Lifetime of hafnium oxide dielectric in thin-film devices fabricated on deformable softening polymer substrate

In this work, we investigate the electrical behavior and reliability of thin-film devices using a high-k dielectric on top of softening polymer. Hafnium oxide (HfO₂) 50 nm thick was used for gate dielectric in both capacitors and thin-film transistors (TFTs) and is deposited by atomic layer deposition at 100 °C. A thermoset thiol-ene/acrylate shape memory polymer (SMP) is used as flexible substrate with softening properties. The SMP belongs to a class of mechanically active materials used to store a metastable shape and return to a globally stable shape upon activation by stimuli, such as temperature, which softens the polymer via a decrease in storage modulus. An average dielectric constant of 13.6 was obtained for the HfO₂ layer after an annealing treatment at 200 °C for two hours in forming gas. Here, a clear dependence between the electrical behavior and the device dimensions was observed. In the same experimental process, indium-gallium-zinc-oxide TFTs with different dimensions were fabricated showing mobility values of approximately 17 cm²/V-s, presenting similar dependence on channel dimensions. Finally, the lifetime projection of the HfO₂ film was estimated from a time-dependent-dielectric-breakdown and leakage current analysis.