Fig. 5 Cross section elemental x-ray analysis of Ag/Cu contacts

Challenges in the printing process manifests themselves in two distinct forms; lift-off of Ag/Ni stack from the front surface and delamination of Ag/Cu contacts between the Ag and Cu. As illustrated by SEM images, these issues not only compromised the mechanical stability of the contacts but also influenced their electrical performance. Figure 6a provides a cross-sectional SEM image of an Ag/Cu contact after undergoing a contact co-firing process at 780°C. The clear separation between the Ag and Cu layers might be attributable to the differential thermal expansion of these metals during the firing process. However, this delamination issue is not apparent in contacts co-fired at peak temperatures below 780°C, underlining the significance of optimal firing conditions for the stability of these bilayer contacts. The SEM image in Fig. 6b exhibits a lift-off scenario with the Ag/Ni stack, where the contact stack detaches from the Si substrate in the middle, while remaining intact at the edges. This occurrence could stem from multiple factors, including differential thermal expansion, interfacial reactions, and inadequate surface preparation, among others. These observations align with previous study [25], which reported similar lift-off and delamination issues in aerosol printed bi and tri stack layers of Ag frit/Ni and Ag frit/Ni/Cu when fired above 790°C peak firing temperature.