Charge and Capacitance Sensitive Field Effect Transistor (CCSFET) for Chemical Sensing

A novel field effect transistor concept is presented, which is suitable for chemical sensing in gases as well as liquids. It consists of two separate components, a capacitor with a control gate and integrated chemical sensitive layer, and a MOS read-out transistor. A floating gate couples both components. The sensors are fully CMOS compatible and have been fabricated on 200 mm silicon wafers. With identical devices, measurements of hydrogen in air and pH values in electrolytes are presented using Pd layer and Ta₂O₅ layer respectively. These results demonstrate the versatility of the sensor. The possibility of detecting charge as well as capacitance variations due to chemical reactions offers new applications regarding phase change measurements and sensor calibration.