We investigated stacking double layer structure, the Y2O3-ZrO2 composite film (YZO) on AlOx, for the field effect passivation with high negative fixed charge densities on p-type Si. The composition spread YZO films were deposited at room temperature by using combinatorial sputtering technique. The fixed charge densities were extracted from the flat band voltage shift in the capacitance-voltage characteristics. The as-deposited ZrO2 film incorporated with 15% Y2O3 stacking on the ALD AlOx structure showed the highest negative fixed charge of -1.9 × 1012 cm-2. The field effect passivation can be controlled by the negative fixed charges in the YZO film depending on the composition and dipole uniformly formed at AlOx/Si interface. After annealing in the oxygen atmosphere, passivation properties deteriorated caused by the Al diffusion at the YZO/AlOx interface.