Nam-Heon Lee

An Alternative Host Material for Long‐Lifespan Blue Organic Light‐Emitting Diodes Using Thermally Activated Delayed Fluorescence

It has been challenging to find stable blue organic light emitting diodes (OLEDs) that rely on thermally activated delayed fluorescence (TADF). Lack of stable host materials well‐fitted to the TADF emitters is one of the critical reasons. The most popular host for blue TADF, bis[2‐(diphenylphosphino)phenyl] ether oxide (DPEPO), leads to unrealistically high maximum external quantum efficiency. DPEPO is however an unstable material and has a poor charge transporting ability, which in turn induces an intrinsic short OLED operating lifespan. Here, an alternative host material is introduced which educes the potential efficiency and device lifespan of given TADF emitters with the appropriateness of replacing the most popular host material, DPEPO, in developing blue TADF emitters. It simultaneously provides much longer device lifespan and higher external quantum efficiency at a practical brightness due to its high material stability and electron‐transport‐type character well‐fitted for hole‐transport‐type TADF emitters.

Lifetime projections and conduction mechanisms for Hafnium based high-k capacitor dielectrics using low thermal budget process

For the first time, we evaluated the long-term lifetime for Hafnium based high-k dielectrics such as HfO/sub 2/ and HfO/sub 2/-Al/sub 2/O/sub 3/ laminates at 25/spl middot/ /spl middot/ and 125/spl middot/ /spl middot/ in capacitor applications. The extracted Weibull slope of HfO/sub 2/ T/sub BD/ distribution shows thickness dependence to be explained by percolation theory. We demonstrate that elevated operation temperature further accelerates HfO/sub 2/ breakdown than HfO/sub 2/-Al/sub 2/O/sub 3/ laminates, resulting from severe temperature dependent leakage currents due to different conduction mechanisms.