Thin film thickness variation measurement using dual LEDs and reflectometric interference spectroscopy model in biosensor

Abstract

The potential of thin film thickness variation measurement method, reflectometric interference spectroscopy (RIfS), for a compact label-free biosensor is investigated. A model to estimate thickness variation is built based on RIfS. A set-up of the sensor having dual Light Emitting Diodes (LEDs) and one photo detector are introduced. To verify the model, sample chips with different thicknesses of silica film layers ranging from 2 to 20nm are used in the experiment. The estimated values are compared with their reference values which are measured by an Atomic Force Microscopy (AFM). Since the chosen LEDs' wavelength is not an ideal one, the comparison shows that the model underestimates the thickness variation. By using dual LEDs and a photo detector with the reliable model, the handheld device for transparent thin film measurement will become practical.