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

Abstract

Crystallization annealing is a crucial process for the formation of ferroelectric phase in HfO2-based ferroelectric thin films. Here, we systematically investigate the impact of annealing process, with temperature varied from 350 ℃ to 550 ℃, on the electricity, ferroelectricity, and reliability of Hf0.5Zr0.5O2 (HZO~7.5 nm) film capacitor. It was found that HZO film annealed at a low temperature of 400℃ can effectively suppress formation of m-phase and reduce the leakage current. The 400 ℃ annealed-HZO film also exhibited preferable ferroelectric properties than that annealed at 350℃ and 550 ℃. Specifically, the 400 ℃-annealed HZO film shows outstanding 2 P r value of 54.6 μC/cm2 at ±3.0 MV/cm, which is relatively high among that of previously reported on HZO film under the same electric field and annealing temperature. When the applied electric field increases to ± 5.0 MV/cm, its 2 P r value can reach a maximum value of 69.6 μC/cm2. In addition, both the 400 ℃ and 550 ℃-annealed HZO film can endure up to ~2.3×108 cycles under a cycling field of 2.0 MV/cm before the occurrence of breakdown. The 72.1% of initial polarization is maintained for 400 ℃-annealed HZO film, while only 44.9% is maintained for 550 ℃-annealed HZO film. Our work demonstrated that HZO film with low crystallization temperature (400 °C) has considerably high ferroelectric polarization, which is significantly important in the applications of ferroelectric memory and negative capacitance transistors.

Optimal parameter space for stabilizing the ferroelectric phase of Hf0.5Zr0.5O2 thin films under strain and electric fields

“…[4,8] Many attempts have been used to stabilize the ferroelectric O-phase in the past decades, including dopants, [27,33,40,41] oxygen vacancies, [42][43][44] mechanical stress, [45][46][47][48][49][50] electric field, [51][52][53][54] crystallographic orientation, [46,55] and annealing or depositing temperature. [56][57][58][59] All these routes essentially tune the relative free energy of the two phases. [20,30,43] In ferroelectric devices, HZO is prepared in thin-films of specific thicknesses, with the increase of HZO thickness, phase transition from the O-phase to the M-phase occurs.…”