High temperature electrical behaviour and failure mechanisms of glass-ceramic dielectrics in thick film multilayers

Abstract

Glass-ceramics are polycrystalline materials obtained from glasses after an appropriate thermal treatment. They are of importance because they offer combinations of physical properties not available with other classes of materials. Glass-ceramics have become established as commercially important materials in fields such as consumer products, applications for the aerospace industry and protective coatings for metals. Recently, their technological importance has also been recognized in the field of microelectronics. Since the end of the eighties great effort has been spent in the development of glass-ceramics suitable as dielectrics in thick film multilayer systems. The construction of complex thick film multilayers can be seriously obstructed by the occurrence of failures during production at high temperatures, and therefore a reliable dielectric is needed. The most important high temperature failures in thick film multilayers are shorting and blistering of the dielectric in between two metal layers. The basic physico-chemical processes causing these failures are insufficiently understood. In particular, the correlation between electrical properties of the glass-ceramic material and the occurrence of these failures is not clear. The temperature region of interest in the study of these failures ranges from room temperature up to 850°C, which complicates the observation of the governing material properties. A further difficulty in the study of the underlying failure mechanisms is given by the intrinsic complexity of the multilayer systems. Thick film dielectrics are composite materials containing amorphous and crystalline phases of various size and chemical composition, which furthermore can interact with the adjacent conductors. In the present work a new approach is undertaken in the study of the high temperature shorting and blistering of glass-ceramic dielectrics in thick film multilayers. While other studies concerning these phenomena often concentrate on off-line results, here the study is mainly based on in-situ observation of the high temperature electrical behaviour of the given materials. The temperature region of interest has been made accessible for in-situ monitoring by the development of an appropriate measurement equipment. With this equipment several properties have been systematically investigated for a set of dielectric materials in different conditions. Since the in-situ resistance and current measurements, normally performed with the patented in-situ electrical measurement method, are inadequate for the study of high ohmic materials, new measurement techniques have been introduced. The in-situ electrical measurement equipment has been modified in order to allow the performance of impedance spectroscopy, e.m.f.'s measurements and the newly developed leakage current measurements with voltage polarity switching. With the various in-situ electrical measurements and analytical techniques, important results have been obtained concerning electrical conduction mechanisms and electrochemical behaviour of glass-ceramic materials in thick film multilayers. It has been possible to detect the occurrence of the high temperature failures and to indicate the most important failure parameters. By combining and comparing the gathered information, important conclusions can be drawn concerning the occurring high temperature processes.