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

It is known that light sensitivity in ion sensitive field effect transistor s (ISFETs) during illumination is due to carrier generation in the silicon substrate. In order to improve this drawback, multi-structure ISFETs: tin o xide/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 sensor s have a linear pH response of about 56-58 mV/pH in a concentration range b etween pH2 and pH10 under room light conditions. Subsequently, the light se nsitivity of the ISFETs with/without aluminum as a light shield were invest igated under 2000 lx white light exposure. The data show that ISFETs with a luminum as a light shield have low light sensitivity compared with ISFETs w ithout aluminum as a light shield. (C) 1999 Elsevier Science S.A. All right s reserved.