Kyoung-Bo Kim

Compositional change of MgO barrier and interface in CoFeB∕MgO∕CoFeB tunnel junction after annealing

Recent experiments have demonstrated high tunneling magnetoresistance (TMR) ratios in magnetic tunnel junctions (MTJs) with the MgO barrier. The CoFeB∕MgO∕CoFeB junctions showed better properties than the CoFe∕MgO∕CoFe junctions because the MgO layer had a good crystalline structure with (001) texture and smooth and sharp interface between CoFeB∕MgO. In this work, the compositional changes in the MgO barrier and at the interface of CoFeB∕MgO∕CoFeB after the CoFeB crystallization were studied in annealed MTJs. X-ray photoelectron spectroscopy depth profiles were utilized for the as-deposited and 340°C annealed specimens. Transmission electron microscope analyses showed that the MgO barrier had (100) texture on CoFeB in the junctions and CoFeB was crystallized in the annealed junctions. B in the bottom CoFeB layer diffused into the MgO barrier and B–oxide was formed at the interface of CoFeB∕MgO∕CoFeB after the CoFeB crystallization. The B behavior will be discussed.

Effects of high pressure annealing on the characteristics of solid phase crystallization poly-Si thin-film transistors

Integrating circuits into organic light emitting diode displays require fabrication of polycrystalline silicon (poly-Si) based thin-film transistors (TFTs) on glass substrates. In this work we evaluated the use of high pressure annealing (HPA) process of poly-Si films in H2O atmosphere to improve TFT characteristics via reducing defect density in poly-Si films. We attempted to develop a HPA process at temperatures below 600°C without causing any glass distortion and reducing the throughput. The HPA-treated poly-Si film was analyzed using various spectroscopic methods such as Raman, x-ray photoelectron spectroscopy, and transmission electron microscope, and the evaluation of the characteristics of TFTs fabricated by such poly-Si films was made. The heating at 550°C with 1MPa H2O vapor increased the carrier mobility from 8.5to20cm2∕Vs and reduced the absolute value of the threshold voltage from 9.6to6.5V, as compared with the conventional solid phase crystallization (SPC) process. The sub-threshold swings a...

Origin of asymmetry of tunneling conductance in CoFeB/MgO/CoFeB tunnel junction

We investigated the top and bottom interfaces of a CoFeB∕MgO∕CoFeB tunnel junction using transmission electron microscope (TEM) and x-ray photoemission spectroscopy (XPS) in order to understand the origin of the asymmetry of dI∕dV in terms of bias polarity. It was found, from a TEM image, that there is no clear cut at the top interface, while the bottom interface has relatively clean boundary. Furthermore, XPS data show that more hydroxides were formed at the top interface than at the bottom interface. These indicate that the hydroxides would hinder the epitaxial crystallinity at the interface in CoFeB∕MgO∕CoFeB tunnel junctions. Therefore, it is most likely that the asymmetry of dI∕dV is caused by the disappearance of minority Bloch state, which is closely correlated with the existence of hydroxides at the top interface of a CoFeB∕MgO∕CoFeB tunnel junction.

P‐21: Investigation of Pattern‐Induced Brightness Non‐Uniformity in AMOLED Displays

We found that pattern-induced line type brightness non-uniformity is related to moire patterns that appear when primary grain boundaries in SLS processed poly-Si are aligned over repetitive TFT patterns such as metal lines. We propose a method to diminish the Moire pattern type non-uniformity by adopting black matrix and top emission TFT structure.

P‐19: Development of Microcrystalline Si for TFT Backplanes

A new composite material based on directly deposited microcrystalline Si (μc-Si) was developed, tested and applied as active layer in top-gate coplanar p-type TFTs. The obtained TFTs characteristics demonstrate high quality of developed μc-Si and possibility of using it in TFT backplanes for AMOLED displays.

Activation barriers of submicron magnetoresistive random access memory cells with single and synthetic antiferromagnet free layers

Thermally activated magnetization reversals of submicron sized magnetic tunnel junctions with NiFe single and NiFe∕Ru∕NiFe synthetic antiferromagnet (SAF) free layers are investigated by varying the pulse durations and current amplitudes in switching pulse measurements. The measured data show good agreement with the switching probability predicted by the Arrhenius-Neel theory and switching behaviors with a single activation energy barrier. Estimated activation barriers for magnetization reversals are higher for magnetic tunnel junctions (MTJs) with SAF free layers than MTJs with single free layers. It is believed that the high activation barrier is achieved by the larger magnetic volume of SAF layers.

Uniformity improvement of SLS poly‐Si TFT AMOLED

Abstract In this study, we attempted to find the origin of brightness non‐uniformity in SLS poly‐Si TFT AMOLED. By developing a suitable SLS process with a compensation circuit, we successfully improved the non‐uniformity from 40% to 1.7%. In addition, we were able to fabricate 2.2? AMOLED display using SLS poly‐Si.