Silicon nitride (Si₃N₄) is an attractive implant material, particularly in orthopedic surgery. Although it has only been on the market for spinal fusion surgery requirements so far, it is also a promising candidate for other implant applications where load-bearing is crucial. In this study, we aimed to examine the potential of making the material surface more advantageous for various implant applications by coating it with a very thin hydroxyapatite (HAp) layer using the atomic layer deposition (ALD) method. This was done to improve the material's bioactivity without sacrificing its mechanical properties. Characterization results showed that using a 3:1 CaO:PO4 ALD cycle ratio resulted in the formation of very fine crystalline HAp after heat treatment at 500 °C. The bioactivity assessment made by immersing the coated film in SBF revealed HAp formation on the surface, and it was observed that the bioactivity of this surface improved compared to the uncoated one

Keywords: Silicon nitride, Atomic layer deposition, Hydroxyapatite