Crack-Free AlN Film Grown on Sputtered-AlN/2D MoS₂ Seed Layers on a Si(100)-Based Wafer: Implications for Radio-Frequency Acoustic Filters

Aluminum nitride (AlN)-based acoustic filters are key devices of radio-frequency communications. However, the performance of electroacoustic resonators remains limited by the crystalline quality of the piezoelectric AlN material. An innovative material strategy that combines different types of materials (2D and 3D materials) and growth techniques is presented here to enhance the crystalline quality of thick AlN films grown on silicon-based substrates. Building upon previous works showing the efficacy of 2D MoS 2 in sputtered-AlN texturing, this paper demonstrates how an in situ thermochemical treatment of the sputtered-AlN/MoS 2 seed layers succeeded by a metal organic vapor phase epitaxy (MOVPE) AlN regrowth significantly enhances the crystalline quality of the AlN layer and avoids the detrimental stack delamination at the weak AlN/MoS 2 interface. This paper shows that a delicate balance in the thickness of the sputtered-AlN film should be found to facilitate species diffusion toward the underlying MoS 2 without compromising its texturizing properties for the subsequent MOVPE AlN regrowth. The sputtered-AlN/MoS 2 seed layers involve a nanometric AlN film of less than 5 nm deposited onto three monolayers of MoS 2 . The heat treatment induces an unexpected chemical and structural nanometric reorganization at the interface, converting the initial lamellar MoS 2 film into a discontinuous covalently bonded MoN x O y film, followed by the appearance of metallic Mo nanoparticles at an elevated temperature. Subsequent MOVPE AlN regrowth on the annealed seed layer stacks enables the growth of thick AlN films of up to 600 nm with a mosaicity of less than 0.3° without delamination or cracks. This approach not only facilitates the integration of thick AlN films on Si-based wafers but also opens avenues for growing III–N or other 3D materials on Si through the intercalation of 2D materials.