Ferroelectric Hafnium Oxide Doped with Aluminum for Nanoscale Devices

In the last few years, doped metal oxides, including hafnium oxide (HfO₂) and zirconium oxide (ZrO₂), were found to possess a ferroelectric phase. As compared to traditional ferroelectric perovskites, ferroelectric HfO₂ has the advantages of a high coercive field, excellent scalability, and good compatibility with CMOS processing. In this project, we systematically studied the material properties of ferroelectric HfO₂ doped with aluminum. We fabricated metal/Al-doped HfO₂/Si capacitors with various compositions, top metal electrodes, annealing temperatures and durations. Comprehensive characterizations were carried out including positive-up-negative-down (PUND) measurements, hysteresis, C-Vs, I-Vs, retention, and endurance. We find that the annealing temperature and duration play a critical role in the ferroelectricity of the HfO₂ film. The remnant polarization is also influenced by the ratio of hafnium to aluminum. The optimized process conditions result in remnant polarization up to ~10 µC/cm² for 20 nm Al-doped HfO₂ with ±10 V program/erase voltages. This new ferroelectric material will enable a series of novel nanoelectronic and photonic devices.