Sintering of silver interlayers in polyimide films

Abstract

Annealing at 220–420 °C and exposure to laser light were used to induce sintering of silver metal interlayers in polyimide films. The sintering process was followed by transmission electron microscopy, electrical conductivity, optical reflectivity measurements, and x-ray scattering. We find that upon sintering at temperatures below Tg≂380 °C of the polymide film, sintering of the silver interlayer is induced. A dramatic increase in both the optical reflectivity (from 32% to 95%) and a hundredfold increase in electrical conductivity are observed upon sintering. Both the average size and the connectivity of the silver particles in the interlayer are increased in the process; however, there is no apparent change in the polymer. High-speed (∼100 ns) high spatial resolution laser writing (∼1 μm) is feasible by a selective sintering process. It is, therefore, of potential interest as a basis for write-once, high-density optical information storage. It is suggested that a surface diffusion mechanism is responsible for the observed sintering process.