Liquid crystal metasurface reflection plate

Abstract

This liquid crystal metasurface reflection plate has: a patch electrode arranged in a matrix shape; a drive electrode overlapping the patch electrode; and a liquid crystal layer between the patch electrode and the drive electrode. The drive electrode is divided into a plurality of sub-drive electrodes, and is configured to make it possible to individually drive the plurality of sub-drive electrodes to locally control an alignment state of the liquid crystal layer in the plane of the patch electrode.

Description

Liquid crystal metasurface reflector

[0001] One embodiment of the present invention relates to a metasurface reflector using liquid crystal that can control the reflection directionality of radio waves.

[0002] A radio wave reflector (also called a metasurface reflector; hereinafter referred to as a "liquid crystal metasurface reflector") has been disclosed that controls the reflection direction of radio waves by utilizing the dielectric anisotropy of liquid crystals (see, for example, Patent Document 1). The liquid crystal metasurface reflector has a patch electrode arranged on the radio wave incident surface, a ground electrode arranged on the opposite side, and a liquid crystal layer provided between the patch electrode and the ground electrode.

[0003] Japanese Patent Application Laid-Open No. 2022-156917

[0004] The liquid crystal metasurface reflector has patch electrodes arranged in a matrix on the radio wave incident surface. By changing the dielectric constant of the liquid crystal material in the area corresponding to each patch electrode and changing the phase of the reflected wave, the liquid crystal metasurface reflector as a whole controls the radio wave reflection direction to a predetermined direction. Therefore, in order to precisely control the radio wave reflection direction, it is necessary to finely control the orientation state of the liquid crystal material.

[0005] A liquid crystal metasurface reflector according to one embodiment of the present invention includes patch electrodes arranged in a matrix, drive electrodes overlapping the patch electrodes, and a liquid crystal layer between the patch electrodes and the drive electrodes. The drive electrodes are divided into multiple sub-drive electrodes, and the multiple sub-drive electrodes can be individually driven to locally control the alignment state of the liquid crystal layer within the plane of the patch electrodes.

[0006] 6A shows the configuration of a liquid crystal metasurface reflector according to one embodiment of the present invention. FIG. 6B shows the circuit configuration for driving the patch electrode and multiple divided drive electrodes of a liquid crystal metasurface reflector according to one embodiment of the present invention. FIG. 6C shows a plan view of a batch electrode and a drive electrode provided on a liquid crystal metasurface reflector according to one embodiment of the present invention. FIG. 6D shows a cross-sectional view of a batch electrode and a drive electrode provided on a liquid crystal metasurface reflector according to one embodiment of the present invention. FIG. 6E shows a plan view of a batch electrode and a drive electrode provided on a liquid crystal metasurface reflector according to one embodiment of the present invention. FIG. 6F shows a plan view of a batch electrode and a drive electrode provided on a liquid crystal metasurface reflector according to one embodiment of the present invention. FIG. 6G shows the pattern of sub-drive electrodes of a liquid crystal metasurface reflector according to one embodiment of the present invention, and the configuration of switching elements, scanning signal lines, and drive signal lines. FIG. 6G shows a cross-sectional view of the pattern of sub-drive electrodes of a liquid crystal metasurface reflector according to one embodiment of the present invention, taken along line C-D in FIG. 6A. FIG. 6G shows the configuration of a liquid crystal metasurface reflector according to one embodiment of the present invention.

[0007] Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention can be implemented in many different forms, and should not be construed as being limited to the description of the following exemplary embodiments. For clarity of explanation, the drawings may show schematic representations of the width, thickness, shape, etc. of each part compared to the actual form. However, these are merely examples and are not intended to limit the interpretation of the present invention. Furthermore, in this specification and each drawing, elements similar to those previously described with reference to the preceding drawings are designated by the same reference numerals (or reference numerals with A, B, etc. suffixed thereto), and detailed descriptions may be omitted as appropriate. Furthermore, the letters "first" and "second" attached to each element are convenient labels used to distinguish each element and have no further meaning unless otherwise specified.

[0008] In this specification, when a component or region is referred to as being "on (or under)" another component or region, unless otherwise specified, this includes not only the case where it is directly above (or directly under) the other component or region, but also the case where it is above (or under) the other component or region, i.e., the case where another component is included between the component or region and above (or under) the other component or region.

[0009] FIG. 1 shows a plan view of a liquid crystal metasurface reflector 100 according to one embodiment of the present invention, viewed from the radio wave incident surface side.

[0010] For the sake of explanation, Fig. 1 indicates the X-axis direction, the Y-axis direction, and the Z-axis direction as indicated by the arrows in the figure. In the figure, the Y-axis direction is perpendicular to the X-axis direction, and the Z-axis direction is perpendicular to the XY plane. The X-axis direction and the Y-axis direction can be read as the first direction and the second direction. The relationship between the three directions, the X-axis direction, the Y-axis direction, and the Z-axis direction, is the same in other figures referred to in this embodiment, unless otherwise specified.

[0011] The liquid crystal metasurface reflector 100 includes a plurality of patch electrodes 102 and a plurality of drive electrodes 104. The plurality of patch electrodes 102 are arranged in the X-axis direction and the Y-axis direction. Similarly, the plurality of drive electrodes 104 are arranged so as to overlap with the plurality of patch electrodes 102. The plurality of patch electrodes 102 are arranged on the incident surface of the radio wave, and the plurality of drive electrodes 104 are arranged on the back surface of the plurality of patch electrodes 102.

[0012] Although not shown in FIG. 1 , a liquid crystal layer is provided between the plurality of patch electrodes 102 and the plurality of drive electrodes 104. The liquid crystal layer is formed of a liquid crystal material having a dielectric anisotropy. The liquid crystal material may have a positive dielectric anisotropy or a negative dielectric anisotropy. In this embodiment, the liquid crystal layer will be described as having a dielectric anisotropy. There are no particular limitations on the type of liquid crystal material that forms the liquid crystal layer. For example, a nematic liquid crystal is used as the liquid crystal material.

[0013] The liquid crystal metasurface reflector 100 has a structure in which a first substrate 150 and a second substrate 152 are stacked on top of each other. The first substrate 150 and the second substrate 152 are insulating substrates. A liquid crystal layer (not shown) is sandwiched between the first substrate 150 and the second substrate 152. The first substrate 150 is disposed on the radio wave incident surface side (front surface), and the second substrate 152 is disposed on the rear surface side of the first substrate 150.

[0014] A plurality of patch electrodes 102 are arranged on a first substrate 150. The plurality of patch electrodes 102 are arranged with gaps between them so that adjacent electrodes do not contact each other. A plurality of drive electrodes 104 are arranged on a second substrate 152. The plurality of drive electrodes 104 are also arranged with gaps between them so that adjacent electrodes do not contact each other.

[0015] The multiple patch electrodes 102 are connected by strip wiring 103. Fig. 1 shows a configuration in which the multiple patch electrodes 102 arranged in the Y-axis direction are connected by the strip wiring 103. The connection of the patch electrodes 102 by the strip wiring 103 is not limited to the example shown in Fig. 1; the multiple patch electrodes 102 arranged in the X-axis direction may be connected by the strip wiring 103, or the multiple patch electrodes 102 may be connected by the strip wiring 103 in both the X-axis direction and the Y-axis direction. The multiple patch electrodes 102 arranged on the first substrate 150 are controlled to have a constant potential. The constant potential can be set as appropriate and may be, for example, ground potential.

[0016] The multiple drive electrodes 104 are used as electrodes for controlling the alignment of liquid crystal molecules in the liquid crystal layer. In plan view, one drive electrode 104 is arranged so as to overlap one patch electrode 102. The drive electrode 104 is divided into multiple electrodes. That is, the drive electrode 104 is composed of multiple sub-drive electrodes 105. The multiple sub-drive electrodes 105 are arranged so as to overlap the patch electrode 102. A drive signal is applied individually to each of the multiple sub-drive electrodes 105. FIG. 1 schematically shows an example in which the drive electrode 104 is composed of four sub-drive electrodes 105, but the multiple sub-drive electrodes 105 are not limited to the configuration shown in the figure. The multiple sub-drive electrodes 105 will be described in detail below.

[0017] The second substrate 152 is provided with a plurality of scanning signal lines 111 and a plurality of driving signal lines 113 for driving the plurality of sub-driving electrodes 105. The plurality of scanning signal lines 111 and the plurality of driving signal lines 113 are arranged corresponding to the arrangement of the plurality of driving electrodes 104. The plurality of scanning signal lines 111 extend in the X-axis direction, and the plurality of driving signal lines 113 extend in the Y-axis direction. The second substrate 152 is further provided with a scanning signal line driving circuit 110, a driving signal line selection circuit 112, and a terminal unit 114. The scanning signal line driving circuit 110 outputs scanning signals to the plurality of scanning signal lines 111, and the driving signal line selection circuit 112 has the function of selecting the plurality of driving signal lines 113. The terminal unit 114 is a portion where signals and power for driving the liquid crystal metasurface reflector 100 are input, and is a contact point with an external circuit. The terminal unit 114 is composed of a plurality of terminal electrodes 115.

[0018] A ground electrode 108 may be provided on the second substrate 152 so as to fill the gaps in the area where the multiple drive electrodes 104 are arranged. The multiple drive electrodes 104 and the ground electrode 108 are arranged so as to be continuous in a plan view, but are arranged so as not to be in direct contact with each other in a cross-sectional view. For example, an insulating layer may be interposed between the multiple drive electrodes 104 and the ground electrode 108. The ground electrode 108 is arranged so as to fill the gaps between the multiple drive electrodes 104, and is controlled so as to maintain a constant potential. The constant potential may be, for example, ground (earth).

[0019] Fig. 2 shows the circuit configuration of multiple sub-drive electrodes 105 that overlap with the patch electrode 102. As shown in Fig. 2, the multiple sub-drive electrodes 105 are arranged in an area that overlaps with the patch electrode 102. Fig. 2 shows, as an example, a configuration in which the multiple sub-drive electrodes 105 are arranged in a matrix in the X-axis and Y-axis directions.

[0020] Switching elements 116 are provided corresponding to each of the multiple sub-drive electrodes 105. Drive signals are applied individually to the multiple sub-drive electrodes 105 by the switching elements 116. Scanning signal lines 111 are provided to control the on / off state of the switching elements 116, and drive signal lines 113 are provided to apply drive signals to the sub-drive electrodes 105 through the switching elements 116. FIG. 2 shows a configuration in which multiple scanning signal lines 111 (first scanning signal line 111A to sixth scanning signal line 111F) extending in the X-axis direction and multiple drive signal lines 113 (first drive signal line 113A to sixth drive signal line 113F) extending in the Y-axis direction are arranged in correspondence with the arrangement of the multiple sub-drive electrodes 105. This circuit configuration makes it possible to drive each of the multiple sub-drive electrodes 105 individually.

[0021] 3 shows a plan view of the patch electrode 102 and the driving electrode 104 provided on the liquid crystal metasurface reflector 100. Similar to the schematic diagram shown in FIG. 1, FIG. 3 shows an example in which the driving electrode 104 is composed of a first sub-driving electrode 105A, a second sub-driving electrode 105B, a third sub-driving electrode 105C, and a fourth sub-driving electrode 105D.

[0022] The first sub-drive electrode 105A, the second sub-drive electrode 105B, the third sub-drive electrode 105C, and the fourth sub-drive electrode 105D are spaced apart at a predetermined interval and arranged to overlap the patch electrode 102. The first sub-drive electrode 105A, the second sub-drive electrode 105B, the third sub-drive electrode 105C, and the fourth sub-drive electrode 105D have the same area. In other words, the area over which the first sub-drive electrode 105A, the second sub-drive electrode 105B, the third sub-drive electrode 105C, and the fourth sub-drive electrode 105D overlap with the patch electrode 102 is equal.

[0023] Each sub-driving electrode 105 is connected to a switching element 116. Specifically, the first sub-driving electrode 105A is connected to the first switching element 116A, the second sub-driving electrode 105B is connected to the second switching element 116B, the third sub-driving electrode 105C is connected to the third switching element 116C, and the fourth sub-driving electrode 105D is connected to the fourth switching element 116D. The first switching element 116A, the second switching element 116B, the third switching element 116C, and the fourth switching element 116D are formed, for example, by thin film transistors. When the first switching element 116A, the second switching element 116B, the third switching element 116C, and the fourth switching element 116D are formed by thin film transistors, each switching element has three terminals: a gate terminal, a signal input terminal, and a signal output terminal.

[0024] 3 , the gate terminals of the first switching element 116A and the second switching element 116B are connected to the first scanning signal line 111A, and the gate terminals of the third switching element 116C and the fourth switching element 116D are connected to the second scanning signal line 111B. Furthermore, the signal input terminals of the first switching element 116A and the third switching element 116C are connected to the first drive signal line 113A, and the signal input terminals of the second switching element 116B and the fourth switching element 116D are connected to the second drive signal line 113B. Furthermore, the signal output terminal of the first switching element 116A is connected to the first sub-drive electrode 105A, the signal output terminal of the second switching element 116B is connected to the second sub-drive electrode 105B, the signal output terminal of the third switching element 116C is connected to the third sub-drive electrode 105C, and the signal output terminal of the fourth switching element 116D is connected to the fourth sub-drive electrode 105D. As described with reference to FIG. 1, the first scanning signal line 111A and the second scanning signal line 111B extend in the X-axis direction, and the first driving signal line 113A and the second driving signal line 113B extend in the Y-axis direction.

[0025] By connecting the first sub-drive electrode 105A, the second sub-drive electrode 105B, the third sub-drive electrode 105C, and the fourth sub-drive electrode 105D to the first switching element 116A, the second switching element 116B, the third switching element 116C, and the fourth switching element 116D, drive signals can be applied individually, making it possible to control the alignment state of the liquid crystal layer for each sub-drive electrode. For example, the sub-drive electrodes 105 can be driven by applying a drive signal having a first voltage level to the first sub-drive electrode 105A and not applying a drive signal to the second sub-drive electrode 105B, the third sub-drive electrode 105C, and the fourth sub-drive electrode 105D. Alternatively, the sub-drive electrodes 105 can be driven by applying a drive signal having a first voltage level to the first sub-drive electrode 105A and the second sub-drive electrode 105B and not applying a drive signal to the third sub-drive electrode 105C and the fourth sub-drive electrode 105D.

[0026] In other words, when the drive signal is two-valued (on (high level) and off (low level)), the example shown in Figure 4 has four sub-drive electrodes 105, so there are five possible signal application patterns: when a drive signal is not applied to all sub-drive electrodes, when a drive signal that turns on is applied to one sub-drive electrode, when a drive signal that turns on is applied to two sub-drive electrodes, when a drive signal that turns on is applied to three sub-drive electrodes, and when a drive signal that turns on is applied to four sub-drive electrodes.

[0027] The size (length and width) of the patch electrode 102 is appropriately set according to the frequency of the target radio wave. The length and width of the patch electrode 102 are set so that it has a shape symmetrical with respect to the vertically and horizontally polarized waves of the incident radio wave. The length of one side of the patch electrode 102 is, for example, approximately half the wavelength of the target radio wave. If the drive electrode 104 of the liquid crystal metasurface reflector 100 is divided into multiple sub-drive electrodes 105 and each sub-drive electrode 105 is driven with a different drive signal, the dielectric constant of the liquid crystal layer changes locally within the plane of the patch electrode 102. However, since the wavelength of the reflected radio wave is longer than the length of one side of the patch electrode 102, and the reflection characteristics are determined by the overall electromagnetic circuit characteristics of the liquid crystal metasurface reflector 100, the reflection characteristics are not affected by the local dielectric constant distribution.

[0028] To precisely control the direction of radio wave reflection by the liquid crystal metasurface reflector 100, it is possible to finely divide the voltage level of the drive signal applied to the liquid crystal layer into multiple levels. However, this method would require complex and large-scale drive circuit and power supply circuit configurations. In contrast, the configuration of this embodiment allows for control of the alignment state of the liquid crystal layer, i.e., the polarization ratio that affects radio wave reflection, by a number corresponding to the number of divisions of the sub-drive electrodes 105, even when using a binary drive signal.

[0029] As described below, the liquid crystal metasurface reflector 100 has a liquid crystal layer thickness of approximately 20 μm to 100 μm, which is larger than the cell gap of liquid crystal panels used as displays. Accordingly, the voltage applied to the liquid crystal layer must also be set higher than that of existing liquid crystal panels. Therefore, existing liquid crystal driver ICs cannot be used, and even if commercially available products were available, there is a concern that the number of gray levels would be limited. In response to these concerns, the liquid crystal metasurface reflector 100 of this embodiment has multiple divided drive electrodes 104 that control the orientation of the liquid crystal layer, allowing the effective dielectric constant of the liquid crystal layer to be controlled in multiple stages, as described above.

[0030] FIG. 4 shows a cross-sectional view corresponding to the line A-B shown in FIG. 3 . As shown in FIG. 4 , the patch electrode 102 is provided on the first substrate 150, and the driving electrodes 104 (first sub-driving electrode 105A, second sub-driving electrode 105B) are provided on the second substrate 152. The first substrate 150 and the second substrate 152 are arranged so that the patch electrode 102 and the driving electrodes 104 (first sub-driving electrode 105A, second sub-driving electrode 105B) face each other, and are spaced apart with a predetermined gap between them. The gap between the first substrate 150 and the second substrate 152 is approximately 20 μm to 100 μm, for example, 40 μm. Although not shown, a spacer may be provided between the first substrate 150 and the second substrate 152 to keep the gap constant.

[0031] A first alignment film 107A is provided on the first substrate 150 so as to cover the patch electrode 102, and a second alignment film 107B is provided on the second substrate 152 so as to cover the drive electrodes 104 (first sub-drive electrode 105A, second sub-drive electrode 105B). A liquid crystal layer 106 is provided so as to be sandwiched between the first substrate 150 and the second substrate 152. The initial alignment state of the liquid crystal layer 106 is regulated by the first alignment film 107A and the second alignment film 107B.

[0032] The second substrate 152 is provided with a first switching element 116A connected to the first sub-driving electrode 105A and a second switching element 116B connected to the second sub-driving electrode 105B. As described above, the first switching element 116A and the second switching element 116B are formed, for example, by thin film transistors. The first switching element 116A and the second switching element 116B are covered with an insulating layer 109. The first sub-driving electrode 105A and the second sub-driving electrode 105B are provided on the insulating layer 109. The first sub-driving electrode 105A and the first switching element 116A, and the second sub-driving electrode 105B and the second switching element 116B are connected by contact holes formed in the insulating layer 109.

[0033] As described above, the first switching element 116A and the second switching element 116B have three terminals: a gate terminal, a signal input terminal, and a signal output terminal. Fig. 4 shows a structure in which the signal input terminal of the first switching element 116A is connected to the first drive signal line 113A, the signal output terminal is connected to the first sub-drive electrode 105A, and the signal input terminal of the second switching element 116B is connected to the second drive signal line 113B, and the signal output terminal is connected to the second sub-drive electrode 105B.

[0034] Although not shown in detail in Fig. 4 , the insulating layer 109 has a structure in which a plurality of insulating films are stacked. The first drive signal line 113A and the second drive signal line 113B are provided in the insulating layer 109 so as to be located in a layer below the first sub-drive electrode 105A and the second sub-drive electrode 105B. Although not shown in Fig. 4 , the first scanning signal line 111A is also provided in the insulating layer 109. The first scanning signal line 111A, the first drive signal line 113A, and the second drive signal line 113B are provided in different layers in the insulating layer 109. The first scanning signal line 111A intersects with the first drive signal line 113A and the second drive signal line 113B, with an insulating layer interposed at the intersection.

[0035] A ground electrode 108 is also provided on the second substrate 152. The ground electrode 108 is provided so as to fill the region where the first sub-driving electrode 105A and the second sub-driving electrode 105B are separated from each other. As shown in Fig. 3 , an insulating layer 109 is interposed between the ground electrode 108 and the first sub-driving electrode 105A and the second sub-driving electrode 105B to prevent them from coming into direct contact with each other.

[0036] Although the ground electrode 108 and the driving electrodes 104 (first sub-driving electrode 105A, second sub-driving electrode 105B) are physically separated, a single ground plane is formed for radio waves (high-frequency radio waves) incident on the liquid crystal metasurface reflector 100. Therefore, it is preferable that the ends of the ground electrode 108 are arranged so as to overlap with the first sub-driving electrode 105A and the second sub-driving electrode 105B.

[0037] 4 shows an example in which the ground electrode 108 is formed in a layer different from the layer in which the switching elements 116 (first switching element 116A, second switching element 116B) are formed, but the configuration of the ground electrode 108 is not limited to this example. The ground electrode 108 may be formed in the same conductive layer as the layer in which the drive signal lines 113 are formed, or may be formed in the same conductive layer as the layer in which the scanning signal lines 111 are formed, for example.

[0038] The first substrate 150 and the second substrate 152 are formed of flat materials such as glass, resin, and metal plates. The layers provided on the first substrate 150 and the second substrate 152 are formed using the following materials. The semiconductor layer forming the switching elements 116 (thin-film transistors) is formed of a silicon semiconductor such as amorphous silicon or polycrystalline silicon, or an oxide semiconductor containing a metal oxide such as indium oxide, zinc oxide, or gallium oxide. The insulating layer 109 may be formed of any insulating material, such as an inorganic insulating material such as a silicon oxide film or a silicon nitride film, or an organic insulating material such as acrylic, epoxy, or polyimide. Wiring such as the scanning signal line 111 and the driving signal line 113, and electrodes such as the driving electrode 104, the ground electrode 108, and the patch electrode 102 are formed of conductive materials, such as metal materials such as aluminum (Al), titanium (Ti), molybdenum (Mo), molybdenum-tungsten (MoW), and copper (Cu).

[0039] 3 shows a configuration in which four sub-driving electrodes 105 (first sub-driving electrode 105A, second sub-driving electrode 105B, third sub-driving electrode 105C, and fourth sub-driving electrode 105D) are arranged in a matrix, but the arrangement of the sub-driving electrodes is not limited to this example. For example, as shown in FIG. 5A , second sub-driving electrodes 105A2, 105B2, 105C2, and 105D2 may be provided to surround four first sub-driving electrodes 105A1, 105B1, 105C1, and 105D1 arranged in a matrix, and third sub-driving electrodes 105A3, 105B3, 105C3, and 105D3 may be provided to surround the outside of these. In other words, a hook-shaped second sub-driving electrode 105A2 is provided adjacent to two side surfaces of a rectangular first sub-driving electrode 105A1 when viewed in a plane, and a hook-shaped third sub-driving electrode 105A3 is provided further outside that, and such a set of sub-driving electrodes (first sub-driving electrode 105A1, second sub-driving electrode 105A2, third sub-driving electrode 105A3) may be arranged rotated 90 degrees so as to have rotational symmetry.

[0040] 5B , a polygonal (modified hexagonal) second sub-drive electrode 105A2 may be provided adjacent to one side of a triangular first sub-drive electrode 105A1 in a plan view, and a triangular third sub-drive electrode 105A3 may be provided outside the first sub-drive electrode 105A2. Such a set of sub-drive electrodes (first sub-drive electrode 105A1, second sub-drive electrode 105A2, and third sub-drive electrode 105A3) may be rotated by 90 degrees to have rotational symmetry. In the configuration of the sub-drive electrode 105 shown in FIGS. 5A and 5B , the first sub-drive electrode 105A1, second sub-drive electrode 105A2, and third sub-drive electrode 105A3 have different areas. In this way, even if the areas of the divided sub-drive electrodes 105 are different, the dielectric constant of the liquid crystal layer 106 can be changed in multiple stages by individually applying drive signals.

[0041] 6A shows the arrangement of the plurality of sub-driving electrodes 105 shown in FIG. 5A, the switching elements 116 (116A1 to 116A3, 116B1 to 116B3, 116C1 to 116C3) provided corresponding to the plurality of sub-driving electrodes 105 (105A1 to 105A3, 105B1 to 105B3, 105C1 to 105C3), the plurality of scanning signal lines 111 (first scanning signal line 111A, second scanning signal line 111AB), and the plurality of driving signal lines 113 (first driving signal line 113A to sixth driving signal line 113F).

[0042] The first sub-drive electrode 105A1 is connected to the first switching element 116A1, the second sub-drive electrode 105A2 is connected to the second switching element 116A2, and the third sub-drive electrode 105A3 is connected to the third switching element 116A3. Gate terminals of the first switching element 116A1, the second switching element 116A2, and the third switching element 116A3 are connected to the first scanning signal line 111A. The input terminal of the first switching element 116A1 is connected to the first drive signal line 113A, the input terminal of the second switching element 116A2 is connected to the second drive signal line 113B, and the input terminal of the third switching element 116A3 is connected to the third drive signal line 113C.

[0043] As shown in the inset of FIG. 6A , the switching element 116 (the inset shows the third switching element 116A3) formed by a thin-film transistor has a semiconductor layer 1162. The first scanning signal line 111A is disposed so as to cross the semiconductor layer 1162 with an insulating layer (not shown) sandwiched therebetween, and the intersection serves as a gate terminal (gate electrode). The first driving signal line 113A forms contact with the semiconductor layer 1162. This contact portion corresponds to a signal input terminal. Furthermore, the semiconductor layer 1162 forms contact with the sub-driving electrode 105 (the third sub-driving electrode 105A3 in the inset). This contact portion corresponds to a signal output terminal.

[0044] Fig. 6B shows the cross-sectional structure between CD shown in Fig. 6A. As shown in Fig. 6B, first sub-drive electrode 105A1 to third sub-drive electrode 105A3 and first sub-drive electrode 105S1 to third sub-drive electrode 105B3 are arranged facing one patch electrode 102. In addition, a liquid crystal layer 106 is provided between the patch electrode 102 and the sub-drive electrodes 105 (105A1 to 105A3, 105B1 to 105B3).

[0045] As shown in FIG. 6A , each sub-drive electrode 105 (105A1 to 105A3, 105B1 to 105B3) is connected to a switching element 116 (116A1 to 116A3, 116B1 to 116B3), and a drive signal is applied to each electrode individually. The liquid crystal metasurface reflector 100 according to this embodiment may have a first operating mode in which drive signals are applied to all sub-drive electrodes 105, and a second operating mode in which drive signals are applied to some of the sub-drive electrodes 105. The second operating mode can subdivide the drive signal application state depending on the number of sub-drive electrodes 105. In the configuration shown in FIG. 6A , 12 sub-drive electrodes 105 (105A1 to 105A3, 105B1 to 105B3, 105C1 to 105C3, 105D1 to 105D3) are provided, and therefore the second operating mode can form 12 drive signal application patterns.

[0046] 6B illustrates a state (denoted by symbol Sg0) in which a first drive signal Sg1 having a predetermined voltage level is applied to the first sub-drive electrodes 105A1 and 105B1 and the second sub-drive electrodes 105A2 and 105B2, and no drive signal is applied to the third sub-drive electrodes 105A3 and 105B3. The first drive signal Sg1 is, for example, a signal that generates a potential difference of +15 V between the first drive signal Sg1 and the patch electrode 102. The first drive signal Sg1 may be a signal whose polarity is periodically reversed. That is, when a potential difference of +15 V is generated between the first drive signal Sg1 and the patch electrode 102 in one cycle, the signal may generate a potential difference of −15 V in the next cycle. The drive signal may reverse polarity at a frequency of, for example, 30 to 120 Hz, for example, 60 Hz.

[0047] Such a first drive signal Sg1 generates an electric field E between the patch electrode 102 and the first sub-drive electrodes 105A1 and 105B1 and the second sub-drive electrodes 105A2 and 105B2. Fig. 6B schematically shows liquid crystal molecules 118 contained in the liquid crystal layer 106. The liquid crystal molecules 118 have a long, thin, rod-like structure. Under the action of the electric field E, the liquid crystal molecules 118 are oriented so that the longitudinal direction of the rod-like molecules is parallel to the direction of the electric field.

[0048] Specifically, between the patch electrode 102 and the first sub-drive electrodes 105A1, 105B1 and the second sub-drive electrodes 105A2, 105B2 to which the first drive signal Sg1 is applied, the liquid crystal molecules 118 are affected by the electric field E and are oriented so that the longitudinal directions of the rod-shaped molecules stand vertically. On the other hand, in the region of the third sub-drive electrodes 105A3, 105B3, no electric field is generated, so the liquid crystal molecules 118 maintain their initial orientation, and the longitudinal directions of the rod-shaped molecules are oriented in a direction parallel to the surface of the second substrate 152 (horizontal direction). As described above, according to the configuration of this embodiment, the drive electrode 104 is divided into multiple sub-drive electrodes 105, so that the orientation state of the liquid crystal molecules 118 can be partially changed from the initial orientation state in the region overlapping with the patch electrode 102.

[0049] The dielectric constant of the liquid crystal layer 106 varies depending on the orientation of the liquid crystal molecules 118. In the configuration according to this embodiment, the orientation of the liquid crystal layer 106 can be locally changed within the plane of the patch electrode 102. As described above, because the wavelength of the reflected radio wave is longer than the length of one side of the patch electrode 102, local dielectric constant components do not directly affect the radio wave reflection characteristics. However, by changing the average value of the dielectric constant of the liquid crystal layer 106 within the plane of one patch electrode 102, it is possible to change the phase of the reflected radio wave. Therefore, by dividing the drive electrode 104 into multiple sub-drive electrodes 105, the effective dielectric constant of the liquid crystal layer 106 can be changed in multiple stages depending on the number of divisions. This allows for precise control of the radio wave reflection direction by the liquid crystal metasurface reflector 100.

[0050] The liquid crystal metasurface reflector 100 is designed to detect radio wave frequency bands including the very high frequency (VHF), ultra-high frequency (UHF), super high frequency (SHF), submillimeter wave (THF), extra high frequency (EHF), and terahertz wave bands. The orientation of the liquid crystal molecules 118 in the liquid crystal layer 106 changes depending on the drive signal applied to the sub-drive electrode 105, but does not change significantly with the frequency of the radio wave incident on the patch electrode 102. Therefore, the dielectric constant of the liquid crystal layer 106 is changed by the sub-drive electrode 105, and the patch electrode 102 reflects the radio wave, allowing for precise control of the phase of the reflected radio wave (the direction of travel of the reflected wave).

[0051] As described above, in the liquid crystal metasurface reflector 100 according to this embodiment, the patch electrodes 102 are connected by strip wiring 103, as shown in Fig. 7. Fig. 7 shows a structure in which the patch electrodes 102 arranged in the Y-axis direction are connected by strip wiring 103, but the connection direction of the strip wiring 103 is not limited to the example shown. The strip wiring 103 may be used to connect the patch electrodes 102 arranged along the X-axis direction, or may be used to connect in both the X-axis and Y-axis directions.

[0052] 7, the width of the strip wiring 103 connecting the patch electrodes 102 may be extremely thin. The width W2 of the strip wiring 103 may be 1 / 100 or less of the length W1 of one side of the patch electrode 102. For example, if the length W1 of one side of the patch electrode 102 is 10 mm, the line width of the strip wiring may be 100 μm or less.

[0053] The strip wiring 103 may have a linear shape in plan view, or may be bent in a crank shape as shown in Fig. 7. The length of the strip wiring 103 is set to a value equal to or greater than the effective wavelength λ of the reflected radio wave. ｇ Specifically, λ ｇIt is preferable that the effective wavelength is within ±10% of the relative dielectric constant ε of the liquid crystal layer. ｓ Based on this, λ is expressed as the following equation (1). ｇ = λ / (ε ｓ ) １／２ (1) By making the length of the strip wiring 103 approximately half the effective wavelength of the radio wave as described above, the current density distribution generated in the patch electrode 102 can be prevented from being disturbed, and reflection loss can be suppressed.

[0054] According to the configuration of the liquid crystal metasurface reflector 100 of this embodiment, by dividing the drive electrode 104 that controls the orientation state of the liquid crystal layer 106 into multiple sub-drive electrodes 105, the effective dielectric constant of the liquid crystal layer 106 against radio waves can be changed in multiple stages, more than the number of gradations (number of voltage levels) of the input drive signal. As a result, even when using a drive circuit with a small number of gradations or a simple circuit configuration consisting only of a power supply circuit, the dielectric constant of the liquid crystal layer 106 can be changed in multiple stages, and the reflection direction of radio waves can be changed in multiple stages.

[0055] The various configurations of the liquid crystal metasurface reflector exemplified as one embodiment of the present invention can be combined as appropriate as long as they are not mutually inconsistent. Furthermore, liquid crystal metasurface reflectors disclosed in this specification and drawings, to which a person skilled in the art has appropriately added, deleted, or modified components, or to which a process has been added, omitted, or conditions have been changed, are also included within the scope of the present invention as long as they contain the gist of the present invention.

[0056] Even if there are other effects and advantages different from those brought about by the aspects of the embodiments disclosed in this specification, those that are clear from the description in this specification or that can be easily predicted by a person skilled in the art are naturally understood to be brought about by the present invention.

[0057] 100: liquid crystal metasurface reflector, 102: patch electrode, 103: strip wiring, 104: drive electrode, 105A: first sub-drive electrode, 105B: second sub-drive electrode, 105C: third sub-drive electrode, 105D: fourth sub-drive electrode, 106: liquid crystal layer, 107A: first alignment film, 107B: second alignment film, 108: ground electrode, 109: insulating layer, 110: scanning signal line drive circuit, 111: scanning signal line, 112: drive signal line selection circuit, 113: drive signal line, 113A: first drive signal line, 113B: second drive signal line, 114: terminal portion, 115: terminal electrode, 116: switching element, 1162: semiconductor layer, 116A: first switching element, 116B: second switching element, 118: liquid crystal molecules, 150: first substrate, 152: second substrate

Claims

1. A liquid crystal metasurface reflector comprising patch electrodes arranged in a matrix, drive electrodes overlapping the patch electrodes, and a liquid crystal layer between the patch electrodes and the drive electrodes, wherein the drive electrodes are divided into a plurality of sub-drive electrodes, and the plurality of sub-drive electrodes can be driven individually to locally control the orientation state of the liquid crystal layer within the plane of the patch electrodes.

2. The liquid crystal metasurface reflector of claim 1, wherein each of the plurality of sub-driving electrodes is connected to a switching element and a driving signal is applied individually via the switching element.

3. The liquid crystal metasurface reflector of claim 1, wherein the areas of the multiple sub-driving electrodes are equal.

4. The liquid crystal metasurface reflector of claim 1, wherein one sub-driving electrode among the plurality of sub-driving electrodes has a different area from another sub-driving electrode.

5. The liquid crystal metasurface reflector of claim 1, wherein the plurality of sub-drive electrodes include a plurality of sub-drive electrodes having a first shape and a plurality of sub-drive electrodes having a second shape different from the first shape, and the plurality of sub-drive electrodes having the first shape and the plurality of sub-drive electrodes having the second shape are arranged to have symmetry in a plane overlapping the patch electrode.

6. The liquid crystal metasurface reflector of claim 1, wherein the plurality of patch electrodes are connected by strip wiring.

7. The liquid crystal metasurface reflector described in claim 6, wherein the width of the strip wiring is 1 / 100 or less of the length of one side of the patch electrode.

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