1D silicon nitride grating refractive index sensor suitable for integration with CMOS detectors

Abdul Shakoor,David R S Cumming,Marco Grande,James Grant

doi:10.1109/jphot.2016.2644962

Abstract

The transformation of nanophotonic sensors from laboratory-based demonstrations to a portable system to ensure widespread applicability in everyday life requires their integration with detectors for direct electrical read out. As complementary metal oxide semiconductor (CMOS) technology has revolutionized the electronics industry, the integration of nanophotonic structures with CMOS technology will also transform the sensing market. However, nanophotonic sensors have to fulfill certain requirements for their integration with CMOS detectors, such as operation in the visible wavelength range, operation in normal incidence configuration, use of CMOS compatible materials, and capability to give large optical intensity change due to resonance wavelength shift. In this paper, we have designed and developed one-dimensional silicon nitride grating structures that satisfy all these conditions simultaneously. The gratings can achieve 1 and 6 nm linewidths for the transverse-electric (TE) and transverse-magnetic (TM) polarizations, respectively, with 90% resonance depth. The experimental linewidth is 8 nm with 55% resonance depth, which is limited by the detector resolution. The experimental sensitivity of the device is 160 nm/refractive index unit (RIU), which translates to a very high intensity sensitivity of 1700%/RIU, which would enable sensing of very small changes in refractive index when integrated with a detector.

Highlights

There is growing interest in developing integrated nanophotonic resonant structures for bio-sensing applications due to their ability to perform quick and label free sensing [1]–[3], high sensitivity [4], [5], and compactness [6], [7] of nanophotonic sensor chips
For integration with complementary metal-oxide semiconductor (CMOS) technology, there are certain requirements that need to be fulfilled by nanophotonic structures which are listed as follows; (i) their resonance wavelength should be below the bandgap of silicon (1100 nm) where it has high absorption especially in the visible range where the responsivity of the CMOS detector is highest, (ii) the structures should operate in a normal incidence configuration (iii) the material used should be CMOS compatible and (iv) the change in light intensity caused by the resonance wavelength shift must be large
In addition to sensitivity, which is the degree of wavelength shift per refractive index unit (RIU) and the most commonly used Figure of Merit (FOM) for resonant nanophotonic refractive index sensors [8], the change in readout optical intensity due to resonance wavelength shift can be increased by narrowing the resonance linewidth and increasing the resonance depth, which is the difference in the transmission level between the resonance dip and the highest background transmission level

Summary

Introduction

There is growing interest in developing integrated nanophotonic resonant structures for bio-sensing applications due to their ability to perform quick and label free sensing [1]–[3], high sensitivity [4], [5], and compactness [6], [7] of nanophotonic sensor chips. Nanophotonic sensors are usually based on the phenomenon of refractive index sensing, where a change in the refractive index, induced by the introduction of an analyte or surface binding of bio-species, causes a shift in the resonance wavelength of the nanostructures. In addition to sensitivity, which is the degree of wavelength shift per refractive index unit (RIU) and the most commonly used Figure of Merit (FOM) for resonant nanophotonic refractive index sensors [8], the change in readout optical intensity due to resonance wavelength shift can be increased by narrowing the resonance linewidth and increasing the resonance depth, which is the difference in the transmission level between the resonance dip and the highest background transmission level. The sensitivity but the role of resonance linewidth and resonance depth becomes significant for a nanophotonic sensor integrated with a detector

Methods

Results

Conclusion