1. (Hf, Zr)O2 ferroelectric materials
- Recently, it was reported that HfO2 show robust ferroelectric (FE) properties when doped with various dopants such as Zr, Si, Y, Al, Gd, La, and Sr. Compared to the conventional ferroelectrics based on perovskite or layered perovskite structure, such as Pb(Zr,Ti)O3 and SrBi2Ta2O9, the FE HfO2-based films showed quite distinctive physical and electrical properties. The HfO2-based films can be extremely thin (film thickness, tf < 10 nm) with feasible ferroelectricity (remnant polarization, Pr ~ 10-40 μC/cm2), whereas the much thicker thicknesses (tf > 100 nm) are required for the stable FE properties of conventional ferroelectrics thin films, especially with the metal-ferroelectric-metal (MFM) configuration. Due to their small thickness, the HfO2-based films are considered promising for the three-dimensional capacitor structure, which is highly required for the future ferroelectric random-access-memory (FeRAM) device according to International Technology Roadmap for Semiconductors. This results from the relatively large bandgap (Eg ~ 5.5 eV), high compatibility with Si, and matured atomic layer deposition (ALD) technique of HfO2-based films. In fact, due to their high Si-compatibility, the non-FE HfO2 thin film has been used as the buffer layer in ferroelectric field-effect-transistor (FeFET) to solve the interfacial problems of conventional ferroelectrics and Si substrate.