Project description

An increased resonance frequency is important for both filter and sensor applications of SAWs. As classical non-semiconductor materials can not be used for SAW resonators operating at frequencies above 2 GHz, GaN can be a reliable solution for higher frequencies. Sezawa confined modes (on GaN/Si and GaN/SiC layered structures) and Lamb (on GaN membranes) have a higher phase velocity than the fundamental Rayleigh mode, so a higher resonance frequency can be obtained for the same finger and interdigit spacing of the nanolithographic IDT. A main target of the project is to investigate the Sezawa mode for GaN/Si and GaN/SiC, using a novel approach based on finite element method. The simulated wave shapes and phase velocities for various propagation modes will be compared with experimental data and will be used for identification of the propagation mode. Simulations and experimental work will be developed for a wide range of values of hk (normalized thickness) parameter. This will be achieved using different thicknesses of GaN epi-wafers and different values of finger/interdigit spacing width (in the range of 100-500 nm). The targeted application is to obtain a temperature sensor with higher sensitivity compared with that obtained for the fundamental mode. The Lamb mode will be investigated targeting a high sensitivity pressure sensor and a dual pressure/temperature sensing structure.
The coupling coefficient k²_eff, and its variation vs. hk, an essential parameter for a SAW resonator, will be investigated for Sezawa and Lamb modes. Our preliminary studies showed that k²_eff, is higher for the Sezawa mode, than for the fundamental Rayleigh mode in a specific interval of hk. Filter structures (having hk in this interval) will be manufactured and analyzed. We expect to have an important decrease of losses compared with filters using the Rayleigh mode. This can give a huge impact to the results, as the demand of reliable SAW filters at frequencies above 5 GHz, is high.

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

The research team

Dr. Alexandru Müller, coordinator, Dr Alexandra (Stefanescu) Nicoloiu, Dr. Ioana (Giangu) Zdru, Dr. Dan Vasilache, Dr. Alina Cristina Bunea, Dr. Adrian Dinescu, Dr. Sergiu Iordanescu, Dr. Dan Neculoiu, Dr. Valentin Buiculescu, Dr. Gina Adam, Phys. Ioana Petrini, Eng. Cristina Buiculescu, Master Student Andrei Alexandru Florescu.