Microwave sintering of ink-jet printed copper nanoparticles

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Additive manufacturing holds the promise for a change of paradigm in fast prototyping and end-consumer fabrication and is no longer restricted to mechanical components rather than a much broader variety products including electronics through printing of electronic circuitry. This emerging technology has already reached industrial maturity e.g. for displays where roll-to-roll (R2R) printing for organic electronics is now becoming standard while it is still in its infancy for other critical electronic components such as non-volatile memories for which our team has been the first to demonstrate a fully printable design in 2017. In order to accelerate the production process, the rate limiting process step at the moment is the sintering of several components and while it is in principle possible to replace some by alternatives that do not require sintering, such a replacement implies design or performance restrictions so that, as one option, faster sintering schemes are taken into consideration. With thermal sintering being the slowest and least selective option, flash light sintering provides a more selective yet substantially more expensive alternative. The purpose of this project is to determine the potential of microwave sintering that would combine the speed of flash light at expenses similar to thermal sintering, which is orders of magnitude more affordable than flash light sintering. Different parameters such as the absorbance of metal nanoparticle inks as a function of layer thickness, the effect of reducing agents and the design of a microwave resonator for sufficiently strong intensities are investigated and the outcome verified by means of SEM, atomic force microscopy and four-point electrical characterization.