formed between the test object 100 and the sensor electrode 22. As described above, the effective dielectric constant of the molding portion 11 can be increased, thereby suppressing the decrease in sensitivity caused by the increase in the distance between the test object 100 and the sensor electrode 22. In addition, when the molding portions 11 and 11C have the same thickness, this embodiment can improve the sensitivity compared to the comparative example.

[0052] Furthermore, the embodiments described above are intended to aid in understanding the present invention and are not intended to limit the present invention. Therefore, the various configurations disclosed in the above embodiments should be understood to include all design changes and equivalents that fall within the scope of the present invention.

[0053] For example, in the capacitive sensor 1A of the above embodiment, although the sensor portion 20 is directly laminated onto the housing 10 through insert molding, it is not limited to this. The sensor portion 20 may be laminated onto the housing 10 through the adhesive layer 40. FIG5 shows an enlarged cross-sectional view of a variation of the capacitive sensor 1A of this embodiment.

[0054] The capacitive sensor 1B in the variation further includes an adhesive layer 40 between the molding portion 11 and the sensor portion 20. This capacitive sensor 1B can be manufactured by separately manufacturing the housing 10 and the sensor portion 20, and then bonding the two together through the adhesive layer 40.

[0055] Even in this variation, similar to the above embodiment, the filler 13 can suppress the decrease in sensitivity that occurs as the distance between the object to be detected 100 and the sensor electrode 22 increases.

[0056] Furthermore, in the above embodiments, the housing 10 serves as an example of an "insulating part" in the present invention. This housing 10 can be used in electronic devices such as touch screens, touchpads, switches, or control panels, but is not limited thereto. On the other hand, the "insulating part" in the present invention can be an insulating member other than the housing 10. For example, the insulating part can be a flexible insulating sheet member. Since such a sheet member is easy to bend, it can be deformed to fit the shape of the parts to be mounted on the capacitive sensors 1A and 1B. Although there are no particular limitations, such a sheet member can be configured along the curved surface of a steering wheel rim to be suitable for applications such as grip sensors.

[0057] Furthermore, although there are no particular limitations, the sensor unit 20 may have a shielding layer formed on the surface or back side of the substrate 21 to shield noise that needs to enter the sensor electrode 22. Alternatively, the substrate 21 may be omitted from the sensor unit 20. [Simplified Explanation of the Diagram]

[0018] FIG1 is a cross-sectional view of a capacitive sensor according to an embodiment of the present invention. FIG2 is an enlarged cross-sectional view of part II of FIG1. ​​FIG3 is a plan view of the sensor part according to an embodiment of the present invention. FIG4(a) is an enlarged cross-sectional view of a capacitive sensor in a comparative example; FIG4(b) is an enlarged cross-sectional view illustrating the function of the conductive filler in the molding part of the capacitive sensor according to an embodiment of the present invention. FIG5 is an enlarged cross-sectional view of a variation of the capacitive sensor according to an embodiment of the present invention.

Claims

1. A capacitive sensor, comprising: The sensor section includes sensor electrodes that form a capacitance with the object being detected; An insulating portion is disposed between the aforementioned object to be detected and the aforementioned sensor electrode; wherein the aforementioned insulating portion includes: an insulator made of an electrically insulating material; and a conductive filler or dielectric filler dispersed in the aforementioned insulator; the aforementioned insulating portion is a rigid shell.

2. The capacitive sensor as described in claim 1, wherein, The aforementioned insulating portion includes the aforementioned conductive filler; and the resistivity of the aforementioned conductive filler is lower than the resistivity of the aforementioned electrical insulating material.

3. The capacitive sensor as described in claim 2, wherein, The aforementioned conductive filler is made of carbon or metallic materials.

4. The capacitive sensor as described in claim 1, wherein, The aforementioned insulating portion includes the aforementioned dielectric filler; the relative permittivity of the aforementioned dielectric filler is higher than the relative permittivity of the aforementioned electrical insulating material.

5. The capacitive sensor as described in claim 4, wherein, The relative permittivity of the aforementioned dielectric filler is equal to or greater than 100.

6. The capacitive sensor as described in claim 4, wherein, The aforementioned dielectric filler is made of metal oxide.

7. A capacitive sensor as described in any one of claims 1 to 6, wherein, The aforementioned insulating portion is directly stacked on the aforementioned sensor portion.

8. A capacitive sensor as described in any one of claims 1 to 6, wherein, The aforementioned capacitive sensor further includes an adhesive layer disposed between the aforementioned insulating portion and the aforementioned sensor portion.

Images