Control of dipole properties in high-k and SiO₂ stacks on Si substrates with tricolor superstructure

The concept of the tricolor superstructure (TCS), which is a triple-layer stack structure containing two types of high dielectric constant (high-k) layers (designated HK1 and HK2) and a SiO₂ layer, is proposed to control the moment and the polarity of the interface dipole layer that are induced at the high-k/SiO₂ interfaces. The interface dipole layer is formed by oxygen ion migration from the layer with higher oxygen areal density (σ) to that with lower σ. When the two high-k materials are selected with the order of σ_HK1 > σ_SiO2 > σ_HK2 in a SiO₂/HK2/HK1/SiO₂ TCS, the dipole directions of the interface dipole layers at the SiO₂/HK2 and the HK1/SiO₂ interfaces are aligned. Additionally, in the transposed SiO₂/HK1/HK2/SiO₂ TCS, the total polarity is reversed. The concept is demonstrated using Al₂O₃ and Y₂O₃ layers because they offer the order of σ_Al2O3 > σ_SiO2 > σ_Y2O3. The two stacking sequence samples composed of SiO₂/Y₂O₃/Al₂O₃/SiO₂ and SiO₂/Al₂O₃/Y₂O₃/SiO₂ that were fabricated using superlattice technique by pulsed laser deposition obviously show opposite dipole polarities. Increasing repetition of the deposited TCS unit also causes the dipole moments to increase systematically. The TCS technique enables control of the properties of the interface dipole layer at high-k/SiO₂ interfaces in amorphous systems.