Lifetime and Failure Analysis of LEDs Driven by the Constant-Amplitude Current with Pulse Width Modulation

The lifetime projection of light-emitting diodes (LEDs) driven by DC current has been addressed by IESNA LM80-80 and TM-21-11. For applications such as visible light communication (VLC) and backlight of displays, the lifetime estimation of LEDs strobed with the pulsed current at various frequencies and duty cycles is in demand. Thus, the lifetime and failure analysis of LEDs driven by constant-amplitude current with pulse width modulation (PWM) is investigated in the present study. It is found that the pulsed loading may introduce more localized current crowding with overheating than the DC current. The induced thermal stress may result in luminous decay and catastrophic failures such as the damage in the current spreading layer and the bonding wire. The lifetime with respect to the peak junction temperature, defined by the highest junction temperature when LEDs driven by the alternating PWM current reach their steady state, is analyzed and presented. It is concluded that the lifetime of LEDs may be divided into 3 regions: the Luminous Decay (LD) region, the Catastrophic Failure (CF) region and the LD+CF region. In the LD region, the projection of lifetime may follow TM-21-11. In the CF region, the sudden failure without significant luminous decay may occur. In the LD+CF region, although lifetime can be projected by LD, the CF may appear before the lifetime projection.