Longitudinal Sound Speed and Thermal Properties of Atomic Layer Deposition-Grown Amorphous AlN/Al2O3 Multilayers with Varying Oxygen Composition

Dielectric AMLs are currently being used in a wide array of applications such as optical coatings, nanoelectronic, energy harvesting, and recovery devices. The relatively low thermal conductivity of AMLs makes it particularly challenging to effectively dissipate the waste heat generated during these applications. The problem is further compounded in AMLs with high interface densities as the non-negligible role of the interfaces leads to additional thermal conductivity reductions. Thus, it is of vital interest to find pathways of modulating interface density of AMLs without sacrificing thermal conductivity. Here, we report on the sound speed and thermal conductivity of a series of amorphous AlN/Al₂O₃ multilayers grown via plasma enhanced atomic layer deposition. To introduce compositional disorder in the AMLs, the oxygen content of the multilayers is systematically varied as function of interface density. The longitudinal sound speed of the AMLs is solely dictated by the composition. The thermal conductivity, on the other hand, is dictated by both composition and interface density. The oxygen content and interfaces act to increase and decrease the thermal conductivity, respectively. Due to such competing influences of the two parameters, the thermal conductivity of the AMLs remains nearly constant as a function of interface density.