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We fabricated a field-effect transistor (FET) with a gate length of 21 nm whose channel material is a c-axis-aligned crystalline In-Ga-Zn oxide (CAAC-IGZO). A CAAC-IGZO FET with a gate length of 21 nm has an extremely low off-state leakage current, a practical driving capability, and tolerance against high temperatures. CAAC-IGZO FETs enable low-power integrated circuits, such as logic and memory in high-temperature environments. Performance estimation of a memory cell using the CAAC-IGZO FET with a gate length of 21 nm revealed that a write time of less than 1 ns and a data retention time of more than 1 h would be possible at 85 • C.INDEX TERMS C-axis-aligned crystalline In-Ga-Zn oxide (CAAC-IGZO), leakage current, nonvolatile memory, random access memory. II. BASIC CHARACTERISTICS OF C-AXIS-ALIGNED CRYSTALLINE IN-GA-ZN OXIDE FET

We fabricated dual-gate CAAC-IGZO FETs with self-aligned top gates and investigated their electrical characteristics. The drain current was larger than expected from the GI capacitance ratio to single-gate FETs. Device simulation results suggest that shallow trap states and increase in electron mobility by self-heating of FETs can explain the large drain current.

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.