Study Of Optical Refractive Index Sensor Based On Si₃N₄ Densely Hexagonal Micro-nano Structure

Refractive index sensor,as a new type of unmarked biosensor technology,has a wide range of applications in physics,chemistry,and biology.Because metal micro-nano structure can excite surface plasmon resonance(SPR)and is extremely sensitive to the changes of its surrounding dielectric environment.Therefore,the sensor based on metal micro-nano structure is a typical representative of unmarked biosensor technology detection.However,metal micro-nano structures have high ohmic loss,heat dissipation and incompatibility with metal oxide semiconductor fabrication process,which make this research rarely achieve practical application.Therefore,pursing low-loss materials to replace metal materials has become one of the research hotspots.Compared with the metal micro-nano structure,the dielectric micro-nano structure has the characteristics of low loss,technology compatibility and magnetic response,which makes it attract wide interest in the optical biosensors.At present,the research of sensors based on dielectric micro-nano structure has become new research of nano-optics and nano-photonics.In this paper,low-loss all-dielectric materials are used to construct high-sensitivity refractive index sensors in the visible and ultraviolet wavelengths.The finite difference time domain(FDTD)method,microsphere self-assembly technology and plasma enhanced chemical vapor deposition(PECVD)coating technology were used to carry out the theoretical design,experimental preparation,and sensing performance test of the silicon nitride micro-nano structure sensor.The main research work is as follows.1.Theoretical design of silicon nitride micro-nano structure sensor.The finite difference time domain(FDTD)method was used to design the silicon nitride micro-nano structure sensor The physical mechanism of resonance modes is analyzed by combining the Mie scattering theory.The excitation conditions and optical properties are explored.The performance of silicon nitride micro-nano structure sensor is theoretically predicted,which provides theoretical basis for the experimental preparation and the test of sensor performance.2.Experimental preparation of silicon nitride micro-nano structure sensor.Wafer-level uniform hexagonal close-packed silicon nitride micro-nano structures were prepared by low cost and high efficiency microsphere self-assembly technology and plasma enhanced chemical vapor deposition(PECVD)technology.During the experiment,the particle size of polystyrene(PS)sphere is 750 nm,and the deposition thickness of silicon nitride shell is 80 nm.By using reactive ion beam etching technology,the particle sizes of PS sphere are continuously controlled by controlling the etching time.Finally,adjustable-size silicon nitride all-dielectric micro-nano structure can be obtained.3.Performance test of silicon nitride all-dielectric micro-nano structure sensor.The optical performance of the densely hexagonal silicon nitride all-dielectric micro-nano structure sensor was tested by UV-visible near-infrared spectrophotometer.The test results showed that the densely hexagonal silicon nitride all-dielectric micro-nano structure sensor presented multiple resonant modes from the ultraviolet to near-infrared regions.We put it into the glycerol solution with different weight ratios and test its optical sensing performance of environmental refractive index change.The sensitivity corresponding to four resonant wavelengths is 655,535,638 and 707 nm/RIU,and the quality factors are 55,22.3,17.2 and37.2,respectively.