Impact of annealing temperature on the ferroelectric properties of W/Hf_0.5Zr_0.5O₂/W capacitor

Crystallization annealing is a crucial process for the formation of the ferroelectric phase in HfO₂-based ferroelectric thin films. Here, we systematically investigate the impact of the annealing process, with temperature varied from 350 °C to 550 °C, on the electricity, ferroelectricity and reliability of a Hf_0.5Zr_0.5O₂ (HZO; 7.5 nm) film capacitor. It was found that HZO film annealed at a low temperature of 400 °C can effectively suppress the formation of the monoclinic phase and reduce the leakage current. HZO film annealed at 400 °C also exhibits better ferroelectric properties than those annealed at 350 °C and 550 °C. Specifically, the 400 °C-annealed HZO film shows an outstanding 2P_r value of 54.6 μC⋅cm⁻² at ± 3.0 MV⋅cm⁻¹, which is relatively high compared with previously reported values for HZO film under the same electric field and annealing temperature. When the applied electric field increases to ± 5.0 MV⋅cm⁻¹, the 2P_r value can reach a maximum of 69.6 μC⋅cm⁻². In addition, the HZO films annealed at 400 °C and 550 °C can endure up to bout 2.3 × 10⁸ cycles under a cycling field of 2.0 MV⋅cm⁻¹ before the occurrence of breakdown. In the 400 °C-annealed HZO film, 72.1% of the initial polarization is maintained while only 44.9% is maintained in the 550 °C-annealed HZO film. Our work demonstrates that HZO film with a low crystallization temperature (400 °C) has quite a high ferroelectric polarization, which is of significant importance in applications in ferroelectric memory and negative capacitance transistors.