Nam-Kyu Song

The Reduction of the Dependence of Leakage Current on Gate Bias in Metal-Induced Laterally Crystallized p-Channel Polycrystalline-Silicon Thin-Film Transistors by Electrical Stressing

The high dependence of the leakage current on the gate bias that is normally observed in metal-induced laterally crystallized polycrystalline-silicon (poly-Si) thin-film transistors (TFTs) can be reduced effectively by electrical stressing. This brief examined the mechanism for the decrease in the high dependence of the leakage current on the gate bias in p-channel poly-Si TFTs by electrical stressing. This effect increased with increasing stress bias that is applied to the gate or drain. The effective decrease in leakage current dependence on the gate bias was attributed to electron trapping in the gate oxide during electrical stressing. It was found that this trapping occurred near the drain junction, and electron detrapping (or trap site regeneration) was also observed after annealing at temperatures above 350degC, resulting in an increase in leakage current. This brief proposes a device structure with a low dependence of the leakage current on the gate bias through light doping at the drain region.

A Fabrication Method for Reduction of Silicide Contamination in Polycrystalline-Silicon Thin-Film Transistors

A major cause of degradations in polycrystalline-silicon (poly-Si) thin-film transistors (TFTs) fabricated by Ni metal-induced lateral crystallization (MILC) is known to be due to the presence of Ni silicides in the channel region. In this letter, we proposed a structure for the reduction of Ni silicides in the MILC region. Also, the electrical properties of poly-Si TFTs which were fabricated with the structure were investigated. It was found that the field-effect mobility and the leakage current of p-channel Ni seed MILC TFTs is significantly improved compared to TFTs fabricated by conventional MILC process.

Improvement of the electrical performance in metal-induced laterally crystallized polycrystalline silicon thin-film transistors by crystal filtering

The electrical performance of the polycrystalline silicon (poly-Si) thin-film transistors (TFTs) is greatly affected by the microstructure of the poly-Si. The crystal filtering method is employed to improve the electrical properties of poly-Si TFTs using metal-induced lateral crystallization by the ordering of Si grains. Experimental results indicated that the field-effect mobility of TFTs having crystal filtered poly-Si is more than 2.5 times higher than that of conventional poly-Si TFTs. It is found that the ordered microstructure is one of the key parameters to improve the electrical performance in poly-Si TFTs.

Effects of Mechanical Stress on the Growth Behaviors of Metal-Induced Lateral Crystallization

Effects of external mechanical stress on the growth behaviors of metal-induced lateral crystallization (MILC) were investigated. Results showed that the MILC growth rate was four times faster by the tensile stress than without stress and two times slower by the compressive stress. In the microstructural analysis, needlelike grains were observed to grow along the direction when the tensile stress was applied, but wider grains grew in random directions when compressive stress was applied. These results confirm the applicability of the MILC growth model.

The Electrical Properties of Unidirectional Metal-Induced Lateral Crystallized Polycrystalline-Silicon Thin-Film Transistors

It has been known that adjacent Pd enhances the crystallization rate in Ni metal-induced lateral crystallization (Ni-MILC) and this knowledge has been used to fabricate the unidirectional MILC thin-film transistors (TFTs), which eliminate the boundary formed at the center of TFT channel in a normal MILC TFTs. It is discovered that the MILC/MILC boundary (MMB) is responsible for the high leakage current and low field- effect mobility. The electrical properties of unidirectional MILC TFTs (Width/Length = 10/10 mum) improved considerably comparing to those of MILC TFTs containing the MMB. The leakage current and field-effect mobility, which have been regarded as obstacles for industrialization of the MILC process, measure to be 2.1 X 10-11 A and 83 cm2/ V ldr s, respectively.

A Study on the Pd/a-Si/Ni Seed Layer for Metal-Induced Lateral Crystallization and Poly-Si TFTs

The effect of Pd on the growth rate of metal-induced lateral crystallization (MILC) from Ni seed and the electrical properties of thin-film transistors (TFTs) fabricated on the films crystallized by MILC were investigated. When the Pd metal is placed on the amorphous-silicon/Ni-seed layer, the MILC growth rate is two to three times faster than that of conventional Ni-MILC, without any degradation of TFTs. These results were explained by a stress that is generated by the formation of Pd2Si

A Method for Fabricating Practically Channel-Corner-Free Polycrystalline Silicon Thin-Film Transistors

The influences of metal-induced laterally crystallized silicon channel corners on the performance and reliability of thin-film transistors (TFTs) were investigated. It was found that the TFT with the channel width, mostly applied to active matrix organic light-emitting diodes, had weak immunity to electrical stresses because of the heaviest weight of silicide-rich channel corner on the channel width by the geometric effect. The proposed TFT fabrication, which is composed of two consecutive adjacent step switches, makes TFTs practically channel-corner-free, resulting in high reliability. Moreover, it enables TFTs to have more current flow paths that maintain a high performance.

Selectively Nucleated Lateral Crystallization of Lead Zirconate Titanate Thin Films Using Titanium Island Seed Layer

We have investigated the selectively nucleated lateral crystallization (SNLC) of lead zirconate titanate (PZT) thin film using a titanium seed. The titanium island seed layer was formed on Pt(200 nm)/SiO2(500 nm)/Si by radio frequency magnetron sputtering and lift-off process at room temperature. Selectively nucleated lateral crystallization happened at 570°C and a rectangular array of PZT single grains was formed after 2 hours annealing. Single-grained PZT thin film by SNLC had a comparable hysteresis property with the poly-grained PZT thin film in spite of the lower crystallization temperature. In addition, it had better leakage and fatigue properties than the poly-grained PZT thin film. Enhanced ferroelectric properties of single-grained PZT could be achieved by grain boundary location control. Also, because Titanium-seeded SNLC needs no additional annealing and etching for the seed formation, it is more advantageous than PZT-seeded SNLC.

Modification of the Seed in SNLC and Its Effect on the Electrical Properties of PZT Thin Films

It is well known that electrical properties of PZT thin films can be considerably improved through Selectively Nucleated Lateral Crystallization (SNLC) process. However, we found out that grain boundaries were formed inside the PZT seed and they extended into the laterally crystallized area. In this work, when the rosette boundary was placed to the edge of the seed periphery, we could increase the number of boundaries were formed during SNLC artificially. So, we studied the effect of these boundaries on the electrical properties of PZT thin films and discussed the origin of the boundary formation through observing the first stage of SNLC.