Investigation of SiO2-B2O3-ZnO-Bi2O3 glass frits on the interface reaction of silver front contacts

Abstract

This work investigates the interface reaction of Ag/Si contact with different Bi2O3 containing glasses in Ag pastes. The Bi2O3 content has a strong effect on the glass transition temperature (Tg) and glass structure. The contact interface is tailored by transmission electron microscopy. For low Tg glass frits, the SiNx layer is decomposed and oxidized, forming a SiO2 layer. Both globules and inverted pyramids of Ag crystallites are observed in the vicinity of the interface. In addition, very small Ag crystallites are well dispersed in the SiO2 layer, which acts as effective sites for tunneling current. The contact formation mechanism can be explained by the electrochemical model. In this model, the Tg of glass frits plays an important role in the solubility and diffusivity of Ag+ and O2− ions in glass. Phase separation is also observed due to dissolution of Si4+ ions into the glass matrix. Current-voltage measurement reveals that glass frits with higher Bi2O3 content form a Ag/Si contact structure with lower resistance at the firing temperature of 850°C.