Influence of electrode structure on generation of third-order nonlinearity in surface acoustic wave devices

Abstract

In this paper we describe the influence of the electrode material on the generation of the third-order nonlinearity in surface acoustic wave (SAW) devices fabricated on a 42°YX-LiTaO3 substrate. It is shown that the crystallinity of the Al layer in the electrode considerably influences the intensity of the third-order nonlinearity. Surprisingly, electrodes with better crystallinity generate stronger third-order nonlinearity. This indicates that the Al layer is one of the major reasons behind its generation. It is also shown that the third-order nonlinearity can be reduced by properly designing the layer stack of the electrodes such that acoustic strain is not concentrated in the Al layer. This means that the acoustic strain in the electrode is one of the main causes of the third-order nonlinearity.

Advances in RF SAW devices: What are demanded?

“…Fig. 7 shows the measured third harmonics (H3) for three SAW resonators using Al electrodes with different Al quality [14]. Note their linear performance are almost the same.…”

Research in Nonlinearity of Surface Acoustic Wave Devices

“…Apart from the possible causes, generation points of nonlinear signals [7][8][9][10][11][12][13][14], whether in the substrate or in electrodes, are also important. Previous works show that the secondorder nonlinearity in SAW devices on 42 • XY-LiTaO 3 (42-LT) substrates is mainly generated by the crystalline asymmetry on the surface of a piezoelectric substrate, and the nonlinear dielectric constant and the electrostrictive constant contribute to the generation of secondorder nonlinear signals.…”

“…Furthermore, the width of the electrode also has a great influence on the nonlinear effect. Usually the wider the electrode width, the more obvious the nonlinear effect [9][10][11][12][13][14].…”

“…Even so, research teams including Qorvo, Murata, and Chiba University [3,6,[8][9][10][11][12][13]22,31] have built and implemented the measurement systems on harmonics and intermodulation of nonlinearity for SAW devices. Moreover, our team also developed a harmonics and intermodulation measurement platform for SAW resonators, filters, and duplexers both on-chip and on PCB board.…”

“…On the other hand, based on the nonlinear generation mechanism, IDT materials are optimized [7][8][9][10][11][12][13][14]. As mentioned above, the third-order is closely related to the acoustic strain in the aluminum electrode, including the higher the crystallinity, the more obvious the nonlinear.…”