Electrostatically protected ion sensitive field effect transistors

Two types of ISFETs with electrostatic protection have been designed and tested. They both utilize an electrically conductive layer incorporated into the gate of the ISFET. This layer is connected via an on-chip MOSFET switch to the outside circuitry. In the first type the conductor is capacitively coupled to the ion-selective membrane and to the solution. In this case the device output is proportional to the time differential of the concentration change. The applicability of this device to high-speed FIA titrations has been tested. In the second device the gate electrically contacts the membrane. In this case the output is identical to that of a conventional ISFET. The signal-to-noise ratio and the electrostatic protection of this ISFET are considerably improved.