The short device lifetime of blue polymer light‐emitting diodes (PLEDs) is still a bottleneck for commercialization of self‐emissive full‐color displays. Since the cathode in the device has a dominant influence on the device lifetime, a systematic design of the cathode structure is necessary. The operational lifetime of blue PLEDs can be greatly improved by introducing a three‐layer (BaF2/Ca/Al) cathode compared with conventional two‐layer cathodes (BaF2/Al and Ba/Al). Therefore, the roles of the BaF2 and Ca layers in terms of electron injection, luminous efficiency, and device lifetime are here investigated. For efficient electron injection, the BaF2 layer should be deposited to the thickness of at least one monolayer (∼3 nm). However, it is found that the device lifetime does not show a strong relation with the electron injection or luminous efficiency. In order to prolong the device lifetime, sufficient reaction between BaF2 and the overlying Ca layer should take place during the deposition where the thickness of each layer is around that of a monolayer.

New low temperature, low cost, small size packaging technology of novel bulk-micromachined MEMS sensor for mobile applications was developed. The sensor was fabricated with the bulk-micromachining process of SOI substrates and composed with a proof mass, membrane and electrodes for capacitance sensing. The sensor device was capped with very thin (130um-thickness) top and bottom silicon cap wafers which have a 80um-depth cavity. Top and bottom cap wafers were bonded with the sensor wafer with a low temperature curing polymer adhesive lower than 200°C. It is needed that the low temperature packaging technology and the passivation of top and bottom sides of the sensor for keeping the sensor performances and preventing stiction of the proof-mass during the molding processes. After bonding the three substrates, the top cap silicon was dry etched to expose bonding pads for the signal interconnection. The ASIC chip was polished to 75um-thickness, diced and bonded on a half-etched 200um-thick lead-frame with a DAF. The diced wafer-level-capped sensor was stacked on the ASIC, wire bonding was accomplished between the sensor and the ASIC, and the ASIC and the lead-frame and finally transfer molding process was done. The developed package is 24-leads QFN and the dimension is 4.0mm×4.0mm×1.1/1.2mm.

We report the failure mode observed in polymer electroluminescent (EL) blue devices based on SB1 (from Samsung Advanced Institute of Technology). Such modes were analyzed using nondestructive and destructive methods. Using nondestructive methods, we investigated the changes in hole and electron mobility and measured transient EL at various times during device life test. We also observed compositional and morphological variation using TEM-EDX, STM, FT-IR, TOF-SIMS and reverse engineering as destructive methods. Electron mobility was reduced by nearly two orders of magnitude during the device lifetime to half initial luminance and was related to the formation of an insoluble layer inside the emitting layer on the anode side. This insoluble layer showed relatively ordered surface morphology and might be a cross-linked layer through the C-O-C bond cleavage process during EL operation. But, contrary to the sulfur migration mechanism into the insoluble layer suggested by CDT, we confirmed no obvious difference of sulfur composition between insoluble and emitting layers. Rather, we observed some degree of Ba diffusion into the emitting layer from decomposition of BaF 2 , however we do not believe this had a major effect on device degradation.