Optimization of the 4 nm-Thick Hf<sub>1–<i>x</i></sub>Zr<sub><i>x</i></sub>O<sub>2</sub> Film\nwith Low Operating Voltage and High Endurance for Ferroelectric Random\nAccess Memory

The\nintegration of ferroelectric-doped HfO<sub>2</sub> thin films\nin advanced memory has been impeded by high coercive fields (<i>E</i><sub>C</sub>), requiring high operation voltages. The extremely\nsmall feature size of the state-of-the-art memory device requires\nfilm thickness <5 nm, causing electrical reliability concerns and\ninefficient ferroelectric orthorhombic phase formation. This research\naddresses these challenges by optimizing 4 nm-thick (Hf,Zr)O<sub>2</sub> (HZO) thin films to enable low-voltage operation with high reliability.\nIt was noted that such an ultrathin film tends to stabilize the tetragonal\nphase compared to the more commonly researched 10 nm-thick HZO film\ndue to the smaller grain size of the thinner film. Therefore, the\ncapacitor fabrication conditions were reevaluated to destabilize the\ntetragonal phase while increasing the desired orthorhombic phase by\ndecreasing the oxygen vacancy (V<sub>O</sub>) concentration in the\nfilm. By adjusting the ozone dose time, Zr ratio, crystallization\nannealing temperature, and TiN capping electrode thickness, the ferroelectric\nproperties of the 4 nm-thick film were significantly enhanced. The\ndecreased V<sub>O</sub> concentration also contributed to improving\nthe capacitor reliability. The optimized 4 nm-thick HZO films exhibited\noutstanding ferroelectric properties, with a double coercive voltage\n(2 <i>V</i><sub>C</sub>) of ∼0.8 V, a double remanent\npolarization (2<i>P</i><sub>r</sub>) of ∼25 μC/cm<sup>2</sup> at ±1 V, and 10<sup>11</sup> endurance, satisfying gigabit\ndensity ferroelectric random access memory requirements.