MICRO LIGHT EMITTING DIODE

A micro light emitting diode includes an epitaxial structure, a first electrode, and a second electrode. The epitaxial structure has a surface. The first electrode and the second electrode are respectively disposed on the surface of the epitaxial structure. The second electrode is located outside the first electrode, and the second electrode is symmetrically disposed with respect to a geometric center of the epitaxial structure.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Taiwan application serial no. 109116828, filed on May 21, 2020. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.

BACKGROUND

Technical Field

The disclosure relates to a light emitting structure, and in particular, to a micro light emitting diode.

Description of Related Art

A micro light emitting diode display device may feature advantages such as low power consumption, high brightness, high color saturation, fast response, and power saving. Moreover, a micro light emitting diode display device may further provide advantages such as good material stability and no image sticking. Accordingly, development on the display technology of the micro light emitting diode display devices has received much attention.

As far as the process is concerned, when a micro light emitting diode is transferred from a growth substrate to a driver circuit substrate, the micro light emitting diode is required to be heated and pressured, so that the micro light emitting diode may be electrically bonded to the driver circuit substrate. Nevertheless, in an existing micro light emitting diode, the N electrode is electrically connected to the N-type semiconductor layer through the design of vias. As such, the P electrode and the N electrode, which are located at the same side of the epitaxial structure and located at the left and right sides, are not evenly pressured. In addition, during transferring, time is required to be spent on accurately aligning the P electrode and the N electrode onto the connection pad of the driver circuit substrate. Therefore, how to allow the electrodes of a micro light emitting diode to be evenly pressured and rapidly aligned during transferring and bonding is an important issue.

SUMMARY

The disclosure provides a micro light emitting diode in which electrodes are not required to be precisely aligned and may be evenly pressured in subsequent transferring and bonding procedures and exhibiting favorable structural reliability.

A micro light emitting diode provided by the disclosure includes an epitaxial structure, a first electrode, and a second electrode. The epitaxial structure has a surface. The first electrode is disposed on the surface of the epitaxial structure. The second electrode is disposed on the surface of the epitaxial structure. The second electrode is located outside the first electrode, and the second electrode is symmetrically disposed with respect to a geometric center of the epitaxial structure.

In an embodiment of the disclosure, the epitaxial structure includes a first-type semiconductor layer, a light emitting layer, a second-type semiconductor layer, and at least one via. The light emitting layer is located between the first-type semiconductor layer and the second-type semiconductor layer, and the at least one via extends from the second-type semiconductor layer to the first-type semiconductor layer. The micro light emitting diode further includes an insulating layer and a conductive material. The insulating layer and the first electrode are disposed on the second-type semiconductor layer and extends to cover an inner wall of the at least one via. The conductive material fills the at least one via and is located between the second electrode and the insulating layer.

In an embodiment of the disclosure, in a top view, a ratio of an area of the at least one via to an area of the second electrode is smaller than or equal to 0.5.

In an embodiment of the disclosure, the at least one via includes two vias located at two opposite sides of the first electrode. The two vias are symmetrically disposed with respect to the geometric center of the epitaxial structure.

In an embodiment of the disclosure, in a top view, an area of the second electrode is greater than an area of the first electrode.

In an embodiment of the disclosure, the second electrode is point-symmetric with respect to the geometric center of the epitaxial structure, or the second electrode is line-symmetric with respect to a line of symmetry of the geometric center.

In an embodiment of the disclosure, a minimum gap is provided between the second electrode and the first electrode, and the minimum gap is greater than or equal to 0.5 microns.

In an embodiment of the disclosure, the first electrode has a first maximum width, the second electrode has a second maximum width, and the second maximum width is smaller than or equal to the first maximum width.

In an embodiment of the disclosure, the first electrode is symmetrically disposed with respect to the geometric center of the epitaxial structure.

In an embodiment of the disclosure, the first electrode and the second electrode are not coplanar.

In an embodiment of the disclosure, a first surface of the first electrode is higher than a second surface of the second electrode.

In an embodiment of the disclosure, a Young's modulus of the first electrode is smaller than a Young's modulus of the second electrode.

In an embodiment of the disclosure, a first surface of the first electrode is lower than a second surface of the second electrode.

In an embodiment of the disclosure, a Young's modulus of the first electrode is greater than a Young's modulus of the second electrode.

In an embodiment of the disclosure, a width of the second electrode is smaller than a distance between the second electrode and the first electrode.

In an embodiment of the disclosure, in a top view, a shape of the epitaxial structure and a shape of the second electrode are conformal, and the second electrode is a ring electrode.

In an embodiment of the disclosure, an interval distance is provided between the second electrode and a surrounding surface of the epitaxial structure, and the interval distance is smaller than or equal to 5 microns and is greater than or equal to 0.5 microns.

In an embodiment of the disclosure, a ratio of a side length of the second electrode to a total side length of the epitaxial structure is greater than or equal to 0.2. A ratio of an area of the second electrode to a total surface area of the epitaxial structure is greater than or equal to 0.2 and is smaller than or equal to 0.8.

In an embodiment of the disclosure, the second electrode has a first electrical property and a second electrical property, the first electrical property is different from the second electrical property, and the second electrical property is identical to an electrical property of the first electrode.

In an embodiment of the disclosure, the first electrode includes a plurality of point electrodes, and the second electrode includes a plurality of linear electrodes.

In an embodiment of the disclosure, the second electrode includes a plurality of electrode portions and a plurality of trace portions, and the electrode portions are respectively connected to the trace portions.

In an embodiment of the disclosure, a material of the electrode portions is different from a material of the trace portions.

In an embodiment of the disclosure, the first electrode includes an electrode portion and a plurality of trace portions, and the trace portions are connected to the electrode portion.

In an embodiment of the disclosure, a material of the electrode portions is different from a material of the trace portions.

A micro light emitting diode provided by the disclosure includes an epitaxial structure, a first electrode, and a second electrode. The first electrode is disposed on the surface of the epitaxial structure. The second electrode is disposed on the surface of the epitaxial structure.

The second electrode is located outside the first electrode, and the second electrode is symmetrically disposed with respect to a geometric center of the first electrode.

To sum up, in the design of the micro light emitting diode provided by the disclosure, since the second electrode located outside the first electrode is symmetrically disposed with respect to the geometric center of the epitaxial structure, in the subsequent transferring and bonding procedures, the first electrode and the second electrode are not required to be precisely aligned and are evenly pressured. In this way, the micro light emitting diode provided by the disclosure may exhibit favorable structural reliability.

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

DESCRIPTION OF THE EMBODIMENTS

FIG. 1Ais a schematic top view of a micro light emitting diode according to an embodiment of the disclosure.FIG. 1Bis a schematic cross-sectional view taken long a line A-A inFIG. 1A. With reference toFIG. 1AandFIG. 1Btogether, in this embodiment, a micro light emitting diode100aincludes an epitaxial structure110a, a first electrode120a, and a second electrode130a. The epitaxial structure110ahas a surface111a. The first electrode120aand the second electrode130aare respectively disposed on the surface111aof the epitaxial structure110a. The second electrode130ais located outside the first electrode120a, and the second electrode120ais symmetrically disposed with respect to a geometric center C of the epitaxial structure110a.

To be specific, the epitaxial structure110aof this embodiment includes a first-type semiconductor layer112, a light emitting layer114, a second-type semiconductor layer116, and at least one via115a(two vias115aare schematically illustrated). The light-emitting layer114is located between the first-type semiconductor layer112and the second-type semiconductor layer116, and the vias115aextend from the second-type semiconductor layer116to the first-type semiconductor layer112. Herein, the two vias115aare located at two opposite sides of the first electrode120a, and the two vias115aare symmetrically disposed with respect to the geometric center C of the epitaxial structure110a. Moreover, the micro light emitting diode100aprovided by this embodiment further includes an insulating layer140and a conductive material150. The insulating layer140and the first electrode120aare disposed on the second-type semiconductor layer116and extends to cover the inner walls of the vias115a. The conductive material150fills the vias115aand is located between the second electrode130aand the insulating layer140. The insulating layer140may electrically insulate the second electrode130afrom the second-type semiconductor layer116. Herein, the first electrode120ais electrically connected to the second-type semiconductor layer116, and the second electrode130ais electrically connected to the first-type semiconductor layer112through the conductive material150. In an embodiment that is not shown, an air gap may be provided between the conductive material150and the second electrode130a, so that the conductive material150may partially contact the second electrode130a, the air gap may act as a buffering space during transfer, and electrical connection may also be performed. The second electrode130aand the conductive material150may be made of different materials. Further, an electrical resistivity of the conductive material150is smaller than that of the second electrode130a, and in this way, an ohmic contact between the conductive material150and the first-type semiconductor layer112is enhanced. Nevertheless, the second electrode130aand the conductive material150may be made of the same material, and the second electrode130aand the conductive material150is integrally formed and manufactured in a same process, so that a process speed may be increased.

Further, with reference toFIG. 1Aagain, in a top view, a shape of the epitaxial structure110aand a shape of the second electrode130aare conformal, so that a pressure may be evenly applied during bonding. A shape of the first electrode120ais different from the shape of the second electrode130a. The second electrode130ais, for example, a closed ring electrode, and the first electrode120ais, for example, a block electrode. Herein, the second electrode130ais implemented as a rectangular ring electrode and surrounds the first electrode120a. The first electrode120amay be treated as an inner electrode, and the second electrode130amay be treated as an outer electrode. A ratio of a side length of the second electrode130ato a total side length of the epitaxial structure110ais greater than or equal to 0.2. If the above ratio is smaller than 0.2, a current may not be evenly distributed. Further, a ratio of an area of the second electrode130ato a total surface area of the epitaxial structure110ais greater than or equal to 0.2 and is smaller than or equal to 0.8. If the above ratio is excessively small, the epitaxial structure110aand the second electrode120amay not be uniformly distributed, and that a current may not be evenly distributed. In an embodiment, one of the first electrode120aand the second electrode130ais a P electrode, and the other one of the first electrode120aand the second electrode130ais a N electrode. Preferably, the first electrode120ais the N electrode, and the second electrode130ais the P electrode. In this way, the epitaxial structure110amay exhibit a large light emitting area and favorable light output efficiency, but the disclosure is not limited thereto.

Further, in a top view, the area of the second electrode130ais greater than an area of the first electrode120a, and the second electrode130amay act as a reflection layer. Preferably, a ratio of areas of the two vias115ato the area of the second electrode130ais smaller than or equal to 0.5. If the above ratio is excessively large, structural strength of the epitaxial structure110amay be decreased. Preferably, the ratio may be smaller than or equal to 0.3 and may be greater than or equal to 0.05, and within this range, the structural strength of the epitaxial structure110aand electrical connection efficiency of the second electrode130aand the first-type semiconductor layer112may both be satisfied. The first electrode120amay be equidistant or may not be equidistant from the second electrode130a. A minimum gap D is provided between the second electrode130aand the first electrode120a, the minimum gap D is greater than or equal to 0.5 microns and is smaller than or equal to 10 microns, and a current may be evenly distributed in this way. The first electrode120amay exhibit an equal width or an unequal width and has a first maximum width W1, and the second electrode130amay exhibit an equal width or an unequal width and has a second maximum width W2. The second maximum width W2is smaller than or equal to the first maximum width W1. In addition, any width W of the second electrode130ais smaller than a distance G between the second electrode130aand the first electrode120a, and a short is prevented from being generated in this way during a transferring and bonding procedure. Moreover, with reference toFIG. 1AandFIG. 1Btogether, an interval distance S is provided between the second electrode130aand a surrounding surface113aof the epitaxial structure110a, and the interval distance S is smaller than or equal to 5 microns and is greater than or equal to 0.5 microns, so that overflowing is prevented from occurring in the subsequent transferring and bonding procedure.

As shown inFIG. 1B, in this embodiment, the first electrode120aand the second electrode130aare coplanar. That is, a first surface122aof the first electrode120ais flush with a second surface132aof the second electrode130a. Further, the second electrode130aof this embodiment may be symmetrically disposed with respect to the geometric center C of the epitaxial structure110a. The geometric center C herein is a geometric center of the epitaxial structure110awhen being viewed from the top. In other embodiments, the surface111aof the epitaxial structure110amay also be viewed from the top to obtain a geometric center of the surface111a, as long as the second electrode130aand the first electrode120aare symmetrically disposed with respect to the epitaxial structure110a. From another perspective, the second electrode130ais line-symmetric with respect to a line of symmetry L of the geometric center C of the epitaxial structure110a. Alternatively, the second electrode130ais symmetric with respect to the line of symmetry L of the geometric center C of the epitaxial structure110aby 180 degrees. In addition, the second electrode130ais symmetrically disposed with respect to the first electrode120a, and the first electrode120ais symmetrically disposed with respect to the geometric center C of the epitaxial structure110a. In this embodiment, the second electrode130ais also symmetrically disposed with respect to the geometric center C1of the first electrode120a.

In short, since the second electrode130alocated outside the first electrode120aand surrounding the first electrode120ais symmetrically disposed with respect to the geometric center C of the epitaxial structure110a, in the subsequent transferring and bonding procedures, the first electrode120aand the second electrode130aare not required to be precisely aligned and may be evenly pressured. In this way, the micro light emitting diode100aprovided by this embodiment may exhibit favorable structural reliability and an increased process margin.

It should be noted that the reference numerals and a part of the contents in the previous embodiment are used in the following embodiments, in which identical reference numerals indicate identical or similar components, and repeated description of the same technical contents is omitted. Please refer to the descriptions of the previous embodiment for the omitted contents, which will not be repeated hereinafter.

FIG. 2Ais a schematic top view of a micro light emitting diode according to another embodiment of the disclosure.FIG. 2Bis a schematic cross-sectional view taken long a line B-B inFIG. 2A. With reference toFIG. 1B,FIG. 2A, andFIG. 2Btogether, a micro light emitting diode100bprovided by this embodiment is similar to the micro light emitting diode100ainFIG. 1B, and a difference therebetween lies in that: an epitaxial structure110bof this embodiment has only one via115b. An inner structure of the epitaxial structure110bis thus prevented from being damaged by vias, and the micro light emitting diode100bprovided by this embodiment accordingly has a large light output area. The second electrode130ahas a ring shape and conforms to an edge of the epitaxial structure110b. As such, weights of left and right sides of the epitaxial structure110bare balanced, and a pressure may thus be evenly applied to the micro light emitting diode100bin the transferring and bonding procedures.

FIG. 3Ais a schematic cross-sectional view of a micro light emitting diode according to another embodiment of the disclosure. With reference toFIG. 3AandFIG. 1Btogether, a micro light emitting diode100cprovided by this embodiment is similar to the micro light emitting diode100ainFIG. 1B, and a difference therebetween lies in that: a first electrode120band the second electrode130aare not coplanar in this embodiment. To be specific, a first surface122bof the first electrode120bis higher than the second surface132aof the second electrode130a, and a Young's modulus of the first electrode120bis smaller than a Young's modulus of the second electrode130a. Therefore, the first electrode120bmay act as a buffer during transferring, so that a pressure applied by a transfer head (not shown) to a center may be reduced during transferring.

FIG. 3Bis a schematic cross-sectional view of a micro light emitting diode according to another embodiment of the disclosure. With reference toFIG. 3BandFIG. 1Btogether, a micro light emitting diode100dprovided by this embodiment is similar to the micro light emitting diode100ainFIG. 1B, and a difference therebetween lies in that: the first electrode120aand a second electrode130bare not coplanar in this embodiment. To be specific, the first surface122aof the first electrode120ais lower than the second surface132aof the second electrode130b, and a Young's modulus of the first electrode120ais greater than a Young's modulus of the second electrode130b. Therefore, the second electrode130blocated outside may act as a buffer during transfer, so that accuracy of alignment performed by the transfer head (not shown) may be improved during transfer.

FIG. 4Ais a schematic top view of a micro light emitting diode according to another embodiment of the disclosure. With reference toFIG. 4AandFIG. 1Atogether, a micro light emitting diode100eprovided by this embodiment is similar to the micro light emitting diode100ainFIG. 1B, and a difference therebetween lies in that: in this embodiment, a shape of an epitaxial structure110eand a shape of a second electrode130eare conformal, and the second electrode130eis implemented as a triangular ring electrode and surrounds the first electrode120a.

FIG. 4Bis a schematic top view of a micro light emitting diode according to another embodiment of the disclosure. With reference toFIG. 4BandFIG. 1Atogether, a micro light emitting diode100fprovided by this embodiment is similar to the micro light emitting diode100ainFIG. 1B, and a difference therebetween lies in that: in this embodiment, a shape of an epitaxial structure110fand a shape of a second electrode130fare conformal, and the second electrode130fis implemented as an elliptical ring electrode and surrounds the first electrode120a.

FIG. 5Ais a schematic top view of a micro light emitting diode according to another embodiment of the disclosure. With reference toFIG. 5AandFIG. 1Atogether, a micro light emitting diode100gprovided by this embodiment is similar to the micro light emitting diode100ainFIG. 1B, and a difference therebetween lies in that: a second electrode130gprovided by this embodiment is an open ring electrode. Further, the second electrode130gincludes a plurality of electrode portions134gseparated from one another, and the electrode portions134gare arranged along a top-view shape of the epitaxial structure110gand surround the first electrode120aThrough theses separated electrode portions134g, good alignment accuracy during transferring may be provided. Moreover, when pressuring and heating are performed during transferring, overflowing to other positions may be prevented from occurring thanks to buffering provided by the second electrode130g.

FIG. 5Bis a schematic top view of a micro light emitting diode according to another embodiment of the disclosure. With reference toFIG. 5BandFIG. 5Atogether, a micro light emitting diode100hprovided by this embodiment is similar to the micro light emitting diode100ginFIG. 5A, and a difference therebetween lies in that: a second electrode130hprovided by this embodiment has only two electrode portions134hlocated on a diagonal line of an epitaxial structure110h. In this way, good alignment accuracy during transferring is provided, light shading is prevented during light output at an electrode side, and light output efficiency may also be enhanced.

FIG. 6Ais a schematic top view of a micro light emitting diode according to another embodiment of the disclosure. With reference toFIG. 6AandFIG. 5Atogether, a micro light emitting diode100iprovided by this embodiment is similar to the micro light emitting diode100ginFIG. 5A, and a difference therebetween lies in that: a second electrode130iprovided by this embodiment includes a first electrode portion134iand a second electrode portion136iseparated from each other. The first electrode portion134ihas a first electrical property, the second electrode portion136ihas a second electrical property, and the first electrical property is different from the second electrical property. In particular, the second electrical property of the second electrode portion136iis identical to an electrical property of the first electrode120a. In short, the second electrode130iis formed by two different electrical properties. As the second electrode130iis formed by two different electrical properties and is designed to be symmetrically disposed, good alignment accuracy during transferring may be provided, and different configuration areas may be provided for different electrical properties of an electrode according to needs, so that a current may be evenly distributed.

FIG. 6Bis a schematic top view of a micro light emitting diode according to another embodiment of the disclosure. With reference toFIG. 6BandFIG. 1Atogether, a micro light emitting diode100jprovided by this embodiment is similar to the micro light emitting diode100ainFIG. 1A, and a difference therebetween lies in that: in this embodiment, a first electrode120jincludes a plurality of point electrodes124j(four point electrodes124jare schematically shown), and a second electrode130jincludes a plurality of linear electrodes134j(two linear electrodes134jare schematically shown). The point electrodes124jare separated from one another and are rectangular block electrodes, and the linear electrodes134jare located at two opposite sides of the point electrodes124jand are rectangular strip electrodes. In this way, electrode uniformity is enhanced and light shading at a center is prevented from occurring.

FIG. 7Ais a schematic top view of a micro light emitting diode according to another embodiment of the disclosure. With reference toFIG. 7AandFIG. 1Atogether, a micro light emitting diode100kprovided by this embodiment is similar to the micro light emitting diode100ainFIG. 1A, and a difference therebetween lies in that: a second electrode130kprovided by this embodiment includes a plurality of electrode portions134kand a plurality of trace portions136k, and the electrode portions134kare respectively connected to the trace portions136k. Herein, a material of the electrode portions134kis different from a material of the trace portions136k, and an electrical resistance of a trace portion136kis smaller than an electrical resistance of an electrode portion134k, so that electrical connection efficiency may be improved. Herein, the material of the electrode portions134kis, for example, a transparent conductive material, and the material of the trace portions136kis, for example, metal. In another embodiment, the electrode portions134kand the trace portions136kare made of the same material or are integrally formed, which still belongs to the protection scope of the disclosure.

FIG. 7Bis a schematic top view of a micro light emitting diode according to another embodiment of the disclosure. With reference toFIG. 7BandFIG. 1Atogether, a micro light emitting diode100lprovided by this embodiment is similar to the micro light emitting diode100ainFIG. 1A, and a difference therebetween lies in that: a first electrode120lprovided by this disclosure includes an electrode portion124land a plurality of trace portions126l, and the trace portions126lare connected to the electrode portion124l. Herein, a material of the electrode portion124lis different from a material of the trace portions126l, and an electrical resistance of a trace portion126lis smaller than an electrical resistance of the electrode portion124l, so that electrical connection efficiency may be improved. Herein, the material of the electrode portion124lis, for example, a transparent conductive material, and the material of the trace portions126lis, for example, metal. In another embodiment, the electrode portion124land the trace portions126lare made of the same material or are integrally formed, which still belongs to the protection scope of the disclosure.

FIG. 7Cis a schematic top view of a micro light emitting diode according to another embodiment of the disclosure. With reference toFIG. 7CandFIG. 1Atogether, a micro light emitting diode100mprovided by this embodiment is similar to the micro light emitting diode100ainFIG. 1A, and a difference therebetween lies in that: a first electrode120mprovided by this embodiment is implemented as a mesh electrode. In this way, the first electrode120mwhose center is applied by a pressure may have an increased buffering space, so that overflowing to the second electrode130amay be prevented from occurring.

FIG. 8is a schematic cross-sectional view of a micro light emitting diode display device according to another embodiment of the disclosure. With reference toFIG. 8, in applications, a plurality of micro light emitting diodes100ainFIG. 1Bmay be transferred and bonded onto a connection pad210of a driver substrate200to form a micro light emitting diode display device10. To be specific, the first electrode120aand the second electrode130asurrounding the first electrode120aof each micro light emitting diode100aare not required to be precisely aligned and may be easily bonded onto the connection pad210of the driver substrate200. In addition, since the second electrode130ais symmetrically disposed with respect to the geometric center C of the epitaxial structure110a, during the transferring and bonding procedures, a pressure may be evenly applied to the first electrode120aand the second electrode130a.

In view of the foregoing, in the design of the micro light emitting diode provided by the disclosure, since the second electrode located outside the first electrode is symmetrically disposed with respect to the geometric center of the epitaxial structure, in the subsequent transferring and bonding procedures, the first electrode and the second electrode are not required to be precisely aligned and are evenly pressured. In this way, the micro light emitting diode provided by the disclosure may exhibit favorable structural reliability.