216
10 Reliability Analysis of Group III Nitride LEDs Devices
AF =
t 1 (F 1 )
t 2 (F 2 )
=
E S stress2
E S stress1
c
.
(10.13)
For LEDs, the t 2 (F 2 ) can be determined by an accelerated life test under the high
voltage V 2 . If c and AF are known, the failure time t 1 (F 1 ) under the normal electrical
stress V 1 can be obtained according to the equation.
The researches about the generation and the protection of ESD have also been the
focus of the reliability research of III-nitride LEDs. The ESD can be generated by
three common modes: machine mode, human body mode, and charged device mode.
The ESD sensitivity test of LEDs is a destructive test. Its main purpose is to obtain
the threshold voltage of the ESD, and to improve the ability of LEDs to avoid the
ESD. Electrical testing, sonic scanning, TEM, SEM, XRD and other testing methods
are needed to screen and detect ESD-failure devices.
In addition to the temperature and electrical stress, humidity can also be applied
as an accelerated variable in the LED accelerated aging test to evaluate the moistureresistant lifetime of the device, such as the temperature, humidity, bias (THB)
accelerated test.
t = A exp(
E a
kT
) · f (ES stress ) · g(R H).
(10.14)
In the equation, t, Aexp (E a /kT), f(ES stress ), and g(RH) represent the average lifetime, the equation factor of Arrhenius model, the function of electric stress influence,
and the function of relative humidity, respectively.
f (ES stress ) =
1
k · E S
c
stress
.
(10.15)
g(RH) = B
1
R H m .
(10.16)
In the equation, m represents the moisture related factor.
10.2.4 Other Factors Affecting the Lifetime
(1) Vibrations variable frequency (VVF) test
The vibration test is performed to detect the robustness of the LED structure and
the stability of the electrical characteristic within the specified vibration frequency
range. The damages of the structure can be caused by the vibration, such as deformation, bending, cracks, fractures, and collisions between components, which will
lead to the fatigue damages to the product. These damages will cause poor contact
of components and affect the process performance such as loose adhesive and in
10 Reliability Analysis of Group III Nitride LEDs Devices
AF =
t 1 (F 1 )
t 2 (F 2 )
=
E S stress2
E S stress1
c
.
(10.13)
For LEDs, the t 2 (F 2 ) can be determined by an accelerated life test under the high
voltage V 2 . If c and AF are known, the failure time t 1 (F 1 ) under the normal electrical
stress V 1 can be obtained according to the equation.
The researches about the generation and the protection of ESD have also been the
focus of the reliability research of III-nitride LEDs. The ESD can be generated by
three common modes: machine mode, human body mode, and charged device mode.
The ESD sensitivity test of LEDs is a destructive test. Its main purpose is to obtain
the threshold voltage of the ESD, and to improve the ability of LEDs to avoid the
ESD. Electrical testing, sonic scanning, TEM, SEM, XRD and other testing methods
are needed to screen and detect ESD-failure devices.
In addition to the temperature and electrical stress, humidity can also be applied
as an accelerated variable in the LED accelerated aging test to evaluate the moistureresistant lifetime of the device, such as the temperature, humidity, bias (THB)
accelerated test.
t = A exp(
E a
kT
) · f (ES stress ) · g(R H).
(10.14)
In the equation, t, Aexp (E a /kT), f(ES stress ), and g(RH) represent the average lifetime, the equation factor of Arrhenius model, the function of electric stress influence,
and the function of relative humidity, respectively.
f (ES stress ) =
1
k · E S
c
stress
.
(10.15)
g(RH) = B
1
R H m .
(10.16)
In the equation, m represents the moisture related factor.
10.2.4 Other Factors Affecting the Lifetime
(1) Vibrations variable frequency (VVF) test
The vibration test is performed to detect the robustness of the LED structure and
the stability of the electrical characteristic within the specified vibration frequency
range. The damages of the structure can be caused by the vibration, such as deformation, bending, cracks, fractures, and collisions between components, which will
lead to the fatigue damages to the product. These damages will cause poor contact
of components and affect the process performance such as loose adhesive and in