Charge injection phenomena at the metal/dielectric interface investigated by Kelvin probe force microscopy

The understanding of charge injection mechanisms at metal/dielectric interfaces is crucial for many applications. A direct probe of such a phenomenon requires a charge measurement method whose spatial resolution is compatible with the characteristic scale of the mechanisms occurring after injection, like charge trapping, and with the geometry of the samples under investigation. In this paper, charge injection at the metal/dielectric interface and their motion in the silicon nitride layer under a tunable electric field are probed at the nanoscale using a technique derived from atomic force microscopy. This was achieved by realizing embedded lateral electrode structures and using a surface potential measurement by Kelvin probe force microscopy to provide voltage, field and charge profiles close to the metal/dielectric interface during and after biasing the electrodes. The influence of electric field enhancement at the interface due to the electrode geometry was accounted for. Electron and hole mobilities were estimated from surface potential profiles obtained under polarization. The charge dynamic was investigated during the depolarization steps.