Polymer thick-films on silicon: a route to hybrid microsystems

The integration of polymer thick-film transducers and silicon offers a low-cost technology for the fabrication of hybrid microsystems. This paper presents a study on the feasibility and processing parameters of this integration. Selected transducer films were printed on silicon wafers covered with aluminum or various passivation layers and also on alumina for comparison. The quality of film adhesion was investigated using standard tape pull and scratch tests. Scanning electron microscopy and energy dispersive X-ray spectra analysis were used to investigate the interface between the films and the substrates. It was found that the films did not contaminate the wafers. We also characterized the film resolution by researching the wetting behavior of the pastes and the quality of printed patterns. The influence of the substrate's thermal coefficient of expansion on the resistance of a carbon polymer film was also analyzed. The experiments showed that the same design rules can be applied on both alumina and silicon substrates. Furthermore, dry and wet methods of etching and cleaning wafers from the thick-films were assessed. An insight into the potential and limitations of the technology is developed by discussing the issues of bonding mechanism, silicon contamination and influence of substrate on the resolution, electrical properties and infrared curing of the films. A design methodology for hybrid microsystems is proposed along with a suggestion for potential applications.