Studies on pH and Nitrate Checkers Made of Semiconductor Devices for Acid Rain Monitoring

Ion-selective field-effect transistors (ISFETs), which are integrated devices for ion-selective electrodes using solid-state microelectronics technology, have attracted much attention for convenient monitoring of acid rain, since conventional analytical procedures are time-consuming. In this paper, some recent results of studies on pH and nitrate checkers made of ISFETs using new sensing materials and their application to samples of acid rain are described. A new pH-sensitive film, TiN was deposited onto the gate of ISFET device using RF plasma-enhanced CVD method. The plasma was generated in a mixture of TiCl₄, N₂ and H₂ gases. The prepared pH-ISFETs showed a linear response and the almost theoretical slope sensitivity of 59 mV per pH change with a rapid response of less than 10 seconds. We have obtained fairly good agreement with the pH values using conventional pH glass electrode. A prototype nitrate-checker was prepared with casting newly designed nitrate-sensing materials, plasticizers and PVC based tetrahydrofuran solution onto the ISFET device. We have obtained good agreement with the values using conventional ion-chromatography at mg L^?1 level.