Field effect transistor type CO/sub 2/ sensor attached with metal carbonate auxiliary phase

FET type CO/sub 2/ sensor operative at room temperature was developed by combining with a metal carbonate auxiliary phase and metal oxide sensing electrode. In an attempt to lower the operating temperature and reduce the humidity dependence, the structure with Li/sub 2/CO/sub 3/-BaCO/sub 3/(1:3)-ITO/Na/sup +/ exchange membrane/FET was fabricated. The resulting device exhibited fairly excellent CO/sub 2/ sensing characteristics at room temperature (30/spl deg/C), although the other devices failed to work at room temperature or suffered disturbance by humidity seriously. The V/sub GS/ for the best device obtained was linear to the logarithm of the CO/sub 2/ concentration, with its slopes indicating n=2.0 of theoretical value where n is the number of reaction electrons involved in the electrochemical reduction per CO/sub 2/. The times for 90% response and 90% recovery to switching-on and-off 3000 ppm CO/sub 2/ were 1 and 2 min, respectively, and all of the response transients reproduced very well in the successive runs.