Nitrogen-doped/non-doped carbon nanotubes (CNTs) were integrated on SiO2/Si and PMMA substrates for understanding the infrared sensing mechanisms. The nanotube structures on SiO2 substrates exhibit a much shorter response time (about 40 ms) than those directly on PMMA substrates (about 1200 ms), indicating the interface effects between CNTs and the substrates. The infrared responses for both structures show a linear relationship with the light power density even at the radiation power as low as 0.1 mW/mm(2). Moreover, a new concept flexible IR detector was designed and fabricated by transferring the CNTs/SiO2 structure onto the PMMA substrate, which exhibits both short response time (50 ms) and good flexibility. The successful detection of human finger movements indicates the practical applications of the CNT-based detectors for the detection of weak thermal or far infrared radiation. (C) 2017 Elsevier B.V. All rights reserved.