Influence of gases on the electrical properties of MIS devices
This thesis studies the effects of gas ambients on the electrical properties of the insulator-semiconductor interface of a MIS capacitor. A microcomputer-controlled instrumentation system has been developed to extract this information from measurement of the a.c. admittance of MOS or MIS devices. The system incorporates several novel developments in circuitry and software which enable these admittance data to be automatically collected and processed in the frequency domain by remote recalibration of the instrumentation. This advancement permits interface state density information to be calculated more quickly and accurately than has been previously possible using manually-operated equipment. The system has been used to investigate the influence of gases on the density of interface states in a MIS capacitor, in particular the palladium/silicon dioxide/silicon structure which is sensitive to hydrogen gas. A distinct change in the distribution of surface state density across the silicon bandgap has been observed upon exposure to a hydrogen ambient. An alternative insulating layer, an organic Langmuir-Blodgett film multilayer of ω-tricosenoic acid, has been characterised and examined, and increased sensitivity of this structure to hydrogen gas has been indicated.