Ferroelectric Phase Formation in Hf_0.5Zr_0.5O₂ Using Dual-Step PLD Growth Strategy for MoS₂ Negative Capacitance Field-Effect Transistors

Hf_0.5Zr_0.5O₂(HZO) is considered a prominent ferroelectric material at the thin film scale, which usually contain cubic(c), monoclinic(m), tetragonal(t) and orthorhombic(o) phases when crystallized. In particular, the asymmetric o-phase has its own ferroelectricity, but it is not easily obtained due to its metastable state. Comparative studies on the HZO grown on Si by pulse laser deposition (PLD) using 1) direct growth (high temperature deposition) and 2) dual step growth (Rapid thermal annealing (RTA) after RT deposition) strategies have been performed. Compared to other processes, PLD is easy to control the oxygen partial pressure, and high energy particles generated by the pulse laser can produce high quality thin film. Although many studies on ferroelectrics have been conducted with the ALD process, there has been no case of applying it to ultra-low power logic applications based on the PLD-HZO. We obtained a polycrystalline HZO by crystallization via direct deposition at a high temperature, whereas a pure o-phase without non ferroelectric m-phase is formed through RTA treatment after RT deposition with maximized ferroelectricity. By capacitance matching with a high-k dielectrics (HfO₂) on HZO grown on a Si, MoS₂ NCFET were driven with subthreshold swing of 20.42 and 26.16 mV/dec in the forward and reverse directions, respectively. By optimizing various parameters of the PLD process to obtain a ferroelectric HZO thin film, and to evaluate the device, it is expected to be a modeling study for the next generation low-power device research.