Dongliang Fu, Jaehoon Chung, Qing Liu, Riazul Raziq, Jack Sheng Kee, Mi Kyoung Park, Suresh Valiyaveettil, Pyng Lee, Polymer coated silicon microring device for the detection of sub-ppm volatile organic compounds, Sensors and Actuators B: Chemical, Volume 257, 2018, Pages 136-142, ISSN 0925-4005, https://doi.org/10.1016/j.snb.2017.10.166.
Abstract:
We present a polymer-coated silicon microring resonator to detect volatile organic compounds (VOC)
gases. Absorption of VOC gases into the polymer alters the refractive index around the microring, which
enables quantification of absorbed gases as a resonance wavelength shift in the resonator. Two different
polymers, hyperbranched polyesteramid and poly(2-vinyl pyridine), are tested as the absorption layers on
the highly sensitive (80 nm/RIU and 10,000 Q-factor) silicon microring resonator. The sensing responses
to VOC gases are characterized by flowing four different gases: styrene, acetone, toluene, and isoprene,
in a wide range of concentration (sub-ppm to 100 ppm range). The hyperbranched polyesteramid coated
sensor shows the highest sensitivity to styrene. Similarly, Poly(2-vinyl pyridine) coated device exhibits
sensitive responses to styrene and acetone. From experiments with a wide range of gas concentrations,
we observe that the sensors have two distinguished characteristics; linear and non-linear response with
respect to gas concentration. To account for it, a dual mode sensing mechanism is proposed; Langmuir
mode (doping effect) in the low concentration (