Measurement of relative adhesion and surface properties of polyimide films using a surfce acoustic wave sensor

Abstract

A surface acoustic wave (SAW) sensor is used to study the relative-humidity response of thin polyimide films on quartz, where interfacial and surface properties are varied. The results show differences in the comparative SAW humidity response for films applied with and without adhesion promoter and with and without a chromium interface layer deposited between the substrate and the polyimide film after temperature and humidity aging. Polyimide films were examined that were both sputter cleaned and non-sputter cleaned. The humidity response is particularly sensitive to the surface treatment of the polyimide film. A theoretical analysis has been done to obtain information on the physical mechanisms responsible for the SAW sensor humidity response. The analysis identifies three primary film properties that can influence this response. These properties are changes in density, elastic constants and stress of the film as a function of humidity. The more dominant of these factors appear to be density and elstic-constant changes. © 1993.