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We have fabricated top-gate field-effect transistors (FETs) based on an oxide semiconductor for high-performance driving capability. The optimization of the plasma treatment enabled a 50-nm-thick gate insulating film and a short channel length of these FETs, enabling a high FET performance.

We used new In-Ga-Zn oxide composition (In:Ga:Zn = from 4:2:3 to 4:2:4.1) to fabricate bottom-gate, top-contact field-effect transistors with high mobility and stability. Here we discuss these improvements in mobility and stability based on experiments and calculations. We succeeded in fabricating a 513-ppi in-cell-type touch panel using this In-Ga-Zn oxide.

A prototype of an 8.34 inch, 1058 ppi 8K4K display is fabricated. This display shall use top-gate self-aligned-type crystalline oxide semiconductor field-effect transistors as the backplane, and will be the smallest 8K display in the world.

A field effect transistor (FET) using c-axis aligned crystalline In–Ga–Zn–O (CAAC-IGZO) for an active layer has an extremely low off-state current, which is much lower than an off-state current of a silicon FET. As we measured and analyzed the off-state current, the voltage drop caused by the off-state current in a memory device was found to approach to a stretched exponential function. This is because in the off-state CAAC-IGZO FET, a small number of carriers move discretely and current does not flow uniformly. The low off-state current was also maintained even when its channel length was scaled down to approximately 50 nm.

We investigated In-Ga-Zn oxide films deposited by two types of sputtering methods: planar magnetron and facing-target. In crystallinity, we found that silicon diffused from SiOx prevents crystallization regardless of the sputtering method. In electrical property, we found that mobility of films deposited by facing-target sputtering less depends on carrier concentration.

Our crystalline In–Ga–Zn oxide (IGZO) thin film has a c-axis-aligned crystal (CAAC) structure and maintains crystallinity even on an amorphous base layer. Although the crystal has c-axis alignment, its a-axis and b-axis have random arrangement; moreover, a clear grain boundary is not observed. We fabricated a back-channel-etched thin-film transistor (TFT) using the CAAC-IGZO film. Using the CAAC-IGZO film, more stable TFT characteristics, even with a short channel length, can be obtained, and the instability of the back channel, which is one of the biggest problems of IGZO TFTs, is solved. As a result, we improved the process of manufacturing back-channel-etched TFTs.

Sharp succeeded the production of high performance LCD using IGZO for the first time in the world. With the extraordinary TFT characteristics, IGZO-TFT LCD can realize (1)lower power consumption and (2)higher touch panel performance than a-Si TFT LCD. In this paper, we report the development of IGZO-TFT and new LCD devices.

In a C-axis aligned crystal (CAAC) IGZO TFT, contact between a CAAC-IGZO film and source and drain electrode was good. In this study, we recognized the existence of n-type IGZO layer serving as contact layer by a novel experimental method where a depth profile of the sheet resistance.

We have fabricated a back-channel-etched TFT using the CAAC-IGZO film that we developed. As a factor of success in manufacturing stable back-channel-etched TFTs, it is considered that CAAC-IGZO has a strong structure because of its crystallinity. For verification, we have compared the cohesive energy of c-IGZO and that of a-IGZO.

Recent studies have shown that IGZO are variously influenced by photoirradiation. In this study, by using measurement results of optical properties and calculation results, a relationship of defect levels in the IGZO films and the SiO2 films to negative-bias photodegradation was examined, and the mechanism of the degradation was revealed.

We report the world's smallest field effect transistors (FETs) with channel lengths of 32 nm including c-axis aligned crystalline (CAAC) In-Ga-Zn-O as their active layers, which achieve low off-state leakage currents. Furthermore, these FETs exhibit excellent subthreshold swing values despite having thick gate insulating film. The FET operation has been achieved owing to the 3D gate structure with a thin active layer, due to the FETs being accumulation-type FETs with intrinsic channels, and due to the dielectric anisotropy of the CAAC crystal structure.

The pulse width of a KrF excimer laser was elongated from 40 to 60 ns by coupling dually split laser beams with different optical paths. By the irradiation of such elongated laser pulses up to 103 times, strontium bismuth tantalate thin films can be crystallized efficiently to perovskite at a substrate temperature of 650 °C, while the irradiation of nonelongated pulses fails to crystallize the films. The crystallized films have high remanent polarization and coercive field values. The presence of the energy threshold and the critical thickness for crystallization to perovskite is suggested.

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.

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.

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.

— 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.

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 world's first 4-inch QVGA LCD and integrated the gate driver and source driver on the display panel.