A carbon nanotube gas sensor using CMOS-based platform

A complementary metal-oxide-semiconductor (CMOS)-based gas sensor platform using a commercially available 0.35 µm CMOS process and the microelectromechanical systems (MEMS) post process was developed in this work. An n-type polysilicon microheater with ∼2 kΩ and a metal thermometer with ∼1 kΩ were integrated within this platform to provide a temperature programming for sensing film preparations and sensor characterizations. After the standard CMOS process, a freestanding micro hotplate was fabricated via an isotropic silicon dry etching. The rapid thermal response (<1 s) and an uniform heating distribution (100°C, standard deviation of 1°C) of this sensor platform were demonstrated. The sensing material was prepared with the mixing of commercially available single-walled carbon nanotubes (SWCNTs) and an organic solvent. Our sensors were tested with three compounds (Octane, Butanol, and Butylacetate) and the good linearity and fast response time (<5 s) were demonstrated. The great sensor sensitivities of the three compounds were obtained (Octane: 0.329 ppm/ppm, Butanol: 0.522 ppm/ppm, and Butylacetate: 0.683 ppm/ppm) at a high concentration range (>1K ppm) and could be used to enhance the specificity of the SWCNTs-based gas sensor.