A Compact Optical Pressure Sensor Based on a III-Nitride Photonic Chip with Nanosphere-Embedded PDMS

Pressure sensing based on high-sensitivity and fast-response photonic devices is essential for various transient and dynamic processes in diverse fields. Therefore, a miniaturized device being capable of precise and reliable detection is highly desired for the development of optical pressure sensors. Here, we develop a compact pressure sensor, showing a sensitivity of 1 μA/kPa and a fast response time of <10 ms, based on a III-nitride photonic chip combined with a PDMS membrane on submillimeter-scale footprints. The emitter and detector are monolithically integrated on a GaN-on-sapphire chip consisting of InGaN/GaN multiquantum wells, enabling quantitative readout for pressure sensing. Self-assembled polystyrene nanospheres are embedded in the PDMS layer and function as an opal-based photonic crystal, transforming the received mechanical signals into optical signals which can be precisely determined through recorded photocurrent. This underlying mechanism of angle-dependent reflective characteristics via the photonic bandgap effect is well fitted by our theoretical simulation. Sensors with opal films embedded at different vertical positions are fabricated, and their corresponding performance is systematically studied and compared through a series of pressure loading/unloading tests. The demonstrated high repeatability, stability, and durability of the developed chip-scale optical pressure sensor, paving the way for its widespread usage.