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A fabrication process is developed to grow c-axis textured aluminum nitride(AlN) films on the sidewall of single crystal silicon (Si) micro-fins torealize fin bulk acoustic wave resonators (FinBAR). FinBARs enable ultra-denseintegration of high quality-factor (Q) resonators and low-loss filters on asmall chip footprint and provide extreme lithographical frequency scalabilityover ultra- and super-high-frequency regimes. Si micro-fins with large aspectratio are patterned and their sidewall surfaces are atomically smoothened. Thereactive magnetron sputtering AlN deposition is engineered to optimize thehexagonal crystallinity of the sidewall AlN film with c-axis perpendicular tothe sidewall of Si micro-fin. The effect of bottom metal electrode and surfaceroughness on the texture and crystallinity of the sidewall AlN film isexplored. The atomic-layer-deposited platinum film with (111) crystallinity isidentified as a suitable bottom electrode for deposition of c-axis textured AlNon the sidewall with c-axis orientation of 88.5 deg and arc-angle of ~12 degaround (002) diffraction spot over film thickness. 4.2 GHz FinBAR prototype isimplemented showing a Q of 1,574 and effective electromechanical coupling(keff2) of 2.75%, when operating in 3rd width-extensional resonance mode. Thelower measured Q and keff2 compared to simulations highlights the effect ofgranular texture of sidewall AlN film on limiting the performance of FinBARs.The developed c-axis textured sidewall AlN film technology paves the way forrealization and monolithic integration of multi-frequency and multi-band FinBARspectral processors for the emerging carrier aggregated wireless communicationsystems.

Growth of C-Axis Textured AlN Films on Vertical Sidewalls of Silicon Micro-Fins