WO2020112425A1

WO2020112425A1 - Method and apparatus for forming a bezel-less display

Info

Publication number: WO2020112425A1
Application number: PCT/US2019/062103
Authority: WO
Inventors: Joshua Monroe Cobb; Ying GENG; Jacques Gollier; Ying Zhang
Original assignee: Corning Incorporated
Priority date: 2018-11-29
Filing date: 2019-11-19
Publication date: 2020-06-04
Also published as: TW202038198A

Abstract

An image guide is positioned adjacent to an edge portion of a display panel, the image guide comprising a plurality of transparent plates assembled at an angle to a plane of the display substrate and extending over a bezel of the display panel. Major surfaces of the transparent plates can be coated with a reflective coating for guiding an image from the display panel to an image output face of the image guide, thereby hiding the bezel from a viewer of the display.

Description

METHOD AND APPARATUS FOR FORMING A BEZEL-LESS DISPLAY

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority of U.S. Provisional Application Serial No. 62/772,787 filed on November 29, 2018 the contents of which are relied upon and incorporated herein by reference in their entirety as if fully set forth below.

TECHNICAL FIELD

[0002] The present disclosure relates to bezel-free display devices such as televisions.

BACKGROUND

[0003] As used herein, the term display device is intended to encompass all devices capable of displaying visual content, including but not limited to computer monitors, including laptops, notebooks, tablets and desktop computer monitors, mobile telephone displays, and television displays. Each of the foregoing devices includes many component parts including the physical case or cabinet in which individual components may reside, circuit boards, circuit elements such as integrated electronic components, and the display panel itself. These display panels can comprise liquid crystal display elements, organic light emitting diode (OLED) display elements, or plasma display elements, and further include the glass or plastic substrates on which many of these elements are disposed and/or enclosed. Typically, the edge portions of the display panels, and the display device itself, are utilized for electrical leads and various other electronic components associated with the operation of the display panel, such as circuits that drive the panel pixels as well as LED illuminators in the case of an LCD display panel. This has resulted in display panel manufacturers encasing the edge portions within and/or behind a bezel, which bezel conceals the foregoing components, but also obscures the edge portions of the display panel thereby reducing the overall image size.

[0004] For esthetic reasons, display panel makers try to maximize the image viewing area of the display panel, provide a more aesthetically pleasing appearance, and minimize the size of the bezel surrounding the image portion of the display panel. However, there are practical limits to this minimization, and current bezel sizes are typically in a range from about 3 millimeters to about 10 millimeters in width. To achieve a goal of no visible bezel at all, an optical solution is described that can give the observer the impression the image produced by the display panel occupies the entire display surface while simultaneously reducing a gap between the image-forming display panel and a display cover plate.

SUMMARY

[0005] According to embodiments described herein, a bezel-free appearance can be provided to a display device by employing a light modifying frame about the display.

[0006] General trends in display design include minimizing where possible the size of the bezel. However, certain technical factors limit the smallest achievable bezel width to about 3 millimeters (mm). To avoid those limitations, one solution includes inserting optical components into the optical path that enlarge the image to cover the bezel. Many conventional approaches utilize Fresnel lens structures to enlarge the image. However, such approaches usually require large air gaps between the Fresnel lens and the display panel, which may not always be desirable.

[0007] Another approach comprises tapered two-dimensional arrays of optical fiber waveguides that can be integrated along edges of the display panel to cover the bezels. However, such approaches can be expensive to fabricate and can require complex electron- assisted vacuum deposition. Accordingly, alternative methods that provide easier, less expensive structures are desirable.

[0008] In one embodiment, a display device is disclosed comprising a display panel configured to display an image, a bezel positioned over an edge portion of the display panel, and an image guide, a first portion of the image guide extending over the bezel and a second portion of the image guide positioned over the display panel adj acent the bezel, the image guide comprising a plurality of transparent plates arranged in a stack, a major surface of each plate defining a plane of the respective plate, each plane of each plate of the plurality of plates parallel with the remaining planes of each plate and oriented at an angle a relative to a viewer- side surface of the display panel, edges of the transparent plates forming an image input face and an image output face opposite the image input face, the image input face defining a plane parallel with the viewer-side surface of the display panel and the image output face defining a plane forming an angle Q with the viewer-side surface of the display panel.

[0009] The angle a can be in a range from about 26° to about 63°. [00010] The display device may further comprise a light diffusing member positioned between the image input face and the display panel. In some embodiments, the diffusing member can be a Lambertian diffusing member. In other embodiments, the diffusing member can be a holographic diffusing member.

[00011] In some embodiments, the plurality of transparent plates can comprise glass.

[00012] In other embodiments, the plurality of transparent plates can comprise a polymer, for example polymethylmethacrylate (PMMA).

[00013] In some embodiments, a maximum height hmax of the image guide can be equal to or less than about 3 times the sum of a width b of the image input face of the image guide and a width D of the bezel.

[00014] In various embodiments, each plate, for example the major surfaces thereof, can be coated with a reflective coating. In some embodiments, the reflective coating can be a dielectric coating. In other embodiments, the coating can be a metallic coating, for example aluminum or silver.

[00015] In various embodiments, the second portion of the image guide is disposed on a cover glass sheet positioned between the second portion and the display panel.

BRIEF DESCRIPTION OF THE DRAWINGS

[00016] These and other aspects are better understood when the following detailed description is read with reference to the accompanying drawings, in which:

[00017] FIG. l is a cross-sectional view of an exemplary display device comprising a display panel and a bezel;

[00018] FIG. 2A is a front view of the display device of FIG. 1 illustrating an image displayed on a display panel of the display device;

[00019] FIG. 2B is a front view of plurality of display devices arranged as a tiled array of display devices, and illustrating obtrusive bezels interrupting the image;

[00020] FIG. 3 is a cross-sectional view of an image guide according to examples of the present disclosure, wherein the image guide is positioned adjacent to an edge portion of a display panel;

[00021] FIG. 4 is a cross-sectional view of a transparent plate that comprises the image guide of FIG. 3; [00022] FIG. 5 is a front view of a display panel comprising a plurality of image guides according to the present disclosure, wherein the plurality of image guides can be assembled together in a frame shape;

[00023] FIG. 6 is a cross-sectional view of the transparent plate of FIG. 4 showing a ray tracing that illustrates the total internal reflection than can occur in the absence of a diffusing member;

[00024] FIG. 7 is a plot of modeled radiance at the output face of the transparent substrate of FIG. 4 where a diffusing member is not present between the image input face of the transparent substrate and the display panel; and

[00025] FIG. 8 is a plot of modeled radiance at the image output face of the transparent substrate of FIG. 4 where a diffusing member is present between the image input face of the transparent substrate and the display panel.

DETAILED DESCRIPTION

[00026] Examples will now be described more fully hereinafter with reference to the accompanying drawings in which example embodiments are shown. Whenever possible, the same reference numerals are used throughout the drawings to refer to the same or like parts. However, aspects may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

[00027] As used herein, a stack refers to a plurality of plates, e.g., transparent glass or plastic plates, major surfaces of the plates arranged side-by-side. In various embodiments, the major surfaces of the plates need not be in direct contact. For example, the glass or plastic major surfaces of glass or plastic plates need not be in direct and intimate contact. In various embodiments, the surfaces of the plates may include a coating disposed thereon such that the coating of one plate in the stack is in contact with the coating of an immediately adjacent plate in the stack.

[00028] As used herein the term transparent refers to an optical transmittance between n input surface and an output surface equal to or greater than about 80% in a wavelength range from about 400 nm to about 800 nm, for example equal to or greater than about 85%, equal to or greater than about 90%, equal to or greater than about 95%, or equal to or greater than about 98%. [00029] The aesthetics of display devices, such as television display panels, computer monitors, laptop display panels, are affected by the size and appearance of a bezel that typically extends around a perimeter of such display devices. The bezel of a display device may be used to house electronics for driving the pixels of the display panel, as well as, in certain instances, to provide backlighting for the display device. For example, an LCD television display panel may include a plurality of light emitting diodes (LEDs) maintained within the bezel region of the display device.

[00030] A trend in the display industry has been to incorporate smaller and smaller bezels. Current bezel widths can be on the order of about 3 to about 10 mm. On the other hand, television models comprising very large display panels have achieved bezel widths as small as 2 mm on at least two borders and 4 mm on the other two borders. However, the presence of a bezel, although small, can still be distracting, especially when the display devices are assembled in a tiled arrangement to form a very large displayed image. The bezels of such tiled display devices give the undesirable appearance of an opaque grid over the image rather than a cohesive large image without seams.

[00031] Embodiments of the present disclosure comprise multiple planar substrates arranged in a stack and deployed about an edge portion of a display panel. For example, an image guiding structure may be deployed in a frame-like arrangement, e.g. in a closed loop, and which planar substrates extend over the display panel bezel.

[00032] Referring to FIG. 1, an exemplary display device 10 is illustrated. Display device 10 comprises a display panel 12 and a bezel 14 arranged around a perimeter of display panel 12. Bezel 14 may hide display drive electronics, and in some embodiments, may also extend over lighting hardware configured to light the display panel portion 12, such as light emitting diodes (LEDs) 16 arranged adjacent edges of a backlighting light guide 18. A width D of bezel 14 can be, for example, in a range from about 3 mm to about 10 mm, although other widths may be used by display device manufacturers and are contemplated herein.

[00033] Shown in FIG. 2A is a front view of single display device 10 depicting an image displayed by display device 10. Bezel 14 forms a frame around the image, but may be distracting to some viewers, and in some embodiments, as illustrated in FIG. 1, bezel 14 can reduce the viewable area of display panel 12. Shown in FIG. 2B is the same image as shown in FIG. 2A but displayed across multiple display devices in a tiled matrix to increase the size of the image. Such an arrangement can be used for a billboard or other large public display. As evident from FIG. 2B, the multiple bezels 14, when arranged side-by-side, obstruct the image, and can be visually displeasing.

[00034] One way to achieve a bezel-concealing display comprises positioning an image guiding structure over an edge portion of the display panel (between the display panel and an observer) such that the image-guiding structure extends the image over the bezel portion of the display device. An observer viewing the image projected by the display panel sees a portion of the image projected over the bezel, thereby effectively hiding the bezel. As described herein, such an image-guiding structure can comprise a plurality of thin transparent plates stacked or laminated together and arranged at an angle relative to a plane of the display panel. Surfaces of the individual transparent plates can be coated, for example with a reflective coating so light rays projected by the display panel undergo total internal reflection within each individual transparent plate and are guided along the plate to an exit face thereof. The cumulative effect of a stack of such plates is to guide the image from edge portions of the display panel to a position over the bezel. Accordingly, an observer viewing the display panel sees an image displayed by the display panel rather than the bezel.

[00035] FIG. 3 illustrates a cross-sectional side view of an exemplary image guide 20 comprising a plurality of thin, transparent plates 22, each transparent plate comprising a vertical height h relative to image input face 24 (see FIG. 4). Image guide 20 can be generally of a wedge shape comprising image input face 24 adjacent to display panel 12 and an opposing image output face 28. Image input face 24 has a width b in a plane parallel with a plane of display panel 12. As shown in FIG. 1 and described above, bezel 14 comprises a width D, and as further shown, image guide 20 can extend at least distance D over bezel 14. Accordingly, the total width W of image guide 20 can be at least D + b. Image guide 20 further comprises a maximum height hmax relative to the viewer-side surface of display panel 12. In embodiments, maximum height hmax of image guide 20 can be in a range from a value equal to D to a value about three times the sum of the bezel width D and the width of image input face 24 of the image guide, b, e.g., (hmax = 3-(D+b)). Image guide 20 can be divided into a first portion 62 and a second portion 64, first portion 62 extending over bezel 14 and second portion 64 positioned over display panel 12. That is, second portion 64 is positioned adjacent bezel 14 and not extending over the bezel.

[00036] Referring to FIG. 4, transparent plates 22 comprise first and second major surfaces 32 and 34. Major surfaces 32, 34 can be planar and disposed at angle a relative to a plane of the display panel to which image guide 20 is coupled (See FIG. 5). Output face 28 can be arranged at an angle Q relative to a plane of display panel 12. Additionally, each transparent plate 22 comprises a first edge surface 36 and a second edge surface 38. First and second edge surfaces 36 and 38 comprise image input face 24 and image output face 28, respectively. In embodiments, h can vary linearly in a direction of width W. For example, h can decrease linearly in a direction perpendicular to and away from bezel 14 so that image guide 20 comprises a wedge-shaped cross-section as shown in FIG. 3.

[00037] In some embodiments, thickness t of the transparent plates 22 can be the same and the angle a can be selected such that a width w' across first edge surface 36 of the transparent plates 22 can be sized to be about a pixel width of an individual pixel of display panel 12, for example in a range from about 0.5 to about 0.9, such as about 0.7 mm. In some embodiments, a can be in a range from about 27° to about 63°, for example in a range from about 27° to about 45° or in a range from about 45° to about 63°. Individual pixels of exemplary display panels comprise multiple sub-pixels, for example red, blue, and green sub-pixels. If the thickness of the transparent plates 22 are less than a pixel width, the input edge of each transparent plate can be positioned over a red, green or blue line of pixels. The resulting image can show color lines and aliasing between the pixel structure and the plate structure. If the thickness of the transparent plates, in combination with angle a, produces an edge surface 36 with a width w' greater than the pixel size, multiple pixels can be coupled into single transparent plates, which can result in reduced image resolution. Transparent plates 22 may be made of any suitable transparent material. For example, in some embodiments, transparent plates 22 may be formed from glass, while in other embodiments, transparent plates 22 may be formed from a polymer such as, for example, polymethylmethacrylate (PMMA).

[00038] Transparent plates 22 may further comprise a coating 40 disposed on first and second major surfaces 32, 34. In some embodiments, coating 40 can be a reflective coating, such as a deposited metal film, e.g., aluminum or silver. The metal film can be deposited, for example, by vapor deposition, by sputter deposition, by evaporation, or by any other suitable film deposition method, including various other thin-film deposition methods as may be known in the art. Alternatively, coating 40 can be a similarly-deposited dielectric film, or a film applied with an adhesive, for example an optically transparent adhesive. In some embodiments, coating 40 may comprise multiple layers, such as a multi-layer dielectric film. For example, Vikuiti™ Enhanced Specular Reflector film manufactured by 3M is a suitable dielectric film. [00039] Modeling has shown that metallic coatings, such as vapor-deposited aluminum or silver, can provide decreased reflectivity compared to multi-layer dielectric films, such as the Vikuiti film described above. For example, an aluminum coating was shown to provide a reflectance of about 80%. Testing on actual deposited aluminum films showed the amount of light transmitted by the resultant image guide was poor.

[00040] Image guide 20 can be formed by placing a second major surface 34 of one transparent plate 22 adjacent a first major surface 32 of another transparent plate 22, with coatings 40 from each transparent plate, when present, disposed therebetween, and repeating, until an image guide 20 having an image input face 24 of suitable width b is produced. Transparent plates 22 may be assembled, for example, by bonding the transparent plates with an adhesive.

[00041] When assembled, image guide 20 comprises image input face 24 and output face 28. As noted above, output face 28 comprises second edge surfaces 38 of transparent plates 22. The edge surfaces 38 comprising output face 28 may be ground and/or polished so that output face 28 comprises a smooth continuous surface that intersects image input face 24 at angle Q, as shown in FIG. 3. In some embodiments, output face 28 can be processed to be a planar surface.

[00042] FIG. 5 illustrates a front view (as seen by a viewer) of a display panel 12 comprising a plurality of image guides 20 positioned adjacent to edge portions of the display panel, over the bezel (not shown), wherein the individual image guides have been assembled together at mitered corners 44 and coupled at comers 44 with an adhesive. As shown in FIGS. 3 - 5, transparent plates 22 can be further arranged such that major surfaces extend in a lengthwise direction parallel to edges of the display panel, e.g., perpendicular to width W. In some embodiments, the image guides may be bonded to a cover plate 48, for example a glass cover plate, positioned over display panel 12. In the embodiment depicted in FIG. 5, the plurality of image guides forms a frame that surrounds display panel 12 and covers the surrounding bezel along the edge portions of the display panel.

[00043] Image guide 20 may further comprise diffusing member 46 positioned between display panel 12 and image input face 24 of image guide 20. Diffusing member 46 may be, for example, a Lambertian diffusing member. Alternatively, diffusing member 46 may be a holographic diffusing member. In some embodiments, diffusing member 46 may diffuse light in a single spatial direction. Diffusing member 46 mitigates against light rays traversing a transparent plate 22 of image guide 20 and having an intensity different that other light rays traversing the same transparent plate. Why this deleterious effect occurs, referred to here as banding, can be seen with the aid of FIG. 6.

[00044] FIG. 6 illustrates two types of light rays that can propagate in transparent plates 22. The first type (Type 1, light ray 50) impinges second edge surface 38 perpendicular to a plane of display panel 12, refracts at edge surface 38, and reflects at first major surface 32 (for simplicity, coating 40 is not depicted). The light ray then reflects a second time, at second edge surface 38, having impinged on second edge surface 38 at the critical angle necessary for total internal reflection, and then traverses the distance between second edge surface 38 and first edge surface 36, in some instances parallel, or nearly parallel, with first and second major surfaces 32, 34.

[00045] The second type of light ray, Type 2 (light ray 52) makes many bounces between the major surfaces of the plate before reaching the display. Consequently, if coating 40 is not sufficiently reflective, Type 2 light rays will be highly attenuated and dark bands may be visible to a viewer. To minimize this banding effect, the reflectivity of the coating can be increased to minimize optical loss at a reflection point (e.g., minimize absorption) and/or the thickness t of the plate can be increased (to decrease the number of lossy reflections).

[00046] There is another reason why high reflectivity coating and thick waveguides may be preferred. Guide 20 comprises multiple plates of different lengths stacked together, with the plate closest to the bezel being the longest. If coating 40 reflectivity is low, giving a low transmittance for the longest plate, then a brightness gradient will be observed across the different plates comprising width b, which may require a complicated backlight with an inverse brightness gradient to compensate.

[00047] The table below summarizes modeled transmittance (presented as a percent of the input intensity) for several coating thicknesses. All transmittances are characterized for the longest plate, closest to the bezel. Transmittances of the shorter plates will be higher, with the shortest plate having the highest transmittance.

Table

[00048] FIG. 7 shows a plot of modeled radiance as a function of viewing angle f for the example where a diffusing member is not present. The plot illustrates a non-uniform radiant output. Positioning diffusing member 46 between image input face 24 and display panel 12 improves the output radiance of the image guide, as depicted by the plot of FIG. 8 showing modeled radiance at the output of the transparent plate when diffusing member 46 is positioned between image input face 24 and display panel 12.

[00049] Image guide 20 may further comprise support member 60 that provides support to the image guide and helps prevent damage to the image guide from external contact, such as contact by other elements of the display device. Support member 60 may be formed from plastic and can be positioned between the bezel and the overhanging (e.g., angled) portion of image guide 20. For example, as shown in FIG. 3, support member 60 may be a wedge-shaped member positioned over bezel 14 and in contact with image guide 20. Support member 60 may be coupled to the outermost transparent plate 22, nearest bezel 14, such as with an adhesive.

[00050] From the description above, the light output of image guide 20 can be affected by the reflectance of reflective coating 40 and the number of times each light ray impinges on the reflective coating. The latter is determined by the position of the light ray relative to the first or second major surfaces. As described above, this can be partially compensated for by the choice of reflective coating, as some materials and structures have a greater reflectance than others.

[00051] Another option to compensate for absorption by the reflective film comprises modifications to the display backlight so that pixels of the display panel located close to the edge of the display panel are illuminated with more light. This can be done by modifying the existing backlight or by adding a separate thin backlight behind the pixels located under the image guide.

[00052] The advantage of this last approach is that the separate edge backlight might stay energized (lighted) even when the display is off without requiring much power consumption, since the surface to illuminate is very small compared to the whole display device. In that instance, the OFF state of the bezel area will not be seen, and the bezel area can be used to display continuous information such as time, temperature, or weather forecasts.

[00053] It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit and scope of the disclosure.

Claims

What is claimed is:

1. A display device comprising:

a display panel configured to display an image;

a bezel positioned over an edge portion of the display panel; and

an image guide, a first portion of the image guide extending over the bezel and a second portion of the image guide positioned over the display panel adjacent the bezel, the image guide comprising a plurality of transparent plates arranged in a stack, a major surface of each plate defining a plane of the respective plate, each plane of each plate of the plurality of plates parallel with the remaining planes of each plate and oriented at an angle a relative to a viewer-side surface of the display panel, edges of the transparent plates forming an image input face and an image output face opposite the image input face, the image input face defining a plane parallel with the viewer-side surface of the display panel and the image output face defining a plane forming an angle Q with the viewer-side surface of the display panel.

2. The display device according to claim 1, wherein the angle a is in a range from about 26° to about 63°.

3. The display device according to claim 1, further comprising a light diffusing member positioned between the image input face and the display panel.

4. The display device according to claim 3, wherein the diffusing member is a Lambertian diffusing member.

5. The display device according to claim 3, wherein the diffusing member is a holographic diffusing member.

6. The display device according to claim 1, wherein the plurality of transparent plates comprise glass.

7. The display device according to claim 1, wherein the plurality of transparent plates comprise a polymer.

8. The display device according to claim 1, wherein a maximum height hmax of the image guide is equal to or less than about 3 times the sum of a width b of the image input face and a width D of the bezel.

9. The display device according to claim 1, wherein each transparent plate comprises a first major surface and a second major surface opposite the first major surface, the first and second major surfaces of each transparent plate coated with a reflective coating.

10. The display device according to claim 9, wherein the reflective coating is a dielectric coating.

11. The display device according to claim 9, wherein the reflective coating is a metallic coating.

12. The display device according to claim 11, wherein the reflective coating comprises aluminum or silver.

13. The display device according to claim 1, wherein the second portion of the image guide is disposed on a cover glass sheet positioned between the second portion and the display panel.