MicroLED display panel

A microLED display panel includes a substrate being divided into a plurality of sub-regions for supporting microLEDs, and a plurality of drivers being correspondingly disposed on surfaces of the sub-regions respectively. The driver includes a low-dropout (LDO) regulator and a drive circuit. The LDO regulator receives a system power, according to which a regulated power is generated and provided for the drive circuit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority of Taiwan Application No. 105131054, filed on Sep. 26, 2016, and Taiwan Application No. 106118892, filed on Jun. 7, 2017, the entire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a display panel, and more particularly to a microLED display panel.

2. Description of Related Art

A micro light-emitting diode (microLED, mLED or μ LED) display panel is one of flat display panels, which is composed of microscopic microLEDs each of a size of 1-10 micrometers. Compared to conventional liquid crystal display panels, the microLED display panels offer better contrast, response times and energy efficiency. Although both organic light-emitting diodes (OLEDs) and microLEDs possess good energy efficiency, the microLEDs, based on group III/V (e.g., GaN) LED technology, offer higher brightness, higher luminous efficacy and longer lifespan than the OLEDs.

Active matrix using thin-film transistors (TFT) may be used in companion with microLEDs to drive a display panel. However, microLED is made by flip chip technology, while TFT is made by complementary metal-oxide-semiconductor (CMOS) process which is more complex than flip chip technology. These two distinct technologies may cause thermal mismatch. A drive current of the microLED is small in gray display, which may be significantly affected by leakage current.

Passive matrix is another driving method performed by a row drive circuit and a column drive circuit, which are disposed on the periphery of a display panel. When the size or the resolution of the display panel increases, output loading and delay of the drive circuits increase accordingly, causing the display panel to malfunction. Therefore, passive matrix is not suitable for large-size microLED display panels.

A need has thus arisen to propose a novel microLED display panel, particularly a large-size or high-resolution display panel, which is capable of maintaining advantages of microLEDs and overcoming disadvantages of driving schemes.

SUMMARY OF THE INVENTION

In view of the foregoing, it is an object of the embodiment of the present invention to provide a microLED display panel capable of effectively reducing loading of drivers, thereby making whole large-size high-resolution microLED display panel feasible. Passive driving scheme is adopted in one embodiment to simplify the process of making display panels, reduce turn-on time of the microLEDs, increase drive current, and effectively minimize effect on gray display due to leakage current.

According to one embodiment, a microLED display panel includes a plurality of microLEDs, a substrate and a plurality of drivers. The substrate is utilized for supporting the microLEDs, and the substrate is divided into a plurality of sub-regions. The drivers are correspondingly disposed on surfaces of the sub-regions respectively. In one embodiment, the microLEDs are driven by a passive driving method. The driver includes a column drive circuit, which transmits column drive signals to first electrodes of the microLEDs on same columns via column conductive wires; and a row drive circuit, which transmits row drive signals to second electrodes of the microLEDs on same rows via row conductive wires. The driver includes a low-dropout (LDO) regulator and a drive circuit, the LDO regulator receiving a system power, according to which a regulated power is generated and provided to the drive circuit.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1Ashows a top view illustrated of a micro light-emitting diode (microLED) display panel100according to one embodiment of the present invention, andFIG. 1Bshows a side view illustrated of the microLED display panel100ofFIG. 1A. The microLED display panel of the embodiment is preferably adaptable to a large-size and high-resolution (e.g., 3840RGB×2160) display panel. In the specification, the size range of the microLED is between 1 and 10 micrometers. However, the size of the microLED may be even smaller due to specific applications or technological advance. In the specification, “large-size” display panel is currently and commonly referred to 10 inches or above display panel. However, “large-size” display panel may be referred to other display size due to specific applications or technological advance. In the specification, “high-resolution” display panel is currently and commonly referred to a display panel with 1080 or above scan lines. However, “high-resolution” display panel may be referred to other amount of scan lines due to specific applications or technological advance.

In the embodiment, the microLED display panel100may include a substrate11for supporting a plurality of microLEDs (now shown). The substrate11may be preferably made of an insulating material (e.g., glass or Acrylic) or other materials suitable for supporting the microLEDs.

According to one aspect of the embodiment, a surface of the substrate11is divided into a plurality of sub-regions101. It is noted that the divided sub-regions101are not physically cut through, and the substrate11is not made by integrating the sub-regions101. In other words, the substrate11or the microLED display panel100is a single or whole entity, or an uncut entity.FIG. 1Ashows a simplified example of how the substrate11is divided into sub-regions101. Take a microLED display panel100with resolution 3840RGB×2160 as an example, the substrate11may be divided into 80×54 sub-regions101, each having resolution 48RGB×40. Nevertheless, this microLED display panel100may be divided into more or less sub-regions101.

According to another aspect of the embodiment, the microLED display panel100may include a plurality of drivers12, which are correspondingly disposed on (e.g., top) surfaces of the sub-regions101respectively. The driver12as exemplified inFIG. 1Amay, but not necessarily, be disposed in the center of the surface of corresponding sub-region101. Each sub-region101as exemplified inFIG. 1Ahas one corresponding driver12. However, in other embodiments, each sub-region101may have plural corresponding drivers12. The driver12of the embodiment may be manufactured as an integrated circuit or chip, which is then bonded on the surface of the sub-region101, for example, by surface-mount technology (SMT) such as chip-on-glass (COG) or flip chip. In one example, the drivers12and the microLEDs are disposed on the same surface of the substrate11.

The microLED display panel100of the embodiment may further include a plurality of timing controllers (TCON)13, which are electrically connected with the substrate11, for example, via a flexible printed circuit board (FPCB), and are further electrically connected with corresponding drivers12, for example, via signal traces (not shown) disposed on the substrate11. In the embodiment, one timing controller13may be electrically connected with at least two drivers12. In other words, the amount of the timing controllers13may be less than the amount of the drivers12. The timing controller13may be electrically connected directly with corresponding drivers12via signal traces. Alternatively, the timing controller13may be electrically connected to one driver12via signal traces, and, after signal buffering, then be electrically connected to another driver12via signal traces.

According to a further aspect of the embodiment, the microLED display panel100may adopt passive driving method for driving the microLEDs.FIG. 2shows a schematic diagram illustrated of passive driving the microLED display panel100. The timing controller13transmits timing control signals and data signals to the driver12. The driver12may include a column drive circuit121and a row (or scan) drive circuit122. The column drive circuit121transmits column drive signals to first electrodes (e.g., anodes) of the microLEDs14on the same columns via column conductive wires1211, and the row drive circuit122transmits row drive signals to second electrodes (e.g., cathodes) of the microLEDs14on the same rows via row conductive wires1221. In the embodiment, the column drive circuit121and the row drive circuit122are made in a single integrated circuit.

According to the embodiment discussed above, the substrate11of the microLED display panel100is divided into sub-regions101, each of which has a corresponding driver12. Therefore, loading of the column drive circuit121and the row drive circuit122may be effectively reduced, thereby making whole large-size high-resolution microLED display panel feasible. Moreover, the microLED display panel100of the embodiment adopts a passive driving method (instead of active driving method using thin-film transistors) for driving the microLEDs14, thereby simplifying the process of making display panels, reducing turn-on time of the microLEDs14, increasing drive current, and effectively minimizing effect on gray display due to leakage current.

FIG. 3shows a cross-sectional view illustrated of a frontside illuminating microLED display panel300according to a first specific embodiment of the present invention. In the embodiment, the microLEDs14and the driver12are disposed above a top surface of the substrate11. Light generated by the microLEDs14primarily emits upward (i.e., frontside illuminating) from the top surface of the substrate11as indicated by arrows.

As exemplified inFIG. 3, each pixel may include a red microLED14R, a green microLED14G and a blue microLED14B. A trace layer15is disposed between a (e.g., top) surface of the substrate11and the microLEDs14and the driver12. The trace layer15is configured to electrically connect the driver12, the microLEDs14and the timing controller13. A light blocking layer16is disposed between adjacent pixels and above the trace layer15. The light blocking layer16of the embodiment may be made of black matrix (BM) or other materials suitable for blocking light. In one embodiment, the light blocking layer16may be optionally disposed among the red microLED14R, the green microLED14G and the blue microLED14B of the same pixel.

A light guide layer17may be disposed above the red microLED14R, the green microLED14G and the blue microLED14B. The frontside illuminating microLED display panel300of the embodiment may further include a cover plate18disposed on a bottom surface of the substrate11. The cover plate18of the embodiment may be made of an opaque material.

FIG. 4shows a cross-sectional view illustrated of a backside illuminating microLED display panel400according to a second specific embodiment of the present invention. In the embodiment, the microLEDs14and the driver12are disposed above a top surface of the substrate11. Light generated by the microLEDs14primarily emits downward (i.e., backside illuminating) from the bottom surface of the substrate11as indicated by arrows.

As exemplified inFIG. 4, each pixel may include a red microLED14R, a green microLED14G and a blue microLED14B. A light blocking layer16is disposed between adjacent pixels and above a (e.g., top) surface of the substrate11. The light blocking layer16of the embodiment may be made of black matrix (BM) or other materials suitable for blocking light. A trace layer15is disposed above the light blocking layer16for electrically connecting the driver12, the microLEDs14and the timing controller13. In one embodiment, the light blocking layer16may be optionally disposed among the red microLED14R, the green microLED14G and the blue microLED14B of the same pixel.

A light guide layer17may be disposed above the red microLED14R, the green microLED14G and the blue microLED14B. The backside illuminating microLED display panel400of the embodiment may further include a cover plate18disposed above the driver12, the trace layer15, the light blocking layer16and the light guide layer17. The cover plate18of the embodiment may be made of an opaque material.

FIG. 5shows an exemplary current-voltage curve of a microLED14. When an operating voltage is greater than a turn-on voltage Vf (e.g., 3 volts), a current greater than a predetermined value may be obtained to normally operate and turn on the micro-LED14. For the microLED display panel100shown inFIG. 1A, a system power for the drivers12is VDDA. However, a voltage drop ΔV exists in the center of the microLED display panel100due to impedance in the conductive wire for transferring the power. Accordingly, the drivers12disposed in the center of the microLED display panel100in fact receive power of VDDA-ΔV, although the drivers12disposed on the periphery of the microLED display panel100receive power of VDDA. For example, assume the voltage drop ΔV is 1 volt and the turn-on voltage Vf is 3 volts. The condition under which the drivers12may be normally operated is VDDA-1>3, that is, VDDA>4 (e.g., VDDA of 5 volts is required). In this situation, the drivers12may be made by low-voltage metal-oxide-semiconductor (MOS) process.

Nevertheless, as the amount of microLEDs14increases, consumed current then increases and a voltage drop ΔV significantly increases accordingly (e.g., increases to 4 volts). The condition under which the drivers12may be normally operated is VDDA-4>3, that is, VDDA>7 (e.g., VDDA of 8 volts is required). In this situation, the drivers12should be made by high-voltage metal-oxide-semiconductor (MOS) process, which results in larger circuit area that is unfavorable for making large-size high-resolution (e.g., 3840RGB×2160) display panel. For overcoming the problems, an architecture of a novel driver12is proposed.

FIG. 6shows a system block diagram illustrated of a driver12according to one embodiment of the present invention. In the embodiment, the driver12may include a low-dropout (LDO) regulator123and a drive circuit120. The LDO regulator123receives a system power VDDA, according to which a regulated power VR (e.g., 5 volts) is generated and provided as a power for the drive circuit120. The LDO regulator123of the embodiment may be implemented according to circuit design of conventional LDO regulators, and details of which are thus omitted for brevity. The drive circuit120of the embodiment may include a column drive circuit121and a row drive circuit122. The LDO regulator123is one of direct-current (DC) linear regulators, which are configured to generate a regulated power VR substantially equal to the system power VDDA. Compared to a switching regulator, the LDO regulator123occupies less circuit area with simpler circuit design and without switching noise. In the embodiment, a smoothing capacitor C may be interposed between the regulated power VR and earth, thereby filtering out high-frequency noise. The smoothing capacitor C may be formed with a metal layer process (instead of extra process) commonly used in display panel manufacturing.

According to the driver12of the embodiment as discussed above, only the LDO regulator123should be made by high-voltage (e.g., greater than 8 volts) MOS process, while the drive circuit120may be made by low-voltage (e.g., less than 8 volts) MOS process. On the contrary, for a driver without LOD regulator123, entire driver12should be made by high-voltage MOS process. As a result, the driver12of the embodiment may significant reduce circuit area and facilitate making large-size or high-resolution display panels.