【Member Papers】Thin Ga₂O₃ insertion layer for phase structure and electrical property evolutions in ferroelectric Hf₀.₅Zr₀.₅O₂ capacitors

      Researchers from the Fudan University have published a dissertation titled "Thin Ga₂O₃ insertion layer for phase structure and electrical property evolutions in ferroelectric Hf_0.5Zr_0.5O₂ capacitors" in Applied Physics Letters.

Project Support

      This work was supported in part by the National Natural Science Foundation of China under Grant Nos. 62027818 and 11974320, in part by the National Key Research and Development Program of China under Grant No. 2021YFB3202500, in part by the Atomic Layer Deposition Equipment for Third-Generation Semiconductor Power Device Fabrication (2024GXGG004), and in part by the MIND Project No. MINDXZ202402.

Background

      The discovery of ferroelectricity in hafnium oxide (HfO₂)-based materials in 2011 constituted a milestone achievement. Compared with conventional perovskite ferroelectrics, HfO₂-based thin films exhibit notable advantages such as superior dielectric properties, robust ferroelectricity, excellent complementary metal–oxide–semiconductor (CMOS) compatibility, and outstanding scalability. These attributes make them ideal candidates for a range of microelectronic devices, including ferroelectric random-access memory (FeRAM), ferroelectric tunnel junctions (FTJs), and ferroelectric field-effect transistors (FeFETs).

Abstract

      In this study, gallium oxide (Ga₂O₃) insertion layers (ILs) of varying thicknesses were embedded within Hf_0.5Zr_0.5O₂ (HZO) films using atomic layer deposition (ALD). Devices with Ga₂O₃ ILs grown for fewer than 4 ALD Ga₂O₃ cycles exhibit a reduction in both remnant polarization (P_r) and coercive field (E_c). Notably, the device incorporating a IL with 2 ALD Ga₂O₃ cycles demonstrates strong performance, achieving a 2P_r of 47.0 μC/cm² and an E_c of 0.92 MV/cm. In contrast, for devices with ILs exceeding 8 ALD Ga₂O₃ cycles, the 2P_r value remains near 18 μC/cm², while E_c increases significantly. These divergent behaviors can be attributed to the different diffusion states of the insertion IL. For a low number of ALD Ga₂O₃ cycles, it is the diffusion of Ga³⁺ ions into the HZO region adjacent to the IL that results in a reduced E_c. Conversely, with higher ALD Ga₂O₃ cycles, the IL forms a continuous layer that physically divides the 10 nm HZO film into two sections, which leads to a further decrease in P_r and an increase in E_c. Furthermore, the progressive disruption of vertical grain boundaries by the growing insertion layer (IL) leads to a continuous decrease in leakage current. This work demonstrates the effective modulation of HZO devices via a Ga₂O₃ insertion layer, offering a methodology and data reference for enhancing device reliability.

Conclusion

      In this work, the effect of a Ga₂O₃ IL on the ferroelectric properties of HZO thin films was systematically investigated, revealing two distinct mechanisms dependent on the IL thickness. At low ALD Ga₂O₃ cycles, Ga³⁺ diffused into the HZO film promotes t-phase formation, concurrently reducing both 2P_r and E_c. Beyond a critical thickness, however, the IL forms a continuous layer that disrupts the HZO crystal structure. This leads to a stabilized 2P_r, due to suppressed Ga³⁺ substitution, and a significantly increased E_c, caused by factors including, but not limited to, the voltage division effect of the interlayer and an increased density of transverse grain boundaries. The continuous decrease in leakage current with increasing IL thickness, a result of disrupted grain boundaries, contributes to improved device endurance. An optimal trade-off was achieved with 2 ALD Ga₂O₃ cycles, which exhibited a high 2P_r of 47.0 μC/cm², a low E_c of 0.92 MV/cm, and endurance improved by approximately two orders of magnitude. Ultimately, this study demonstrates that Ga₂O₃ ILs provide an effective strategy for modulating the ferroelectric behavior of HZO, offering clear guidance for tailoring these films for diverse applications.