Enhanced power durability of surface acoustic wave filter with Al/Ti/Cu/Ti electrodes

A series of 2.1 GHz surface acoustic wave filters with Al/Ti/Cu/Ti four-layer electrode using different Cu thickness were fabricated. Power durability test show an improvement from 24.5 dBm to 28 dBm by electrode with Al (111 nm)/Ti (5 nm)/Cu (15 nm)/Ti (5 nm) to widely used Al (155 nm)/Ti (5 nm). The different frequency response, electrode morphologies before and after power durability test indicate different failure mechanism of these samples. By checking the microstructures and distribution of elements in those conditions, the enhanced power durability can be attributed to: 1) using of Cu layer, 2) fine grain strengthening, 3) solution strengthening. Concurrently, Increased resistance of electrode induced by electrode structure design and atoms diffusion will deteriorate filter performance and accelerate atoms migration. In this work Al (111 nm)/Ti (5 nm)/Cu (15 nm)/Ti (5 nm) made a compromise in the above factors and achieved higher resistance to acoustomigration, which is promising for higher power surface acoustic wave filters.