CA2364201A1

CA2364201A1 - Optical interference member for matrix displays

Info

Publication number: CA2364201A1
Application number: CA002364201A
Authority: CA
Inventors: Peter G. Hofstra; David J. Johnson
Original assignee: Luxell Technologies Inc
Current assignee: Luxell Technologies Inc
Priority date: 2001-12-03
Filing date: 2001-12-03
Publication date: 2003-06-03
Also published as: WO2003049210A1; AU2002349232A1

Abstract

An optical interference member is provided for use with active matrix or other patterned displays. In one embodiment, the optical interference members is configured to reduce incident ambient on the display through the use of thin film optical interference layers that are located on the display in locations not occupied by light emitting pixels or other light emitting means. In an active matrix display, the optical interference members can be coated upon the bus lines which connect to each of the transistors within the display, thereby presenting a black matrix which surrounds each pixel and provides improved contrast enhancement.

Description

Optical Interference Member for Matrix Displays Field of the Invention The present invention relates generally to active matrix displays or other patterned displays, and more particularly relates to patterned displays incorporating filters or other means to reduce reflectance of ambient light.
Background of the Invention Many display technologies are well known and such technologies are continuing to advance rapidly. For example, modern active matrix display technology can be incorporated into display devices that are relatively lightweight, thin, and which provide high resolution and richly coloured pictures for televisions, computer monitors, and more generally, for a wide variety of display devices that can be incorporated into appliances like personal digital assistants and cellular telephones. While current active matrix displays can be expensive, it is expected that further research will result in advances that will can reduce the costs of such displays and lead to overall greater usage of active matrix display devices.
Active matrix displays are proving to be superior in many ways to older display technologies such as cathode-ray tubes ("CRT"). However, the problem of "glare" off of active matrix displays is also a concern, just as with older CRTs. "Glare" can be defined as ambient light that is reflected off of the device and back towards the viewer, thereby reducing the contrast and overall performance of the display device.
Thus, it is also known to incorporate technology to reduce reflectance into displays and thereby improve their performance. In the case of active matrix displays (or indeed, any other type of pixellated display) it is known to use a black matrix of filtering material. The black matrix is mounted in a complementary fashion to the matrix of pixels in the display, such that the black matrix is a generally continuous filter that surrounds each pixel. Black matrices are described in a number of patents and patent applications, and method for preparation of same", EP 716 334 to Steigerwald ("Steigerwald #1");
"Transmissive Display Device Having Two Reflection Metallic Layers of Differing Reflectances", US 6,067,131 to Sato ("Sato"); "Anti-reflector black matrix display devices comprising three layers of zinc oxide, molybdenum and zinc oxide", US
5,570,212 to Steigerwald ("Steigerwald #2"); "Anti-reflector Black Matrix Having Successively A Chromium Oxide Layer, a Molybdenum Layer And a Second Chromium Oxide Layer", US 5,566,011 to Steigerwald ("Steigerwald #3"); and, "Low Reflectance Shadow Mask", US 5,808,714 to Rowlands et al. ("Rowlands"). One particular disadvantage to Steigerwald #1, Steigerwald #2 Steigerwald #3 and Rowlands is that they are confined to black matrix structures having specific sets of materials. A more general discussion of applying a black matrix as applied to a display having colour filters is found in US Patent 5,587,818 to Lee ("Lee").
However, such prior art black matrix structures are not always useful or practical to incorporate into display devices. For example, prior art black matrix structures are frequently formed as a separate unit from the display, thereby eventually requiring the assembly of the black matrix structure to the display structure, such as by mounting the black matrix structure to the front of the display.
It is also known to use optical interference to reduce reflectance in various thin film display technologies, such as electroluminescent devices ("ELD"s). For example, reducing reflectance of ambient light can be achieved by using additional thin film layers sandwiched between one or more layers of the ELD, which are configured to achieve destructive optical interference of the ambient light incident on the display, thereby substantially reducing reflected ambient light. Optical interference technology is discussed in detail in U.S. Patent 5,049,780 to Dobrowolski et al., ("Dobrowolski") and the applicant's copending U.S. Application 09/361,137 and filed on July 27, 1999, to Hofstra et al. ("Hofstra") The contents of both of these documents are incorporated herein by reference. In addition to enhancing contrast, the optical interference contrast enhancement apparatuses discussed in Dobrowolski and Hofstra also reduce pixel blooming and solar loading - another advantage of such apparatuses over certain other types of anti-reflection technologies.
The teachings of Dobrowolski and Hofstra can be useful in reducing reflectance of ambient light in ELDs, either organic or inorganic. The teachings of Dobrowolski and Hofstra can also be used to reduce reflectance in active matrix or other patterned displays, when the optical interference technology taught therein is incorporated in conjunction with the ELD. However, the teachings of Dobrowolski and Hofstra are not directed to active matrix technologies and therefore devices requiring contrast enhancement will generally rely upon prior art black matrix technologies, such as that taught in Steigerwald #1, Steigerwald #2 Steigerwald #3, Rowlands or Sato.
Summary of the Invention It is therefore an object of the present invention to provide a optical interference member which obviates or mitigates at least one of the disadvantages of the prior art.\
In an aspect of the invention, there is provided a display device comprising a plurality of light emitting members patterned to present an image to a viewer and a plurality of bus lines that are operable to provide an electrical signal to each of the light emitting members. At least a portion of the bus lines are in substantially the same viewing plane as the image. The display further comprises an optical interference member intermediate the viewer and the bus lines, the optical interference member is patterned to substantially correspond with at least a portion of one of the bus lines. The optical interference member is operable to reduce a reflection of ambient light back towards a viewer using optical interference.
Brief Description of the Drawings The present invention will now be described, by way of example only, with reference to certain embodiments shown in the attached Figures in which:
Figure 1 is a schematic representation of a partial cross-section of a portion of an active matrix display in accordance with an embodiment of the invention;
Figure 2 is a partial front view along the line II-II of Figure 1;

Figure 3 is a schematic representation of a specific implemenation of the optical inteference member shown in Figure 1; and, Figure 4 is a schematic representation of a partial cross-section of a portion of an active matrix display in accordance with ano embodiment of the invention.
Detailed Description of the Invention Referring now to Figures l and 2, an active matrix display in accordance with an embodiment of the invention is indicated generally at 20. As seen in Figure 1, display 20 includes a substrate 24 made from glass or any other suitable substrate material. Display 20 includes a plurality of light emitting pixels that are deposited onto substrate 24. Figures 1 and 2 both show a single pixel indicated at 28.
In turn each pixel 28 is comprised of a front electrode 32, a light emitting member 36 and a rear electrode 40. The exact configuration of each pixel 28 is not particularly limited, and thus can be based on inorganic electroluminescent display technology, organic electroluminescent display, plasma display technology, liquid crystal display technology or the like. Depending on the type of pixel 28, it will thus be understood that the exact materials and/or configurations of electrode 32, light emitting member 36 and rear electrode 40 will be chosen correspondingly. Furthermore, pixel 28 may include additional layers, as required, such as work function matching layers and/or transport layers where light emitting member 36 is based on an organic electroluminescent display material. Alternatively, where member 36 is based on an inorganic electroluminescent display material, then dielectric layers may be added. It is thus to be understood that, in general, pixel 28 can be based on a variety of technologies, and accordingly, the formations of such pixels 28 on substrate 24 will be performed according to known techniques specific to the type of technology.
Such formations may include, for example, successively depositing both light emitting member 36 and rear electrode 40 as two continuous layers along the entirety of substrate 24, thereby covering the remaining components of display 20.
Accordingly, pixel 28 is operable to create emitted light, indicated as Lem in Figure 1, towards a viewer 44 located in front of display 20.
Regardless of the technology used for pixel 28, it is presently preferred for the present embodiment that front electrode 32 be formed from a transmissive conducting material, such as indium tin oxide (ITO). Rear electrode 40 can be formed from either a transparent or reflecting metal, depending on whether display 20 is a transparent display.
A plurality of gate bus lines 48 perpendicular to a plurality of source bus lines 52 form a matrix on display 20. While gate bus lines 48 are deposited directly onto substrate 24, source bus lines 52 are deposited behind gate bus lines 48.
Thus, source bus lines 52 and substrate 24 sandwich gate bus lines 48. Intersections of bus lines 48 and 52 are separated by an insulator 56 to electrically isolate each set of lines 48 and 52. Accordingly bus lines 48 and 52 surround each pixel 28.
Gate bus lines 48 are attached to the gate input of a transistor 60 (or other switching means) respective to each pixel 28. Similarly, source bus lines 52 are attached to the source input of transistor 60. A drain 64 interconnects transistor 60 and front electrode 32. (While not required, it is contemplated that drain 64 can also be coated with an optical interferemence member, (not shown)). Those of skill in the art will now recognize that device 20 will include appropriate electronics, generally along its periphery, which can individually address each pixel 28, and accordingly such electronics are operable to activate each pixel 28 by applying the proper electrical signals to the gate and source of the transistor 60 respective to pixel 28.
Gate bus lines 48 and source bus lines 52 are each composed of an optical interference member OI and a conducting layer C. As described above, conducting layer C allows each line 48 and 52 to carry electrical signals to each transistor 60 in the usual manner. However, as will be explained in greater detail below, optical interference member OI cooperates with conducting layer C in order to reduce reflections back towards viewer 44 of ambient light incident upon display 20.
Ambient light is indicated as Lamb in Figure 1, whereas reflected light is indicated as Lref In Figure 1.
The materials, composition, and thicknesses of optical interference member OI
and conducting layer C are chosen to allow conducting layer C to perform its conducting duties, while causing ambient light Lamb to destructively interfere with itself, upon its reflection off of bus lines 48 and 52 such that the overall amount of reflected light L~ef back towards viewer 44 is reduced.

Referring now to Figure 3, a presently preferred configuration of optical interference member OI and conducting layer C for each bus line 48 and 52 is shown in substantially the same view as Figure 1, but in isolation from the other components of device 20. According to Figure 3, each optical interference member OI is comprised of a semi-absorbing layer 70 which is oriented the closest towards viewer 44. Optical interference member OI is also comprised of a substantially transparent layer 74 that is mounted behind semi-absorbing layer 70. Finally conducting layer C
is mounted behind semi-absorbing layer 70 of optical interference member OI.
Each layer 70, 74 of optical member OI and conducting layer C, of each set of bus lines 48 and 52 (separated by insulator 56) can be successively deposited as complete layers on substrate 24 in the order shown in Figure 3, and then the actual bus lines 48 and 52 can be etched into the above-described matrix pattern using known techniques. Other techniques for forming each bus line 48 and 52 according to the configuration shown in Figure 3 will occur to those of skill in the art.
The thickness and material of semi-absorbing layer 70 is chosen so that semi-absorbing layer 70 is partially reflective, partially absorbing and partially transmissive of ambient light La",b Accordingly, a portion of ambient light La",b incident on layer 70 is partially reflected off of layer 70, while a remaining portion passes into semi-absorbing layer 70. A portion of the light passing through layer 70 is absorbed, being dissipated as a small amount of heat. The remaining amount of light is passed directly through layer 70. The extinction coefficient and the thickness of the material of layer 70 is chosen so that the reflection from layer 70, neglecting optical interference, is preferably at least about thirty-five percent. Similarly, the transmissivity through layer 70 should also be about thirty-five percent. The remaining amount of light is absorbed and dissipated as a small amount of heat. It is presently preferred that a wavelength of about SSOnm be chosen (roughly the middle of the spectrum of visible light) when choosing the above extinction coefficient, thickness and/or material of layer 70. One suitable material and thickness for layer 70 is Chromium or Aluminum, having a thickness of about 100 t~ . As an alternative magnesium silver (Mg:Ag) having a thickness of about 185 ~ can also be used for layer 70. Other suitable materials (and for which appropriate thicknesses can be chosen) for layer 70 can include inconel or nickel. Still further materials for layer 70 can include Cu, Au, Mo, Ni, Pt, Rh, Ag, W, Co, Fe, Ge, Hf, Nb, Pd, Re, V, Si, Se, Ta, Y, Zr. Still other material and thicknesses for layer 70 will occur to those of skill in the art.
The remaining amount of light which is transmitted completely through layer 70, then passes through substantially transparent layer 74. The extinction coefficient and the thickness of the material of layer 74 is chosen such that transmission through layer 74 (using the same wavelength of about SSOnm as used to select layer 70) is greater than about eighty percent, but preferably at least about ninety percent. One suitable material and thickness for layer 74 is indium tin oxide (ITO) having a thickness of about 540 ~. Other suitable materials (and for which appropriate thicknesses can be chosen) for layer 74 can include Aluminum Silicon Monoxide or Chromium Silicon Monoxide. Additional materials for layer 74 can include A1z03, SiOz, ZrOz, HfOz, Scz 03, TiOz, Laz03, MgO, Taz O5, ThOz, Y203, CeOz, A1F3, CeF3, Na3 A1F6, LaF3, MgFz, ThF₄, ZnS, Sbz 03, Biz 03, PbFz, NdF3, Ndz O~, Pr60~~, SiO, NaF, ZnO, LiF, Gd03. Still further materials and thicknesses for layer 74 will occur to those of skill in the art.
Thus, the light that passes through layer 74 to reach conductor C is reflected off of conductor C. Thus, conductor C is preferably a reflective material, such as Aluminum, having a thickness such that conductor C is not transparent and is suitable for carrying electrical signals along its respective bus line 48 or 52.
The light that is reflected off of conductor C then passes back through layer 74, again through layer 70 (where still a further portion of it is absorbed) and then the final remainder of the light reflected off of conductor C exits layer 70, at which point it is out of phase with the light originally reflected off of layer 70.
Because these two reflections are out of phase, they destructively interfere, thereby reducing reflected light Lee back towards viewer 44. The inventors believe that, (if desired) through careful selection of materials, thicknesses and extinction coefficients for optical interference member OI, the two reflections off of layer 70 can have substantially the same intensities and be about one-hundred-and-eighty degrees out of phase, thereby substantially eliminating reflected light Lref~
While the foregoing describes an optical interference member OI having two layers, other configurations of optical interference members OI are within the scope of the invention. Additional, or fewer layers can be used to form optical interference members OI as desired. For example, it is contemplated that optical interference member OI could be formed from a single layer of semi-absorbing material. The thickness, material and index of refraction are chosen in order to achieve destructive optical interference of reflected ambient light La",b. Such materials, thicknesses and indeces of refraction are discussed in detail in the Applicant's copending application entitled "Contrast Enhancement Apparatus", filed in the Canadian Patent Office on July 04, 2001, and bearing application number 2,352,390, the contents of which are incorporated herein by reference.
Referring now to Figure 4, a display in accordance with another embodiment of the invention is indicated generally at 20a. Display 20a is substantially identical in construction and operation to display 20 of Figure l, except that display 20a includes two optical interference members, OIa and OIb which are affixed to both sides of each conductor C. The optical interference member OIa affixed to the side of each 1 S conductor C that is closest to substrate 24 is identical to the optical interference member OI in display 20 of Figure 1. However, the second optical interference member OIb affixed to the side of each conductor C that is closest to rear electrode 40 is substantially identical in structure to optical interference OIa, but operates to reduce pixel blooming, as light which is emitted from the back of light emitting members 32 which are adjacent to the light emitting member 32 shown in Figure 4 can be eliminated by optical interference member OIb. Those of skill in the art will now recognize that optical interference member OIb can be constructed from one or more layers of material, as previously described, excepted that optical interference member OIb is modified so that it reduces light that is incident from the side of display 20a that is opposite to substrate 24.
Pixel blooming from a second light emitting member (not shown) that is adjacent to the light emitting member 32 is represented with the arrows marked "LemA" in Figure 4. This pixel blooming emitted light LemA is thus shown reflecting off of rear electrode 40, and then striking optical interference member OIb of source bus line 52. Thus, optical interference member OIb is operable to reduce emitted light LemA using destructive interference, thereby reducing the amount of emitted light Le",A that passes through the front electrode 32 shown in Figure 4.

While only specific combinations of the various features and components of the present invention have been discussed herein, it will be apparent to those of skill in the art that desired subsets of the disclosed features and components and/or alternative combinations of these features and components can be utilized, as desired.
For example, other display technologies can be instead of light-emtting pixels.
Instead, each pixel could be a shutter means that passes light emitted from a back light when the pixel is activated.
Furthermore, while the embodiments herein have referred to pixellated displays, it is to be understood that other patterned displays are within the scope of the invention.
Furthermore, it is to be understood that the teachings herein can be modified to work with bottom emission or top emission active matrix displays.
In addition, in the embodiment shown in Figure 1, it is contemplated that optical interference member OI of line 52 can be made from an insulating material and thereby obviate the need for insulator 56, provided enough of conducting layer C
of line 52 is left exposed to make the required contact with transistor 60.
Furthermore, the enough herein can be used in conjunction with the optical inteference members taught in Dobrowlowski and/or Hofstra.
The present invention provides a novel optical interference member that is integrally formed over the bus lines of an active matrix or other patterned display. By coating the otherwise reflective bus lines with the optical interference member, unwanted ambient light towards the viewer can be reduced, while allowing the emitted light to travel towards the viewer without having to pass through the filter.
Additionally, in certain embodiments, the integral formation the bus lines with the optical interference member can offer simplified manufacturing techniques, obviating the need for forming a black matrix separately from the conducting bus lines.

Claims

1. A display device comprising:
a plurality of light emitting members patterned to present an image to a viewer;
a plurality of bus lines that are operable to provide an electrical signal to activate or deactivate each of said light emitting members, at least a portion of said bus lines being in substantially the same viewing plane as said image;
and an optical interference member intermediate said viewer and said bus lines, said optical interference member being patterned substantially correspondingly to at least a portion of one of said bus lines, said optical interference member operable to reduce a reflection of ambient light back towards a viewer.

2. The display device according to Claim 1 wherein said bus lines include a set of gate bus lines and a set of source bus lines substantially perpendicular to said gate bus lines such that said bus lines define a matrix to surround each said light emitting member to define an individual pixel.

3. The display according to Claim 2 wherein said pixel is based on inorganic electroluminescent display technology.

4. The display according to Claim 2 wherein said pixel is based on organic electroluminescent display technology.

5. The display according to Claim 2 wherein said pixel is based on liquid crystal display technology.

6. The display according to Claim 2 wherein said pixel is based on plasma display technology.

7. The display according to Claim 2 wherein said pixel is based on plasma display technology.

8. The display according to claim 2 wherein a first said optical interference member coats each of said gate bus lines and each of said source bus lines.

9. The display according to claim 2 wherein said bus lines are reflective and said optical interference member is composed of a semi-absorbing layer positioned towards to said viewer and a substantially transparent layer positioned towards said bus line, such that said semi-absorbing layer, said transparent layer and said bus lines cooperate to product out-of phase reflections of ambient light that detructively interfere to thereby reduce reflected ambient light.

10. The display according to claim 9 wherein said semi-absobring layer is made from aluminum having a thickness of about 100 angstroms and said substantially transparent layer is made from indium tin oxide having a thickness of about 540 angstroms.

11. The display according to claim 9 wherein an extinction coefficient and thickness of a material chosen for said semi-absorbing layer is such that semi-absorbing layer has a reflectance, negelecting optical interference, of about thirty-five percent, a transmissivity of about thirty-five percent.

12. The display according to claim 11 wherein an extinction coefficient and thickness of a material chosen for said substantially transparent layer is such that substantially transparent layer has a transmissivity of about ninety percent.

13. The display according to claim 9 wherein said semi-absorbing layer is made from one of Cu, Au, Mo, Ni, Pt, Rh, Ag, W, Co, Fe, Ge, Hf, Nb, Pd, Re, V, Si, Se, Ta, Y, Zr and said substantially transparent layer is made from one of A12O3,SiO2, ZrO2, HfO2, Sc2 O3, TiO2, La2O3, MgO, Ta2 O5, ThO2, Y2O;, CeO2, A1F3, CeF3, Na3 A1F6, LaF3, MgF2, ThF₄, ZnS, Sb2 O3, Bi2 O3, PbF2, NdF3, Nd2 O3, Pr6O11, SiO, NaF, ZnO, LiF, GdO3.

14. The display according to claim 1 having an additional optical interference member positioned such that said bus lines are between said additional optical interference member and said veiwer, said additional optical interference member being patterned substantially correspondingly to at least a portion of one of said bus lines, said optical interference member operable to reduce blooming of a light emitting member.

15. A display device comprising:
a plurality of light emitting members patterned to present an image to a newer;
a plurality of bus lines that are operable to provide an electrical signal to activate or deactivate each of said light emitting members, at least a portion of said bus lines being in substantially the same viewing plane as said image;
and an optical interference member member positioned such that said bus lines are between said optical interference member and said veiwer, said optical interference member being patterned substantially correspondingly to at least a portion of one of said bus lines, said optical interference member operable to reduce blooming of a light emitting member.