OPTICAL DEVICE WITH PHOTO DETECTOR
[Technical Field]
The present invention relates to an optical device equipped with a photo detector.
[Background Art]
Recently, a s L ED ( Light E mitting D iode) i s u sed a s a I ight s ource of LCD (Liquid Crystal Display), it is desired to have an apparatus for controlling optical output of LED. LED used as a LCD light source is composed of three light sources of red, blue and green, in which optical output of each light source should have a uniform output ratio to each other. The optical output of LED varies according to types of LED for different colors, used temperature and used time. The red LED is made of AIGaInP and has a driving voltage of 2V to 2.5V. A general LED is driven at 2OmA and has an optical output increasing in proportional to the driving current. When the driving current exceeds a certain point, the increase rate of the optical output is reduced. The blue or green LED is based on AIGaInN and has a driving voltage of 3V to 4V. Like the red LED, they are typically driven at 2OmA and the increase rate of the optical output is reduced when the driving current exceeds a certain point.
Also, a feature of the optical output of LED is the change in the optical output properties according to the used temperature. It is general that when i
the operation temperature is increased, the optical output is decreased.
Another feature of the optical output of LED is reduction in the optical output according to the used time. As time goes, the properties of the device are deteriorated. For these reasons, in order to obtain a constant optical output, the optical output emitted from LED is monitored and the driving current is adjusted according to the monitored optical output. Therefore, it is important to drive an LED to have a constant optical output by monitoring the change in the optical output. In FIG. 1, it is shown that a method for LED driving and light detection in an LCD according to the conventional technology. In the past, an LED 1 is disposed at one side of the LCD and a device 3 for detecting the optical output is disposed at the opposite side of the LCD panel 2. The LED used in this technology is composed of red, blue and green. The device is driven at a given current and the optical intensity is measured by a photo detector. Based on the measurement, the current for driving the LED is adjusted so that the optical output is suitable for each color.
US PAT No. 5,757,829 discloses a power monitor system 360 comprising a substrate 314 and a substrate 352 mounted thereon in a flip chip form, as shown in FIG. 2 and FIG. 3, in which the substrate 352 is provided with a photo diode 350. The substrate 352 is disposed over the substrate 314 and is provided with a photo diode 350 which is disposed to be optically aligned with VCSEL 310 (Vertical Cavity Surface Emitting Lasers) so that the light
emitted from VCSEL 310 c an e nter t he p hoto d iode 35O d irectly. Here, t he method for mounting the flip chip is performed using well known semiconductor technologies such as bump bonding, conductive epoxy and the like.
As shown in FIG. 4, the power monitor system 360 further comprises a power control device 370 and can constantly maintain light emission of VCSEL 310, 312 by receiving signal 372 from the photo diode 350 and outputting power 374 to VCSEL 310, 312.
However, according to US PAT No. 5,757,829 the photo diode 350 for light detecting is bonded in a flip chip form and the substrate 314 is separately provided with VCSEL 310 for light detection and VCSEL 312 for light emission.
[Disclosure] [Technical Problem]
Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art, and it is an object of the present invention to provide an optical device equipped with a photo detector which can detect optical output of a light emitting device such as LED (Light Emitting Diode) and LD (Laser Diode) so as to constantly maintain the optical output of these devices. Also, it is another object of the present invention to provide an optical device equipped with a light emitting device comprising an active layer to emit light and a photo d etector w hich can detect the light emitted from the active layer, in which the light emitting device is protected from reverse static
electricity.
It is a further object of the present invention to provide an optical device equipped with a l ight emitting device comprising an active l ayer to emit l ight and a photo detector which can detect the light emitted from the active layer, in which the light emitting device has light emitting efficiency improved. [Technical Solution]
To accomplish the above objects of the present invention, according to the present invention, there is provided an optical device comprising: a photo detector including a first conductive type semiconductor layer, a second conductive type semiconductor layer and a depletion layer formed between the first conductive type semiconductor layer and the second conductive type semiconductor layer; and a light emitting device bonded to the photo detector in a flip chip form and including a plurality of compound semiconductor layers having an active layer for generating light by recombination of electrons a nd holes, wherein the light produced in the active layer of the light emitting device is detected in the depletion layer of the photo detector.
Here, the light emitting device means a device capable of generating light (photon) through recombination of electrons and holes, such as LED (Light Emitting Diode) or LD (Laser Diode) and the photo detector means a device capable of detecting light (photon) such as a photo diode.
When the first conductive type is p-type the second conductive type is n-type, while when the first conductive type is n-type the second conductive type is p-type.
The compound semiconductor layer may be formed of, for example, AlχlnyGa1-x-yN (0<x<1 , 0<y<1, 0<x+y≤1) or GaAs.
The first and second conductive type semiconductor layers are preferably made of silicon. Also, the present invention provides an optical device comprising: a light emitting device including a plurality of compound semiconductor layers having an active layer for generating light by recombination of electrons a nd holes, a light-transmittable substrate disposed over the plurality of compound semiconductor layers, and a first conductive electrode and a second conductive electrode disposed under the plurality of compound semiconductor layer; a nd a p hoto detector bonded to t he I ight e mitting d evice i n a f lip c hip form and electrically connected to the light emitting device by the first conductive electrode and the second conductive electrode of the light emitting device to detect light emitted from the active layer of the light emitting device to the lower part of the plurality of the compound semiconductor layers.
Here, the optical device according to the present invention is characterized in that the optical device comprises a light emitting device in a flip chip form to emit light generated in an active layer to the direction of the substrate side and a light receiving device at the opposite side of the substrate of the light emitting device, in which the optical output is controlled in feedback so that the optical output of the light emitting device is maintained constantly.
Also, the present invention provides an optical device comprising: a light emitting device including an active layer for emitting light and a photo
detector for detecting the light emitted from the active layer, wherein the photo detector includes a semiconductor layer for forming a zener diode which is reversely connected to the light emitting device.
Also, the present invention provides an optical device comprising: a photo detector including a first conductive type semiconductor layer, a second conductive type semiconductor layer and a depletion layer formed between the first conductive type semiconductor layer and second conductive type semiconductor layer, and a light emitting device bonded to the photo detector and including a plurality of compound semiconductor layers having an active layer to generate I ight b y recombination of electrons and holes, wherein the light generated in the active layer of the light emitting device is detected in the depletion layer of the photo detector.
[Advantageous Effects]
According to the present invention, it is possible method to detect the optical output of the light emitting device by integrating a light emitting device such as LED on a photo detector such as photo diode in a flip chip form.
Also, according to the present invention, it is possible to effectively release heat generated in an active layer of a light emitting device through a photo detector which serves as a substrate. Also, according to the present invention, it is possible to constantly maintain the optical output of a light emitting device in a flip chip form by detecting the light output of the light emitting device in the back of the optical output direction.
Also, according to the present invention, it is possible to emit light stably since there is no influence of reverse static electricity.
Also, according to the present invention, it is possible to effectively release the generated heat, to increase the total amount of light emitted to the top and to detect the light emitted between the lattices by depositing a metal thin layer in a lattice form at the bottom upon junction up assembling of a light emitting device such as LED.
[Description of Drawings] Further objects and advantages of the invention can be more fully understood from the following detailed description taken in conjunction with the accompanying drawings in which:
FIG. 1 is a view showing the method for driving an LED and detecting light in a conventional LCD; FIGs. 2 to 4 are views showing a power monitor system disclosed in
US PAT NO. 5,757,829;
FIG. 5 is a view showing the optical device equipped with a photo detector according to the present invention;
FIG. 6 is a view schematically showing the electrical connection of the optical device of FIG. 5;
FIG. 7 is a view showing another embodiment according to the present invention;
FIG. 8 is a view schematically showing the electric connection of the
optical device of FIG. 7;
FIG. 9 is a view schematically showing another embodiment according to the present invention;
FIG. 10 is a view schematically showing another embodiment according to the present invention;
FIG. 11 is a view schematically showing another embodiment according to the present invention;
FIG. 12 is a view schematically showing the electric connection of the optical device of FIG. 11 ; FIG. 13 is a view schematically showing another embodiment according to the present invention;
FIG. 14 is a view showing the electric connection of the optical device according to another embodiment of the present invention;
FIG. 15 is a view showing another embodiment according to the present invention; and
FIG. 16 is a view showing a metal thin layer in a lattice shape of FIG. 15.
[Mode for Invention] Now, the present invention is described in detail with reference to the drawings.
FIG. 5 shows an optical device 100 equipped with a photo detector 10 according to the present invention. Preferably, a silicon semiconductor is
used as a substrate 11, which is formed of a p-type semiconductor layer 11. An n-type semiconductor layer 12 is formed on a part of the p-type semiconductor layer 11 by ion injection or diffusion to form a p-n diode.
When no voltage or reverse voltage is applied on the p-n diode, a depletion layer 13 is formed on the p-n diode junction. As light 40 from the outside enters into the depletion layer 13, electron-hole is formed to generate photocurrent. The photocurrent varies according to the output of the entering light and the intensity of the light emitted from a light emitting device 30 (LED 30 in the present example) which is disposed over the p-n diode can be detected.
Metal pads 51, 52, 53 are formed on the substrate 11 with the p-n junction to connect an exterior electrode and bonding wires 91, 92, 93 are connected to the metal pads 51, 52, 53. An n-type electrode 61 is formed between the metal pad 51 on the p-type semiconductor layer 11 and an n-type compound semiconductor layer 71 of the LED 30, while a p-type electrode 62 is formed between the metal pad 52 on the n-type semiconductor layer 12 and a p-type compound semiconductor layer 72 of the LED 30. For insulation of the n-type electrode 61 of the LED 30, an insulating layer 81 is formed on the surface of the p-type semiconductor layer 11 and the metal pad 52 is formed for electrical connection to the n-type electrode 61 of the LED 30.
Referring to FIG. 5, the LED 30 is attached onto the silicon substrate 11 having the metal pads 51 , 52, 53 formed thereon, in which the LED 30 is in the form of upside down. Such upside down arrangement is called "flip chip
technology" which is well known as described above.
The LED 30 is equipped with the p-type electrode 62 and the n-type electrode 61. When (+) electric power (now shown) is applied on the p-type electrode 62, an active layer 73 of the LED 30 emits light through recombination of electrons and holes. The p-type electrode 62 of the LED 30 is connected to the n-type semiconductor layer 12 of the silicon p-n diode 10 through the metal pad 52 while the n-type electrode 61 of the LED 30 is connected to the metal pad 51 formed on the insulating layer 81 of the substrate 11. Then, the bonding wires 91, 92, 93 are connected to the metal pad 51 , 52, 53. By such electric connection, as shown in FIG. 6, through the bonding wire 91 , 92, 93, the LED 30 and the photo detector, or silicon p-n diode 10 can be electrically connected to the exterior.
In case of a blue or green LED, the light emitted from the active layer 73 of the LED 30 is radiated upward through a transparent substrate (ex. Sapphire) and a part of the light 40 is radiated downward. The light radiated downward 40 is absorbed in the depletion layer 13 of the silicon p-n diode 10, whereby the photocurrent in the p-n diode is varied according to the intensity of the optical output. The LED 30 formed on the silicon substrate 11 can be any type of LEDs such as red, blue, green, ultraviolet and far infrared LEDs. FIG. 7 shows another embodiment of the present invention, in which an n-type semiconductor layer is used as a silicon substrate 111, a p-type semiconductor layer 112 is partially formed by ion injection or diffusion to form a p-n diode. In this embodiment, a light emitting device 30 comprises an
n-type electrode 61 and a p-type electrode 62 and the n-type electrode 61 is connected to the p-type semiconductor layer 112. FIG. 8 schematically shows the electrical connection according to the embodiment of FIG. 7.
FIG. 9 schematically shows another embodiment of the present invention, in which a LED 30 is connected to a reverse zener diode 300 in parallel. It is known that a blue or green LED based on AIGaInN has generally very weak reverse static electricity. In order to solve this problem, the reverse zener diode 300 is connected to the LED 30 in parallel so that the reverse electro static discharge characteristic can be remarkably improved. FIG. 9 shows an optical device in which a zener diode 300 is connected to the construction of FIG. 5 and FIG. 10 shows an optical device in which a zener diode 300 is connected to the construction of FIG. 7 as another embodiment according to the present invention.
FIG. 11 shows another embodiment of the present invention, in which an optical device 1001 comprises a light emitting device, for example an LED 1030 and a photo detector 1010 for detecting light generated by recombination of electrons and holes in an active layer 1033 of the LED 1030 through a depletion layer 1013.
The photo detector 1010 comprises a substrate 1011 formed with a p-type silicon semiconductor layer, an n-type silicon semiconductor layer 1012 formed on a part of the substrate 1011 by ion injection or diffusion, and a depletion layer 1013 formed between the substrate 1011 formed with a p-tyep silicon semiconductor layer and the n-type silicon semiconductor layer 1012.
FIG. 12 schematically shows the electrical connection of the optical device according to the embodiment of FIG. 11. In addition to the photo detection function, the photo d etector 1 010 further c omprising a zener diode 1040 reversely connected to the LED 1030 in parallel is electrically connected to the LED 1030. For this construction, the photo detector 1010 comprises an n-type silicon semiconductor layer 1014 for the zener d iode on a part of the substrate 1011 and the n-type silicon semiconductor layer 1014 for the zener diode is electrically connected to a p-side electrode 1062 of the LED 1030 through a metal pad 1052. The metal pad 1052 may be electrically connected to the exterior through a bonding wire 1092. An n-side electrode 1061 of the LED 1030 is electrically connected to the substrate 1011 formed of a p-type silicon semiconductor layer through a metal pad 1051. The metal pad 1051 may be electrically connected to the exterior through a bonding wire 1091. On the n-type silicon semiconductor layer 1012 of the photo detector 1010, a metal pad 1053 is disposed, and the metal pad 1053 may be electrically connected to the exterior through a bonding wire 1093.
As shown in FIG. 12, according to the present invention including the zener diode 1040 reversely connected to the LED 1030 in parallel, the LED 1030 can be safely protected through the zener diode 1040, even when reverse static electricity is applied on the LED 1030.
FIG. 13 shows another embodiment of the present invention. Unlike the embodiment of FIG. 11 , an optical device 1002 comprises a substrate 1031 of an LED 1030 disposed at the lower part and connected to a photo detector
1010 through a soldering member 1070. As the substrate 1031 , a sapphire substrate is commonly used. Since the sapphire substrate 1031 is an insulator, it is not necessary to provide an additional construction for insulation with the photo detector 1010. The LED 1030 is provided with bonding wires 1091a, 1092a and the photo detector 1010 is provided with metal pads 1051 , 1052, 1053 and bonding wires 1091b, 1092b, 1093. For the electrical connection as shown in FIG. 12, the bonding wire 1091a is connected to the bonding wire 1091b and the bonding wire 1092a is connected to the bonding wire 1092b. FIG. 14 schematically shows the electrical connection of an optical device according to another embodiment of the present invention. This electrical connection is constructed by forming the substrate 1031 of the photo detector 1010 of FIG. 13 into an n-type silicon semiconductor layer, forming the n-type silicon semiconductor layer 1012 and the silicon semiconductor layer 1014 for zener diode into p-type, connecting the bonding wire 1091a to the bonding wire 1092b and connecting the bonding wire 1091b to the bonding wire 1092a.
FIG. 15 shows an optical device according to another embodiment of the present invention. In order to m inimize the change in device properties caused by heat generation of the LED 1030 and to increase the amount of emitted light, a metal thin layer 1050 in a lattice form shown in FIG. 16 is deposited on the substrate 1031 of the LED 1030. The metal thin layer 1050 transfers heat generated in the LED 1030 to the lower part and reflects the light
produced in the LED 1030 to the upward, increasing the amount of emitted light. Meanwhile, since the photo detector 1010 cannot detect light when all the light is reflected by the metal thin layer 1050, the metal thin layer 1050 is formed in a lattice shape, as shown in FIG. 16, whereby a part of light is released between the lattices for detection of the change in the light amount. This metal thin layer 1050 can be applied to the optical device of FIG. 5 which is not equipped with a zener diode.