Layered Precursor‐Guided Growth of Nondegenerate Amorphous In 2 O 3 Approaching the Thickness Limit

Oxide semiconductors are promising channel materials for ultrathin electronics. However, conventional growth methods often produce excess carriers, poor stability, and interfacial issues, limiting their electronic applications. Here, we present a layered precursor‐guided synthesis of atom‐thin amorphous indium oxide (In 2 O 3 ) by oxidizing a layered InSe precursor within a back‐end‐of‐line (BEOL)‐compatible thermal budget. The oxide thickness is precisely controlled by the number of precursor layers, enabling In 2 O 3 as thin as 0.63 nm at the physical thickness limit. By avoiding localized nucleation and island coalescence issues, the resulting In 2 O 3 exhibits atomically smooth surfaces and excellent electrostatic uniformity with potential variations below 22 meV. Capacitance‐voltage analyses confirm a carrier density of 2.8 × 10 18 cm −3 in the nondegenerate regime and a low interface trap density of 10 10 ∼10 11 cm −2 ·eV −1 . We further demonstrate reproducible enhancement‐mode transistors with sub‐3 nm channels, featuring near‐zero threshold voltage, a low subthreshold swing (SS) of ∼74 mV/dec, a negligible hysteresis of < 10 mV, and robust gate‐stress stability. This work establishes a reliable route for integrating ultrathin, high‐performance amorphous oxide semiconductors, pushing the limits of next‐generation nanoelectronics.