The impact of rapid thermal annealing for the ferroelectricity of undoped sputtered HfO2 and its wake-up effect.

Fundamental aspects of ferroelectric HfO 2 , a fluorite-type oxide, are not understood yet. This is evident by different theories regarding, e.g., the wake-up effect or the antiferroelectric-like behavior of HfO 2 manufactured with different doping or deposition techniques. Therefore, we focus on sputtered and undoped HfO 2 to gain deeper understanding of the ferroelectric properties of pure HfO 2. A temperature gradient on a 10 × 10 mm 2 substrate during rapid thermal annealing led to different ferroelectric device performances in terms of remnant polarization and the wake-up effect. The results from the electrical characterization are compared to observations by transmission electron microscopy, performed on pristine and trained samples in plan-view as well as in cross section. We observed that different temperature treatments caused effects at the interfaces of the TiN electrodes and also affected the microstructure and defect concentration of the HfO 2 itself. Devices from the hot corner showed wake-up free ferroelectricity with a remnant polarization below 10 μ C / cm 2 , whereas devices from the cold corner showed a strong wake-up effect with remnant polarization starting from 0 to above 20 μ C / cm 2 after 10 6 cycles. After observing a small structural transformation in trained devices, we attributed this strong wake-up effect to gradual ferroelastic switching of pristine [110] oriented grains with in-plane polarization to partially out-of-plane polarization, while the predominantly ⟨ 111 ⟩ oriented grains in the hot corner can suppress the wake-up effect. [ABSTRACT FROM AUTHOR]