Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package – With large area flexible electrodes in press contact with...
Reexamination Certificate
1999-07-12
2003-01-21
Flynn, Nathan J. (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
With large area flexible electrodes in press contact with...
C257S461000, C257S607000, C257S089000, C257S098000, C257S099000, C257S100000, C257S103000, C257S309000, C257S618000, C257S647000, C257S485000, C257S200000, C257S201000, C257S463000, C257S102000, C313S498000, C313S499000, C313S500000, C313S501000, C313S502000, C313S503000, C313S504000, C313S512000
Reexamination Certificate
active
06509651
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a new LED which emits complex light with a spectrum having two peaks, in particular, relates to a single LED having a substrate and an active layer which produces neutral colors, e.g., pink, redpurple, orange, yellow or white color by synthesizing the band gap emission from the active layer and the fluorescence from the substrate.
This application claims the priority of Japanese Patent Applications No. 10-212381 (212381/1998) filed on Jul. 28, 1998 and No. 10-323401 (323401/1998) filed on Nov. 13, 1998, which are incorporated herein by reference.
2. Description of Prior Art
There are already various high luminous LEDs for emitting various monochromatic colors on sale. The LEDs having an active layer of AlGaAs or GaAsP are prevalent as red color LEDs. Red color LEDs emitting red light more than several candelas (Cd) are produced at a low cost. The LEDs emitting the colors other than red are also prevailing. Green-yellowgreen LEDs are produced by utilizing gallium phosphide (GaP) as an active layer. Blue LEDs are made by employing silicon carbide (SiC) as an active layer. Blue-green LEDs are produced on an active layer of gallium indium nitride (GaInN). Orange-yellow LEDs are also fabricated by employing aluminum gallium indium phosphide (AlGaInP) as an active layer. The green-yellowgreen GaP LEDs, blue SiC LEDs, blue-green GaInN LEDs and orange-yellow AlGaInP LEDs are pragmatic and low cost LEDs. In these LEDs, the substrates are GaAs, GaP, SiC, sapphire and so on.
The following are the relations between the monochromatic colors and the active layers of the LEDs on the market.
(1) red LED . . . AlGaAs, GaAsP
(2) green-yellowgreen LED . . . GaP
(3) blue LED . . . SiC
(4) blue-green LED . . . GaInN
(5) orange-yellow . . . AlGaInP
All the prior LEDs make use of the emission produced by the band gap transition of electrons induced by an injection current. The wavelength of the emitted light is uniquely determined by the band gap obtained by a relation of &lgr;=hc/Eg, where “&lgr;” is the wavelength of the emitted light, “h” is Planck's constant, “c” is the light velocity and “Eg” is the band gap of the active layer. Since the light includes a single wavelength, the LEDs are all monochromatic. Since the recombination of a hole and an electron makes a photon (light quanta), the spectrum of the emitted light has a narrow peak at &lgr;=hc/Eg.
The LEDs make primary colors (RGB) and several neutral colors. The neutral colors are still monochromatic colors having a single peak in the spectrum. The colors which the conventional LEDs can produce are red, orange, yellow, yellowgreen, green, bluegreen, blue, bluepurple and purple. These colors are primary colors (RGB), neutral colors between red and green or neutral colors between green and blue. Of course, the primary colors (RGB) are monochromatic. Besides, the neutral colors made by the current LEDs are essentially monochromatic colors. There is no LED which can produce the neutral colors between red and blue or the neutral colors among red, green and blue by a single LED structure.
An assembly of more than three LEDs emitting three primary colors (RGB) can make neutral colors. Any colors can be produced by assembling three primary color LEDs. However, an assembly of more than three different LEDs will complicate the LED structure and enhance the cost of the production.
The contrivance for integrating the colors into a uniform tone is also necessary. The purpose of the present invention is to provide a single LED which can make neutral colors.
Lightening and displaying require the light sources of neutral colors (e.g., redpurple, pink) between red and blue or the light sources of neutral colors (various tones of white) among red, blue and green in stead of monochromatic colors. Conventional LEDs are all monochromatic. Neutral colors are essential for lightening and displaying. Thus, fluorescent lamps or incandescent lamps are still used at present for illuminating or displaying.
The lightening or displaying light sources have the advantages of convenient handling and historical familiarity. Incandescent bulbs, fluorescent tubes or lamp apparatuses are cheap and easily obtainable. Incandescent lamps and fluorescent lamps can be directly driven by the commercial power sources. Incandescent lamps and fluorescent lamps enjoy the advantages of matured technology. However, incandescent lamps have a drawback of a short lifetime. Fragile filaments force us to renew the incandescent lamps frequently. Incandescent lamps are plagued with low lightening efficiency. Most of the power is consumed as heat. Having a longer lifetime, fluorescent lamps are suffering from bulky, long and heavy apparatuses.
LEDs have an advantage of high efficiency, since LEDs directly convert electric current into light. Another strong point of LEDs is a long lifetime. Light weight is a further merit of LEDs. LEDs are already used for displaying devices which demand only primary colors. However, the applications of LEDs to displays are still restricted, since white, redpurple and pink cannot be produced by current LEDs. At present, assembling a plurality of different color LEDs is an available solution of making neutral colors, which raises the cost through complicating the structure.
There is only a single trial of synthesizing white color by an LED. The trial makes a white color LED by assembling a high luminous blue LED having a GaInN active layer and a YAG (yttrium aluminum garnet) phosphor of yellow. The technology of making blue GaInN-LEDs by growing a GaN crystal on a sapphire substrate and growing a GaInN active layer on the GaN film has been established. The white LED is an application of the GaInN blue LEDs. The white LED was proposed by, Shuji Nakamura & Gerhard Fasol, “The Blue Laser Diode (GaN Based Light Emitters and Lasers)”, January 1997, Springer, p 216-221(1997).
FIG.
1
(
a
) and FIG.
1
(
b
) show the proposed white LED. A GaN layer and a GaInN active layer are grown on the sapphire substrate. A blue LED chip
5
is bonded on a bottom of a cavity
4
of a stem
2
. A p-electrode (anode) and an n-electrode (cathode) are on the upper surface of the LED, and these electrodes are connected with the stems
2
and
3
by wires. The cavity
4
is filled with a YAG phosphor
6
covering the GaInN blue LED
5
. The YAG is a yellow phosphor which absorbs blue light and emits yellow light.
Conventional, ordinary LEDs or PDs adopt an (n-type or p-type) conductive substrate. The bottom of LEDs or PDs is an (n- or p-) electrode. The bottom electrode is bonded directly on the stem. Another electrode on the top is connected to another stem by a wire. The ordinary LED has only a single wire. But the GaInN blue light LED which consists of a GaN layer, a GaInN layer or so on an insulating sapphire substrate requires two (n- and p-) electrodes on the top, since the bottom of the LED chip is not an n-electrode at all. The blue light LED on the sapphire substrate makes use of two wires for connecting two top electrodes with the stems. When an electric current is injected from the anode via the chip to the cathode, the GaN-type (GaInN active layer) LED emits blue light. A part of the blue light from the LED passes the YAG phosphor
6
and goes out of the YAG pond
6
as blue light. The rest of the blue light is absorbed by the YAG
6
. The YAG
6
converts the blue light to yellow light which has a longer wavelength. Yellow light and blue light are synthesized to white light. Namely, human eyes feel the unified color of the blue light from the GaN LED and the yellow light from the YAG as white.
The original LED light is a positive, inherent emission caused by the band gap transition of electrons. The fluorescent light is a passive parasitic emission induced by a fall of electrons to the ground state which have been lifted by the blue light via an excited state to an emission level in the phosphor. The emission levels make light of energy lower than the original blue LED emission.
Matsubara Hideki
Motoki Kensaku
Takebe Toshihiko
Erdem Fazli
Flynn Nathan J.
Smith , Gambrell & Russell, LLP
Sumitomo Electric Industries Ltd.
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