Probing Charge Dynamics and Defects of High k Dielectric Layered Stacks via Ionizing Radiation

Integrating high k dielectrics in metal-oxide-semiconductor (MOS) devices has been revolutionary for advancing conventional semiconductor devices due to their low leakage and thermal stability at low effective oxide thicknesses. However, charge dynamics and defect states occurring in multilayer stacks of disordered metal oxides are not well understood. Previous characterizations of these materials have been limited in their assessment of trap evolution. Here, we report how ionizing radiation can serve as a charge injection tool to study how electron-hole pairs can become trapped in the layer stack. Trapping can occur via a mismatch in electron and hole mobility as well as engineered by design of the dielectric layers, which form energy barriers from offsets in their respective valence and conduction band edges. Charge trapped in oxide traps or interface traps create a charge buildup, resulting in a measurable shift in the flatband voltage of a MOS capacitor. After irradiation, time-series capacitance-voltage measurements can reveal room-temperature annealing which yields information on the placement and movement of these charges. By varying thicknesses and stacking order of the different metal oxide layers, we develop a physical picture of how to manipulate the transport and recombination of charge in defect states by design.



The Center for Integrated Nanotechnologies, a U.S. DOE user facility, partially supported this work. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.