Paper NS-TuP16
Formation of Ag Nano-net for Application to Flexible Electronics

Tuesday, October 20, 2015, 6:30 pm, Room Hall 3

Electronics built on flexible substrate creates a wide range of exciting consumer products. Many of the developed or under developed flexible electronics, such as displays, sensors, solar cells and artificial electronic skin, are based on very thin organic or polymer substrates and some may suitable for roll-to-roll manufacturing. The ability of bending, rolling, and elastically stretching defines the electronics’ degree of flexibility. The structure of a generic electronics is composed of a substrate, back-electrode, active layers, front-electrode, and encapsulation. To make the structure flexible, all components must bendable to some degree without losing their function. However, in-organic thin film materials used for building the device layers are rigid and brittle. They often result in peeling, cracking or rupture when devices are subjected to mechanical strain and/or thermal stress. In the case of flexible CuInSe2-based solar cells, one of the challenge tasks is to improve cracking or rupture issues of the Mo back-contact. In our previous studies, the Mo layer deposited on polyimide (PI) substrate showed that the Mo layer will not crack until the PI substrate curving to 20 mm in diameter either tensile or compressive stress applied.

Silver possesses the highest electrical conductivity of any element and the highest thermal conductivity of any metal. Silver is also a very ductile and malleable element. Its plasticity properties capable of extent or deform without fracture. Embedded Ag nanowires (NWs) into transparent conducting oxide (TCO) films, such as AZO or ITO, has been intensively studied recently. However, the Ag NWs are just stacked together, the junction resistance of the two Ag NWs is larger than 1G ohms. Lower junction re-sistance and junction reliability need to be further improved for its application to reliable flexible electronics.

Ag atoms can migrate easily from (100) to (111) surface to lower its surface energy upon annealing. The Ag NWs are fused at the junctions after thermal annealing. The surface migration can happen as low as 90^oC. The Ag NW splits into several dome-shaped Ag nano-particles if over-annealing is performed. Conditions for forming Ag nano-net (NN)with fused junctions are studied using tube furnace and rapid thermal annealing systems. NW density, temperature, and annealing time are the key factors affecting Ag NN’s formation. When embedding in Al2O3-doped ZnO film, a 40-80% (dep. on NW density) further reduction in film resistivity can be achieved as compare fused NW junctions to that of non-fused junctions. Developing of Ag NN and all other detailed results will be presented in the conference.