The behaviour of gold metallized AlN/Si and AlN/glass based SAW structures as temperature sensors.

Thin AlN piezoelectric layers have been deposited on high resistivity Si and glass substrates by reactive RF magnetron sputtering, in order to manufacture one port GHz operating SAW type resonators to be used as temperature sensors. The growth morphology surface topography, crystallographic structure and crystalline quality of the AlN layers have been analysed. Advanced nano-lithographic techniques have been used to manufacture structures having interdigitated transducers with fingers and finger interdigit spacing width in the 250 - 170 nm range. High resonance frequency ensures the increase of the sensitivity, but also of its normalized value, the temperature coefficient of frequency (TCF). The resonance frequency shift vs. temperature has been measured in the -267 - +150 °C temperature range, using a cryostat set-up adapted for on wafer microwave measurements up to 50 GHz. The sensitivity and the TCF were determined in the 23 - 150 °C temperature range for all measured structures. High values for the sensitivity as well as for the TCF have been obtained. The performances are compared with previous results obtained for GaN/Si GHz operating sensors. For the first time, a numerical method based on finite element technique and coupling of modes was implemented in order to simulate the variation of the resonance frequency of the envisaged AlN/Si and AlN/glass SAW structures within the 25 - 150 °C temperature range.