Patent Application
20060017876
One or more embodiments of the present invention relate to displays and methods for fabricating such displays, which methods include imprint lithography techniques.
Recent developments in information communication have increased demand for various types of display devices. In response to this demand, various flat panel displays such as, for example and without limitation, liquid crystal displays or liquid crystal display devices (LCDs), plasma display panels (PDPs), electro luminescent displays (ELDs), and vacuum fluorescent displays (VFDs) have been developed. As used herein, LCDs include both direct viewing LCDs and projection type LCDs. LCDs have been used widely as mobile displays such as, for example and without limitation, displays for telephones and notebook computers because of, among other things, their small size, light weight, thin profile, and low power consumption. In addition to their use as mobile displays, LCDs have been developed as general displays as a replacement for Cathode Ray Tubes (CRTs) in computer monitors and televisions.
A typical LCD comprises: (a) an LCD panel that includes a liquid crystal layer for displaying a picture (typically the LCD panel is formed from first and second substrates, for example, glass substrates, that are bonded together—while being separated by a predetermined interval—with a liquid crystal interposed between the two substrates); (b) a light source; (c) electrodes; and (d) circuit components for applying driving voltages to the liquid crystal panel (for example, a driver circuit and a power supply circuit). Such a typical LCD provides a display by utilizing variations in polarization states of a light ray transmitted through the liquid crystal layer. The polarization state of the light ray is changed by orientation directions of liquid crystal molecules, which orientation directions, in turn, are changeable by applying a voltage to the liquid crystal layer. Portions of the driver circuit and power supply circuit may either form integral parts of the LCD panel or be mounted on the LCD panel.
As further shown in
As is well known, substrates 701 and 702 have a gap between them which is maintained by a number of spacers, for example, spacer 720 shown in
Another method for fabricating an LCD entails using a liquid crystal dropping method rather than the liquid crystal injection method described above. In accordance with such an alternative method, a sealant (for example, a UV sealant) is coated on a first substrate having a TFT array formed thereon to a thickness of approximately 30 μm, and liquid crystal is dropped on the substrate interior of the sealant, which interior includes the TFT array area (as such, a liquid crystal injection inlet is not provided in the sealant). The substrate is typically mounted on a table in a vacuum chamber, and a second substrate, having a color filter array formed thereon, is held in the vacuum chamber over the first substrate. The second substrate is moved downward in a vertical direction, the substrates are aligned, and they are moved toward each other until the second substrate comes into contact with, and bonds with, the first substrate through the sealant (as is well known, further alignment steps may be interposed). Next, the sealant is hardened (for example, UV rays are directed to the sealant or the temperature is raised to set it). Next, the bonded substrates may be cut into individual panels, and each panel may be polished and inspected.
In a variant of the above-described alternative, liquid crystal is dropped or applied on the first substrate, and a sealant is coated on the second glass substrate. Next, the two substrates are brought together for bonding and spreading the liquid crystal between the substrates uniformly. Next, the sealant is set. Next, the bonded substrates may be cut into individual panels, and each panel may be polished and inspected. Although it has been described that the liquid crystal is dispensed on a substrate having a TFT array, and the sealant is coated on a substrate having a color filter array, the sealant may be applied to both substrates, or the liquid crystal and the sealant may be applied on either of the substrates.
One problem with such prior art methods relates to the sealing process because the sealant is unconstrained and provides process variability which results in quality issues and poor manufacturing yields.
An LCD has numerous functional requirements, including light transmission characteristics, operational response time, viewing angle, and contrast. Many of those requirements are impacted by alignment characteristics of liquid crystal molecules in the LCD. Indeed, uniformly aligned liquid crystal molecules are important to the electro-optical characteristics of an LCD, and the alignment characteristics of the LCD are provided by an alignment layer. As is well known, alignment films are typically formed in the following manner. First, an organic polymer film, for example, a polyimide film, is deposited over a substrate on which electrodes and circuit components are provided. Next, the surface of the organic polymer film is mechanically rubbed with a cloth in a predetermined direction, thereby obtaining an alignment film having the function of aligning the liquid crystal molecules in the predetermined direction. While the rubbing technique is a simple process, it has problems. For example, various process variables related to rubbing are difficult to accurately control. Further, dust adsorption, unwanted scratches generated by the rubbing, and damage to TFTs caused by static electricity can also result from the rubbing. Still further, in the rubbing treatment, pressure cannot always be applied uniformly. As a result, the liquid crystal molecules may have their pretilt angles disturbed so as to form rubbing stripes in small domains of the liquid crystal layer. Such problems reduce manufacturing yields and the performance of LCDs. Because of the forgoing problems, significant effort has been expended in developing alternative alignment techniques.
One type of such alternative techniques involves photo-alignment methods which include photo-decomposition, photo-polymerization, and photo-isomerization. In accordance with such methods, optical anisotropy is brought about in a polymer layer by inducing a photo-reaction after most of the molecules facing a polarizing direction in disorderly-aligned polymer molecules have absorbed light. To form a photo-alignment layer using a photo-alignment material, the photo-alignment material is uniformly coated on a substrate. The photo-alignment layer material is then thermally treated and dried in an oven. Subsequently, a structure that assists anisotropy of the liquid crystals is attained by irradiating polarized UV rays onto the exposed surface of the photo-alignment layer.
Prior art photo-alignment materials, and LCDs using the same, have problems. For example, the alignment tends to be easily broken by thermal, physical, electrical, and photo shocks. Further, the alignment tends to be hard to restore.
Another alternative alignment technique is disclosed in an article by S. Park et al. entitled “Aligning Liquid Crystals Using Replicated Nanopatterns,” PSI Scientific Report 2002/Volume VII, p. 85, March 2003. The disclosed alignment technique entails producing alignment layers for liquid crystal cells using imprint lithography. As disclosed in the article, PMMA was coated on a surface, and relief patterns were imprinted in the PMMA using imprint lithography. Then, the relief patterns were opened to the substrate by etching, and a hydrophobic silane (for example, (tridecafluro-1,1,2,2-tetrahydrooctyl)-trichlorosilane (TFS), was deposited from the gas phase over the opened relief patterns. Finally, a lift-off process of the remaining PMMA left alignment patterns of TFS on the substrate. One problem to be solved with this method is how to integrate the generation of such an alignment method with fabrication of an LCD panel as described above.
In light of the above, there is a need for displays and methods to improve fabrication of such displays that overcome one or more of the above-identified problems.
One or more embodiments of the present invention satisfy one or more of the above-identified needs in the art. In particular, one embodiment of the present invention is a method for fabricating a display that comprises: (a) fabricating a sealing wall having a first height about a periphery of first display structures that have been fabricated on a first substrate; (b) fabricating a containment wall having a second height about the periphery and outside the sealing wall, the second height being less than the first height; (c) dispensing a sealing material between the sealing wall and the containment wall; (d) contacting a second substrate having second display structures to the first substrate; and (e) setting the sealing material to bond the first and second substrates.
One or more embodiments of the present invention relate to methods for fabricating displays such as, for example and without limitation, liquid crystal display devices (LCDs) using imprint lithography.
Next, in accordance with one or more embodiments of the present invention, sealing wall 150 (portions 1501 and 1502 are shown in the cross-sectional view of
In accordance with one or more embodiments of the present invention, wall sealing wall 150 may be an oxide (for example, SiOx), a nitride (for example, SiNx), an oxynitride (SiOxNy), or any other suitable material. Sealing wall 150, and optional separation posts 155, may be formed utilizing any one of a number of fabrication techniques that are well known to those of ordinary skill in the art such as masking techniques and etching techniques to provide openings (through structure and layers on substrate 100) to substrate 100. Then, in accordance with any one of a number of methods that are well known to those of ordinary skill in the art, sealing wall 150, and optional separation posts 155 are formed to provide the structural configuration illustrated in
In accordance with one or more embodiments of the present invention, containment wall 160 may be formed by the same technique and material used to form sealing wall 150. Alternatively, containment wall 160 may be formed utilizing imprint lithography techniques wherein containment wall 160 is formed from an imprinting material, for example and without limitation, an acrylate or any low viscosity, UV curable liquid, by depositing the imprinting material for containment wall 160 as a series of drops along a path on substrate 100 upon which containment wall 160 is to be formed. Then, as shown in
Next, in accordance with one or more embodiments of the present invention, an imprinting material from which alignment layer 380 (portions 3801 and 3802 are shown in the cross-sectional view of
Referring to
Referring to
To facilitate filling of recessions 28a, the imprinting material is provided with the requisite properties to fill recessions 28a while covering the predetermined portion of surface 32 with a contiguous formation of the imprinting material.
Referring to
Exemplary radiation source 22 may produce ultraviolet radiation; however, any known radiation source may be employed. The selection of radiation employed to initiate the polymerization of the imprinting material in imprinting layer 34 is known to one skilled in the art and typically depends on the specific application which is desired. As one can readily appreciate, the plurality of features on imprint template 28, for example, recessions 28a and protrusions 28b, may correspond to virtually any feature required to create a containment wall, sealing wall, separation posts, and/or an alignment layer.
As is well known, imprint template 28 may be formed from various conventional materials, such as, for example and without limitation, fused-silica, quartz, silicon, organic polymers, siloxane polymers, borosilicate glass, fluorocarbon polymers, metal, hardened sapphire and the like.
As mentioned above, the imprinting material is deposited on substrate 31 as a plurality of discrete and spaced-apart droplets 36. The combined volume of droplets 36 is such that the imprinting material is distributed appropriately over an area of surface 32 where imprinting layer 34 is to be formed. As a result, imprinting layer 34 is spread and patterned concurrently, with the pattern being subsequently set into imprinting layer 34 by exposure to radiation, such as ultraviolet radiation. As a result of the deposition process, it is desired that the imprinting material have certain characteristics to facilitate rapid and even spreading of material 36a in droplets 36 over surface 32 so that all thicknesses are substantially uniform. Desirable characteristics include having a low viscosity, for example and without limitation, in a range of about 0.5 to about 5 centepoise (csp), as well as the ability to wet surface of substrate 31 and imprint template 28 and to avoid subsequent pit or hole formation after polymerization.
The constituent components that form the imprinting material to provide the aforementioned characteristics may differ. This results from substrate 31 being formed from a number of different materials. As a result, the chemical composition of surface 32 varies dependent upon the material from which substrate 31 is formed. For example, substrate 31 may be formed from silicon, plastics, glass, composites thereof, and so forth.
As is well known, to ensure proper release from an imprint template, a minimum surface energy is desired, for example and without limitation, by proper alignment of hydrophobic groups in the imprinting material at its interface with a surface of the imprint template. In accordance with one particular method of imprinting, the surface of the imprint template is pre-treated utilizing a surfactant solution consisting of 0.1% FSO-100 in isopropyl alcohol (“IPA”), and the imprinting material includes a small amount of FSO-100 (FSO-100 is a surfactant that is available under the designation ZONYL® FSO-100 from DUPONT™ (FSO-100 has a general structure of R1R2 where R1=F(CF2CF2)Y, with Y being in a range of 1 to 7, inclusive and R2=CH2CH2O(CH2CH2O)XH, where X is in a range of 0 to 15, inclusive). FSO-100 is a fluorinated surfactant having a molecular weight of about 600, and it aligns efficiently at the surface of the imprint template with hydrophobic —CF3 groups projecting towards the surface of the imprint template. Such alignment is promoted by pre-treating the surface (prior to pre-treatment utilizing a surfactant solution consisting of 0.1% FSO-100 in IPA) to create silanol bonds on the surface.
Alternatively, one may use a different fluorinated surfactant from FSO-100, and in particular, a fluorinated surfactant that is available under the designation 3M Novec™ Fluorosurfactant FC-4432 (hereafter referred to as FC-4432) from 3M Company St. Paul, Minn. FC-4432 is a non-ionic polymeric fluorochemical surfactant belonging to a class of coating additives which provide low surface tensions in organic coating systems. The composition of FC-4432 is 87% polymeric fluorochemical actives, 7% non-fluorochemical actives, 5% 1-methyl-2-pyrudiinone, and <1% toluene. FC-4432 is a wetting, leveling and flow control agent for radiation curable polymer coating systems, and continues to be active throughout the curing process. FC-4432 is the first in a new line of fluorochemical surfactants from the 3M Company based on perfluorosulfate (PFBS), where PFBS refers collectively to perfluorobutane sulfonyl compounds including perfluorobutance sulfonates. In addition, such PFBS-based surfactants with only four perfluorinated carbon atoms offer improved environmental properties. The molecular weight of FC-4432 is about 4000, and because of its higher molecular weight than that of FSO-100, the fluorinated groups of FC-4432 align differently at the surface of an imprint template than those in FSO-100. In particular, besides —CF3 groups of FSO-100, FC-4432 has a higher percentage of —CF2 groups when compared to FSO-100. Because a —CF2 group provides a higher surface energy than a —CF3 group, the presence of a higher percentage of —CF2 groups in FC-4432 provides a material having better wetting than FS-100. However, despite its higher surface energy, a —CF2— group is hydrophobic enough so that its use produces a material having a good release property. In addition, it is believed that the higher molecular weight of FC-4432 (when compared to that of FSO-100) causes FC-4432 to act like a loosely packed coil structure that results in more porous molecular packing of surfactant molecules at the surface of the imprint template. It is further believed that this coil structure helps enhance wetting over that provided by FSO-100 in addition to that provided by the presence of a higher percentage of —CF2 groups in FC-4432 when compared to FSO-100.
An exemplary composition for the imprinting material that utilizes the surfactant FC-4432 is produced by mixing (with exemplary proportions being given in weight): (i) acryloxymethylpentamethyldisiloxane (for example and without limitation, about 37 gm) which is available under the designation XG-1064 from Gelest, Inc. of Morrisville, Pa., (ii) isobornyl acrylate (“IBOA”) (for example and without limitation, about 42 gm) which is available under the designation SR 506 from Aldrich Chemical Company of Milwaukee, Wis., (iii) ethylene glycol diacrylate (for example and without limitation, about 18 gm) which is available under the designation EGDA from Aldrich Chemical Company of Milwaukee, Wis., (iv) a UV photoinitiator, for example and without limitation, 2-hydrozy-2-methyl-1-phenyl-propan-1-one (for example and without limitation, about 3 gm) which is available under the designation Darocur 1173 from CIBA® of Tarrytown, N.Y.), and (iv) FC-4432 (for example and without limitation, about 0.5 gm). The above-identified composition may also include stabilizers that are well known in the chemical art to increase the operational life of the composition. In a typical such embodiment, the surfactant comprises less than 1% of the imprinting material. However, the percentage of the surfactant may be greater than 1%.
Another manner by which to improve the release properties of imprint template 28 includes conditioning the pattern of imprint template 28 by exposing the same to a conditioning mixture including an additive that will remain on imprint template 28 to reduce the surface energy of the imprint template surface. An exemplary additive is a surfactant.
The following describes a method for imprint lithography that utilizes one or more embodiments of the above-described imprinting material. As a first step, the surface of a quartz imprint template is pre-treated to create hydrophilic bonds at the surface, for example and without limitation silanol (Si—OH) bonds. In accordance with one or more embodiments of the present invention, the surface of the imprint template is dipped in a 2.5:1 solution of H2SO4 and H2O2 to hydrolyze the surface, i.e., to create silanol bonds at the surface. As a next step, the surface is further pre-treated by spraying the surface of the imprint template with a diluted FC-4432 solution (for example and without limitation, 0.1% FC-4432 in IPA). Exposure of the surface of the imprint template may be achieved by virtually any method known in the art, including dipping the surface into a volume of pre-treatment solution, wiping the surface with a cloth saturated with pre-treatment solution, and spraying a stream of pre-treatment solution onto the surface. The IPA in the pre-treatment solution may be allowed to evaporate before using the imprint template 28. In this manner, the IPA facilitates removing undesired contaminants from the surface while leaving the surfactant. Because the surfactant includes a hydrophobic, fluorine-rich end, and a hydrophilic end, the silanol bonds promote alignment of the surfactant so that the hydrophilic end “attaches” to the —OH end of the silanol bonds, and the hydrophobic, fluorine-rich end points away from the surface. In a next step, a gap between the imprint template and the substrate may be purged of air (mainly O2 and N2) using, for example and without limitation, an ˜5 psi Helium purge. In a next step, the imprinting material containing the FC-4432 surfactant is applied to the substrate, for example and without limitation, by placing a pattern of substantially equidistant droplets of imprinting material on the substrate, by spin-coating, or by any other method known to those of ordinary skill in the art. Next, the familiar steps of imprint lithography are carried out, i.e., exposure to actinic radiation to polymerize the imprinting material; and separation of the imprint template and the substrate.
The embodiments of the present invention described above are exemplary. Many changes and modifications may be made to the disclosure recited above, while remaining within the scope of the invention. The scope of the invention should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents. For example, one or more embodiments of the present invention are applicable for use in fabricating a reflection type LCD device, a transflective (i.e., transmission/reflection) type LCD device, a plasma panel device, and so forth.
