New Applications of Metal-Insulator-Semiconductor Structures

The purpose of this paper is to review the use of metal-insulator-semiconductor (MIS-) structures in other areas than normally thought of. The new applications, which include gas and ion sensing with field effect devices, have been shown a large interest during the last few years. The content of the paper is to a large extent based on our own research on gas sensitive MIS-devices and on charge storage in organic materials. First we deal with the study of organic insulators (and conductors) with C(V) -techniques. Special attention is paid to charge storage in materials like chlorophyll and fatty acids. Furthermore the work on ion sensitive MIS-structures is reviewed. These devices, which are operated in an electrolyte, are MIS-structures in a broad sense since they normally lack gate metal. A theory is developed for the expected threshold voltage change in the presence of titrable groups on the insulator surface. Finally gas sensitive MIS-structures are discussed. They are based on the use of catalytic metals like Pd or Pt as gate metals of MIS-devices. The ability of these metals to dissociate hydrogen and some hydrogen containing molecules and to dissolve hydrogen atoms has led to the development of devices which are sensitive to small amounts of H 2 , NH 3 and H 2 S for example. The function of these devices and some recent experimental results are discussed.