High-frequency V-doped ZnO/SiC surface acoustic wave devices with enhanced electromechanical coupling coefficient

The rapid development of large-volume and high-speed mobile communication systems has increased the demand for high-frequency and wide-band surface acoustic wave (SAW) devices. In this work, ZnO films and V-doped ZnO (V:ZnO) films with (0002) orientation were grown on SiC substrates using a magnetron sputtering method. High-frequency SAW resonators with the resonant frequency ranging from 4 GHz to 6 GHz were fabricated on the above structures. V:ZnO/SiC SAW resonators exhibited a significantly increased electromechanical coupling coefficient (K2) in the range of 2.80%–5.12%, in a wide normalized thickness range, which is more than a 75% increase compared to that of ZnO-based SAW resonators. Besides, the high quality factor Q ranging from 431 to 593 and an improvement in the figure of merit value were observed for the V:ZnO/SiC SAW resonators operating at 4–6 GHz. Finally, 4.58 GHz SAW filters using V:ZnO films with a larger bandwidth and a lower insertion loss were achieved. This work clearly shows that the ZnO/SiC SAW properties can be improved by V doping, and the V:ZnO/SiC structures have great potential for application in high-frequency and wide-band SAW filters.