Printed Radio Frequency Electronics: Achieving High Performance Using Additive Manufacturing
Throughout the past decade, the field of printed electronics has seen a rapid expansion in the available materials and tooling capabilities. The drive for functional passive device components that retain the flexibility of three-dimensional design is underscored by the need for materials that are competitive with those found in conventional processing techniques. Presently, most inks and resins used in additive manufacturing suffer from poor performance due to inherent materials flaws and are not suitable for the next generation of high performance devices in their current state. The inability to be competitive with traditionally processed materials precludes many interesting and novel device designs from becoming fully realized within arenas such as advanced RF circuit design, electronics packaging, and aerospace. At its core, the successful implementation of additive manufacturing within a diverse array of industries has become a materials problem. The aim of this dissertation is twofold: to present the challenges associated with additive manufacturing for high performance RF passive devices and to elucidate the approaches necessary to achieve success. The most ubiquitous method for printing metal components to date is to use nanoparticle-based inks; I first discuss a systematic study of the microstructural evolution of these materials as a result of thermal annealing, which elucidates the extent to which processing is required to see significant changes to the internal grain distribution. In the following chapter I delve into an alternative method of metallization, printed reactive metal inks. Here, I develop a predictive multiscale electronic transport model which correlates microstructure to measured conductivity and identifies a strategy to approach the practical conductivity limit for printed metals. Next, I characterize reactive silver ink up to 20 GHz and extract the fundamental insertion loss of the metal via bisect de-embedding. Comparison against models and conventional plated copper yields virtually identical levels of loss, which is highly promising for long-term adoption of this method. Finally, I apply this technique to fully-3D printed architectures in the form of a band-stop filter that demonstrates unique characteristics owing to its 3D shape. Combined, this dissertation serves to reveal the materials science fundamentals within additive device design, processing, characterization and that are necessary for higher performance and could impact the aerospace and communications industries in a significant way for years to come.