Deep UV sensors using surface acoustic wave oscillators fabricated on single crystalline AlN films grown on sapphire substrates

Epitaxial single crystal AlN thin films have been obtained on (001) sapphire substrates by helicon sputtering system at growth temperature of 450°C. Surface acoustic wave (SAW) filters were fabricated on AlN/sapphire. The center frequency is 354.2MHz, which corresponds to a phase velocity of 5667 m/s. The insertion loss and sidelobe rejection were about 24.9dB and 11.4dB, respectively. The value of TCF is measured to be −74.9 ppm/°C and −65.76 ppm/°C at 0.4 µm and 1 µm of film thickness, respectively. The temperature coefficient of frequency (TCF) of AlN/sapphire shows proportional to the film thickness. A frequency downshift about 43 KHz was observed when the UV source with the wavelength of around 200nm and 12 mW/cm
²
of power density radiates the surface of SAW devices.