Garret McKerricher

Fully Inkjet Printed RF Inductors and Capacitors Using Polymer Dielectric and Silver Conductive Ink With Through Vias

In this paper, fully inkjet printed multilayer capacitors and inductors are fabricated and characterized using poly 4-vinylphenol (PVP) ink as the dielectric layer and silver nanoparticle ink as the conductor. Inkjet printed through vias, created with a novel dissolving method are used to make RF structures in a multilayer inkjet printing process. The vias have been realized in a 350-nm PVP film and exhibit resistance better than 0.1 Ω. Spiral inductors from 10 to 75 nH have been realized with maximum quality factors around five. The 10-nH inductor exhibits a self-resonant frequency slightly below 1 GHz. Metal-insulator-metal capacitors are realized with densities of 50 pF/mm2. These capacitors demonstrate values ranging from 16 to 50 pF. The 16-pF capacitor shows a self-resonant frequency over 1.5 GHz. The successful implementation of inductors and capacitors in an all inkjet printed multilayer process with vias is an important step toward fully inkjet-printed large area and flexible RF systems.

Robust Design of a Particle-Free Silver-Organo-Complex Ink with High Conductivity and Inkjet Stability for Flexible Electronics.

Currently, silver-nanoparticle-based inkjet ink is commercially available. This type of ink has several serious problems such as a complex synthesis protocol, high cost, high sintering temperatures (∼200 °C), particle aggregation, nozzle clogging, poor shelf life, and jetting instability. For the emerging field of printed electronics, these shortcomings in conductive inks are barriers for their widespread use in practical applications. Formulating particle-free silver inks has potential to solve these issues and requires careful design of the silver complexation. The ink complex must meet various requirements, such as in situ reduction, optimum viscosity, storage and jetting stability, smooth uniform sintered films, excellent adhesion, and high conductivity. This study presents a robust formulation of silver-organo-complex (SOC) ink, where complexing molecules act as reducing agents. The 17 wt % silver loaded ink was printed and sintered on a wide range of substrates with uniform surface morphology and excellent adhesion. The jetting stability was monitored for 5 months to confirm that the ink was robust and highly stable with consistent jetting performance. Radio frequency inductors, which are highly sensitive to metal quality, were demonstrated as a proof of concept on flexible PEN substrate. This is a major step toward producing high-quality electronic components with a robust inkjet printing process.

All inkjet printed 3D microwave capacitors and inductors with vias

For the first time we present a method to create all inkjet printed multilayer RF passive components including vias. Although there has been previous work on multilayer RF components, they are not fully inkjet printed and involve complicated processing techniques such as laser cutting, conductive epoxy, or reactive ion etching. This work demonstrates a truly all inkjet printed solution with a novel dissolving method for vias realization. A major issue with inkjet printing is often surface roughness, however by processing these materials at low temperature surface roughness <;20nm RMS has been obtained which allows for high quality components to be fabricated and allows for stacked multilayer designs.

A Fully Inkjet-Printed 3-D Honeycomb-Inspired Patch Antenna

The ability to inkjet print three-dimensional objects with integrated conductive metal provides many opportunities for fabrication of radio frequency electronics and electronics in general. Both a plastic material and silver conductor are deposited by inkjet printing in this work. This is the first demonstration of a fully 3-D multijet printing process with integrated polymer and metal. A 2.4-GHz patch antenna is successfully fabricated with good performance proving the viability of the process. The inkjet-printed plastic surface is very smooth, with less than 100 nm root mean square roughness. The printed silver nanoparticles are laser sintered to achieve adequate conductivity of 1e6 S/m while keeping the process below 80°C and avoiding damage to the polymer. The antenna is designed with a honeycomb substrate that minimizes material consumption. This reduces the weight, dielectric constant, and dielectric loss, which are all around beneficial. The antenna is entirely inkjet-printed including the ground plane conductor and achieves an impressive 81% efficiency. The honeycomb substrate weighs 20 times less than a solid substrate. For comparison, the honeycomb antenna provides an efficiency nearly 15% greater than a similarly fabricated antenna with a solid substrate.

Crude oil water-cut sensing with disposable laser ablated and inkjet printed RF microfluidics

This paper presents the first microwave microfluidic crude oil/water cut sensor. Anhydrous crude oil is been tested and the device provides a measurable frequency shift of 500MHz at 50% (vol.) water content and a 50MHz shift for a 5% (vol.) water concentration. The sensor is realized with a low-cost direct write fabrication method. This involves laser ablation, inkjet printing, laser heating, along with low temperature thermal compression bonding of Poly (methylmethacrylate) (PMMA) sheets. By using localized laser sintering a conductivity of 2.5e6 S/m is achieved for silver nanoparticle ink without the need to heat the entire substrate above its glass transition temperature of (105 °C). The dielectric properties of PMMA are characterized to 1 GHz and a simulation model is offered for analyzing the dielectric properties of crude oil. This work demonstrates that a small form factor and low cost device is capable of precise water-cut measurements.

Lightweight 3D printed microwave waveguides and waveguide slot antenna

In this work we demonstrate a lightweight 3D printed waveguide and slot antenna. The waveguide is 78% air by weight with a mass of only 2.2 g/cm which is roughly one ninth that of similar sized solid copper/bronze standard waveguide. Interior scaffolding provides structural strength with insignificant dielectric loss. A 3D Systems 5500 MultiJet printer and an acrylic photo-initiated polymer are used to fabricate the structure. This approach provides an extremely smooth surface with 100 nm root mean square surface roughness. Simulations show that a slotted waveguide antenna can achieve an efficiency of 90% with a copper coating. To demonstrate the concept a waveguide and antenna are fabricated using an easily applied but low conductivity coating. Although the coating is about 20 times less conductive than copper the antenna still achieves a good efficiency of 60%. This approach is a step towards realizing low cost lightweight waveguide microwave circuits and antennas for space born and satellite communications.

Radio frequency feedback method for parallelized droplet microfluidics

This paper reports on a radio frequency micro-strip T-resonator that is integrated to a parallel droplet microfluidic system. The T-resonator works as a feedback system to monitor uniform droplet production and to detect, in real-time, any malfunctions due to channel fouling or clogging. Emulsions at different W/O flow-rate ratios are generated in a microfluidic device containing 8 parallelized generators. These emulsions are then guided towards the RF sensor, which is then read using a Network Analyzer to obtain the frequency response of the system. The proposed T-resonator shows frequency shifts of 45MHz for only 5% change in the emulsions water in oil content. These shifts can then be used as a feedback system to trigger alarms and notify production and quality control engineers about problems in the droplet generation process.