# Patent

## Title
Display panel and system for displaying images utilizing the same

## Abstract

An embodiment of the invention provides a display panel, which includes a substrate having a pixel region and a peripheral region, a control element overlying the pixel region of the substrate, a conducting layer overlying the substrate in the peripheral region, a first insulating layer overlying the conducting layer in the peripheral region, wherein a ratio between an area of the first insulating layer and an area of the conducting layer in the peripheral region is between about 0.27 and 0.99, a lower electrode layer overlying the first insulating layer, and a second insulating layer overlying the lower electrode layer.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
This Application is a Continuation of pending U.S. patent application Ser. No. 12/758,123, Apr. 12, 2010, which claims priority of Taiwan Patent Application No. 98112151, filed on Apr. 13, 2009, the entirety of which is incorporated by reference herein.


BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a display panel and a system for displaying images utilizing the same, and in particular relates to an AM-OLED panel and design method thereof.
2. Description of the Related Art
Active light emitting devices, such as light emitting diodes and organic light emitting diodes, have been widely used in flat panel displays, wherein active-matrix organic light emitting diode (AM-OLED) panels have attracted much attention due to characteristics, such as thin dimension, light weight, spontaneous luminescence with high luminance efficiency, low power consumption, wide viewing angle, high contrast, high-response speed, and full color.
For AM-OLED panels, wide and long metal traces, for example metal traces having widths larger than 100 μm, are generally used as power lines around a peripheral region of the panel for providing power needed for display. The metal traces in the peripheral region and electrode layers (anode or cathode) in a pixel region may be in the same layer formed simultaneously. However, the metal traces in the peripheral region are relatively wide and occupy a relatively large area. Thus, the surface topography (or surface morphology) of the metal traces is quite different from that of the electrode layers in the pixel region. For example, the metal traces in the peripheral region may have insufficient surface roughness, thus negatively affecting the quality of the subsequently formed material layers. For example, an insulating layer formed overlying the metal traces in the peripheral region may be too thin to effectively isolate two metal traces underlying and overlying the insulating layer, respectively. Thus, a short may occur between the two metal traces, negatively and seriously affecting the operation of the display panel. Moreover, because the metal traces in the peripheral region have a relatively large area, high stress may be generated in the metal traces.
Therefore, a display panel having improved quality is desired.
BRIEF SUMMARY OF THE INVENTION
In accordance with an embodiment of the invention, a display panel is provided, which includes a substrate having a pixel region and a peripheral region, a control element overlying the pixel region of the substrate, a conducting layer overlying the substrate in the peripheral region, a first insulating layer overlying the conducting layer in the peripheral region, a lower electrode layer overlying the first insulating layer, and a second insulating layer overlying the lower electrode layer, wherein a ratio between an area of the first insulating layer and an area of the conducting layer in the peripheral region is between about 0.27 and 0.99.
In accordance with another embodiment of the invention, a system for displaying images is provided, which includes a display element including the display panel of the invention.
A detailed description is given in the following embodiments with reference to the accompanying drawings.



BRIEF DESCRIPTION OF THE DRAWINGS
The present invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:
FIGS. 1A-1E are cross-sectional views showing the steps for forming a display panel according to an embodiment of the present invention;
FIGS. 2A-2D are top views showing the insulating layer overlying the conducting layer according to embodiments of the present invention;
FIG. 3 is a top view showing a portion of a display panel according to an embodiment of the present invention; and
FIG. 4 is a schematic diagram showing a system for displaying images according to an embodiment of the present invention.



DETAILED DESCRIPTION OF THE INVENTION
By designing openings in an insulating layer underlying a conducting trace, for example a metal trace, formed in a peripheral region in a display panel of an embodiment of the invention, the surface morphology of the conducting trace may be adjusted to further ensure a subsequently formed insulating layer having a sufficient thickness. Thus, short between an upper electrode layer and a lower electrode layer serving as conducting traces in the peripheral region may be prevented.
FIGS. 1A-1E are cross-sectional views showing the steps for forming a display panel in accordance with an embodiment of the present invention. FIG. 3 is a top view showing a portion of a display panel in accordance with an embodiment of the present invention, wherein the cross-sectional views shown in FIGS. 1A-1D are taken along the line A-A′ of FIG. 3. For simplicity, detailed elements in a pixel region are not shown in FIG. 3.
As shown in FIG. 1A, a substrate 100 is provided, which has a pixel region 1 and a peripheral region 2. In one embodiment, a buffer layer (not shown) may be formed overlying the substrate 100, which may include a silicon oxide, silicon nitride, silicon oxynitride, or combinations thereof. Then, conventional methods may be performed to form an active layer 102, a dielectric layer 104, a gate electrode, and an upper electrode of a capacitor on the substrate 100 to form control elements of the display panel, such as transistors T1 and T2 and a capacitor C. Dielectric layers 106a and 106b are formed overlying the above mentioned elements. The dielectric layers 106a and 106b may include a silicon oxide, silicon nitride, silicon oxynitride, stacked layers thereof, or combinations thereof. Depending on requirement, different regions of the active layer 102 may be doped with different kinds of dopants to form, for example, source regions, drain regions, and lower electrode regions of the capacitors. In another embodiment, a light doping process may first be performed, followed by a heavy doping process after the gate electrodes are defined. Thus, LDD regions may be formed adjacent to the channel regions. Then, the dielectric layers 104, 106a, and 106b are patterned to form openings 106d and 106e respectively exposing the source region of the transistor T1 and the drain region of the transistor T2.
Referring to FIGS. 1B and 3, a conductive material deposition process and a selective etching process are performed to form a conducting layer 112 overlying the substrate 100 in the pixel region 1 and the peripheral region 2. The conducting layer 112 in the pixel region 1 fills into the openings 106d and 106e respectively exposing the source region of the transistor T1 and the drain region of the transistor T2 (as shown in FIG. 1A) and is electrically connected to the transistors T1 and T2 to serve as a data line. Meanwhile, the conducting layer 112 in the peripheral region 2 is formed on the substrate 100. First trenches 113 may be formed in the conducting layer 112 in the peripheral regions 2. The first trench 113 allows the stress to be released from the conducting layer 112 with larger area in the peripheral region 2. In addition, photoresist formed during the manufacturing process may be removed easily due to the forming of the first trench 113. It should be appreciated that types or location of the first trench 113 are not limited to what are shown in FIG. 3.
Referring to FIGS. 1C and 3, an insulating material forming process and a selective etching process are performed to form a first insulating layer 108 on the conducting layer 112 in the peripheral region 2. Meanwhile, the first insulating layer 108 is also formed overlying the substrate 100 in the pixel region 1. The first insulating layer 108 in the pixel region 1 has a contact opening 111 exposing the insulating layer 108 in the peripheral region 2 has at least an opening 119 exposing the conducting layer 112. Thus, the first insulating layer 108 is island-shaped. For example, the first insulating layer 108 includes a plurality of separate square island regions as shown in FIG. 3. A ratio between an area of the first insulating layer 108 in the peripheral region 2 and an area of the conducting layer 112 thereunder is between about 0.27 and about 0.99, preferably between about 0.67 and about 0.80. In this embodiment, the first insulating layer 108 is formed by coating an organic insulating material using a spin coating method and by a photolithography and etching process. In one embodiment, the first insulating layer 108 in the peripheral region 2 fills into the first trench 113 in the conducting layer 112.
In one embodiment, a dielectric layer 106c may be formed overlying the dielectric layer 106b in the pixel region 1 before the forming of the first insulating layer 108.
Referring to FIGS. 1D and 3, a conductive material deposition process and a selective etching process are then performed to conformally form a lower electrode layer 114 overlying the first insulating layer 108 in the pixel region 1 and the peripheral region 2. The lower electrode layer 114 may include at least a metal layer and/or other conducting layers. The lower electrode layer 114 in the pixel region 1 fills into the contact opening 111 (as shown in FIG. 1C) exposing the conducting layer 112 and is electrically connected to the conducting layer 112 serving as the data line. The lower electrode layer 114 in the peripheral region 2 is conformally formed overlying the first insulating layer 108 and has at least a recessed portion 121. In addition, the lower electrode layer 114 in the peripheral region 2 and the conducting layer 112 thereunder together serve as a conducting line, such as a power line, which may have a relatively wide line width and large area.
It should be appreciated that because the first insulating layer 108 in the peripheral region 2 has the opening 119, an upper surface of the conformally formed lower electrode layer 114 has a recessed portion 121 disposed corresponding to the position of the opening 119. The recessed portion 121 has a width w ranging between about 2.5 μm and about 300 μm. A spacing b between two adjacent recessed portions 121 is between about 20 μm and about 80 μm. A depth d of the recessed portion 121 is between about 0.08 μm and about 0.30 μm, preferably about 0.1 μm. In brief, the upper surface of the lower electrode layer 114 in the peripheral region 2 has protruding structures 123 since the upper surface has the recessed portion 121 corresponding to the opening 119 (as shown in FIG. 1C).
Further, in one embodiment, the upper surface of the lower electrode layer 114 in the peripheral region 2 has a surface roughness ranging between about 5% and about 40%. In another embodiment, the lower electrode layer 114 has a surface roughness ranging between about 10% and about 30%. In yet another embodiment, the lower electrode 114 has a surface roughness ranging between about 15% and about 25%, wherein the surface roughness is defined as a ratio between total area of an upper surface area and a side surface of the protruding structures 123 of the lower electrode layer 114 and a projection area of the entire lower conducting layer 114. Specifically, the surface roughness is the area percentage occupied by the upper surface area and the side surface area of the protruding structures 123.
Because the lower electrode layer 114 in the peripheral region 2 has a wider line width (or a larger area) and has high stress, at least a second trench 115 may be formed in the lower electrode layer 114 in the peripheral region 2 in one embodiment. The second trench 115 allows release of the high stress generated in the lower electrode layer 114 with large area in the peripheral region 2.
Referring to FIG. 1E, an organic insulating material is applied overlying the lower electrode layer 114 in the pixel region 1 and the peripheral region 2 by, for example spin coating. Then, a photolithography process and an etching process are performed to selectively etch the organic insulating material and to form a second insulating layer 110. The second insulating layer 110 in the pixel region 1 has an opening exposing the lower electrode layer 114 and serves as a pixel definition layer (PDL). It should be appreciated that because of the design of the opening 119 of the first insulating layer 108 in the peripheral region 2, the ratio between the area of the first insulating layer 108 in the peripheral region 2 and that of the conducting layer 112 thereunder is between about 0.27 and about 0.99. Thus, the upper surface of the subsequently formed lower electrode layer 114 has the recessed portions 121 having specific sizes and spacings. Specifically, the lower electrode layer 114 has a specific surface roughness ensuring a sufficient organic insulating material to be retained during the spin coating process for forming the second insulating layer 110. Therefore, the second insulating layer 110 in the peripheral region 2 may have sufficient thickness t3 ranging between about 1.5 μm and about 3 μm, preferably between about 2.9 μm and about 2.6 μm.
In one embodiment, the second insulating layer 110 formed in the pixel region 1 has a thickness t1 equal to the thickness t3 of the second insulating layer 110 in the peripheral region 2. Alternatively, the difference between the thicknesses of the second insulating layer 110 in the pixel region 1 and the peripheral region 2 is minimal.
Then, a light emitting layer 118 and an upper electrode layer 116 are formed overlying the second insulating layer 110 in the pixel region 1 to complete the fabrication of a display panel according to an embodiment of the invention. The upper electrode layer 116 is also formed overlying the second insulating layer 110 in the peripheral region 2.
As mentioned above, the surface morphology of the lower electrode layer 114 in the peripheral region 2 may be adjusted through the design of the opening 119 of the first insulating layer 108. The upper surface of the lower electrode layer 114 in the peripheral region 2 has specific recessed portions 121 and protruding structures 123, thus ensuring a sufficient organic insulating material to be retained during the spin coating process. Therefore, the second insulating layer 110 in the peripheral region 2 may have sufficient thickness, which is capable of preventing short between the lower electrode layer 114 and the upper electrode layer 116.
In addition, the first trench 113 and the second trench 115 are formed in the conducting layer 112 and the lower electrode layer 114 in the peripheral region 2, respectively, which are capable of releasing the high stress and improving the reliability of the display panel.
In the peripheral region 2, the type or layout of the openings 119 formed in the first insulating layer 108 is not limited to what is shown in FIG. 3. For example, in one embodiment, the openings 119 formed in the first insulating layer 108 in the peripheral region 2 may be arranged in an array, as shown in FIG. 2A. In another embodiment, the openings 119 may have shapes of squares or rectangles, such as that shown in FIG. 2D, or circles, polygons, or other irregular shapes (not shown). In yet another embodiment, the openings 119 formed in the first insulating layer 108 in the peripheral region 2 may cause the first insulating layer 108 to be island-shaped and to have separate island regions, as shown in FIG. 2B. The island regions may also be arranged in an array. Further, the first insulating layer 108 is not limited to have square island regions as shown in FIG. 2B. The first insulating layer 108 may have circle island regions and square island regions arranged irregularly, as shown in FIG. 2C.
In addition, the embodiment of the invention is not limited to AM-OLED panels and can be applied in other display panels.
FIG. 4 schematically shows a system for displaying images in accordance with an embodiment of the present invention, which is implemented as a display element 600 or an electronic element 800, such as a mobile phone, digital camera, personal digital assistant, portable computer, personal computer, television, vehicle display, or portable DVD. In this embodiment, the display element 600 comprises a display panel 400 according to an embodiment of the invention, such as the display panel shown in FIG. 3. In addition, in another embodiment, the display element 600 may be a portion of the electronic element 800. As shown in FIG. 4, the electronic element 800 comprises the display element 600 and an input element 700. The input element 700 is coupled to the display element 600 for providing signals, for example image signals, to the display element 600 to display images.
In addition, the display panel of the embodiment of the invention may be applied in kinds of electronic elements, such as a mobile phone, digital camera, personal digital assistant, portable computer, personal computer, television, vehicle display, or portable DVD.
While the invention has been described by way of example and in terms of the embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.

## Claims

1. A display panel, comprising:
a substrate having a pixel region and a peripheral region;
a control element overlying the pixel region of the substrate;
a metal layer overlying the substrate in the peripheral region and in the pixel region;
a first insulating layer formed on the metal layer in the peripheral region and having a plurality of openings exposing the metal layer, wherein a ratio between an area of the plurality of openings and an area of the metal layer in the peripheral region is between about 0.01 and 0.73;
a lower electrode layer overlying the first insulating layer and filling into the plurality of openings of the first insulating layer to be electrically connected to the metal layer;
a second insulating layer overlying the lower electrode layer;
an upper electrode layer disposed on the second insulating layer; and
a light emitting layer formed between the lower electrode layer and the upper electrode layer in the pixel region.

2. The display panel as claimed in claim 1, wherein an upper surface of the lower electrode layer has at least a recessed portion disposed corresponding to one of the plurality of openings.

3. The display panel as claimed in claim 2, wherein a width of the recessed portion is between about 2.5 μm and about 300 μm.

4. The display panel as claimed in claim 2, wherein a spacing between the recessed portions is between about 20 μm and about 80 μm.

5. The display panel as claimed in claim 2, wherein a depth of the recessed portion is between about 0.08 μm and about 0.30 μm.

6. The display panel as claimed in claim 1, wherein the second insulating layer has a thickness ranging between about 1.5 μm and about 3.0 μm.

7. The display panel as claimed in claim 1, wherein an upper surface of the lower electrode layer has a surface roughness ranging between about 5% and about 40%.

8. The display panel as claimed in claim 1, wherein the lower electrode layer further comprises a second trench.

9. The display panel as claimed in claim 1, wherein the second insulating layer is a coated organic insulating layer.

10. A system for displaying images, comprising:
a display element comprising the display panel as claimed in claim 1.

11. The system for displaying images as claimed in claim 10, further comprising:
an electronic element, wherein the electronic element comprises:
the display panel; and
an input element coupled to the display element and providing a signal to the display element for displaying images.

12. The display panel as claimed in claim 1, wherein the first insulating layer formed on the metal layer in the peripheral region further has a first portion and a second portion spaced apart from the first portion in a view of a cross-section vertical to the substrate.

13. The display panel as claimed in claim 1, wherein the metal layer in the peripheral region serves as a pad.

14. A display panel, comprising:
a substrate having a pixel region and a peripheral region;
a control element overlying the pixel region of the substrate;
a metal layer overlying the substrate in the peripheral region and in the pixel region;
a first insulating layer formed on the metal layer in the peripheral region, wherein the first insulating layer has a first portion, and a second portion spaced apart from the first portion in a view of a cross-section vertical to the substrate, and wherein the metal layer is disposed between the first portion and the second portion and a width of the first insulating layer above the metal layer is smaller than that of the metal layer;
a lower electrode layer overlying the first insulating layer electrically connected to the metal layer;
a second insulating layer overlying the lower electrode layer;
an upper electrode layer disposed on the second insulating layer; and
a light emitting layer disposed between the lower electrode layer and the upper electrode layer in the pixel region.

15. The display panel as claimed in claim 14, wherein the first insulating layer formed on the metal layer in the peripheral region has a plurality of openings exposing the metal layer, and a direction of the width is through at least two of the plurality of openings.

16. The display panel as claimed in claim 14, wherein the first insulating layer formed on the metal layer in the peripheral region has a plurality of openings exposing the metal layer, and a direction of the width is along an arranging direction of the plurality of openings.

17. The display panel as claimed in claim 14, wherein the first insulating layer formed on the metal layer in the peripheral region has a plurality of openings exposing the metal layer, and the lower electrode layer overlying the first insulating layer fills into the plurality of openings.

18. The display panel as claimed in claim 14, wherein the metal layer in the peripheral region serves as a pad.