LED ARRAY FORMED BY INTERCONNECTED AND SURROUNDED LED CHIPS
A light emitting diode array includes a first light emitting diode having a first electrode and a second light emitting diode having a second electrode. The first and second light emitting diodes are separated. A first polymer layer is positioned between the light emitting diodes. An interconnect located at least partially on the first polymer layer connects the first electrode to the second electrode. A permanent substrate is coupled to the light emitting diodes. The permanent substrate is coupled to the side of the light emitting diodes with the interconnect. A second polymer layer at least partially encapsulates the side of the light emitting diodes opposite the permanent substrate (the side opposite the interconnect).
Latest NCKU RESEARCH AND DEVELOPMENT FOUNDATION Patents:
- Boost converter with fast transient response
- All-MOSFET voltage reference circuit with stable bias current and reduced error
- Doppler radar sensor with bondwire interconnection
- Reliability based keyframe switching system and method adaptable to ICP
- Single-ended successive approximation register analog-to-digital converter
1. Field of the Invention
The present invention relates to a semiconductor light emitting component, and more particularly to a light emitting diode (LED) array and a method for manufacturing the LED array.
2. Description of Related Art
Epitaxial structure 104 is usually made of GaN-based semiconductor material or InGaN-based semiconductor material. During the epitaxy growth process, GaN-based semiconductor material or InGaN-based semiconductor material epitaxially grows up from epitaxial substrate 102 to form n-type doped layer 108 and p-type doped layer 110. When the electrical energy is applied to epitaxial structure 104, light emitting portion 112 at junction of n-type doped layer 108 and p-type doped layer 110 generates an electron-hole capture phenomenon. As a result, the electrons of light emitting portion 112 will fall to a lower energy level and release energy with a photon mode. For example, light emitting portion 112 is a multiple quantum well (MQW) structure capable of restricting a spatial movement of the electrons and the holes. Thus, a collision probability of the electrons and the holes is increased so that the electron-hole capture phenomenon occurs easily, thereby enhancing light emitting efficiency.
Electrode unit 106 includes first electrode 114 and second electrode 116. First electrode 114 and second electrode 116 are in ohmic contact with n-type doped layer 108 and p-type doped layer 110, respectively. The electrodes are configured to provide electrical energy to epitaxial structure 104. When a voltage is applied between first electrode 114 and second electrode 116, an electric current flows from the second electrode to the first electrode through epitaxial structure 104 and is horizontally distributed in epitaxial structure 104. Thus, a number of photons are generated by a photoelectric effect in epitaxial structure 104. Horizontal light emitting diode 100 emits light from epitaxial structure 104 due to the horizontally distributed electric current.
A manufacturing process of horizontal light emitting diode 100 is simple. However, horizontal light emitting diodes can cause several problems such as, but not limited to, current crowding problems, non-uniformity light emitting problems, and thermal accumulation problems. These problems may decrease the light emitting efficiency of the horizontal light emitting diode and/or damage the horizontal light emitting diode.
To overcome some of the above mentioned problems, vertical light emitting diodes have been developed.
In recent years, wide-bandgap nitride-based LEDs with wavelength range from the ultraviolet to the shorter wavelength parts of the visible spectra have been developed. LED devices can be applied to new display technologies such as traffic signals, liquid crystal display TVs, and backlights of cell phones. Due to the lack of native substrates, GaN films and related nitride compounds are commonly grown on sapphire wafers. Conventional LEDs (such as those described above) are inefficient because the photons are emitted in all directions. A large fraction of light emitted is limited in the sapphire substrate and cannot contribute to usable light output. Moreover, the poor thermal conductivity of the sapphire substrate is also a problem associated with conventional nitride LEDs. Therefore, freestanding GaN optoelectronics without the use of sapphire is a desirable technology that solves this problem. The epilayer transferring technique is a well-known innovation in achieving ultrabright LEDs. Thin-film p-side-up GaN LEDs with highly reflective reflector on silicon substrate made by a laser lift-off (LLO) technique, combined with n-GaN surface roughening, have been established as an effective tool for nitride-based heteroepitaxial structures to eliminate the sapphire constraint. The structure is regarded as a good candidate for enhancing the light extraction efficiency of GaN-based LEDs. However, this technique is also subject to the electrode-shading problem. The emitted light is covered and absorbed by the electrodes, which results in reduced light efficiency.
Thin-film n-side-up devices GaN LEDs with interdigitated imbedded electrodes may improve light emission by reducing some of the electrode-shading problem. While thin-film n-side-up devices GaN LEDs provide enhanced properties compared to thin-film p-side-up devices GaN LEDs, there is still a need for improved structures and processes for making both p-side-up and n-side-up devices.
Furthermore, horizontal light emitting diode 100 and vertical light emitting diode 200 typically are packaged in single-die manners, which does not facilitate manufacturing a large area light source. In view of the problems discussed above with reference to
In certain embodiments, a light emitting diode array includes a first light emitting diode having a first electrode and a second light emitting diode having a second electrode. The second light emitting diode is separated from the first light emitting diode by a gap. A first polymer layer fills the gap between the first light emitting diode and the second light emitting diode. The first polymer layer may partially cover at least a portion of the surface of the first light emitting diode and at least a portion of the surface of the second light emitting diode. An interconnect is located at least partially on the first polymer layer that connects the first electrode to the second electrode. A permanent substrate is coupled to a side of the light emitting diodes with the interconnect. A second polymer layer at least partially encapsulates a side of the light emitting diodes opposite the permanent substrate.
In certain embodiments, a method for forming a light emitting diode array includes forming a first light emitting diode and a second light emitting diode separated by a gap on a temporary substrate. The gap between the light emitting diodes is filled with a first polymer layer. The first polymer layer covers at least a portion of the surface of the first light emitting diode and at least a portion of the surface of the second light emitting diode. An interconnect is formed between a first electrode on the first light emitting diode and a second electrode on the second light emitting diode. The interconnect is formed at least partially on the first polymer layer. A permanent substrate is coupled to a side of the light emitting diodes with the interconnect. The temporary substrate is removed from the light emitting diodes. The side of the light emitting diodes from which the temporary substrate has been removed is at least partially encapsulated in a second polymer layer.
In certain embodiments, a light emitting diode array includes a first light emitting diode having a first electrode and a second light emitting diode having a second electrode. The second light emitting diode is separated from the first light emitting diode by a gap. A first polymer layer fills the gap between the first light emitting diode and the second light emitting diode. The first polymer layer may partially cover at least a portion of the surface of the first light emitting diode and at least a portion of the surface of the second light emitting diode. An interconnect is located at least partially on the first polymer layer that connects the first electrode to the second electrode. A permanent substrate is coupled to a side of the light emitting diodes with the interconnect. A second polymer layer that at least partially encapsulates a side of the light emitting diodes opposite the interconnect.
Features and advantages of the methods and apparatus of the present invention will be more fully appreciated by reference to the following detailed description of presently preferred but nonetheless illustrative embodiments in accordance with the present invention when taken in conjunction with the accompanying drawings in which:
While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. The drawings may not be to scale. It should be understood that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but to the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims.
DETAILED DESCRIPTION OF EMBODIMENTSIn the context of this patent, the term “coupled” means either a direct connection or an indirect connection (e.g., one or more intervening connections) between one or more objects or components.
Referring to
First, an LED structure (not shown) is formed on first substrate 314. Next, a separating process (e.g., dicing, cutting, etching, or lasing) is performed to separate the LED structure into a number of LEDs 304 on first substrate 314, as shown in
As shown in
Next, as shown in
In certain embodiments, after the polymer removal process and anodes 308 and cathodes 310 are exposed, a surface hydrophilic modification is performed on the polymer surface (e.g., oxygen plasma) to transform the originally hydrophobic surface into a hydrophilic surface. Therefore, a subsequently formed metal-based interconnect can have improved adhesion to first polymer layer 502.
Subsequently, as shown in
Following formation of interconnects 312 on first polymer layer 502, adhesive layer 508 may be formed over the interconnects and the first polymer layer, as shown in
Adhesive layer 508 may be used to bond LED array 500 to second substrate 510, as shown in
Following bonding to second substrate 510, first substrate 314 is removed from LED array 500, as shown in
After exposure of the surface of LED array 500 opposite interconnects 312 and first polymer layer 502, external electrical connections (either vertical or horizontal) may be made to one or more of LEDs 304 (e.g., the outermost LEDs, rightmost LED 304A and leftmost LED 304D, as depicted in
Following formation of either external vertical connections 516 or external horizontal connections 518, the exposed surface of LED array 500 (e.g., the surface of the LED array with the external connections) is encapsulated in a second polymer layer.
In certain embodiments, the exposed surface of LED array 500 is encapsulated such that substantially the entirety of the exposed surface of the LED array is encapsulated (covered) by second polymer layer 520 (e.g., no portions of the surface of LED array 500 remain exposed). In certain embodiments, second polymer layer 520 encapsulates the exposed surface of LED array 500 while leaving at least part of the external interconnects (e.g., external vertical connections 516 or external horizontal connections 518) exposed such that external connections can be made to the LED array.
In certain embodiments, second polymer layer 520 includes polymer material such as, but not limited to, transparent silicone or a combination of silicone and phosphor. In some embodiments, second polymer layer 520 includes polymer material the same as the polymer material of first polymer layer 502. For example, second polymer layer 520 can be made of a photoresist material, for example, polymethylglutarimide (PMGI) or SU-8. Second polymer layer 520 isolates (encapsulates) LED array 500 from the ambient environment. This encapsulation protects LED array 500 from mechanical damage and environmental influence. In certain embodiments, the encapsulation enhances the light extraction through the curved dome of second polymer layer 520 (e.g., a hemispherical transparent dome), which has a higher refractive index than air.
Separated (isolated) LEDs 304A, 304B, 304C may be formed by depositing epitaxial layers across the substrate and subsequently separating (or isolating) sections of the deposited layers to form the separated (isolated) LEDs. A dicing or cutting saw or a laser may be used to separate the LEDs and form separated LEDs 304A, 304B, 304C on first substrate 314. In some embodiments, an etching process is used to separate the LEDs and form separated LEDs 304A, 304B, 304C on first substrate 314.
The epitaxial layers may be formed on first substrate 314 using conventional epitaxial techniques known in the art such as metal organic chemical vapor deposition (MOCVD). In certain embodiments, the epitaxial layers include gallium nitride (GaN) layers formed in multiple deposition processing steps to form GaN LEDs. For example, the epitaxial layers may include a light emitting layer (e.g., a multiple quantum well layer) sandwiched between n-type and p-type doped layers.
Following formation of separated LEDs 304A, 304B, 304C on first substrate 314, the upper surface of the LEDs may be bonded to second substrate 602 with first adhesive layer 604, as shown in
Following bonding to second substrate 602, first substrate 314 is removed from LEDs 304A, 304B, and 304C, as shown in
After removal of first substrate 314, third substrate 606 may be bonded to LEDs 304A, 304B, and 304C with second adhesive layer 608, as shown in
Following bonding of third substrate 606 to LEDs 304A, 304B, and 304C, first adhesive layer 604 and second substrate 602 may be removed from the LEDs, as shown in
After formation of first polymer layer 502, series interconnects 312 are formed on top of first polymer layer 502 to connect the anodes and cathodes of adjacent LEDs. Because of the relatively smooth surface profile of first polymer layer 502, the subsequently formed metal-based interconnects 312 may have thin and smooth profiles. The thin and smooth profiles may provide improved performance and reliability as compared to the conventional interconnect with complex profiles and sharp corners depicted in
Following formation of interconnects 312 on first polymer layer 502, the interconnects and the first polymer layer may be encapsulated in second polymer layer 520, as shown in
In some embodiments, portions of one or more LEDs (e.g., outermost LEDs 304A and 304C) are not encapsulated to allow for external connections (e.g., vertical or horizontal external connections) to LED array 600 through the selected LEDs. External connections may be made to the selected LEDs as described herein. In some embodiments, external connections are made before encapsulating LED array 600 in second polymer layer 520.
LEDs 304A, 304B, 304C may be formed by depositing epitaxial layers across first substrate 314. The epitaxial layers may be formed on first substrate 314 using conventional epitaxial techniques known in the art such as metal organic chemical vapor deposition (MOCVD). In certain embodiments, the epitaxial layers include gallium nitride (GaN) layers formed in multiple deposition processing steps to form GaN LEDs. For example, the epitaxial layers may include a light emitting layer (e.g., a multiple quantum well layer) sandwiched between n-type and p-type doped layers.
As shown in
Following formation of LEDs 304A, 304B, 304C on first substrate 314, the upper surface of the LEDs may be bonded to second substrate 602 with first adhesive layer 604, as shown in
Following bonding to second substrate 602, first substrate 314 is removed from LEDs 304A, 304B, 304C, as shown in
After removal of the first substrate, third substrate 606 may be bonded to LEDs 304A, 304B, 304C with second adhesive layer 608, as shown in
After bonding of third substrate 606 to LEDs 304A, 304B, 304C, first adhesive layer 604 and second substrate 602 are removed from the LEDs, as shown in
After removal of first adhesive layer 604 and second substrate 602 from LEDs 304A, 304B, 304C, the epitaxial layers and third substrate 606 are separated along the dashed lines (shown in
After separating LEDs 304A, 304B, 304C, polymer material is deposited into gaps 306 and on LEDs 304A, 304B, and 304C to form first polymer layer 502, as shown in
After formation of first polymer layer 502, series interconnects 312 are formed on top of first polymer layer 502 to connect the anodes and cathodes of adjacent LEDs. Following formation of interconnects 312 on first polymer layer 502, the interconnects and the first polymer layer may be encapsulated in second polymer layer 520, as shown in
In some embodiments, portions of one or more LEDs (e.g., outermost LEDs 304A and 304C) are not encapsulated to allow for external connections (e.g., vertical or horizontal external connections) to LED array 600 through the selected LEDs. External connections may be made to the selected LEDs as described herein. In some embodiments, external connections are made before encapsulating LED array 600 in second polymer layer 520. Second polymer layer 520 isolates (encapsulates) LED array 600 from the ambient environment. This encapsulation protects LED array 600 from mechanical damage and environmental influence. In certain embodiments, the encapsulation enhances the light extraction through the curved dome of second polymer layer 520 (e.g., a hemispherical transparent dome), which has a higher refractive index than air.
It is to be understood the invention is not limited to particular systems described which may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting. As used in this specification, the singular forms “a”, “an” and “the” include plural referents unless the content clearly indicates otherwise. Thus, for example, reference to “a device” includes a combination of two or more devices and reference to “a material” includes mixtures of materials.
Further modifications and alternative embodiments of various aspects of the invention will be apparent to those skilled in the art in view of this description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the general manner of carrying out the invention. It is to be understood that the forms of the invention shown and described herein are to be taken as the presently preferred embodiments. Elements and materials may be substituted for those illustrated and described herein, parts and processes may be reversed, and certain features of the invention may be utilized independently, all as would be apparent to one skilled in the art after having the benefit of this description of the invention. Changes may be made in the elements described herein without departing from the spirit and scope of the invention as described in the following claims.
Claims
1. A light emitting diode array, comprising:
- a first light emitting diode comprising a first electrode;
- a second light emitting diode comprising a second electrode, wherein the second light emitting diode is separated from the first light emitting diode by a gap;
- a first polymer layer positioned between the first light emitting diode and the second light emitting diode;
- an interconnect located at least partially on the first polymer layer that connects the first electrode to the second electrode;
- a permanent substrate coupled to a side of the light emitting diodes comprising the interconnect; and
- a second polymer layer that at least partially encapsulates a side of the light emitting diodes opposite the permanent substrate.
2. The array of claim 1, further comprising a third polymer layer that bonds the permanent substrate to the light emitting diodes.
3. The array of claim 1, wherein the first light emitting diode and the second light emitting diode are surrounded by polymer.
4. The array of claim 1, further comprising an external interconnect coupled to a third electrode on at least one of the light emitting diodes, wherein at least a portion of the external interconnect is not encapsulated by the second polymer layer.
5. The array of claim 1, wherein the permanent substrate comprises a reflective layer.
6. The array of claim 1, wherein the permanent substrate comprises an insulating layer.
7. The array of claim 1, wherein the first polymer layer comprises photoresist.
8. The array of claim 1, wherein the second polymer layer comprises silicone.
9. The array of claim 1, wherein the array comprises an n-side up array.
10. A method for forming a light emitting diode array, comprising:
- forming a first light emitting diode and a second light emitting diode on a temporary substrate;
- forming a first polymer layer between the first light emitting diode and the second light emitting diode;
- forming an interconnect between a first electrode on the first light emitting diode and a second electrode on the second light emitting diode, wherein the interconnect is formed at least partially on the first polymer layer;
- coupling a permanent substrate to a side of the light emitting diodes comprising the interconnect;
- removing the temporary substrate from the light emitting diodes; and
- at least partially encapsulating the side of the light emitting diodes from which the temporary substrate has been removed in a second polymer layer.
11. The method of claim 10, further comprising bonding the permanent substrate to the light emitting diodes with an adhesive layer.
12. The method of claim 10, wherein the first light emitting diode and the second light emitting diode are separated by a gap, and the method further comprising forming the first polymer layer by covering the light emitting diodes and filling the gap between the diodes with a polymer material, patterning the polymer material, and removing portions of the polymer material according to the pattern to form the first polymer layer.
13. The method of claim 10, further comprising forming an external interconnect to a third electrode on at least one of the light emitting diodes, wherein at least a portion of the external interconnect is not encapsulated by the second polymer layer.
14. The method of claim 10, wherein the temporary substrate is temporarily bonded to the light emitting diodes with an adhesive layer, and wherein the adhesive layer is removed when the temporary substrate is removed.
15. The method of claim 10, wherein the permanent substrate comprises a reflective layer.
16. The method of claim 10, wherein the permanent substrate comprises an insulating layer.
17. The method of claim 10, wherein the first polymer layer comprises photoresist.
18. The method of claim 10, wherein the second polymer layer comprises silicone.
19. A light emitting diode array, comprising:
- a first light emitting diode comprising a first electrode;
- a second light emitting diode comprising a second electrode, wherein the second light emitting diode is separated from the first light emitting diode;
- a first polymer layer positioned between the first light emitting diode and the second light emitting diode;
- an interconnect located at least partially on the first polymer layer that connects the first electrode to the second electrode;
- a permanent substrate coupled to a side of the light emitting diodes comprising the interconnect; and
- a second polymer layer that at least partially encapsulates a side of the light emitting diodes opposite the interconnect.
20. The array of claim 19, further comprising a third polymer layer that bonds the permanent substrate to the light emitting diodes.
21. The array of claim 19, wherein the first light emitting diode and the second light emitting diode are surrounded by polymer.
22. The array of claim 19, further comprising an external interconnect coupled to a third electrode on at least one of the light emitting diodes, wherein at least a portion of the external interconnect is not encapsulated by the second polymer layer.
23. The array of claim 19, wherein the permanent substrate comprises a reflective layer.
24. The array of claim 19, wherein the permanent substrate comprises an insulating layer.
25. The array of claim 19, wherein the first polymer layer comprises photoresist.
26. The array of claim 19, wherein the second polymer layer comprises silicone.
27. The array of claim 19, wherein the array comprises an n-side up array.
Type: Application
Filed: Nov 2, 2011
Publication Date: Aug 2, 2012
Applicants: NCKU RESEARCH AND DEVELOPMENT FOUNDATION (Tainan City), PHOSTEK, INC. (Taipei City)
Inventors: Ray-Hua Horng (Taichung City), Yi-An Lu (Chiayi City), Heng Liu (Sunnyvale, CA)
Application Number: 13/287,542
International Classification: H01L 33/08 (20100101);