Printed Ag nanoparticles on Evaporated Au System: Impact of Microstructure on Mechanical and Electrical Properties
Abstract
Nanoparticles have attracted tremendous interest for their thermodynamic size effect which is particularly valuable to reduce their sintering temperature. This asset is exploited for the fabrication of flexible electronic devices using printing technologies, especially interconnection features. Those printed interconnections require both a low electrical resistivity and high mechanical properties which are largely correlated with microstructure. In this paper, the combined effects of the substrate crystalline orientation and the sintering condition have been demonstrated to have a significant impact on microstructures. Silver nanoparticles with a mean diameter of 30 nm were inkjet-printed on {100} silicon substrates coated with either amorphous Si3N4 or with strongly textured {111} Ti/Au. The crystallographic texture and grain size of those printed films have been investigated after being sintered up to 500°C at 50°C/s using Electron Back-Scattered Diffraction. The results shows that a {111} fiber texture is developed above 300°C only on oriented films through out-of-plane diffusion. Electrical resistivity shows no dependency on texture since it is mainly affected by grain size. An optimal value of 3.4 μΩ.cm is achieved at 300°C using a fast sintering ramp of 10°C/s. Regarding the Young's modulus of nanofilms, nanoindentation measurements exhibited an oscillation between 38 GPa for smaller crystallites to 81 GPa for the biggest, which is compatible with wire bonding process.