Texture-enhanced Al-Cu electrodes on ultrathin Ti buffer layers for high-power durable 2.6 GHz SAW filters

Abstract

Achieving high resistance to acoustomigration and electromigration in the electrodes used in high-power and high-frequency surface acoustic wave (SAW) filters is important to mobile communications development. In this study, the effects of the Ti buffer layers on the textures and acoustomigration and electromigration resistances of the Al-Cu electrodes were studied comprehensively. The results demonstrate that both power durability and electromigration lifetime are positively correlated with the Al-Cu electrode texture quality. Ultrathin (∼2 nm) Ti can lead to the strongest Al-Cu (111) textured electrodes, with a full width at half maximum of the rocking curve of 2.09°. This represents a remarkable enhancement of the power durability of high-frequency 2.6 GHz SAW filters from 29 dBm to 35 dBm. It also produces lifetime almost 7 times longer than those of electrodes without Ti buffer layers in electromigration tests. X-ray diffraction and transmission electron microscopy analyses revealed that these improved acoustomigration and electromigration resistances can be attributed primarily to the reductions in overall and large-angle grain boundaries in the highly Al-Cu (111) textured electrodes. Furthermore, the growth mechanism of highly Al-Cu texture films is discussed in terms of surface-interface energy balance.

Surface Acoustic Wave Devices Using Lithium Niobate on Silicon Carbide

“…The reduction process increases the dc electrical conductivity of the wafer, thus mitigating the spurious pyroelectric charging effects during thermal cycling [64]. Meanwhile, strengthened electrodes will suppress acoustomigration in IDTs and thus improving the power durability of acoustic filters, such as Al alloy [67], [68], layered structure [67], [69], highly textured Al film [70]- [72], and passivation layer [73], [74]. We believe that power handling is limited predominately by the electrodes, and has not yet reached the thermal nonlinearity limit.…”

Growth and Characterization of Al (111) Thin Film on Piezoelectric Wafers for SAW Device Fabrication for Space Applications

“…In the case of even higher power levels, catastrophic failure can occur, leading to complete device failure. To overcome this problem, different techniques like epitaxial growth of Al film [7,8], Cu-Al based metal electrodes [9,10], multilayered metal electrodes [4,11,12], and Al electrodes with Ni [13] and Ti [9,14] underlayer have been employed. SAW-induced stress at the interface of a piezoelectric wafer and metal film is higher [15] than in other locations on the metal film.…”