Ferroelectric HfxZr1-xO2 for Next Generation Non-volatile Memory Applications and Its Reliability


December 2021


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To keep up with the increasing memory demands, developing memories with higher densities, speed and energy efficiency is necessary at different levels of the memory hierarchy. Ferroelectric materials have been considered alternative memory components; however, the conventional perovskite-based ferroelectric materials pose several challenges due to CMOS integration, high thermal budget, and scaling to sub 70 nm thicknesses. In this regard, the discovery of ferroelectricity in doped HfO2 thin films was revolutionary as HfO2 is already employed in front end CMOS as a high-k dielectric material for scaled thicknesses (<10 nm) . Additionally, doping HfO2 films with ZrO2, i.e., Hf0.5Zr0.5O2 (HZO) showed stable ferroelectric phase crystallization at back-end of line compatible temperatures (<450 °C). This dissertation addresses some critical issues on the stress-induced crystallization of the ferroelectric phase in HZO films, the reliability properties of metal-ferroelectric-metal (MFM) structures, scaling ferroelectric HZO films on silicon substrates, and their reliability. First, the driving forces for the crystallization of pure ferroelectric phase in HZO thin films were addressed and the role of the TiN top electrode in phase crystallization at low process temperatures (400 °C) is studied. Then, the reliability of 10 nm thick HZO films was studied, and the various ferroelectric device reliability properties and mechanisms were evaluated for metal-ferroelectricmetal structures. Finally, the ferroelectric HZO films were integrated directly on silicon for FeFET applications and the effect of ferroelectric device reliability based on scaling HZO films on silicon structures was studied.



Engineering, Materials Science