10 GHz-Range Surface Acoustic Wave Low Loss Filter Measured at Low Temperature

The 10 GHz-range surface acoustic wave (SAW) is of great importance in the field of physical acoustics and application of SAW devices, for example, in mobile and wireless communications. The temperature dependency of the propagation attenuation at 10 GHz-range is measured using the three-transducer system with an electrode width of less than 0.1 µm, which is fabricated using an electron beam exposure and lift-off technique. The results show that the attenuation at room temperature is about 1.5 dB/(100 λ) at 10 GHz. Next, the temperature dependency of the insertion loss of a floating electrode reflection type unidirectional transducer (FEUDT) whose electrodes are respectively fabricated from Al and the superconductor Nb, is investigated experimentally. In the case of Al-FEUDT at 8 GHz, the insertion loss at a low temperature is about 8.5 dB, which is 3.4 dB lower than the insertion loss at room temperature. The main cause of decrease in the insertion loss is the decrease in the resistivity of the very thin and narrow metal electrodes. The results of Nb-FEUDT show a marked decrease in the insertion loss around the critical temperature T c =9.23 K.