LED devices

Details LED devices LED devices

2002-03-14

2003-12-09

Vu, David (Department: 2821)

Electric lamp and discharge devices

With luminescent solid or liquid material

Solid-state type

C362S329000

Reexamination Certificate

active

06661167

ABSTRACT:

BACKGROUND OF INVENTION
The present invention relates to optoelectronic devices such as light emitting diode (LED) devices.
Light emitting diode chips or “LED chips” include thin layers of semiconductor material of two opposite conductivity types, referred to as p-type and n-type. The layers are disposed in a stack, one above the other, with one or more layers of n-type material in one part of the stack and one or more layers of p-type material in the other part of the stack. For example, the various layers may be deposited in sequence on a substrate to form a wafer. The wafer is then cut apart to form individual dies or chips which constitute separate LEDs. The junction between the p-type and n-type material may include directly abutting p-type and n-type layers, or may include one or more intermediate layers which may be of any conductivity type or which may have no distinct conductivity type. In operation, electric current passing through the diode is carried principally by electrons in the n-type layers and by electron vacancies or “holes” in the p-type layers. The electrons and holes move in opposite directions toward the junction and recombine with one another at the junction. Energy released by electron-hole recombination is emitted as light. As used in this disclosure, the term “light” includes radiation in the infrared and ultraviolet wavelength ranges, as well as radiation in the visible range. The wavelength of the light depends on factors including the composition of the semiconductor materials and the structure of the junction.
Commonly, electrodes are connected to the n-type and p-type layers near the top and bottom of the stack. The materials in the electrodes are selected to provide low-resistance interfaces with the semiconductor materials. The electrodes, in turn, are provided with pads suitable for connection to wires or other conductors which carry current from external sources. The pad associated with each electrode may be a part of the electrode, having the same composition and thickness of the electrode, or may be a distinct structure which differs in thickness, composition, or both from the electrode itself.
Some LED chips have electrodes on the bottom surface of the bottom semiconductor layer. For example, the various layers may be deposited in sequence on an electrically conductive substrate, and the substrate may be left in place on the bottom surface to act as a bottom electrode. However, LED chips formed from certain semiconductor materials normally use nonconductive substrates to promote proper formation of the semiconductor layers. The nonconductive substrate typically is left in place, so that an electrode cannot be readily provided on the bottom surface of the bottom layer. For example, gallium nitride-based materials such as GaN, AlGaN, InGaN and AlInGaN are used to form LED chips emitting light in various wavelength ranges including blue and ultraviolet. These materials typically are grown on insulating substrates such as sapphire or alumina.
LED chips incorporating an insulating substrate often include a bottom electrode at a location on the stack above the substrate but below the junction. Typically, the upper layer or layers of the stack are removed after formation of the stack in a region covering part of the area of each die, so as to provide an upwardly-facing lower electrode surface on a layer at or near the bottom of the stack in each die. This leaves a region referred to as a “mesa” projecting upwardly from the lower electrode surface and covering the remaining area of the die. The area of the die occupied by the lower electrode surface typically does not emit light. It is desirable to keep the horizontal extent of this inactive area as small as possible.
The LED chip and a pair of electrical contacts are typically packaged in a material that is transparent to the light emitted from the LED chip to provide an LED device, allowing light to emerge from the package. The packaging material is typically a thermoset material, such as epoxy or thermoplastic material. The materials that are customarily used for LED packaging usually have a refractive index that is lower than the LED chip and the substrate material. The lower refractive index of the packaging material relative to the LED chip reduces the amount of light emitted out of the LED device because of the relatively high critical angle loss of the light emitted from the LED chip. The critical angle loss is caused by the total internal reflection of light incident to the LED chip surfaces at angles greater than the critical angle. The critical angle refers to the angle of incidence of light at the LED surface of the LED chip for which the refraction angle of the light at the package surface is 90° to the normal. When the critical angle is greater, more light can escape the LED chip into the package. Using a packaging material that has a lower refractive index than the LED chip material decreases the critical angle and reduces the light that can escape from the LED chip.
Attempts have been made to package LED chips in materials having higher refractive indices than the customarily used epoxy and plastic materials to improve the light extraction from LED devices. Additionally, chips have been packaged in reflector cups and encapsulated with package material to improve light extraction from the LED chip by reflecting light from the underside of the LED chip mounted on the reflector cup. Despite these attempts, heretofore there still existed a desire to improve light extraction from LED chips.
The present invention contemplates a new and improved LED device and process for manufacturing and/or using the same which overcomes the above-referenced problems and others.
SUMMARY OF INVENTION
In accordance with an aspect of the present invention, a light emitting diode device includes a light emitting diode chip and an encapsulant surrounding the light emitting diode chip. The encapsulant is substantially spherical in shape, and an electrically conductive path extends from the light emitting diode chip to a periphery of the encapsulant such that the light emitting diode chip is selectively energized to produce light by applying electricity to the electrically conductive path at the periphery of the encapsulant.
In accordance with another aspect of the present invention, a method of manufacturing a light emitting diode device is provided. The method includes providing a light emitting diode chip and surrounding the light emitting diode chip with a substantially spherical encapsulant. Further, an electrically conductive path is provided extending from the light emitting diode chip to a periphery of the encapsulant such that the light emitting diode chip is selectively energized to produce light by applying electricity to the electrically conductive path at the periphery of the encapsulant.
In accordance with yet another aspect of the present invention, a method of producing light includes providing a light emitting diode chip and surrounding the light emitting diode chip with a substantially spherical encapsulant. The method further includes providing an electrically conductive path extending from the light emitting diode chip to a periphery of the encapsulant and applying electricity to the electrically conductive path at the periphery of the encapsulant such that the light emitting diode chip is energized to produce light.
One advantage of the present invention is enhanced light extraction from an LED device as compared to similar LED devices with other packaging and/or encapsulation designs.
Another advantage of the present invention is ease and flexibility of manufacturing.
Yet another advantage of the present invention is the ability to accurately determine k factor and/or readily model LED chip characteristics such as view angle.
Still further advantages and benefits of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiments.


REFERENCES:
patent: 5865529 (1999-02-01), Yan

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