1. Field of Invention
The present invention relates to a method for forming a thin-film structure of a light-emitting device via nanoimprint and, more particularly, to a method for providing a light-emitting device with a thin-film structure of precursor such as a sol-gel material and spin-on glass via nanoimprint.
2. Conventional Methods
Conventionally, a method for transferring a pattern comprises a serial complex photolithography procedure, includes the steps of coating photo-resist, baking, exposure, development and etc. Furthermore, an expensive EUV stepper is demanded to achieve small line width of the pattern. It is however difficult for a conventional photolithography method to obtain a nano-scaled line width pattern, as well as the expansive EUV stepper may increase the process cost.
On the other hand, nanoimprint is proposed to transfer nanoscale patterns in an easier way. In nanoimprint, a mold, stamp or template is pressed on photo-resist so that the photo-resist is mechanically deformed for transferring a pattern. Once made, the mold can be used to form nanostructures repeatedly. Nanoimprint is therefore economic and promising.
Nanoimprint can be classified into two categories: hot embossing nanoimprint and UV-curing nanoimprint. In hot embossing nanoimprint, a mold is pressed on a polymer or resin that has been heated to a temperature higher than the glass transition temperature. The mold is removed from the polymer or resin after the polymer or resin is cooled. Thus, micro- to nanoscale patterns is replicated onto the polymer or resin. After a series of fabrication process, the patterns can be transferred onto substrate.
In UV-curing nanoimprint, a UV light source is used to expose the photo-resist via pressing a patterned transparent mold onto the photo-resist at room temperature and then induce a cross-linking reaction of the photo-resist. A series of fabrication process also demanded to transfer the patterns from the photo-resist to the substrate.
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Although the typical nanoimprints and step and flash photolithography can be used to form nano-scaled patterns on substrate in high throughput, the patterns is formed on the resist first and then transferred to the substrate by series procedures. They all require extra steps to ensure the fidelity of the patterns, as discussed above.
Another concerning of this invention is focusing on providing a light extraction structure of LED with an easier fabrication method without a complex photolithography process.
The refractive indexes of semiconductors used to make light-emitting diodes (“LED”s) are high. There is loss of light due to total reflection on the surface and at the interface. For example, the refractive index of GaP is 3.5, and only 19% of light is extracted because of total reflection.
LED manufacturers are working hard to reduce the cost of luminance per unit area so that the LED can be accepted in the market as the solid lighting source. Conventionally, a roughing surface texture is made on the surface of the LED or a reflecting metal mirror is added into the LED to increase the light extraction efficiency of the LED. The improvement of LED can be even bigger with the use of photonic crystal, for the photonic crystal not only enhances the light extraction but also modifies the lighting profile.
The effectiveness of the photonic crystals depends on the structures of photonic crystals, such as the pattern geometry, the size of diameter, the space between the holes etc. For example, a quasi-photonic crystal can be made to cast a specific lighting profile, such as a conic beam profile, of a LED.
However, it is difficult to transfer good fidelity periodic surface structure onto LED. The LED manufacturers are forced to make expensive light-emitting devices by sol-gel methods based on index-matching glue and beam-directing optical methods.
The present invention is therefore intended to obviate or at least alleviate the problems encountered in conventional methods.
It is the primary objective of the present invention to provide a method for forming a thin-film structure of a light-emitting device via nanoimprint.
To achieve the foregoing objective, the method includes the steps of providing a light-emitting element, providing a film on the light-emitting element via spin-coating a precursor on the light-emitting element, forming a pattern on the film by nanoimprint; and curing the film. Thus, the precursor is transformed into the demanded structure.
Other objectives, advantages and features of the present invention will be apparent from the following description referring to the attached drawings.
The present invention will be described via detailed illustration of several embodiments versus the prior art referring to the drawings wherein:
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The light-emitting element 10 is an LED in the first embodiment. The method according to the invention can however be used to make other semiconductor products such as liquid crystal display panels, solar cells and wafers.
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In practice, the material of the first semiconductor layer 31 and that of the second semiconductor layer 33 can be exchanged. That is, the first semiconductor layer 31 can be a p-type dosed semiconductor layer while the second semiconductor layer 33 can be an n-typed dosed semiconductor layer.
The first semiconductor layer 31 and the second semiconductor layer 33 often exhibit extremely high refractive indexes. Therefore, total reflection often occurs on the surface and at the interface, and causes loss of light. For example, the refractive index of GaP is 3.5, and only 19% of the light emitted from a light-emitting device including semiconductor layers made of GaP can be extracted because of the total reflection on the surface and at the interface.
To increase the light-extraction rate, the precursor 34 is made with the textured structure 340 to increase the transmittance of the light-emitting device 3. The textured structure 340 is made on the precursor layer 34 by nanoimprint. At first, precursor is coated on the second semiconductor layer 33 to form the precursor layer 34. Then, a mold is pressed on the precursor layer 34, thus transferring a pattern onto the precursor layer 34 from the mold. Finally, the precursor layer 34 is cured to form the textured structure 340.
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As mentioned above, in a method for making a thin-film structure via nanoimprint according to the present invention, a sol-gel material or SOG is used as precursor and nanoimprint is used to make a textured structure of an LED with a high light-extraction rate. The method of the present invention is simpler than the photolithography addressed in the Conventional methods that includes the steps of coating a photo-resist layer, baking, exposure, development and etc.
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The present invention has been described via the detailed illustration of the embodiments. Those skilled in the art can derive variations from the embodiments without departing from the scope of the present invention. Therefore, the embodiments shall not limit the scope of the present invention defined in the claims.
Number | Date | Country | Kind |
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098142283 | Dec 2009 | TW | national |