Radio wave reflecting device and method for driving radio wave reflecting device

Abstract

The radio wave reflecting device is provided with a plurality of radio wave reflecting elements arranged in a matrix of m rows and n columns. Each of the plurality of radio wave reflecting elements has a first electrode, a liquid crystal layer on the first electrode, and an electrically floating second electrode on the liquid crystal layer. The driving method includes applying a control potential based on a reference potential to the first electrode without applying a potential to the second electrode during the first frame period. In the first frame period, the sum of the control potentials applied to the first electrodes of the plurality of radio wave reflecting elements is 0 V. M and n are each independently selected from natural numbers of 6 or more, and n is an even number.

Description

Technical Field

[0001] One embodiment of the present invention relates to a radio wave reflection device and a driving method thereof. Background Art

[0002] Liquid crystal molecules have dielectric anisotropy. Therefore, by adjusting the electric field applied to the liquid crystal layer containing the liquid crystal molecules to control the orientation of the liquid crystal molecules, the dielectric constant of the liquid crystal layer can be controlled. Metal surfaces that utilize this property to control the reflection characteristics of liquid crystal layers with respect to radio waves are known (see, for example, Patent Documents 1 and 2).

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 11-103201

[0006] Patent Document 2: Japanese Patent Application Publication No. 2019-530387 Summary of the Invention

[0007] One embodiment of the present invention is to provide a radio wave reflection device having a new structure and a driving method thereof. Alternatively, one embodiment of the present invention is to provide a radio wave reflection device having low manufacturing cost and low power consumption and a driving method thereof.

[0008] One embodiment of the present invention is a method for driving a radio wave reflection device. The radio wave reflection device includes a plurality of radio wave reflection elements arranged in a matrix of m rows and n columns. Each of the plurality of radio wave reflection elements includes a first electrode, a liquid crystal layer on the first electrode, and an electrically floating second electrode on the liquid crystal layer. The driving method includes applying a control potential based on a reference potential to the first electrode during a first frame period without applying a potential to the second electrode. During the first frame period, the sum of the control potentials applied to the first electrodes of the plurality of radio wave reflection elements is 0 V. m and n are each independently selected from natural numbers greater than or equal to 6, with n being an even number.

[0009] One embodiment of the present invention is a radio wave reflecting device. The radio wave reflecting device includes a plurality of radio wave reflecting elements arranged in a matrix of m rows and n columns. Each of the plurality of radio wave reflecting elements includes a first electrode, a liquid crystal layer on the first electrode, and an electrically floating second electrode on the liquid crystal layer. m and n are each independently selected from natural numbers greater than or equal to 6, with n being an even number. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 This is a schematic plan view of a radio wave reflecting device according to one embodiment of the present invention.

[0011] Figure 2This is a schematic end view of a radio wave reflecting device according to one embodiment of the present invention.

[0012] Figure 3A This is a schematic plan view of a counter substrate of a radio wave reflection device according to one embodiment of the present invention.

[0013] Figure 3B This is a schematic cross-sectional view of a counter substrate of a radio wave reflection device according to one embodiment of the present invention.

[0014] Figure 4 This is a schematic plan view of a radio wave reflecting device according to one embodiment of the present invention.

[0015] Figure 5 This is a timing chart showing a method of driving the radio wave reflection device according to one embodiment of the present invention.

[0016] Figure 6 This is a schematic plan view illustrating a method for driving a radio wave reflection device according to one embodiment of the present invention.

[0017] Figure 7A This is a schematic diagram illustrating a method for driving a radio wave reflection device according to one embodiment of the present invention.

[0018] Figure 7B This is a schematic diagram illustrating a method for driving a radio wave reflection device according to one embodiment of the present invention.

[0019] Figure 8A This is a schematic diagram illustrating a method for driving a radio wave reflection device according to one embodiment of the present invention.

[0020] Figure 8B This is a schematic diagram illustrating a method for driving a radio wave reflection device according to one embodiment of the present invention.

[0021] Figure 8C This is a schematic diagram illustrating a method for driving a radio wave reflection device according to one embodiment of the present invention.

[0022] Figure 9A This is a schematic diagram illustrating a method for driving a radio wave reflection device according to one embodiment of the present invention.

[0023] Figure 9B This is a schematic diagram illustrating a method for driving a radio wave reflection device according to one embodiment of the present invention.

[0024] Figure 9C This is a schematic diagram illustrating a method for driving a radio wave reflection device according to one embodiment of the present invention.

[0025] Figure 10A This is a schematic diagram illustrating a method for driving a radio wave reflection device according to one embodiment of the present invention.

[0026] Figure 10B This is a schematic diagram illustrating a method for driving a radio wave reflection device according to one embodiment of the present invention.

[0027] Figure 10C This is a schematic diagram illustrating a method for driving a radio wave reflection device according to one embodiment of the present invention.

[0028] Figure 11A This is a schematic diagram illustrating a method for driving a radio wave reflection device according to one embodiment of the present invention.

[0029] Figure 11B This is a schematic diagram illustrating a method for driving a radio wave reflection device according to one embodiment of the present invention.

[0030] Figure 11C This is a schematic diagram illustrating a method for driving a radio wave reflection device according to one embodiment of the present invention. DETAILED DESCRIPTION

[0031] Hereinafter, various embodiments of the present invention will be described with reference to the drawings, etc. However, the present invention can be implemented in various forms without departing from the gist of the present invention, and the description of the embodiments illustrated below is not to be interpreted as limiting.

[0032] To clarify the description, the width, thickness, shape, etc. of various parts in the drawings may be schematically illustrated compared to the actual form, but this is merely an example and does not limit the interpretation of the present invention. In this specification and each figure, elements having the same function as elements described in the previous figure may be denoted by the same reference numerals, and repeated descriptions may be omitted.

[0033] In this specification and claims, when expressing a manner of arranging another structure on a certain structure, when simply expressed as "on", unless otherwise specified, it includes two situations: a situation where the other structure is arranged directly above the certain structure in a manner of being in contact with the certain structure; and a situation where the other structure is arranged above the certain structure with the other structure interposed therebetween.

[0034] 1. Composition of radio wave reflection device

[0035] The following describes the structure of a radio wave reflection device, one embodiment of the present invention. This radio wave reflection device is a so-called liquid crystal metal surface reflector. It utilizes the change in dielectric constant caused by the orientation change of the liquid crystal layer due to an electric field to reflect the incident radio waves in any direction. The frequency of the radio waves that can be reflected is not limited, for example, it ranges from 400 MHz to 50 GHz. Typically, this radio wave reflection device can reflect radio waves in the 400 MHz to 6.0 GHz band, the 2.5 GHz to 4.7 GHz band, and the 24 GHz to 50 GHz band.

[0036] Figure 1 FIG. 1 shows a schematic top view of the radio wave reflection device 100. The radio wave reflection device 100 includes a substrate 102 and a Figure 1 A plurality of patterned insulating films, semiconductor films, and conductive films are formed between the opposing substrates not shown in the figure. By appropriately stacking these films, a plurality of radio wave reflecting elements 130 arranged in a matrix of m rows and n columns are formed. In addition to the radio wave reflecting elements 130, the radio wave reflecting device 100 also includes a gate line driving circuit 104 and a signal line driving circuit 106 for supplying a variety of signals to the radio wave reflecting elements 130. The gate line driving circuit 104 and the signal line driving circuit 106 can be formed by insulating films, semiconductor films, and conductive films formed on the substrate 102, or by mounting an integrated circuit formed on a semiconductor substrate on the substrate 102. The gate line driving circuit 104 can be one or more. In the latter case, as shown in FIG. Figure 1 As shown, two gate line driving circuits 104 may be arranged on the substrate 102 with a plurality of radio wave reflecting elements 130 interposed therebetween. The signal line driving circuit 106 is arranged on one side of the substrate 102. Here, m and n are independently selected from natural numbers greater than 6, and n is an even number.

[0037] Multiple gate lines and multiple signal lines (in Figure 1 (not shown) extend from the gate line driver circuit 104 and the signal line driver circuit 106, respectively, and are electrically connected to the radio wave reflection element 130. A plurality of terminals 108 are also provided on the substrate 102. Various signals for driving the radio wave reflection element 130 are supplied via the terminals 108 from an external circuit (not shown). The gate line driver circuit 104 and the signal line driver circuit 106 generate gate signals based on the supplied signals, control the potential, and supply the signals to the radio wave reflection element 130.

[0038] 2. Structure of the radio wave reflection element

[0039] (1) Overall composition

[0040] Figure 2A schematic diagram of a partial cross section of the radio wave reflection device 100 is shown in FIG. The radio wave reflection element 130 is connected to an element circuit including at least one transistor. Each element circuit may also include multiple transistors and one or more capacitor elements. Figure 2 In the illustrated example, one transistor 150 , one radio wave reflecting element 130 connected thereto, and a portion of an adjacent radio wave reflecting element 130 are illustrated.

[0041] according to Figure 2 As can be seen, the element circuit and the radio wave reflecting element 130 are provided on the substrate 102 directly or via a primer layer 112 of any structure. The structure of the transistor included in the element circuit is not limited and can be a bottom-gate transistor or a top-gate transistor. Alternatively, the transistor can have gate electrodes above and below the semiconductor film. Figure 2 The transistor illustrated in the figure is a bottom-gate transistor and is composed of a gate electrode 152, a gate insulating film 154 on the gate electrode 152, a semiconductor film 156 on the gate insulating film 154, and a pair of terminals 158 and 160 on the semiconductor film 156. A planarization film 164 is provided on the transistor 150, and the radio wave reflecting element 130 is formed thereon. As an optional configuration, interlayer insulating films 162 and 166 may be provided between the transistor 150 and the planarization film 164, and on the planarization film 164, respectively.

[0042] The radio wave reflecting element 130 includes a first electrode (also called a patch electrode) 132, a first orientation film 134 on the first electrode 132, a liquid crystal layer 136 on the first orientation film 134, a second orientation film 138 on the liquid crystal layer 136, and a second electrode 140 on the second orientation film 138. The second electrode 140 is provided on the counter substrate 110 (either directly or via an overcoat layer 114 of an arbitrary structure). Figure 2 The first electrode 132 is electrically connected to the transistor 150 via an opening provided in the interlayer insulating film 162, the planarizing film 164, etc., thereby supplying a control potential from the signal line driving circuit 106 to the radio wave reflecting element 130. These structures are described below.

[0043] (2) Substrate and counter substrate

[0044] The substrate 102 and the counter substrate 110 are provided to impart physical strength to the radio wave reflecting device 100 and to provide a surface for arranging the radio wave reflecting element 130. The substrate 102 and / or the counter substrate 110 are flexible. The substrate 102 and the counter substrate 110 can be made of inorganic insulators such as glass and quartz; semiconductors such as silicon; polymers such as polyimide, polycarbonate, and polyester; or metals such as aluminum, copper, and stainless steel. When using conductive materials such as metals, it is preferable to form a film comprising an insulator such as silicon oxide or silicon nitride as the undercoat 112 and overcoat 114 on the surface where the radio wave reflecting element 130 is provided, i.e., the surface of the substrate 102 facing the counter substrate 110 and the surface of the counter substrate 110 facing the substrate 102. The substrate 102 and the counter substrate 110 can transmit or not transmit visible light.

[0045] (3) Transistor

[0046] The gate electrode 152, gate insulating film 154, semiconductor film 156, terminals 158 and 160 that constitute the transistor 150, and the interlayer insulating films 162 and 166 and planarizing film 164 that cover the transistor 150 can be formed using known materials and appropriately applying known methods, so detailed descriptions are omitted. In short, the gate electrode 152 and terminals 158 and 160 are formed by forming a film containing a metal such as tantalum, molybdenum, titanium, or aluminum using sputtering, chemical vapor deposition (CVD), or the like, and then patterning it appropriately using a photolithography process. The semiconductor film 156 is formed as a film containing a Group 14 element such as silicon, or a film containing an oxide of a Group 13 element such as indium or gallium. The semiconductor film 156 can also be formed using sputtering or CVD. The gate insulating film 154 and the interlayer insulating films 162 and 166 contain silicon-containing inorganic compounds such as silicon oxide and silicon nitride and are formed using sputtering or CVD. The planarizing film 164 is made of a polymer such as acrylic resin, epoxy resin, polyimide, polyamide, or silicone resin, and can be formed using a wet film forming method such as spin coating, inkjet, or printing. Providing the planarizing film 164 allows the radio wave reflecting element 130 to be formed on a flat surface.

[0047] (4) Radio wave reflection element

[0048] The first electrode 132 of the radio wave reflecting element 130 comprises a metal such as copper, aluminum, tungsten, molybdenum, or titanium, or an alloy comprising at least one of these metals. Alternatively, the first electrode 132 may comprise a light-transmitting conductive oxide such as indium-zinc oxide (IZO) or indium-tin oxide (ITO). The first electrode 132 may have a single-layer structure or a stacked structure comprising layers of different compositions. For example, a stacked structure may comprise a layer comprising a conductive oxide and a layer comprising the aforementioned metal or alloy. Alternatively, to impart light transmittance to the radio wave reflecting device 100 having the first electrode 132 comprising a metal or alloy, the first electrode 132 may have a mesh-like shape.

[0049] The first orientation film 134 provided on the plurality of first electrodes 132 is provided to control the orientation of liquid crystal molecules constituting a liquid crystal layer 136 provided on the first orientation film 134. The first orientation film 134 can be provided continuously across the plurality of radio wave reflecting elements 130. In other words, the first orientation film 134 can be provided so as to be shared by all radio wave reflecting elements 130 without being separated from each other between adjacent radio wave reflecting elements 130.

[0050] The first alignment film 134 comprises a polymer such as polyimide or polyester. The first alignment film 134 is formed using a wet film-forming method such as inkjet, spin coating, printing, or dip coating, and its surface is rubbed. Alternatively, the first alignment film 134 can be formed using a photo-alignment process.

[0051] The liquid crystal layer 136 includes liquid crystal molecules. The structure of the liquid crystal molecules is not limited. Therefore, the liquid crystal molecules may be nematic liquid crystals, smectic liquid crystals, cholesteric liquid crystals, or chiral liquid crystals. The thickness of the liquid crystal layer 136 is, for example, not less than 20 μm and not more than 50 μm, or not less than 30 μm and not more than 50 μm. Although not shown, spacers may be provided within the liquid crystal layer 136 to maintain this thickness throughout the entire radio wave reflection device 100. It should be noted that when a liquid crystal display device adopts the aforementioned thickness of the liquid crystal layer 136, the high responsiveness required for displaying video cannot be achieved, making it very difficult to function as a liquid crystal display device.

[0052] The second orientation film 138 is also provided to control the alignment of liquid crystal molecules and has the same structure as the first orientation film 134. The second orientation film 138 also extends continuously across adjacent radio wave reflecting elements 130 and can be shared by multiple radio wave reflecting elements 130. The first and second orientation films 134, 138 are arranged so that the direction in which the first orientation film 134 aligns the liquid crystal molecules is parallel to the direction in which the second orientation film 138 aligns the liquid crystal molecules. The first and second orientation films 134, 138 align the liquid crystal molecules in a fixed direction.

[0053] Similar to the first electrode 132, the second electrode 140 may also include a metal such as copper, aluminum, tungsten, molybdenum, or titanium; an alloy containing at least one of these metals; or a conductive oxide such as ITO or IZO. The second electrode 140 may have a single-layer structure or a stacked structure comprising layers of different compositions. The second electrode 140 may also be formed using a sputtering method, a CVD method, or the like. The second electrode 140 may be provided for each radio wave reflecting element 130, or may be provided as a single integrated electrode across multiple radio wave reflecting elements 130, so as to be shared by the multiple radio wave reflecting elements 130.

[0054] Here, in the radio wave reflection device 100, the second electrode 140 is electrically floating and does not receive a signal or potential from an external circuit. Therefore, as shown in the schematic top view of the counter substrate 110 viewed from the substrate 102 side ( Figure 3A ) and a schematic diagram of a cross section along the dot-dash line AA′ therein ( Figure 3B ), the second electrode 140 can be provided so that its entirety is sealed (enclosed) between the counter substrate 110 and the second orientation film 138. In the case where the overcoat layer 114 is provided, the second electrode 140 can be provided so that its entirety is sealed (enclosed) between the overcoat layer 114 and the second orientation film 138.

[0055] 3. Driving method of radio wave reflection device

[0056] Next, a method of driving the radio wave reflection device 100 will be described. Figure 4 1 is a schematic top view showing the arrangement of the radio wave reflecting elements 130 in the radio wave reflecting device 100. As described above, the plurality of radio wave reflecting elements 130 are arranged in a matrix of m rows and n columns. The gate lines G1 to G2 are used to supply gate signals to the transistors Tr connected to the plurality of radio wave reflecting elements 130 arranged in each row. m The gate line driving circuit 104 extends from the source lines S1 to S2 for supplying control potentials to the transistors Tr connected to the plurality of radio wave reflection elements 130 arranged in each column. n The radio wave reflection elements 130 located in each row are connected to the same gate line G via the element circuit, and the radio wave reflection elements 130 located in each column are connected to the same source line S via the element circuit. Figure 4 The transistor Tr shown is a switching transistor for controlling the on / off of each element circuit, and may also be a transistor 150 connected to the radio wave reflection element 130 (see FIG. Figure 2), or a transistor different from the transistor 150. Therefore, the transistor Tr may be directly connected to the radio wave reflection element 130, or may be connected to the radio wave reflection element 130 via another transistor or a capacitor. By supplying a gate potential to the gate of the transistor Tr via the gate line G, the element circuit is turned on, and the signal lines S1 to S2 are connected. n A control potential is supplied to the first electrode 132 of the radio wave reflecting element 130 .

[0057] Figure 5 An example of a timing diagram showing the present driving method is shown. This diagram shows changes in the potential applied to the gate line G and the signal line S during two fixed-time frames (the first frame period FP1 and the second frame period FP2). The time of each frame period FP is appropriately selected from a range of, for example, 1 / 60 second to 1 second. Each frame period FP is divided into m sub-frame periods SFP1 to SFP2. m In each subframe period SFP, a control potential is supplied to the n radio wave reflecting elements 130 arranged in a row for writing. Note that since the second electrode 140 is electrically floating, no potential is applied to the second electrode 140 .

[0058] according to Figure 5 It can be seen that in one frame period FP, the first to mth sub-frame periods SFP1 to SFP m The gate signal is supplied to one gate line G in each subframe period SFP. That is, the potential of the gate line G changes from the potential that turns off the transistor Tr (hereinafter referred to as the potential Low for convenience) to the voltage that turns on the transistor Tr (hereinafter referred to as the potential High for convenience). m The gate signals are supplied in sequence.

[0059] (1) Residual protection against DC voltage

[0060] While the potential High is supplied to one gate line G, the first electrodes 132 of the radio wave reflection elements 130 arranged in the row are connected via the signal lines S1 to S2. nA control potential is supplied to the element circuit and applied to the first electrode 132. The magnitude of the control potential is determined by the reflection direction of the radio wave incident on the radio wave reflecting device 100. When the magnitude of the control potential is defined relative to a reference potential of 0 V, the radio wave reflecting device 100 is driven so that the sum of the control potentials of the first electrodes 132 simultaneously written to during each subframe period SFP is 0 V (or substantially 0 V, for example, less than ±0.1 V or less than ±0.2 V. The same shall apply hereinafter). That is, during each frame period FP, the radio wave reflecting device 100 is driven so that the sum of the control potentials supplied to the first electrodes 132 of the radio wave reflecting elements 130 arranged in each row is 0 V. The reference potential may be, for example, the ground potential or the potential of the second electrode 140.

[0061] Here, as Figure 6 As shown, the control potential supplied to the first electrode 132 of the radio wave reflection element 130 is set to V(x, y). x and y are variables representing the row and column numbers, respectively. x is a natural number selected from 1 to m, and y is a natural number selected from 1 to n. In the first subframe period SFP1, the potential of the gate line G1 is High (see Figure 5 ), from the signal line driver circuit 106 via the signal lines S1 to S m The control potentials V(1, 1) to V(1, n) are supplied to the first electrode 132. At this time, the sum of the control potentials V(1, 1) to V(1, n) is 0 V. In the subsequent second subframe period SFP2, the potential of the gate line G2 becomes High, and the signal line driving circuit 106 transmits the gate line G2 via the signal lines S1 to S2. m Control potentials V(2,1) to V(2,n) are supplied. At this time, the sum of the control potentials V(2,1) to V(2,n) is also 0 V. This is the same for all rows. Generally speaking, in each frame period SF, in the xth subframe period SFP x The control potentials V(x, 1) to V(x, n) applied to the first electrodes 132 of the radio wave reflecting elements 130 arranged in the xth row are partially positive relative to the reference potential and partially negative relative to the reference potential, with the total being 0 V. The number of radio wave reflecting elements 130 with positive and negative control potentials is the same. Therefore, in one frame period FP, the total of the control potentials V(1, 1) to V(m, n) applied to all first electrodes 132 is also 0 V. It should be noted that in each frame period FP, the total of the control potentials applied to the first electrodes 132 of the radio wave reflecting elements 130 in each column (i.e., the total of V(x, 1) to V(x, m)) may or may not be 0 V.

[0062] As described later, the radio wave reflecting device 100 employs so-called inversion drive. If the liquid crystal layer 136 contains a trace amount of ions, the ionic charge may accumulate, generating a bias component (DC component). However, as described above, during each frame period, by driving the radio wave reflecting device 100 so that the sum of the control potentials in each row reaches 0V, the charge in the electrically floating second electrode 140 is eliminated. Therefore, there is no need to supply a signal to the second electrode 140 to adjust its potential in order to eliminate the DC component. This contributes to the simplification of the structure of the radio wave reflecting device 100 and reduces manufacturing costs. Furthermore, since there is no need to supply a signal or potential to the second electrode 140, the burden on the external circuitry during driving is reduced, resulting in lower power consumption.

[0063] (2) Control of reflection direction

[0064] In the radio wave reflecting element 100 having the above structure, the first orientation film 134 and the second orientation film 138 align the liquid crystal molecules in the same direction. Therefore, when no potential difference is applied between the first electrode 132 and the second electrode 140, no longitudinal electric field is generated in the liquid crystal layer 136, and the liquid crystal molecules are splay-oriented. Since the orientation of the liquid crystal layer 136 between the radio wave reflecting elements 130 is the same, the dielectric constant is also constant within the liquid crystal layer 136. Therefore, Figure 7A As shown by the dotted arc, the radio wave incident from the second electrode 140 side ( Figure 7A The solid hollow arrow in the figure is reflected by the surface of the first electrode 132, and the expansion (phase shift) of the generated reflected wave does not change. As a result, the incident radio wave is reflected by the radio wave reflecting element 100, giving a reflected wave ( Figure 7A (dashed hollow arrow in the figure).

[0065] On the other hand, if a potential difference is applied between the first electrode 132 and the second electrode 140, the generated longitudinal electric field causes the liquid crystal molecules to stand upright and bend-align. At this time, if longitudinal electric fields of different strengths are generated between the radio wave reflecting elements 130, the dielectric constant of the liquid crystal layer 136 varies between the radio wave reflecting elements 130 according to the strength of the longitudinal electric field. As a result, Figure 7B As shown by the dotted arc, the phase shift of the reflected wave changes, and with it, the incident radio wave ( Figure 7B The change of the reflection direction (see Figure 7B The reflection direction can be controlled by changing the intensity of the longitudinal electric field formed in the radio wave reflecting element 130.

[0066] To control the reflection direction of radio waves incident on the radio wave reflecting element 100, the orientation of the liquid crystal molecules contained in the liquid crystal layer 136 is controlled, causing the dielectric constant of the liquid crystal layer 136 to periodically vary. The orientation of the liquid crystal molecules is determined by the absolute value of the control potential. Therefore, during each frame period FP, the absolute value of the control potential is continuously and periodically increased or decreased in the row and / or column directions.

[0067] Specifically, when the control potential is varied in the row direction, all radio wave reflecting elements 130 arranged in each row are divided into a plurality of element blocks containing the same number of radio wave reflecting elements 130 as the number of consecutively arranged elements. The number of element blocks is an even number. Specifically, in each row, all radio wave reflecting elements 130 are divided into k element blocks each containing j consecutively arranged radio wave reflecting elements 130. j is a natural number greater than or equal to 1, k is a natural number greater than or equal to an even number, and the product of j and k is n.

[0068] exist Figures 8A to 11C The control potential applied to the first electrodes 132 of the radio wave reflection elements 130 arranged in one row (row x) or one column (column y) is schematically shown. In this driving method, the absolute value of the control potential is further fixed in each element block ( Figure 8A ) or increase or decrease the absolute value of the control potential in the order of the columns ( Figure 8B 、 Figure 8C ). When the absolute value of the control potential is fixed to a certain value, the absolute value of the control potential can be 0V, or it can be greater than or less than 0V. In each component block, the positive and negative (polarity) of the control potential can be arbitrarily determined. Therefore, in each component block, the polarity of the control potential can be as follows Figures 8A to 8C The same as shown, can also be Figures 9A to 9C . In the former case, the polarity of the control potential can be the same between adjacent element blocks, but it is preferably alternately reversed. In the latter case, it is preferable to alternate the polarity of the control potential on a column-by-column basis within each element block. This shortens the distance traveled by the DC component charge, enabling more efficient charge elimination. However, as described above, during each frame period FP, the radio wave reflection device 100 is driven so that the sum of the control potentials in each row is 0 V.

[0069] Furthermore, to ensure uniform reflection directions of radio waves within the radio wave reflecting device 100, the magnitude and variation of the control potential are preferably the same across all element blocks. In other words, the radio wave reflecting device 100 is preferably driven during each frame period FP so that the absolute value of the control potential applied to the first electrodes 132 of the radio wave reflecting elements 130 selected every j columns in each row is the same, and the polarity relative to the reference voltage alternates. In other words, the radio wave reflecting device 100 is preferably driven during each frame period FP so that the absolute value of the control potential continuously increases or decreases in each row, enabling selection of j consecutively arranged radio wave reflecting elements 130.

[0070] For example, Figure 8B 、 Figure 9B To explain specifically by way of example, the control potentials V(x, 1), V(x, j+1), V(x, 2j+1), and V(x, 3j+1) of the 1st column, the j+1th column, the 2j+1th column, and the 3j+1th column have the same absolute value, but alternate polarities (i.e., the polarities are reversed in the order of the columns). Furthermore, in the xth row, as the radio wave reflecting elements 130 continuously arranged with the absolute value of the control potential continuously increasing, for example, the radio wave reflecting elements 130 assigned control potentials of V(x, 1) to V(x, j) or the radio wave reflecting elements 130 assigned control potentials of V(x, j+1) to V(x, 2j) can be selected. By driving the radio wave reflecting device 100 in this manner, it is possible to reflect radio waves in a direction rotating around an axis parallel to the row direction. It should be noted that Figure 8A 、 Figure 9A The case where j is 1 is shown. In this case, the absolute value of the control potential is the same in each row, and the intensity of the longitudinal electric field generated in the liquid crystal layer 136 is also constant, so when observed from the row direction, radio waves are regularly reflected.

[0071] The same applies when varying the control potential in the column direction. Specifically, in each column, all radio wave reflecting elements 130 are divided into h element blocks, each consisting of g radio wave reflecting elements 130 arranged in a row. g and h are each independently a natural number greater than or equal to 1, and the product of g and h is m. The number of element blocks h can be either an even or odd number. However, when the radio wave reflecting device 100 is driven in each frame period SF so that the sum of the control potentials applied to the first electrodes 132 of the radio wave reflecting elements 130 arranged in each column is 0 V, the number of element blocks h is set to an even number.

[0072] Furthermore, the absolute value of the control potential is fixed in each element block ( Figure 10A ) or increase or decrease the absolute value of the control potential in the order of rows ( Figure 10B 、 Figure 10C ). In each component block, the polarity of the control potential can be determined arbitrarily. In each component block, the polarity of the control potential can be determined as follows Figures 10A to 10CThe same as shown, can also be Figure 11A and Figure 11B As shown, the polarity of the control potential is the same in all component blocks. Alternatively, Figure 11C As shown, the polarity of the control potential may be different in each element block. When the polarity of the control potential is the same in each element block, it is preferable to set h to an even number, and the polarity of the control potential is reversed between adjacent element blocks ( Figures 10A to 10C When the polarity of the control potential is different in each element block, it is preferable to alternate the polarity of the control potential in each element block ( Figure 11C ). As a result, the movement distance of the charge that causes the DC component is shortened, and the charge can be eliminated more efficiently.

[0073] Furthermore, similar to the control in the row direction, in order to make the reflection direction of radio waves uniform within the radio wave reflecting device 100, it is preferable to drive the radio wave reflecting device 100 during each frame period so that the absolute value of the control potential applied to the first electrode 132 of the radio wave reflecting elements 130 selected every g rows in each column is the same. In other words, it is preferable to drive the radio wave reflecting device 100 during each frame period FP so that the absolute value of the control potential in each column continuously increases or decreases, thereby enabling the selection of g consecutively arranged radio wave reflecting elements 130.

[0074] For example, Figure 10B 、 Figure 11B For example, the absolute values ​​of the control potentials V(1, y), V(g+1, y), V(2g+1, y), and V(3g+1, y) in row 1, row g+1, row 2g+1, and row 3g+1 are the same. The polarities of these control potentials may be alternated (i.e., the polarity is reversed in the order of the rows). Figure 10B ) can also be fixed ( Figure 11B ). Furthermore, in the y-th row, as the radio wave reflecting elements 130 arranged continuously with the absolute values ​​of the control potentials continuously increasing, for example, radio wave reflecting elements 130 assigned control potentials of V(1, y) to V(g, y) or radio wave reflecting elements 130 assigned control potentials of V(g+1, y) to V(2g, y) can be selected. By driving the radio wave reflecting device 100 in this manner, radio waves can be reflected in a direction rotating around an axis parallel to the column direction. It should be noted that Figure 10A and Figure 11A The case where g is 1 is shown. In this case, the control potential is the same in each column, and the intensity of the longitudinal electric field generated in the liquid crystal layer 136 is constant. Therefore, when viewed from the row direction, radio waves are regularly reflected.

[0075] By adopting the above-described driving method, it is possible to prevent the generation of a DC component and to arbitrarily control the reflection direction of an incident radio wave in both the row direction and the column direction.

[0076] (3) Reverse drive

[0077] During the driving process of the radio wave reflection element 100, in order to prevent the temporary fixation of the orientation of the liquid crystal molecules due to the accumulation of ionic components or the polarization of the liquid crystal molecules (also known as image sticking (burn-in)), so-called inversion driving is adopted. That is, the radio wave reflection element 100 is driven so that the direction of the longitudinal electric field generated in the liquid crystal layer 136 is reversed every frame period FP. Specifically, Figure 5 As shown, the control potential applied to each first electrode 132 during one frame period (first frame period FP1) is inverted relative to the reference potential during the subsequent frame period (second frame period FP2). Therefore, if the reference potential is 0V, the potential V(x, y) applied to the first electrode 132 of the radio wave reflection element 130 in row x and column y during the first frame period FP1 will have its polarity reversed to -V(x, y) during the second frame period FP2. This inversion drive prevents charge accumulation caused by trace impurities in the liquid crystal layer 136, polarization of the liquid crystal molecules, and image retention (screen burn-in).

[0078] As described above, in the radio wave reflecting device 100 of the present invention, in the plurality of radio wave reflecting elements 130 arranged in m rows and n columns, the second electrode 140 opposite the patch electrode (first electrode 132) to which the control potential is applied is electrically floating. Furthermore, during each frame period FP, the radio wave reflecting device 100 is driven in each row so that the sum of the control potentials applied to the first electrodes 132 of the radio wave reflecting elements 130 is 0 V. Therefore, the charge that causes the generation of the DC component is eliminated within the electrically floating second electrode 140, eliminating the need for potential adjustment of the second electrode 140. Therefore, by applying the embodiments of the present invention, a radio wave reflecting device with a simplified structure can be provided at low cost. Furthermore, a radio wave reflecting device that can be driven with low power consumption can be provided.

[0079] As embodiments of the present invention, the above-mentioned embodiments can be appropriately combined and implemented as long as they do not conflict with each other. In addition, embodiments of the radio wave reflection element or radio wave reflection device based on each embodiment, as long as the gist of the present invention is retained and those skilled in the art appropriately add, delete, or modify the design of the components, or add, omit, or modify the conditions of the engineering, are all within the scope of the present invention.

[0080] Even if there are other effects different from the effects brought about by the above-mentioned embodiments, effects that can be known from the description of this specification or that can be easily predicted by those skilled in the art should naturally be regarded as brought about by the present invention.

[0081] Description of Reference Numerals

[0082] 100: Radio wave reflecting element, 102: Substrate, 104: Gate line driving circuit, 106: Signal line driving circuit, 108: Terminal, 110: Counter substrate, 112: Undercoat layer, 114: Overcoat layer, 130: Radio wave reflecting element, 132: First electrode, 134: First orientation film, 136: Liquid crystal layer, 138: Second orientation film, 140: Second electrode, 150: Transistor, 152: Gate electrode, 154: Gate insulating film, 156: Semiconductor film, 158: Terminal, 160: Terminal, 162: Interlayer insulating film, 164: Planarization film, 166: Interlayer insulating film.

Claims

1. A method for driving an electric wave reflection device, wherein: The radio wave reflecting device includes a plurality of radio wave reflecting elements arranged in a matrix of m rows and n columns. Each of the plurality of radio wave reflecting elements includes a first electrode, a liquid crystal layer on the first electrode, and an electrically floating second electrode on the liquid crystal layer. The driving method includes applying a control potential based on a reference potential to the first electrode during a first frame period without applying a potential to the second electrode. During the first frame period, the total of the control potentials applied to the first electrodes of the plurality of radio wave reflection elements is 0 V. m and n are each independently selected from natural numbers greater than or equal to 6, and n is an even number.

2. The driving method according to claim 1, wherein: During the first frame period, the total of the control potentials in each row is 0V.

3. The driving method according to claim 1, wherein: In each row, the plurality of radio wave reflecting elements are divided into k element blocks, each of which has j radio wave reflecting elements arranged in series. During the first frame period, in each row, the control potentials applied to the first electrodes of the radio wave reflecting elements selected every j columns have the same absolute value and alternate polarities with respect to the reference potential. j is a natural number greater than or equal to 1, k is a natural number greater than or equal to an even number, and the product of j and k is n.

4. The driving method according to claim 3, wherein: j is 1.

5. The driving method according to claim 3, wherein: During the first frame period, in each element block, the absolute value of the control potential continuously increases or decreases in the order of the columns. The driving method according to claim 1 , wherein: In each column, the plurality of radio wave reflecting elements are divided into h element blocks, each of which has g radio wave reflecting elements arranged continuously. In the first frame period, in each column, the absolute values ​​of the control potentials applied to the first electrodes of the radio wave reflection elements selected for each row are the same. g is a natural number greater than or equal to 1, h is a natural number greater than or equal to 2, and the product of g and h is m.

7. The driving method according to claim 6, wherein: In the first frame period, in each column, the polarities of the control potentials applied to the first electrodes of the radio wave reflecting elements selected every g rows are alternated with respect to the reference potential.

8. The driving method according to claim 6 or 7, wherein: g is 1.

9. The driving method according to claim 6, wherein: During the first frame period, in each element block, the absolute value of the control potential continuously increases or decreases in the order of the rows.

10. The driving method according to claim 1, wherein: The method further includes inverting the control potential with respect to the reference potential in a second frame period following the first frame period.

11. The driving method according to claim 1, wherein: The first frame period includes the first subframe period to the mth subframe period. During the first subframe period to the m-th subframe period, the control potential is applied to each of the first electrodes of the radio wave reflection elements arranged in the first row to the m-th row.

12. An electric wave reflection device, wherein: The radio wave reflecting device includes a plurality of radio wave reflecting elements arranged in a matrix of m rows and n columns. Each of the plurality of radio wave reflecting elements includes a first electrode, a liquid crystal layer on the first electrode, and an electrically floating second electrode on the liquid crystal layer. m and n are each independently selected from natural numbers greater than or equal to 6, and n is an even number.

13. The radio wave reflecting device according to claim 12, wherein: Each of the plurality of radio wave reflecting elements further comprises: a first alignment film between the first electrode and the liquid crystal layer; and a second alignment film between the liquid crystal layer and the second electrode.

14. The radio wave reflecting device according to claim 12, wherein: The second electrode is configured not to be supplied with a signal from an external circuit.

15. The radio wave reflecting device according to claim 13, wherein: It also includes a substrate and a counter substrate located above and below each of the plurality of radio wave reflecting elements. The second electrode is sealed between the second alignment film and the counter substrate.

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