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Packaging technique for the fabrication of polarized light emitting diodes 実績あり

外国特許コード F110003768
整理番号 E06716US1
掲載日 2011年7月4日
出願国 アメリカ合衆国
出願番号 47218606
公報番号 20060284206
公報番号 7518159
出願日 平成18年6月21日(2006.6.21)
公報発行日 平成18年12月21日(2006.12.21)
公報発行日 平成21年4月14日(2009.4.14)
優先権データ
  • 60/692,514P (2005.6.21) US
発明の名称 (英語) Packaging technique for the fabrication of polarized light emitting diodes 実績あり
発明の概要(英語) A polarized light emitting diode (LED) includes a marker indicating a polarization direction.
A package for the LED also includes a marker indicating the polarization direction.
The markers on the LED and package are used for mutual alignment, wherein the LED is attached in a favorable orientation with respect to a package, so that the polarization direction of emitted light from the package is apparent.
The marker is placed on the LED before die separation and the marker is placed on the package before alignment.
The marker on the LED comprises a photolithographic pattern, an asymmetric die shape, a notch on the die, or a scratch on the die, while the marker on the package comprises an electrode shape or pattern, an asymmetric package shape, a notch on the package, or a scratch on the package.
Finally, the LED or package may be installed in an external circuit or system that also indicates the polarization direction.
従来技術、競合技術の概要(英語) BACKGROUND OF THE INVENTION
1.
Field of the Invention
The present invention relates to a packaging technique for the fabrication of polarized light emitting diodes.
2. Description of the Related Art
Light emitting diodes (LEDs) have been used in the last thirty years as indicator lamps, local illuminators, and optical transmitters, among their many applications.
In the last ten years, high-brightness AlInGaN-based blue and green LEDs have been developed for, and have started to emerge in, general lighting and full-color display applications.
In terms of LED fabrication, because of the incoherent and unpublicized light emission from conventional LEDs, it is not essential to define a particular die orientation of an LED package when the die is attached to the package.
In common LED fabrication, die orientation is only significant when an LED wafer is diced, that is why LED photolithographic patterning onto a wafer is carried out by aligning the patterns along crystallographic directions.
This alignment process makes die separation reliable and results in higher production yield.
In the case of AlInGaN LEDs prepared on an insulating substrate (for example, sapphire), where two electrical contacts are made on one side of an LED die, die orientation in relation to the package is significant in terms of position of the positive and negative metal contacts.
These alignments for reliable die separation and electrical contacts are common practice for any semiconductor devices, not necessarily only in LED fabrication.
However, LED die alignment has never been considered in fabrication in terms of emitted light properties.
Internal electrical polarization is a unique property of the (Al,In,Ga)N system compared to other semiconductors used in optoelectronics, and this property originates in the hexagonal crystallographic structure of the (Al,In,Ga)N material system.
FIG. 1 is a schematic of a generic hexagonal wütrite crystal structure 100 and typical crystallographic planes of interest 102, 104, 106, 108 with principal crystallographic axes or directions 110, 112, 114, 116 identified therein, wherein the fill patterns are intended to illustrate the planes of interest 102, 104 and 106, but do not represent the materials of the structure 100.
Electrical polarization is created in the hexagonal structure due to its lack of inversion symmetry along the c-axis.
For example, in the case of GaN shown in FIG. 2, along the c-axis gallium atoms (action, positively charged) and nitrogen atoms (anion, negatively charged) are positioned alternately and as a whole, electric neutrality is maintained.
However, because of the lack of inversion symmetry there exists an internal electric field along the c-axis when the atoms are displaced from their ideal positions relative to each other along this axis.
Since atoms in the AlInGaN system usually do not maintain their ideal positions, this polarization field almost always exists along the c-axis.
For this reason, the c-plane is called a polar plane.
Polarization fields do not exist along any of the a-axes or m-axes, due to the inversion symmetry along these particular axes.
For this reason, a-planes and m-planes are called non-polar planes.
For these planes, the polarization vector, which expresses direction and strength of polarization field, is parallel to the planes, since the net polarization vector is parallel to the c-axis.
AlInGaN materials are conventionally grown in the c-direction (direction along c-axis), and therefore on the c-plane.
LEDs grown on the c-plane emit light with negligible light polarization.
On this plane, the polarization field has no in-plane component and the isotropic mechanical stress within the c-plane in a quantum well (QW) structure of an LED does not change the nature of carrier recombination in the QW.
It has recently become possible to prepare AlInGaN LEDs on a-planes and m-planes.
These LEDs exhibit linearly polarized light emission.
The polarization field is in a particular direction (c-direction) in the plane, and the stress in the QW is anisotropic due to different degrees of lattice mismatch between the substrate and QW in the two perpendicular directions in the plane.
The inventors have confirmed the emitted light from these non-polar LEDs is linearly polarized in a direction perpendicular to the c-axis.
Linearly polarized light is an electromagnetic wave that has its electric field only in one plane perpendicular to its propagation.
Non-polarized light has its electric field evenly distributed in directions in planes perpendicular to its propagation.
A principle application for polarized light is backlighting for liquid crystal displays (LCDs), in which LEDs are beneficial due to their compactness and energy efficiency compared to conventional cold cathode fluorescent tubes. (Al,In,Ga) N LEDs prepared on a semi-polar plane have also been confirmed to emit polarized light.
The projection of the polarization vector, which is parallel to the c-axis, lies in the semi-polar plane, similar to the non-polar plane case.
What is needed in the art are simplified methods of fabricating polarized LEDs and packaging such LEDs.
The present invention satisfies those needs.

特許請求の範囲(英語) [claim1]
1. A polarized light emitting diode (LED) apparatus, comprising: at least one LED, for emitting polarized light, including at least one first marker indicating a light polarization direction of the LED;
and
a package, for containing the LED, including at least one second marker indicating a light polarization direction of the package;
wherein the LED is positioned within the package by aligning the first marker with the second marker.
[claim2]
2. The polarized LED apparatus of claim 1, wherein the LED is attached in a favorable orientation with respect to the package, so that the light polarization direction of emitted light from the LED is apparent.
[claim3]
3. The polarized LED apparatus of claim 1, wherein the first marker on the LED and the second marker on the package are used for mutual alignment.
[claim4]
4. The polarized LED apparatus of claim 1, wherein the first marker is placed or defined on the LED before die separation and the second marker is placed or defined on the package before alignment.
[claim5]
5. The polarized LED apparatus of claim 1, wherein the first marker on the LED comprises a photolithographic pattern, an electrode shape or pattern, an asymmetric die shape, a notch on the die, ot a scratch on the die.
[claim6]
6. The polarized LED apparatus of claim 1, wherein the second marker on the package comprises an electrode shape or pattern, an asymmetric package shape, a notch on the package, or a scratch on the package.
[claim7]
7. The polarized LED apparatus of claim l, wherein the LED is installed in an external circuit or system that utilizes the light polarization, and the external circuit or system includes at least one third marker indicating a light polarization direction of the external circuit or system, wherein the package is positioned within the external circuit aligning the second marker with the third marker.
[claim8]
8. The polarized LED apparatus of claim 1, wherein the package contains an array of the polarized LEDs.
[claim9]
9. A method of fabricating a polarized light emitting diode (LED) apparatus, comprising: obtaining at least one LED, for emitting polarized light, including at least one first marker indicating a light polarization direction of the LED;
obtaining a package, for containing the LED, including at least one second marker indicating a light polarization direction of the package;
and
positioning the LED within the package by aligning the first marker with the second marker.
[claim10]
10. The method of claim 9, wherein the light polarization direction is determined from the LED's crystallographic orientation.
[claim11]
11. The method of claim 9, wherein the LED is attached in a favorable orientation with respect to the package, so that the polarization direction of emitted light from the LED is apparent.
[claim12]
12. The method of claim 9, wherein the first marker on the LED and the second marker on the package are used for mutual alignment.
[claim13]
13. The method of claim 12, wherein the first marker is placed or defined on the LED before die separation and the second marker is placed or defined on each package before alignment.
[claim14]
14. The method of claim 12, wherein the first marker on the LED comprises a photolithographic pattern, an electrode shape or pattern, an asymmetric die shape, a notch on the die, or a scratch on the die.
[claim15]
15. The method of claim 12, wherein the second marker on the package comprises an electrode shape or pattern, an asymmetric package shape, a notch on the package, or a scratch on the package.
[claim16]
16. The method of claim 9, wherein the LED is installed in an external circuit or system that utilizes the light polarization, and the external circuit or system includes at least one third marker indicating a light polarization direction of the external circuit or system, wherein the package is positioned within the external circuit by aligning the second marker with the third marker.
[claim17]
17. The method of claim 9, wherein the package contains an array of the polarized LEDs.
[claim18]
18. A light emitting diode (LED) apparatus, comprising: at least one LED, having at least one orientation dependent emission characteristic, including at least one first marker indicating an orientation of the LED for which the orientation dependent emission characitinsoc is a maximum;
and
a package, for containing the LED, including at least one second marker indicating an orientation of the package for which the orientation dependent emission characteristic is a maximum;wherein the LED is positioned within the package by aligning the first marker with the second marker.
[claim19]
19. A method of fabricating at least one light emitting diode (LED) apparatus, comprising: obtaining at least one LED, having an orientation dependent emission characteristic, including at least one first marker indicating an orientation of the LED for which the orientation dependent characteristic is a maximum;
and
obtaining a package, for containing the LED, including at least one second marker indicating an orientation of the package for which the orientation dependent emission characteristic is a maximum;wherein the LED is positioned within the package by aligning the first marker with the second marker.
  • 発明者/出願人(英語)
  • MASUI HISASHI
  • NAKAMURA SHUJI
  • DENBAARS STEVEN P
  • JAPAN SCIENCE AND TECHNOLOGY AGENCY
国際特許分類(IPC)
米国特許分類/主・副
  • 257/98
  • 257/81
  • 257/91
  • 257/99
  • 438/25
  • 438/26
参考情報 (研究プロジェクト等) ERATO NAKAMURA Inhomogeneous Crystal AREA
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