Optimization of Multi-Layered Thin Films for Minimizing Resistive Losses in Acoustic Resonators

In this study, the optimization of multi-layered thin films to minimize resistive losses in acoustic resonators is explored. The structures used for the investigation, built up of two distinctive metal layers, are fabricated using a series of high-end equipment found in the Cmi at EPFL. Particularly, the Metal Two layer was deposited using the LAB600, Spider600, and DP650 machines for precise fabrication. Photolithography was used coupled with the Suss MA6 Gen3 Mask Aligner, and the VPG200 for creating precise mask patterns. The fabricated structures were characterized using the two-point probe in the ANEMS laboratory while other sheet resistance measurements were taken with the R50 4p machine, to ensure uniformity and desired electrical properties. Additionally, a mathematical model to systematically evaluate the substantial amounts of data gathered was developed together with intuitive MATLAB codes to automatically sort and plot the results. The study underscores the importance of executing an etch in between neighboring metal layers to remove a parasitic oxide layer that inevitably forms when the wafer is in contact with oxigen with very promising results. Furthermore, meticulous process control and the use of advanced fabrication techniques are found to be essential in achieving high-quality multi-layered thin films for NEMS applications.