Forming ohmic Ag/SnO2 contacts

• Ohmicity of silver/SnO2 contacts depends on SnO2 layer׳s surface morphology.
• Junctions formed between silver and intergranular regions on SnO2 promote ohmicity.
• Junctions between large SnO2 grains and silver present nonlinear I–V.
• Field assisted Ag migration to intergranular region converts nonlinear I–V to linear.

SnO2 layers are commonly used as transparent conductors in optoelectronic devices and as chemoresistive sensing elements in chemical sensors. Durable metal/SnO2 contacts of ohmic quality are required to provide their connections to the external circuitry. Here, we investigate the current–voltage characteristics of the silver/SnO2 junctions of different microstructures and determine the experimental conditions which render the deposited silver/SnO2 contacts ohmic. Silver films deposited by thermal evaporation in vacuum on polycrystalline SnO2 layers form ohmic quality contacts, but those prepared by industrially popular silver paste printing on larger grain tin oxide layers demonstrate microstructure-dependent diode-like behavior. It is experimentally established that while the connections between SnO2 grain surface and silver are diode-like in nature, those formed between silver and the intergranular regions on the oxide layer promote ohmic behavior. A technique is proposed for the elimination of the diode-like instabilities from the paste printed contacts.