GaN/SiC based surface acoustic wave structures for hydrogen sensors with enhanced sensitivity

In this article, we present an application of GaN/SiC heterostructures for Surface Acoustic Wave (SAW) hydrogen sensors with enhanced sensitivity. We demonstrate that the mass-loading sensitivity of such sensors can be increased by using shorter acoustic wavelengths and by confining the acoustic wave energy in an epitaxial waveguide. The effect of different Rayleigh-like modes on the mass-loading sensitivity is also discussed. The SAW wavelength-dependent phase and group velocity and electromechanical coupling constants were determined from electrical measurements. The outcome was used to design a microwave SAW delay-line oscillator. Its sensing characteristics are presented. The oscillator frequency shift was larger than 60 kHz after exposure to 1000 ppm H2/N2. The sensor reaction time was about 12 s for the same sensing conditions at room temperature.