Vibration sensor

Abstract

The present invention suppresses deterioration of detection capability of a vibration sensor that uses liquid crystal.　This vibration sensor comprises: a first substrate and a second substrate disposed to face each other; a first electrode disposed on one surface of the first substrate; a second electrode disposed on one surface of the second substrate; and a liquid crystal layer disposed at least between the first electrode and the second electrode, and having spontaneous polarization. The liquid crystal layer is composed of a liquid crystal material that exhibits a nematic phase or a smectic A phase at room temperature, the liquid crystal material containing one or more types of liquid crystal molecules having a main backbone and first and second side-chain portions respectively located at two ends of the main backbone. In the liquid crystal molecules, the main backbone contains a quaterphenyl derivative, the first side-chain portion contains an alkoxy group having 2 to 5 carbon atoms, the second side-chain portion contains an alkyl group and / or an alkoxy group having 2 to 10 carbon atoms, and the main backbone has one or two fluorine groups.

Description

Vibration Sensor

[0001] The present disclosure relates to a vibration sensor (pressure sensor).

[0002] Japanese Patent No. 2709318 (Patent Document 1) describes a piezoelectric element in which a liquid crystal layer made of ferroelectric liquid crystal is disposed between a pair of substrates each having an electrode, and pressure is detected by utilizing changes in spontaneous polarization generated in the liquid crystal layer due to pressure. From the description in this document, it is believed that the ferroelectric liquid crystal in this piezoelectric element refers to a liquid crystal material exhibiting a chiral smectic C phase.

[0003] However, as is obvious to those skilled in the art, it is extremely difficult to stabilize the orientation state of the liquid crystal layer when using a liquid crystal material that exhibits a chiral smectic C phase. Therefore, when the orientation state of the liquid crystal layer is changed by applying pressure or vibration to be detected, the initial orientation state of the liquid crystal layer cannot be maintained. In other words, with continued use as a pressure or vibration sensor, the spontaneous polarization of the liquid crystal layer gradually decreases due to the orientation disorder of the liquid crystal layer, which in turn reduces the detection capability, leaving room for improvement.

[0004] Patent No. 2709318

[0005] One object of a specific aspect of the present disclosure is to provide a technique that can suppress a decrease in the detection capability of a vibration sensor that uses a liquid crystal.

[0006] A vibration sensor according to one aspect of the present disclosure includes: a first substrate and a second substrate arranged opposite each other; a first electrode arranged on one side of the first substrate; a second electrode arranged on one side of the second substrate; and a liquid crystal layer having spontaneous polarization and arranged at least between the first electrode and the second electrode, wherein the liquid crystal layer is constructed using a liquid crystal material including one or more types of liquid crystal molecules having a main skeleton and first side chain portions and second side chain portions present at both ends of the main skeleton, the liquid crystal material exhibiting a nematic phase or a smectic A phase at room temperature, and wherein the liquid crystal molecules have a main skeleton including a quaterphenyl derivative, the first side chain portion including an alkoxy group having 2 to 5 carbon atoms, and the second side chain portion including an alkyl group and / or an alkoxy group having 2 to 10 carbon atoms, and the main skeleton has one or two fluorine groups.

[0007] According to the above configuration, a technique is provided that can suppress a decrease in the detection capability of a vibration sensor that uses a liquid crystal.

[0008] FIG. 1 is a schematic cross-sectional view showing the configuration of a vibration sensor (pressure sensor) according to one embodiment. FIG. 2A is a schematic diagram showing an example of the structure of liquid crystal molecules constituting a liquid crystal layer. FIG. 2B is a diagram showing a specific example of the structure of liquid crystal molecules. FIGS. 3A and 3B are diagrams showing specific examples of the structure of liquid crystal molecules, respectively. FIGS. 4A and 4B are model diagrams illustrating the alignment state of a liquid crystal layer, respectively. FIG. 5 is a model diagram illustrating another alignment state of a liquid crystal layer. FIG. 6 is a diagram showing an example of an output voltage obtained when vibration is applied to the vibration sensor of this embodiment. FIG. 7 is a diagram showing an example of a circuit configuration for obtaining an output voltage. FIG. 8 is a diagram showing a measurement example of spontaneous polarization in the liquid crystal layer of a vibration sensor. FIG. 9 is a diagram showing a measurement example of X-ray diffraction in the liquid crystal layer of a vibration sensor.

[0009] 1 is a schematic cross-sectional view showing the configuration of a vibration sensor (pressure sensor) according to one embodiment. The vibration sensor 1 of this embodiment mainly comprises a first substrate 11 and a second substrate 12 arranged opposite each other, and a liquid crystal layer 17 arranged between them.

[0010] The first substrate 11 and the second substrate 12 are each a glass substrate, a resin film substrate, etc. The first substrate 11 and the second substrate 12 may be a transparent substrate or an opaque substrate depending on the application of the vibration sensor 1.

[0011] The first electrode 13 is provided on one surface side of the first substrate 11 (the side facing the second substrate 12). The second electrode 14 is provided on one surface side of the second substrate 12 (the side facing the first substrate 11). The first electrode 13 and the second electrode 14 may each be configured using a transparent conductive film such as an ITO (indium tin oxide) film, or may be configured using a metal film.

[0012] The first alignment film 15 is provided on one surface of the first substrate 11, more specifically on one surface of the first electrode 13 (the side facing the second substrate 12). The second alignment film 16 is provided on one surface of the second substrate 12, more specifically on one surface of the second electrode 14 (the side facing the first substrate 11).

[0013] For example, a horizontal alignment film for a general liquid crystal can be used as the first alignment film 15 and the second alignment film 16. At least one of the first alignment film 15 and the second alignment film 16 may be a vertical alignment film for a general liquid crystal. It is also preferable that the first alignment film 15 and the second alignment film 16 have been subjected to an alignment treatment such as a rubbing treatment.

[0014] The liquid crystal layer 17 is disposed between the first substrate 11 and the second substrate 12 so as to have interfaces in contact with the first alignment film 15 and the second alignment film 16. There are no particular limitations on the thickness of the liquid crystal layer 17, but it can be, for example, about 2 to 5 μm. A sealing material 18 is provided around the liquid crystal layer 17 for sealing.

[0015] The liquid crystal layer 17 has an initial alignment state (alignment state when no voltage is applied) that depends on the types of the first alignment film 15 and the second alignment film 16. For example, when both the first alignment film 15 and the second alignment film 16 are horizontal alignment films, the alignment state of the liquid crystal layer 17 becomes a homogeneous alignment.

[0016] When one of the first alignment film 15 and the second alignment film 16 is a horizontal alignment film and the other is a vertical alignment film, the alignment state of the liquid crystal layer 17 is a hybrid alignment. When both the first alignment film 15 and the second alignment film 16 are vertical alignment films, the alignment state of the liquid crystal layer 17 is a homeotropic alignment.

[0017] 2A is a diagram showing a schematic example of the structure of liquid crystal molecules constituting a liquid crystal layer. The liquid crystal molecules constituting the liquid crystal layer used in this embodiment are configured to include an elongated skeleton (main skeleton) 50, which is a rigid structural portion, and first and second side chains 51 and 52, which are flexible portions disposed at both ends of the skeleton 50 in the longitudinal direction.

[0018] The first side chain portion 51 is a side chain that is shorter than the second side chain portion 52, and is specifically an alkoxy group having 2 to 5 carbon atoms. The second side chain portion 52 is a relatively long alkyl group, and is specifically an alkyl group having 2 to 10 carbon atoms. Note that the second side chain portion 52 may partially be an alkoxy group.

[0019] The skeleton 50 has a structure including at least four cyclic structures such as benzene rings, cyclohexane rings, and pyrimidine rings. The skeleton 50 may have a structure including a mixture of benzene rings, cyclohexane rings, and pyrimidine rings. The total number of benzene rings and cyclohexane rings in the skeleton 50 is preferably four or five. In the present application, this skeleton 50 is referred to as a "quaterphenyl derivative." More specifically, the skeleton 50 has a structure in which, for example, four cyclic structures such as benzene rings and cyclohexane rings are arranged in a straight line. Alternatively, the skeleton 50 may have five cyclic structures arranged in a straight line. In this case, the skeleton 50 is composed of four benzene rings and one cyclohexane ring, with the cyclohexane ring being located closer to the second side chain 52.

[0020] Alternatively, one of the cyclic structural portions may be a pyrimidine ring. In this case, it is preferable that the pyrimidine ring is located at the end connected to the second side chain portion 52, and that the two nitrogen molecules are located on the opposite side from the second side chain portion 52.

[0021] Furthermore, the skeleton 50 has a fluorine group, which is a polar term, at the position of the second or third cyclic structural unit counting from the second side chain unit 52, i.e., at a position near the center of the skeleton 50 in the longitudinal direction. In this case, the number of fluorine groups may be one or two. By having such a fluorine group, a dipole moment is generated in the liquid crystal molecule in a direction closer to the lateral direction than the longitudinal direction. Here, the direction closer to the lateral direction means a direction in which the angle with the lateral direction is smaller than the angle with the longitudinal direction.

[0022] In summary, the liquid crystal molecular structure preferably has at least a quaterphenyl derivative as the skeleton 50, has one or two fluorine groups near the center of the skeleton 50, has a first side chain 51 that is a short alkoxy group (having 2 to 5 carbon atoms) and a second side chain 52 that is a long alkyl group (having 2 to 10 carbon atoms), and has the fluorine group formed on the third benzene ring counting from the second side chain 52. A portion of the second side chain 52 may be an alkoxy group.

[0023] FIG. 2B shows a specific example of a liquid crystal molecule structure that satisfies the above characteristics. The illustrated liquid crystal molecule has two fluorine groups on the third benzene ring, counting from the second side chain portion 52. In this liquid crystal molecule, a dipole moment m is generated in the minor axis direction of the liquid crystal molecule at the position of each fluorine group, as indicated by the dotted arrows in the figure. Note that, unlike the illustrated example, in a liquid crystal molecule with only one fluorine group, a dipole moment may be generated in a direction slightly tilted from the minor axis direction of the liquid crystal molecule depending on the position. Other specific examples of liquid crystal molecular structures are shown in FIG. 3A. FIG. 3A shows examples of a liquid crystal molecule with one fluorine group, a liquid crystal molecule with five ring structures, a liquid crystal molecule with a mixture of benzene and cyclohexane rings, and a liquid crystal molecule with a pyrimidine ring.

[0024] In this embodiment, the liquid crystal layer 17 is formed using a liquid crystal material containing liquid crystal molecules having the above-described characteristics. In a preferred embodiment, the liquid crystal layer 17 is formed using a liquid crystal material in which the temperature characteristics are adjusted so that the liquid crystal layer 17 can operate at room temperature (e.g., 25°C) by mixing multiple types of liquid crystal molecules having the above-described characteristics and different structures. For example, it is preferable to mix 10 or more types of liquid crystal molecules. In this case, the liquid crystal material forming the liquid crystal layer 17 can also be a mixture of liquid crystal molecules having a structure that does not have only the fluorine group among the above-described characteristics (see FIG. 3(B) as an example). In this embodiment, the liquid crystal layer 17 is formed including liquid crystal molecules having the structure illustrated in FIG. 3(A) and liquid crystal molecules having the structure illustrated in FIG. 3(B).

[0025] In this embodiment, the liquid crystal layer 17 is formed using liquid crystal molecules having the above structure and a liquid crystal material to which no chiral agent has been added. Liquid crystal molecules with the above characteristics do not have an asymmetric carbon in their molecular structure, so the liquid crystal layer 17 does not exhibit a chiral smectic C phase. Furthermore, when the liquid crystal layer 17 is formed using liquid crystal molecules with the above characteristics, a uniform alignment state is easily obtained, and alignment disturbance does not occur even when vibration or pressure is applied. Therefore, the liquid crystal layer 17 is considered to be a nematic phase with fluidity or a smectic A phase, which is a phase with low crystallinity (low order phase).

[0026] FIG. 4A is a model diagram illustrating the alignment state of a liquid crystal layer. The ellipsoids represent the schematic diagram of each liquid crystal molecule, and the arrows drawn in the minor axis direction of each liquid crystal molecule indicate the direction of the dipole moment. In the illustrated example, the first alignment film 15 and the second alignment film 16 are horizontal alignment films, and the alignment treatment directions R1 and R2 applied to each are parallel, resulting in a homogeneous alignment of the liquid crystal molecules in the liquid crystal layer 17. Furthermore, the liquid crystal layer 17 is in a smectic A phase, in which the liquid crystal molecules are aligned in a substantially unidirectional direction and have a layered structure in which they are aligned substantially parallel to the layer normal. The dipole moments of the liquid crystal molecules are aligned downward in the figure, resulting in a spontaneous polarization P in the liquid crystal layer 17 as a whole, in a substantially unidirectional direction. As shown in FIG. 4B, the liquid crystal layer 17 may also be in a nematic phase, in which the liquid crystal molecules are ordered in a substantially unidirectional direction but do not have a layered structure. The alignment treatment directions R1 and R2 may be anti-parallel.

[0027] Strictly speaking, it is conceivable that some of the liquid crystal molecules may have dipole moments pointing in other directions, such as opposite directions. Furthermore, when multiple types of liquid crystal molecules are mixed, the dipole moments may have slightly different orientations, specifically, the dipole moments of some liquid crystal molecules may be pointing downward and the dipole moments of other liquid crystal molecules may be pointing diagonally downward. Even in these cases, a relatively large proportion of liquid crystal molecules with dipole moments pointing downward or diagonally downward in the figure are likely to generate spontaneous polarization P in the liquid crystal layer 17 as a whole, pointing downward or diagonally downward in the figure. The reason for this asymmetry in the dipole moment direction may be that the liquid crystal molecules with the above-described characteristics have different side chains on both sides of the skeleton 50, which may make it easier for the liquid crystal molecules to align in the same direction.

[0028] Figure 5 is a model diagram illustrating another alignment state of the liquid crystal layer. The ellipsoids represent the schematic diagram of each liquid crystal molecule, and the arrows drawn in the minor axis direction of each liquid crystal molecule indicate the direction of the dipole moment. In the illustrated example, one of the first alignment film 15 and the second alignment film 16 is a horizontal alignment film and the other is a vertical alignment film. The alignment treatment direction R3 applied to the horizontal alignment film is to the right in the figure, resulting in a hybrid alignment of the liquid crystal molecules in the liquid crystal layer 17. In this case, the liquid crystal layer 17 does not exhibit a clear layer structure, and is considered to be in a nematic phase or a similar phase (an intermediate structure between nematic and smectic A phases). The direction of the dipole moment of each liquid crystal molecule changes continuously within the liquid crystal layer 17, and a spontaneous polarization P is generated in the liquid crystal layer 17 in the lower right direction in the figure.

[0029] It is also possible that, even in this model, some of the liquid crystal molecules have dipole moments pointing in opposite directions. Furthermore, when multiple types of liquid crystal molecules are mixed, the dipole moments may point in slightly different directions. Even in these cases, however, a relatively large proportion of liquid crystal molecules have dipole moments pointing downward or diagonally downward in the figure, which is likely to result in a spontaneous polarization P in the liquid crystal layer 17 as a whole that points diagonally downward in the figure.

[0030] FIG. 6 is a diagram showing an example of an output voltage obtained when vibration is applied to the vibration sensor of this embodiment. In the diagram, the vertical axis represents the output voltage, and the horizontal axis represents time. FIG. 7 is a diagram showing an example of a circuit configuration for detecting this output voltage. As shown in FIG. 7 , one end of the vibration sensor 1 (e.g., the first electrode 13) is connected to one end of a capacitance element 70, and the other end of the vibration sensor 1 (e.g., the second electrode 14) is connected to the other end of the capacitance element 70, thereby connecting the two elements as a whole in a closed loop, and an oscilloscope 71 is connected to both ends of the capacitance element 70. Then, the output voltage generated in the capacitance element 70 when vibration or pressure is applied to the vibration sensor 1 is observed using the oscilloscope 71.

[0031] At points a and b shown in Figure 6, pressure was applied for a relatively short time, and at points c, d, and e, pressure was applied for a relatively long time. As shown in the figure, the output voltage varies depending on the length of time the pressure is applied, and it can be seen that a longer pressure application time results in a higher output voltage. Also, at point f shown in Figure 6, a relatively strong pressure was applied for a relatively short time, and at point g, a pressure similar to that at point f was applied for a relatively short time. As can be seen from the figure, a longer pressure application time results in a higher output voltage. In other words, it can be seen that vibration or pressure can be detected by using the vibration sensor 1 of this embodiment.

[0032] FIG. 8 shows a measurement example of spontaneous polarization in a vibration sensor's liquid crystal layer. This example shows spontaneous polarization in a vibration sensor whose liquid crystal layer 17 is constructed using a liquid crystal material primarily containing the liquid crystal molecules illustrated in FIG. 2B. This liquid crystal material has phase transition temperatures near -20°C, 80°C, and 108°C. It exhibits an isotropic phase (I phase) at temperatures above 108°C, a nematic phase between 80°C and 108°C, a smectic A phase between -20°C and 80°C, and a higher-order smectic phase (e.g., smectic C phase) or a crystalline phase below -20°C. As shown in the figure, the material exhibits hysteresis characteristics associated with polarization reversal, and exhibits a relatively large value of spontaneous polarization.

[0033] Figure 9 shows an example of X-ray diffraction measurement of the liquid crystal layer of a vibration sensor. This figure shows an example of spontaneous polarization measurement in a vibration sensor in which the liquid crystal layer 17 is constructed using a liquid crystal material primarily containing the liquid crystal molecules illustrated in Figure 2(B) above. The measurement temperature was 17°C. The other graph in the figure shows an expanded range up to a diffraction intensity of 0.5. Analysis based on the diffraction peaks estimates 2θ = 3.25° and molecular length d = 27.1 Å. This molecular length d is approximately equal to the actual molecular length of the liquid crystal molecules, 27.8 Å (see Figure 2(B)). Therefore, it is estimated that the liquid crystal molecules in the liquid crystal layer 17 are arranged in a monolayer structure rather than a bilayer structure.

[0034] Hereinafter, several examples of vibration sensors and comparative examples will be described.

[0035] Example 1: A vibration sensor was fabricated using a 1.1 mm thick glass substrate as the first substrate 11 and a 0.7 mm thick glass substrate as the second substrate 12. The cell thickness (liquid crystal layer thickness) was 2 μm. The first electrode 13 and the second electrode 14 were each constructed of an ITO film, with the overlapping area of ​​the two electrodes measuring 15 mm x 15 mm in a planar view. The first alignment film 15 and the second alignment film 16 were each horizontal alignment films, and were subjected to rubbing treatment under rubbing conditions commonly known to those skilled in the art. The first substrate 11 and the second substrate 12 were arranged so that the respective alignment directions were antiparallel. The liquid crystal material constituting the liquid crystal layer 17 was a liquid crystal material primarily containing the liquid crystal molecules illustrated in FIG. 2B above. The injection temperature during formation of the liquid crystal layer 17 was 105°C. In other words, the liquid crystal was injected in the nematic phase. A pressure of 7 N was applied to the vibration sensors of each example for the same period, and their output voltages were measured. The capacitance of the capacitive element 70 in the detection circuit (see FIG. 7) was 100 nF (the same applies to the other examples described below). Comparing the examples, the example using a 0.7 mm thick glass substrate produced a higher output voltage. This is thought to be because using a thinner glass substrate allows pressure (vibration) to be more easily transmitted to the liquid crystal layer, resulting in a greater change in alignment in the liquid crystal layer. Furthermore, no alignment disturbance occurred in the liquid crystal layer 17 even after pressure was applied (the same applies to the other examples described below).

[0036] Example 2 Vibration sensors were fabricated under the same conditions as in Example 1, using 0.7 mm thick glass substrates as the first substrate 11 and the second substrate 12. However, the injection temperature during formation of the liquid crystal layer 17 was divided into three patterns: 85°C, 105°C, and 125°C. Vibration sensors were fabricated for each. A pressure of 7 N was applied to each vibration sensor for the same period of time, and the output voltages were measured. The vibration sensor fabricated at an injection temperature of 105°C produced the largest output voltage, while the vibration sensor fabricated at an injection temperature of 125°C produced the smallest output voltage. In other words, a tendency was observed in which a higher output voltage was obtained for the same pressure conditions when the liquid crystal material was injected in the nematic phase than when it was injected in the isotropic phase. This suggests that the injection temperature is preferably set to a temperature that exhibits the nematic phase.

[0037] (Example 3) Under the same conditions as Example 2, vibration sensors were fabricated in four patterns: an injection temperature of 105°C with a parallel alignment treatment direction, an injection temperature of 105°C with an anti-parallel alignment treatment direction, an injection temperature of 125°C with a parallel alignment treatment direction, and an injection temperature of 125°C with an anti-parallel alignment treatment direction. A pressure of 7 N was applied to the vibration sensors of each example for the same period of time, and their output voltages were detected. In a comparison at an injection temperature of 105°C, the parallel alignment vibration sensor produced a higher output voltage. On the other hand, in a comparison at an injection temperature of 125°C, the anti-parallel alignment vibration sensor produced a higher output voltage. In a comparison between the anti-parallel alignments, the 105°C injection temperature vibration sensor produced a higher output voltage. From these results, it can be said that the injection temperature is more preferably a condition that results in injection in the nematic phase.

[0038] (Example 4) Under the same conditions as Example 2, vibration sensors were fabricated in four patterns: an injection temperature of 105°C and a cell thickness of 2 μm, an injection temperature of 105°C and a cell thickness of 4 μm, an injection temperature of 125°C and a cell thickness of 2 μm, and an injection temperature of 125°C and a cell thickness of 4 μm. All orientation treatment directions were anti-parallel. When the injection temperature was 125°C, a decrease in output voltage was observed in both the vibration sensors with cell thicknesses of 2 μm and 4 μm. When the injection temperature was 105°C, a relatively large output voltage was obtained for each cell thickness, and almost no difference due to cell thickness was observed.

[0039] (Example 5) A vibration sensor was fabricated using 50 μm-thick polyamide film substrates as the first substrate 11 and the second substrate 12. Furthermore, in this example, the first alignment film 15 and the second alignment film 16 were not provided, and no alignment treatment was performed on either side of the first substrate 11 or the second substrate 12. The cell thickness was 4 μm. Other conditions were the same as in Example 1. A pressure of 7 N was applied to the vibration sensor of this example for the same period of time, and the output voltages were detected. A relatively large output voltage was obtained. Furthermore, compared to the vibration sensors of Examples 1 to 4, which used glass substrates, the output voltage had less noise and a high S / N ratio. It can be seen that the output voltage can be increased by using a thin, flexible resin film substrate.

[0040] Example 6 A vibration sensor was fabricated under the same conditions as in Example 5, with a 0.7 mm thick glass substrate placed on either the first substrate 11 side alone or on the outside of both the first substrate 11 and the second substrate 12. The glass substrate and the polyamide film substrate were bonded together with an adhesive. A pressure of 7 N was applied to the vibration sensor of this example for the same period of time, and the output voltages were measured. The output voltages were low.

[0041] (Example 7) A vibration sensor was fabricated using 0.7 mm thick glass substrates as the first substrate 11 and the second substrate 12. The cell thicknesses were 2 μm and 4 μm. A horizontal alignment film was used for the first alignment film 15, and a rubbing treatment was performed under rubbing conditions commonly known by those skilled in the art. A vertical alignment film was used for the second alignment film 16, and no alignment treatment such as rubbing was performed. The other conditions were the same as in Example 1. A pressure of 7 N was applied to the vibration sensors of each example for the same period of time, and their output voltages were detected. When comparing the vibration sensors of each example, there was almost no difference in output voltage due to differences in cell thickness. A larger output voltage was obtained compared to examples such as Example 1, in which the liquid crystal layer 17 was homogeneously aligned.

[0042] (Comparative Example) As a comparative example, a vibration sensor was fabricated using a liquid crystal layer aligned in a surface-stabilized manner using a liquid crystal material (i.e., a ferroelectric liquid crystal material) exhibiting a chiral smectic C phase at room temperature. 0.7 mm-thick glass substrates were used as the first substrate 11 and the second substrate 12. The cell thickness was 2 μm. The first electrode 13 and the second electrode 14 were each composed of an ITO film, with the overlapping area of ​​the two electrodes measuring 15 mm x 15 mm in a planar view. The first alignment film 15 and the second alignment film 16 were each horizontal alignment films, and were subjected to rubbing treatment under rubbing conditions commonly known to those skilled in the art. The first substrate 11 and the second substrate 12 were positioned so that the orientation directions of the respective substrates were antiparallel. A pressure of 90 N was applied to this vibration sensor in eight separate sessions, each for 15 seconds, and the resulting output voltage was measured. Compared to the output voltage at the start of pressure application, the output voltage after 15 seconds of pressure application decreased to less than one-fifth. Furthermore, the alignment of the liquid crystal layer 17 was disturbed, and the alignment did not return to normal even after the pressure was removed.

[0043] As described above, according to the above-described embodiment and examples, a technique is provided that can suppress a decrease in the detection capability of a vibration sensor that uses a liquid crystal.

[0044] In detail, in the vibration sensors of the embodiments, compared to conventional sensors using liquid crystal materials exhibiting chiral smectic C phase, the use of liquid crystal materials exhibiting a lower order phase, smectic or nematic, makes it easier to obtain a uniform alignment state in the liquid crystal layer, and has a high ability to restore the original alignment state even after the alignment state is disturbed when pressure or vibration is applied, making it possible to suppress a decrease in detection ability.

[0045] Furthermore, in conventional vibration sensors using inorganic materials such as barium titanate, the inorganic material layer used for detection is hard and has a small amount of displacement in response to pressure, etc., making it unsuitable for flexible applications that require flexibility and a large shrinkage rate, whereas the vibration sensors of the embodiments and the like are suitable for flexible applications due to the flexibility (fluidity) of the liquid crystal layer. Furthermore, in conventional vibration sensors using organic piezoelectric materials such as PVDF (polyvinylidene fluoride polymer), a poling process is required to polarize the piezoelectric layer, but in the vibration sensors of the embodiments and the like, the liquid crystal layer has spontaneous polarization, so poling does not necessarily have to be performed.

[0046] Furthermore, the vibration sensors of the embodiments and the like can be mass-produced using processes that are almost identical to the manufacturing processes for conventional liquid crystal elements, and have the advantage that a stable alignment state of the liquid crystal layer can be easily obtained, resulting in little variation in the characteristics (performance) of individual units.

[0047] The vibration sensor according to the present disclosure can be easily made flexible and can be used, for example, to measure pulse, pulse waves, and blood pressure, and can also be used to detect pressure and vibration in various situations other than biological detection.

[0048] It should be noted that the present disclosure is not limited to the contents of the above-described embodiments, and various modifications can be made within the scope of the gist of the present disclosure. For example, the device conditions and process conditions shown in the above-described embodiments are merely examples, and are not intended to limit the scope of the present disclosure.

[0049] The present disclosure has the following additional features: (Additional Note 1) A vibration sensor comprising: a first substrate and a second substrate arranged opposite each other; a first electrode arranged on one side of the first substrate; a second electrode arranged on one side of the second substrate; and a liquid crystal layer having spontaneous polarization and arranged at least between the first electrode and the second electrode, wherein the liquid crystal layer is formed using a liquid crystal material containing one or more types of liquid crystal molecules having a main skeleton and first and second side chain portions located at both ends of the main skeleton, the liquid crystal material exhibiting a nematic phase or a smectic A phase at room temperature, the main skeleton of the liquid crystal molecules containing a quaterphenyl derivative, the first side chain portion containing an alkoxy group having 2 to 5 carbon atoms, and the second side chain portion containing an alkyl group and / or an alkoxy group having 2 to 10 carbon atoms, and the main skeleton containing one or two fluorine groups. (Supplementary Note 2) The vibration sensor according to Supplementary Note 1, wherein the main skeleton of the liquid crystal molecule has four cyclic structural parts arranged in a line, and the four cyclic structural parts are composed of four benzene rings, three benzene rings and one cyclohexane ring, or two benzene rings and two cyclohexane rings. (Supplementary Note 3) The vibration sensor according to Supplementary Note 1, wherein the main skeleton of the liquid crystal molecule has four cyclic structural parts arranged in a line, and the four cyclic structural parts are composed of three benzene rings and one pyrimidine ring. (Supplementary Note 4) The vibration sensor according to Supplementary Note 1, wherein the main skeleton of the liquid crystal molecule has five cyclic structural parts arranged in a line, and the five cyclic structural parts are composed of four benzene rings and one cyclohexane ring. (Supplementary Note 5) The vibration sensor according to Supplementary Note 2 or 3, wherein the fluorine group is included in the second cyclic structural part counting from the first side chain part. (Supplementary Note 6) The vibration sensor according to Supplementary Note 4, wherein the fluorine group is located in the third cyclic structure counting from the first side chain portion. (Supplementary Note 7) The vibration sensor according to Supplementary Note 2 or 4, wherein the cyclohexane ring is located on a side closer to the second side chain portion. (Supplementary Note 8) The vibration sensor according to Supplementary Note 3, wherein the pyrimidine ring is located at a position connected to the second side chain portion, and two nitrogen molecules of the pyrimidine ring are located on the opposite side to the second side chain portion.(Supplementary Note 9) The vibration sensor according to any one of Supplementary Notes 1 to 8, comprising: a first alignment film provided to cover the first electrode; and a second alignment film provided to cover the second electrode, wherein the first alignment film and the second alignment film are both horizontal alignment films. (Supplementary Note 10) The vibration sensor according to any one of Supplementary Notes 1 to 8, comprising: a first alignment film provided to cover the first electrode; and a second alignment film provided to cover the second electrode, wherein the first alignment film is a horizontal alignment film and the second alignment film is a vertical alignment film.

[0050] 1: vibration sensor (pressure sensor), 11: first substrate, 12: second substrate, 13: first electrode, 14: second electrode, 15: first alignment film, 16: second alignment film, 17: liquid crystal layer, 18: sealing material, 50: skeleton, 51: first side chain, 52: second side chain

Claims

1. A vibration sensor comprising: a first substrate and a second substrate arranged opposite each other; a first electrode arranged on one side of the first substrate; a second electrode arranged on one side of the second substrate; and a liquid crystal layer having spontaneous polarization and arranged at least between the first electrode and the second electrode, wherein the liquid crystal layer is constructed using a liquid crystal material containing one or more types of liquid crystal molecules having a main skeleton and first and second side chains located at both ends of the main skeleton, the liquid crystal material exhibiting a nematic phase or a smectic A phase at room temperature, wherein the main skeleton of the liquid crystal molecules contains a quaterphenyl derivative, the first side chains contain alkoxy groups having 2 to 5 carbon atoms, and the second side chains contain alkyl and / or alkoxy groups having 2 to 10 carbon atoms, and the main skeleton has one or two fluorine groups.

2. The vibration sensor according to claim 1, wherein the main skeleton of the liquid crystal molecule has four ring structures arranged in a straight line, and the four ring structures are composed of either four benzene rings, three benzene rings and one cyclohexane ring, or two benzene rings and two cyclohexane rings.

3. The vibration sensor according to claim 1, wherein the main skeleton of the liquid crystal molecule has four linearly arranged ring structures, and the four ring structures are composed of three benzene rings and one pyrimidine ring.

4. The vibration sensor according to claim 1, wherein the main skeleton of the liquid crystal molecule has five ring structures arranged in a straight line, and the five ring structures are composed of four benzene rings and one cyclohexane ring.

5. The vibration sensor according to claim 2 or 3, wherein the fluorine group is present in the second ring structure portion counting from the first side chain portion.

6. The vibration sensor according to claim 4, wherein the fluorine group is located in the third ring structure portion counting from the first side chain portion.

7. The vibration sensor according to claim 2 or 4, wherein the cyclohexane ring is arranged on a side closer to the second side chain portion.

8. The vibration sensor according to claim 3, wherein the pyrimidine ring is located at a position where it is connected to the second side chain portion, and the two nitrogen molecules of the pyrimidine ring are located on the opposite side of the second side chain portion.

9. The vibration sensor according to claim 1, comprising: a first alignment film provided to cover the first electrode; and a second alignment film provided to cover the second electrode, wherein the first alignment film and the second alignment film are both horizontal alignment films.

10. The vibration sensor according to claim 1, comprising: a first alignment film provided to cover the first electrode; and a second alignment film provided to cover the second electrode, wherein the first alignment film is a horizontal alignment film and the second alignment film is a vertical alignment film.

Images