Jae-Hong Jeon

The Effect of Passivation Layers on the Negative Bias Instability of Ga-In-Zn-O Thin Film Transistors under Illumination

Ga-In-Zn-O (GIZO) thin film transistors (TFTs) with disparate passivation structures were fabricated and their stabilities were compared. The devices were subjected to a negative bias stress with simultaneous exposure to visible light. TFT that incorporates a dual passivation composed of a SiO x layer grown at a relatively high temperature with an additional SiN x film deposited shows only -0.8 V V th shift, whereas a -5.7 V shift was observed for a TFT covered by a single SiO 2 film. The device degradation is susceptible to the ability of protecting external moisture, which may adsorb on the surface of the GIZO semiconductor to create donor states therein.

Double-layered passivation film structure of Al2O3/SiNx for high mobility oxide thin film transistors

The optimization of the passivation process for oxide thin film transistors with high carrier mobility was investigated. Hydrogen incorporation into oxide channels during the deposition of SiNx could degrade device stability and uniformity, especially for high-mobility devices. A novel double-layered passivation film structure composed of Al2O3/SiNx was proposed, in which thin and dense Al2O3 film prepared by atomic layer deposition was introduced underneath the SiNx layer. In-Ga-Zn-O TFT passivated with the proposed double-layered films showed no significant negative shift in turn-on voltage, even after passivation. The field-effect mobility and subthreshold swing were typically measured as 27.7 cm2 V−1 s−1 and 0.11 V/dec, respectively. Hydrogen doping was effectively protected by the introduction of Al2O3 as thin as 15 nm.

Device reliability under electrical stress and photo response of oxide TFTs

Abstract— The stability of oxide TFTs has been the main focus of this research and is probably the most crucial requirement for the successful application to flat-panel displays. Although the high Fermi level of oxide semiconductors makes TFTs basically stable under electrical stress, the device reliability under diverse variations of electrical stress is affected by materials such as active semiconductors and gate insulators, processes for the formation of back/front channels and passivation layers, and device configurations among other things. How these factors affect the device reliability have been investigated and a review of the stability is presented. In addition, several categories of the light instability of oxide TFTs is presented and the origin is discussed.

A Study of Parameters Related to the Etch Rate for a Dry Etch Process Using NF3/O2 and SF6/O2

The characteristics of the dry etching of :H thin films for display devices using SF6/O2 and NF3/O2 were investigated using a dual-frequency capacitively coupled plasma reactive ion etching (CCP-RIE) system. The investigation was carried out by varying the RF power ratio (13.56 MHz/2 MHz), pressure, and gas flow ratio. For the :H film, the etch rates obtained using NF3/O2 were higher than those obtained using SF6/O2 under various process conditions. The relationships between the etch rates and the usual monitoring parameters—the optical emission spectroscopy (OES) intensity of atomic fluorine (685.1 nm and 702.89 nm) and the voltages and —were investigated. The OES intensity data indicated a correlation between the bulk plasma density and the atomic fluorine density. The etch rate was proportional to the product of the OES intensity of atomic fluorine and the square root of the voltages on the assumption that the velocity of the reactive fluorine was proportional to the square root of the voltages.

P-61: A Study on the Galvanic Reaction between Cu and Mo as Well as MoW for TFT-LCDs by Using a Zero-Resistance Ammeter

Recently, copper metallization has been widely developed in TFT-LCD industry, because of its lowest electrical resistivity compared to aluminum and its alloys. In addition, the copper metallization becomes a more significant issue in a high frequency driving technology for large sized TFT-LCD panel. Since copper has a low adhesion force against the glass substrate, copper is inevitably used with an aid of an adhesive metal layer such as Ti, Ta and Mo. When dissimilar metals like copper and molybdenum are exposed together in a wet etchant, a typical galvanic reaction occurs and this results in an undercutting of copper line or partial stains on the metal surface after drying. The suitable taper angle of Cu line is difficult to obtain especially coupled with pure molybdenum. Such failures often lead to a bad performance of thin film transistor and the display quality. There are many literatures related to the copper metallization for TFT. However, a systematic approach on the galvanic reaction occurred in copper multilayered system has not been made. In this work, we investigated a feasibility of molybdenum alloy film (MoW) for copper metallization on the basis of the thin film analysis and the advanced electrochemical techniques such as Zero Resistance Ammeter (ZRA) method.

A comparative study of algorithm for fluid simulation of high density plasma discharges

A new algorithm for steady-state fluid simulation of high density, low temperature plasma discharge is suggested. The restriction on simulation time step and a new method to overcome it is discussed. For a comparison of the new method with a previous other method, a one-dimensional fluid simulation of inductively coupled plasma discharge is studied.

Light Response of Top Gate InGaZnO Thin Film Transistor

The light stability of top gate indium gallium zinc oxide (IGZO) thin film transistor (TFT) has been investigated under gate bias and constant current stress to explore the possibility of active matrix display applications. While the halogen lamp irradiation onto the device under positive gate bias stress caused just -0.18 V of threshold voltage shift (ΔVth), it resulted in -15.1 V shift under negative gate bias stress. When the white light extracted from the halogen lamp of 100 µW/cm2 power illuminated the device under constant current stress, operation voltage shifted just -0.05 V for 21 h. The result shows good promise for the application of highly stable IGZO TFT to active matrix organic light emitting diodes (AMOLEDs).

P‐107: Low Voltage Driving Color Active Matrix Electrophoretic Display

We have prepared ZnO TFT driving color AMEPD using nano-scale electrophoretic ink particles made by invented modified emulsion process. New concept of color filter using silver halide technology — similar with photographic technology-which is suitable for reflective EPD application was adapted to develop color filters. To get rid of align process for color filters and TFT arrays, transparent ZnO TFT with low temperature process was fabricated. In case of monochrome EPD, the contrast ratio was 23:1 at operating voltage of ± 10V. Zone color prototype AMEPD was fabricated with silver halide color filter.

79.2: Wet Patterning of Thin Films in Vertical Transfer Wet Station for TFT Manufacturing

Compared with tilt transfer wet station, vertical etching system has a many advantages that are 50% space savings, higher throughput and good etch uniformity over an entire glass for thin film transistor application. The aim of the present work is to analysis on a vertical etching system to improve the process factors. The computational fluid dynamics analysis is used to testify the change of the etch uniformity as a function of tilt angle of the glass substrate.

P-22: Electrical Stability of ZnO TFT during Gate-Bias Stress

We fabricated TFTs with ZnO thin film as an active layer. Electrical bias stress test of ZnO TFT was also carried out. The results of stress test of ZnO TFT differed from those of a-Si:H TFT. Therefore, the instability of ZnO TFT cannot be explained by conventional degradation mechanisms of a-Si:H TFT. The variance of some factors in the fabrication process showed a certain trend in the results of bias stress. A possible mechanism of abnormal behavior under the gate bias stress was discussed.