A combinatorial ternary composition spread method, which included continuous ternary and binary compositions, was applied for new materials exploration for the future gate stack structure, Rapid estimation of pertivity are carried out by microwave microscope as well as conventional C-V measurement. Structural analyses are performed systematically by combinatorial X-ray diffraction equipment. Higher dielectric region are observed in (HfO 2)x(Y2O3)y(Al 2O3)z and ternary composition area. Al 2O3 was found to have an ability that prevents HfD 2-Y2O3 alloy from crystallization. We found that HfxYxAlzO ternary oxide is a candidate of stable amorphous high-k gate dielectric material with stable interface on Si substrate. The reason of this stability could be explained by charge neutrality based on the phase diagram which is concluded by thermodynamics.