WO2011107928A1 - Led with transparent package - Google Patents

Led with transparent package Download PDF

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Publication number
WO2011107928A1
WO2011107928A1 PCT/IB2011/050847 IB2011050847W WO2011107928A1 WO 2011107928 A1 WO2011107928 A1 WO 2011107928A1 IB 2011050847 W IB2011050847 W IB 2011050847W WO 2011107928 A1 WO2011107928 A1 WO 2011107928A1
Authority
WO
WIPO (PCT)
Prior art keywords
led
light
emitting
active layer
present
Prior art date
Application number
PCT/IB2011/050847
Other languages
French (fr)
Inventor
Filip Marcel Denise BRUYNEEL
Alfred Peeters
Lieve Lea Andrea Lanoye
Dirck Seynaeve
Pieter Jan Delva
Jens Albert Margriet De Mey
Original Assignee
Koninklijke Philips Electronics N.V.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Koninklijke Philips Electronics N.V. filed Critical Koninklijke Philips Electronics N.V.
Publication of WO2011107928A1 publication Critical patent/WO2011107928A1/en

Links

Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/48—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor body packages
    • H01L33/52—Encapsulations

Definitions

  • the present invention relates to a light emitting diode (LED) comprising at least one side-emitting die having a light-generating active layer, and an at least partly transparent housing.
  • LED light emitting diode
  • a light emitting diode is a semiconductor light source used in many different application areas, such as alphanumeric displays, LED lamps replacing conventional light bulbs, backlighting for liquid crystal display (LCD) televisions and laptop displays, outdoor message boards, etc.
  • the radiation pattern of a LED is said to be Lambertian, i.e. the LED has an omni-directional radiation pattern resulting in a viewing angle of approximately 180°.
  • optical elements such as lenses, reflectors, diffusers, etc., are required for refracting the omni-directional light emitted by the LED. These optical elements are costly and bulky, and for these reasons cannot be used in many applications.
  • United States patent application having publication no US 2008/0188020 discloses arranging a top-emitting LED on a transparent substrate and molding a lens over the LED to form a 360° wide view angle LED package.
  • an LED comprising at least one side-emitting die having a light-generating active layer and an at least partly transparent housing.
  • a surface of the light- generating active layer is substantially parallel to an LED submount.
  • LED in a 360 degree rotationally symmetrical pattern. This narrower light beam results in a viewing angle of about 50-70° around the side-emitting LED.
  • an example of a prior art LED uses a lens to attain a wide viewing angle, which is undesirable for cost and size reasons.
  • the transparency of the LED housing may be achieved by using transparent material or by making the LED housing thin enough such that the light can be transmitted through the housing.
  • the LED comprises at least two side-emitting dies having a respective light-generating active layer being arranged to generate light of different wavelengths, e.g. wavelengths resulting in red and green light, respectively.
  • a tri-colour LED may be achieved since mixed red and green light appears to be yellow, which effect is attained when both the red and green light is on.
  • the LED comprises at least three side-emitting dies having a respective light-generating active layer being arranged to generate light of different wavelengths, e.g. wavelengths resulting in red, green and blue light, respectively.
  • a true multi-color LED also known as an RGB
  • an LED device comprising the side-emitting LED discussed hereinabove, which LED device further comprises a substrate on which the LED is arranged?
  • the substrate is at least partly transparent. This has the advantage that the viewing angle can be even wider than 270°.
  • Figure 1 shows radiation patterns of three different types of LEDs available from Philips Lumileds
  • Figure 2 illustrates an LED according to an embodiment of the present invention
  • Figure 3 illustrates differences in outcoupling of light when comparing two types of prior art LEDs with an LED according to an embodiment of the present invention
  • Figure 4 illustrates an LED according to a further embodiment of the present invention.
  • Figure 5 illustrates beam paths of an LED in case transparent substrates and non-transparent substrates are used, respectively.
  • Figure 1 illustrates radiation patterns of three different types of LEDs available from Philips Lumileds.
  • the radiation patterns of Figures la and b correspond to top-emitting LEDs whereas the radiation pattern of Figure lc corresponds to a side-emitting LED.
  • the y- axis indicates relative intensity whereas the x-axis indicates outcoupling angle relative to the normal of the LED. Is should be noted that LEDs can come in many different forms and shapes depending on the actual application, but the typical radiation patterns are those illustrated in Figure 1.
  • Figure la shows the radiation pattern of a so called Lambertian LED.
  • the Lambertian LED typically has a wide viewing angle.
  • Figure lb shows the radiation pattern of a Batwing LED.
  • the Batwing LED has a narrower viewing angle than the Lambertian.
  • Figure lc shows the radiation pattern of a side-emitting LED directing a light beam 90° off the normal of the LED (i.e. 90° off the optical axis of the LED) in a 360 degree rotationally symmetrical pattern.
  • FIG. 2 illustrates an LED 20 according to an embodiment of the present invention. It should be noted that the LED of Figure 2 is illustrated in a principal manner.
  • the LED 20 comprises a die 21 having a light-generating active layer 22.
  • Anode 23 is connected to a p-type side of the die, and cathode 24 is connected to an n-type side of the die. Thus, a p-n junction is formed.
  • a sufficient forward current is applied, current flows from the p-side (anode) to the n-side (cathode), and the active layer 22 emits light.
  • the die 21 is side-emitting, and the housing 25 encapsulating the die 21 is transparent, or at least partly transparent, such that a viewing angle of more than 180° can be obtained.
  • a viewing angle also known as outcoupling angle
  • the transparency of the LED housing 22 can be achieved by using transparent material or by making the LED housing thin enough such that the light can be transmitted through the housing.
  • the LED is arranged with more than one die.
  • the LED may be arranged with two dies, one for emitting red light and another for emitting green light. With these two dies, a tri-colour LED may be achieved since mixed red and green light appears to be yellow, which effect is attained when both the red and green light is on.
  • a true multi-color LED is accomplished by arranging the LED with three dies, one for emitting red light, another for emitting green light and still a further die for emitting blue light, thereby creating an RGB LED.
  • Figure 3 illustrates differences in outcoupling of light when comparing two types of prior art LEDs with an LED according to an embodiment of the present invention.
  • FIG 4 illustrates an LED 20 according to a further embodiment of the present invention.
  • the LED 20 comprises a die 21 having a light-generating active layer 22.
  • the die 21 is side-emitting, and the housing 25 encapsulating the die 21 is transparent, or at least partly transparent, such that a viewing angle of more than 180° can be obtained.
  • the surface of the light-generating active layer 22 is substantially parallel to a submount 26 on which the LED is mounted.
  • the submount 26 contains electrodes 28 to which the anode and cathode of the die 21 is connected, respectively.
  • the electrodes 28 are electrically connected to pads on the bottom of the submount (e.g. via through holes), to which pads a substrate 27 such as a printed circuit board can be attached.
  • the submount 26 and the associated electrodes act as an electrical interface between the die 21, via the electrodes 28 and the substrate.
  • the LED 20 is surface mounted to the substrate 27 by soldering the submount 26 to the substrate.
  • the viewing angle can be even wider than 270° since LED light impinging on the substrate will travel through the same.

Landscapes

  • Engineering & Computer Science (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Manufacturing & Machinery (AREA)
  • Computer Hardware Design (AREA)
  • Power Engineering (AREA)
  • Fastening Of Light Sources Or Lamp Holders (AREA)
  • Led Device Packages (AREA)

Abstract

The present invention relates to a light emitting diode (LED, 20) comprising at least one side-emitting die (21) having a light-generating active layer (22), and an at least partly transparent housing (25). With an LED of the present invention, the inventors have concluded that it is possible to accomplish a viewing angle of up to about 270° without using optical elements such as lenses, reflectors, diffusers, etc.

Description

LED with transparent package
FIELD OF THE INVENTION
The present invention relates to a light emitting diode (LED) comprising at least one side-emitting die having a light-generating active layer, and an at least partly transparent housing.
BACKGROUND OF THE INVENTION
A light emitting diode (LED) is a semiconductor light source used in many different application areas, such as alphanumeric displays, LED lamps replacing conventional light bulbs, backlighting for liquid crystal display (LCD) televisions and laptop displays, outdoor message boards, etc.
The radiation pattern of a LED is said to be Lambertian, i.e. the LED has an omni-directional radiation pattern resulting in a viewing angle of approximately 180°. In order to accomplish a greater viewing angle, optical elements such as lenses, reflectors, diffusers, etc., are required for refracting the omni-directional light emitted by the LED. These optical elements are costly and bulky, and for these reasons cannot be used in many applications.
United States patent application having publication no US 2008/0188020 discloses arranging a top-emitting LED on a transparent substrate and molding a lens over the LED to form a 360° wide view angle LED package.
SUMMARY OF THE INVENTION
It is an object of the present invention to overcome this problem, and to provide an improved LED having a wide viewing angle.
According to a first aspect of the invention, this and other objects are achieved by an LED comprising at least one side-emitting die having a light-generating active layer and an at least partly transparent housing.
With an LED of the present invention, the inventors have concluded that it is possible to accomplish a viewing angle of up to about 270° without using optical elements such as lenses, reflectors, diffusers, etc. In a preferred embodiment, a surface of the light- generating active layer is substantially parallel to an LED submount.
With prior art top-emitting LEDs, it is in general only possible to achieve a maximum viewing angle of about 180°. Further, with prior art side-emitting LEDs having non-transparent housings, a rather narrow light beam is directed 90° off the normal of the
LED in a 360 degree rotationally symmetrical pattern. This narrower light beam results in a viewing angle of about 50-70° around the side-emitting LED. As can be seen hereinabove, an example of a prior art LED uses a lens to attain a wide viewing angle, which is undesirable for cost and size reasons.
The transparency of the LED housing may be achieved by using transparent material or by making the LED housing thin enough such that the light can be transmitted through the housing.
In an embodiment of the present invention, the LED comprises at least two side-emitting dies having a respective light-generating active layer being arranged to generate light of different wavelengths, e.g. wavelengths resulting in red and green light, respectively.
With these two dies, a tri-colour LED may be achieved since mixed red and green light appears to be yellow, which effect is attained when both the red and green light is on.
In another embodiment of the present invention, the LED comprises at least three side-emitting dies having a respective light-generating active layer being arranged to generate light of different wavelengths, e.g. wavelengths resulting in red, green and blue light, respectively. With these three dies, a true multi-color LED (also known as an RGB
LED) is accomplished.
Further provided is an LED device comprising the side-emitting LED discussed hereinabove, which LED device further comprises a substrate on which the LED is arranged? In an embodiment, the substrate is at least partly transparent. This has the advantage that the viewing angle can be even wider than 270°.
Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following description. Those skilled in the art realize that different features of the present invention can be combined to create embodiments other than those described in the following. BRIEF DESCRIPTION OF THE DRAWINGS
This and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing embodiment(s) of the invention, in which:
Figure 1 shows radiation patterns of three different types of LEDs available from Philips Lumileds;
Figure 2 illustrates an LED according to an embodiment of the present invention;
Figure 3 illustrates differences in outcoupling of light when comparing two types of prior art LEDs with an LED according to an embodiment of the present invention;
Figure 4 illustrates an LED according to a further embodiment of the present invention; and
Figure 5 illustrates beam paths of an LED in case transparent substrates and non-transparent substrates are used, respectively.
DETAILED DESCRIPTION
Figure 1 illustrates radiation patterns of three different types of LEDs available from Philips Lumileds. The radiation patterns of Figures la and b correspond to top-emitting LEDs whereas the radiation pattern of Figure lc corresponds to a side-emitting LED. The y- axis indicates relative intensity whereas the x-axis indicates outcoupling angle relative to the normal of the LED. Is should be noted that LEDs can come in many different forms and shapes depending on the actual application, but the typical radiation patterns are those illustrated in Figure 1.
Figure la shows the radiation pattern of a so called Lambertian LED. The Lambertian LED typically has a wide viewing angle.
Figure lb shows the radiation pattern of a Batwing LED. The Batwing LED has a narrower viewing angle than the Lambertian.
Figure lc shows the radiation pattern of a side-emitting LED directing a light beam 90° off the normal of the LED (i.e. 90° off the optical axis of the LED) in a 360 degree rotationally symmetrical pattern.
Figure 2 illustrates an LED 20 according to an embodiment of the present invention. It should be noted that the LED of Figure 2 is illustrated in a principal manner. The LED 20 comprises a die 21 having a light-generating active layer 22. Anode 23 is connected to a p-type side of the die, and cathode 24 is connected to an n-type side of the die. Thus, a p-n junction is formed. When a sufficient forward current is applied, current flows from the p-side (anode) to the n-side (cathode), and the active layer 22 emits light. In this embodiment, the die 21 is side-emitting, and the housing 25 encapsulating the die 21 is transparent, or at least partly transparent, such that a viewing angle of more than 180° can be obtained. The inventors have come to the conclusion that, with an LED having a side- emitting die and transparent housing 22, a viewing angle (also known as outcoupling angle) of 270° can be obtained, without using further optical components.
The transparency of the LED housing 22 can be achieved by using transparent material or by making the LED housing thin enough such that the light can be transmitted through the housing.
In embodiments of the present invention, the LED is arranged with more than one die. For instance, the LED may be arranged with two dies, one for emitting red light and another for emitting green light. With these two dies, a tri-colour LED may be achieved since mixed red and green light appears to be yellow, which effect is attained when both the red and green light is on. In a further embodiment of the invention, a true multi-color LED is accomplished by arranging the LED with three dies, one for emitting red light, another for emitting green light and still a further die for emitting blue light, thereby creating an RGB LED.
Figure 3 illustrates differences in outcoupling of light when comparing two types of prior art LEDs with an LED according to an embodiment of the present invention.
In Figure 3 a, typical radiation of a prior art top-emitting LED is shown.
Generally, a viewing angle of almost 180° can be obtained. In Figure 3b, typical radiation of a prior art side-emitting LED is shown. Generally, a smaller outcoupling angle is attained, due to a narrower radiation pattern.
On the other hand, in Figure 3 c showing radiation of an LED in accordance with the present invention, it can be seen that the view angle accomplished is much wider; up to about 270°.
Figure 4 illustrates an LED 20 according to a further embodiment of the present invention. Again, the LED 20 comprises a die 21 having a light-generating active layer 22. The die 21 is side-emitting, and the housing 25 encapsulating the die 21 is transparent, or at least partly transparent, such that a viewing angle of more than 180° can be obtained. As can be seen in Figure 4, the surface of the light-generating active layer 22 is substantially parallel to a submount 26 on which the LED is mounted. The submount 26 contains electrodes 28 to which the anode and cathode of the die 21 is connected, respectively. The electrodes 28 are electrically connected to pads on the bottom of the submount (e.g. via through holes), to which pads a substrate 27 such as a printed circuit board can be attached. Thus, the submount 26 and the associated electrodes act as an electrical interface between the die 21, via the electrodes 28 and the substrate. Typically, in this configuration, the LED 20 is surface mounted to the substrate 27 by soldering the submount 26 to the substrate.
With an LED device according to Figure 4, comprising both an LED in accordance with embodiments of the present invention, as well as a substrate being transparent, the viewing angle can be even wider than 270° since LED light impinging on the substrate will travel through the same.
This is illustrated in Figure 5, where the dashed arrows on the right-hand side of the LED show beam path in case a prior art non-transparent substrate would be used, thus resulting in light rays reflected at the substrate. The solid-line arrows on the left-hand side of the LED shows beam path in case a transparent substrate according to an embodiment of the present invention is be used, in which case light will travel trough the substrate.
The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. The described embodiments are therefore not intended to limit the scope of the invention, as defined by the appended claims.

Claims

CLAIMS:
1. A light emitting diode (LED, 20) comprising
at least one side-emitting die (21) having a light-generating active layer (22), and
an at least partly transparent housing (25).
2. The LED (20) according to claim 1, comprising
at least two side-emitting dies having a respective light-generating active layer being arranged to generate light of different wavelengths.
3. The LED (20) according to claim 2, said at least two dies being arranged to generate red and green light, respectively.
4. The LED (20) according to claim 1, comprising
at least three side-emitting dies having a respective light-generating active layer being arranged to generate light of different wavelengths.
5. The LED (20) according to claim 4, said at least three dies being arranged to emit red, green and blue light, respectively.
6. The LED (20) according to any one of the preceding claims, wherein a surface of said light-generating active layer (22) is substantially parallel to an LED submount (26).
7. A LED device comprising the side-emitting LED (20) according to any one of the preceding claims, the LED device further comprising
a substrate (27) on which the LED is arranged.
8. The LED device according to claim 7, said substrate (27) being at least partly transparent.
PCT/IB2011/050847 2010-03-02 2011-02-28 Led with transparent package WO2011107928A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
EP10155111.7 2010-03-02
EP10155111 2010-03-02

Publications (1)

Publication Number Publication Date
WO2011107928A1 true WO2011107928A1 (en) 2011-09-09

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PCT/IB2011/050847 WO2011107928A1 (en) 2010-03-02 2011-02-28 Led with transparent package

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Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20030107894A1 (en) * 2001-12-10 2003-06-12 Mize John V. Illumination apparatus and light emitting diode and method of use
US20050017259A1 (en) * 2003-07-25 2005-01-27 Han Kwan-Young Chip light emitting diode and fabrication method thereof
JP2006054217A (en) * 2004-08-09 2006-02-23 Rohm Co Ltd Light emitting diode chip and chip type light emitting element comprising it
US20070030694A1 (en) * 2005-08-08 2007-02-08 Lg Philips Lcd Co., Ltd. Backlight assembly and liquid crystal display having the same
US20070176186A1 (en) * 2006-01-27 2007-08-02 San Bao Lin Light emitting device for enhancing brightness
US20080188020A1 (en) 2007-02-05 2008-08-07 Kuo Wei-Min Method of LED packaging on transparent flexible film
WO2009022316A2 (en) * 2007-08-16 2009-02-19 Koninklijke Philips Electronics N.V. Optical element coupled to low profile side emitting led

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20030107894A1 (en) * 2001-12-10 2003-06-12 Mize John V. Illumination apparatus and light emitting diode and method of use
US20050017259A1 (en) * 2003-07-25 2005-01-27 Han Kwan-Young Chip light emitting diode and fabrication method thereof
JP2006054217A (en) * 2004-08-09 2006-02-23 Rohm Co Ltd Light emitting diode chip and chip type light emitting element comprising it
US20070030694A1 (en) * 2005-08-08 2007-02-08 Lg Philips Lcd Co., Ltd. Backlight assembly and liquid crystal display having the same
US20070176186A1 (en) * 2006-01-27 2007-08-02 San Bao Lin Light emitting device for enhancing brightness
US20080188020A1 (en) 2007-02-05 2008-08-07 Kuo Wei-Min Method of LED packaging on transparent flexible film
WO2009022316A2 (en) * 2007-08-16 2009-02-19 Koninklijke Philips Electronics N.V. Optical element coupled to low profile side emitting led

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Publication number Publication date
TW201145599A (en) 2011-12-16

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