Study of built-in stress distribution in AlGaN/GaN/AlN heterostructure based cantilevers for mechanical sensing in harsh environments
Résumé
Some industrial areas as oil, automotive and aerospace industries, require electromechanical systems working in harsh environments. A solution is to use III-V materials alloys having semiconductor, piezoelectric and pyroelectric properties. These materials, particularly nitrides such as GaN or AlN, enable advanced design of devices suitable for harsh environment. A micromechanical structure based on AlGaN/GaN/AlN cantilevers coupled with a High Electron Mobility Transistor (HEMT) is stress-sensitive and can act as a mechanical sensing device suited to harsh environments. The study of stress distribution after the structure release is necessary to assess its possible influence on the HEMT output. In this article, we propose a method to evaluate these stresses that is based on topology measurements. By coupling numerical modelling and laser interferometry measurements, both intrinsic and residual stresses, respectively the stress before and after release, are calculated. These results are then corroborated by stress measurements using MicroRaman spectroscopy. A residual stress distribution ranging from 140 MPa to 260 MPa is obtained in the HEMT area. However, the influence of this stress can be neglected against the influence of spontaneous polarization in GaN alloys.