The hydrogen sensitivity of catalytic metal-insulator-semiconductor (MIS) devices has been known for almost 30 years [1,2]. With Pd or Pt as the metal gate the electronic properties of the device are influenced by hydrogen and the device can thereby be used as a gas sensor for hydrogen and hydrogen containing gases. Hydrogen sensors will no doubt be of great interest in the future, when hydrogen is expected to play an increasing and important role in power production. Already today there are wide spread experiments and tests with fuel-cell cars and buses which run on hydrogen [3]. Hydrogen detection will for example be essential during the hydrogen production, (remember that hydrogen is an energy carrier and not an energy source) and during different types of chemical processes where hydrogen is involved. For hydrogen storage purposes, leak detection will also be crucial.
MIS sensors have been used for several years, but there are still a lot of questions left to be answered. In general one could say that there are four important properties to investigate and improve for these types of sensors:
• Sensitivity
• Selectivity
• Stability
• Speed of response and recovery
Field-effect devices based on silicon are for instance limited to operation temperatures below approximately 500 K. The selectivity of field-effect devices for gas sensing would be improved if their operation temperature could increase. One way to solve this problem is to change the semiconductor material into a semiconductor material with a larger bandgap e.g. silicon carbide. Changing the catalytic gate material will of course be critical for the sensitivity and selectivity of the devices.
The work presented in this thesis concerns the fundamental study of Pt-based MIS devices, where hydrogen adsorption on the Pt surface and at the Pt-insulator interface is in focus. Also the influence of the insulator surface properties has been investigated.
The thesis is divided into eight chapters. Chapter 2 concerns gas sensors in general and the MIS-structure in more detail. Chapter 3 and 4 give short introductions to surface physics and catalysis. Both areas are important in understanding the sensors response and for evaluating the results. Jn the fifth chapter the equipment and analytical methods that have been used are presented. Chapter 6 gives some suggestion for future work and chapter 8 contains 2 papers intended for publication and which are the essence of the research performed.