Fabrication of New Planar-Type Microsensor Attached with Spin-Coated Thin Film of Tin Dioxide and Its Thermal and CO Sensing Characteristics

Abstract

A new planar-type microsensor in which a gas-sensing layer was surrounded by a platinum heater horizontally on the same plane of a diaphragm was fabricated by a simple silicon micromachining technique using only 3 masks for photolithography. The gas sensing layer of SnO₂ or Sb-doped SnO₂ was spin-coated from each sol solution and trimmed into the designated dimensions by chemical etching with an aqueous HI solution. Computer simulation of thermal properties showed that the uniformity of temperature over the sensing layer was fairly good as expected, although there were some discrepancies between the temperatures of the sensing layer simulated and observed under given heater power conditions because of the simplified simulation model used. The fabricated microsensor proved a fairly good performance for sensing CO gas in air at 250°C.