Reflectance-based Photonic Crystal Liquid Sensors Made of ALD TiO2

Abstract

A promising concept for a photonic crystal sensor for liquid sensing applications is introduced. The two dimensional photonic crystals are fabricated using a recently developed Atomic layer deposition ARrays Defined by Etch-back technique (AARDE) to obtain large functional surfaces and dense pillar arrays. Photonic signals are collected by means of reflectance, which facilitates optical couplings and decreases fabrication steps. Large TiO2 pillar arrays (3mm × 3mm in size) with pillar radius of 220nm, height of 890nm and pitch of 800nm are realized. A 300nm thick SiN membrane is used to seal the sensor and to prevent liquid evaporation, while allowing light penetration. To examine the sensing capability of the fabricated PCs, optical measurements are performed with liquids with various refractive indices (water, acetone and isopropanol). Explicit peaks are observed shifting towards higher wavelengths in the designed wavelength range of 1.35 – 1.55μm (infrared) as the index of the measured liquid increases. A high sensitivity of 537nm per refractive index unit is found for different peak series.