Spin-on nanoparticle tin oxide for microhotplate gas sensors

A colloidal suspension of tin oxide nanoparticles is used to prepare a high ly sensitive gas sensing film on a microhotplate. Fabrication consists of s pin-coating the solution over an array of micromachined hotplates and annea ling. A thermolithographic process using a nitrocellulose coating is demons trated. Scanning electron microscopy images show the films to be smooth and consisting of 10 nm particles. Response to methanol shows a resistance cha nge of a factor of two between zero-grade dry air and a concentration of 10 nmole/mole (10 ppB) at an operating temperature of 350 degreesC. Sensitivi ty is observed at operating temperatures as low as 150 degreesC, with gener ally lower recovery times. Tests comparing the response in saturated humid air and dessicated dry air show that recovery to wet air exposures is great ly accelerated at temperatures above 300 degreesC. Stable response with no evident poisoning of the sensor was observed in a run lasting 120 h consist ing of methanol and ethanol exposures. Temperature-programmed sensing was u sed to create different response patterns in air, methanol, and toluene, us eful for identification of a detected gas. The results suggest colloidal su spensions may be used in combination with the microhotplate platform to pro duce a low-power, highly sensitive, device that is fabricated using planar technology. Published by Elsevier Science B.V.