In situ electron holography study of charge distribution in high-κ charge-trapping memory

Charge-trapping memory with high-κ insulator films is a candidate for future memory devices. Many efforts with different indirect methods have been made to confirm the trapping position of the charges, but the reported results in the literatures are contrary, from the bottom to the top of the trapping layers. Here we characterize the local charge distribution in the high-κ dielectric stacks under different bias with in situ electron holography. The retrieved phase change induced by external bias strength is visualized with high spatial resolution and the negative charges aggregated on the interface between Al2O3 block layer and HfO2 trapping layer are confirmed. Moreover, the positive charges are discovered near the interface between HfO2 and SiO2 films, which may have an impact on the performance of the charge-trapping memory but were neglected in previous models and theory.