A new volcano-shaped patterned sapphire substrate (VPSS), which enhances the light extraction efficiency (LEE) of GaN-based light emitting diodes (LEDs), was presented. The Monte Carlo ray-tracing method shows that the VPSS with a crater slope angle of about 50 has the highest LEE. To compare the optical characteristics, 380 nm ultraviolet LEDs were grown on an optimized VPSS, hemispherical PSS (HPSS), and planar sapphire substrate by metal-organic chemical vapor deposition (MOCVD). As a result, the extraction efficiency of the LED grown on the optimized VPSS was estimated to be almost 2.8 times larger than that of the planar sapphire substrate and was enhanced 1.6 times compared with that of the LED grown on the HPSS. #

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Time-dependent dielectric breakdown (TDDB) measurements were used to predict lifetime of Cdlow-k interconnects. A voltage ramp test (Vramp) was performed in the beginning, to determine appropriate TDDB stress conditions. The low-field "E-Model" was then used to extrapolate to MTTF at 3.3V and 100°C. The calculated E-Model parameters are comparable to other published results. It was observed that thermally-induced difFusion dominates the lifetime extrapolation by at least two orders of magnitude. By delaying the Cu diffision process by relevant interface engineering, reliability of Cdlow-k interconnects can be improved.