With the gradual emergence of wearable application devices, such as smart glasses, smart watches, etc., the display industry's demand for flexible display devices has been increased. Organic Light Emitting Display (OLED) has the attributes of self-illumination, no need of backlight, thin thickness, wide viewing angle, fast response, and so on. Such attributes bring in the advantages for flexible displays. With the competition of flexible OLEDs, traditional liquid crystal display technology has gradually adopted flexible substrates to make breakthroughs in the direction of flexibility and curved surfaces. It can be seen that the era of flexible and curved display is approaching.
FIG. 1 shows a schematic diagram of a border design of a conventional display screen. At present, the upper and left/right borders of the display screen are compressed to a very small border to meet the requirements of the full screen at this stage, but at the lower border, due to the need of data line fan-out and reserved chip (IC) bonding areas and flexible circuit board (FPC) bonding areas, further compression of the lower boundary has become a technical problem to be solved.
FIG. 2 shows a schematic diagram of another conventional display screen border design. In order to further compress the lower boundary, the current common solution is to use the COF (circuit on film) method, that is, only the FPC binding area is reserved in the lower border area, and the chip binding is directly placed on the FPC. The application of the COF technology can be implemented. The boundary is compressed to about 3 mm or even 2 mm, but there is still a large gap with respect to the left and right boundaries <1 mm. How to realize a full perimeter narrow border becomes the next key breakthrough direction of the display device.
At the same time, at present, the small-size display adopts the backlight module side-edge solution as shown in FIG. 3, in which the LED light bar is located at the lower boundary of the display, and the LED itself has a certain thickness. Since the LED is adopted as a point light source, it needs to diffuse the light uniformly by the astigmatism of the light guide plate to avoid the hotspot phenomenon in the near light, and requires a certain mixing distance. The compression of the mixed light distance is usually accompanied by the backlight efficiency. The drastic attenuation causes the backlight bottom frame of the existing center-size liquid crystal module to have a certain limit (about 2 mm). Therefore, even if the lower boundary of the liquid crystal display device cell is compressed to the same size as the left and right boundaries, it is still necessary to consider the lower boundary distance of the effective display area (AA area). When the lower boundary of the liquid crystal cell is compressed to a very narrow level, the lower border of the backlight will instead become the key constraint for achieving a full-screen (extremely narrow border).
The direct-type has the advantage of having a narrow frame and has been widely used in the large-size display field, but is facing the problem of increased thickness. Smaller mini-LEDs (micro-LEDs) can be arranged at a smaller pitch to achieve a smaller light mixing distance, providing greater possibilities for light, thin, and narrow light sources for small direct-lit backlights. The size of the mini-LED is usually less than 1 mm, and the spacing between adjacent LEDs is also less than 1 mm. FIG. 4 is a schematic view of a conventional micro-LED array emitting backlight module, which mainly includes a driving substrate 10, a micro-LED 20 array, a fluorescent film 30, a diffusion sheet 40, and a brightness enhancement film 50 from bottom to top. When the micro-LED array 20 forms a backlight module, it usually needs to match the diffusion sheet 40 and the brightness enhancement film 50 shown in FIG. 4, in which the incident light of the micro-LED 20 re-enters the interior of the backlight after being reflected by the brightness enhancement film 50. The spacing between adjacent micro-LEDs 20 is too small, and the occupied area of the micro-LED 20 does not provide effective reflection, and thus light recovery can only be performed through the limited reflection area between the adjacent micro-LEDs 20.
FIGS. 5A and 5B are schematic side and top views of a conventional micro-LED array light emitting backlight module. The driving substrate 10 is provided with a high reflection layer 60 in addition to the array of micro-LEDs 20, and the fluorescent film 30 covers the driving substrate 10. Due to the fact that the conventional micro-LED array light-emitting backlight module reflection area cannot be arranged with a conventional high-reverse structure, a high-reflection layer 60 such as a white oil (coating) is usually used instead, but the actual reflectance can only reach about 90%. The 99.9% reflectivity of the conventional reflective sheet has certain disadvantages in brightness efficiency. The high-reflective layer 60 such as white oil is usually prepared through spin coating and a photolithography process. In order to prevent the reflective layer from blocking the electrically conductive pad 21 of the micro-LED 20, the electrode 10 is usually driven on the drive substrate 10. A certain inhibited area is set around the disc and between adjacent micro-LED positive-negative (PN) electrode pads 21 to prevent the high reflective layer 60 from covering the electrode pads 21 due to process errors, although the inhibited area is single The area is small, but the overall area occupies a large proportion, resulting in the inevitable loss of light efficiency. Simply increasing the accuracy of etching can hardly overcome the above problems.
USPTO Backgrounds
USPTO Backgrounds