Ju-Pyung Lee

Degradation mechanism of organic light-emitting device investigated by scanning photoelectron microscopy coupled with peel-off technique

The authors present space-resolved spectroscopic data on organic layers of a degraded organic light-emitting device. The data were obtained using a scanning photoelectron microscope (SPEM) coupled with peel-off technique to directly probe the uncontaminated organic layers, which were covered with cathode layer. The SPEM images of the degraded device show different and small size distributions of tris-8-hydroxy quinoline aluminum (Alq3) and hole-transport layers compared to that of as-prepared device. The analysis indicates that bonding strength between Alq3 and cathode layers and between the Alq3 and hole transport layers becomes weak as the device degrades, presumably due to structural deformation of the organic layers.

Scanning photoelectron microscopic study of top-emission organic light-emitting device degradation under high-bias voltage

The degradation process of a top-emission organic light-emitting device (TOLED) under high-bias voltage was investigated using a scanning photoelectron microscope (SPEM). The TOLED was in situ biased to reveal the degraded area inside the SPEM chamber. The SPEM data showed a volcano-type structure inside the degraded area. The overall results of the spectroscopic analysis suggest that strong degradation was accompanied by an eruption underneath the cathode layer. It is posited that the hot gases from the erupted area separated the cathode layer from the organic layer, forming a large bubble, and that, as the bubble exploded, the pressure of the gas blew away the cathode layer.

RAID-optimal data placement in a hybrid solid-state drive

Flash-based solid-state drives (SSD) are widely accepted from mobile devices to enterprise storage arrays. They are best known for delivering low power consumption and high random I/O performance that far exceeds hard-disk drives (HDD). One configuration to enhance performance and reliability further is to connect multiple SSDs to a RAID controller. In this paper, we propose an intelligent, hybrid SSD that is optimized in distributed-parity RAID schemes by recognizing data-parity block sequence and placing parity blocks in higher endurance memory cells. The experimental results show that our predictive data placement extends SSD lifetime by 31% on average, compared to the history-based hot data placement.

Preemptibility-aware responsive multi-core scheduling

We propose a novel responsive scheduling technique to minimize the scheduling latency of a real-time process in the multi-core architecture, called the preemptibility-aware scheduling (PAS). Modern complex operating systems contain numerous long interrupt-disabled and non-preemptible sections, and consequently these sections obstruct the immediate handling of urgent interrupts and the rapid scheduling of interrupt-driven real-time tasks, causing significant latency between interrupt arrival and process scheduling. The proposed PAS guarantees that before an urgent interrupt occurs, at least one among multiple CPU cores is always in both interrupt-enabled and preemptible sections, so that the incoming urgent interrupt can always be handled with no significant delay by such CPU core. Experimental results show that the worst-case latency can be reduced by 27-96%.

Utilization analysis of trim-enabled NAND flash memory

In this paper, we present a novel probabilistic model of the utilization for trim-enabled NAND flash memory devices. This model provides a simple and powerful method to reason about the performance of NAND flash memory, given its capacity and the frequency of write operations.