Ferroelectric Hafnium and Zirconium Oxide: Enablers for New Device Concepts
19.11.2018 von 17:15 bis 18:00
Ferroelectric behavior of thin, doped hafnium oxide films caused by a non-centrosymmetric orthorhombic phase was reported recently. Ferroelectric properties and crystal structure of doped HfO2 thin films were investigated for material parameters, processing conditions and at different temperatures. Piezo-response force microscopy (PFM) in conjunction with transmission electron microscopy (TEM) measurements revealed a domain size in the order of single grains with a grain diameter of ~20-30 nm in lateral and the physical film thickness in horizontal direction. Some of these grains showed an orientational relationship mainly to the bottom electrode. A qualitative model describing the influence of basic parameters like stress, dopant and oxygen vacancy concentration, surface and interface energy of grains, on the crystal structure of HfO2 was proposed. In addition, the influence of these parameters on the field cycling behavior was examined. This revealed the wake-up effect in doped HfO2 to be dominated by a combination of interface-induced effects and field induced phase transitions. Finally, different HfO2 based device approaches are discussed and their performance compared. A non-volatile DRAM concept based on the field induced ferroelectric properties of ZrO2 is presented. Detailed electrical characterization show high endurance and retention values that can be extrapolated to 10 years while providing the speed of FE memories during low power operation.