Tadashi Serikawa

15.2: Development of Driver-Integrated Panel Using Amorphous In-Ga-Zn-Oxide TFT

We designed, prototyped, and evaluated LCD integrated with a gate driver and a source driver using amorphous In-Ga-Zn-Oxide TFTs having bottom-gate bottom-contact structure, thereby obtaining TFTs with superior characteristics. Then, we prototyped the worlds first 4-inch QVGA LCD and integrated the gate driver and source driver on the display panel.

21.3: 4.0 In. QVGA AMOLED Display Using In‐Ga‐Zn‐Oxide TFTs with a Novel Passivation Layer

We have developed a 4.0 inch QVGA AMOLED display using amorphous In-Ga-Zn-Oxide TFTs, focusing on a passivation layer. Threshold voltage of the TFTs can be controlled to have “normally off” characteristics by using SiOx with a low hydrogen content. Besides, small subthreshold swing and high saturation mobility are obtained.

Low-temperature fabrication of high-mobility poly-Si TFTs for large-area LCDs

A low-temperature process developed for fabrication of high-mobility polycrystalline silicon thin-film transistors (poly-Si TFTs) is discussed. Its main feature is the use of a sputter-deposited Si film followed by laser irradiation and a sputter-deposited gate SiO/sub 2/ film. The poly-Si TFTs have a mobility of 350-cm/sup 2//V-s. They have been successfully applied to peripheral circuits for large-area liquid-crystal displays (LCDs). >

A model of current—Voltage characteristics in polycrystalline silicon thin-film transistors

An empirical model for the current-voltage characteristics of polycrystalline silicon thin-film transistors is presented. The model was constructed based on the premise that the potential barrier height at the grain boundary depends on both the gate and drain voltages. Polycrystalline silicon film transistors having a coplanar structure were fabricated. Measurements demonstrated excellent agreement with calculations for n-channel devices. In addition, carrier-trap density and grain-boundary mobility, which have strong influences on electrical characteristics, were obtained from this model.

High-quality polycrystalline Si TFTs fabricated on stainless-steel foils by using sputtered Si films

We have developed a low-temperature fabrication process (/spl les/ 200/spl deg/C for high-quality polycrystalline Si thin-film transistors (poly-Si TFTs) on flexible stainless-steel foils. The fabrication processes is realized through sputter deposition of thin films, including active-Si and gate-SiO/sub 2/ films, crystallization of Si films by KrF excimer laser irradiation, and inductively coupled plasma hydrogenation. High-quality n- and p-channel poly-Si TFTs are successfully fabricated without suffering from problems of substrate bending, film ablation, or cracking in films. The resulting n- and p-channel poly-Si TFTs showed mobilities of 106 and 122 cm/sup 2//V/spl middot/s, respectively. This paper describes the deposition and properties of the sputtered Si films and the fabrication process and electrical characteristics of the poly-SiTFTs.

Electrical Characteristics of High-Mobility Fine-Grain Poly-Si TFTs from Laser Irradiated Sputter-Deposited Si Film

Electrical characteristics of n-channel fine-grain polycrystalline silicon thin-film transistors (poly-Si TFTs) fabricated from a sputter-deposited Si film irradiated with laser light have been measured. The fine-grain poly-Si TFTs have attained a high mobility of 383 cm2/Vs despite a small grain size from 40 nm to several hundred nanometers. The high-mobility fine-grain poly-Si TFTs feature decreases in mobility with gate voltage and decreases in drain current with temperature in a manner similar to single-crystal MOSFETs. They also show a low carrier trap state density Nst at grain boundaries of 5.6×1011 cm-2. High mobility in the poly-Si TFTs is due to a low Nst.

High-Mobility Poly-Si Thin Film Transistors Fabricated on Stainless-Steel Foils by Low-Temperature Processes Using Sputter-Depositions

High mobility n- and p-channel polycrystalline Si thin film transistors (poly-Si TFTs) are successfully fabricated on flexible stainless-steel foils through low-temperature processes (200°C). In the low-temperature process, all films in the poly-Si TFT including active Si and gate SiO2 films are deposited by glow-discharge sputtering and the Si films are crystallized by KrF excimer laser irradiation. Resulting n- and p-channel poly-Si TFTs show excellent characteristics of mobility of 106 cm2/Vs and 66 cm2/Vs, respectively. Moreover, they show low off-currents of 1×10-10 A and on/off current ratios as high as 1×106. Thus, these poly-Si TFTs are very promising for driver circuits and switching devices in novel flat panel displays of lightweight and mechanically strong liquid crystal displays and light emitting displays.

Electrical characteristics of MOSFET's utilizing Oxygen—Argon sputter-deposited gate Oxide films

This paper presents a detailed look at the electrical characteristics of MOSFETs utilizing oxygen-argon sputter-deposited gate-oxide films for low-temperature MOSFET fabrication. The gate-oxide films are deposited at low temperature (200°C) by oxygen-argon sputtering of an SiO2target. The MOSFETs so formed are confirmed to have triode characteristics. Moreover, oxygen mixing makes it possible to considerably improve the MOSFET field-effect mobility and subthreshold slope over those of argon-only sputter-deposited film to 700 cm2/Vs and 170 mV/decade. These improvements are found to be caused by the remarkable reduction in surface-state density. These results confirm the usefulness of oxygen-argon sputter-deposited gate-oxide films for MOSFET fabrication at low temperature.

Electrical analysis of high-mobility poly-Si TFTs made from laser-irradiated sputtered Si Films

Polysilicon thin-film transistors (TFTs) fabricated from laser-irradiated sputtered Si films are electrically analyzed for carrier trap state density N/sub st/, temperature dependence of drain current, Hall effect, and potential profile in the channel. The field-effect mobility of the poly-Si TFTs increases 390 cm/sup 2//V-s with decreasing N/sub st/. With N/sub st/ decreasing, the activation energy obtained from the temperature dependence of drain current changes from a positive to a negative value which is almost equal to the value for single-crystal MOSFETs. Carrier velocity increases as N/sub st/ is decreased, but carrier concentration is nearly independent of N/sub st/. Plateau regions of zero electric field were observed in poly-Si TFTs with high N/sub st/. Therefore, it is concluded that high mobility occurs as a result of increasing carrier velocity, and electric field and of lowering the potential barrier by reducing N/sub st/. >

Development of Liquid Crystal Display Panel Integrated with Drivers Using Amorphous In–Ga–Zn-Oxide Thin Film Transistors

We designed, prototyped, and evaluated a liquid crystal panel integrated with a gate driver and a source driver using amorphous In–Ga–Zn-oxide thin film transistors (TFTs). Using bottom-gate bottom-contact (BGBC) thin film transistors, superior characteristics could be obtained. We obtained TFT characteristics with little variation even when the thickness of the gate insulator (GI) film was reduced owing to etching of source/drain (S/D) wiring, which is a typical process for the BGBC TFT. Moreover, a favorable ON-state current was obtained even when an In–Ga–Zn-oxide layer was formed over the S/D electrode. Since the upper portion of the In–Ga–Zn-oxide layer is not etched, the BGBC structure is predicted to be effective in thinning the In–Ga–Zn-oxide layer in the future. Upon evaluation, we found that the prototyped liquid crystal panel integrated with the gate and source drivers using the TFTs with improved characteristics had stable drive.