Optical Millinewton Force Sensors Based on GaN Devices Integrated With Bionic-Structured PMDS Films

In this work, optical millinewton force sensors are developed by integrating GaN devices with bionic-structured polydimethylsiloxane (PDMS) films. The chip-scale GaN-on-sapphire devices incorporating light emitters and photodetectors are fabricated using wafer-level microfabrication. Large-area bionic microstructures of varying size scales are patterned on the PDMS films using four different types of plant leaves as molding templates. The deformable PDMS film can efficiently modulate the light coupled into the detector during force loading, which endows the GaN devices with high sensitivity to millinewton forces. The force-sensing capabilities of the sensors are thoroughly investigated and compared. The device integrated with optimized film exhibits sensing characteristics with a sensitivity of
$0.145 ~\mu \text{A}$
/mN in the range of 0–290 mN and a sub-millinewton resolution of 0.165 mN. The developed optical sensor provides the attractive features of low-cost fabrication, high compactness, fast response, and high stability, making it highly valuable for millinewton force detection in practical applications.