Effect of the nucleation process on freestanding AlN/diamond SAW filter characteristics

In this work, the effect of diamond nucleation process on freestanding AlN/diamond SAW device performances was studied. Before diamond deposition, silicon substrate were mechanically nucleated, using an ultrasonic vibration table with sub-micron diamond slurry, and bias enhanced nucleated (BEN). Freestanding diamond layers obtained on mechanically scratched Si substrates exhibit a surface roughness of R_MS=13nm whereas very low surface roughness (as low as R_MS≤1 nm) can be achieved on BEN diamond layer. Propagation losses (α) and electromechanical coupling coefficient (K²) have been measured as a function of the operating frequency and the normalized AlN film thickness (kh_AlN=2πh_AlN/λ). Experimental results show that the propagation losses strongly depend on nucleation technique while the electromechanical coupling coefficient slightly depends on nucleation technique.