WO2025205098A1 - Sensor - Google Patents

Abstract

A sensor according to an embodiment of the present invention comprises: a touch panel; a first electrode; a piezoelectric film; a second electrode; a first adhesive disposed between the touch panel and the first electrode; a second adhesive connected between the first electrode and the piezoelectric film; and a third adhesive disposed between the piezoelectric film and the second electrode.

Description

Sensor

The present invention relates to a deformation detection sensor that detects deformation of a detection object.

Patent Document 1 discloses a piezoelectric sensor that uses a piezoelectric film. The piezoelectric film is sandwiched between a detection electrode and a ground electrode. The piezoelectric sensor detects pressure by detecting the potential difference generated between the detection electrode and the ground electrode.

International Publication No. 2023/153430

When a piezoelectric sensor such as that disclosed in Patent Document 1 is combined with a touch panel (capacitive sensor), the following two types of capacitance are mainly generated.
(1) Capacitance between the touch panel and the piezoelectric sensor
(2) Capacitance within the piezoelectric sensor To improve the sensitivity of the touch panel, it is preferable that the capacitance of (1) is small. To improve the sensitivity of the piezoelectric sensor, it is preferable that the capacitance of (2) is large. To reduce the capacitance of (1), for example, it is sufficient to increase the distance between the touch panel and the piezoelectric sensor. However, if the distance between the touch panel and the piezoelectric sensor is increased, it becomes difficult to transmit the distortion generated by the touch panel to the piezoelectric sensor, and the sensitivity of the piezoelectric sensor decreases.

The present invention therefore aims to provide a sensor that combines the sensitivity of a touch panel with the sensitivity of a piezoelectric sensor.

A sensor according to one embodiment of the present invention comprises a touch panel, a first electrode, a piezoelectric film, a second electrode, a first adhesive disposed between the touch panel and the first electrode, a second adhesive connected between the first electrode and the piezoelectric film, and a third adhesive disposed between the piezoelectric film and the second electrode.

The dielectric constant ε1 of the first adhesive is smaller than the dielectric constant ε2 of the second adhesive and the dielectric constant ε3 of the third adhesive.

In this way, in the sensor of the present invention, by setting the dielectric constant ε1 of the first adhesive placed between the touch panel and the first electrode of the piezoelectric sensor to a small value, the capacitance between the touch panel and the piezoelectric sensor is reduced, thereby improving the sensitivity of the touch panel without increasing the distance between the touch panel and the piezoelectric sensor.

This invention makes it possible to achieve both the sensitivity of the touch panel and the sensitivity of the piezoelectric sensor.

FIG. 1A is a plan view of an electronic device 1 equipped with a sensor 10, and FIG. 1B is a side view of the electronic device 1. As shown in FIG. FIG. FIG. 10 is a partial cross-sectional view of a sensor 4 according to a second modified example. FIG. 10 is a partial cross-sectional view of a sensor 4 according to a third modified example. 10 is a partial cross-sectional view of the sensor 4, showing an example of the arrangement of the display device 5. FIG. 10 is a partial cross-sectional view of the sensor 4, showing another example of the arrangement of the display device 5. FIG.

FIG. 1(A) is a plan view of electronic device 1 equipped with sensor 10. FIG. 1(B) is a side view of electronic device 1. FIG. 2 is a cross-sectional view of sensor 10.

Electronic device 1 is an information processing terminal such as a smartphone. Electronic device 1 comprises a housing 2, a surface glass 3, a sensor 4, and a display device 5. The surface glass 3, sensor 4, and display device 5 are rectangular when viewed from the front.

The housing 2 houses various circuits for the information processing terminal. The display device 5 is made up of an LCD or OLED and displays images.

Figure 2 is a partial cross-sectional view of the sensor 4, omitting the housing 2, surface glass 3, and display device 5. The sensor 4 includes a touch panel 11, a first adhesive 12, a first electrode 13, a second adhesive 14, a piezoelectric film 15, a third adhesive 16, and a second electrode 17.

The touch panel 11 is a capacitance sensor that detects the user's touch operation and touch position on the front glass 3. The capacitance generated on the touch panel 11 is the sum of the static capacitance to the ground Cp and the increased capacitance Cf due to the touch operation. Therefore, the sensitivity of the touch panel 11 increases as the capacitance to the ground Cp decreases.

The first adhesive 12 is disposed between the touch panel 11 and the first electrode 13, connecting the touch panel 11 and the first electrode 13. The first electrode 13 is, for example, a ground electrode.

The second adhesive 14 is disposed between the first electrode 13 and the piezoelectric film 15, connecting the first electrode 13 and the piezoelectric film 15.

The third adhesive 16 is disposed between the piezoelectric film 15 and the second electrode 17, connecting the piezoelectric film 15 and the second electrode 17. The second electrode 17 is, for example, a detection electrode.

When the surface glass 3 is pressed by a finger or the like, the sensor 4 deforms along with the surface glass 3. The piezoelectric film 15 is polarized by this deformation, generating a potential difference between the first electrode 13 and the second electrode 17. Therefore, the first electrode 13, second adhesive 14, piezoelectric film 15, third adhesive 16, and second electrode 17 form a piezoelectric sensor.

The piezoelectric film 15 is made of uniaxially stretched polylactic acid (PLA) or PVDF. The polylactic acid is either L-type polylactic acid (PLLA) or D-type polylactic acid (PDLA). Polylactic acid generates piezoelectricity through molecular orientation processing such as stretching, so there is no need for poling processing like with other polymers such as PVDF or piezoelectric ceramics. Furthermore, polylactic acid does not have pyroelectric properties. Therefore, polylactic acid does not polarize due to the user's body temperature, making it ideal for use in electronic devices that are touched by the user's fingers, such as this embodiment.

Polylactic acid is a chiral polymer whose main chain has a helical structure, and exhibits piezoelectricity when oriented in a specific axial direction. This piezoelectricity is expressed by the piezoelectric tensor component d14, with the thickness direction of the film as the first axis and the direction in which the polylactic acid molecules are oriented as the third axis.

If the piezoelectric film 15 is oriented in a direction (stretching direction) that orients the polylactic acid molecules in a direction that intersects the long and short sides, polarization will occur due to expansion and contraction in the long or short side direction. For example, if the piezoelectric film 15 is stretched in a direction that is approximately 45° to the long and short sides, polarization will occur due to expansion and contraction in the long or short side direction, and an output will appear as a piezoelectric sensor. The stretching direction may also be approximately 0° (90°).

The angle of the stretching direction of the piezoelectric film 15 is not limited to an exact 45° angle relative to the long and short sides, but can be any angle close to 45°. However, the closer the stretching angle is to 45° or 0° relative to the long and short sides, the more efficiently the deflection of the long and short sides can be detected.

Therefore, in this embodiment, approximately 45° refers to an angle within a predetermined range with 45° as the center, for example, approximately 45°±10°. These specific angles can be determined appropriately according to the overall design, taking into account the sensor's intended use and the characteristics of each component. The same applies when the extension direction is 0° (90°).

In this way, the piezoelectric sensor can detect the deflection of the front glass 3 with high sensitivity.

As mentioned above, the sensitivity of the touch panel 11, which is a capacitance sensor, increases as the ground capacitance Cp decreases. The ground capacitance Cp is expressed as Cp = (ε1·S)/d (where S is the area of the first adhesive 12 and d is the thickness of the first adhesive 12).

The sensitivity of the piezoelectric sensor is determined by the coupling capacitance between the first electrode 13 and the second electrode 17. The larger the capacitance C2 of the second adhesive 14 and the capacitance C3 of the third adhesive 16, the greater the coupling capacitance between the first electrode 13 and the second electrode 17.

Furthermore, the dielectric constant ε1 of the first adhesive 12 in the sensor 4 of this embodiment is smaller than the dielectric constant ε2 of the second adhesive 14 and the dielectric constant ε3 of the third adhesive 16. Therefore, the sensor 4 of this embodiment can improve the sensitivity of the touch panel without increasing the thickness of the first adhesive 12 (the distance between the touch panel 11 and the piezoelectric sensor).

(Variation 1)
In Modification 1, the dielectric constant ε1 of the first adhesive 12 is less than 3, and the dielectric constant ε2 of the second adhesive 14 and the dielectric constant ε3 of the third adhesive 16 are each equal to or greater than 3. It is more preferable that the dielectric constant ε2 of the second adhesive 14 and the dielectric constant ε3 of the third adhesive 16 are each equal to or greater than 5. This allows the sensor 4 of Modification 1 to further improve the sensitivity of the touch panel without increasing the thickness of the first adhesive 12 (the distance between the touch panel 11 and the piezoelectric sensor).

(Variation 2)
3 is a partial cross-sectional view of the sensor 4 according to the modified example 2. In the sensor 4 according to the modified example 2, the thickness of the third adhesive 16 is greater than the thickness of the second adhesive 14. More preferably, the thickness of the third adhesive 16 is at least twice the thickness of the second adhesive 14.

This configuration makes it difficult for deformation in the thickness direction that occurs when the front glass 3 is pressed to be transmitted to the second electrode 17. As a result, the second electrode 17 is less susceptible to deformation than the piezoelectric film 15.

The configuration of variant 2 suppresses deformation of the second electrode 17, thereby suppressing damage to the second electrode 17. This improves the reliability of the sensor 4.

(Variation 3)
4 is a partial cross-sectional view of sensor 4 according to Modification 3. In sensor 4 according to Modification 3, fourth adhesive 18 is further attached to second electrode 17, and third electrode 19, which is a ground electrode, is attached to fourth adhesive 18.

In the configuration of variant 3, ground electrodes are provided on both the top and bottom surfaces of the second electrode 17, which is the detection electrode, thereby improving the noise resistance of the sensor 4.

(Example of arrangement of display device 5)
Fig. 5 is a partial cross-sectional view of the sensor 4, showing an example of the arrangement of the display device 5. Fig. 6 is a partial cross-sectional view of the sensor 4, showing another example of the arrangement of the display device 5.

In the example shown in FIG. 5, the sensor 4 includes a fifth adhesive 20 disposed between the second electrode 17 and the display device 5. That is, the display device 5 is attached to the sensor 4 via the fifth adhesive 20, which is attached to the second electrode 17. Also, in the example shown in FIG. 5, the first electrode 13 and the second electrode 17 include a transparent electrode material.

In the example of Figure 5, the sensor 4 is placed on the top side of the display device 5. In other words, the sensor 4 is not placed between the inside of the housing 2 of the electronic device 1 and the display device 5. Therefore, the electrical characteristics of the sensor 4 do not affect other electronic components placed between the housing 2 of the electronic device 1 and the display device 5.

In the example shown in FIG. 6, the sensor 4 includes a fifth adhesive 20 disposed between the touch panel 11 and the display device 5. The fifth adhesive 20 connects the touch panel 11 and the display device 5. The display device 5 is attached to the sensor 4 via the first adhesive 12, which is attached to the first electrode 13.

In the example of Figure 6, the piezoelectric film 15 of the sensor 4 is placed on the underside of the display device 5. The piezoelectric film 15 detects deformation of the display device 5, with the display device 5 as the deformation detection target. The display device 5 deforms together with the front glass 3 and touch panel 11. No object for deformation detection is placed below the piezoelectric film 15. Therefore, in the example of Figure 6, the piezoelectric film 15 is more likely to deform in response to the deformation of the front glass 3 than in the example of Figure 5, and deformation can be detected with higher accuracy.

In both the examples shown in Figures 5 and 6, the user can launch application programs or perform various operations on the electronic device 1 by manipulating objects displayed on the display device 5 with their fingers, etc.

The configuration of this embodiment can be summarized as follows.
(1)
Touch panel and
A first electrode;
a piezoelectric film;
A second electrode;
a first adhesive disposed between the touch panel and the first electrode;
a second adhesive connected between the first electrode and the piezoelectric film;
a third adhesive disposed between the piezoelectric film and the second electrode;
A sensor comprising:
The dielectric constant ε1 of the first adhesive is smaller than the dielectric constant ε2 of the second adhesive and the dielectric constant ε3 of the third adhesive.
Sensor.

(2) In (1) above, the dielectric constant ε1 is less than 3, and the dielectric constant ε2 and the dielectric constant ε3 are 3 or greater.

(3) In (1) or (2) above, the thickness of the third adhesive is greater than the thickness of the second adhesive.

(4) In (3) above, the thickness of the third adhesive is at least twice the thickness of the second adhesive.

(5) In any of (1) to (3) above, the device further includes a third electrode that is a ground electrode, and a fourth adhesive disposed between the second electrode and the third electrode.

(6) In any of (1) to (5) above, the device further comprises a display device and a fifth adhesive disposed between the second electrode and the display device, and the first electrode and the second electrode contain a transparent electrode material.

(7) In any of (1) to (5) above, the device further comprises a display device and a fifth adhesive disposed between the first electrode and the display device, the first adhesive connecting the touch panel and the display device.

The description of this embodiment is illustrative in all respects and is not restrictive. The scope of the present invention is indicated by the claims, not by the above-described embodiments. Furthermore, the scope of the present invention is intended to include all modifications that are equivalent in meaning to and within the scope of the claims.

1: Electronic device 2: Housing 3: Surface glass 4: Sensor 5: Display device 10: Sensor 11: Touch panel 12: First adhesive 13: First electrode 14: Second adhesive 15: Piezoelectric film 16: Third adhesive 17: Second electrode 18: Fourth adhesive 19: Third electrode 20: Fifth adhesive

Claims (7)

Touch panel and
A first electrode;
a piezoelectric film;
A second electrode;
a first adhesive disposed between the touch panel and the first electrode;
a second adhesive connected between the first electrode and the piezoelectric film;
a third adhesive disposed between the piezoelectric film and the second electrode;
A sensor comprising:
The dielectric constant ε1 of the first adhesive is smaller than the dielectric constant ε2 of the second adhesive and the dielectric constant ε3 of the third adhesive.
Sensor. The dielectric constant ε1 is less than 3, and the dielectric constant ε2 and the dielectric constant ε3 are 3 or more.
The sensor of claim 1 . The thickness of the third adhesive is greater than the thickness of the second adhesive.
The sensor according to claim 1 or 2. The thickness of the third adhesive is at least twice the thickness of the second adhesive.
The sensor of claim 3 . a third electrode that is a ground electrode;
a fourth adhesive disposed between the second electrode and the third electrode;
Further provided with
The sensor according to any one of claims 1 to 4. a display device;
a fifth adhesive disposed between the second electrode and the display device;
Equipped with
the first electrode and the second electrode include a transparent electrode material;
The sensor according to any one of claims 1 to 5. a display device;
a fifth adhesive disposed between the first electrode and the display device;
Equipped with
the first adhesive connects the touch panel and the display device;
The sensor according to any one of claims 1 to 5.