ISFET INCORPORATED IN A DIFFERENTIAL AMPLIFIER.

The output of the ISFET (Ion Sensitive Field Effect Transistor) was obtained as a voltage signal. To achieve the temperature compensation, a differential amplifier composed of an ISFET and a MOSFET was fabricated. Polycrystalline silicon was used for the connection between the devices and the MOSFET gate electrode. The entire device surface was covered with Si//3N//4/SiO//2 to ensure the waterproof properties of the device. As a result, the MOSFET could be located near the ISFET and both FETs could be processed in the same manner. The fabricated ISFET produced the voltage signal in accordance with the change in its gate membrane potential. The sensitivity of the device ws 49 mV/pH. Temperature compensation in the ISFET was achieved with a temperature coefficient minus 0. 8 mV/ degree C.