Method for photo-imageable lacquer deposition for a display device

Information

  • Patent Grant
  • 6727048
  • Patent Number
    6,727,048
  • Date Filed
    Thursday, December 20, 2001
    23 years ago
  • Date Issued
    Tuesday, April 27, 2004
    21 years ago
Abstract
A method for photo-imageable lacquer deposition for a display device. In one embodiment, a layer of photo-imageable lacquer is deposited on top of a faceplate of a display device. Portions of the lacquer layer are removed and selected portions of the lacquer layer remain deposited in the sub-pixel areas of the faceplate.
Description




FIELD OF THE INVENTION




The field of the invention relates to the manufacture of display devices. More specifically, the present invention pertains to producing a lacquer layer in the manufacture of display devices.




BACKGROUND OF THE INVENTION




For over 30 years, companies have searched for ways to construct a thin, low-power version of the conventional cathode ray tube (CRT). These efforts have led to a number of flat panel display technologies. None, including liquid crystal displays (LCDs) have met all of the needs for improved power, brightness, efficiency, video response, viewing angle, operating temperature, packaging, full color gamut, ruggedness, and scaleability.




Among the obstacles encountered in fabricating thin cathode ray displays is the deposition of a lacquer layer on the faceplate of the display prior to adding an aluminum layer. The aluminum layer is used to act as a mirror behind each sub-pixel in the display faceplate to reflect the light photons back toward the viewer of the display screen to create a brighter image. Surface irregularities in the aluminum layer scatter these photons and reduce the efficiency of the aluminum layer in reflecting light to the viewer, thus degrading the brightness of the display. The lacquer layer provides a supporting structure when the aluminum layer is deposited so that the aluminum layer is deposited upon an even surface and will reflect light evenly toward the viewer.




One method of depositing the lacquer layer is known as a “float lacquer” process.

FIGS. 1A-C

are cross section views showing the steps in a prior art float lacquer process. In

FIG. 1A

, a faceplate


101


is submerged in a solvent


102


such as water. In

FIG. 1B

, a thin layer of lacquer


103


is deposited or floated on top of water layer


102


. The water is then drained from the tank and, as the water level subsides, lacquer layer


103


is deposited upon faceplate


101


. In

FIG. 1C

, the level of water layer


102


in the sub-pixels


104


of faceplate


101


is then further reduced by evaporation and an aluminum layer is deposited directly on top of lacquer layer


103


. If the aluminum layer were to be deposited directly upon the phosphor particles within sub-pixels


104


, it would conform to the surface of the phosphor particles and have a very irregular surface which would reflect light back to the phosphor particles unevenly. During a subsequent baking operation, the remnants of lacquer layer


103


are removed as they can absorb electrons from the cathode and cause phosphor degradation if they remain.




The float lacquer process, however, is time consuming and is vulnerable to operator error. The amount of time it takes to set up the float tank and allow the water to become still enough to deposit lacquer layer


103


means the process is not well suited to larger scale manufacturing processes. Additionally, there can be variations in lacquer layer


103


as large as 30% using the float lacquer process, resulting in an irregular aluminum surface. This causes a non-uniform screen appearance and degrades the efficiency and brightness of the display.




The structure of thin CRTs limits the choice of lacquers in a float lacquer process to soft materials with very high elongation. High elongation is necessary to obtain a scaffold for the reflective aluminum to be applied without “tenting” over the sub-pixel regions. Tenting can be caused by an excessive amount of lacquer on the faceplate which makes the surface of the aluminum balloon and rupture when the lacquer and remaining water is baked out. Tenting can be detrimental, not only to the faceplate, but also during final assembly when support structures, inserted to provide greater structural integrity, can cause the aluminum layer to break which leads to electrical arcing in the finished display assembly. Tenting causes non-uniform screen appearance and reduced efficiency and brightness.





FIG. 2A

shows an exemplary display screen


200


which has undergone aluminum layer deposition and solvent bake out. The surface of aluminum layer


250


overlies sub-pixel areas


203


containing phosphor particles


202


. Aluminum layer


250


has undergone tenting in the sub-pixel regions during the bake out step and now has a convex surface profile from the viewers direction (the direction of arrow


260


) rather than a flat surface. Due to the convex profile, light photons will now be scattered by the aluminum layer rather than directed to the viewer and the efficiency and brightness of the display are thus decreased.




Materials with high elongation are also soft materials, which means that the lacquer layer will be very conformal around the phosphor particles in the sub-pixels. In

FIG. 2B

, a highly conformal lacquer layer


201


has been deposited upon a layer of phosphor particles


202


contained in a sub-pixel


203


. An aluminum layer deposited upon this lacquer layer will take on the shape of the conformal lacquer layer during the subsequent baking step to remove the lacquer layer and any remaining solvents. This causes the aluminum to also take on an irregular shape which reduces the reflectivity of the aluminum layer and can cause a grainy appearance in the display due to bad uniformity. To smooth the aluminum, a thicker lacquer layer (<1 μin thickness) is usually deposited on a regular CRT. Due the lower voltages used in a thin CRT, a thinner layer of aluminum is necessary to prevent excess electron energy loss. However, this thin aluminum layer is susceptible to blistering and breakage during the bake out if the lacquer layer is greater than 1 μin thickness. In summary, using a thin lacquer layer creates an excessively conformal aluminum layer and using a thicker lacquer layer leads to tenting and rupturing of the aluminum layer.




Accordingly, the need exists for a method for depositing a lacquer layer in the sub-pixel areas of a display device which will result in a smooth, highly reflective aluminum layer that is electrically and mechanically robust. It is also desirable that this method, while meeting the above stated needs, should be applicable to large scale manufacturing processes.




SUMMARY OF THE INVENTION




The present invention is a method for selectively removing a lacquer layer so that so that the remaining lacquer is disposed in the sub-pixel areas of a display device, resulting in a smooth, highly reflective aluminum layer that is electrically and mechanically robust. It is also desirable that this method, while meeting the above stated needs, should be applicable to large scale manufacturing processes.




In one embodiment, a layer of thermally degradable, photo-imageable lacquer is deposited on top of a faceplate of a display device. Portions of the lacquer layer are etched and removed using photolithography methods and selected portions of the lacquer layer remain deposited in the sub-pixel areas of the faceplate. This remaining layer will then later be decomposed thermally and degraded into volatile products that will disappear during subsequent vacuum processes.




In another embodiment, the faceplate of the display device is used as the mask for defining which portions of the photo-imageable lacquer layer remain in the sub-pixel areas. This has an added advantage in that a mask does not have to be created and aligned over the faceplate to image the lacquer layer.











These and other advantages of the present invention will become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiments which are illustrated in the various drawing figures.




BRIEF DESCRIPTION OF THE DRAWINGS




The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments of the present invention and, together with the description, serve to explain the principles of the invention. Unless specifically noted, the drawings referred to in this description should be understood as not being drawn to scale.





FIGS. 1A-1C

are cross section views of a display pixel area during a prior art lacquer layer deposition.





FIGS. 2A-B

are cross section views showing disadvantages in fabricating a display device using prior art lacquer deposition methods.





FIGS. 3A-3C

are cross section views of a display pixel area during a lacquer layer deposition in accordance with embodiments of the present invention.





FIG. 4

is a flow chart of the steps involved in accordance with one embodiment of the present invention.





FIGS. 5A-5C

are cross section views of a display pixel area during a lacquer layer deposition in accordance with embodiments of the present invention.





FIG. 6

is a flow chart of the steps involved in accordance with another embodiment of the present invention.











DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT




Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. While the present invention will be described in conjunction with the preferred embodiments, it will be understood that they are not intended to limit the present invention to these embodiments. On the contrary, the present invention is intended to cover alternatives, modifications, and equivalents, which may be included within the spirit and scope of the present invention as defined by the appended claims. Furthermore, in the following detailed description of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be obvious to one of ordinary skill in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been described in detail so as not to unnecessarily obscure aspects of the present invention.





FIGS. 3A-3C

are cross section views of a display pixel area during a lacquer layer deposition process as set forth in one embodiment of the current invention as set forth in flow chart


400


of FIG.


4


. For purposes of clarity, the following discussion will utilize the cross section views of

FIGS. 3A-3C

in conjunction with flow chart


400


of

FIG. 4

, to clearly describe one embodiment of the present invention. As will be described in detail below, the present invention is a method for photo-imageable lacquer deposition for a display device.




With reference to FIG.


3


A and to step


410


of

FIG. 4

, a photo-imageable lacquer layer


310


is deposited. Photo-imageable lacquer layer


310


is deposited upon a faceplate having a glass layer


320


and sub-pixel areas


330


which are separated by portions of a black matrix screen


325


. The black matrix screen serves to provide an opaque contrasting background for the sub-pixels and results in a more defined image for the display device. Sub-pixel areas


330


contain the phosphor particles


335


of the display device. In the present embodiment, photo-imageable lacquer layer


310


is polymethyl methacrylate (positive resist). With a positive resist lacquer, the portions exposed to light are later removed. With a negative resist lacquer, the portions not exposed to light are later removed. While the present embodiment recites polymethyl methacrylate, the present invention is well suited to utilize a variety of positive and negative resist lacquers in photo-imageable lacquer layer


310


.




Because the present invention does not use the float lacquer process, low elongation lacquers can be utilized. The advantage of utilizing a low elongation lacquer in the fabrication of a display device above the prior art is that a low elongation lacquer forms a less conformal layer upon the phosphor particles (e.g., phosphor particles


335


) in sub-pixel areas


330


of faceplate


320


. This means that a non-conformal lacquer layer can be deposited which is not so thick as to cause tenting and bursting in the aluminum layer. This leads to a more uniform aluminum layer which reflects light to the viewer more evenly and facilitates a brighter, more efficient display device. The float lacquer method relies upon high elongation lacquers which form a much more conformal lacquer layer and create an aluminum layer which reflects light photons less efficiently back toward the viewer.




Photo-imageable lacquer layer


310


may be deposited by spray deposition, spin deposition, printing, and extrusion. While the present embodiment recites these specific deposition methods, the present invention is well suited to utilize other methods to deposit photo-imageable lacquer layer


310


. Photo-imageable lacquer layer


310


is deposited in a blanket deposition upon faceplate


320


. After being deposited upon faceplate


320


, photo-imageable lacquer layer


310


is dried.




The present invention is much quicker than the float lacquer process and more suitable for large scale manufacturing processes. One of the greatest disadvantages of using a float lacquer process is that excessive time is lost in waiting for the water in the tank to become still and flat prior to depositing the lacquer layer. This makes the float lacquer process time consuming, economically inefficient, and unsuited to large scale manufacturing processes. If the water is not allowed to become still, the lacquer layer will be of non-uniform thickness which can cause an irregular aluminum layer. Because photo-imageable lacquer layer


310


is not deposited using the float lacquer process, the present invention does not require this wait and is more applicable to large scale manufacturing processes.




With reference to FIG.


3


B and to step


420


of

FIG. 4

, a mask (e.g., pattern mask


340


) is aligned above photo-imageable lacquer layer


310


. Mask


340


has openings in it that cover sub-pixel areas


330


. Alternatively, a mask may be created with openings in the areas corresponding with sub-pixel areas


330


.




Photolithography techniques are often used in the fabrication of semiconductor structures. In one photolithography process, a pattern mask (e.g., pattern mask


340


of

FIG. 4

) that defines the size and shape of a component in a semiconductor structure is positioned above a photosensitive layer (e.g., photo-imageable lacquer layer


310


) that has been applied over a layer of material. In one embodiment of the present invention, pattern mask


340


has openings which define the sub-pixel areas


330


of faceplate


320


. However, pattern mask


340


may have openings which define the areas between the sub-pixels. A stepper holds the pattern mask over the photoresist and the pattern image is projected onto the photoresist through a lens. The pattern is then imprinted onto the photoresist, for example, by hardening the portion of the photoresist that is exposed through the pattern mask, while the other (unexposed) portion of the photoresist remains relatively soft.




Alternatively, the portion of the photoresist exposed to the light becomes softer than the unexposed portion. The softer portion of the photoresist is then removed, leaving only the harder portion on the layer. Thus, in this manner, the pattern is reproduced in the photoresist on the surface of the layer. It is appreciated that this description applies to steps performed in the process of the present embodiment.




Referring still to FIG.


3


B and to step


430


of

FIG. 4

, portions of photo-imageable lacquer layer


310


are exposed to light. The light may be e-beam, ultra-violet (UV) light, deep UV light, or another wavelength to which photo-imageable lacquer layer


310


reacts. In one embodiment, photo-imageable lacquer layer


310


can be a lacquer which softens when exposed to light (positive resist). The portions of photo-imageable lacquer layer


310


underlying the openings of pattern mask


340


correspond to the areas between the sub-pixels. When lacquer layer


310


is exposed, the areas between sub-pixel areas are now softened and the lacquer within sub-pixel areas


330


remains hardened.




In another embodiment, photo-imageable lacquer layer


310


can be a lacquer which crosslinks when exposed to light (negative resist). In this embodiment, pattern mask


340


has openings corresponding with sub-pixel areas


330


. When lacquer layer


310


is exposed to light, the sub-pixel areas are now crosslinked and the lacquer between the sub-pixel areas


330


remains soluble.




With reference to FIG.


3


C and to step


440


of

FIG. 4

, portions of photo-imageable lacquer layer


310


are removed. Photo-imageable lacquer layer is developed with a solvent such as methyl isobutyl ketone to remove the softer areas which were not underlying openings in pattern mask


340


and hardened during step


430


of FIG.


4


. While methyl isobutyl ketone is recited in the present embodiment, the present invention is well suited to utilizing a variety solvents for this purpose. After developing photo-imageable lacquer layer


310


, a selected portion of photo-imageable lacquer layer


310


remains deposited in sub-pixel area


330


. Subsequently, an aluminum reflective layer is deposited upon photo-imageable lacquer layer


310


and faceplate


320


undergoes a second drying (e.g., baking) during which the remaining portion of photo-imageable lacquer layer


310


is removed as it can cause phosphor degradation if it remains in contact with phosphor particles


335


.




The advantage of the present invention over the prior art is that photo-imageable lacquer


310


remains in the sub-pixel areas


330


and not on the rows and columns between the sub-pixel areas. The float lacquer process leaves a lacquer layer across the entire surface of faceplate


320


, including the rows and columns. Tenting of a subsequently deposited aluminum layer is a frequent problem, particularly when lacquer is deposited in the rows and columns between sub-pixels when the faceplate is later baked to remove solvents from the sub-pixels. The present invention, by leaving photo-imageable lacquer layer


310


in the sub-pixel areas


330


, is able to avoid this problem.





FIGS. 5A-5C

are cross section views of a display pixel area during a lacquer layer deposition process as set forth in one embodiment of the current invention as set forth in flow chart


600


of FIG.


6


. For purposes of clarity, the following discussion will utilize the cross section views of

FIGS. 5A-5C

in conjunction with flow chart


600


of

FIG. 6

, to clearly describe one embodiment of the present invention. As will be described in detail below, the present invention is a method for photo-imageable lacquer deposition for a display device.




With reference to FIG.


5


A and to step


610


of

FIG. 6

, a photo-imageable lacquer layer


510


(a negative resist) is deposited. As in

FIG. 3

, photo-imageable lacquer layer


510


is deposited upon black matrix screen


325


having sub-pixel areas


330


.




Again, the present invention does not use the float lacquer process which allows the use of low elongation lacquers. This allows the deposition of a lacquer layer which is less conformal to the phosphor particles in sub-pixel areas


330


and is not so thick as to cause tenting and bursting in the aluminum layer. This leads to a more uniform aluminum layer which reflects light to the phosphor particles more evenly and facilitates a brighter, more efficient display device.




Photo-imageable lacquer layer


510


may be deposited by spray deposition, spin deposition, printing, and extrusion. While the present embodiment recites these specific deposition methods, the present invention is well suited to utilize other methods to deposit photo-imageable lacquer layer


510


. Photo-imageable lacquer layer


510


is deposited in a blanket deposition upon black matrix screen


325


. After being deposited upon screen


325


, photo-imageable lacquer layer


310


is dried.




Again, the present invention is much quicker than the float lacquer process and more suitable for large scale manufacturing processes. One of the greatest disadvantages of using a float lacquer process is that excessive time is lost in waiting for the water in the tank to become still and flat prior to depositing the lacquer layer. This makes the float lacquer process time consuming, uneconomical, and unsuited to large scale manufacturing processes. If the water is not allowed to become still, the lacquer layer will be of non-uniform thickness which can cause an irregular aluminum layer. Because photo-imageable lacquer layer


510


is not deposited using the float lacquer process, the present invention does not require this wait and is more applicable to large scale manufacturing processes.




With reference to FIG.


5


B and to step


620


of

FIG. 6

, a negative resist photo-imageable lacquer layer


510


is exposed to light through faceplate


320


itself. Light will penetrate and/or scatter off of and around the phosphor particles to expose portions of photo-imageable lacquer layer


510


. Additionally, the phosphor particles will also give off light in their respective spectrums. At the same time, the black matrix screen


325


serves as a pattern mask which prevents light from reaching portions of photo-imageable lacquer layer


510


. In this embodiment, the present invention has the previously mentioned advantages over the prior art and eliminates the steps of creating a pattern mask (e.g., pattern mask


340


of

FIG. 3

) and aligning it over photo-imageable lacquer layer


510


. Black matrix screen


325


now acts as the pattern mask, resulting in additional savings of time and money.




With reference to FIG.


5


C and to step


630


of

FIG. 6

, portions of photo-imageable lacquer layer


510


are removed. Photo-imageable lacquer layer is developed with a solvent to remove the soluble areas which were not exposed to light in step


620


. After developing photo-imageable lacquer layer


510


, a selected portion of photo-imageable lacquer layer


510


remains in sub-pixel areas


330


. The portions of photo-imageable lacquer layer


510


which were exposed to light remain in the sub-pixel areas


330


, while those portions which were masked by black matrix screen


325


are removed. After this, an aluminum reflective layer is deposited upon photo-imageable lacquer layer


510


and faceplate


320


undergoes a second drying (e.g., baking). During the baking, remaining portions of photo-imageable lacquer layer


510


are removed as they will desorb gas due to electron impingement and destroy the vacuum and can cause phosphor degradation if they remain in contact with phosphor particles


335


.




The present invention is a method for selectively removing a lacquer layer so that so that the remaining lacquer is disposed in the sub-pixel areas of a display device, resulting in a smooth, highly reflective aluminum layer that is electrically and mechanically robust. The present invention is also applicable to large scale manufacturing processes.




The preferred embodiment of the present invention, a method for photo-imageable lacquer deposition for a display device, is thus described. While the present invention has been described in particular embodiments, it should be appreciated that the present invention should not be construed as limited by such embodiments, but rather construed according to the following claims.



Claims
  • 1. A method for depositing a lacquer layer for a display device comprising:depositing a photo-imageable lacquer layer upon a faceplate of said display device; and removing a portion of said photo-imageable lacquer layer, where in a selected portion of said photo-imageable lacquer layer remains deposited within a sub-pixel area of said faceplate.
  • 2. The method for depositing a lacquer layer for a display device as recited in claim 1, wherein said depositing further comprises depositing a layer of photo-imageable polymethyl methacrylate upon said faceplate.
  • 3. The method for depositing a lacquer layer for a display device as recited in claim 1, wherein said depositing further comprises depositing said photo-imageable layer by a process selected from the group consisting of spray deposition, spin deposition, printing, and extrusion.
  • 4. The method for depositing a lacquer layer for a display device as recited in claim 1, wherein said depositing further comprises drying said photo-imageable lacquer layer.
  • 5. The method for depositing a lacquer layer for a display device as recited in claim 1, wherein said removing further comprises exposing said photo-imageable lacquer layer to light through a pattern mask.
  • 6. The method for depositing a lacquer layer for a display device as recited in claim 5, wherein said removing further comprises:creating said pattern mask, wherein said pattern mask has an opening defining said remaining portion of said photo-imageable lacquer layer; aligning said pattern mask on top of said faceplate; and exposing said photo-imageable lacquer layer to said light through said pattern mask.
  • 7. The method for depositing a lacquer layer for a display device as recited in claim 5, wherein said removing further comprises:creating said pattern mask, wherein said pattern mask covers said remaining portion of said photo-imageable lacquer layer; aligning said pattern mask on top of said faceplate; and exposing said photo-imageable lacquer layer to said light through said pattern mask.
  • 8. The method for depositing a lacquer layer for a display device as recited in claim 5, wherein said removing further comprises developing said photo-imageable lacquer-layer with a solvent.
  • 9. The method for depositing a lacquer layer for a display device as recited in claim 5, wherein said removing further comprises removing portions of said photo-imageable lacquer layer exposed to said light.
  • 10. The method for depositing a lacquer layer for a display device as recited in claim 5, wherein said removing further comprises removing portions of said photo-imageable lacquer layer not exposed to said light.
  • 11. The method for depositing a lacquer layer for a display device as recited in claim 1 wherein said method further comprises a second drying of said photo-imageable lacquer layer and wherein said photo-imageable lacquer layer is removed.
  • 12. A method for depositing a lacquer layer for a display device comprising:depositing a photo-imageable lacquer layer upon a faceplate of said display device; aligning a pattern mask having an opening in an area not defined by a sub-pixel area above said photo-imageable lacquer layer and exposing an area underlying said opening to light; and removing a portion of said photo-imageable lacquer layer, wherein a selected portion of said photo-imageable lacquer layer underlying said opening remains deposited within a sub-pixel area of said faceplate.
  • 13. The method for depositing a lacquer layer for a display device as recited in claim 12, wherein said depositing further comprises depositing a layer of polymethyl methacrylate upon said faceplate.
  • 14. The method for depositing a lacquer layer for a display device as recited in claim 12, wherein said depositing further comprises depositing said photo-imageable layer by a process selected from the group consisting of spray deposition, spin deposition, printing, and extrusion.
  • 15. The method for depositing a lacquer layer for a display device as recited in claim 12, wherein said depositing further comprises drying said photo-imageable lacquer layer.
  • 16. The method for depositing a lacquer layer for a display device as recited in claim 12, wherein said light has a wavelength in the deep ultra violet portion of the spectrum.
  • 17. The method for depositing a lacquer layer for a display device as recited in claim 12, wherein said removing further comprises developing said photo-imageable lacquer layer with a solvent.
  • 18. The method for depositing a lacquer layer for a display device as recited in claim 12, wherein said method further comprises a second drying of said photo-imageable lacquer layer and wherein said photo-imageable lacquer layer is removed.
  • 19. A method for depositing a lacquer layer for a display device comprising:depositing a photo-imageable negative resist type lacquer layer upon a faceplate of said display device; exposing said photo-imageable negative resist type lacquer layer to light through said faceplate; and removing portions of said photo-imageable negative resist type lacquer layer not subjected to said exposing, wherein a portion of said photo-imageable negative resist type lacquer layer remains deposited within a sub-pixel area of said faceplate.
  • 20. The method for depositing a lacquer layer for a display device as recited in claim 19, wherein said depositing further comprises depositing said photo-imageable negative resist type lacquer layer by a process selected from the group consisting of spray deposition, spin deposition, printing, and extrusion.
  • 21. The method for depositing a lacquer layer for a display device as recited in claim 19, wherein said depositing further comprises drying said photo-imageable negative resist type lacquer layer.
  • 22. The method for depositing a lacquer layer for a display device as recited in claim 19, wherein said removing further comprises developing said photo-imageable negative resist type lacquer layer with a solvent.
  • 23. The method for depositing a lacquer layer for a display device as recited in claim 19, wherein said method further comprises a second drying of said photo-imageable negative resist type lacquer layer and wherein said photo-imageable negative resist type lacquer layer is removed.
US Referenced Citations (4)
Number Name Date Kind
3603830 Gallaro et al. Sep 1971 A
5470681 Brunner et al. Nov 1995 A
6022652 Haven et al. Feb 2000 A
20020190643 Cummings et al. Dec 2002 A1