S.Y. Yoon

The distribution of Cu and resultant resistivity change in sputter deposited Al–Cu film as a conductive layer

Abstract As a conductive layer, sputter-deposited Al–Cu 1 at.% thin film was investigated, with particular focus on the effect of Cu precipitates and film strain on the electric conductivity. The 400-nm-thick film was deposited on Si wafer and heat-treated at 200 and 480 °C. Cu precipitation was investigated using electron microscopy and film strain using XRD. As a result of heat treatment, changes in the electric resistivity showed the same trend as the film strain. This study concluded that the trends in resistivity and film stress could be related to Cu precipitation to some extent. In other words, the resistivity changes depending on whether the precipitates are coherent with the Al matrix and on the distribution of the precipitates.

Effect of triplet multiple quantum well structures on the performance of blue phosphorescent organic light-emitting diodes

We investigate multiple quantum well [MQW] structures with charge control layers [CCLs] to produce highly efficient blue phosphorescent organic light-emitting diodes [PHOLEDs]. Four types of devices from one to four quantum wells are fabricated following the number of CCLs which are mixed p- and n-type materials, maintaining the thickness of the emitting layer [EML]. Remarkably, such PHOLED with an optimized triplet MQW structure achieves maximum luminous and external quantum efficiency values of 19.95 cd/A and 10.05%, respectively. We attribute this improvement to the efficient triplet exciton confinement effect and the suppression of triplet-triplet annihilation which occurs within each EML. It also shows a reduction in the turn-on voltage from 3.5 V (reference device) to 2.5 V by the bipolar property of the CCLs.

Optimization of the Organic Lightemitting Diodes with a Red Phosphor

We demonstrate very high efficiency electro phosphorescence in organic light-emitting diodes (OLEDs) employing a phosphorescent molecule doped into a conductive host material. Electrophosphorescent OLEDs were fabricated with bis(2-(2′-benzo[4,5-a]thienyl)pyridinato-N,C3′) iridium(acetylacetonate) [btp2Ir(acac)] as a pure red phosphor which has photoluminescence spectrum centered at 615 nm. The device structure was as follows; ITO/2-TNATA/NPB/btp2Ir(acac) doped in host/BCP/Alq3/Liq/Al. CBP, BCP and Alq3 were used as a host, and the concentration of btp2Ir(acac) was varied from 8 to 11%. The device with 11% btp2Ir(acac) doped in Alq3 showed saturated electroluminescence (EL) peak at 615 nm and an efficiency of 4.76 cd/A with an initial brightness of 1100 cd/m2. The CIE coordinates of the device showed x = 0.67, y = 0.32 at a current density of 1 mA/cm2. The photoluminescence spectrum of Alq3 centered at 510 nm is sufficiently overlap with absorption of dopant, therefore, energy transfer from host to guest is efficient.

Effect of NiO sputtering condition to the exchange anisotropy of NiFe/NiO bilayer

Summary form only given, as follows. Summary form only given. As an application for spin-valve type giant magnetoresistance (GMR) devices, exchange biased NiFe/NiO bilayers have been studied extensively. The current study focuses on the formation of a second phase at the NiO layer and resultant change of the exchange anisotropy in the bilayers. The NiFe/NiO bilayers were deposited on silicon wafers by sputtering and a Ta capping was applied on the bilayer. Target materials were Ni/sub 81/Fe/sub 19/ alloy and NiO oxide. Ar pressure effects on the magnetic properties of the NiO film were studied under constant conditions of input power and film thickness. Rutherford backscattering spectroscopy (RBS) and X-ray photoelectron spectroscopy (XPS) were used to investigate the composition and the chemical state of the NiO film. The magnetic properties of NiO changed with Ar pressure. The exchange bias field (Hex) shows a maximum at 1 mTorr Ar pressure and the coercivity at 2.5 mTorr. The antiferromagnetism of NiO was destroyed gradually with increasing Ar pressure This destruction of antiferromagnetism occurs mainly at the interface of NiO and NiFe, due to the formation of an amorphous phase. RBS results show that there are two Ni oxide phases, antiferromagnetic NiO and nonmagnetic Ni/sub 2/O/sub 3/. We conclude that the amorphous Ni/sub 2/O/sub 3/ phase results in the destruction of exchange anisotropy of NiFe/NiO bilayers.

The effect of controlled P1 and P2 in synthetic spin valve with Mn–Ir–Pt exchange biasing layer

Abstract Synthetic top and bottom spin valves including the Mn–Ir–Pt/Co–Fe (P1)/Ru/Co—Fe (P2) synthetic pinned layer were prepared by controlling the thickness difference (Δ t =P1–P2) of Co–Fe layers. The effective exchange field ( H eff,ex ) and giant magnetoresistance (GMR) properties of both synthetic type SVs were investigated as a function of Δ t . The H eff,ex was dependent largely on the Δ t . The GMR properties are strongly dependent on the stacking sequence of synthetic SVs and Δ t . Based on the magnetic and electrical properties at room temperature, the thermal stability of synthetic SVs was also evaluated at various elevated temperatures in both types of SVs.