Fabrication of a multi-structure ion sensitive field effect transistor with a ph sensing layer of a tin oxide thin film

Abstract

A sensitive material-tin oxide (SnO,) obtained by thermal evaporation or by r.f. reactive sputtering is used as a high-pH-sensitive material for a Multi-Structure Ion Sensitive Field Effect Transistor. The multi-structure of this Ion Sensitive Field Effect Transistor (ISFET) includes SnO,/SiO,gate ISFET or SnO,/Si,N,/SiO,gate ISFET respectively, and which have high performances such as a linear pH sensitivity of approximately 56˜58 mV/pH in a concentration range between pH2 and pH10. A low drift characteristics of approximately 5 mv/day, response time is less than 0.1 second, and an isothermal point of this ISFET sensor can be obtained if the device operates with an adequate drain-source current. In addition, this invention has other advantages, such as the inexpensive fabrication system, low cost, and mass production characteristics. Based on these characteristics, a disposal sensing device can be achieved. Thus, this invention has a high feasibility in Ion Sensitive Field Effect Transistor.