Study On Hybrid Nanoimprint Lithography And The Fabrication Of Waveguide Sampling Grating

Nanoimprint lithography has been widely studied due to its low-cost,high through-output and high-resolution.It has been developed and demonstrated as a steady and reliable nano-pattern transfer technique in recent years.This thesis details the hybrid nanoimprint lithography and its applications.We propose a simple and costless method to fabricate the imprint mold which is the essential in nanoimprint lithography.A grating silicon mold with a period of 550 nm was successfully fabricated via doublelayer resist.A large scale(4 inch)pillar array with a period of 600 nm was duplicated from the master hole-structure mold using PDMS and three-layer resist.We also used this replicated silicon mold to electroplate the stress-free nickel mold for thermal nanoimprint lithography.When the duty ratio of the master mold was extremely low,the hybrid mold we used here was full of flaws,we increased the thickness of the UVcurable resist to solve the problem.As a demonstration,we transferred the master molds with periods of 300?400?500 and 600 nm dot arrays to hole arrays,respectively.This method provides an easy and low-cost way to prolong the master molds' lives and to acquire various molds with complementary structures.With the development of the communication services,the demand for large capacity increases rapidly.Wavelength division multiplexing(WDM)technology is widely used to increase the information capacity at present.The key components are multi-wavelength DFB semiconductor laser array(MLA)and various passive filters.All these devices need the waveguide grating structures.To realize the specific functions,chirp or phase shift gratings are often designed.While fabricating a chirp or phase shift grating in nano scale is quite expensive and time-consuming with e-beam lithography(EBL).According to the Reconstruction-equivalent-chirp(REC)theory,the change of the initial phase of the sampling structure changes the initial phase of the Fourier sub-gratings,i.e.the nanogratings,and the change of the sampling period changes the period of the nanogratings as well.Since the sampling structures are usually micrometer scales,the phase and the period can be simply changed by the mask,thus REC theory provides a convenient way for the fabrication process.Firstly a uniform 20 nm thick nickel grating with a period of 278 nm was formed on the surface of silicon on insulator(SOI)substrate using nanoimprint lithography,followed by photolithography to form sampling structure.After fabricating the waveguide and coupler using EBL,we finally acquire sample grating array in SOI ridge waveguides which can be used as filters for multi-wavelength laser array to increase the monochromaticity of laser.