Electrode structure, micro light emitting device, and display panel

This application claims the priority benefit of Taiwan application serial no. 108139427, filed on Oct. 31, 2019. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.

The disclosure relates to an electrode structure, a micro light emitting device, and a display panel, and in particular relates to an electrode structure for preventing a short circuit, a micro light emitting device using the electrode structure, and a display panel using the electrode structure and the micro light emitting device.

A micro LED (micro light emitting diode) display has advantages such as low power consumption, high brightness, high color saturation, fast response time, and power saving, and what is more, a micro LED display has good material stability and is free of image sticking. Therefore, the development of the display technology for micro LED displays has drawn a lot of attention.

In terms of the manufacturing process, in the process of transferring a micro LED from a growth substrate to a driving circuit substrate, it is required to heat and pressurize the micro LED so as to electrically bond the micro LED to the driving circuit substrate. However, in this transfer bonding process, the electrode of the micro LED and the pad on the driving circuit substrate may short-circuit due to misalignment, which impairs the reliability of the micro LED display.

The disclosure provides an electrode structure for preventing a short circuit caused by misconnection.

The disclosure also provides a micro light emitting device that uses the electrode structure to provide a buffering effect during a bonding process.

The disclosure further provides a display panel that uses the electrode structure and the micro light emitting device to achieve favorable reliability.

An electrode structure of the disclosure includes a first electrode and a second electrode disposed opposite to each other. The first electrode has a first side and a second side. The second side is located between the first side and the second electrode. The first electrode has a maximum vertical length and a minimum vertical length from the first side to the second side, and a ratio of the minimum vertical length to the maximum vertical length is less than 0.8. The second electrode and the first electrode are separated by a first vertical gap and a second vertical gap, and the second vertical gap is greater than the first vertical gap.

In an embodiment of the disclosure, the first side has a first horizontal length, a second horizontal length is present between the maximum vertical length and the minimum vertical length, and a ratio of the second horizontal length to the first horizontal length is greater than 0.2.

In an embodiment of the disclosure, the first electrode further has a plurality of third sides, the third sides connect the first side and the second side, and the minimum vertical length is a vertical length of each of the third sides.

In an embodiment of the disclosure, the second side is bent and includes a straight part and a plurality of inclined parts. The inclined parts respectively connect the straight part and the third sides. Each of the inclined parts has a third horizontal length, and a ratio of the third horizontal length to the first horizontal length is greater than 0.2.

In an embodiment of the disclosure, the second side is curved and tangent to a reference tangent at a point. A connection line between the point and the adjacent third side, and the second side define an enclosed region. An extension line of the third side, the reference tangent, and the connection line form a virtual triangle, and an area of the enclosed region is smaller than an area of the virtual triangle.

In an embodiment of the disclosure, a ratio of the area of the enclosed region to the area of the virtual triangle is less than or equal to 0.6.

In an embodiment of the disclosure, a ratio of the first vertical gap to the second vertical gap is less than 0.8.

In an embodiment of the disclosure, a projection plane of the first electrode on a horizontal plane and a projection plane of the second electrode on the horizontal plane are symmetrical.

In an embodiment of the disclosure, the first electrode has a first orthographic projection area on a horizontal plane, and the second electrode has a second orthographic projection area on the horizontal plane. The first orthographic projection area is different from the second orthographic projection area.

In an embodiment of the disclosure, a ratio of the first orthographic projection area to the second orthographic projection area is greater than 0.2 and less than 5, but not equal to 1.

A micro light emitting device of the disclosure includes an epitaxial structure layer and an electrode structure. The epitaxial structure layer has a surface, and the electrode structure is disposed on the surface of the epitaxial structure layer. The electrode structure includes a first electrode and a second electrode disposed opposite to each other. The first electrode has a first side and a second side. The second side is located between the first side and the second electrode. The first electrode has a maximum vertical length and a minimum vertical length from the first side to the second side, and a ratio of the minimum vertical length to the maximum vertical length is less than 0.8. The second electrode and the first electrode are separated by a first vertical gap and a second vertical gap, and the second vertical gap is greater than the first vertical gap.

In an embodiment of the disclosure, the surface of the epitaxial structure layer has a length, and a ratio of the first vertical gap to the length is greater than 0.1.

In an embodiment of the disclosure, the first electrode has a first orthographic projection area on the surface, and the second electrode has a second orthographic projection area on the surface. The first orthographic projection area is different from the second orthographic projection area.

In an embodiment of the disclosure, the surface has an area, and a ratio of a sum of the first orthographic projection area and the second orthographic projection area to the area is less than 0.8 and greater than 0.2.

A display panel of the disclosure includes a circuit substrate, at least one electrode structure, and at least one micro light emitting device. The electrode structure is disposed on the circuit substrate and includes a first electrode and a second electrode disposed opposite to each other. The first electrode has a first side and a second side. The second side is located between the first side and the second electrode. The first electrode has a maximum vertical length and a minimum vertical length from the first side to the second side, and a ratio of the minimum vertical length to the maximum vertical length is less than 0.8. The second electrode and the first electrode are separated by a first vertical gap and a second vertical gap, and the second vertical gap is greater than the first vertical gap. The micro light emitting device is disposed on the circuit substrate and electrically connected to the electrode structure.

In an embodiment of the disclosure, the micro light emitting device includes: an epitaxial structure layer having a surface; and a light emitting device electrode structure disposed on the surface of the epitaxial structure layer and including a first light emitting device electrode and a second light emitting device electrode disposed opposite to each other. The micro light emitting device is electrically connected to the electrode structure via the light emitting device electrode structure. The second light emitting device electrode and the first light emitting device electrode are separated by a third vertical gap and a fourth vertical gap, and the fourth vertical gap is greater than the third vertical gap.

In an embodiment of the disclosure, the micro light emitting device includes: an epitaxial structure layer having a surface; and a light emitting device electrode structure disposed on the surface of the epitaxial structure layer and including a first light emitting device electrode and a second light emitting device electrode disposed opposite to each other. The micro light emitting device is electrically connected to the first electrode and the second electrode of the electrode structure via the first light emitting device electrode and the second light emitting device electrode respectively. An orthographic projection area of the first light emitting device electrode and the first electrode on the circuit substrate after the first light emitting device electrode and the first electrode are connected is different from an orthographic projection area of the second light emitting device electrode and the second electrode on the circuit substrate after the second light emitting device electrode and the second electrode are connected.

Based on the above, in the design of the electrode structure of the disclosure, the first electrode meets the condition that the ratio of the minimum vertical length to the maximum vertical length is less than 0.8, and the first electrode and the second electrode meet the condition that the second vertical gap is greater than the first vertical gap. With the above structural design, the electrode structure of the disclosure prevents a short circuit caused by misconnection, and because of the design of the electrode structure, the micro light emitting device using the electrode structure of the disclosure provides a buffering effect in the process of being bonded to the circuit substrate. As a result, the display panel using the electrode structure and the micro light emitting device of the disclosure has favorable reliability.

To make the aforementioned and other features and advantages of the disclosure more comprehensible, several embodiments accompanied with drawings are described in detail as follows.

The accompanying drawings are included to provide a further understanding of the disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the disclosure and, together with the description, serve to explain the principles of the disclosure.

FIG. 1A is a cross-sectional view of a display panel according to an embodiment of the disclosure.

FIG. 1B is a partial top view of the display panel of FIG. 1A .

FIG. 1C is a top view of an electrode structure and a circuit substrate of FIG. 1A .

FIG. 2A is a top view of a micro light emitting device according to an embodiment of the disclosure.

FIG. 2B is a top view of a micro light emitting device according to another embodiment of the disclosure.

FIG. 2C is a top view of a micro light emitting device according to yet another embodiment of the disclosure.

FIG. 2D is a top view of a micro light emitting device according to yet another embodiment of the disclosure.

FIG. 1A is a cross-sectional view of a display panel according to an embodiment of the disclosure. FIG. 1B is a partial top view of the display panel of FIG. 1A . FIG. 1C is a top view of an electrode structure and a circuit substrate of FIG. 1A . First, referring to FIG. 1A and FIG. 1 B, in the present embodiment, the display panel 10 includes a circuit substrate 100 , at least one electrode structure (three electrode structures 200 are shown as an example), and at least one micro light emitting device 300 (three micro light emitting devices 300 are shown as an example). The electrode structure 200 and the micro light emitting device 300 are both disposed on the circuit substrate 100 , and the electrode structure 200 is located between the micro light emitting device 300 and the circuit substrate 100 . The micro light emitting device 300 and the electrode structure 200 are electrically connected to the circuit substrate 100 . Here, the circuit substrate 100 is, for example, a complementary metal-oxide-semiconductor (CMOS) substrate, a liquid crystal on silicon (LCOS) substrate, a thin film transistor (TFT) substrate or other substrates having a working circuit. Nevertheless, the disclosure is not limited thereto.

Referring to FIG. 1C , the electrode structure 200 of the present embodiment includes a first electrode 210 and a second electrode 220 disposed opposite to each other. In the top view, the first electrode 210 has a first side 212 , a second side 214 , and a plurality of third sides 216 . The second side 214 is located between the first side 212 and the second electrode 220 , and the third sides 216 connect the first side 212 and the second side 214 . Here, the first side 212 and the third sides 216 are straight, and the second side 214 is curved.

In particular, in the direction X, the first electrode 210 has a maximum vertical length L 1 and a minimum vertical length L 2 from the first side 212 to the second side 214 . The minimum vertical length L 2 is less than the maximum vertical length L 1 . Preferably, the minimum vertical length L 2 is the vertical length of the third side 216 , and a ratio of the minimum vertical length L 2 to the maximum vertical length L 1 is less than 0.8. That is to say, the shape of the first electrode 210 is not rectangular, but is wide in the middle and gradually becomes narrower toward the periphery. A ratio greater than or equal to 0.8 may cause the width at the periphery to be insufficient and affect the yield of the subsequent bonding process.

Referring again to FIG. 1C , the second electrode 220 and the first electrode 210 have a shortest vertical distance therebetween, which is a first vertical gap G 1 . Each of the third sides 216 of the first electrode 210 and the second electrode 220 have a shortest vertical distance therebetween, which is a second vertical gap G 2 . The second vertical gap G 2 is greater than the first vertical gap G 1 . Preferably, a ratio of the first vertical gap G 1 to the second vertical gap G 2 is less than 0.8. That is to say, the gap between the first electrode 210 and the second electrode 220 is narrow in the middle and gradually becomes wider toward the periphery. A ratio greater than or equal to 0.8 may cause the width at the periphery to be insufficient and affect the yield of the subsequent bonding process.

As shown in FIG. 1C , the contour of the first electrode 210 and the contour of the second electrode 220 of the present embodiment are substantially symmetrical. That is to say, the structural form of the second electrode 220 and the structural form of the first electrode 210 are identical, and an edge of the first electrode 210 is aligned with an edge of the second electrode 220 . The above facilitates the manufacturing of the electrodes and provides a larger buffering space in the bonding process. Here, a projection plane of the first electrode 210 on the circuit substrate 100 and a projection plane of the second electrode 220 on the circuit substrate 100 are symmetrical.

Referring again to FIG. 1B , when the micro light emitting device 300 is bonded to the electrode structure 200 on the circuit substrate 100 , a first electrode 322 (that is, a first light emitting device electrode of a light emitting device electrode structure) and a second electrode 324 (that is, a second light emitting device electrode of the light emitting device electrode structure) located on the same side of an epitaxial structure layer 310 respectively correspond to the first electrode 210 and the second electrode 220 of the electrode structure 200 . As described above, the first electrode 210 meets the condition that the ratio of the minimum vertical length L 2 to the maximum vertical length L 1 is less than 0.8, and the first electrode 210 and the second electrode 220 meet the condition that the second vertical gap G 2 is greater than the first vertical gap G 1 . With the above structural design, the electrode structure 200 of the present embodiment prevents a short circuit caused by misconnection and provides a buffering effect during the bonding process. As a result, the display panel 10 using the electrode structure 200 of the present embodiment has favorable reliability.

It is to be noted that some of the reference numerals and parts of the above-described embodiments are also used in the following embodiments, wherein the same reference numerals denote the same or similar elements, and the descriptions thereof are omitted to avoid repetition. Please refer to the above embodiments for descriptions of the omitted parts.

FIG. 2A is a top view of a micro light emitting device according to an embodiment of the disclosure. Referring to FIG. 1B and FIG. 2A , the micro light emitting device 300 a of the present embodiment is similar to the micro light emitting device 300 of FIG. 1B , and the difference therebetween is: the shapes of the first electrode 322 and the second electrode 324 of the micro light emitting device 300 of FIG. 1B are rectangles with rounded corners. Otherwise, the electrode structure 320 a of the micro light emitting device 300 a of the present embodiment has the same structural design as the electrode structure 200 disposed on the circuit substrate 100 described above.

Specifically, the micro light emitting device 300 a includes the epitaxial structure layer 310 and the electrode structure 320 a . The epitaxial structure layer 310 has a surface 312 , and the electrode structure 320 a is disposed on the surface 312 of the epitaxial structure layer 310 , wherein the surface 312 has a length L 3 in the direction X. The electrode structure 320 a includes a first electrode 322 a and a second electrode 324 a disposed opposite to each other. In the top view, the first electrode 322 a has a first side S 11 , a second side S 12 , and a plurality of third sides S 13 . The second side S 12 is located between the first side S 11 and the second electrode 324 a , and the third sides S 13 connect the first side S 11 and the second side S 12 . Here, the first side S 11 and the third sides S 13 are straight, and the second side S 12 is curved.

In particular, in the direction X, the first electrode 322 a has a maximum vertical length L 11 and a minimum vertical length L 12 from the first side S 11 to the second side S 12 . The minimum vertical length L 12 is less than the maximum vertical length L 11 . Preferably, the minimum vertical length L 12 is the vertical length of the third side S 13 , and a ratio of the minimum vertical length L 12 to the maximum vertical length L 11 is less than 0.8. That is to say, the shape of the first electrode 322 a is not rectangular, but is wide in the middle and gradually becomes narrower toward the periphery. A ratio greater than or equal to 0.8 may cause the width at the periphery to be insufficient and affect the yield of the subsequent bonding process.

Furthermore, the second electrode 324 a and the first electrode 322 a have a shortest vertical distance therebetween, which is a first vertical gap G 11 (may be regarded as a third vertical gap). Each of the third sides S 13 of the first electrode 322 a and the second electrode 324 a have a shortest vertical distance therebetween, which is a second vertical gap G 12 (may be regarded as a fourth vertical gap). The second vertical gap G 12 is greater than the first vertical gap G 11 . Preferably, a ratio of the first vertical gap G 11 to the second vertical gap G 12 is less than 0.8. That is to say, the gap between the first electrode 322 a and the second electrode 324 a is narrow in the middle and gradually becomes wider toward the periphery. Further, a ratio of the first vertical gap G 11 to the length L 3 of the surface 312 is greater than 0.1, so as to prevent the reliability from decreasing due to an overly small gap between the first electrode 322 a and the second electrode 324 a.

Referring again to FIG. 2A , the first side S 11 of the first electrode 322 a of the present embodiment has a first horizontal length H 1 . A minimum horizontal distance is present between the maximum vertical length L 11 and the minimum vertical length L 12 , and this distance is a second horizontal length H 2 . A ratio of the second horizontal length H 2 to the first horizontal length H 1 is greater than 0.2. Furthermore, the second side S 12 is tangent to a reference tangent P at a point T, and a connection line L between the point T and the adjacent third side S 13 , and the second side S 12 define an enclosed region S. An extension line E of the third side S 13 , the reference tangent P, and the connection line L form a virtual triangle B. In particular, the area of the enclosed region S is smaller than the area of the virtual triangle B, and a ratio of the area of the enclosed region S to the area of the virtual triangle B is less than or equal to 0.6. A ratio greater than 0.6 may cause the surrounding buffering space to be small enough and affect the yield of the subsequent bonding process.

In addition, as shown in FIG. 2A , the contour of the first electrode 322 a and the contour of the second electrode 324 a are symmetrical. That is to say, the structural form of the second electrode 324 a and the structural form of the first electrode 322 a are identical, and an edge of the first electrode 322 a is aligned with an edge of the second electrode 324 a . Here, a projection plane of the first electrode 322 a on the surface 312 and a projection plane of the second electrode 324 a on the surface 312 are symmetrical.

FIG. 2B is a top view of a micro light emitting device according to another embodiment of the disclosure. Referring to FIG. 2A and FIG. 2B , the micro light emitting device 300 b of the present embodiment is similar to the micro light emitting device 300 a of FIG. 2A , and the difference therebetween is: the shapes of the first electrode 322 b and the second electrode 324 b of the electrode structure 320 b of the present embodiment are different from the shapes of the first electrode 322 a and the second electrode 324 a of the electrode structure 320 a . The shapes of the first electrode 322 b and the second electrode 324 b have bevels.

Specifically, the first side S 21 of the first electrode 322 b is straight, and the second side S 22 is bent and includes a straight part S 221 and two inclined parts S 222 . The inclined part S 222 connects the straight part S 221 and the third side S 23 . The first side S 21 of the first electrode 322 b has a first horizontal length H 1 ′, and each of the inclined parts S 222 has a third horizontal length H 3 . A ratio of the third horizontal length H 3 to the first horizontal length H 1 ′ is greater than 0.2. The above facilitates the manufacturing of the electrodes and provides a larger buffering space in the bonding process.

Like the design of FIG. 2A , the first electrode 322 b of the present embodiment has a maximum vertical length L 21 from the first side S 21 to the second side S 22 , and each of the third sides S 23 has a minimum vertical length L 22 . A ratio of the minimum vertical length L 22 to the maximum vertical length L 21 is less than 0.8. The second electrode 324 b and the first electrode 322 b have a first vertical gap G 21 therebetween, and each of the third sides S 23 of the first electrode 322 b and the second electrode 324 b have a second vertical gap G 22 therebetween. The second vertical gap G 22 is greater than the first vertical gap G 21 . Here, a projection plane of the first electrode 322 b on a horizontal plane (such as the surface 312 ) and a projection plane of the second electrode 324 b on the horizontal plane are symmetrical. That is to say, the structural form of the second electrode 324 b and the structural form of the first electrode 322 b are identical, and an edge of the first electrode 322 b is aligned with an edge of the second electrode 324 b.

FIG. 2C is a top view of a micro light emitting device according to yet another embodiment of the disclosure. Referring to FIG. 2B and FIG. 2C , the micro light emitting device 300 c of the present embodiment is similar to the micro light emitting device 300 b of FIG. 2B , and the difference therebetween is: the first electrode 322 c and the second electrode 324 c of the electrode structure 320 c of the present embodiment have different sizes. Specifically, the first electrode 322 c has a first orthographic projection area A 1 on the surface 312 , and the second electrode 324 c has a second orthographic projection area A 2 on the surface 312 . The first orthographic projection area A 1 is different from the second orthographic projection area A 2 . Here, the first orthographic projection area A 1 is smaller than the second orthographic projection area A 1 . However, the disclosure is not limited thereto. In other embodiments, the first orthographic projection area A 1 may be larger than the second orthographic projection area A 2 . A ratio of the first orthographic projection area A 1 to the second orthographic projection area A 2 is greater than 0.2 and less than 5, but not equal to 1. Further, the surface 312 has an area A 3 , and a ratio of a sum of the first orthographic projection area A 1 and the second orthographic projection area A 2 to the area A 3 is less than 0.8 and greater than 0.2. An overly large ratio may cause a reduction in the buffering space, but an overly small ratio may cause a decrease in the process yield.

FIG. 2D is a top view of a micro light emitting device according to yet another embodiment of the disclosure. Referring to FIG. 2C and FIG. 2D , the micro light emitting device 300 d of the present embodiment is similar to the micro light emitting device 300 c of FIG. 2C , and the difference therebetween is: the shape of the first electrode 322 c of the electrode structure 320 d of the present embodiment is different from the shape of the second electrode 324 d . Here, the shape of the second electrode 324 d is the same as the shape of the second electrode 324 a of FIG. 2A , both of which have an arc edge.

It is worth mentioning that, in other embodiments not shown, the electrode structures 320 a , 320 b , 320 c , and 320 d shown in FIG. 2A , FIG. 2B , FIG. 2C , and FIG. 2D may also serve as the above-described electrode structure on the circuit substrate, which still falls within the scope of the disclosure.

To conclude the above, in the design of the electrode structure of the disclosure, the first electrode meets the condition that the ratio of the minimum vertical length to the maximum vertical length is less than 0.8, and the first electrode and the second electrode meet the condition that the second vertical gap is greater than the first vertical gap. With the above structural design, the electrode structure of the disclosure prevents a short circuit caused by misconnection, and because of the design of the electrode structure, the micro light emitting device using the electrode structure of the disclosure provides a buffering effect in the process of being bonded to the circuit substrate. As a result, the display panel using the electrode structure and the micro light emitting device of the disclosure has favorable reliability.

Although the disclosure has been described with reference to the above embodiments, they are not intended to limit the disclosure. It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed embodiments without departing from the scope or spirit of the disclosure. In view of the foregoing, it is intended that the disclosure covers modifications and variations provided that they fall within the scope of the following claims and their equivalents.