Characteristic Analysis of SAW Filters Fabricated Using GaN Thin Films

The surface morphology and characteristic parameters were analyzed for surface acoustic wave (SAW) filters, fabricated on epitaxially grown undoped GaN thin films on sapphire substrates. GaN thin films with good surface morphology (rms = 0.21 nm) were obtained. SAW filters with unapodized interdigital transducer/GaN/sapphire structure were used to estimate the characteristic parameters. The phase velocity and temperature coefficient of frequency (TCF) were 5550–4900 m/s and —60.8 to —50.0 ppm/°C in the temperature range between —25 and 50 °C at kh = 0.25–1.26, respectively. The fact that the temperature coefficient is even better at higher frequency explains that the SAW filters fabricated using GaN thin films would have a strong potential for GHz band applications.