Lifetime Prediction of Current-and Temperature-Induced Degradation in Silicone-Encapsulated 365 nm High-Power Light-Emitting Diodes

Abstract

We report on the degradation mechanisms and dynamics of silicone encapsulated ultraviolet A (UV-A) high-power light-emitting diodes (LEDs), with a peak wavelength of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\mathrm {365~ \text {n} \text {m} }}$ </tex-math></inline-formula> . The stress tests were carried out for a period of 8665 hours with forward currents between <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\mathrm {350~ \text {m} \text {A} }}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\mathrm {700~ \text {m} \text {A} }}$ </tex-math></inline-formula> and junction temperatures up to 132°C. Depending on stress condition, a significant decrease in optical power could be observed, being accelerated with higher operating conditions. Devices stressed at a case temperature of 55 °C indicate a decrease in radiant flux between 10- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\mathrm {40~\%}}$ </tex-math></inline-formula> varying with measurement current, whereas samples stressed at higher case temperatures exhibit crack formation in the silicone encapsulant accompanied by electromigration shorting the active region. The analyzed current and temperature dependency of the degradation mechanisms allows to propose a degradation model to determine the device lifetime at different operating parameters. Additional stress test data collected at different aging conditions is used to validate the model’s lifetime predictions.