PD/NI Metal-Oxide-Semiconductor Hydrogen Sensor Utilizing a Segregated PD-TI Adhesion Layer

A novel technique has been developed that incorporates an adhesion layer into a hydrogen sensor that is based on a MOS structure. Previous structures containing no adhesion layer exhibited long-term drift and device failure due to delamination of the gate. While devices that did incorporate a normal adhesion layer lost all of their sensitivity. This is the first demonstration of combining virtues of an adhesion layer for a noble metal on insulator while retaining hydrogen sensitivity in a field effect sensor. The design issues related to utilizing Pd films for hydrogen sensors are presented. The recipes for fabricating the sensors are described. The method for monitoring MOS sensors are discussed and the circuitry used for data acquisition is described. The mathematics necessary to understand the device physics of the MOS structures and the relation to hydrogen sensing is presented. The electrical characterization of these devices and responses to hydrogen are compared to other MOS structures. One fabrication method yielded devices with fast response and long-term stability; however, short term phenomena resulted in hysteresis. A second fabrication method yielded devices that were slow responding and drifted on long-term scale; however, showed stable short-term responses and less hysteresis. Both structures show similar hydrogen sensitivity to previous devices without an adhesion layer; however, the gate regions are more strongly bonded to the nitride layer