Reduction of effective dielectric constant of gate insulator by low-resistivity electrodes

On metal–oxide–semiconductor capacitors, the effective dielectric constant (keff) values extracted from high-frequency capacitance–voltage measurements were found to decrease when gate electrodes of very low resistivity were used. The equivalent-oxide thickness increase reaches about 1 nm with the low-resistivity electrodes. We examined gate insulators of SiO2, Al2O3, and HfO2 and gate electrodes of Al, TiN, Au, Cr, and TaN. The equivalent-oxide thickness increase can be prevented by inserting a high-resistivity metal film only 0.3 nm thick between the very low-resistivity metal and the insulator. The present results suggest that keff is reduced by the screening of ionic insulators with free electrons of the metal due to a quantum effect.