Interface Engineering in Chip-Scale GaN Optical Devices for Near-Hysteresis-Free Hydraulic Pressure Sensing.

In this work, a compact, near-hysteresis-free hydraulic pressure sensor is presented through interface engineering in a GaN chip-scale optical device. The sensor consists of a monolithic GaN-on-sapphire device responsible for light emission and detection and a multilevel microstructured polydimethylsiloxane (PDMS) film prepared through a low-cost molding process using sandpaper as a template. The micro-patterned PDMS film functions as a pressure-sensing medium to effectively modulate the reflectance properties at the sapphire interface during pressure loading and unloading. The interface engineering endows the GaN optical device with near-hysteresis-free performance over a wide pressure range of up to 0-800 kPa. Verified by a series of experimental measurements on its dynamic responses, the tiny hydraulic sensor exhibits superior performance in hysteresis, stability, repeatability, and response time, indicating its considerable potential for a broad range of practical applications.