Suppression of Electromagnetic Crosstalk by Differential Excitation for SAW Generation

Abstract

Surface acoustic waves (SAWs) hold a vast potential in various fields such as spintronics, quantum acoustics, and electron-quantum optics, but an electromagnetic wave emanating from SAW generation circuits has often been a major hurdle. Here, we investigate a differential excitation method of interdigital transducers (IDTs) to generate SAWs while reducing the electromagnetic wave. The results show that electromagnetic waves are suppressed by more than 90% in all directions. This suppression overcomes the operating limits and improves the scalability of SAW systems. Our results promise to facilitate the development of SAW-based applications in a wide range of research fields.

Figures (4)

• Figure 1: (a) Schematic diagram of the excitation method. Top: single excitation, bottom: differential excitation. The SAW generation signal $V(\phi)$ is input into the pads connecting to the comb-like electrodes of the IDT, and the SAWs and electromagnetic waves (EM) are generated. In the case of the single excitation, the electromagnetic wave originated from $V(\phi)$ is emitted from the high-frequency circuit such as metal pads. In the case of the differential excitation, the two types of electromagnetic waves originated from $V(\phi)$ and $V(\phi+\pi)$ destructively interfere with each other and cancel out. (b) Schematic diagram of the experimental setup and the device for the differential excitation.
• Figure 2: Two-dimensional simulation results of the cancellation effect due to the interference between two circular waves with opposite phases: Wave A and Wave B. The wave centers correspond to metal pads 110µ m apart on our device, where a resonant ac voltage is applied to excite SAWs. Top left: Wave A - a frequency 1GHz, a phase 0, a velocity 3e8m/s, from point A (0µ m,55µ m). Top right: Wave B - a frequency 1GHz, a phase $\pi$, a velocity 3e8m/s, from point B (0µ m,-55µ m). Lower left: Combined Wave - interference pattern resulting from the combination of Wave A and Wave B, showing the cancelation effect. Lower right: Combined Wave (Detailed View) - Detailed interference pattern with a narrowed amplitude range.
• Figure 3: Time-resolved measurements on the IDT with the single excitation and the differential excitation. Trace of the detector response for the resonant ac voltage(1GHz, a time span 60ns, a peak-to-peak amplitude 350mV). The blue line represents the SAW and the electromagnetic wave signals obtained from the single excitation, with the SAW on the right and the previously detected electromagnetic wave on the left. The red line represents the obtained signal from the differential excitation, where the SAW amplitude is similar to the single excitation while the electromagnetic component is significantly suppressed
• Figure 4: Spatial dependence of electromagnetic-wave suppression. A schematic of the sample is shown in the middle. Surrounding plots are electromagnetic waves detected on each metal pad with the single and the differential excitation. The numbers of the metal pads in the schematic correspond to the numbers of the plots. The suppression effect is almost same for all positions. The change in the amplitude of the electromagnetic waves from the results in Fig. \ref{['figure3']} can be attributed to the different design of the metal pads for detection.