Fabrication Of Optical Microring Resonator Biosensors

Microring resonator biosensor shows promising because of its robustness, lable-free detection mechanism, mature CMOS fabrication technology, low cost and high sensitivity achieved by the long lifetime of photons that circle in the ring, which increases the probability of photons interacting with analytes. Based on planar waveguides, it not only allows surface chemical modifications, but can also be integrated with other optoelectronic devices and microfluidic handling, leading to highly integrated and intelligent sensing systmes. Furthermore, it offers a unique advantage of reducing the device size without sacrificing the sensitivity by virtue of the resonance. Therefore, micoring resonator biosensor is highly sensitive that can detect minute amount of analytes. Supported by the National Science Foundation of China, the fabrication and sensing application of the microring resonator are systematically studied in this thesis.The sensing mechanism of the microring resonator biosensor was intrudoced and the optical parameters were analyzed of which the Q factor determines the sensitivity. Fabrication of the microring resonator biosensors based on silicon nitride and silicon waveguide systems was realized. By using thermal oxidation, Low pressure chemical vapor deposition (LPCVD), optical lithography, inductively coupled plasma etcher (ICP) and plasma enhanced chemical vapor deposition (PECVD) processes, the silicon nitride microring resonators with smallest feature size of 1 urn and waveguide sidewall roughness of less than 30 nm were fabricated and by using e-beam lithography (EBL) and ICP processes, the silicon microring resonators with smallest feature size of 160 nm and waveguide sidewall roughness of less than 10 nm were fabricated. Optical characterization of the as fabricated microring resonators based on transmission mechanism was done by using tunable light rource, optical transmission alignment system and optical spectrometer and Q factors of the devices as high as 25000 were measured.The microring resonators were later packaged to serve as a sealed chemical sensing system. Glucose solutions with various concentrations were detected by the system which results in a linear corresponding curve between the resonance wavelength shifts and the concentrations with a sensitivity of 10^-4RIU. Bacillus Anthracis ssDNA solutions with various concentrations by surface sensing mechanism with the microring resonators were detected and linear corresponding curves with sensitivity of n-mole per liter were achieved.Fabrication of nanoscale optical grating coupler, silicon rich silicon oxide microdisk and annular photonic crystals (APC), which are supposed to be integrated with the microring biosensor as optical coupler, light source and polarization controller on chip, was discussed. Nanoscale optical grating coupler with smallest features of 40 run in a dense fashion and waveguide sidewall roughness of less than 10 nm was realized. The fabrication process of silicon rich silicon oxide microdisk devices by using PECVD, high temperature annealing, e-beam lithography, ICP etching and RIE etching processes was studied and the microdisks with smallest diameter of 4μm were realized. Annular photonic crystals was fabricated by using atomic layer depositon (ALD), EBL, ICP, reactive ion etcher (RIE) and wet etching and a self-alignment technique was developed to achieve a precise nanoscale alignment resolution.