Selective GaN growth on patterned hBN for transferring MEMS onto flexible substrates – FLEXIGAN

The FlexiGaN project aims at implementing and optimizing the selective growth of III-N layers and heterostructures onto pre-patterned hexagonal boron nitride (hBN) to fabricate high mechanical quality electromechanical systems (MEMS) that can subsequently be transferred onto flexible substrates.
Due to its unique properties, namely high intrinsic crystalline quality, chemical inertness, piezoelectric and piezoresistive properties and the presence of a two-dimensional gas at the gallium nitride (GaN)/AlGaN interface for efficient transduction schemes, the use of GaN heterostructures should pave the road to flexible MEMS sensors for implantable and harsh environment applications.
The innovative process proposed for FlexiGaN is based on the selective area van der Waals epitaxy method, a concept proposed by the International Research Laboratory Georgia Tech-CNRS and first demonstrated in 2019. Selective growth of III-N layers onto hBN alleviates the need for subsequent etching steps classically used to create MEMS geometries and enables the convenient mechanical lift-off and transfer of III-N patterned heterostructures onto another substrate, possibly flexible. Hence, this technique can ultimately reduce the amount of material used in the fabrication of MEMS and completely change the post-processing needed after material growth because devices can be individually lifted without laser lift-off or substrate etching.
This process has been used to individualize chips at wafer level but not yet for the direct realization of geometrically defined mechanical structures with micrometric features. Hence, we will adapt this van der Waals epitaxy method to the one-step fabrication of MEMS structures where we will study the influence of the III-N layer growth and transfer process onto the semiconductor layer mechanical and electrical properties. As a proof of concept, a flexible MEMS-based resonant gas sensor that alleviates the need of a sensitive layer by measuring the physical properties of the gas will be manufactured and tested.
To tackle the objectives of the project, we have gathered an interdisciplinary and experienced consortium with complementary expertise in metalorganic vapor phase epitaxy and nitride electronics (IRL GT-CNRS), microelectronic fabrication (Institut Lafayette), analog electronics for MEMS (LAAS-CNRS), and MEMS modelling, characterization and application to gas sensing (IMS).