Kwang-Ryul Kim

Hybrid Laser Cutting for Flat Panel Display Glass

A new laser glass cutting technology using femtosecond and CO2 lasers is presented. Mechanical breaking after scribing using a femtosecond laser was evaluated and compared with the hybrid method for the cutting of flat panel display (FPD) glass. Various laser fluences were tested to determine the threshold energy and optimum grooving conditions without microcracks. The hybrid method was very effective for the FPD glass microfabrication and for performing full cutting without the mechanical breaking process. Consequently, it was found that the FPD panel was clearly cut using the method and the methodologies were very effective even for a mass-production cutting system.

High performance nonvolatile memory using SiO2/SiOx/SiOxNy stack on excimer laser-annealed polysilicon and the effect of blocking thickness on operation voltage

Silicon-rich SiOx material is a good charge storage candidate for memory applications that promise a large memory window and low operation voltage. Nonvolatile memory (NVM) devices fabricated on excimer laser-annealed polysilicon using SiO2/SiOx/SiOxNy (OOxOn) structure are investigated with SiO2 blocking thicknesses changing from 15 to 20 to 30 nm. The Si-rich SiOx material exposed numerous non-bridging oxygen hole-centre defect sources and a rich silicon phase in the base material. These defects, as well as amorphous silicon clusters existing in the SiOx layer, enhance the charge storage capacity of the device. Retention properties were ensured by 3.2 nm SiOxNy tunnelling layer growth via N2O plasma-assisted oxynitridation. NVM characteristics showed a retention exceeding 85% of the threshold voltage shift after 104 s and greater than 70% after 10 years. Depending on the blocking thickness of 15, 20 or 30 nm, operating voltages varied from ±9 to ±13 V at a programming/erasing duration of only 1 ms. These excellent operating properties of the OOxOn structure make it a potential competitor among the new generation of memory structures on glass.

Effects of electron trapping and interface state generation on bias stress induced in indium–gallium–zinc oxide thin-film transistors

The electrical characteristics of bias temperature stress (BTS) induced in amorphous indium–gallium–zinc oxide thin-film transistors (a-IGZO TFTs) were studied. We analyzed the threshold voltage (VTH) shift on the basis of the effects of positive bias temperature stress (PBTS) and negative bias temperature stress (NBTS), and applied it to the stretched-exponential model. Both stress temperature and bias are considered as important factors in the electrical instabilities of a-IGZO TFTs, and the stretched-exponential equation is well fitted to the stress condition. VTH for the drain current–gate voltage (IDS–VGS) curve and flat-band voltage (VFB) for the capacitance–voltage (C–V) curve move in the positive direction when PBTS is induced. However, in the case of NBTS, they move slightly in the negative direction. To clarify the VTH shift phenomenon by electron and hole injection, the average effective energy barrier (Eτ) is extracted, and the extracted values of Eτ under PBTS and NBTS are about 1.33 and 2.25 eV, respectively. The oxide trap charges (Not) of PBTS and NBTS calculated by C–V measurement are 4.4 × 1011 and 1.49 × 1011 cm−2, respectively. On the other hand, the border trap charges of PBTS and NBTS are 6.7 × 108 and 1.7 × 109 cm−2, respectively. This indicates that the increased interface trap charge, after PBTS is induced, captures electrons during detrap processing from the border trap to the conduction band, valence band, and interface trap.

Direct write patterning of ito film by femtosecond laser ablation

Indium tin oxide (ITO) is a commonly used conducting transparent oxide film (CTO) used in flat panel display applications. The ITO needs to be patterned during panel fabrication to form pixels and to repair defects. Direct write laser ablation is sometimes employed for this purpose and it is important that the substrate material and remaining ITO be affected as little as possible by the laser ablation. In this investigation, femtosecond laser ablation of ITO was studied to identify laser processing parameters which cleanly ablated ITO with a minimum of damage to a glass substrate and surrounding ITO. The material used for the experiments was glass with a deposited ITO film thickness of approximately 150 nm. The Ti:Sapphire chirp pulse amplified femtosecond laser used for the experiments had a wavelength of 775nm and produced pulses with a duration of 150 fs at a rate of 2 kHz. The pulse energy was attenuated with thin film polarizers and was focused by a 10x microscope objective with NA=0.6 and 25.4 mm focal length achromatic lens, producing a calculated minimum spot sizes of 2.5 µm and 6.5 µm respectively. The fiber-based femtosecond laser used for experiments had a wavelength of 1045 nm and pulses with a duration of 500 fs at a rate of 100 kHz. It was focused with a 20x microscope objective to spot sizes of 3.6 µm and 6.3 µm. Ablation was carried out at a sufficiently high panel scanning speed that single ablation spots could be studied. The pulse energy was adjusted to determine feasible spot diameters and depths which could be ablated into the ITO without damaging the glass substrate. Ablation of lines without glass damage was also demonstrated. The beam from the Ti:Sapphire laser was also used focused at the tip of an atomic force microscope (AFM) and the feasibility of nanomachining was demonstrated with this apparatus.Indium tin oxide (ITO) is a commonly used conducting transparent oxide film (CTO) used in flat panel display applications. The ITO needs to be patterned during panel fabrication to form pixels and to repair defects. Direct write laser ablation is sometimes employed for this purpose and it is important that the substrate material and remaining ITO be affected as little as possible by the laser ablation. In this investigation, femtosecond laser ablation of ITO was studied to identify laser processing parameters which cleanly ablated ITO with a minimum of damage to a glass substrate and surrounding ITO. The material used for the experiments was glass with a deposited ITO film thickness of approximately 150 nm. The Ti:Sapphire chirp pulse amplified femtosecond laser used for the experiments had a wavelength of 775nm and produced pulses with a duration of 150 fs at a rate of 2 kHz. The pulse energy was attenuated with thin film polarizers and was focused by a 10x microscope objective with NA=0.6 and 25.4 mm fo...

Low-Temperature Solid Phase Epitaxial Regrowth of Silicon for Stacked Static Random Memory Application

Solid phase epitaxy (SPE) techniques have been studied to realize stacked static random memory (SRAM) devices. Among the candidates including epitaxial lateral overgrowth (ELO) and laser epitaxial growth (LEG) techniques, SPE is the most stable and cost-effective scheme since it is fulfilled by the deposition of amorphous silicon layers and the subsequent low temperature annealing using conventional furnace equipment which has been used for several decades in semiconductor fabrication. We introduced silicon seeds for the epitaxial realignment of amorphous silicon within the contact window by the selective epitaxial growth (SEG) of single-crystalline silicon. The role of process variables associated with channel silicon deposition on SPE was investigated. The efficiency of SPE was quantified by electron back-scatter diffraction (EBSD) measurement, which visualizes the fraction of the orientation in a channel silicon layer. SiH4 ambient during the ramp-up stage in the deposition of amorphous silicon layers showed superior epitaxial realignment to N2 ambient, which was mainly due to the suppression of interfacial layer formation. Electrical characteristics such as on-current distribution and static noise margin indicated SPE to be feasible for high-density stacked SRAM application.

Laser micromachining of CNT/Fe/Al2O3 nanocomposites

Abstract CNT/Fe/Al 2 O 3 mixed powders were synthesized from Fe/Al 2 O 3 nanopowders using thermal CVD for the homogeneous dispersion of carbon nanotubes CNTs. CNTs consisted of MWNT, and the diameter was approximately 20-30 nm. After sintering, CNTs were homogenously located throughout Al 2 O 3 grain boundary and were buckled. A femto-second laser installed with special optical systems was used for micromachining of the nanocomposites. The relationship between material ablation rate and energy fluence was theoretically investigated and compared with experimental results from cross-sectional SEM analysis. The nanocomposites which have higher content of CNT show a fairly good machining result due to its higher thermal conductivity and smaller grain size as well as lower light transmittance.

Effect of Series Resistance on Field-Effect Mobility at Varying Channel Lengths and Investigation into the Enhancement of Source/Drain Metallized Thin-Film Transistor Characteristics

The degradation in device performance due to parasitic resistance along the source and drain electrodes is a serious problem in thin-film transistor fabrication. The effect of this series resistance on the field-effect mobility has been discussed and solutions for the reduction of this unexpected resistance were studied in this work. From the derivation of the drain current, it was shown that the additional resistance had a greater influence on short-channel devices. The ratio of the series resistance to the channel resistance determined the amount of degradation to the field-effect mobility. A thin-film transistor using an aluminum-metallized source/drain was suggested; it showed an improvement in comparison with the conventional doped source/drain device, with a maximum mobility of 105 cm2 V-1 s-1. However, significant degradation of the mobility in the short-channel cases exposed the limitations of the structure. By employing doping for the source/drain metallized structure the maximum mobility reached a value of 150 cm2 V-1 s-1. The decrease in the mobility caused by the channel length decrease was also improved. This study clearly explained the problem of additional resistance on the field-effect mobility of thin-film transistors and the achievements of a device using a self-aligned fabrication process with metallized electrodes.

Investigation of Aluminum Metallized Source/Drain Thin Film Transistors Using a Self-Aligned Fabrication Process

For a better thin film transistor performance, metal silicide has been studied in order to enhance the conductivity of the source and drain electrodes. Although aluminum does not form a metal silicide with silicon, the two materials interpenetrate in an induced crystallization process. In such a structure, aluminum can act as a p-type dopant in the silicon lattice. In this work, aluminum metallized source/drain thin film transistors with excimer laser-annealed polycrystalline silicon were fabricated using a simple self-aligned process. The source/drain regions were patterned with a lift-off process. The n-channel characteristics of the as-deposited aluminum source/drain were explored and an improvement in the performance was observed after a heat treatment at 250 °C for 1 h. The devices treated at 350 °C for 10 h exhibited p-channel characteristics. The device characteristics were compared with another fabricated p-type doped source/drain structure. A remarkable enhancement in the performance of the aluminum metallized source/drain devices was observed. These structures yielded a peak field effect mobility of about 105 cm2V-1s-1. The simple fabrication process and resulting enhancement in device performance makes this type of structure ideal for use in thin film transistors on glass.