A NEW STRUCTURED ISFET WITH INTEGRATED Ti/Pd/Ag/AgCl ELECTRODE AND MICROMACHINED BACK-SIDE P~+ CONTACTS

摘要

To eliminate the need for a separate reference electrode and facilitate the use of an ion-sensitive field-effect transistor (ISFET) in a measurement system, a planar Ti/Pd/Ag/AgCI quasi reference electrode integrated with ISFET in one chip has been developed. This new planar integrated quasi reference electrode, without filling any internal reference solution, has stable sensing characteristics and a satisfactory lifetime suitable for disposable sensing applications. Long-term stability measurement over 60 hours shows an average drift of 0.035 mV/hr. SiO_2/Ta_2O_5 was used for the sensing insulator, backside electrical contacts to the ISFET were adopted which make encapsulation easier. The fabricated pH sensors characterized in standard pH solutions show a linear sensitivity of 56 mV/pH. These results agree very well with the theoretical value of 59 mV/pH. Dynamic response and hysteresis characteristics of the pH-sensor are also studied and discussed.