BiSb and YPtBi Buffer Layers for Stable SOT Crystal Orientation

A buffer layer comprising Cr, Mo, W, or their alloys is introduced between the substrate and the BiSb layer. This intermediary buffer layer serves multiple functions: it provides a lattice-matched template that promotes desired crystal orientations in BiSb, acts as a thermal barrier to protect the BiSb from substrate-induced stress and thermal degradation, and facilitates controlled epitaxial growth. The buffer layer effectively mediates between the high-temperature substrate and the low-melting-point BiSb material, enabling thermal stability while preserving the giant spin Hall effect.

The buffer layer acts as a diffusion barrier that mediates between the BiSb layer and the underlying substrate. During thermal annealing processes, the buffer layer prevents Sb atoms from migrating into the substrate while maintaining the electrical conductivity of the BiSb layer. The buffer layer's crystalline structure provides a stable interface that reduces film roughness and suppresses Sb migration, thereby eliminating the harmful effect without compromising the giant spin Hall effect.

The buffer layer is deposited first to create a nucleation template that controls grain formation in the subsequent BiSb layer. By establishing a fine-grained buffer layer with specific orientation, the invention promotes the growth of BiSb with controlled grain sizes and reduced surface roughness. This preliminary structuring of the buffer layer makes the BiSb layer easier to fabricate with precise dimensions and properties, while maintaining high electrical conductivity.