Ion sensitive field effect transistor with amorphous tungsten trioxide gate for pH sensing

In this study, the pH sensitive properties of the amorphous tungsten trioxi de (a-WO3) thin films by rf sputtering system from a-WO3 target have been i nvestigated. The a-WO3 thin films with 600-4750 Angstrom thickness were dep osited on the electrolyte-insulator-semiconductor (EIS) structure maintaine d at room temperature and a total pressure of 30 mTorr in Ar mixed O-2 gas for 0.5-2 h, and we could obtain the electrical resistivity of the a-WO3 fi lms, was about 7.8 x 10(5)-4.5 x 10(9) Omega-cm. The EIS structure with a-W O3 thin films can be used to detect the ion sensitivity and can be explaine d by C-V curve in the different acidic buffer solutions (pH = 1-7) using th e C-V measurement. In addition, the a-WO3 thin films were also deposited on the double layer structure of a-WO3/SiO2 gate ion sensitive field effect t ransistor (ISFET), and these devices were packaged with epoxy. Then, we can obtain the shift of the linear region threshold voltage (Delta V-T) of the ISFET devices in the acidic solutions (pH = 1-7). The a-WO3 materials exhi bited a fairly high response, and the sensitivity was about 50 mV/pH. (C) 2 000 Elsevier Science S.A. All rights reserved.