Liquid crystal drive structure, reflect array, phase shifter, phased array antenna

Abstract

The present invention makes it possible to increase the falling response time of a thick-film liquid crystal, to reduce a driving voltage, etc.　An electric field in a first direction based on a potential difference between electrodes provided to sandwich a liquid crystal layer and to face each other in the first direction orthogonal to the liquid crystal layer, and / or an electric field in a second direction based on a potential difference between electrodes provided at a predetermined distance from each other in the second direction parallel to the liquid crystal layer is applied to the liquid crystal layer to change the high-frequency dielectric constant.

Description

Liquid crystal drive structure, reflect array, phase shifter, phased array antenna

[0001] The present invention relates to a liquid crystal driving structure, for example, a liquid crystal driving structure for a high frequency wireless communication element.

[0002] In recent years, communication methods beyond 5G have attracted attention because they enable simultaneous connection of multiple terminals and faster data transmission speeds. However, as communication methods beyond 5G use higher frequencies, the reception area of ​​radio waves (electromagnetic waves) becomes limited. The reason for the narrow reception area is that millimeter waves emitted from base stations have very high frequencies, resulting in weak diffraction and preventing them from getting around buildings, trees, automobiles, and other moving objects. To solve the problem of blind zones caused by obstacles outside the line of sight, the use of reflect arrays (RAs, hereinafter referred to as "RAs") has attracted attention.

[0003] One possible approach, described in detail below, is to control the orientation of liquid crystal molecules using a low-frequency AC voltage based on phase control utilizing the dielectric anisotropy of nematic liquid crystals, thereby controlling the reflected beam of high-frequency electromagnetic waves. However, a thicker liquid crystal layer is generally required to effectively change the dielectric constant of the liquid crystal. As a result, problems such as a very long fall response time of the liquid crystal molecules have been reported. To address this issue, methods using polymer-dispersed liquid crystals or polymer-stabilized liquid crystals have been reported (see, for example, Patent Document 1). However, due to the high proportion of polymer material in the liquid crystal layer and the dense dispersion of the polymer structure, problems such as an increase in driving voltage and a decrease in the amount of phase modulation are unavoidable.

[0004] Patent No. 6090482

[0005] The present invention has been made in view of the above-mentioned problems, and one of its objects is to propose a liquid crystal driving structure that can realize a faster fall response time and a reduced driving voltage in a thick-film liquid crystal.

[0006] According to one aspect of the present invention, the liquid crystal driving structure applies to the liquid crystal layer at least one of an electric field in a first direction based on a potential difference between electrodes arranged opposite to each other in a first direction perpendicular to the liquid crystal layer and an electric field in a second direction based on a potential difference between electrodes arranged at a predetermined interval in a second direction parallel to the liquid crystal layer, thereby changing the high-frequency dielectric constant. According to another aspect of the present invention, the liquid crystal driving structure described above may be included in a reflectarray, a phase shifter, or a phased array antenna for controlling high-frequency electromagnetic waves.

[0007] According to the present invention, it is possible to achieve a faster fall response time and a reduced driving voltage in thick-film liquid crystal.

[0008] Schematic diagram of an expansion of a communication area using a reflectarray. Conceptual diagram of the operating principle of a reflectarray. (1) A diagram showing the operating principle (vertical electric field driving) of a bidirectional electric field driven element according to an embodiment. (2) A diagram showing the operating principle (lateral electric field driving) of a bidirectional electric field driven element according to an embodiment. (1) A diagram showing an example of the configuration of an element for measuring response time using a bidirectional electric field driven element according to an embodiment. (2) A diagram showing an example of the configuration of a comb-tooth electrode. (1) A diagram showing an example of the time characteristics of transmitted light intensity when a transverse electric field and a longitudinal electric field are applied. (2) A diagram showing an example of the time characteristics of transmitted light intensity when a longitudinal electric field and a transverse electric field are applied. A diagram showing an example of an image in which hue is distributed according to the director tilt angle of liquid crystal molecules. A diagram showing an example of an image in which hue is distributed according to the director tilt angle of liquid crystal molecules. A diagram showing an example of a graph in which capacitance change is measured. Conceptual diagram of dielectric constant change according to electrode pitch. (1) A diagram showing an example of the structure of a device to which a bidirectional electric field driven element according to an embodiment is applied. (2) A diagram showing another example of the structure of a device to which a bidirectional electric field driven element according to an embodiment is applied.

[0009] An example of an embodiment of the present invention will now be described with reference to the drawings. The components described in this embodiment are merely examples and are not intended to limit the scope of the present invention.

[0010] In this embodiment, we propose a two-way electric field driving method for a thick-film liquid crystal device for a millimeter-wave phase-modulating reflective array. As a result, we show that high-speed response and improved phase modulation of liquid crystal molecules are possible by designing the electrode shape and elastic orientation behavior.

[0011] As mentioned above, communication methods beyond 5G have been attracting attention in recent years because they enable simultaneous connection of multiple terminals and faster data transmission speeds. However, communication methods beyond 5G limit the radio wave reception area. The reason for the narrow reception area is that millimeter waves emitted from base stations have very high frequencies, which result in weak diffraction and prevent signals from getting around buildings, trees, and other structures. To solve the problem of blind zones, the use of RA, for example, has attracted attention.

[0012] Figure 1 shows a schematic diagram of expanding a communication area using RA, and Figure 2 shows a conceptual diagram of RA. As shown in Figure 1, RA enables communication in areas beyond line-of-sight by reflecting millimeter waves transmitted from a base station. To track moving devices, the beam direction must be swung. Therefore, as shown in Figure 2, reflectors are periodically arranged, and the phase of the scattered waves is changed by changing the electrical length of each element. This allows for arbitrary control of the direction of the reflected beam. As a typical example of phase control, research has been conducted on modulating the phase of radio waves by using varactor diodes as reflectors to change the capacitance. However, when using varactor diodes, the semiconductor's resistance loss is large at high frequencies. Furthermore, their nonlinear characteristics distort the current, generating harmonics, which can potentially interfere with other frequency bands.

[0013] Therefore, the present inventors focused on phase control utilizing the dielectric anisotropy of nematic liquid crystals. This method is characterized by controlling the orientation of liquid crystal molecules using a low-frequency AC voltage, thereby controlling the direction of the reflected beam. However, a thick liquid crystal layer (50 μm or thicker) is generally required to effectively change the dielectric constant of the liquid crystal. As a result, the fall response time of the liquid crystal molecules becomes very long. To address this issue, devices using polymer-dispersed liquid crystals or polymer-stabilized liquid crystals have been reported. However, these devices have problems such as increased driving voltage and reduced phase modulation due to the dense polymer structure and high proportion of polymer material in the liquid crystal layer.

[0014] Specifically, a high driving voltage of, for example, 100 V or more is required. One method for performing fine division driving within the element plane of the RA is to adopt a driving method (active driving method) in which transistors are used to drive the liquid crystal element, but the increase in driving voltage is a major obstacle.

[0015] Therefore, in this embodiment, in order to enable high-speed response and to simultaneously suppress the driving voltage and ensure the amount of phase modulation, a bidirectional electric field driving structure is proposed that uses electrodes (e.g., comb-shaped electrodes) provided at a predetermined interval on one side of the liquid crystal layer. In this embodiment, a liquid crystal element incorporating the bidirectional electric field driving structure is proposed, and the basic operation of the liquid crystal orientation change of the fabricated element is evaluated.

[0016] 2. Operating principle of two-way electric field drive structure The return of alignment (relaxation of molecular alignment) of a liquid crystal element when the electric field is generally removed is achieved by the alignment restraint force generated from the surface of the alignment film and the elastic effect of the liquid crystal alignment. The fall response time when an alignment restraint force is applied is proportional to the square of the thickness of the liquid crystal layer. Here, we will explain the principle of two-way electric field drive elements.

[0017] For convenience, horizontal alignment films (e.g., films with abrasion-treated surfaces made of thin polymer films such as polyimide) are provided on the upper and lower substrates, and the initial alignment state of the liquid crystal molecules is set to a horizontal orientation. The term "rising" refers to aligning the liquid crystal molecules vertically (vertical alignment), and the term "falling" refers to returning the liquid crystal molecules from the vertical alignment state to the initial alignment (horizontal alignment).

[0018] FIG. 3 illustrates the operating principle of the bidirectional electric field-driven element 1 according to this embodiment. As shown in FIG. 3, the bidirectional electric field-driven element 1 is configured such that a voltage is applied between vertically arranged electrodes or horizontally arranged electrodes by a low-frequency AC power supply 10, which generates a bias voltage for driving the liquid crystal. The resulting electric field acts on the liquid crystal layer. Although an AC power supply is used in this embodiment, the alignment of the liquid crystal molecules may also be controlled by a DC power supply. For example, a vertical electric field is applied during startup, as shown in FIG. 3(1), and a horizontal electric field is applied during shutdown (when returning from a vertically aligned state to the initial alignment), as shown in FIG. 3(2). The application of these electric fields speeds up the shutdown response, which is a key feature of the proposed bidirectional electric field-driven structure. Furthermore, because no polymeric material is added to the liquid crystal layer, a reduced drive voltage is expected.

[0019] More specifically, the liquid crystal driving structure in this embodiment applies at least one of the following electric fields to the liquid crystal layer: an electric field in a first direction based on a potential difference between electrodes arranged opposite each other in a first direction perpendicular to the liquid crystal layer, and an electric field in a second direction based on a potential difference between electrodes arranged at a predetermined interval in a second direction parallel to the liquid crystal layer.

[0020] Here, the first direction may be a direction perpendicular to the liquid crystal layer (vertical direction, lengthwise direction), and the second direction may be a direction parallel to the liquid crystal layer (parallel direction, horizontal direction). Note that the directions do not have to be strictly perpendicular or parallel, but may be approximately perpendicular or parallel. Furthermore, it is sufficient that the electrodes are arranged in a positional relationship in which they face each other across the liquid crystal layer in the first direction perpendicular to the liquid crystal layer, and that the electrodes are arranged at a predetermined interval in the second direction parallel to the liquid crystal layer.

[0021] In the liquid crystal drive structure of this embodiment, electrodes are provided at a predetermined interval on one of the upper and lower substrates so that electric fields are applied in two directions, the first direction and the second direction. In other words, stripe-shaped electrodes (stripe electrodes) are provided on one of the substrates. These electrodes are used for horizontal drive and may be referred to as "horizontal drive electrodes" for convenience. The predetermined interval at which these horizontal drive electrodes are provided may be referred to as the "electrode pitch" or simply the "pitch." As an example, a substrate made of a transparent material such as a glass substrate may be used as the substrate. However, this is not limited thereto, and materials such as resin (including synthetic resin) may also be used. Furthermore, the substrate does not necessarily have to be transparent to visible light, but a material with low dielectric loss at high frequencies is preferable.

[0022] 3 , for example, a first substrate layer LA is configured above the liquid crystal layer LL, and includes a substrate 11 (a glass substrate, for example), lateral drive electrodes (first electrodes) 13 provided on the substrate 11 at an inter-electrode pitch, and an alignment film (horizontal alignment film) 16 configured to cover the lateral drive electrodes 13. Also, a second substrate layer LB is configured below the liquid crystal layer LL, and includes the substrate 11, electrodes 15 provided on the substrate 11, and an alignment film 16 configured to cover the electrodes 15.

[0023] For example, the electrode 15 connected to ground is connected to the power supply ground side of the low-frequency AC power supply 10. Of adjacent transverse drive electrodes 13, 13, one transverse drive electrode 13 is connected to the output side of the low-frequency AC power supply 10 without using a switch SW, and the other transverse drive electrode 13 can be connected to the output terminal of the low-frequency AC power supply 10 or the ground terminal via the switch SW. Control of the switch SW switches the connection destination of the other transverse drive electrode 13 to the output terminal of the low-frequency AC power supply 10 or the ground terminal. A state in which the other transverse drive electrode 13 is connected to the output terminal of the low-frequency AC power supply 10 is defined as a first state of the switch SW, and a state in which the other transverse drive electrode 13 is connected to the ground terminal is defined as a second state of the switch SW. In the first state of the switch SW, voltages are applied from the one and other transverse drive electrodes 13 to the electrodes 15. In the second state of the switch SW, the application of voltage from the other horizontal drive electrode 13 to the electrode 15 is released, and voltage is applied from one horizontal drive electrode 13 to the other horizontal drive electrode 13 .

[0024] For example, as shown in Fig. 3A , during startup, by setting the switch SW to the first state, an electric field in a first direction is formed based on the potential difference between each horizontal drive electrode 13 and electrode 15. This electric field acts on the liquid crystal layer LL, aligning the liquid crystal molecules in the first direction. On the other hand, as shown in Fig. 3B , during shutdown, by setting the switch SW to the second state, an electric field in a second direction (an electric field in a direction from one horizontal drive electrode 13 to the other horizontal drive electrode 13) is formed based on the potential difference between the horizontal drive electrodes 13 provided at the inter-electrode pitch. This electric field acts on the liquid crystal layer LL, aligning the liquid crystal molecules in the second direction. In this way, by switching the switch SW, either the electric field in the first direction or the electric field in the second direction can be applied to the liquid crystal layer LL (the electric field in the first direction or the electric field in the second direction can be selectively applied to the liquid crystal layer LL).

[0025] In this example, even when the switch SW is in the second state, the output side of the low-frequency AC power supply 10 is connected to one of the adjacent horizontal drive electrodes 13, 13, and the ground side is connected to the electrode 15, so that an electric field component in the first direction exists.

[0026] Here, when the switch SW is in the second state, the electrode 15 may be switched to a state where it is not connected to ground. This makes it possible to minimize the effect of the electric field component in the first direction on the liquid crystal layer LL in the second state to a level where it can be almost ignored. Even when the electrode 15 is connected to ground in the second state, it is possible to significantly minimize the effect of the electric field component in the first direction on the liquid crystal layer LL by adjusting the applied voltage. That is, by setting the switch SW to the first state, it is possible to apply only the electric field component in the first direction to the liquid crystal layer LL. By setting the switch SW to the second state, it is possible to apply only the electric field component in the second direction to the liquid crystal layer LL, or to apply both the electric field component in the first direction and the electric field component in the second direction to the liquid crystal layer LL. In this way, by controlling the switch SW, it is possible to apply at least one of the electric field in the first direction and the electric field in the second direction to the liquid crystal layer LL.

[0027] This configuration allows voltage driving for both the rising and falling edges without using elastic relaxation of the liquid crystal alignment, significantly shortening the response time. For example, even with a liquid crystal layer as thick as 100 μm, a response time of several tens of milliseconds can be achieved.

[0028] 3. Response time measurement using a bidirectional electric field-driven element 3.1 Element structure Figure 4 shows an example of the structure of an element used to measure the response time using a bidirectional electric field-driven element. For example, an element as shown in Figure 4(1) was fabricated. Specifically, a bidirectional electric field-driven element was fabricated using a glass substrate with comb-shaped electrodes. The comb-shaped electrodes may be one example of the above-mentioned lateral drive electrode 13, and may be configured as shown in Figure 4(2), for example. The width of the comb-shaped electrodes is called the "electrode width," and the spacing between the electrodes is called the "electrode pitch" (described above).

[0029] It may be difficult to switch between the vertical and horizontal electric fields due to the limitations of the capacitance measurement system. Therefore, in addition to the bidirectional electric field driving element having the structure proposed in this embodiment, an element capable of applying a horizontal electric field to a liquid crystal cell made of a substrate coated with a vertical alignment film may be fabricated.

[0030] As an example, a parallel alignment film was applied to a comb-tooth electrode substrate with comb-tooth electrodes as lateral drive electrodes 13, a parallel alignment film was applied to a full-surface electrode substrate with electrodes 15, and a 50 μm-thick Mylar film spacer was used to create an empty cell (the gap between the glass substrates). A nematic liquid crystal with positive dielectric anisotropy was then injected into the cell. (Negative dielectric anisotropy nematic liquid crystals can also be used; in this case, the liquid crystal molecules are driven perpendicular to the electric field.) This resulted in a liquid crystal layer thickness of 50 μm. The dimensions of the comb-tooth electrodes were set to 10 μm and 50 μm interelectrode pitches and 10 μm widths. To compare response times, a parallel alignment film was applied to a uniform electrode substrate, and two upper and lower electrode substrates were fabricated. Liquid crystal cells were fabricated using the same process (this serves as a reference sample). Because impedance matching must be considered when applying a high-frequency voltage, a low-frequency bias voltage was applied in this experiment to evaluate the response time of transmitted light intensity, which depends on the spatial alignment disorder of the liquid crystal layer. This utilizes the phenomenon that incident light is scattered due to spatial disturbance of the orientation during in-plane switching, weakening the transmitted light that travels straight ahead.

[0031] 3.2 Response time measurement system and experimental conditions To measure the transmitted light intensity, the element is irradiated with light from a halogen lamp using an optical microscope. The intensity of the transmitted light to the liquid crystal layer is converted into a voltage waveform and observed. The response time can be measured from the amount of change in transmitted light intensity when the direction of the electric field applied to the liquid crystal layer in a bidirectional electric field driven element is switched. The applied voltage was a square wave of 1 kHz (duty ratio 50%).

[0032] The response when the electric field direction applied to the liquid crystal layer is switched from horizontal to vertical is defined as the vertical electric field response time (vertical electric field response time), and the response when switching from vertical to horizontal is defined as the horizontal electric field response time (horizontal electric field response time). The driving voltage value was 30 Vrms. The response time was defined as the time when the change in light intensity converged to 90% or more after voltage application.

[0033] 3.3 Evaluation of response time measurement results The response time measurement results for the reference sample are summarized in Table 1. For comparison with the proposed structure, a general liquid crystal device with full-surface electrode substrates on both the top and bottom sides was used as the reference sample, and the measured response time is listed.

[0034] Figure 5 also shows the time characteristics of transmitted light intensity when longitudinal and transverse electric fields are applied. As shown in Figure 5(1), the longitudinal electric field response time of the bidirectional electric field-driven element is 177 ms when the electrode pitch is 10 μm and 35 ms when the electrode pitch is 50 μm. As shown in Figure 5(2), the transverse electric field response time of the bidirectional electric field-driven element is 3 ms when the electrode pitch is 10 μm and 49 ms when the electrode pitch is 50 μm. The transverse electric field response time of the bidirectional electric field-driven element with an electrode pitch of 50 μm was approximately 480 times faster than that of the reference sample (falling edge response time of the reference sample in Table 1: 24,000 ms, bidirectional electric field-driven element with a pitch of 50 μm: transverse electric field: 49 ms). These results confirm that voltage application during the falling edge enables high-speed response of liquid crystal molecules.

[0035] However, from the above results, it was found that the device with an inter-electrode pitch of 50 μm took approximately 16 times longer to respond to the transverse electric field than the device with an inter-electrode pitch of 10 μm (Table 1: bidirectional electric field drive element with a pitch of 50 μm: transverse electric field 49 ms, and with a pitch of 10 μm: transverse electric field 3 ms). Under the same applied voltage conditions, the longer the inter-electrode pitch, the weaker the electric field strength, which is thought to be the reason for the slower response due to the weakened effect of the electric field on the driving of the liquid crystal.

[0036] 4 Evaluation of liquid crystal alignment state 4.1 Evaluation of liquid crystal molecular behavior using a simulator The alignment state of the two-way electric field driving device was evaluated using LCDMaster2D (manufactured by Shintech Co., Ltd.) This liquid crystal alignment calculation software performs numerical simulations based on the theory of elasticity of liquid crystals.

[0037] 6 and 7 are examples of images expressing the in-plane distribution of molecular tilt angles by hue. The average tilt angles of liquid crystal molecules calculated by image analysis of the hue distributions in Figs. 6 and 7 are summarized in Table 2.

[0038] According to Table 2, when the electrode pitch was 10 μm, the difference in the average tilt angle of the liquid crystal molecular director between the longitudinal and transverse electric fields was 4.9°. On the other hand, when the electrode pitch was 50 μm, the difference in the average tilt angle was 7.2°, indicating that the rotational movement of the liquid crystal molecules was greater when the electrode pitch was 50 μm. In a thin liquid crystal layer, sufficient liquid crystal movement can be obtained by driving with an electric field. However, in a thick liquid crystal layer, the electric field does not reach deep into the layer, so it is thought that the liquid crystal inside moves due to the propagation of elastic orientation.

[0039] 4.2 Evaluation of Capacitance Measurement The capacitance due to voltage driving of liquid crystal molecular alignment was evaluated as follows. The amount of change in capacitance when a voltage was applied to the element was measured. However, due to the limitations of the capacitance measurement device, it was difficult to switch between vertical and horizontal electric fields. Therefore, in addition to the structure of the two-way electric field drive element shown in Figure 4, an element was fabricated that could apply a horizontal electric field to a liquid crystal cell made with a substrate coated with a vertical alignment film.

[0040] Figure 8 shows an example graph of capacitance change measured when a low-frequency AC voltage of 30 Vrms was applied for 100 ms to a device fabricated with a vertical alignment film. An elastic constant measurement device (EC-1, manufactured by Toyo Corporation) was used to measure capacitance. Using the values ​​obtained from the graph in Figure 8, the capacitance change per unit length was calculated to be 1.9E-09 F for an interelectrode pitch of 10 μm and 2.0E-09 F for an interelectrode pitch of 50 μm, indicating a larger capacitance change at an interelectrode pitch of 50 μm. These results suggest that a larger dielectric constant change can be obtained by increasing the interelectrode pitch. Since the liquid crystal layer is approximately 50 μm thick, a ratio of the interelectrode pitch in the lateral electric field to the liquid crystal layer thickness of approximately 1:1 is preferred.

[0041] Here, if the inter-electrode pitch of the horizontal electric field is increased, the liquid crystal driving region driven by the application of the horizontal electric field increases in the vertical direction, but the liquid crystal driving region driven by the application of the vertical electric field decreases in the horizontal direction.On the other hand, if the inter-electrode pitch of the horizontal electric field is decreased, the liquid crystal driving region driven by the application of the vertical electric field increases in the horizontal direction, but the liquid crystal driving region driven by the application of the horizontal electric field decreases in the vertical direction. Therefore, to solve this problem, when an electric field in a first direction (vertical direction) is applied to the liquid crystal layer (for example, the first state of the switch SW), an output voltage is applied to each first electrode 13 to increase the liquid crystal drive area in the horizontal direction, while when an electric field in a second direction (horizontal direction) is applied to the liquid crystal layer (for example, the second state of the switch SW), a potential difference is applied between the first electrodes 13 that are spaced apart from the first electrode 13 to which the output voltage is applied, rather than between the first electrodes 13 adjacent to the first electrode 13 to which the output voltage is applied, thereby effectively lengthening the pitch between the first electrodes 13 that form the horizontal electric field (applying a horizontal electrode skip driving method). This makes it possible to maximize the liquid crystal drive area during both vertical drive and horizontal drive.

[0042] For example, the spacing between the electrodes forming the transverse electric field may be variable depending on the thickness of the liquid crystal layer applied to the bidirectional electric field drive element. For example, if the physical pitch between the first electrodes 13 is 50 μm, a voltage is applied to all of the first electrodes 13 when a vertical electric field is applied (first state), regardless of the thickness of the applied liquid crystal layer. Here, the switch may be controlled so that (i) if the applied liquid crystal layer thickness is 50 μm, the transverse drive electrode 13 (spaced 50 μm) adjacent to the transverse drive electrode 13 connected to the output terminal of the power supply is connected to the ground terminal when a horizontal electric field is applied (second state); (ii) if the applied liquid crystal layer thickness is 100 μm, every other transverse drive electrode 13 (spaced 100 μm) is connected to the ground terminal when a horizontal electric field is applied (second state); and (iii) if the applied liquid crystal layer thickness is 150 μm, every other transverse drive electrode 13 (spaced 150 μm) is connected to the ground terminal when a horizontal electric field is applied (second state). Conversely, the switches may be controlled to switch the lateral drive electrodes 13 on the output terminal side.

[0043] Figure 9 shows a conceptual diagram of the above results. Figure 9(1) shows the case where the inter-electrode pitch is narrow, and Figure 9(2) shows the case where the inter-electrode pitch is wide. As shown in Figure 9(2), widening the inter-electrode pitch spreads the lateral electric field in the thickness direction, increasing the proportion of tilted liquid crystal molecules, which leads to an increase in the amount of change in dielectric constant. On the other hand, in areas away from the high-potential electrodes, the electric field strength is weak, and the influence of elastic force becomes dominant, which is thought to result in a decrease in response speed.

[0044] From the above results, it is possible that there is a trade-off between the amount of change in dielectric constant and the response speed depending on the inter-electrode pitch length.

[0045] 5. Functions and Effects of the Embodiments The liquid crystal driving structure of this embodiment applies at least one of the following electric fields to the liquid crystal layer: a first-directional electric field based on a potential difference between electrodes arranged opposite each other in a first direction perpendicular to the liquid crystal layer, and a second-directional electric field based on a potential difference between electrodes arranged at a predetermined distance in a second direction parallel to the liquid crystal layer. Voltage driving is possible for both the rising and falling edges without relying on elastic relaxation of the liquid crystal alignment, significantly shortening the response time. For example, even with a thick liquid crystal film approximately 100 μm thick, response times of several tens of milliseconds can be achieved. Furthermore, the liquid crystal layer does not require the use of a polymer material as disclosed in Patent Document 1, and the absence of polymer-induced restraints allows for reduced driving voltage. For example, the device can be driven at a low driving voltage of 30 V or less, enabling it to be driven by transistors such as thin-film transistors. Furthermore, as shown in experimental results, adjusting the predetermined distance (inter-electrode pitch) between electrodes arranged in the second direction parallel to the liquid crystal layer spatially expands the driving region of liquid crystal molecules with dielectric anisotropy, thereby efficiently achieving a change in dielectric constant. As a result, it becomes possible to adjust the high frequency dielectric constant and effectively control the phase of high frequency radio waves.

[0046] Furthermore, according to this embodiment, an electric field in the first direction is applied to the liquid crystal layer based on application of a predetermined voltage to first and second electrodes provided opposite to each other in a first direction, thereby orienting the liquid crystal molecules in the first direction. On the other hand, an electric field in the second direction is applied to the liquid crystal layer based on application of a predetermined voltage to first electrodes provided at a predetermined interval in a second direction, thereby orienting the liquid crystal molecules in the second direction.

[0047] The liquid crystal driving structure of this embodiment can be suitably applied to the above-mentioned reflect array, etc. Other examples will be described later.

[0048] 6 Other Embodiments 6.1 Driving Method In the above-described electric field-driven element (bidirectional electric field-driven element 1), it is possible to mount transistors on both the upper and lower substrates. However, this would increase the mounting cost. Furthermore, while setting the driving voltage is relatively easy for binary gradations, it can be difficult to set the driving voltage when switching from one intermediate gradation to another, for example.

[0049] Therefore, a liquid crystal driving structure as described below may be applied. For example, as the initial alignment state, a vertical alignment process is performed to align the liquid crystal molecules in the vertical direction. Note that, as an example, the vertical alignment process is described here as the initial alignment state, but the same effect can be achieved by performing a horizontal alignment process to align the liquid crystal molecules in the horizontal direction as the initial alignment state.

[0050] An element common electrode, which is an electrode for vertical electric field drive and corresponds to the above-mentioned electrode 15, is provided as an electrode common to the elements (pixels). When controlling to a middle gradation state, a voltage corresponding to the gradation is applied to the horizontal drive electrodes 13 so that the liquid crystal molecules are tilted by a horizontal electric field from the initial state, thereby analogically controlling the alignment direction of the liquid crystal molecules. During refreshing, a reset voltage, which is a large voltage equal to or greater than a set value (or exceeding the set value), is applied to the element common electrode and the horizontal drive electrodes 13 to control the liquid crystal molecules to instantly align in the vertical direction.

[0051] In this case, by providing a common electrode for all elements on one of the upper and lower layers and controlling the orientation as described above, it is not necessary to mount a transistor for each element, and it is sufficient to mount the transistor on only one side. As a result, the electrode and drive element configuration is simple, and costs can be reduced.

[0052] Furthermore, by applying a voltage corresponding to the gradation to the segment electrodes for in-plane driving, an unstable transient state in which the voltage and liquid crystal elasticity are not balanced can be avoided, ensuring gradation reproducibility.

[0053] Another method for achieving high-speed half-tone driving is to simultaneously apply both vertical and horizontal electric fields. This method (a vertical-horizontal electric field balanced driving method) can be used. By varying the strength of the vertical and horizontal electric fields, the rotation angle of the liquid crystal molecules can be adjusted to a predetermined balance. This method is also largely unaffected by the liquid crystal elasticity, achieving high-speed driving. In this case, for example, a first power supply for the vertical electric field (for applying a voltage between the first electrodes 13 and 15) and a second power supply for the horizontal electric field (for applying a voltage between the first electrodes 13) can be separately provided. By separately controlling the voltages applied by the first power supply and the second power supply, the desired half-tone driving can be achieved at high speed.

[0054] The liquid crystal driving structure of this example changes the high-frequency dielectric constant by applying to the liquid crystal layer both an electric field in a first direction based on the potential difference between electrodes arranged opposite each other in a first direction perpendicular to the liquid crystal layer, and an electric field in a second direction based on the potential difference between electrodes arranged at a predetermined interval in a second direction parallel to the liquid crystal layer.

[0055] 6.2 Device Structure and Electrode Materials Figure 10 shows an example of the structure of a device using the above-described electric field-driven element (two-way electric field-driven element). For example, as shown in Figure 10(1), a dielectric substrate 11a, which is a type of substrate 11, is provided on the upper substrate layer LA' as viewed in the drawing, and a resonant conductor is formed on this dielectric substrate 11a. The resonant conductor may be a resonant element conductor 17 for each liquid crystal element. The resonant element conductor 17 controls the reflection phase or transmission phase of radio waves (e.g., millimeter waves), thereby changing the incident direction and reflection or transmission direction of the radio waves. In addition, an insulating layer 18, which covers the lateral drive electrode 13 with an insulating film, is formed on the dielectric substrate 11a on which the resonant element conductor 17 is formed, so that the lateral drive electrode 13 is not electrically connected to the resonant element conductor 17.

[0056] On the other hand, on the substrate layer LB′ on the lower side in the drawing, a ground conductor 19 is provided on the dielectric substrate 11 a. In this configuration, the ground conductor 19 may function as the electrode 15.

[0057] The transverse drive electrode 13 may be configured as an extremely thin conductive film to minimize absorption of millimeter-wave radio waves. Specifically, the extremely thin conductive film may be configured as a conductive film having a thickness of 1 μm or less. The transverse drive electrode 13 may also be configured as a mesh-like conductive film.

[0058] To reduce loss, the lateral drive electrode 13 may be formed as a conductive film using a predetermined material with high conductivity. Examples of useful materials include highly conductive metals, metal oxides, organic materials (organic conductive materials), and carbon compounds. Alternatively, the lateral drive electrode 13 may be formed as a transparent conductive film using a transparent conductive material (e.g., metal oxides containing ITO (indium tin oxide), organic conductive materials containing PEDOT / PSS, etc.). For example, IZO (indium zinc oxide) may be used as a transparent conductive material. For example, conductive carbon may be used as a conductive carbon compound. For example, ITO has high conductivity and high translucency, and can be manufactured as a high-quality thin film or ultrathin film using film formation methods such as vacuum deposition and sputtering. Furthermore, ITO can be easily formed on a substrate. Furthermore, electrode patterns can be easily formed using wet etching or the like.

[0059] In this device, the horizontal field may be applied by the lateral drive electrodes 13 on the upper layer, and the vertical field may be applied by the lateral drive electrodes 13 and the ground electrodes.

[0060] According to this configuration, by using an ultra-thin conductive film as the lateral drive electrode, which has almost no absorption of high-frequency millimeter-wave band radio waves used in, for example, 5G high-speed, large-capacity communications, the resonant element conductor and the lateral drive electrode can be configured separately. This also allows for the optimal design of the liquid crystal drive state and the high-frequency design to be performed independently.

[0061] For example, in the device shown in Figure 10 (2), a dielectric substrate 11a is provided on the substrate layer LB'' on the upper side of the drawing, and a resonant element conductor 17 is formed on this dielectric substrate 11a. In this configuration, the resonant element conductor 17 may function as the electrode 15.

[0062] On the other hand, on the substrate layer LA'' on the lower side in the drawing, a ground conductor 19 is provided on the dielectric substrate 11a, and an insulating layer 18 including the transverse drive electrode 13 is formed. In this configuration, depending on the polarization, the transverse drive electrode 13 may also be used as a ground electrode.

[0063] In this device, a horizontal electric field is applied by the lateral drive electrode 13 on the lower layer, and a vertical electric field is applied by the resonant element electrode and the lateral drive electrode 13 .

[0064] With this configuration, the ground conductor and the horizontal drive electrode can be separated by using an ultra-thin conductive film that absorbs almost no high-frequency millimeter-wave radio waves, which are used in, for example, 5G high-speed, large-capacity communications, which also allows for the optimization of the liquid crystal drive state and the high-frequency design to be performed independently.

[0065] 6.3 Application Examples of Liquid Crystal Driving Structure The liquid crystal driving structures described in the above and other embodiments can be applied to various devices that include the liquid crystal driving structure and can control high-frequency electromagnetic waves (capable of controlling the phase of high-frequency electromagnetic waves). In addition, they can be applied to high-frequency devices that use not only millimeter waves but also microwaves.

[0066] For example, in addition to the reflectarray described above, which reflects high-frequency electromagnetic waves in a desired direction, a phase shifter that outputs high-frequency electromagnetic waves whose phase is shifted relative to the input high-frequency electromagnetic waves, or a phased array antenna that can provide directionality in the transmission and reception of high-frequency electromagnetic waves by having such a phase shifter, the above-mentioned electric field driving element (two-way electric field driving element) may be provided in such a device and driven by the liquid crystal driving structure of the present invention. For example, the liquid crystal driving structure of the present invention may be applied to the phase shifters described in JP 2021-101511 A and JP 2021-101531 A (e.g., those in which a liquid crystal layer is provided in the gap between opposing first and second substrates) and phased array antennas (e.g., those comprising antenna elements, phase shifters, phase control circuits, etc., and each of the parallel-arranged phase shifters is connected to an antenna element), and the above publications are incorporated herein by reference.

[0067] REFERENCE SIGNS LIST 11 Substrate 13 Lateral drive electrode 15 Electrode 16 Alignment film 17 Resonance element conductor 18 Insulation film 19 Ground conductor

Claims

1. A liquid crystal driving structure that changes the high-frequency dielectric constant by applying at least one of an electric field in a first direction based on a potential difference between electrodes arranged opposite each other in a first direction perpendicular to the liquid crystal layer across the liquid crystal layer, and an electric field in a second direction based on a potential difference between electrodes arranged at a predetermined interval in a second direction parallel to the liquid crystal layer.

2. A liquid crystal driving structure as claimed in claim 1, wherein the strength of the electric field in the first direction and the strength of the electric field in the second direction are adjustable.

3. A liquid crystal driving structure as described in claim 1, wherein, based on application of a predetermined voltage to a first electrode and a second electrode arranged opposite each other in the first direction, an electric field in the first direction is applied to the liquid crystal layer to orient the liquid crystal molecules in the first direction, and, based on application of a predetermined voltage to the first electrodes arranged at the predetermined interval in the second direction, an electric field in the second direction is applied to the liquid crystal layer to orient the liquid crystal molecules in the second direction.

4. A liquid crystal driving structure as claimed in claim 3, wherein the first electrodes for forming an electric field in the second direction can be selected from the first electrodes provided at the predetermined intervals in the second direction.

5. A liquid crystal driving structure as described in claim 3, in which, in an initial alignment state in which the liquid crystal molecules are aligned in the first direction, the alignment of the liquid crystal molecules is changed based on application of a voltage corresponding to a gradation to the first electrodes provided at the specified intervals in the second direction.

6. A liquid crystal driving structure as described in claim 5, wherein an electric field in the first direction is applied to the liquid crystal layer based on application of a reset voltage to the first electrode and the second electrode, thereby aligning the liquid crystal molecules in the first direction.

7. A liquid crystal driving structure according to claim 6, wherein the second electrode is an electrode common to the elements.

8. A liquid crystal driving structure as described in claim 3, in which, in an initial alignment state in which the liquid crystal molecules are aligned in the second direction, the alignment of the liquid crystal molecules is changed based on application of a voltage corresponding to a gradation to the first electrode and the second electrode.

9. A liquid crystal driving structure as described in claim 8, wherein, based on application of a reset voltage to the first electrodes arranged at the predetermined intervals in the second direction, an electric field in the second direction is applied to the liquid crystal layer, thereby aligning the liquid crystal molecules in the second direction.

10. A liquid crystal driving structure according to claim 9, wherein the second electrode is an electrode common to the elements.

11. A liquid crystal driving structure as described in claim 1, wherein first electrodes are provided at the specified intervals in the second direction, and the first electrodes are configured as extremely thin conductive films using a specified material with high conductivity.

12. A liquid crystal driving structure according to claim 11, wherein the predetermined material is any one of a metal, a metal oxide, an organic material, and a carbon compound.

13. A reflect array comprising a liquid crystal driving structure according to any one of claims 1 to 12, for controlling high-frequency electromagnetic waves.

14. A phase shifter for controlling high frequency electromagnetic waves, comprising a liquid crystal driving structure according to any one of claims 1 to 12.

15. A phased array antenna including a liquid crystal driving structure according to any one of claims 1 to 12, for controlling high frequency electromagnetic waves.

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