The major objective of this project consists in the design, manufacturing and characterization of dual pressure and temperature sensors based on surface acoustic wave (SAW) resonators fabricated on thin GaN and GaN/Si membranes. Rayleigh and Lamb resonance (occurring only on SAWs supported on thin membranes), will allow the determination of both parameters using a single device. Advanced nanolithography and micromachining techniques will be used in fabrication. We will use (i) membrane supported SAW resonator and (ii) membrane supported SAW resonator, with backside metallization. The second configuration introduces a supplementary critical step in manufacturing, but promises a major improvement for two fundamental parameters of the device, the coupling coefficient and the quality factor, parameters important also for the sensing application. The thickness of the GaN membranes is in the range of 0.7-1.3 μm. The GaN/Si membranes are 10-25 μm thin, to support higher pressures. We target to increase for the first time the operating frequency above 10 GHz (Rayleigh mode) and above 15 GHz (Lamb mode). Subsequently the pressure and temperature sensitivities of the membrane supported SAW structures will increase. In order to achieve such high resonance frequencies, the active area of the SAW, the interdigitated transducer (IDT), will be designed by e-beam nanolithography, finger and interdigit spacing widths being varied between 80 nm and 150 nm. New simulation method will be implemented by coupling FEM COMSOL with coupling of modes in order to optimize the parameters of the SAW structures. An original encapsulation will be developed, a very challenging task due to the thin membrane supporting the active element (IDT) which should be reached by the pressure and temperature. The structures behavior will be tested simultaneously in the 1 – 20 Bar pressure range and between 20 and 150 °C temperature range. Beyond state-of-the-art sensitivities are expected.