Aluminium nitride thin films directly grown on conducting boron-doped nanocrystalline diamond films without using buffer layer for high frequency applications

Aluminium Nitride (AlN)-diamond hetero-structures are promising candidates for high frequency acoustic wave resonator applications. This paper reports the electrical, piezoelectric and mechanical properties of AlN films directly grown on boron-doped nanocrystalline diamond (B-NCD) films. X-ray diffraction (XRD) and Raman spectroscopy were used to determine the crystallinity of B-NCD and AlN films. The resistivity (∼8 × 107 Ω.m) and dielectric constant (∼14) were obtained from the electrical characterisation of the fabricated Al/AlN/B-NCD capacitors. Piezoelectric coefficient (d33, 4.3 pmV−1) of AlN films was measured by piezo force microscopy (PFM) technique. Nanoindentation technique was used to determine the hardness (∼14 GPa) and elastic modulus (∼202 GPa) of AlN films. These different properties of AlN/B-NCD/Si (1 0 0) hetero-structure show that it will provide a high-performance platform to realize high frequency resonators for 5G applications.