WO2007040465A1

WO2007040465A1 - Luminescent display and method of making the same

Info

Publication number: WO2007040465A1
Application number: PCT/US2005/033017
Authority: WO
Inventors: David Paul Ciampa; Farzad Parsapour
Original assignee: Thomson Licensing
Priority date: 2005-09-15
Filing date: 2005-09-15
Publication date: 2007-04-12

Abstract

A display is provided, comprising: a glass anode plate (110) having a patterned black matrix (122) thereon with openings (116) there through, and a plurality of individual luminescent elements (17R, 17G, 17B) formed within the openings of the black matrix, wherein each of the individual luminescent elements precisely fills its respective opening and the plan view surface area of the individual luminescent elements is substantially the same as the plan view surface area of its respective opening. A method for forming this display is also described wherein the black matrix is positioned between a luminescent mask (130) and the luminescent material during patterning, and apertures in the luminescent mask are aligned with openings in the black matrix and are wider than the openings.

Description

LUMINESCENT DISPLAY AND METHOD OF MAKING THE SAME

Field of the Invention

The present invention is related to forming luminescent elements for a display and more particularly to using a matrix array of the an plate of the display as a defining mask for photolithographically printing the luminescent elements onto the plate.

Background of the Invention

In one type of Field Emission Display (FED), the anode plate has a matrix array consisting of both horizontal and vertical lines. The size of the rectangular openings created by this array depends upon the line- width control in the printing of the matrix lines. Currently, the matrix array is printed onto the FED anode plate using a contact-print process. Line-width errors in this process have been measured to be as high as 0.0009 inches (0.0005 inches on average). The misregister of the phosphor rectangles with their respective matrix openings can be fairly large (e.g. 0.0009 in.) depending on the register of the matrix array and the lines of the phosphor mask. If a phosphor mask is used to define the phosphor rectangles, then even with perfect registration between the matrix array and the lines of the phosphor mask, the phosphor rectangles will vary in size due to line width errors and the phosphor may not completely fill the openings. Moreover, since spacers will be placed onto the horizontal matrix lines, it is difficult simply to make the phosphor rectangles oversized to compensate for the variations in opening size without making the matrix lines undesirably large.

With conventional phosphor printing techniques, misalignment or misregister of the phosphor with the matrix opening can be expected. Having such misalignment wastes phosphor material and can reduce light output. Further, because the errors associated with the printing of the phosphor can be random, one can also expect non-uniform color balance throughout the display screen.

As such, the need exists for a display such as a field emission display and a method of making the same where the luminescent elements are not misaligned or misregistered, light output is optimized and no luminescent material is wasted.

Summary of the Invention

A display is provided, comprising: an anode plate having a patterned black matrix thereon with openings therethrough, and a plurality of individual luminescent elements formed within the openings of the black matrix, wherein each of the individual luminescent elements precisely fills its respective opening and the plan view surface area of the individual luminescent elements is substantially the same as the plan view surface area of its respective opening. A method for forming this display is also described wherein the black matrix is positioned between a luminescent mask and the luminescent material during patterning, and apertures in the luminescent mask are aligned with openings in the black matrix and are wider than the openings.

This invention uses the matrix array itself as a mask for forming luminescent elements in combination with a luminescent mask with an oversized aperture. Thus, the problems with line-width error are eliminated, and each luminescent element is custom-fit to its opening. Another important feature provided by this invention is that it virtually eliminates the need for hyper-stringent registration between the matrix and luminescent mask. Another advantage of this invention is that no vacuum is needed as it would be for contact printing. Brief Description of the Drawings

Fig. 1 is a sectional view of an anode plate and luminescent mask aligned for forming luminescent elements according to an existing process; Fig. 2 is a sectional view of an anode plate and luminescent mask aligned for forming luminescent elements according to an exemplary embodiment of the present invention;

Fig. 3 is a plan view of an anode plate of a display having luminescent elements formed using an existing contact printing method, and shows luminescent element-to-matrix alignment; Fig. 4 is a plan view of an anode plate formed according to an exemplary embodiment of the present invention, showing luminescent element-to-matrix alignment; and

Fig. 5 is a flow chart of the method of creating a display screen according to an exemplary embodiment of the present invention.

Detailed Description of the Invention

Fig. 1 shows a previous attempt at printing a luminescent screen such as a phosphor screen for a display device such as a field emission display (FED). The printing process used an anode plate 10 in a type of contact printing, which is a method similar to that used to produce a matrix array 20. In this scheme, a phosphor layer 14 is formed over the matrix array 20, which is formed on a glass plate 11. Then, a phosphor mask 30 is aligned with the matrix array 20, specifically, an aperture 35 in a masking layer 32 of the phosphor mask 30 is aligned between vertical lines 22 of the matrix array 20, where a phosphor element is desired. The aperture 35 in the masking layer 32 of the phosphor mask 30 defines the phosphor rectangles 14 (see Fig. 3). The matrix array 20 also comprises horizontal matrix lines 21. Fig. 3 shows an example of the misalignment or misregister that one can expect between the phosphor deposits and the openings when printing phosphor deposits according prior practice. The edges of the printed phosphor elements 17R, 17B, 17C do not precisely and accurately align with the openings 16 of the matrix array 20. Note that the dotted profiles are part of the printed phosphor elements 17R, 17B, 17C that cover the matrix array 20. This means that the edges of the printed phosphor elements 17R, 17B, 17C are not precisely and accurately positioned with the edges of the printed matrix 18R, 18B, 18G. Having such misalignment wastes phosphor material (because phosphor overlapping the matrix array 20 is does not contribute to light output) and can reduce light output (because any portion of the openings 16 which are not covered with phosphor will not contribute light output). Further, because the errors associated with the printing of the phosphor are random, one can also expect non-uniform color balance throughout the display screen. Note that because such a process is random, some elements can be aligned, even though Fig. 3 does not show such an element. Fig. 5 shows a flow chart of the method of creating a display screen such as for an

FED according to an exemplary embodiment of the present invention. Figs 2 and 4 show views of the display screen, which could be an FED, according to an exemplary embodiment of the present invention. A matrix array 120 of horizontal lines 121 and vertical lines 122 can be contact printed onto a plate 110, which can be flat and be glass and can have a thickness of about 1.1 mm. In one example, the lines can have a pitch PH of 0.008 inches in the horizontal direction (with 0.004 inch line-widths) and a pitch PV of 0.024 inches in the vertical direction, thus creating a web of openings 116 which can be rectangular and will eventually be filled with luminescent material such as phosphor.

A luminescent layer 114 is deposited over the flat glass plate 110, covering the matrix lines 121, 122 and filling the openings 116. A luminescent mask 130 is set beneath the matrixed anode plate 110 as shown in Fig. 2. The luminescent mask 130 can have vertically oriented lines 132 (i.e., a patterned masking layer) with no horizontal line structure, because the horizontal lines 121 in the matrix array 120 can serve to block actinic light in the respective horizontal regions (in systems where the manufacture has horizontal lines 121). Note that the lines (masking layer) 132 of the luminescent mask are designed to block two of the matrix openings 116, but are smaller in width than three vertical matrix lines 122 and two openings 116 (i.e., the aperture 135 (W_op) in the luminescent mask 130 is wider than the opening 116 (W_om) between the vertical matrix lines 122), so that the luminescent mask 130 does not define the matrix openings 116. Instead, the vertical matrix lines 122 will define where the light will impinge the luminescent materiall l4 (and thus be cross-linked), while the luminescent mask 130 will only serve to block the openings 116 that are not intended to receive the particular luminescent material. In this way, it does not matter if there are variations in the matrix line- width - the luminescent elements 114 (left after removal of the non cross-linked material) will always exactly cover the openings 116, wherein the edges of the printed luminescent elements 117R, 117B, 117C do precisely and accurately align with the edges of the printed matrix 118R, 118B, 118G as shown in Fig. 4. Note that the registration between the luminescent mask 130 and the vertical matrix array lines 122 does not have to be perfect in this scheme. The lines 132 of the luminescent mask 130 simply have to block two of the openings 116 and not impinge on the third opening.

In a preferred embodiment of the invention, the light that impinges on the luminescent mask is both perpendicular to the luminescent mask and is collimated. However, deviations from the light being perpendicular and collimated have yielded excellent results. For example, when a light source was held at a distance of more than 37 inches from a plate having a 5 inches in the diagonal dimension, each luminescent element 114 precisely filled the corresponding opening 116 as shown in Fig. 4. Additionally, it was determined that an elongated light source oriented perpendicular to the openings 35 provides good patterning of the luminescent material, due to reduced shadow effects.

Next a method for manufacturing a display such as field emission display with luminescent elements 114R, 114B, 114G that precisely fill openings 116 in a matrix pattern of black lines 121, 122 according to an exemplary embodiment of the present invention will be described. Fig. 5 shows a flow chart of the method.

In step 210, a glass anode plate 110 is provided having a patterned black matrix 121,

122 on an interior side thereof. The matrix has interspersed sets of red openings, green openings and blue openings 116.

In step 220, a blanket coating from a slurry is applied on the interior side of the glass anode plate 110. The slurry comprises a luminescent material of one color (i.e., red, blue or green) and photoresist.

Step 230 involves aligning a luminescent mask 130 having an opaque portion or masking layer 132 with the glass anode plate 110. The luminescent mask 130 may comprise black lines printed on the glass anode plate 110, and an aperture portion 135, wherein the opaque portion 132 completely covers two sets of the openings 116. The aperture portion 135, in plan view, completely exposes a third set of the openings 116, whereby only the light that passes through both the aperture portion 135 and the third set of the openings 116 can harden the slurry. The constraint on the mask aperture is that the width (Wop) of the vertical component of the openings 116 cannot be larger than the sum of the width (WQM) of opening 116 (which is to be exposed) plus the width (WR) of the vertical matrix line 122 to the right of the opening 116 and the width (WL) of the vertical matrix line 122 to the left of the opening 116. Step 230, also involves exposing the slurry to actinic light through a luminescent mask 130 on an exterior side of the glass anode plate 110. Ideally, collimated light that is perpendicular to the surface of the glass anode plate 110 is preferred, but practically the light does not need to be collimated to take advantage of the invention.

After the slurry is patterned, step 240 is employed developing the first luminescent color, which is preferably red. In this step, the portions of the slurry that were not hardened are removed (usually with some pressurized developer solution) to form individual luminescent elements 114R of the one color. Note that while red elements are formed in this step, the order of forming the different color luminescent elements can be changed.

Then in step 250, a blanket coating of another slurry is applied on the interior side, where the slurry comprises a luminescent material of another color (blue) and photoresist. In step 260, this slurry is preferably exposed to collimated, actinic light through a luminescent mask 130 on an exterior side of the glass anode plate 110 that has an aperture 135 that completely exposes a different set of openings 116 to pattern luminescent elements 114B of a different color. This is followed by developing in step 270 leaving behind the patterned second color luminescent material.

Finally in step 280, a blanket coating of another slurry is applied on the interior side, where the slurry comprising a luminescent material of yet another color (green) and photoresist. In step 290, this slurry is preferably exposed to collimated, actinic light through a luminescent mask 130 on an exterior side of the glass anode plate 110 that has an aperture

135 that completely exposes a different set of openings 116 to pattern luminescent elements 114G of a different color. This is followed by developing in step 300 leaving behind the patterned third color luminescent material.

In sum, a display according to this invention will have a glass anode plate having a patterned black matrix having openings in one dimension being W_OMR for red, W_OMB for blue, and W_OMG for green in a given triad, wherein red, green and blue luminescent elements are formed within the openings of the black matrix, each of the individual luminescent elements substantially fills its respective opening, and the plan view surface area of the individual luminescent elements is substantially the same as the plan view surface area of its respective opening. Substantially filling includes the luminescent elements absolutely mirroring the profile of the respective openings, i.e., the widths of the red, blue and green luminescent elements will be W_OMR, WO_MB and W_OMG? respectively. Further, substantially filling can also include the situation where the widths of the red, blue and green luminescent elements are within 0.001 in. of the widths W_OMR, W_OMB and W_OM_G, respectively, and the respective centers of the luminescent elements being within 0.0005 in. of the centers of their respective matrix openings.

Within the scope of the invention and meaning of substantially filled, some overexposure can be utilized by increasing exposure time or light intensity through the luminescent mask 130. (Overexposure may cause some of the luminescent elements to exceed the respective values of WOMR, WOMB and WOM_G-) Conceivably a manufacturer may want to target some overexposure in their manufacturing to ensure that the hardening threshold of every photoresist batch is exceeded. (It is recognized that the hardening threshold of photoresist formulations can drift for a variety of reasons, e.g. age of formulations, variations in sensitizer, polymers, or other photoresist components, variations in environmental conditions, etc.) One of the benefits of the invention is that even with overexposure the widths of the luminescent elements will not grow rapidly and will be well controlled; as such, the widths of such luminescent elements can still be considered substantially filled.

The foregoing illustrates some of the possibilities for practicing the invention. Many other embodiments are possible within the scope and spirit of the invention. For example, a feature of the invention is the utilization of the method in only portions of the screen array or the utilization of the method to print only some or one color luminescent elements. It is, therefore, intended that the foregoing description be regarded as illustrative rather than limiting, and that the scope of the invention is given by the appended claims together with their full range of equivalents.

Claims

What is Claimed is:

1. A display, comprising: a glass anode plate having a patterned black matrix thereon with openings therethrough; and a plurality of individual luminescent elements formed within the openings of the , black matrix, wherein each of the individual luminescent elements substantially fills its respective opening and the plan view surface area of the individual luminescent elements is substantially the same as the plan view surface area of its respective opening.

2. The display of claim 1, wherein the individual luminescent elements are defined by the patterned black matrix.

3. The display of claim 2, wherein the individual luminescent elements are patterned by exposure to collimated, actinic light through the patterned black matrix and an aperture in a luminescent mask.

4. The display of claim 3, wherein the aperture in the luminescent mask is larger than openings of the black matrix.

5. A method of manufacturing a display comprising the steps of:

(a) providing a glass anode plate having a patterned black matrix on an interior side thereof, wherein the matrix has interspersed sets of red openings, green openings and blue openings;

(b) applying a blanket coating of a slurry on the interior side, the slurry comprising a luminescent material of one color and photoresist;

(c) exposing the slurry to actinic light through a mask on an exterior side of the glass anode plate, the mask having an opaque portion and an aperture, wherein the opaque portion completely covers two sets of the openings and the aperture portion, in plan view, completely exposes a third set of the openings, whereby only the light that passes both through the aperture portion and the third set of the openings hardens the slurry;

(d) removing the portions of the slurry that were not hardened to form individual luminescent elements of the one color; and

(e) repeating steps (b) through (d) with slurries containing the other two colors and masks exposing the other two sets of openings in the matrix to form individual luminescent elements of the other two colors.

6. The method of claim 5, wherein the light in step (c) is provided by an elongate light source oriented essentially perpendicular to the aperture portion of the mask.

7. The method of claim 5, wherein the light in step (c) is collimated.

8. A method of manufacturing a display comprising the steps of:

providing a plate having a patterned black matrix on an interior side thereof, wherein the matrix has interspersed sets of openings for different color luminescent elements; applying a blanket coating of a slurry on the interior side, the slurry comprising a luminescent material for one color luminescent element and photoresist;

exposing the slurry to actinic light through a mask on an exterior side of the plate, the mask having an aperture portion and an opaque portion, wherein the aperture portion, in plan view, completely exposes one set of the openings, whereby only the light that passes both through the aperture portion and the one set of the openings hardens the slurry and the opaque portion completely covers all other sets of the openings; and

removing the portions of the slurry that were not hardened to form a set of the one color luminescent elements.