The influence of isothermal annealing on tin oxide thin film for pH-ISFET sensor

The aim of this paper is to investigate pH sensitivity of tin oxide thin fi lms prepared by thermal evaporation, and the influences of isothermal annea ling on its characteristics. A series of capacitance-voltage (C-V) curves o f SnO2/SiO2/Si electrolyte insulator semiconductor (EIS) diodes are used to evaluate pH sensitivity of tin oxide thin films. The results show that tin oxide thin films las grown) have linear pH sensitivities of approximately 58 mV/pH in a concentration range between pH 2 and pH 10. However, pH sensi tivity decreases after the isothermal annealing processes at 300 degrees C, 400 degrees C, and 500 degrees C in N-2 ambiance for 1 h; and pH sensitivi ty goes further down to only 33 mV/pH, after annealing in N-2 ambiance for 15 h. This phenomenon influences the structure of tin oxide thin films, whi ch will undergo phase transition from amorphous to polycrystal after the is othermal annealing process. Moreover, the characteristics of the tin oxide gate ion-sensitive field-eff ect transistor (ISFET) (SnO2/SiO2 gate ISFET), where the tin oxide is forme d under optimum condition, is also presented in this paper. (C) 2000 Elsevi er Science S.A. All rights reserved.