WO1988009268A1

WO1988009268A1 - Process for forming multicolored tfel panel

Info

Publication number: WO1988009268A1
Application number: PCT/US1988/001680
Authority: WO
Inventors: William Albert Barrow; Richard Timothy Tuenge; Hal Merritt
Original assignee: Planar Systems, Inc.
Priority date: 1987-05-20
Filing date: 1988-05-16
Publication date: 1988-12-01
Also published as: JPH04504923A

Abstract

A process for forming a multicolored TFEL display panel by depositing a first color phosphor laminate comprising top (54) and bottom (51) insulating layers, an intermediate phosphor layer (52) and optionally, an etch stop layer (50), across transparent row electrodes (48) upon a substrate (46). The laminate is masked and etched to leave first strips (52) of color phosphor sandwiched between top (54) and bottom (51) insulating layers. Next, a second color phosphor laminate is deposited over said first strips which is masked and etched to leave second color phosphor strips (62) overlapping the first strips. Third strips (72) may be added in the same manner. The strips (52, 62, 72) comprise different color-producing electroluminescent materials repeating in a predetermined sequence across the substrate. A single pixel area may include a set of strips which through drive techniques, one or more, may be selectively energized to provide color displays ranging from dual monochromatic to full color displays.

Description

PROCESS FOR FORMING MULTICOLORED TFEL PANEL

The following invention relates to a multi- colored TFEL panel and a process for making the same which may provide a full color display using a plural¬ ity of electroluminescent phosphor stripes having dif¬ fering color-producing properties patterned on a single substrate. AC-driven monochromatic TFEL devices such as that depicted in Inazaki, et al., U.S. Patent No. 3,946,371 comprising five layers, namely, a pair of insulating layers sandwiching an electroluminiscent phosphor layer, and a pair of electrodes in turn sand- wiching the insulating layers, with the entire laminar structure being supported on a substrate of glass or other transparent material, are well known. Such TFEL devices with associated power supply, matrix-addressing and logic circuitry, are utilized as flat screen display monitors for portable computers for military and commercial applications. However, it is desirable, particularly for the purposes of improving the legibi¬ lity and usefulness of such display devices, to have the information presented in more than one color. At the present time multicolored display capability in computers is provided principally by color CRT devices but it would be desirable, particularly in applications requiring portability and light weight, that a flat screen display be available with this capability as well.

Such displays have been provided in the past by the use of TFEL panels having multiple layers of electroluminescent material of differing color- producing capabilities. Such a device is shown in Chang, U.S. Patent No. 4,155,030. The device of the Chang patent includes multiple layers of electrolumi¬ nescent materials wherein each layer includes a phosphor having a different color-emitting charac¬ teristic. This technique, however, requires multiple transparent layers of electroluminescent materials and insulators. Some disadvantages to a multicolored, multilayered structure include the requirement for a larger number of electronic devices and interconnec¬ tions to the layers, more complex drive electronics, and cost. There may also be parallax effects and cross-talk with multilayered, multicolored screens. The most important disadvantage is that this structure has never been made reliable. All known devices of this type exhibit catastrophic failure modes.

SUMMARY OF THE INVENTION The present invention utilizes a single layer which includes a plurality of stripes of phosphor material having differing light-emitting and color- producing capabilitieso The stripes are arrang^'ed as parallel lines on a substrate so that the different types of color-producing phosphor material to be utilized in the display alternate from one stripe to the next in a predetermined sequence. For example, if red, green and blue are the colors to be utilized in the screen, the phosphors having these color-emitting properties will be patterned on the screen in stripes according to the sequence red-green-blue. This sequence will repeat across the substrate.

Each color-producing stripe will have a row or column electrode uniquely associated with it so that the electrode is arranged co-linearly with the stripe but separated from the stripe by an insulator. In this way the energization of each color-producing stripe may be separately controlled by the panel's drive elec¬ tronics. Column electrodes are used so that pixel capacitance may be minimized. An example of a drive scheme suitable for use with such a structure is shown in a co-pending patent application Serial No. 729,974 entitled Driving Architecture For Matrix Addressed TFEL Display which is assigned to the same assignee.

The color stripes may be etched one color at a time using a dry etching process. Each color may comprise a laminate including a top insulating layer, a phosphor layer, and a bottom insulating layer. A "stop" layer which resists the etching process may be used on at least the first laminate. This prevents the etch from damaging the row electrodes during the etching of the first color laminate, and makes it possible to stop the etch between the top insulator of one laminate and the bottom insulator of the next lami¬ nate in etching the second and third color laminates. The process includes depositing a first color phosphor laminate, which includes the stop layer, across the substrate and transparent row electrodes, and placing photoresistive material in the form of a mask across the laminate. The laminate is etched in a plasma etcher or reactive ion etcher which leaves stripes of a first color phosphor sandwiched between top and bottom insulator layers. .Next, a second color phosphor lami¬ nate is deposited on the substrate over the first color stripes and a different mask is used. This time the mask is designed to leave stripes of a second phosphor color after the etching process which slightly overlap the stripes of the first color. The stripes of a third color may be added in the same way. Like the stop layer, the overlap prevents the row electrodes, which extend perpendicular to the stripes, from being etched through by repeated exposures as each color pattern is deposited.

It is a primary object of this invention to provide a compact and inexpensive multicolored TFEL screen. Yet a further object of this invention is to provide a multicolored TFEL screen through the use of a matrix including stripes of phosphors having differing color-producing properties arranged in side-by-side relation across a single substrate.

Yet a further object of this invention is to provide a dry etching process for making a multicolor screen of the character described above.

The foregoing and other objectives, features and advantages of the present invention will be more readily understood upon consideration of the following detailed description of the invention taken in conjunc- tion with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of a portion of the structure of a multicolored TFEL screen constructed according to the present invention.

FIG. 2 is a schematic plan view of a portion of a multicolored screen constructed according to the process of the invention.

FIG. 3A is a sectional view of a portion of a TFEL panel undergoing the first step of the etching process of the present invention.

FIG. 3B is a sectional view of the TFEL panel of FIGc 3A subsequent to the first etching step of the process of the invention_ FIG. 3C is a sectional view of the TFEL panel of FIG. 3A undergoing the second etching step of the process of the invention.

FIG. 3D is a sectional view of the TFEL panel of FIG. 3C subsequent to the second etching step of the etching process of the invention.

FIG- 3E is a sectional view of the TFEL panel of FIG. 3D prepared for the third etching step of the present invention.

FIG. 3F is a sectional view of the TFEL panel of FIG. 3E subsequent to the third etching step of the present invention. FIG. 3G is a sectional view of the TFEL panel of FIG. 3F with column electrodes deposited on each color-producing phosphor laminate.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a substrate 10 which may be constructed of glass, for example, includes column electrodes 12, 14 and 16, respectively. A thin layer of insulating material 18 is deposited on top of the substrate covering the column electrodes. The column electrodes 12, 14 and 16 are transparent electrodes, the construction of which is well known in the art. Stripes of patterned phosphors 20, 22 and 24 are placed on top of the insulating layer 18. Covering the pat- terned phosphor stripes 20, 22 and 24 is a second insu¬ lator 26. Row electrodes 28, 30 and 32 are placed on top of insulator 26 and are disposed orthagonally with respect to the patterned phosphor stripes 20, 22 and 24 and the column electrodes 12, 14 and 16. At a viewing angle which is normal to the front of the screen 10 the intersection between one of the row electrodes 28, 30 or 32 and three of the column electrodes 12, 14 and 16 forms .a single pixel. The pixel may be colored either red, green or blue depending upon which of the column electrodes are energized, or may emit light which is a combination of two or more of the patterned phosphor stripes 20, 22 and 24. Thus, a gray code may be employed regulating the relative intensity level of the light emitted by any combination of stripes 22, 20 and 24 to provide a full color display.

The red, green and blue patterned phosphors stripes 24, 22 and 20, respectively, are patterned across the screen 10 in repeating groups utilizing the same red-green-blue sequence. The fact that the dif¬ ferent colored stripes are patterned on the substrate 10 in side-by-side relation make this structure espeσially appropriate for thin-film transistor driving techniques. In such a case a thin-film switching and/or control circuit may be used for each inter¬ section of a patterned phosphor stripe with its orthogonally-disposed electrode. For example, the intersection of electrode 32 and patterned phosphors stripe 24 would form, a single pixel which may be controlled by a thin-film switching and/or control circuit dedicated to that pixel and located adjacent to it.

Appropriate materials for the patterned phosphor stripes include strontium sulfide doped with cerium fluoride SrS:CeF3) for producing a blue color; zinc sulfide doped with terbium fluoride (ZnS; bF3) for producing a green color; and calcium sulfide doped with Europium CaS.Eu for producing a red color. Also, any of the above materials could be used with each other or with yellow-emitting ZnS.Mn to produce screens having only dual color characteristics. Referring now to FIG. 2, row electrodes 32,

34, 36 and 38 are deposited on the substrate (not shown in FIG. 2). Electrodes 32, 34, 36 and 38 are scanning or row electrodes which are scanned in sequence once per frame in a predetermined scanning pattern, usually from top to bottom. These electrodes are constructed of transparent material, usually indium tin oxide (ITO) . These electrodes may be made relatively wide to provide maximum conductivity. This is important because the ITO transparent conductive material has a relatively high sheet resistance. Making these lines wide increases their conductivity which, in turn, per¬ mits rapid charging. Data electrodes 40, 42 and 44 are placed on the screen after the etching process to be described below. Each of the data electrodes 42, 40 and 44 sandwich a phosphor stripe of a predetermined color. In a full color screen, for example, electrode 40 may be dedicated to a phosphor which emits a blue color , electrode 42 may be dedicated to a phosphor which emits a green color, and electrode 44 may be dedicated to a phosphor which emits a red color. The electrodes 40, 42 and 44 are typically constructed of aluminum which has a low sheet resistance and can therefore be narrow without significantly increasing the time that it takes to fully charge. The column or data electrodes are energized with a relatively low modulation voltage, which, when added algebraically with the relatively high scanning voltages on the scanning electrodes 32, 34, 36 and 38, cause the phosphor material sandwiched therebetween to emit visible light. The color stripes are arranged so that they are energized by data electrodes 40, 42 and 44. Thus, each pixel comprises the intersection of a scanning electrode and three data electrodes 40, 42 and 44. This is more efficient than splitting the pixels in the row direction because for each pixel a column would need to be energized three times as fast and three times as often. For example, electroluminescence may be caused by charging the scanning electrodes in sequence with a voltage of minus 160 volts and selec¬ tively energizing data electrodes such as electrodes 40, 42 and 44 with a voltage of approximately 50 volts. This creates a composite voltage across the panel, for lit pixels, of 210 volts which is sufficient to cause luminescence. This arrangement provides low power operation of the panel and permits a high refresh rate. It also provides greater reliability since the top electrodes do not have to cross the edges of the phosphor stripes.

Referring to FIG. 3A, substrate 46 supports an ITO electrode layer 48. According to the process of the invention, a laminate film comprising a "stop" layer of aluminum oxide 50, a bottom dielectric layer 51, a light-emitting phosphor layer 52 of a first color, and a top insulator layer 54 is deposited atop the ITO electrode layer 48. The stop layer may be com¬ posed of AI2O3 and have a thickness of 200 A. Next, a mask which may include photoresistive strips 56 and 58 is placed atop the phosphor laminate comprising layers 50, 51, 52 and 54. The panel of FIG. 3A is placed in a plasma or reactive ion etching machine where it is treated with a.corrosive gas in the presence of a high- intensity electric field. As a result, the top insula¬ tor layer 54 and the phosphor layer 52 and the bottom insulator 51 are etched away from the stop layer 50 except in regions covered by photoresistive mask strips 56 and 58. Subsequently in FIG. 3C a second thin-film phosphor laminate comprising a stop layer 60, a bottom insulator 61, a color-producing phosphor layer of a second color 62 and a top insulator layer 64 is deposited on the substrate 46. A second mask com¬ prising strips of photoresistive material 66 and 68 is arranged atop the second thin-film phosphor laminate and the panel once again subjected to the dry etching process. This time, however, the photoresistive strips 66 and 68 are dimensioned so that the second thin-film laminate overlaps the first thin-film phosphor stripes 52. This overlap prevents the ITO layer in the region between lines of different colors from being etched through by repeated exposure to the corrosive gas as each color pattern is defined.

Referring to FIG. 3E a third thin-film laminate comprising a stop layer 70, a bottom insulator 71, a phosphor layer of the third color-producing phosphor 72 and a top insulator layer 74 are deposited on top of thin-film phosphor stripes 52 and 62 and their top insulators. A mask containing photoresistive material 76 is placed atop the stack and the panel is once again placed in the etcher. The result is shown in FIG. 3F wherein portions of all three thin-film laminates are arranged as overlapping phosphor stripes 52, 62 and 72 on substrate 46. The last step of the process, which is shown in FIG. 3G, comprises placing top electrodes 40, 42 and 44 extending colinearly and on top of the individual phosphor stripes 52, 62 and 72. In some cases it may be desirable to omit the bottom stop layer 50 or in the alternative, to omit stop layers 60 and 70. If the etch process can be closely monitored, for example, using a laser inter¬ ferometer and/or an optical spectrometer, it may be possible to know when the etch process has reached the ITO layer. Subsequent laminate layers may use a stop layer to closely control the etching process and make sure that the process is halted when the stop layer has been reached. The terms and expressions which have been employed in the foregoing specification are used therein as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims which follow.

Claims

WE CLAIM:

1. A method of constructing a multicolored TFEL display screen comprising the steps of: (a) depositing on a substrate a first set of elongate transparent electrodes; (b) depositing over said first set of electrodes a thin-film laminate of a first color-producing phosphor; - (c) etching said thin-film laminate to leave thin-film laminate stripes of said first color-producing phosphor extending perpendicular to said transparent electrodes; (d) depositing a second thin-film laminate of a second color-producing phosphor on top of said thin-film laminate stripes of said first color-producing phosphor;

(e) etching said thin-film laminate to leave stripes of a second color-producing phosphor lying adjacent to and extending parallel to said stripes of said first color-producing phosphor; and

(f) depositing a second set of elongate electrodes over said first and second stripes of thin-film laminates to extend colinearly therewith.

2. The method of claim 1 wherein said first set of transparent electrodes are scanning electrodes and said second set of electrodes are data electrodes.

3. The method of claim 1 wherein said first and second thin-film laminates each comprise a bottom insulating layer, a phosphor layer, and a top insulating layer.

4. The method of claim 1 wherein said etching steps are performed by a dry etching process.

5. The method of claim 3 wherein said bottom insulating layer contains an etch stop layer comprising a thin dielectric material of a composition that is more resistive to the etching process than the other layers of the thin-film laminates.

6. The method of claim 6 wherein said etch stop layer is AL2O3.

7. The method of claim 7 wherein the thickness of said etch stop layer is about 200 A.

8. The method of claim 1 wherein the etching step of step (e) is conducted so that each of said stripes of said second color-producing phosphor slightly overlaps each of said stripes of said first color-producing phosphor.

9. The method of claim 8, further including the steps of repeating said (d) and (e) with a third thin-film laminate wherein said first, second and third color-producing phosphor produce red, green and blue visible light, respectively.

10. The method of claim 4 wherein said dry etching process comprises placing a photoresistive mask over said thin-film laminates and exposing said thin- film laminates to a corrosive gas within an electric field, said mask comprising elongate photoresistive strips corresponding to the dimensions of said phosphor stripes.

11. The method of claim 10 wherein said photoresistive strips used in the etching step of step (e) are dimensioned to be wide enough to cause stripes of said second color-producing phosphor to overlap the stripes of said first color-producing phosphor.

12. The method of claim 9 wherein the bottom insulating layers of said second and third thin film laminates contain etch stop layers.