Masashi Tsubuku

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.

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.

Single crystalline In?Ga?Zn oxide films grown from c-axis aligned crystalline materials and their transistor characteristics

In this study, we analyzed the crystallinity of c-axis aligned crystalline In?Ga?Zn oxide (CAAC-IGZO) and single crystalline (sc) IGZO films. CAAC-IGZO films were formed on (111)-oriented yttria-stabilized-zirconia substrates by magnetron sputtering using a target. Sc-IGZO films were obtained by annealing CAAC-IGZO films at 1200 ?C. The proportion of Zn in the composition changed during growth of the films, and as a result, sc-InGaO3(ZnO)3 films were obtained. By using CAAC-IGZO films as the starting material, sc-IGZO films were formed even without a ZnO layer. This is presumably because the CAAC-IGZO film originally exhibits c-axis orientation. In addition, the characteristics of transistors fabricated using sc-IGZO and CAAC-IGZO films were compared, and no significant difference in current drivability, i.e., field-effect mobility, was observed between the different transistors. In this sense, CAAC-IGZO films that require no high temperature annealing are favorable for industrialization.

76.1: High Aperture Ratio LCD Display using In-Ga-Zn-Oxide TFTs without Storage Capacitor

By using oxide semiconductors, we succeeded in prototyping a 3.4-inch QHD LCD panel whose aperture ratio is high and pixels do not include a storage capacitor. The aperture ratio is increased from 40 % to 59%, resulting in reduction of power consumption in a backlight unit.

Correlation between crystallinity and oxygen vacancy formation in In–Ga–Zn oxide

We study the effect of indium–gallium–zinc oxide (IGZO) crystallinity on oxygen vacancies that play an important role in the characteristics of IGZO-based devices. Optical and electrical measurements revealed that deep defect levels due to oxygen vacancies are largely eliminated in c-axis-aligned crystal IGZO (CAAC-IGZO), which has increased crystallinity without clear grain boundaries. In this study, the correlation between crystallinity and oxygen vacancy formation has been examined by first-principles calculations to investigate the effect of oxygen vacancies in IGZO. Furthermore, the likelihood of oxygen vacancy formation at an edge portion of single-crystal IGZO has been verified by observations of oxygen atoms at the edge region of the IGZO film by annular bright-field scanning transmission electron microscopy (ABF-STEM). Experimental and calculation results show that the high crystallinity of IGZO is important for the inhibition of oxygen vacancies.

Driver-circuits-integrated LCDs based on novel amorphous In-Ga-Zn-oxide TFT

— A liquid-crystal panel integrated with a gate driver and a source driver by using amorphous In—Ga—Zn-oxide TFTs was designed, prototyped, and evaluated. By using the process of bottom-gate bottom-contact (BGBC) TFTs, amorphous In—Ga—Zn-oxide TFTs with superior characteristics were provided. Further, for the first time in the world, a 4-in. QVGA liquid-crystal panel integrated with a gate driver and a source driver was developed by using BGBC TFTs formed from an oxide semiconductor. By evaluating the liquid-crystal panel, its functionality was successfully demonstrate. Based on the findings, it is believed that the novel BGBC amorphous In—Ga—Zn-oxide TFT will be a promising candidate for future large-screen backplanes having high definition.