Contactless electrical sintering of silver nanoparticles on flexible substrates

Contactless rapid electrical sintering (RES) is demonstrated using microwave power. The method is implemented by coupling the near-field electric field of a sintering head across an underlying nanoparticle layer. We provide appropriate biasing conditions required for controlled power delivery and demonstrate real-time monitoring of the process by measuring the reflected power at 1.8 GHz. A small-scale sintering head is designed and fabricated on a printed circuit board (PCB). The PCB head is shown to provide a tenfold improvement in sintering efficiency when compared to a sintering head with a less focused electric field pattern. Finally, a high-power coaxial sintering head, with a narrow electrode spacing and biasing conditions similar to the PCB head, is used for demonstrating contactless RES over an air gap. Silver nanoparticle patterning inkjet printed on a temperature-sensitive flexible substrate is efficiently sintered in two passes with 50-W input power and 25-mm/s processing speed, when the vertical working distance to the constantly moving substrate is 1 mm. The demonstrated sintering technology can be applied to a number of printed electronics applications.