Understanding the stress effect of TiN top electrode on ferroelectricity in Hf0.5Zr0.5O2 thin films

We conducted a comprehensive investigation on the influence of TiN thickness and stress on the ferroelectric properties of Hf Zr-0.5 O-0.5 (2 )thin films. TiN top electrode layers with varying thicknesses of 2, 5, 10, 30, 50, 75, and 100 nm were deposited and analyzed. It was observed that the in-plane tensile stress in TiN films increased with the thickness of the TiN top electrode. This is expected to elevate the tensile stress in the Hf Zr-0.5 O-0.5( 2) film, consequently leading to an enhancement in ferroelectric polarization. However, the effect of stress on the ferroelectric behavior of Hf 0.5Zr O-0.5 (2) films exhibited distinct stages: improvement, saturation, and degradation. Our study presents novel findings revealing a saturation and degradation phenomenon of in-plane tensile stress on the ferroelectric properties of polycrystalline Hf Zr-0.5 (0.5)O( 2 )films, thereby partially resolving the discrepancies between experimental observations and theoretical predictions. The observed phase transformation induced by tensile stress in Hf (0.5)Zr( 0.5)O( 2 )films played a crucial role in these effects. Furthermore, we found that the impact of the TiN top electrode thickness on other factors influencing ferroelectricity, such as grain size and oxygen vacancies, was negligible. These comprehensive results offer valuable insights into the influence of stress and TiN top electrode thickness on the ferroelectric behavior of Hf (0.5)Zr( 0.5)O( 2 )films.