This Non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No(s). 095147368, filed in Taiwan, Republic of China on Dec. 18, 2006, the entire contents of which are hereby incorporated by reference.
1. Field of Invention
The invention relates to an electroluminescent device with high efficiency and a fabrication method thereof.
2. Related Art
A light emitting diode (LED) is a cold lighting element, which releases lights when energy released after electrons and holes are combined in a semiconductor material. According to different used materials, various monochromatic lights with different wavelengths are outputted. The LEDs may be mainly classified into a visible light LED and an invisible light (infrared) LED. Compared with the conventional lighting manner of a light bulb or lamp, the LED has advantages of power save, vibration resist, and high flicker speed, so that the LED has become an indispensable and important element in the daily life.
Referring to
Typically, an epitaxy substrate serves as the transparent substrate 11, and the transparent adhesive layer 12 is composed of an organic adhesive material. Because the thermal conductivity coefficients of the epitaxy substrate and the organic adhesive material are low, a better heat dissipating path for the LED element 10 cannot be provided. Thus, the accumulated heat generated when the LED device 1 is operating cannot be easily dissipated, and the lighting efficiency of the LED device 1 is influenced.
Because the development of the LED in the current stage still has the problem of too-low lighting efficiency, the manufacturers have paid their attention to take out the photons generated in the LED element 10 effectively, and to reduce the nonessential heat generated by the continuous reflection of the photons in the LED element 10. On the other hand, the manufacturers also pay their attention to solve the problem of the heat dissipation in the LED element 10 so that the operating temperature of the overall LED device 1 can be lowered, and the lighting efficiency of the LED device 1 can be finally enhanced.
In view of the foregoing, the present invention is to provide an electroluminescent device and a fabrication method thereof capable of effectively enhancing the current dispersing efficiency and effectively reducing the heat.
To achieve the above, the present invention discloses a fabrication method for an electroluminescent device. The fabrication method includes the steps of providing a plate, forming at least one light emitting diode (LED) element on the plate, forming a patterned transparent conductive layer on the LED element, forming a reflection layer on the patterned transparent conductive layer, adhering a substrate to the reflection layer, and removing the plate. Herein, the LED element includes a first semiconductor layer, an electroluminescent layer and a second semiconductor layer arranged in order, and the first semiconductor layer is formed on the plate.
To achieve the above, the present invention also discloses an electroluminescent device including a substrate, a reflection layer, at least one LED element, a first contact electrode and a second contact electrode. The reflection layer is formed on the substrate, and the patterned transparent conductive layer is disposed on the reflection layer. The LED element is formed on the patterned transparent conductive layer and includes a first semiconductor layer, an electroluminescent layer and a second semiconductor layer arranged in order. The second semiconductor layer is disposed on the patterned transparent conductive layer and the reflection layer. The first contact electrode is electrically connected to the first semiconductor layer. The second contact electrode is electrically connected to the second semiconductor layer.
As mentioned above, the electroluminescent device and the fabrication method thereof according to the present invention have the following features. Firstly, a patterned transparent conductive layer, which may be formed with a plurality of island patterns by way of, for example, etching, is provided in the electroluminescent device. Thus, an LED element may have a uniform current distribution due to the patterns of the patterned transparent conductive layer so that the current blocking phenomenon can be effectively avoided. In addition, the reflection layer is provided so that a good ohmic contact between the patterned transparent conductive layer and the reflection layer is formed, and an interface for scattering and reflecting light is provided so that the external light acquiring and lighting efficiency can be effectively enhanced. In addition, the substrate and the reflection layer have the high thermal conductivity, the heat dissipation of the LED element can be enhanced more effectively as compared with the prior art.
The invention will become more fully understood from the detailed description given herein below illustration only, and thus is not limitative of the present invention, and wherein:
The present invention will be apparent from the following detailed description, which proceeds with reference to the accompanying drawings, wherein the same references relate to the same elements.
Referring to
In this embodiment, the substrate 21 has a high thermal conductivity coefficient and is made of the material selecting from one of the group consisting of silicon (Si), gallium arsenide (GaAs), gallium phosphide (GaP), silicon carbide (SiC), boron nitride (BN), aluminum nitride (AlN), aluminum (Al), copper (Cu) and combinations thereof.
The reflection layer 22 is formed on the substrate 21, and the patterned transparent conductive layer 23 is disposed on the reflection layer 22. As shown in
In this embodiment, the material of the reflection layer 22 is a material with high reflectivity, and the concave-convex surface of the reflection layer 22 provides good light reflecting and scattering effects so that external light acquiring efficiency can be enhanced. The reflection layer 22 may be made of platinum (Pt), gold (Au), silver (Ag), palladium (Cr), nickel (Ni), platinum (Pd), titanium (Ti), aluminum (Al) or combinations thereof. In addition, a good ohmic contact is formed through the connection between the reflection layer 22 and the transparent conductive layer 23 in this embodiment so that the resistance value can be reduced and the lighting efficiency of the electroluminescent device 2 can be thus increased. Further, the transparent conductive layer 23 also serves as a bonding layer, as shown in
The LED element 24 is formed on the patterned transparent conductive layer 23 and includes a first semiconductor layer 241, an electroluminescent layer 242 and a second semiconductor layer 243. The second semiconductor layer 243, the electroluminescent layer 242 and the first semiconductor layer 241 are sequentially formed on the patterned transparent conductive layer 23 and the reflection layer 22. In this embodiment, the LED element 24 may be formed on the patterned transparent conductive layer 23 with independent island patterns. Herein, the second semiconductor layer 243 is in contact with the patterned transparent conductive layer 23 and the reflection layer 22, as shown in
As mentioned hereinabove, the first semiconductor layer 241 is an n-type semiconductor layer and the second semiconductor layer 243 is a p-type semiconductor layer in this non-limitative embodiment. Of course, the first semiconductor layer 241 and the second semiconductor layer 243 may be the applications of the n-type semiconductor layer and the p-type semiconductor layer, and may be exchanged according to the actual requirement.
The first contact electrode 25 is electrically connected to the first semiconductor layer 241, and the second contact electrode 26 is electrically connected to the second semiconductor layer 243. Descriptions will be made in detail according to an example, in which the first contact electrode 25 and the second contact electrode 26 are located at the same side of the substrate 21. As shown in
In addition to the first contact electrode 25 formed on the first semiconductor layer 241, a rough structure or an anti-reflection layer 245 may be disposed on a light outputting surface 244 of the LED element 24 (i.e., on a position at the side of the first semiconductor layer 241 without the first contact electrode 25) for guiding out lights so as to effectively enhance light outputting efficiency, as shown in
In addition, as shown in
As mentioned hereinabove, the electroluminescent device 2 of this embodiment uses the insulating layer 28, the adhesive layer 27 and the substrate 21, each of which has characteristic of high thermal conductivity coefficient, so that the operating temperature of the LED element 24 can be sufficiently decreased. Also, the electroluminescent device 2 has the advantages of withstanding high current and may be fabricated to have a large area so that the overall lighting efficiency of the electroluminescent device 2 is greatly enhanced.
In order to make the content of the electroluminescent device 2 of the present invention clearer, the fabrication method of the electroluminescent device according to the preferred embodiment of the invention will be described with reference to
In the step S1, the plate 20 is provided. The plate 20 is a temporary plate used when the LED element 24 is being fabricated. The material of the plate 20 includes, for example, aluminum oxide (Al2O3). After the plate 20 is properly cleaned, the epitaxial layer growth of the LED element 24 may be performed subsequently.
In the step S2, the LED element 24 is formed on the plate 20. That is, the first semiconductor layer 241, the electroluminescent layer 242 and the second semiconductor layer 243 sequentially grow on the plate 20. In this non-limitative embodiment the first semiconductor layer 241 may be an n-type semiconductor layer, and the second semiconductor layer 243 may be a p-type semiconductor layer.
In the step S3, the patterned transparent conductive layer 23 is formed on the LED element 24. In this embodiment, a material, such as indium tin oxide, cadmium tin oxide, antimomy tin oxide, beryllium (Be), germanium (Ge), nickel (Ni), aurum (Au) or combinations thereof, is deposited on the second semiconductor layer 243 of the LED element 24. Then, the deposited material is patterned using a photo lithography process and an etching process, wherein the etching process may be implemented by using dry-etching or wet-etching process in conjunction with the physical etching and/or chemical etching processes. In this embodiment, the patterned transparent conductive layer 23 may include a plurality of island patterns. The etching step may be terminated according to different etching depths. For example, the etching step may be terminated on a position of the patterned transparent conductive layer 23 with an arbitrary depth so that the patterned transparent conductive layer 23 has the continuous island pattern structures, as shown in
In the step S4, the reflection layer 22 is formed on the patterned transparent conductive layer 23. In this embodiment, a material with high reflectivity such as platinum (Pt), aurum (Au), silver (Ag), Chromium (Cr), nickel (Ni), palladium (Pd), titanium (Ti), aluminum (Al) or combinations thereof, is deposited on the patterned transparent conductive layer 23. The reflection layer 22 formed on the patterned transparent conductive layer 23 has a concave-convex surface according to the patterned structure of the patterned transparent conductive layer 23 and is in ohmic contact with the patterned transparent conductive layer 23. Thus, the overall lighting efficiency can be effectively enhanced by increasing the external light acquiring efficiency and decreasing the resistance value.
The fabrication method may further include a step S41 after the step S4. In the step S41, an insulating layer 28 is formed over the reflection layer 22. In this embodiment the material of the insulating layer 28 is an insulating with a high thermal conductivity coefficient, such as aluminum nitride or silicon carbide, and the insulating layer 28 is formed over the reflection layer 22 by way of reactive sputtering, non-reactive sputtering, high-temperature nitriding and high-temperature powder sintering.
In the step S5, the substrate 21 is adhered to the reflection layer 22. In this embodiment, the substrate 21 is adhered to the insulating layer 28 through an adhesive layer 27. Herein, the adhesive layer 27 may be coated on the reflection layer 22/insulating layer 28 or the substrate 21, and then the substrate 21 is adhered to the insulating layer 28. In addition, the adhesive layer 27 may partially cover or completely cover the surface of the reflection layer 22/insulating layer 28. Each of the substrate 21 and the adhesive layer 27 has high thermal conductivity, and the material of the substrate 21 is selected from at least one of the group consisting of silicon (Si), gallium arsenide (GaAs), gallium phosphide (GaP), silicon carbide (SiC), Boron Nitride (BN), aluminum nitride (AlN), aluminum (Al), copper (Cu) and combinations thereof The material of the adhesive layer 27 may be a silver paste, a tin paste, a tin-silver paste, or any other conductive adhesive material, such as alloy, metal or a eutectic bonding material, and may include a leaded or unleaded conductive adhesive material.
The fabrication method may further include, after the step S5, a step S51 of turning over the electroluminescent device to remove the temporary plate subsequently.
In the step S6, the temporary plate 20 for the growth of the LED element 24 is removed. In this embodiment, the step of turning over the electroluminescent device may be performed after the step S6.
The fabrication method may further include, after the step S6, a step S7 of forming a first contact electrode 25 electrically connected to the first semiconductor layer 241. In this embodiment, the first contact electrode 25 is formed on one side of the first semiconductor layer 241. In the step S7, a rough structure or an anti-reflection layer 245 is formed on a position at the side of the first semiconductor layer 241 without the first contact electrode 25 so that the opportunity of guiding out the light may be increased.
In addition, the fabrication method may further include, after the step S6, a step S7′ of removing a portion of the LED element 24, as shown in
In addition, the fabrication method may further include, after the step S7′, a step S71′ of removing a portion of the patterned transparent conductive layer 23 according to different island patterns of the patterned transparent conductive layer 23. Then, the second contact electrode 26 is formed on the removed portion (step S8), and electrically connected to the second semiconductor layer 243.
In summary, the electroluminescent device and the fabrication method thereof according to the invention have the following features. Firstly, a patterned transparent conductive layer, which may be formed with a plurality of island patterns by way of, for example, etching, is provided in the electroluminescent device. Thus, an LED element may have a uniform current distribution due to the patterns of the patterned transparent conductive layer so that the current blocking phenomenon can be effectively avoided. Also, the reflection layer is provided so that a good ohmic contact between the patterned transparent conductive layer and the reflection layer is formed, and an interface for scattering and reflecting light is provided so that the external light acquiring and lighting efficiency can be effectively enhanced. In addition, the substrate and the reflection layer have high thermal conductivity, the heat dissipation of the LED element can be enhanced more effectively as compared with the prior art.
Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternative embodiments, will be apparent to persons skilled in the art. It is, therefore, contemplated that the appended claims will cover all modifications that fall within the true scope of the invention.
Number | Date | Country | Kind |
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095147368 | Dec 2006 | TW | national |