Broadband, on-chip surface enhanced Raman spectroscopy realized using CMOS compatible manufacturing

Surface enhanced Raman spectroscopy takes advantage of high electric field strengths, enhanced by collective electron oscillations in metals known as plasmons, to detect small concentrations of nearby molecules. This technique has been employed for quite some time as a method to detect biological analytes. It is not a widespread commercial technique, however, due to fabrication complications and the difficulty of making these devices compatible with other components needed for its use.

Raza et al. published a method to fabricate a surface enhanced Raman spectroscopy device using CMOS compatible methods for on-chip fabrication. Such a device could be fabricated adjacent to other required components, including the laser, filter, sensor, etc., and are all self-contained on the same chip. Using atomic layer deposition and deep UV lithography to fabricate the device allows the use of nonplanar substrates for large scale manufacturing processing.

While the manufacturability of this technology is impressive, the device also shows promising performance. Instead of using localized plasmons isolated on small nanostructures, the authors utilized propagating plasmons along a metal slot waveguide microns in length and at only a 15-nanometer gap. Even though the electric field enhancement is moderate as compared to the nanoantennas used in fundamental research, the figure of merit, or the metric to detect analytes, is higher due to the increased active area in the beam.

The Raman signal is enhanced over a broadband wavelength range due to the propagating nature of the plasmon enhancement. This result is highly reproducible and advantageous to detect a larger variety of analytes using a range of possible excitation wavelengths within the therapeutic window, which is optimal for biological samples.

Source: “ALD assisted nanoplasmonic slot waveguide for on-chip enhanced Raman spectroscopy,” by Ali Raza, Stéphane Clemmen, Pieter Wuytens, Muhammad Muneeb, Michiel Van Daele, Jolien Dendooven, Christophe Detavernier, Andre Skirtach, and Roel Baets, APL Photonics (2018). The article can be accessed at https://doi.org/10.1063/1.5048266 .