Polymer coated silicon microring device for the detection of sub-ppm volatile organic compounds

•A polymer-coated silicon microring resonator to detect volatile organic compounds (VOC) gases is presented.•Two distinguished characteristics (linear and non-linear) have been observed in a wide range of gas concentration.•Dual sensing mechanism is proposed to account for the two distinguished sensing responses successfully.•Detection of VOC gases (styrene and acetone) as low as 100ppb has been achieved with the developed sensors. 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 (80nm/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 100ppm 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 (