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Ferroelectric nanolaminates have drawn wide attention due to the process convenience of atomic layer deposition (ALD) method and their superior performance. In this work, HfO2/ZrO2 nanolaminates were prepared by alternately depositing HfO2 and ZrO2 single layer with ALD technology. The crystal structures and electrical properties were comprehensively investigated and analyzed. Compared with HfZrO4 solid solution, HfO2/ZrO2 nanolaminates showed much lower leakage current density and similar ferroelectricity, which was beneficial for the improvement of device life. The highest remnant polarization of 17.7 μC cm−2 was achieved in HfO2/ZrO2 nanolaminates with a ratio of 12:12, exhibiting a good endurance of exceeding 5 × 109 cycles. The effects of film thickness and laminated structure on the electrical properties and fatigue performance were also discussed. The differences in ferroelectricity and leakage current were originated from the different grain sizes. The small roughness, fine grains and enough crystallization are essential for the better ferroelectric properties. This work provides a comparison between doped films and laminated films and reveals the thickness dependence on the ferroelectric properties of HfO2/ZrO2 nanolaminates.

Due to the full compatibility with modern complementary-metal-oxidesemiconductor (CMOS) technology and scalable capability, HfO2-based ferroelectric films have been considered as the most potential materials in micro-nano non-volatile memories. However, despite great achievements, the existence of poor interface still poses a great threat to the improve of ferroelectricity and polarization stability. Here, the excellent ferroelectricity and reliability in the 21.6 nm-thick Hf0.5Zr0.5O2 (HZO) films are reported through interface modification by inserting an ultrathin Al2O3 (AO) layer using atomic layer deposition method. Improved polarization and stability are achieved in HZO/AO bilayers with the AO thickness below 2.4 nm. When the thickness of AO dielectric layer is 1.6 nm, the maximum remnant polarization reaches 30.19 μC/cm2 and the leakage current is decreased by 2 ~ 3 orders of magnitude. The strong interface polarization resulted from the electrostatic coupling between HZO and AO films contributes to the improved ferroelectricity of HZO films. Furthermore, the AO layer, as a dielectric capacitor after switching or during non-switching, can block the electron injection from bottom electrode and therefore improve the cycling reliability. This work demonstrates that an inlaid dielectric layer with much lower dielectric constant can significantly enhance the electrical properties of ferroelectric films.

Ferroelectricity and polarization-switching behavior were investigated in Hf0.5Zr0.5O2 films from 25°C to 150°C. It is found that a large remnant polarization (Pr) of about 30 μC/cm2 is achieved, and Hf0.5Zr0.5O2 films behave a good stability in a wide range of temperature. By analyzing the physical mechanism of leakage current, it indicates that electron conduction mechanism obeys Schottky emission at low voltages, and Fowler-Nordheim (F-N) tunneling mechanism along with space-charge-limited-conduction (SCLC) at high voltages. The temperature dependent polarization switching and related leakage current behaviors reveal a strong thermal activation of the oxygen vacancies, which can explain the varieties of ferroelectricity and leakage current under different temperatures.