Leakage current behavior in MIM capacitors and MISM organic capacitors with a thin AlO_x insulator

This is a systematic study of how leakage current behaviors are affected according to the capacitor structures. We fabricated two types of capacitors, a metal-insulator-metal (MIM) capacitor and a metal-insulator-organic semiconductor-metal (MISM) capacitor with an ultra-thin AlO_X insulator. In the MIM capacitors, the Fermi-level alignment induced by the difference of the work functions between the top and bottom electrodes leads to the polarity dependence of the leakage current features. In contrast, for the MISM organic capacitors, it is found that the type of organic semiconductor dominantly determines the characteristics of the polarity dependence. These structure-dependent differences of leakage current in a fundamental constituent of the capacitor provide a scientific platform for designing more complex devices for precise operation.