Ternary amorphous oxide semiconductor of In–Ga–O system for three-dimensional integrated device application

In2O3-based oxide semiconductors are potential materials for supporting the development of next-generation integrated devices with low power consumption, such as back-end-of-line-compatible transistors and ferroelectric memories. Currently, these are standard semiconductor materials used in display research and industrial fields; however, their physical properties and functions must be optimized and reviewed to accelerate integrated device applications. This study proposed a concept for developing thermally stable amorphous oxide semiconductor materials for three-dimensional ferroelectric memory applications. We focused on ternary amorphous oxide semiconductors in terms of the atomic layer deposition process, thermal stability of the amorphous phase, and electrical properties. The electrical properties of ternary In–X–O (X = Al, Ga, Zn, or Sn) in a thin-film transistor fabricated using a high-temperature process were evaluated and compared. A ternary In–Ga–O system satisfied the stability of mobility over 20 cm2/Vs and threshold voltage close to 0 V under high temperature annealing up to 600 °C, which implies compatibility with HfO2-based ferroelectric device applications. The designed amorphous In–Ga–O induced a ferroelectric phase of Zr-doped HfO2 and exhibited sufficient semiconducting properties even after annealing at 500 °C in an N2 atmosphere. In addition, we developed an atomic layer deposition process for fabricating In–Ga–O. The atomic-layer-deposited In–Ga–O channel exhibited thermal stability, field-effect mobility over 20 cm2/Vs, and a subthreshold swing below 80 mV/decade, which was nearly identical to that of the sputter-deposited channel. The ternary In–Ga–O can be considered a potential material for future memory applications. This study provides a unique perspective on the design of oxide semiconductor materials for integrated devices.