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.

We report, in this paper, that crystalline In–Ga–Zn-oxide (IGZO) can be formed over an amorphous surface or over an uneven surface by a sputtering process at lower than 500 °C through the purification of IGZO. Crystalline IGZO, in which no clear grain boundary is observed, shows c-axis alignment but random a- and b-axis orientations without alignment. This crystal morphology differs from other morphologies that have been known thus far, such as single crystal and polycrystal morphologies. Our model for understanding the formation of this crystal morphology [c-axis-aligned crystal (CAAC)] is also discussed. Upon thermal annealing of a deposited film at lower than 500 °C, nanocrystal regions remaining in the CAAC can be converted into the CAAC structure. Accordingly, I off can be at the yA/µm (10−24 A/µm) level at 85 °C. It has been proven that by utilizing normally-off characteristics even with L/W = 40 nm/40 nm (actual size: L/W = 68 nm/34 nm), the fabrication of a three-dimensional (3D) LSI with a 3D oxide semiconductor/Si hybrid structure is feasible.

To clarify the origin of the major donor states in indium gallium zinc oxide (IGZO), we report measurement results and an analysis of several physical properties of IGZO thin films. Specifically, the concentration of H atoms and O vacancies (V O ), carrier concentration, and conductivity are investigated by hard X-ray photoelectron spectroscopy, secondary ion mass spectroscopy, thermal desorption spectroscopy, and Hall effect measurements. The results of these experiments suggest that the origin of major donor states is H occupancy of V O sites. Furthermore, we use first-principles calculations to investigate the influence of the coexistence of V O and H in crystalline InGaO 3 (ZnO) m (m ¼ 1). The results indicate that when H is trapped in V O , a stable complex is created that serves as a shallow-level donor. V C 2014 AIP Publishing LLC.

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 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.