Improved liquid crystal cell

Abstract

A liquid crystal cell (5) is disclosed. The liquid crystal cell comprises at least two substrates (10a, 10b) transparent to the visible part of the light spectrum, a liquid crystal layer (18) enclosed between the substrates, and a stack of functional layers formed on the substrates and enclosed between the substrates and the liquid crystal layer. The stack comprises, in a direction from the substrates towards the liquid crystal layer, a first dielectric layer (12a, 12b), a transparent electrode layer (14a, 14b) and a second dielectric layer (16a, 16b). The refractive index of the first dielectric layer is between the refractive index of the substrates and the transparent electrode layer. The refractive index of the second dielectric layer is between the refractive index of the transparent electrode layer and the liquid crystal layer. The refractive index of the liquid crystal layer corresponds to a homeotropic alignment of the liquid crystal material of the liquid crystal layer.

Description

[Technical field]

[0001] The present disclosure relates to a liquid crystal cell. The present disclosure further relates to a method for manufacturing a substrate for use in a liquid crystal cell.

[0002] A typical three-dimensional volumetric display (VD) is constructed using a rear image projection unit and a stack of switching light diffusion elements. Traditionally, the light diffusion elements are implemented as liquid crystal cells filled with polymer-free chiral nematic liquid crystals. The homeotropic layer of the liquid crystal cell is made of polyimide. The substrate of the liquid crystal cell is typically indium tin oxide (ITO) glass. ITO is used as a transparent electrode layer and is separated from the mineral glass substrate by a sputtered silicon dioxide (SiO2) layer of the order of a few tens of nanometers. ITO glass can also be used as a flexographically printed silicon dioxide (SiO2) layer. x The light diffusing element is treated with an additional layer of silicon oxide (SiO x A single layer or multiple layers of silicon oxide can be formed on the transparent electrode layer with a thickness on the order of tens to hundreds of nanometers. Vacuum deposition techniques can be used to deposit silicon oxide.

[0003] The refractive index of the glass substrate and the silicon dioxide (SiO2) layer are similar, both around 1.5, whereas the refractive index of the ITO electrode layer is typically in the range of 1.9-2.1. x The refractive index of the silicon oxide (SiO x The refractive index of the homeotropic polyimide layer is approximately 1.5, whereas that of the liquid crystal layer is approximately 1.7. xIt does not improve the refractive index matching between the LC layer and the liquid crystal layer. The difference in refractive index within the liquid crystal cell creates internal interfaces that are highly reflective. When used in display applications, this adversely affects image contrast, image brightness, and the resistance of the light diffusing element to ambient lighting conditions.

[0004] In addition, flexographically printed silicon oxide (SiO x The problem with the ZnSe layer is that it has a significant number of structural defects, i.e. hole-like defects, which locally reduce the dielectric resistance of the light-diffusing element and may also cause electrical breakdown of the light-diffusing element. During operation, the light-diffusing element is exposed to high voltages and withstands electric field strengths in the range of 8-20 MV / m across the cell gap.

[0005] Silicon oxide (SiO x Another problem with using silicon oxide is that it is a nonstoichiometric silicon dioxide (SiO2) that has dangling oxygen bonds. It must therefore be passivated by annealing in an oxygen atmosphere. Otherwise, the light diffusing element is susceptible to absorbing volatile organic compounds and moisture from the air, forming defects and causing electrical breakdown. This requires an additional process step, annealing, which is quite time-consuming (usually several hours).

[0006] Depending on the total area of ​​the light diffusing element, the ITO electrode layer can be patterned, for example in a comb shape, to confine local current flow and thereby prevent complete breakdown if a conducting channel is formed in the liquid crystal layer. However, such patterning introduces scattering areas on the interior surface of the light diffusing element, which adversely affects the perceived image quality during use.

[0007] Conventional processes for manufacturing substrates for use in liquid crystal cells are multi-step processes that provide dielectric resistance and switching properties at the expense of degraded optical performance. Thus, there is a need for improved light diffusing elements in terms of improved resistance to high driving voltages and improved optical performance. Abstract

[0008] The present disclosure relates to improved liquid crystal cells. The present disclosure also relates to improved methods for manufacturing substrates for use in liquid crystal cells. Furthermore, the present disclosure also seeks to provide solutions to existing problems of conventional liquid crystal cells.

[0009] According to a first aspect, an embodiment of the present disclosure provides a liquid crystal cell as follows. · at least two substrates transparent to the visible portion of the light spectrum; a liquid crystal layer enclosed between said at least two substrates; a stack of functional layers formed on the at least two substrates and encapsulated between a given substrate and the liquid crystal layer; The stack includes, in a direction from the predetermined substrate toward the liquid crystal layer, a first dielectric layer; · a transparent electrode layer; a second dielectric layer; a refractive index of the first dielectric layer in a range between the refractive index of the given substrate and the refractive index of the transparent electrode layer; The refractive index of the second dielectric layer is in a range between the refractive index of the transparent electrode layer and the refractive index of the liquid crystal layer, the refractive index of the liquid crystal layer corresponding to homeotropic alignment of the liquid crystal material of the liquid crystal layer.

[0010] According to a second aspect, an embodiment of the present disclosure provides a method for manufacturing a substrate, the method comprising: forming a first dielectric layer over a substrate; forming a transparent electrode layer over the first dielectric layer; forming a second dielectric layer over the transparent electrode layer; the first dielectric layer is formed such that the refractive index of the first dielectric layer is in a range between the refractive index of the substrate and the refractive index of the transparent electrode layer; The second dielectric layer is formed such that the refractive index of the second dielectric layer is in a range between the refractive index of the transparent electrode layer and the refractive index of the liquid crystal material, which corresponds to a homeotropic orientation of the liquid crystal material.

[0011] Embodiments of the present disclosure substantially eliminate or at least partially address the aforementioned problems in the prior art and improve the optical efficiency of liquid crystal cells by minimizing undesirable reflections from internal interfaces between different layers.

[0012] Further aspects, advantages, features and objects of the present disclosure will become apparent from the accompanying drawings and detailed description of illustrative embodiments, taken in conjunction with the appended claims.

[0013] It will also be appreciated that features of the present disclosure can be combined in various combinations without departing from the scope defined by the appended claims. [Brief description of the drawings]

[0014] The foregoing summary, as well as the following detailed description of exemplary embodiments, will be better understood when read in conjunction with the accompanying drawings. For the purpose of illustrating the disclosure, example configurations of the disclosure are shown in the drawings. However, the disclosure is not limited to the specific methods and apparatus disclosed therein. Also, the drawings are not drawn to scale. Similar elements are designated by the same numerals wherever possible. Embodiments of the present disclosure will now be described, by way of example only, with reference to the following drawings, in which: [Figure 1A] 1 is a schematic diagram of a cross section of a liquid crystal cell according to various embodiments of the present disclosure. [Figure 1B] 1 is a schematic diagram of a cross section of a liquid crystal cell according to various embodiments of the present disclosure. [Diagram 2]This shows how the refractive index (n) of a dielectric layer made from silicon oxynitride (SiOxNy) varies with the nitrogen concentration (atmosphere %) in the gas mixture used for sputtering. [Diagram 3] This shows how the refractive index (n) of a dielectric layer varies with the relative concentrations (i.e., partial pressure ratio) of oxygen and nitrogen in a gas mixture. [Figure 4] 1 illustrates steps of a method for manufacturing a substrate according to one embodiment of the present disclosure. In the accompanying drawings, underlined numbers are used to represent the item at which the number is located or adjacent to the number. Numbers without underlines are associated with the item identified by the line extending from the number. When a number is not underlined and is written with an arrow, the number is used to identify the generic item to which the arrow points. Detailed Description of the Embodiments

[0015] The following detailed description illustrates embodiments of the present disclosure and how they may be practiced. Although several forms for carrying out the present disclosure have been disclosed, those skilled in the art will recognize that other forms for carrying out the present disclosure are possible.

[0016] According to a first aspect, an embodiment of the present disclosure provides a liquid crystal cell as follows. · at least two substrates transparent to the visible portion of the light spectrum; a liquid crystal layer enclosed between said at least two substrates; a stack of functional layers formed on the at least two substrates and encapsulated between a given substrate and the liquid crystal layer; The stack includes, in a direction from the predetermined substrate toward the liquid crystal layer, a first dielectric layer; · a transparent electrode layer; a second dielectric layer; a refractive index of the first dielectric layer in a range between the refractive index of the given substrate and the refractive index of the transparent electrode layer; The refractive index of the second dielectric layer is in a range between the refractive index of the transparent electrode layer and the refractive index of the liquid crystal layer, the refractive index of the liquid crystal layer corresponding to homeotropic alignment of the liquid crystal material of the liquid crystal layer.

[0017] According to a second aspect, an embodiment of the present disclosure provides a method for manufacturing a substrate, the method comprising: forming a first dielectric layer over a substrate; forming a transparent electrode layer over the first dielectric layer; forming a second dielectric layer over the transparent electrode layer; the first dielectric layer is formed such that the refractive index of the first dielectric layer is in a range between the refractive index of the substrate and the refractive index of the transparent electrode layer; The second dielectric layer is formed such that the refractive index of the second dielectric layer is in a range between the refractive index of the transparent electrode layer and the refractive index of the liquid crystal material, which corresponds to a homeotropic orientation of the liquid crystal material.

[0018] The liquid crystal cell described above has improved optical and dielectric properties compared to liquid crystal cells of the prior art. The refractive indexes of the first and second dielectric layers are adjusted to be between the refractive indexes of their respective adjacent layers (i.e., the layers between which they are sandwiched). The first and second dielectric layers act as a barrier to prevent free ions and impurities from migrating from the substrate to the transparent electrode layer and further into the liquid crystal layer, but also as layers for matching the refractive index. That is, there is no abrupt change in the refractive index from one layer to another in the liquid crystal cell. This minimizes unwanted reflections from the internal interfaces between the different layers, improving the optical efficiency of the liquid crystal cell.

[0019] The liquid crystal cells described above can be applied in image reproduction. As an example, the liquid crystal cells can be implemented as light diffusing elements (i.e., transient light shutters) in solid volumetric three-dimensional displays. As an example, a volumetric three-dimensional display can employ a stack of such light diffusing elements together with a rear image projection unit. This allows the volumetric three-dimensional display to have a multi-focal display architecture and to form a three-dimensional image that is visible to the unaided human eye.

[0020] In some embodiments, the at least two substrates are flexible. In this regard, the at least two substrates are made of optically transparent organic materials in some embodiments. By way of example, the substrates may be implemented as sheets or films made of polycarbonate, poly(methyl methacrylate), and the like. The technical advantages of employing such flexible substrates in liquid crystal cells are that the liquid crystal cells are thinner, lighter, more robust with significantly reduced susceptibility to breakage, and more durable than liquid crystal cells employing conventional rigid glass substrates.

[0021] Alternatively, the at least two substrates can be made of mineral glass, which can be display glass, soda-lime glass, quartz, or other similar glass materials.

[0022] In some embodiments, the at least two substrates are also transparent to the infrared portion of the light spectrum.

[0023] In some embodiments, at least the second dielectric layer is silicon oxynitride (SiO x N y In some embodiments, the first dielectric layer also comprises silicon oxynitride (SiO x N y In some embodiments, the first dielectric layer comprises silicon dioxide (SiO2), silicon oxide (SiO x )

[0024] The dielectric layer is silicon oxynitride (SiO x N y There are many technical advantages to using silicon oxide (SiO x ) the dielectric strength of the dielectric layer is significantly improved compared to dielectric layers made from flexographically printed SiO x The characteristic of SiO is the presence of pore-like structural defects. x Sputtering silicon oxynitride (SiO2) improves quality but suffers from dangling oxygen bonds and requires annealing as a passivation process. x N y The dielectric constant of silicon oxynitride (SiO) depends on the ratio of oxygen to nitrogen in it. x N y ) has a dielectric constant in the range of 6-10, while silicon oxide (SiO x ) has a much smaller dielectric constant, in the range of 3.3-4.4, while typical polyimides used in conventional liquid crystal displays have a dielectric constant of about 3.6. x ) has many dangling oxygen bonds, which interact with the molecules of the liquid crystal material to form silicon oxide (SiO x In this regard, the inclusion of nitrogen in silicon oxynitride eliminates such dangling bonds, thereby making the dielectric layer less susceptible to the effects of moisture and volatile organic compounds. x There is no need to perform thermal annealing in an oxygen atmosphere, as in the case of a dielectric layer containing . As a result, many impurities in the liquid crystal cell can be minimized, thereby minimizing the premature failure rate and preventing cell failure. Furthermore, at least the second dielectric layer is free of structural defects such as holes, improving the overall dielectric strength of the liquid crystal cell, so there is no need to pattern the transparent electrode layer to limit local current. Since no scribe lines or ablation lines exist in the liquid crystal cell, no unnecessary light scattering occurs. As a result, the transparency of the liquid crystal cell is improved. Therefore, the optical properties of the liquid crystal cell are greatly improved.

[0025] As described above, the refractive indexes of the first and second dielectric layers are adjusted to be between the refractive indexes of the adjacent layers (i.e., the layers sandwiching them). In this regard, silicon oxynitride (SiO x N y The use of silicon dioxide (SiO ) allows the refractive index of the first and second dielectric layers to be adjusted over a wide range, for example 1.5-1.8 or even higher. As an example, the refractive index of the first dielectric layer can be adjusted to be in the range of 1.6 to 1.7. x ), silicon oxynitride (SiO x N y ), the degree to which the refractive index can be adjusted is lower. However, it is still possible to adjust the refractive index by using silicon oxide (SiO x ) can be used as the first dielectric layer.

[0026] In some embodiments, the first and second dielectric layers are formed on the substrate using a suitable plasma deposition (PVD) process. One example of a PVD process is a reactive sputtering process, which uses a conductive or semiconductive sputtering target in a reactive atmosphere. A preferred sputtering process compatible with embodiments of the present disclosure is medium frequency (MF) magnetron reactive sputtering, also known as magnetron ion sputtering. Sputtering is used to form silicon oxynitride (SiO x N yThe technical advantage of depositing a SiO 2 layer is that it has lower internal stress, which results in reduced substrate warpage, compared to conventional silicon oxide layers, which in turn minimizes optical defects associated with selective reflection due to the Fabry-Perot effect. Magnetron ion sputtering also provides high yields and is therefore suitable for large scale manufacturing. In addition, in some embodiments, the first and second dielectric layers can be formed by atomic layer deposition. However, PVD has advantages over atomic layer deposition in terms of cost, deposition speed, quality, and process control.

[0027] Silicon oxynitride (SiO x N y When the dielectric layer is formed by depositing silicon oxide (SiO ), argon can be used as a carrier gas in a mixture of oxygen and nitrogen, and silicon can be used as a semiconducting sputtering target. The sputtering target can be a planar silicon target or a rotating silicon target. In the specific case of using oxygen and nitrogen as reactive components in the gas mixture, it is possible to use the same sputtering target for forming the first and second dielectric layers. The first and second dielectric layers can each be formed of silicon oxide (SiO ). x ) or silicon oxynitride (SiO x N y It will be appreciated that when formed by deposition of at least two different sputtering targets are required, which makes the process of forming these dielectric layers somewhat more complicated.

[0028] In some embodiments, silicon oxynitride (SiO x N y The relative concentrations of oxygen and nitrogen in silicon oxynitride (SiO ) are varied to gradient the refractive index of at least one of the first and second dielectric layers. x N yThe relative concentrations of oxygen and nitrogen in the first and second dielectric layers depend on the molar ratio, the volume ratio, or the partial pressure of oxygen and nitrogen in the vacuum chamber in which the sputtering process is performed. As an example, a dielectric layer can be created by forming a number of thin successive sub-layers (e.g., 3, 4, 5 or more layers). Different relative concentrations (relative concentrations of oxygen and nitrogen) are used in forming the different sub-layers. The refractive index of the dielectric layer thus formed varies in a gradient. In some embodiments, the relative concentrations of oxygen and nitrogen are varied (i.e., adjusted) in real time to linearly change the refractive index through the thickness of at least one of the first and second dielectric layers.

[0029] The first and second dielectric layers are preferably thickened compared to conventional liquid crystal cells. In some embodiments, the thickness of the first dielectric layer is in the range of 50 nm to 200 nm. The thickness of the first dielectric layer can be from 50 nm, 55 nm, 60 nm or 65 nm to 80 nm, 100 nm, 140 nm or 200 nm. As an example, the thickness of the first dielectric layer is in the range of 60 nm to 80 nm. In some embodiments, the thickness of the second dielectric layer is in the range of 70 nm to 500 nm. The thickness of the second dielectric layer can be from 70 nm, 120 nm, 150 nm or 175 nm to 150 nm, 200 nm, 250 nm, 350 nm or 500 nm. As an example, the thickness of the second dielectric layer is in the range of 150 nm to 250 nm.

[0030] The second dielectric layer is silicon oxynitride (SiO x N y A further technical advantage of using silicon oxynitride (SiO ) to form the second dielectric layer is that it facilitates homeotropic alignment of the molecules of the liquid crystal material. Throughout this disclosure, the term "homeotropic alignment" refers to a state in which the rod-like molecules of the liquid crystal material are aligned perpendicular to a given substrate. In other words, the "homeotropic alignment of the liquid crystal material" is the alignment of the molecules of the liquid crystal material that relates to a state in which the liquid crystal layer is optically transparent. Silicon oxynitride (SiO ) is used to form the second dielectric layer. x N yWhen depositing a second dielectric layer (silicon oxynitride (SiO x N y Molecules of liquid crystal material in direct contact with or in close proximity to a silicon oxynitride (SiO x N y ) improves the switching speed of the liquid crystal cell (the speed at which the liquid crystal cell switches from a first optical state to a second optical state) compared to conventional homeotropic polyimide layers. Here, the first optical state and the second optical state may be optically diffuse and optically clear states of the liquid crystal cell, respectively. The optically diffuse state corresponds to a focal conic state of the liquid crystal material, and the optically clear state corresponds to a homeotropic alignment of the liquid crystal material.

[0031] In some embodiments, the second dielectric layer is etched to support an orientation other than homeotropic. Such etching can be performed, for example, as angled ion etching. As an example, such etching can achieve an orientation in the range of 60 degrees to 89 degrees for the molecules of the liquid crystal material. The use of such off-homeotropic alignment can provide a potentially useful compromise between switching from the first optical state to the second optical state and switching from the second optical state to the first optical state. It will be appreciated that the use of homeotropic alignment increases the switching speed from the first optical state to the second optical state (i.e., from the diffuse state to the transparent state) compared to the switching speed from the second optical state to the first optical state (i.e., from the transparent state to the diffuse state). On the other hand, off-homeotropic alignment is compatible with the objective of achieving a reduction in the total time required for a complete switching cycle, which is important in the practical application of image output with such liquid crystal cells.

[0032] In some embodiments, the transparent electrode layer comprises indium tin oxide (ITO), zinc oxide (ZnO) doped with aluminum or hydrogen, or a mesh of metal nanowires.

[0033] The sheet resistance of the transparent electrode layer, which includes indium tin oxide (ITO), is between 40 ohms / square and 150 ohms / square.

[0034] The transparent electrode layer can also be deposited using a PVD process. As an example, indium tin oxide (ITO) can be deposited by DC magnetron sputtering. In this case, a planar indium tin oxide (ITO) target can be employed.

[0035] In some embodiments, the liquid crystal material is a polymer-free cholesteric liquid crystal. In some embodiments, the liquid crystal material is a chiral nematic liquid crystal. Chiral nematic liquid crystals include a nematic crystal base and a chiral dopant added at 1-10% by weight (for example, 5 grams of chiral dopant and 95 grams of nematic crystal base). The concentration of the chiral dopant depends on the helical twisting power of the chiral dopant. For chiral dopants with high twisting power, in some embodiments, the concentration of the chiral dopant is in the range of 1-4% by weight. In some embodiments, the concentration is in the range of 2-2.5% by weight. For chiral dopants with low twisting power, in some embodiments, the concentration of the chiral dopant is in the range of 4-10% by weight. In some embodiments, the concentration is in the range of 8-8.5% by weight. In practical terms, "% by weight" generally refers to (x) grams by weight of dopant in (x+y) grams by weight of the total liquid crystal material, ie, x / (x+y)%.

[0036] The technical advantage of using such liquid crystal materials is that, in contrast to liquid crystal materials containing polymers, the manufacturing process is simplified since no photopolymerization step is required, which improves the yield and reproducibility of the manufacturing process. From an electro-optical point of view, the absence of a network polymer to provide stability results in a faster response time for switching between the aforementioned optical states of the liquid crystal cell upon application or removal of an electric field.

[0037] In some embodiments, the liquid crystal cell further comprises a plurality of spacers disposed between the at least two substrates. The thickness of the liquid crystal layer depends on the size of the spacers. The use of such spacers ensures a uniform thickness of the liquid crystal cell, resulting in uniform optical properties across the entire area of ​​the liquid crystal cell. In some embodiments, the refractive index of the plurality of spacers is selected to correspond to the refractive index of the liquid crystal layer in the second optical state, i.e., the optically transparent state. This can minimize unwanted reflections from internal interfaces between the plurality of spacers and the liquid crystal material, improving the optical efficiency of the liquid crystal cell.

[0038] In some embodiments, the liquid crystal cell also includes a sealing shell of polymer material that seals the liquid crystal layer between the at least two substrates. The sealing shell protects the liquid crystal material from air and dust (ambient atmosphere), thus ensuring reliable operation of the liquid crystal cell. The polymer material can be deposited around the liquid crystal cell when the at least two substrates are pressed together, and then polymerized to form the sealing shell.

[0039] When filling the liquid crystal material, at least one of the at least two substrates is coated with a number of spacers. The liquid crystal material can be filled using various techniques. One of them employs capillary action in a vacuum chamber, where the liquid crystal cell is sealed to leave a port and filled with the liquid crystal material by capillary action. Another of these techniques is the ODF (One Drop Fill) process. This process is a direct filling process, where droplets of liquid crystal material are directly dispensed onto one of the at least two substrates (treated with a stack of functional layers) before the at least two substrates are pressed together to seal the liquid crystal cell. Directly dispensing droplets of liquid crystal material requires a precise microdispenser.

[0040] The present disclosure also relates to the above-mentioned method, which is carried out before assembling a liquid crystal cell. The various embodiments and variants disclosed above with respect to the first aspect above apply mutatis mutandis to the method.

[0041] In some embodiments, in this method, at least the first and second dielectric layers are formed on the substrate using magnetron ion sputtering.

[0042] In some embodiments, in the method, at least the second dielectric layer is silicon oxynitride (SiO x N y In this regard, silicon oxynitride is deposited using a silicon target and an atmosphere of oxygen, nitrogen and an inert gas. In some embodiments, the first dielectric layer is silicon oxynitride (SiO x N y ).

[0043] In some embodiments, the step of forming a dielectric layer comprises forming a silicon oxynitride (SiO x N y) to produce a gradient in the refractive index of at least one of the first and second dielectric layers. As an example, a dielectric layer can be created by forming a number of thin, successive sub-layers. Different relative concentrations (relative concentrations of oxygen and nitrogen) are used in forming the different sub-layers. As a result, the refractive index of a given dielectric layer changes in a graded manner. In some embodiments, the relative concentrations of oxygen and nitrogen are varied (i.e., adjusted) in real time to produce a linear change in refractive index through the thickness of at least one of the first and second dielectric layers. Additionally, in some embodiments, layers having a refractive index of nx=(n2-n1) / 2 or close thereto (within ±10%) can be used, where n1 and n2 are the refractive indices that need to be matched.

[0044] Advantageously, the above-described method may be performed as a single integrated process. For purposes of illustration only, the first and second dielectric layers may be silicon oxynitride (SiO x N y Consider an exemplary implementation formed by depositing silicon oxynitride (SiO x N y In one embodiment, the method is carried out in a first deposition zone where a SiO 2 (SiO 3 ) is deposited and in a second deposition zone where, for example, indium tin oxide (ITO) is deposited. In this implementation, the method is carried out on the substrate without having to leave the vacuum chamber. The substrate, from which contamination has been removed, is processed as follows: A first dielectric layer is formed in a first deposition zone. Translocating the substrate to a second deposition zone. A second deposition zone forms a transparent electrode layer. The substrate is returned to the first deposition zone. A second dielectric layer is formed in a first deposition zone.

[0045] The second deposition zone is isolated from the first deposition zone in a manner that avoids the possibility of cross-contamination.

[0046] In some embodiments, the method further includes etching the second dielectric layer to support an orientation other than homeotropic. Such etching may be performed using reactive ion etching. The etching step may be performed following the previous steps illustrated in the examples without breaking the vacuum condition. Alternatively, the etching step may be performed as a separate step in a separate vacuum chamber.

[0047] [Experimental Results]

[0048] Silicon oxynitride (SiO x N y It has been experimentally observed that the preferred thickness of the first dielectric layer is in the range of 60 nm-80 nm (e.g., 70 nm), and the preferred thickness of the second dielectric layer is in the range of 175 nm-225 nm (e.g., 200 nm). x N y It has been experimentally observed that the use of a homeotropic polyimide layer improves the switching speed of liquid crystal cells compared to cells using a conventional homeotropic polyimide layer. The average improvement in switching speed is in the range of 2-5% compared to cells using a conventional homeotropic polyimide layer.

[0049] [Detailed description of the drawing]

[0050] 1A and 1B are schematic cross-sectional views of a liquid crystal cell 5 according to various embodiments of the present disclosure. at least two substrates depicted as elements 10a and 10b; a stack of functional layers formed on each of the substrates 10a, 10b; a first dielectric layer depicted as elements 12a and 12b; · a transparent electrode layer depicted as elements 14a and 14b; a second dielectric layer depicted as elements 16a and 16b; a liquid crystal layer 18 located between at least two substrates 10a, 10b; Equipped with.

[0051] Referring to FIG. 1B, in some embodiments, the liquid crystal cell 5 further comprises: a plurality of spacers depicted as elements 20a and 20b; · a sealing shell depicted as elements 22a and 22b; Equipped with.

[0052] Those skilled in the art will appreciate that Figures 1A and 1B depict simplified structures of liquid crystal cell 5 for clarity. These diagrams should not unduly limit the scope of the claims herein. Those skilled in the art will recognize numerous variations, alternatives, and modifications of the embodiments of the present disclosure.

[0053] Figure 2 shows the structure of silicon oxynitride (SiO x N y ) varies with the nitrogen concentration (atmosphere %) in the gas mixture used for sputtering.

[0054] On the other hand, FIG. 3 shows how the refractive index (n) of a certain dielectric layer changes with the relative concentrations (i.e., partial pressure ratio) of oxygen and nitrogen in a mixed gas.

[0055] From Figures 2 and 3 it can be seen that the refractive index of the dielectric layer can vary linearly with the nitrogen concentration in the gas mixture.

[0056] 4 shows steps of a method for manufacturing a substrate according to one embodiment of the present disclosure. In step S4.1, a first dielectric layer is formed on the substrate. In step S4.2, a transparent electrode layer is formed on the first dielectric layer. In step S4.3, a second dielectric layer is formed on the transparent electrode layer. In this method, the first dielectric layer is formed such that its refractive index is in a range between the refractive index of the substrate and the refractive index of the transparent electrode layer.

[0057] Meanwhile, the second dielectric layer is formed such that its refractive index is in a range between the refractive index of the transparent electrode layer and the refractive index of the liquid crystal material, where the refractive index of the liquid crystal material corresponds to a homeotropic alignment of the liquid crystal material.

[0058] The steps described above are merely exemplary and may include alternative steps, i.e., one or more steps may be added, one or more steps may be removed, or one or more steps may be performed in a different order, without departing from the scope of the appended claims.

[0059] The embodiments of the present disclosure described above can be modified without departing from the scope defined by the appended claims. The terms "including," "comprising," "incorporating," "having," "being," and the like used to describe and claim the present disclosure are intended to be interpreted in a non-exclusive manner, i.e., to allow for the presence of items, parts, or components not expressly described. The absence of a specification that an element is plural does not preclude the presence of a plurality of such elements. The terms "first," "second," "third," and the like used in this specification do not indicate order, quantity, or importance, but are merely used to distinguish one element from another.

Claims

1. A liquid crystal cell, comprising: - At least two substrates transparent to the visible portion of the optical spectrum; - A liquid crystal layer encapsulated between the at least two substrates; - A stack comprising a plurality of functional layers formed on the at least two substrates and encapsulated between a predetermined substrate and the liquid crystal layer; wherein the stack, in a direction from the predetermined substrate towards the liquid crystal layer, - A first dielectric layer; - A transparent electrode layer; - A second dielectric layer; and has the refractive index of the first dielectric layer is in the range between the refractive index of the predetermined substrate and the refractive index of the transparent electrode layer, the refractive index of the second dielectric layer is in the range between the refractive index of the transparent electrode layer and the refractive index of the liquid crystal layer, and the refractive index of the liquid crystal layer corresponds to the homeotropic alignment of the liquid crystal material of the liquid crystal layer, A liquid crystal cell.

2. The liquid crystal cell according to claim 1, wherein the liquid crystal material is a chiral nematic liquid crystal obtained by adding 1-10% by mass of a chiral dopant to a nematic crystal base.

3. The liquid crystal cell according to claim 1, wherein at least the second dielectric layer contains silicon oxynitride.

4. The liquid crystal cell according to claim 3, wherein the relative concentrations of oxygen and nitrogen in the silicon oxynitride are varied such that at least one of the refractive indices of the first dielectric layer and the second dielectric layer has a gradient.

5. The liquid crystal cell according to claim 1, wherein the thickness of the first dielectric layer is in the range of 50 nm - 200 nm.

6. The liquid crystal cell according to claim 1, wherein the thickness of the second dielectric layer is in the range of 70 nm - 500 nm.

7. The liquid crystal cell according to claim 1, wherein the second dielectric layer is etched to support an alignment other than homeotropic alignment.

8. The liquid crystal cell according to claim 1, wherein the transparent electrode layer comprises any one of indium tin oxide (ITO), zinc oxide doped with aluminum or hydrogen (ZnO), and a mesh of metal nanowires.

9. The liquid crystal cell according to claim 1, wherein the at least two substrates are flexible.

10. A method for manufacturing a substrate, comprising: - Forming a first dielectric layer on the substrate; - Forming a transparent electrode layer on the first dielectric layer; - Forming a second dielectric layer on the transparent electrode layer; and including The first dielectric layer is formed such that the refractive index of the first dielectric layer is within a range between the refractive index of the substrate and the refractive index of the transparent electrode layer. The second dielectric layer is formed such that the refractive index of the second dielectric layer is within a range between the refractive index of the transparent electrode layer and the refractive index of the liquid crystal material, and the refractive index of the liquid crystal material corresponds to the homeotropic alignment of the liquid crystal material. Method. Claim 11 The method according to claim 10, wherein at least the second dielectric layer contains silicon oxynitride, and the silicon oxynitride is deposited using a silicon target and an atmosphere of oxygen, nitrogen, and an inert gas. Claim 12 The method according to claim 11, wherein forming the dielectric layer includes forming a gradient in the refractive index of at least one of the first dielectric layer and the second dielectric layer by changing the relative concentration of oxygen and nitrogen in the silicon oxynitride. Claim 13 The method according to claim 10, further comprising etching the second dielectric layer to support an alignment other than the homeotropic alignment.

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