Seok-Woon Lee

Low temperature poly-Si thin-film transistor fabrication by metal-induced lateral crystallization

A new low temperature crystallization method for poly-Si TFTs was developed: Metal-Induced Lateral Crystallization (MILC). The a-Si film in the channel area of a TFT was laterally crystallized from the source/drain area, on which an ultrathin nickel layer was deposited before annealing. The a-channel poly-Si TFTs fabricated at 500/spl deg/C by MILC showed a mobility of 121 cm/sup 2//V/spl middot/s, a threshold voltage of 1.2 V, and an on/off current ratio of higher than 10/sup 6/. These electrical properties are much better than TFTs fabricated by conventional crystallization at 600/spl deg/C.

Pd induced lateral crystallization of amorphous Si thin films

A thin palladium layer (∼40 A) was selectively formed on top of amorphous silicon films before annealing and the effects of palladium layer on the crystallization behavior of the amorphous silicon films were investigated. It was observed that the amorphous silicon right under the Pd layer could be crystallized to grain sizes of several hundred angstroms by annealing at 500 °C. In addition, the area between the Pd thin pads, patterned by lithography, was found to be crystallized to grain sizes of a few tens of microns in length by the same annealing. Such lateral crystallization was found to reach more than 100 μm in some cases. The lateral crystallization phenomenon might be useful for the fabrication of low temperature polycrystalline‐Si thin film transistors, providing large‐grained Si films.

Resistive memory switching in epitaxially grown NiO

Epitaxial NiO films have been fabricated on SrRuO3 films prepared on SrTiO3 single-crystal substrates. The x-ray diffraction spectra and transmission electron microscopy confirm the epitaxial growth of NiO with atomically flat surfaces on the SRO electrode. The I-V measurements of epitaxial NiO show the resistive memory switching behavior with a change in the polarity of the voltage bias, in contrast with the switching behavior of polycrystalline NiO by a single polarity. The I-V characteristics of epitaxial NiO prepared under various synthesis conditions and electrodes are presented, which suggests an important role of interfaces between NiO and electrodes on the resistive switching behavior.

Electrical characteristics of MILC poly-Si TFTs with long Ni-offset structure

We have observed that B/sub 2/H/sub 6/-doped amorphous silicon (a-Si) showed a faster growth rate of metal-induced lateral crystallization (MILC) than that of undoped a-Si. From the analysis of the microstructure, it was thought that boron atoms could help modify the growth behavior from that of a branched crystal network to unidirectional crystal growth with few branches and that growth rate could to be enhanced. By using this good crystalline structure at the boundary region between the source/drain and channel, we have successfully fabricated p-type poly-Si thin-film transistors with good electrical properties with a MILC process.

Low‐temperature dopant activation and its application to polycrystalline silicon thin film transistors

Low‐temperature activation of dopants in amorphous silicon films was achieved by a new method and high‐performance polycrystalline silicon thin film transistors were fabricated through its application. It was found that the dopants implanted into amorphous silicon were activated simultaneously with the crystallization of amorphous silicon. With the help of a thin nickel layer, the thermal budget for dopant activation and crystallization was considerably reduced, from 600 °C (30 h) to 500 °C (5 h). Even without plasma hydrogenation, the n‐channel polycrystalline silicon thin film transistors fabricated at temperatures below 500 °C showed a mobility of 120 cm2/V s, which is much higher than that of conventional devices fabricated at 600 °C.

Effect of cobalt addition on the liquid-phase sintering of W-Cu prepared by the fluidized bed reduction method

A new process, fluidized bed reduction (FBR) method, was applied for fabrication of uniform W-Cu sintered material. Liquid-phase sintering was carried out to obtain fully densified W-Cu composite, and the effect of cobalt addition on the sintering behavior was investigated. It was found that fully densified material could not be obtained even after sintering at 1200 °C for 4 hours in the case of 75W-25Cu, while more than 96 pct density could be obtained as soon as the sintering temperature reached 1200 °C when 0.5 wt pct cobalt was added prior to the sintering. It has been found that the wetting angle of the liquid copper is reduced significantly by the addition of cobalt, and the formation reaction of Co7W6 intermetallic compound at the surface of the tungsten powder is mainly responsible for the enhancement of the densification process.

Room Temperature Fabrication of Micro-Crystalline Silicon Films for Tft's By Ecr Pecvd

Microcrystalline silicon films were formed at room temperature without hydrogen dilution by ECR PECVD. Microwave power more than 400 W was necessary to get crystalline films and the crystallinity increased with the power thereafter. Addition of hydrogen and argon enhanced the crystalline phase formation and the deposition rate, the reason of which was found that hydrogen etched silicon films and argon addition drastically increased the etch rate. Annealing of the films showed that microcrystalline silicon films formed by ECR PECVD have a small fraction of amorphous phase. TFTs using silicon nitride and doped/undoped microcrystalline silicon films were fabricatedd with whole processes at room temperature.