Long Range Cooperative and Local Jahn-Teller Effects in Nanocrystalline Transition Metal Thin Films

Abstract

The group IVB TM elemental oxides, TiO2, ZrO2 and HfO2, have emerged as candidate materials for advanced gate dielectrics for scaled Si microelectronics. Additionally, complex oxides, comprised of TM oxides and ordinary oxides, or TM and rare earth (RE) atom oxides are also being considered by the microelectronics community in the context of combining microprocessor and memory Si chip functions with additional types of functionality derived from complex oxides. This functionality includes ferroelectric and/or ferromagnetic storage or switching, which are generally enabled by Jahn-Teller (J-T) effects. The properties and reliabilities of both elemental and complex TM oxides are closely correlated with intrinsic TM-atom bonding defects, where J-T local bonding distortions are expected to be important. Defect centers can also be associated with impurity atoms, e.g., TM atoms that are not a constituent of the host TM oxide. J-T distortions in defect centers can manifest themselves in two ways: (1) adversely, as traps and/or charged defects that reduce carrier transport, or (2) positively, as centers which provide a pathway to control of nano-grain symmetry and thin film morphology, and promote changes in long range order as required for ferroelectric or ferromagnetic behavior.