Multi-structure ion sensitive field effect transistor with a metal light shield

It is known that light sensitivity in ion sensitive field effect transistors (ISFETs) during illumination is due to carrier generation in the silicon substrate. In order to improve this drawback, multi-structure ISFETs: tin oxide/Al/insulator/Si ISFET devices are investigated in this study. In this structure, aluminum is used as a light shield, and the tin oxide is used as a pH sensitive layer. We have developed SnO2/Si3N4/SiO2/Si ISFETs and SnO2/Al/Si3N4/SiO2/Si ISFETs, respectively. The pH sensitivity of these devices was measured and the data shows that the SnO2/Al/S3N4/SiO2/Si ISFET sensors have a linear pH response of about 56-58 mV/pH in a concentration range between pH2 and pH10 under room light conditions. Subsequently, the light sensitivity of the ISFETs with/without aluminum as a light shield were investigated under 2000 lx white light exposure. The data show that ISFETs with aluminum as a light shield have low light sensitivity compared with ISFETs without aluminum as a light shield. (C) 1999 Elsevier Science S.A. All rights reserved.