Liquid crystal cell assembly

Abstract

A method comprising: forming a spacer structure material layer in situ on a film assembly, and patterning the spacer structure material layer in situ on the film assembly to define a spacer structure for a liquid crystal cell array at least in the active area of ​​the liquid crystal cell; applying a counter assembly to the film assembly after dispensing a sealant material onto one or more of the two assemblies in a corresponding sealant deposition area surrounding each active area of ​​the liquid crystal cell array, and after dispensing one or more drops of liquid crystal material onto one or more of the two assemblies in each active area of ​​the liquid crystal cell array; pressing the two assemblies together so as to spread the droplets of liquid crystal material over the active area; wherein, after pressing, the sealant material for each liquid crystal cell interfaces with the liquid crystal material for the corresponding liquid crystal cell; and wherein each of the sealant deposition areas has a corresponding inner perimeter, and the method further comprises controllably varying the inner perimeter dimension across the liquid crystal cell array to compensate for changes in one or more characteristics of the spacer structure across the liquid crystal cell array.

Description

Technical Field

[0001] The present invention relates to a method for assembling a liquid crystal cell. Background Art

[0002] A liquid crystal (LC) cell generally includes two half cells defining a cell gap therebetween, and a liquid crystal material filling the cell gap.

[0003] Pre-fabricated spacing elements (e.g., spacing spheres / beads / fibers) dispersed between the two half-cells have been used to define a cell gap with a precise thickness between the two half-cells in the finished cell; however, using an ordered array of spacing structures built into one or both of the half-cells has the advantage of positional control. For the example of a pixelated display device, it is preferred to place the spacing structures of the active area in the black matrix area between the pixel areas.

[0004] The inventors of the present application have endeavored to develop a mass production technology that involves processing a large-area plastic film assembly (mother assembly) to produce a plurality of LC cells from the mother assembly.

[0005] refer to Figure 4 The inventors of the present application have observed local defects in a group of LC cells produced from a single mother assembly, and have identified a correlation between the occurrence of these defects in the LC cells and the position occupied by the LC cells within the mother assembly from which they were produced. The defects observed include (a) bubbles and (b) defects that manifest themselves as color non-uniformities when the undriven LC cell is observed between polarizers oriented at 45 degrees to each other, and defects that manifest themselves as yellow spots when the LC cell is driven white between two polarizers oriented at 90 degrees to each other. The inventors of the present application have attributed the occurrence of these defects to small variations in the spacing structure properties (starting thickness, elasticity) over areas of the mother assembly. Summary of the invention

[0006] The present invention provides a method, which includes: forming a spacer structure material layer in situ on a film component, and patterning the spacer structure material layer in situ on the film component to define a spacer structure for a liquid crystal cell array at least in the active area of ​​the liquid crystal cell; applying a counter component to the film component after dispensing a sealant material onto one or more of the two components in the corresponding sealant deposition area surrounding each active area of ​​the liquid crystal cell array, and after dispensing one or more drops of liquid crystal material onto one or more of the two components in each active area of ​​the liquid crystal cell array; pressing the two components together so as to spread the droplets of liquid crystal material on the active area; wherein, after pressing, the sealant material for each liquid crystal cell interfaces with the liquid crystal material for the corresponding liquid crystal cell; and wherein each of the sealant deposition areas has a corresponding inner perimeter, and the method also includes controllably varying the inner perimeter size across the liquid crystal cell array to compensate for changes in one or more characteristics of the spacer structure across the liquid crystal cell array.

[0007] According to one embodiment, the method comprises predicting changes in one or more characteristics of the spacer structure based on measurements of the spacer structure in one or more production tests; and wherein controllably varying the inner perimeter dimension across the liquid crystal cell array is based on the predicted changes.

[0008] According to an embodiment, the one or more characteristics of the spacing structure include a height of the spacing structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Embodiments of the present invention are described in detail below by way of example only with reference to the accompanying drawings, in which:

[0010] Figure 1 Two early stages of a method according to an embodiment of the invention are shown;

[0011] Figure 2 Shows Figure 1 the subsequent stages of the method;

[0012] Figure 3 It further shows Figure 2 The components shown in ; and

[0013] Figure 4 It shows local defects occurring in a group of LC cells manufactured from a single mother assembly without the use of the present invention. DETAILED DESCRIPTION

[0014] In an exemplary embodiment, the technology is used to manufacture an organic liquid crystal display (OLCD) device, which includes an organic transistor device (e.g., an organic thin film transistor (OTFT) device) for controlling components. The OTFT includes an organic semiconductor (e.g., an organic polymer or a small molecule semiconductor) for the semiconductor channel. The technology of the present invention can also be applied to the production of LC cells of other types of devices, such as adaptive lens devices, etc.

[0015] refer to Figure 1 , the description of an example of a method according to an embodiment of the present invention begins with the in-situ formation of a layer of spacer structure material 14 on a large-area film assembly (mother assembly) 2. The mother assembly 2 already includes a large-area support film and a stack of layers formed in-situ on the large-area support film. The stack defines an array of pixel electrodes for a plurality of LC cells, and circuitry for each LC cell for independently addressing each pixel electrode through conductors extending beyond the edges of the corresponding pixel electrode array. In this example, the area occupied by the pixel electrode array for the LC cell is the active area (AA) of the LC cell.

[0016] In this example, mother component 2 provides half cells for twelve LC cells, but Figure 1 and Figure 2 Only three of the twelve half units are shown.

[0017] In this example, the support film is a sub-100 micron thick plastic film, such as a triacetyl cellulose (TAC) film; and the circuit for independently controlling the potential at each pixel electrode through a conductor outside the active area of ​​the display device is an active matrix circuit. For each LC cell, the stack defines a corresponding thin film transistor (TFT) for each pixel electrode. The stack defines a source-drain conductor pattern and a gate conductor pattern for each LC cell. The source conductor pattern for the LC cell defines: (i) an array of source conductors, each source conductor providing a source electrode for a corresponding TFT row, and each source conductor extending outside the active display area; and (ii) an array of drain conductors, each drain conductor contacting a corresponding pixel electrode. The gate conductor pattern for the LC cell defines an array of gate conductors, each gate conductor providing a gate electrode for a corresponding TFT column, and each gate conductor extending outside the active display area. The terms "row" and "column" together refer to any pair of substantially orthogonal relative directions. Each pixel electrode is associated with a respective unique combination of source and gate conductors, whereby each pixel electrode can be addressed independently via the source and gate conductors.

[0018] In this example, the stack includes an organic polymer semiconductor layer formed in situ on a support film by solution processing, which provides a semiconductor channel for the above-mentioned TFT. The stack also includes an organic polymer insulator / dielectric layer also formed in situ on a support film by solution processing.

[0019] The production of this mother assembly 2 is designed to produce the same array of pixel electrodes and the same circuitry for each of the twelve LC cells.

[0020] In this example, in-situ formation of the spacer material layer 14 on the mother component 2 includes depositing a film of a solution of the spacer material, which is deposited by a liquid processing technique (e.g., spin coating) on ​​the uppermost isolation layer 16 of the stack above the entire upper surface of the mother component 2. In this example, the spacer material is an organic polymer material (e.g., a photoresist material) whose solubility in a developer solvent can be changed by exposure to radiation. Using a simple binary photomask, the spacer material layer 14 is exposed to a radiation image (negative or positive, depending on the type of photoresist material used for the spacer material) of the desired pattern for the spacer array 14. The resulting latent solubility image is then developed using the developer solvent above to produce a corresponding array of spacers 14a, 14b, 14c for twelve LC cells. By controlling the position of the above photomask with reference to alignment marks defined by one or more conductor patterns in the stack, the position of each spacer 14 relative to the underlying circuitry can be controlled.

[0021] There is no difference between the twelve LC cells in terms of the manner in which the spacing structure material layer is formed or patterned, with the goal of producing an identical array of spacing structures having identical properties for all twelve cells. However, as described above, the inventors of the present application have identified defects in production LC cells which the inventors believe are due to unintended variations in the spacing structure properties over the area of ​​the large area mother assembly 2.

[0022] In this example, the uppermost isolation layer 16 (on which the spacer structure is formed) comprises the same photoresist material as the photoresist material used for the spacer structure. The entire uppermost isolation layer 16 is made insoluble in the solvent used to deposit the spacer structure material layer 14 by flood radiation exposure.

[0023] In this example, a liquid crystal orientation surface is provided for each LC cell by a technique including the following steps: after forming an array of spacer structures 14, a polyimide material layer 18 is in-situ formed on the mother component 2, and the upper surface of the resulting workpiece is subjected to a rubbing treatment to produce microgrooves on the exposed surface of the polyimide layer 18. Another example of a technique for producing an LC orientation surface is a photo-orientation technique, which uses irradiation instead of mechanical means to obtain a surface for controlling the orientation of the LC material.

[0024] Reference Figure 2 and 3 , curable sealant material 8a-8l is dispensed onto the mother assembly 2 in respective sealant deposition areas that completely surround respective active areas of the LC cell. Figure 2, droplets of LC material 6a, 6b, 6c are dispensed onto the mother component 2 in the active area AA of the LC cell. In this example, one drop of LC material is dispensed for each LC cell. A dispenser is used to automatically dispense the LC material droplets, which does not distinguish between the individual LC cells. The LC material dispenser is configured to dispense the same volume of LC material for each LC cell. As described above, the sealant material 8a-8l is deposited in each sealant deposition area completely around the active area AA of each LC cell. The sealant 8a-8l can diffuse from these sealant deposition areas during the mother component assembly (LC cell assembly) described below, but the extent of such diffusion of the sealant is expected to be substantially the same for all LC cells. After the mother component assembly (cell assembly) described below, in the completed LC cell, the sealant material 8a-8l interfaces with the LC material and prevents the LC material from lateral diffusion beyond the inner perimeter IP (the extent to which the sealant limits the LC material 6 to which it can diffuse laterally). The dispensing of the curable sealant material 8a-8l is also automatic, but the sealant dispenser is set up so that a difference is produced between at least two LC cells in the inner perimeter dimension of the sealant deposition area (the area defined by the inner perimeter IPa-IPl). The set-up aspects of the sealant dispenser are determined based on test observations of variations in the properties (pre-compression thickness, elasticity) of the spacer structure 14 across the area of ​​the mother component 2, and these variations in the properties of the spacer structure 14 are compensated for by adjusting the area in which the LC material can diffuse. In this example, in one or more test runs after the process for mass production, local measurements of the height of the spacer structure 14 (i.e., the height of the spacer structure layer after patterning to define the spacer structure 14) are taken (using 3D microscopy or white light interferometry) at multiple points across the area of ​​the mother component 2. Predictions of process characteristic variations in the height of the spacer structure across the mother component are generated from these local measurements. For one or more LC cell regions in the mother component where it is predicted (based on the test run measurements above) that the height of the spacing structure is less than the height of the spacing structure of other LC cell regions of the mother component 2, the inner perimeter IPa-IPl dimensions of the sealant deposition area are set to be larger (proportional to the predicted spacing structure height difference) than the other regions of the mother component 2, thereby preventing the LC from being overfilled in the completed LC cells of these LC cell regions. Similarly, for those LC cell regions in the mother component where it is predicted (based on the test run measurements above) that the height of the spacing structure 14 is less than that of other LC cell regions, the inner perimeter IPa-IPl dimensions of the sealant deposition area are set to be smaller (proportional to the predicted spacing structure height difference) than the other LC cell regions of the mother component 2, thereby preventing the LC from underfilling the completed LC cells.

[0025] After dispensing the sealant 8a-81 and the LC material 6a, 6b, 6c, a counter mother component 4 (which provides a counter half-cell for all twelve LC cells) is applied to the mother component 2; and the two mother components 2, 4 are pressed together under vacuum in a relatively short time (typically less than 60 seconds) to assemble the LC cells.

[0026] The pressing of the two mother assemblies 2, 4 together is continued until, for example, pressure measurements (or time measurements, for example in the case of a pressing process with a known pressure-time curve) indicate a calculated value necessary to further spread the droplets of LC material over the respective active area AA (and bring the LC material 6a, 6b, 6c into contact with the sealant material 8a-8l) and to fully define the LC fill. The calculation of the final pressure value (i.e., the pressure value at which the pressing is stopped) takes into account the compressibility of the spacing structure material. As described above, the pressing process may also result in some diffusion of the sealant material 8a-8l (i.e., some change in the inner peripheral dimensions of the area occupied by the sealant 8a-8l), but the degree of diffusion is expected to be substantially the same for all LC cells across the entire area of ​​the mother assemblies 2, 4.

[0027] In the case where the two female components 2, 4 are thus pressed together under vacuum, curing (partial or complete) of the sealant 8a-8l is performed, for example, by UV irradiation through the sealant material of the female components (and a relatively rigid carrier temporarily adhered to the female components to support the female components during the production and unit assembly process). The cured sealant 8a-8l serves to hold the female components together after the external force pressing the two female components 2, 4 together is removed.

[0028] In this example, the resulting mother component assembly is subjected to a heat pressing process to release the relatively rigid carrier from the mother component assembly. In this example, the heat pressing process is performed in an oven at a temperature higher than the clearing temperature Tc of the LC material 6a, 6b, 6c for a duration of about 1 to 120 minutes, in which the sealant material 8a-8l includes a heat curable component (e.g., an epoxy component) in addition to a UV curable component (e.g., an acrylic component), and the heat curable component is cured by the heat of the heat pressing process. Alternatively, the sealant material 8a-8l does not include a heat curable component, and the sealant material is completely cured by the above-mentioned UV curing process.

[0029] In this example, the second mother assembly 4 further includes a large-area support film (e.g., another sub-100 micron plastic film such as triacetyl cellulose (TAC)) and provides a color filter array 10 for each LC cell. A liquid crystal orientation surface 12 is also provided on one surface of the second mother assembly. In this example, a polyimide material layer 12 ( Figure 2As shown) (through the color filter array 10 of the second mother component 4), and the surface of the polyimide layer 12 is mechanically rubbed to generate micro grooves in the exposed surface of the polyimide layer 12 to provide the liquid crystal alignment surface.

[0030] In the absence of any overlying electric field generated by the potential difference between the pixel electrode and the counter electrode (which may or may not be part of the same half-cell as the pixel electrode array, depending on the type of LC cell), the liquid crystal orientation surfaces of the two components 2, 4 are used to control the orientation of the directors of the LC material.

[0031] In one example, both the photo-spacer structures 14 and the uppermost isolation layer 16 (directly below the photo-spacer structures 14) include a cross-linked epoxy-based photoresist, referred to as SU-8.

[0032] As mentioned above, examples of the technology according to the present invention have been described in detail above with reference to specific processing details, but the technology can be more widely applicable within the general teachings of the present application. In addition, according to the general teachings of the present invention, the technology according to the present invention can include additional processing steps not described above, and / or omit some processing steps described above.

[0033] In addition to any modifications explicitly mentioned above, it will be apparent to those skilled in the art that various other modifications may be made to the described examples within the scope of the invention.

[0034] Applicants hereby independently disclose each individual feature described herein and any combination of two or more such features, to the extent that such feature or combination can be performed based on the present description as a whole with the common general knowledge of a person skilled in the art, regardless of whether such feature or combination of features solves any problem disclosed herein, and without limiting the scope of the claims. Applicants indicate that aspects of the present invention may consist of any such individual feature or combination of features.

Claims

1. A method, characterized in that The method includes: forming a spacer structure material layer in situ on a film assembly, and patterning the spacer structure material layer in situ on the film assembly to define a spacer structure for a liquid crystal cell array at least in an active area of ​​the liquid crystal cell; applying a counter assembly to the film assembly after dispensing a sealant material onto one or more of the two assemblies in a corresponding sealant deposition area surrounding each active area of ​​the liquid crystal cell array, and after dispensing one or more drops of liquid crystal material onto one or more of the two assemblies in each active area of ​​the liquid crystal cell array; pressing the two assemblies together so as to spread droplets of liquid crystal material over the active area; wherein, after pressing, the sealant material for each liquid crystal cell interfaces with the liquid crystal material for the corresponding liquid crystal cell; and wherein each of the sealant deposition areas has a corresponding inner perimeter, and the method also includes controllably varying an area defined by the inner perimeter across the liquid crystal cell array so as to compensate for changes in one or more characteristics of the spacer structure across the liquid crystal cell array.

2. The method according to claim 1, characterized in that: The method includes predicting changes in the one or more characteristics of the spacer structure based on measurements of the spacer structure in one or more production tests; and wherein controllably varying an area defined across the inner perimeter of an array of liquid crystal cells is based on the predicted changes.

3. The method according to claim 1 or 2, characterized in that: The one or more characteristics of the spacing structure include a height of the spacing structure.

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