Improved resistance to electromigration and acoustomigration of Al interdigital transducers by Ni underlayer

The structure and morphology of Al interdigital transducers as a function of Ni underlayer thickness were studied. The Al (111) texture intensity increases first and then decreases as Ni underlayer thickness increases. 6-nm Ni underlayer results in the strongest Al (111) texture with flattest surface, which exhibits almost 10 times longer life in electromigration measurement than those without Ni underlayer. 1.5 GHz surface acoustic wave filters fabricated with Al film on 6-nm Ni underlayer also have improved power durability compared with those without Ni underlayer from 29.0 to 32.5 dBm. It is observed that those fine grains in the 6-nm Ni underlayer greatly enhance Al (111) texture. Together with increased adhesion force, strong Al (111) texture accounts for the improved resistance to electromigration and acoustomigration via the reduction of gains boundaries, resistivity, and fine grains at the interface, which is promising for high power surface acoustic wave filters.