Yuichiro Seki

Study on Surface Acoustic Wave Characteristics of SiO2/Interdigital-Transducer/ZnO/Diamond Structure and Fabrication of 2.5 GHz Narrow Band Filter

Surface acoustic wave (SAW) characteristics of the SiO2/interdigital-transducer(IDT)/ZnO/diamond structure were studied theoretically and experimentally. It was found that the 2nd mode in this structure can provide a zero temperature coefficient of frequency (TCF) as well as high velocity of 10,000 m/s and a large electromechanical coupling coefficient of 1.4%. Utilizing this wave, a 2.5 GHz narrow-band SAW filter was successfully fabricated with IDTs of 0.9 µm finger width, which resulted in superior characteristics for a retiming filter with a small insertion loss of 6.7 dB, Q value of 660 and small frequency deviation of 100 ppm in the temperature range from -40 to 85°C. The insertion loss is smaller than any other retiming filters which have ever been reported with quartz, a conventional SAW material, and also the frequency deviation with temperature is smaller than that in the case of ST-cut quartz.

High power durability of diamond surface acoustic wave filter

The power durability of the ZnO/diamond surface acoustic wave (SAW) filter was investigated and compared with the LiTaO/sub 3/ SAW filter. The ZnO/diamond SAW filter maintained linearity of the input-output relation up to the input power of 36 dBm at 2.90 GHz, whereas the LiTaO/sub 3/ SAW filter, which operated at 822 MHz, was nonlinear above the input power of 23 dBm and degraded significantly at 27.7 dBm. The input power dependence of the time to failure was also investigated for both SAW filters. It was found that the ZnO/diamond SAW filter was durable for 8 dB higher input power than that of the LiTaO/sub 3/ SAW filter even at 3.5 times higher frequency. These results indicate the extremely high power durability of the ZnO/diamond SAW filter.