Fig. 1: Structure of the optical airflow sensor.

Schematic diagrams of the a proposed airflow sensor and b structural layout of the GaN chip. c Schematic illustrations of the fabrication process of the PDMS membrane and the corresponding optical images at different stages. Microphotographs of the d frontside and e backside of the PDMS membrane with Al film. Magnified image of the packaged chip f before and g after coverage of the PDMS membrane. h Optical image of the resultant airflow sensor