Objectives

Objective 1: Investigation of Sezawa propagation mode on GaN/Si and GaN/SiC materials, which have the property to be “slow on fast” and are the most used GaN based layered structures in microwave/acoustic devices applications of GaN.

Approach: A novel simpler approach based onfinite element method will be used to obtain the wave shapes at different resonance frequencies that occur in the response of the device. The simulated wave shapes for various propagation modes and the simulated resonance frequencies (and their corresponding acoustic velocities) will be compared with experimental values and will be used for identification of the propagation mode. Simulations and experimental work will be developed for a wide range of values of the hk parameter. This will be achieved using different thicknesses of GaN epitaxial wafers as well as different values of finger/interdigit spacings width (in the range of 100-500 nm).

Objective 2: GaN/SiC SAW temperature sensors based on Sezawa propagation mode will be developed and their performances will be compared with the Rayleigh mode results.

Approach: The resonance frequency shift of the SAW structures analyzed in Objective 1 vs. temperature will be used for temperature determinations. The Rayleigh and the Sezawa mode frequency shifts vs. temperature will be determined simultaneously in a wide temperature range (from -268ºC to +150ºC) and the results regarding the sensitivity and temperature coefficient of frequency, TCF, will be compared. As the Sezawa mode resonance frequency is higher, a higher sensitivity is expected for the sensors based on this mode.

Objective 3: Investigation of Lamb mode targeting pressure and temperature sensor applications. Comparison with Rayleigh mode.

Approach: Different SAW structures will be manufactured based on micromachining and nanolithographic processing of GaN/Si, obtaining various GaN membranes. The influence of the IDT position on the active area (membrane) will be analyzed. The resonance frequencies will be extracted from experiment and FEM simulations will be used for a correct identification of the Lamb propagation mode. Measurements will be performed in Nitrogen atmosphere in the range of 1-5 Bars. The pressure sensitivity and PCF will be extracted for the Lamb mode and compared to the Rayleigh mode results.

Objective 4: Coupling coefficient for the Sezawa mode, k²_eff, vs. normalized thickness, hk,analysis and exploratory study of Sezawa and Lamb propagation mode based SAW face to face filters.

Approach: The coupling coefficient will be analyzed and experimentally determined for the Sezawa and Lamb modes. For hk values wherek²_eff, is higher for the superior propagation modes than for the fundamental Rayleigh mode, face to face SAW band-pass filters having different fingers and interdigitated spacing widths will be manufactured on GaN/Si, GaN/SiC and on GaN membranes. In this way, the possibility of using superior propagation modes will be exploited to improve the performances of high frequency SAW band-pass filters (higher values ofk²_eff,can substantially reduce losses).