Inkjet-Printed Sol-Gel Titania Precursor Atop MEMS Resonator for Precise Frequency Control and Tuning

This article presents the design, fabrication, and characterization of microelectromechanical systems (MEMS) resonators functionalized with titanium dioxide (TiO₂) droplets deposited via inkjet-printing technology. The integration of oxygen-deficient sol-gel TiO₂ precursors onto piezoelectric MEMS resonators demonstrates a novel approach to postprocessing frequency tuning and sensor functionalization. The fabricated devices consist of aluminum nitride (AlN) piezoelectric resonators manufactured using the PiezoMUMPs process, with the subsequent deposition of TiO₂ droplets using a custom-formulated ink. Experimental results demonstrate that the resonant frequency can be digitally tuned by controlling the number of deposited droplets (0-50), achieving a tuning sensitivity of about 200 Hz per droplet. The mode shape of the tuned resonator was not affected by such deposition. The performance of the modified resonator also remained stable after over 41 h of operation. The crystalline phase of the TiO₂ (amorphous, anatase, or rutile) was found to have a significant influence on the performance of the device. This work establishes inkjet printing as a viable, scalable, precise, and partially reversible method for MEMS postprocessing, opening pathways for integrated chemical sensor arrays, tunable filters, and multifunction microsystems, enabling multifunctional microsystems where postfabrication frequency tuning combines with TiO₂'s sensing and photocatalytic capabilities for integrated chemical sensor arrays and self-cleaning resonant devices.