JP2000188425A - Light emitting diode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent damage to a luminous element due to static electricity or surge voltage and improve the luminous element without impairment of characteristics intrinsic to LED by connecting a capacitor in parallel with the luminous element. SOLUTION: If the capacitance of a capacitor 32 is multiplied by a factor of 10 by suppressing voltage rise against surge applied to the capacitor 32 and parallel-connecting the capacitor 32, voltage rise is suppressed to approx. 1/10 against surge with a pulse width sufficiently shorter than the time constant of CR. As for static electricity, the capacitance of a human body is 200 pF or so, and voltage is inversely proportional to capacitance. If a capacitor 32 with a capacitance of 2000 pF, for example, is connected in parallel, therefore, the voltage is suppressed to 1/10. Therefore, it follows that even if a human body is charged at 500V and is brought into contact with LED 31, the LED is subjected to a voltage of no more than 50V or so. Thus, a light emitting diode which is protected against static electricity and surge voltage and does not impair characteristics intrinsic to LED chips is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting diode using a nitride semiconductor light emitting device capable of emitting light from an ultraviolet region to a visible light, and particularly to a light emitting device which is damaged under a voltage below which a human is shocked. It is intended to provide a light emitting diode having excellent luminous efficiency.

[0002]

2. Description of the Related Art Light-emitting diodes emit light of a small size, efficiently and colorfully. In addition, since it is a semiconductor element, there is no fear of breaking the ball. Furthermore, it has a feature that it has excellent initial drive characteristics and is resistant to vibration and blinking. In particular, a nitride semiconductor (In _x Al _y Ga _1-xy N, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1) is used as a light emitting element capable of emitting light with high luminance from near ultraviolet to red.
Since light-emitting diodes using GaN have been put to practical use, they have begun to be rapidly used in various fields.

However, it is difficult for a nitride semiconductor to form a semiconductor having excellent crystallinity. At present, a nitride semiconductor is formed on a sapphire substrate or a SiC substrate via a buffer layer. A light-emitting element using such a nitride semiconductor has low withstand voltage because of poor crystallinity. In particular, the composition of the light-emitting layer
The crystallinity tends to decrease as a nitride semiconductor containing l or In and having an emission peak in the ultraviolet region or the long wavelength side of visible light is formed.

Further, in order to further improve the luminous efficiency, the light emitting layer is formed of an extremely thin film having a single quantum well structure or a multiple quantum well structure. Therefore, there is a problem that a light-emitting element using a nitride semiconductor having excellent characteristics having a small size, high efficiency, high output at a small current and high output is easily broken by a small electrostatic voltage. For example, a light emitting diode whose normal light emitting layer is made of AlGaInP and can emit red and infrared light has a withstand voltage of about 2 KV,
The withstand voltage of a light-emitting diode whose light-emitting layer is made of InGaN and emits blue, green, and yellow light is only about 0.5 kV or less. In particular, it is about 0.2 KV or less for a nitride semiconductor light emitting device containing Al that can emit ultraviolet light. (Note that the resistance to the light emitting element is 0 ohm, and a withstand voltage test is performed by passing a current from the 200 pF capacitor to the light emitting element by switching.)

A light emitting diode made of such a group III nitride semiconductor is liable to break down due to an electric shock due to the structure of the light emitting element. In particular, when the light emitting diode and the light emitting diode mounted component are handled in a dry atmosphere or an environment where the light emitting diode is easily charged, the light emitting diode may be broken by static electricity.

In recent years, light-emitting diodes have begun to be used in various fields. However, when the light-emitting diodes are incorporated into automobile parts, a serious problem arises. Specifically, a surge voltage may be applied to a light emitting diode mounted on a vehicle at the time of starting, and there is a risk that the light emitting diode may be destroyed.

In order to prevent destruction due to static electricity, a conductive sponge, a case containing an antistatic agent or the like is used when transporting the light emitting diode. Further, measures such as humidity control, human body grounding, and installation of a static eliminator can be taken at the workplace where the light emitting diodes are mounted. However, these countermeasures against static electricity can lower the charging voltage, but it is difficult to completely eliminate destruction due to static electricity.

As a countermeasure against static electricity and surge voltage taken on the LED device side, there is a resistor built-in type LED device in which a resistor for overcurrent prevention is connected in series to enable a constant voltage drive of the LED device alone. . It is possible to absorb and mitigate the energy of surge by this resistance. However,
There is a problem that the characteristics of the LED chip are greatly impaired, for example, it is necessary to supply the power consumed by the built-in resistor to the LED device.

A particularly serious problem is that the withstand voltage of a light-emitting diode made of a group III nitride semiconductor is extremely low as compared with other light-emitting diodes, and the limit at which a human body feels a shock is about 2 KV. This is because it is difficult to determine whether the nitride semiconductor device is destroyed when electricity of less than this value flows.

[0010]

At present, it is difficult to completely eliminate the generation of static electricity and completely eliminate the occurrence of surges due to ON / OFF of a power supply and a measuring instrument. Therefore, it is necessary to protect against static electricity and surge by using the light emitting diode alone.
The characteristics of the ED chip are greatly impaired. Therefore, the present invention does not impair the inherent characteristics of the LED,
It is another object of the present invention to provide a light emitting diode having excellent light emitting efficiency without damaging the light emitting element against static electricity and surge voltage.

[0011]

According to the present invention, there is provided a light emitting diode having a light emitting element using a group III nitride semiconductor for a light emitting layer, wherein a capacitor is electrically connected to the light emitting element in parallel.

A light emitting diode according to a second aspect of the present invention has a double hetero structure in which the light emitting element is formed on a sapphire substrate.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventor has conducted various experiments,
By connecting a capacitor with an appropriate capacitance in parallel with the nitride semiconductor light emitting device, we have found a light emitting diode that is protected against static electricity and surge voltage without substantially affecting loss or drive pulse. The invention has been reached.

That is, the present invention incorporates the circuit shown in FIG. 1 in a light emitting diode, so that the light emitting diode alone protects the LED chip against static electricity and surge voltage without impairing the characteristics inherent to the LED chip. A light emitting diode was obtained.

In the light emitting diode of the present invention in which a capacitor is connected in parallel to the LED chip, this capacitor has a function of suppressing an increase in voltage with respect to an applied surge or charge. For example, when a surge is applied, a surge voltage is applied as it is when the capacitance is almost 0, but when a capacitor is connected and has a capacitance C, the voltage becomes E.
= E ₀ · e ^{-t / CR} (E: element voltage, E ₀ : applied voltage,
e: natural logarithm, t: time, C: capacity, R: resistance). As can be seen from the equation, if the capacitance C is increased by a factor of 10 by connecting the capacitors in parallel, the voltage rise can be suppressed to about one-tenth for a surge having a pulse width sufficiently shorter than the time constant of CR. With respect to static electricity, the capacitance of the human body is about 200 pF, and the voltage is inversely proportional to the capacitance. For example, if a capacitor having a capacitance of 2000 pF is connected in parallel, the voltage becomes 1 / (2000 /
200) = 1/10. In this example, the human body is 5
It is charged to 00V, and even if you touch the LED, 5
The voltage is applied only about 0V.

In the present invention, the capacitance of the connected capacitor is selected to be an appropriate value in consideration of the response speed and the size of the element, but the practical range is 1000 to 10000 pF.

From the above, by incorporating a circuit for connecting a capacitor in parallel to an LED chip,
It is possible to obtain a light emitting diode that is protected from static electricity and surge voltage and does not impair the characteristics inherent to the LED chip.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in more detail below with reference to embodiments which are embodiments of the present invention. However, the present invention is not limited to this. [Example 1] First, an LED chip made of a nitride semiconductor is formed on a sapphire substrate that has been cleaned in advance by using the MOCVD method. A sapphire substrate was placed in a reaction vessel of an MOCVD apparatus, and baked at 800 ° C. while flowing hydrogen gas. Next, TMG (trimethyl gallium) gas as a source gas, hydrogen gas as a nitrogen gas and a carrier gas were flown, and GaN was formed as a buffer layer to a thickness of 150 ° on a sapphire substrate at a substrate temperature of 550 ° C.

After the formation of the buffer layer, the flow of the raw material gas is stopped, the film forming temperature is raised to 1050 ° C., and TM is used as the raw material gas.
G, nitrogen gas and hydrogen gas as carrier gas
Type GaN was formed into a film with a thickness of 1.5 μm. Subsequently, an n-type GaN layer for forming an n-type electrode is formed on the n-type GaN. While maintaining the film forming temperature, TM
G, a nitrogen gas, and a hydrogen gas and a silane gas as a carrier gas were flowed to form an n + -type GaN film having a thickness of 2.3 μm. While maintaining the film formation temperature, TMG as a source gas, hydrogen gas as a nitrogen gas and a carrier gas are flowed on the n + -type GaN, and undoped GaN and Si-doped GaN are flown.
Is formed in 20 cycles. Note that modulation doping is performed in which the impurity concentration of the GaN layer is different. Modulation-doped G
On the aN layer, GaN of 250 ° and a thickness of 30 are used as an active layer.
多重 has a multiple quantum well structure in which InGaN is repeated six times, and constitutes an active layer having GaN at both ends.

More specifically, while maintaining the film formation temperature at 1050 ° C., TMG as a source gas, hydrogen gas as a nitrogen gas, and a hydrogen gas as a carrier gas flow on the modulation-doped GaN layer to form undoped GaN at 30 °. . continue,
The film forming temperature is lowered to 800 ° C. while flowing only the carrier gas. A TMI (trimethyl indium) gas, a TMG gas, a nitrogen gas, and a hydrogen gas as a carrier gas are flowed as raw material gases, and undoped InGaN is supplied at 25%.
The film is formed at 0 °. After repeating this for 6 cycles, finally, the film forming temperature is set to 1050 ° C., and TMG,
An active layer is formed by flowing undoped GaN at 30 ° by flowing a hydrogen gas as a nitrogen gas and a carrier gas.

Next, on the active layer, a superlattice p-type clad layer is formed as a p-type clad layer in which Mg-doped AlGaN having a thickness of 40 ° and Mg-doped InGaN having a thickness of 25 ° are repeated five times. While maintaining the film formation temperature at 1050 ° C., a TMG gas, a TMA (trimethylaluminum) gas, a nitrogen gas, a hydrogen gas as a carrier gas, and a Cp ₂ Mg (cyclopentadienyl magnesium) gas as a p-type dopant are used as source gases. Introduce p-type AlG
aN is deposited at 40 °.

Finally, while the film formation temperature is maintained at 1050 ° C., the source gas is TMG gas, nitrogen gas, hydrogen gas as a carrier gas and Cp ₂ Mg as an impurity gas, and Mg-doped GaN is formed as a p-type contact layer. Let it.

After forming the nitride semiconductor wafer, the active layer and the like are removed by RIE so that the n-type contact layer can be partially exposed. Thereafter, an electrode is formed on each of the p-type and n-type contact layers by using sputtering. Each LED chip is formed by scribing the nitride semiconductor wafer. Thus, an active layer having a multiple quantum well structure is formed on the sapphire substrate, and a light emitting device which is a nitride semiconductor having a double hetero structure is formed.

FIG. 2 is a schematic view showing a light emitting diode of a can type package according to an embodiment of the present invention. Hereinafter, a light emitting diode made of a nitride semiconductor will be created based on this drawing. LED chip 31 obtained above
Is bonded to the receiving portion of the gold-plated stem 33 with an Ag paste 36. Next, a ceramic capacitor 32 having a capacity of 2000 pF is bonded to the flat portion of the periphery of the storage portion of the stem with an Ag paste 36. This capacitor 32 is a ceramic capacitor having a structure in which a pair of electrodes are formed via a ceramic layer.

Inner lead 33a and LED chip 31
Of the n-side extraction electrode (negative pole side)
b and the p-side extraction electrode (+ pole side) of the LED chip 31 are connected by wire bonding with a gold wire 35. The inner lead 33a of the stem is electrically insulated from the storage part of the stem 33 and the mount lead 33b. Next, the extraction electrode of the ceramic capacitor 32 and the inner lead 3
3a is connected by wire bonding with a gold wire 35.

Finally, the cap 34 and the flange of the stem 33 are welded and sealed by resistance welding in an N ₂ atmosphere, so that the mount lead 33b is a positive pole, the inner lead 33a is a negative pole, and the ceramic capacitor 32 is LE.
Light emitting diodes connected in parallel to the D chip 31 were formed.

The light-emitting diode thus obtained was evaluated for electrostatic withstand voltage. FIG. 5 shows a test circuit of the device used for the evaluation. The specification of the power supply V is a DC voltage with a maximum voltage of 3 kV and a maximum current of 3 mA.
F and the resistance R were set to 0Ω. The capacitor C was designed to withstand the test voltage sufficiently, and the changeover switch S was designed to have high insulation resistance, low contact, and no chattering. In addition, the wiring between the test equipment and the DUT should be as short as possible,
The stray capacitance was 5% or less of the capacitance of the capacitor C. In the test method, the switch S of the device is set to the power supply V side, and the test voltage is charged in the capacitor C. The changeover switch S is set to the sample side to discharge. Next, the same operation is repeated while changing the polarity of the test voltage. The test voltage was set to a maximum of 2.5 kV in 100 V steps.

The evaluation results of the electrostatic withstand voltage of the light emitting diode obtained in this example were confirmed to withstand 1.0 kV in both the forward and reverse directions. This is sufficient for normal handling.

[Embodiment 2] FIG. 3 shows a light emitting diode of a surface mounting type. 3 is a front view, and the lower figure is a cross-sectional view.

First, a silver-plated copper lead frame 4
1 is formed by punching, and a plastic package 42 serving as an outer frame of the light emitting diode is formed on the lead frame 41 by an injection molding method. Next, the LED chip 43, which is a gallium nitride-based compound semiconductor, is bonded to the exposed portion of the lead frame 41 in the housing portion of the plastic package 42 with the epoxy resin 46. Furthermore, a ceramic capacitor 44 having a capacity of 2000 pF is bonded to the exposed portion of the lead frame 41 in the storage portion of the plastic package 42 with an Ag paste 47. Lead frame 41 in which LED chip 43 of plastic package 42 is joined and lead frame 41 in which ceramic capacitor 44 is joined.
Are electrically insulated by plastic. LED
The lead frame 41 to which the chip 43 is bonded and the n-side extraction electrode (negative pole side) of the LED chip 43 are connected by wire bonding, and the lead frame 41 to which the ceramic capacitor 44 is bonded and the extraction electrode of the LED chip 43 are connected by wire bonding with a gold wire 45. I do. Next, the lead frame 41 in which the extraction electrode of the ceramic capacitor 44 and the LED chip 43 are joined.
Are connected by a wire 45 by wire bonding.

Next, a transparent epoxy resin having a high light transmittance is filled in the housing portion of the plastic package 42. Lead frame 41 protruding from outer frame of plastic package 42
Is cut into an optimum shape, and finally, the leads are bent along the outer frame of the plastic package 42. As described above, the ceramic capacitor 4
4 were connected in parallel to form a surface mount type light emitting diode.

The thus obtained light emitting diode of the present embodiment was evaluated for electrostatic withstand voltage by the same method as in Example 1. As a result, as in Example 1, the forward and reverse directions were 1.0 kV.
It was confirmed that it could endure. This is sufficient for normal handling.

[Embodiment 3] FIG. 4 is a sectional view of a light emitting diode of a shell type resin mold type. First, a copper lead frame 51 plated with silver is formed by punching. The formed lead frame 51 has a cup, which is an accommodating portion of the LED chip 52, at the tip of the mount lead 51a, and a flat portion at the lower part of the cup to which the capacitor chip 53 can be joined.

An LED chip 52, which is a gallium nitride-based compound semiconductor, is bonded to a housing portion of the lead frame 51 with an epoxy resin 56. Then, the inner lead 51b
5 and a surface mount type multilayer ceramic capacitor 53 having a capacitance of 2000 pF, as shown in FIG.
Are bonded with an Ag paste.

Inner lead 51b and LED chip 52
Of the n-side extraction electrode (− pole side) of the
a and the p-side extraction electrode (+ pole side) of the LED chip 52 are connected by wire bonding with a gold wire 54. The inner lead 51b is electrically insulated from the mount lead 51a.

The LED chip 52 and the multilayer ceramic capacitor 54 are protected from external stress, moisture, dust, etc.
In addition, for the purpose of obtaining appropriate light distribution characteristics, it is molded with an epoxy resin having excellent light transmittance. The molding can be performed by inserting the lead frame formed above into a shell-shaped mold frame containing an epoxy resin and curing by heating. From the above,
A light emitting diode of a shell type resin mold type in which a multilayer ceramic capacitor 53 was connected in parallel with the LED chip 52 was formed.

The thus obtained light emitting diode of the present embodiment was evaluated for electrostatic withstand voltage in the same manner as in Example 1. As a result, as in Example 1, the forward and reverse directions were 1.0 kV.
It was confirmed that it could endure. This is sufficient for normal handling.

[0038]

As described above, according to the present invention,
By connecting a capacitor in parallel with the LED chip, it is protected from static electricity and surge voltage, and LED
It is possible to obtain a light emitting diode that does not impair the characteristics inherent to the chip.

[Brief description of the drawings]

FIG. 1 shows a circuit diagram of a light emitting diode of the present invention.

FIG. 2 is a perspective view of a light emitting diode which is a can type package according to the first embodiment.

FIGS. 3A and 3B are a front view and a cross-sectional view of a surface-mount type light emitting diode according to a second embodiment. FIGS.

FIG. 4 is a schematic cross-sectional view of a light-emitting diode of a shell type resin mold type according to a third embodiment.

FIG. 5 shows a circuit diagram of an electrostatic withstand voltage evaluation test apparatus.

[Explanation of symbols]

 21, 31, 43, 52 ... LED chip 22, 32, 44, 53 ... capacitor 35, 45, 54 ... gold wire 41, 51 ... lead frame 33 ... stem 34 ... Cap 42: Plastic package 58: Mold resin 36, 47, 57: Ag paste 46, 56: Epoxy resin

Claims (2)

[Claims] 1. A light-emitting diode having a light-emitting element using a group III nitride semiconductor for a light-emitting layer, wherein a capacitor is electrically connected to the light-emitting element in parallel. 2. The light emitting diode according to claim 1, wherein said light emitting element has a double hetero structure formed on a sapphire substrate.