Microwave sintering of ink-jet printed copper nanoparticles

加法制造有望改变快速原型制造和终端消费者制造的模式，不再局限于机械部件，而是更广泛的产品，包括通过印刷电子电路的电子产品。这一新兴技术已经达到工业成熟，例如在显示器方面，有机电子的卷筒到卷筒(R2R)打印现在正在成为标准，而对于其他关键电子元件，例如非易失性存储器，我们的团队在2017年率先展示了完全可打印的设计。为了加快生产过程，目前的限速工艺步骤是几个部件的烧结，虽然原则上可以用不需要烧结的替代方案来取代一些，但这种替代意味着设计或性能限制，因此，作为一种选择，更快的烧结方案被考虑在内。由于热烧结是速度最慢、选择性最低的选择，闪速轻烧提供了一种选择性更高、成本也高得多的选择。这个项目的目的是确定微波烧结的潜力，它将结合闪光的速度，而费用与热烧结相似，后者比闪光烧结便宜几个数量级。研究了不同的参数，如金属纳米墨水的吸光度随膜厚的变化、还原剂的影响以及足够强的微波谐振器的设计，并用扫描电子显微镜、原子力显微镜和四点电学表征手段对结果进行了验证。

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.